Flaky brass powder and golden ink for offset printing

Abstract

The present invention provides a flaky brass powder which contains only a small amount of coarse particles, is less likely to cause printing failure, is sufficiently processed into flakes, and contains an appropriate amount of particles having a particle diameter of 1 μm or less, so that a golden printed matter obtained by offset printing using a golden ink containing the flaky brass powder of the present invention dispersed therein exhibits a golden color with high metallic luster and has excellent hiding power.SOLUTION: The flaky brass powder has a median size (D50) of 2 μm or more and 5 μm or less, a D90 / D50 ratio of 1.8 or less, and a particle-size-distribution integrated value of particles having a particle size of 1 μm or less of 0.4% or more and 33% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flake brass powder and a gold ink having the flake brass powder dispersed therein. More specifically, the flake brass powder has little coarse powder, making it less likely to cause printing defects, is sufficiently processed into flakes, and contains an appropriate amount of particles with a particle size of 1 μm or less. The gold ink having the flake brass powder dispersed therein is a gold ink that produces gold printed matter with a high metallic luster and excellent hiding power. [Background technology]

[0002] Generally, gold ink for offset printing uses flake brass powder as a pigment.

[0003] Flake brass powder is mainly an alloy powder of copper and zinc, and is also called bronze powder or gold powder.

[0004] The flake brass powder mainly used is an alloy powder with a composition of 75% copper and 25% zinc by weight, which is close to golden in color, or an alloy powder with a composition of 90% copper and 10% zinc by weight, which is a slightly reddish gold in color.

[0005] Generally, flake brass powder is produced by crushing an alloy of copper and zinc into flakes using various crushers, such as a media stirring mill (typically a ball mill) or a stamp mill, and then performing a surface treatment called "glazing" using fatty acids or the like.

[0006] Offset printing is a printing method also known as planographic printing. It involves a two-stage process: oil-based printing ink is applied only to the image area of ​​a plate cylinder wrapped around a printing plate, with the image area made oil-philic and the non-image area made hydrophilic. The ink is then transferred to the contacting blanket cylinder, and printed onto the printing paper.

[0007] Offset printing is characterized by its ability to produce very fine lines, and is used in many commercial printing processes, including newspapers.

[0008] In offset printing, a common method is to use gold ink, in which gold pigment such as flake brass powder is dispersed in an oil-based varnish, and print the gold areas separately on top of paper that has already been printed normally.

[0009] When offset printing is performed using gold ink with flake brass powder dispersed in it, the surface of the coating is covered with the flake brass powder, giving it a golden metallic luster.

[0010] However, if the particle size of the flake brass powder is too large, problems arise such as print defects such as blurring, and particles that are not sufficiently flaky can reduce the metallic gloss of the coating film.

[0011] On the other hand, if the pulverization process is continued until all the coarse powder is gone, the amount of fine powder will increase.

[0012] If there is too much fine powder, the color of the flake brass powder will turn black due to diffuse reflection of light, and the flake brass powder particles will not float uniformly on the surface of the printed coating film, resulting in a decrease in the metallic gloss of the coating film.

[0013] Furthermore, offset printing is required to ensure that the background does not show through after printing (hereinafter referred to as "hiding power").

[0014] To obtain sufficient hiding power with gold ink containing dispersed flake brass powder, it is necessary to include very fine particles to fill the gaps between the printed particles.

[0015] Therefore, there is a need for the development of a flake brass powder that can be used to produce a gold ink that has little coarse powder, is less likely to cause printing defects, has sufficient flake processing so that the color tone of the flake brass powder does not turn black, and can produce gold printed matter that has excellent hiding power and metallic luster. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Patent Publication No. 2002-309305 Summary of the Invention [Problem to be solved by the invention]

[0017] Patent Document 1 describes a method for producing fine flake metal powder for use in gold or copper metallic printing inks.

[0018] The fine flake metal powder produced by the method described in Patent Document 1 has a wide particle size distribution and contains coarse particles, which results in a problem of low metallic luster in gold printed matter obtained by offset printing.

[0019] The present invention has as its technical objective the resolution of the above-mentioned problems, and as a result of numerous prototypes and experiments, it has been discovered that if the flake brass powder has a median diameter (D50) measured using a laser diffraction particle size distribution analyzer of 2 μm or more and 5 μm or less, a D90 / D50 of 1.8 or less, and the particle size distribution integrated value of particles with a particle diameter of 1 μm or less is 0.4% or more and 33% or less, there will be little coarse powder and printing defects such as blurring will be unlikely to occur, and the powder will be sufficiently processed into flakes and contain an appropriate amount of fine powder with a particle diameter of 1 μm or less.Therefore, gold printed matter obtained by printing with gold ink in which the flake brass powder of the present invention is dispersed will have a gold color with high metallic luster and excellent hiding power, and it will be possible to produce a gold ink that is suitable for offset printing, and the above-mentioned technical objective has been achieved. [Means for solving the problem]

[0020] The above technical problems can be solved by the present invention as follows.

[0021] The present invention provides a flake brass powder having a median diameter (D50) measured with a laser diffraction particle size distribution analyzer of 2 μm or more and 5 μm or less, a D90 / D50 ratio of 1.8 or less, and an integrated particle size distribution value of particles having a particle diameter of 1 μm or less of 0.4% or more and 33% or less.

[0022] The present invention also provides a gold ink obtained by dispersing the above-mentioned flake brass powder in a varnish.

[0023] The present invention also provides the gold ink, wherein 50 parts by weight or more and 150 parts by weight or less of flake brass powder is dispersed in 100 parts by weight of varnish.

[0024] The present invention also relates to the above gold ink for offset printing. [Effects of the Invention]

[0025] The flake brass powder of the present invention focuses on the particle size distribution of flake brass powder obtained by mechanical pulverization, and while the D50 is 2 μm to 5 μm, the D90 / D50 is reduced to 1.8 or less, and the particle size distribution integrated value of particles with a particle diameter of 1 μm or less is 0.4% or more and 33% or less.

[0026] The gold ink in which the flake brass powder of the present invention is dispersed is a gold ink that is less susceptible to printing defects such as blurring caused by coarse powder.

[0027] In addition, because the flake brass powder of this invention is sufficiently processed into flakes and contains an appropriate amount of fine powder with a particle diameter of 1 μm or less, gold printed matter obtained using gold ink with the flake brass powder dispersed therein has excellent hiding power and a high metallic luster.

[0028] Therefore, the gold ink containing the dispersed flake brass powder of the present invention can be suitably used in offset printing. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention provides a flake brass powder that can be used to prepare gold ink suitable for offset printing.

[0030] The alloy composition of brass is not particularly limited, but alloy powder of 75% copper and 25% zinc, which is close to golden yellow, or 90% copper and 10% zinc, which is a slightly reddish gold, is suitable.

[0031] The median diameter (hereinafter referred to as "D50") of the flaky brass powder in the present invention measured with a laser diffraction particle size distribution analyzer is preferably 2 μm to 5 μm, and more preferably 2 μm to 3.5 μm.

[0032] If D50 is less than 2 μm, the small particles will cause diffuse reflection of light, resulting in a black color tone of the flake brass powder, and the flake brass powder particles will not float uniformly on the surface of the printed coating film, which may reduce the metallic gloss of the coating film.

[0033] If D50 is greater than 5 μm, there is a possibility that a certain number of coarse particles with a particle diameter of 10 μm or more will be present in the overall particle size distribution. This coarse powder will not be transferred well to the plate cylinder during the offset printing process, and printing will not be possible at a sufficient density, which may result in fading or a reduction in the metallic gloss of the coating film.

[0034] Even if D50 is in the range of 2 μm to 5 μm, coarse powder may be generated in flake brass powder produced by mechanical pulverization depending on the pulverization conditions.

[0035] However, the flake brass powder of the present invention has a D90 / D50 of 1.8 or less, thereby limiting the content of coarse powder.

[0036] The D90 / D50 of the flaky brass powder of the present invention is preferably 1.8 or less, and more preferably 1.7 or less.

[0037] If D90 / D50 exceeds 1.8, coarse particles may cause fading or reduce the metallic gloss of the coating film.

[0038] In the present invention, particles having a particle diameter of 1 μm or less preferably account for 0.4% to 33% of the total particle size distribution, and more preferably 3% to 10%.

[0039] Particles with a particle size of 1 μm or less have the ability to fill in the gaps between particles larger than 1 μm on the surface of the printed coating, thereby improving the hiding power of the coating.

[0040] If the particle size distribution cumulative value of particles with a particle diameter of 1 μm or less is less than 0.4%, the gaps between the flake brass powder particles cannot be sufficiently filled, and hiding power may be low. If it exceeds 33%, the fine particles may cause the flake brass powder to turn black, and the metallic gloss of the coating film after printing may be reduced.

[0041] Hiding power refers to the ability of gold ink to cover the underlying surface when printed on paper, preventing it from showing through. It can be determined by printing on top of a black area printed on the paper and visually checking whether the underlying surface shows through, or by printing on highly transparent paper such as tracing paper using a metal spatula and then visually checking the transparency when viewed from the back.

[0042] D50, D90 and the integrated value of particles with a particle size of 1 μm or less can be measured and calculated using a laser diffraction particle size distribution measurement method.

[0043] The laser diffraction particle size distribution measurement method involves irradiating particles dispersed in a solvent with laser light and analyzing the intensity of the scattered light generated, thereby determining the particle size distribution in terms of spheres equivalent to the volume.

[0044] The flake brass powder of the present invention can be produced by mechanically pulverizing the flake brass powder and classifying the pulverized powder with an air classifier or the like.

[0045] The flake brass powder of the present invention can be dispersed in a varnish using a mixer or a metal spatula to prepare a gold ink.

[0046] The amount of flake brass powder contained in the gold ink is not particularly limited, but it is recommended that 50 to 150 parts by weight of flake brass powder be dispersed in 100 parts by weight of varnish.

[0047] The varnish is not particularly limited. Examples of binder resins for offset printing varnishes include rosin-modified phenolic resins, rosin-modified maleic acid resins, and rosin-modified alkyd resins. [Example]

[0048] The present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these. Examples 2 to 7 and Comparative Examples 1 to 4 were prepared in the same manner as Example 1 unless otherwise specified.

[0049] Example 1 Gas atomized brass powder consisting of an alloy composition of 75 wt% copper and 25 wt% zinc was pulverized by a stamp mill to obtain flake brass powder.

[0050] The obtained flake brass powder was measured using a laser diffraction particle size distribution analyzer (SALD-2300 / Shimadzu Corporation), and the D50 was found to be 4.869 μm, the D90 / D50 was 2.033, and the particle size distribution integrated value of particles smaller than 1 μm was 0.707%.

[0051] The obtained flake brass powder was classified using an air classifier (Turboplex 50ATP / manufactured by Hosokawa Micron Corporation) to obtain flake brass powder with a D50 of 2.945 μm, a D90 / D50 of 1.699, and a particle size distribution integrated value of particles less than 1 μm of 3.683%.

[0052] The obtained flake brass powder was surface-treated with stearic acid and then polished.

[0053] 100 parts by weight of the gloss-treated flake brass powder was mixed with 100 parts by weight of a varnish for offset printing made of rosin-modified phenolic resin using a painting knife to prepare a gold ink.

[0054] The gold ink thus prepared was used for offset printing using a printability tester (RI Tester, manufactured by Kokubo Seimitsu Co., Ltd.), and then allowed to dry naturally at room temperature for 24 hours, yielding a gold printed matter of Example 1.

[0055] Example 2 Gas atomized brass powder consisting of an alloy composition of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 4.869 μm, a D90 / D50 of 2.033, and a particle size distribution integrated value of 0.707% for particles smaller than 1 μm.

[0056] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 2.556 μm, a D90 / D50 of 1.665, and a particle size distribution integrated value of particles less than 1 μm of 5.069%, which was then subjected to a glazing treatment.

[0057] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to produce the gold printed matter of Example 2.

[0058] Example 3 Gas atomized brass powder consisting of an alloy of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 3.428 μm, a D90 / D50 of 2.130, and a particle size distribution integrated value of 3.371% for particles smaller than 1 μm.

[0059] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 2.432 μm, a D90 / D50 of 1.747, and a particle size distribution integrated value of particles less than 1 μm of 7.169%, which was then subjected to a glaze treatment.

[0060] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to produce the gold printed matter of Example 3.

[0061] Example 4 Gas atomized brass powder consisting of an alloy composition of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 3.630 μm, a D90 / D50 of 2.011, and a particle size distribution integrated value of 2.680% for particles smaller than 1 μm.

[0062] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 2.247 μm, a D90 / D50 of 1.757, and a particle size distribution integrated value of particles less than 1 μm of 9.230%, and then subjected to a glazing treatment.

[0063] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to produce the gold printed matter of Example 4.

[0064] Example 5 Gas atomized brass powder consisting of an alloy composition of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 3.630 μm, a D90 / D50 of 2.011, and a particle size distribution integrated value of 2.680% for particles smaller than 1 μm.

[0065] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 2.611 μm, a D90 / D50 of 1.691, and a particle size distribution integrated value of particles less than 1 μm of 6.353%, and then subjected to a glazing treatment.

[0066] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to produce the gold printed matter of Example 5.

[0067] Example 6 Gas atomized brass powder consisting of an alloy composition of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 7.794 μm, a D90 / D50 of 2.823, and a particle size distribution integrated value of 0.491% for particles smaller than 1 μm.

[0068] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 4.550 μm, a D90 / D50 of 1.772, and a particle size distribution integrated value of particles of 1 μm or less of 0.471%, which was then subjected to a glaze treatment.

[0069] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to produce the gold printed matter of Example 6.

[0070] Example 7 Gas atomized brass powder consisting of an alloy composition of 90% copper and 10% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 7.751 μm, a D90 / D50 of 1.935, and a particle size distribution integrated value of 0.085% for particles smaller than 1 μm.

[0071] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 3.781 μm, a D90 / D50 of 1.747, and a particle size distribution integrated value of particles of 1 μm or less of 1.342%, which was then subjected to a glaze treatment.

[0072] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to produce the gold printed matter of Example 7.

[0073] (Comparative Example 1) Gas atomized brass powder consisting of an alloy composition of 90% copper and 10% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 4.076 μm, a D90 / D50 of 2.141, and a particle size distribution integrated value of 6.384% for particles smaller than 1 μm.

[0074] The obtained flake brass powder was subjected to a glazing treatment without classification.

[0075] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to obtain a gold printed matter of Comparative Example 1.

[0076] (Comparative Example 2) Gas atomized brass powder consisting of an alloy composition of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 1.542 μm, a D90 / D50 of 1.861, and a particle size distribution integrated value of 33.863% for particles smaller than 1 μm.

[0077] The obtained flake brass powder was subjected to a glazing treatment without classification.

[0078] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to obtain a gold printed matter of Comparative Example 2.

[0079] (Comparative Example 3) Gas atomized brass powder consisting of an alloy composition of 75% copper and 25% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 7.794 μm, a D90 / D50 of 2.823, and a particle size distribution integrated value of 0.491% for particles smaller than 1 μm.

[0080] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a D50 of 6.064 μm, a D90 / D50 of 2.482, and a particle size distribution integrated value of particles less than 1 μm of 0.615%, which was then subjected to a glaze treatment.

[0081] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to obtain a gold printed matter of Comparative Example 5.

[0082] Comparative Example 4 Gas atomized brass powder consisting of an alloy composition of 90% copper and 10% zinc by weight was pulverized using a stamp mill to obtain flake brass powder with a D50 of 7.751 μm, a D90 / D50 of 1.935, and a particle size distribution integrated value of 0.085% for particles smaller than 1 μm.

[0083] The obtained flake brass powder was classified using an air classifier to obtain flake brass powder with a particle size distribution of D50 of 5.011 μm, D90 / D50 of 1.724, and no distribution below 1 μm, and then subjected to a glazing treatment.

[0084] Gold ink was prepared using the gloss-treated flake brass powder, and then offset printed and naturally dried to obtain a gold printed matter of Comparative Example 4.

[0085] (gloss value 60°) The 60° gloss value of each gold printed matter of the Examples and Comparative Examples was measured using an appearance analyzer Rhopoint IQ (manufactured by Rhopoint Instruments Ltd.).

[0086] (Metallic luster) The metallic gloss of each gold printed matter of the Examples and Comparative Examples was visually observed.

[0087] Gold printed matter having a metallic gloss was evaluated as "good", and gold printed matter without a metallic gloss was evaluated as "poor".

[0088] (Concealment) 0.2 g of each of the gold inks of the Examples and Comparative Examples was printed on tracing paper by scraping with a metal spatula.

[0089] The printed tracing paper was held up to a light source and visually evaluated to see if the printed area was clearly darker than the non-printed area, as "◎", if it was slightly darker, as "◯", and if it was equally bright, as "×".

[0090] The results of the Examples are shown in Table 1, and the results of the Comparative Examples are shown in Table 2.

[0091] [Table 1]

[0092] [Table 2]

[0093] The gold ink of the example in which flake brass powder was dispersed had excellent hiding power, and the gloss value of the coating film at 60° after offset printing was high, even higher than that of each comparative example.

[0094] It was also verified that the gold print had a high metallic luster when visually inspected. [Industrial Applicability]

[0095] The flake brass powder of the present invention has little coarse powder and is less likely to cause printing defects, is sufficiently processed into flakes, and contains an appropriate amount of particles with a particle diameter of 1 μm or less.Therefore, gold printed matter obtained by offset printing using gold ink in which the flake brass powder of the present invention is dispersed exhibits a gold color with high metallic luster and excellent hiding power. Therefore, the present invention has high industrial applicability.

Claims

1. A flaky brass powder having a median diameter (D50) measured by a laser diffraction particle size distribution analyzer of 2 μm or more and 5 μm or less, a D90 / D50 ratio of 1.8 or less, and an integrated value of particle size distribution of particles having a particle diameter of 1 μm or less of 0.4% or more and 33% or less.

2. 2. A gold ink comprising the flake brass powder of claim 1 dispersed in a varnish.

3. 3. The gold ink according to claim 2, wherein 50 parts by weight or more and 150 parts by weight or less of flake brass powder is dispersed in 100 parts by weight of varnish.

4. 4. The gold ink according to claim 2 or 3, which is for offset printing.

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