Ink for aqueous flexographic printing

Abstract

To provide ink for aqueous flexographic printing which does not contain a synthetic resin that is mainly produced from fossil resources (petroleum, coal, natural gas and the like) in a varnish, similarly, does not contain an organic solvent mainly produced from fossil resources in a varnish, extends exhaustion of fossil resources, and considers environment.SOLUTION: There is provided ink for aqueous flexographic printing in which a varnish is composed of a binder component and a solvent of the binder component, wherein the binder component of the varnish is hydroxypropyl methylcellulose, the solvent is water, a synthetic resin produced mainly using a fossil resource is not contained in the binder component, and an organic solvent is not contained as the solvent.SELECTED DRAWING: None

Description

[Technical field]

[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 mainly from fossil resources (oil, coal, natural gas, etc.) in the varnish in order to contribute to preventing the depletion of fossil resources, and similarly does not contain organic solvents produced mainly from fossil resources in the varnish, thereby suppressing VOC (volatile organic compound) emissions, prolonging the depletion of fossil resources, and being environmentally friendly. (Hereinafter, "water-based flexographic printing ink" may be abbreviated to "water-based flexographic ink.")

[0002] Water-based flexographic printing is a type of letterpress printing that uses soft materials made of rubber or resin. This is a printing method in which ink is applied to a plate and then printed. It is used for printing on cardboard, paper bags, cloth, and in recent years, labels, film, food packaging, etc. [Background technology]

[0003] The components of flexographic inks are roughly divided into color materials, varnishes (also called vehicles), and additives. Usually, pigments are used as color materials (coloring materials), and acrylic or urethane synthetic resins are used as binder components in varnishes, and water, various organic solvents, vegetable oils, and the like are used as solvents. (See Patent Document 1

[0066] to

[0070] ,

[0072] to

[0074] , etc. below.) In particular, Patent Document 1

[0085] below shows that binder resins are used for water-based liquid inks, and as shown in Patent Document 1

[0066] to

[0070] below, synthetic resins produced mainly from fossil resources are used for these resins, and the binder components of varnishes for flexographic printing inks that are actually manufactured and sold often use synthetic resins produced mainly from fossil resources. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7333572 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, it has been found that if the binder component of the varnish is not made from synthetic resin components derived from fossil resources, as described above, and solvents mainly derived from petroleum resources such as mineral oil are not used either, but instead cellulose is used as the binder component of the varnish. Since cellulose is a renewable resource, it is expected that resource depletion and environmental burdens can be reduced. However, it has been found that this causes problems in that the adhesion and fixing function of the printed image to the printing medium is reduced, and the printed image can become dirty when rubbed with a finger, a phenomenon known as chalking.

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

[0007] The present invention aims to provide a flexographic printing ink that does not use synthetic resin components (including asphalt) obtained mainly by synthesizing compounds derived from fossil resources as the binder component of the varnish, but instead uses hydroxypropyl methylcellulose, which is a cellulose raw material component, and has a low ratio of fossil resources used in the processing step using fossil resources, and uses water as the solvent component of the varnish, thereby preventing the depletion of fossil resources due to the synthetic resin used as the binder component being mainly obtained by synthesizing fossil resources, reducing the environmental load, and yet achieving satisfactory printability without using synthetic resin components obtained mainly by synthesizing fossil resources. [Means for solving the problem]

[0008] That is, the flexographic printing ink of the present invention is (1) A water-based flexographic printing ink comprising a varnish comprising 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.

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

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

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

[0012] (5) In the water-based flexographic printing ink described in the above item (3), the content of the defoaming agent is preferably 0.1 to 3 parts by mass per 1 to 20 parts by mass of the 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 hydroxypropylmethylcellulose.

[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 the above item (4), the anti-wear agent is preferably at least one selected from the group consisting of polyethylene wax and polypropylene wax. Effect of the Invention

[0016] (1) Although the flexographic ink of the present invention does not use a synthetic resin produced primarily from compounds derived from fossil resources that are at risk of depletion as a binder component of the varnish, it reduces problems such as smearing when the printed area is rubbed and offset when printed items are layered, and provides an ink that can be used industrially and practically in flexographic printing.

[0017] In addition, 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 and 30 to 90 parts by mass of water, it is possible to provide an ink that maintains the ink viscosity and ensures drying properties and transferability to printing paper, which is preferable.

[0018] As described in the above item (3) of the present invention, by further configuring the ink as a water-based flexographic printing ink to contain a defoaming agent, it is possible to provide an ink that can eliminate thickening and poor ink adhesion caused by bubbles generated 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 abrasion-resistant agent, it is possible to provide an ink with improved abrasion resistance to printed matter, which is preferable.

[0020] As described in the above item (5) of the present invention, the content of the defoaming agent is preferably 0.1 to 3 parts by mass per 1 to 20 parts by mass of hydroxypropyl methylcellulose, whereby an ink can be provided which does not suffer from thickening or poor ink adhesion due to bubbles generated during printing.

[0021] As described in the above item (6) of the present invention, the content of the abrasion-resistant agent is preferably 0.1 to 5 parts by mass per 1 to 20 parts by mass of hydroxypropyl methylcellulose, which is preferable since it provides an ink with sufficiently improved abrasion resistance to printed matter.

[0022] As described in the above item (7) of the present invention, in a preferred embodiment, the defoaming agent is a surfactant, which makes it possible to provide an ink that does not suffer from thickening or poor ink adhesion due to bubbles generated 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 provides abrasion resistance to printed matter, which is preferable. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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. 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 been conventionally used as yellow pigments in flexographic inks.

[0025] Similarly, examples of magenta pigments that can be used include 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] Examples of inorganic coloring pigments include carbon black for black, zinc oxide for white, and titanium oxide. Other examples of coloring inorganic pigments include red iron oxide and yellow lead, but are not limited to these.

[0028] Inorganic extender pigments are used as necessary to act as extenders or to adjust fluidity, strength, gloss, viscosity, and adhesion, and examples thereof include calcium carbonate, silicic anhydride, clay, kaolinite, talc, etc. The amount of inorganic extender pigments used is not particularly limited, and therefore may not 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 the color pigment used is not particularly limited, but as a guideline, yellow, magenta, cyan, and black are used in an amount 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 a white pigment, the amount may be slightly larger than the amounts of the above colors, and the amount is used in an amount 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 each color ink, it is also possible to use a pigment of another color as a complementary color or to add an ink composition of another color.

[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 constituting the varnish.

[0032] In the present invention, hydroxypropyl methylcellulose is used as a binder component constituting the varnish. Hydroxypropyl methylcellulose uses cellulose as the main raw material, and although a small amount of a compound derived from petroleum resources is used to process it to make it water-soluble, it is mainly made of cellulose derived from renewable plants, and approximately 76% by mass of it is made from biological resources. Rosin-modified phenolic resin is also partially composed of components derived from biological resources, but the proportion is approximately 50% by mass. Therefore, in the present invention, a synthetic resin produced mainly using fossil resources is a synthetic resin in which components derived from fossil resources account for approximately 50% by mass or more.

[0033] In the present invention, the solvent component of the varnish is water, and no organic solvent or petroleum-based solvent such as mineral oil is 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 1-20 parts by mass of hydroxypropyl methylcellulose to 30-90 parts by mass of water, and preferably 5-15 parts by mass of hydroxypropyl methylcellulose to 70-85 parts by mass of water.

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

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

[0037] The defoaming agent may be a surfactant, of which nonionic surfactants are particularly preferred because they have a high defoaming effect.

[0038] The amount of the defoaming agent used is 0.1 to 3 parts by mass, and 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 has the effect of preventing scratches and abrasion 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, and preferably 1 to 3 parts by mass, per 1 to 20 parts by mass of hydroxypropylmethylcellulose for each color ink.

[0041] In addition, from the viewpoints of improving the dispersibility of the pigment, improving the wetting properties, and preventing precipitation, lecithin or sorbitan fatty acid ester may be added in small amounts, and from the viewpoint of adjusting the fluidity, gelling agents, butyl hydroxyl toluene, and other antioxidants may be added in small amounts as appropriate, but these are not particularly required for the flexographic ink of the present invention.

[0042] To manufacture 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. EXAMPLES

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

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

[0045] [Table 1]

[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 Co., Ltd.) to obtain 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 the prints of Examples 1 and 2. The evaluation results are shown in Table 2.

[0048] [Table 2]

[0049] [Evaluation item 1: Viscosity] 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 prints was measured using a spectrophotometer (eXact manufactured by Xrite).

[0051] [Evaluation item 3: Abrasion resistance] An abrasion resistance test was performed on the printed surface of the obtained print using an optical vibration abrasion tester (Tester Sangyo Co., Ltd.) under conditions of a load of 200 g and 100 strokes back and forth, and the degree of scratches on the ink coating surface was visually evaluated. ◎: No scratches 〇: There are minor scratches △: There is considerable damage. ×: Scratches all over the surface.

[0052] [Evaluation item 4: Antifoaming] 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 after and 2 minutes later was visually compared and evaluated. ◎: No bubbles remaining immediately or after 2 minutes 〇: Almost no foam remains after 2 minutes. △: Some foam remains after 2 minutes ×: No reduction in foam was observed from immediately after application until 2 minutes later.

[0053] From the above results, the water-based black ink compositions and printed matter obtained in Examples 1 and 2 can reduce the environmental load while providing performance equivalent to that of general water-based inks.

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

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

Claims

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

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

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

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

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

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

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

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