CN117801602A - Magnetic color-changing ink for offset printing color-changing package and preparation method thereof - Google Patents

Abstract

The present invention relates to the technical field of color-changing inks, and in particular to a magnetic color-changing ink for offset printing color packaging and a preparation method thereof. According to parts by mass, this ink includes 17-20 parts of petroleum hydrogenated light fraction, 3-4 parts of melamine resin, 5-10 parts of magnetic color-changing pigment, 20-35 parts of ink binder, and 2-5 parts of photoinitiator, diluted 5-10 parts of agent, 0.1-1 part of aluminate, 0.05-0.2 part of defoaming agent, 0.05-0.5 part of degelling agent, 25-35 parts of active monomer; the magnetic color-changing pigment includes a pigment core and a package A coating layer covering the pigment core, the coating layer is colorless and transparent, and the light transmittance of the coating layer changes under the action of a magnetic field. The magnetic color-changing ink disclosed in the present invention can be screen-printed on the surface of offset-printed colored packaging, and exhibits a good magnetochromic effect.

Description

Magnetic color-changing ink for offset printing color packaging and preparation method thereof

Technical field

The present invention relates to the technical field of color-changing inks, and in particular to a magnetic color-changing ink for offset printing color packaging and a preparation method thereof.

Background technique

With the development of society and the continuous improvement of people's aesthetic level, the requirements for the effect of packaging printing have become increasingly in-depth and detailed. In some products that have requirements for their own value and characteristics, in addition to basic requirements such as printing color and stability, , Packaging printed matter also needs to complete special effects such as color changes, which puts forward new demands for printing inks. The above-mentioned color-changing effect is mainly achieved by color-changing ink. Current color-changing inks have developed into multiple categories, which are generally divided into thermochromic inks, fluorescent color-changing inks, infrared color-changing inks, luminous color-changing inks, magnetic inks, water-sensitive color-changing inks, etc. based on different functional materials.

Traditional magnetic ink generally only mixes iron oxide powder and other magnetic substances into ordinary ink for printing, and is used in fields such as tickets, bank books, and ID cards. The general principle is to use magnetic substances such as iron oxide or a mixture of iron oxide and cobalt as color, so that the magnetic detector can detect and decode the magnetic signal. In order to combine the information recording function of traditional magnetic ink with the color change and anti-counterfeiting effects of color-changing ink, some researchers have tried to combine the two to obtain magnetic color-changing ink that has both characteristics. For example, the Chinese patent application CN1088239 of the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences is a magnetic color-changing ink and its printing method and application. Magnetism is added to the colorless transparent ink, and multi-layer color-changing inks are symmetrically plated on both sides of the magnetic coating. The magnetic film crushing material of the film has both general visual effects and dual anti-counterfeiting functions of professional equipment, and can be used for identification in vending machines, fast money counting machines and other devices.

However, the magnetic color-changing ink in the prior art still has the following problems: 1. The primary color of the existing magnetic color-changing ink based on iron oxide particles is single, usually black or brown. Since the background color is relatively dark, on the one hand, it limits the printing ability. On the other hand, it also makes it difficult to observe the color changes of related patterns under the influence of magnetism. 2. Since existing magnetic color-changing inks generally contain layers of oxide or magnetic alloy powder materials, when forming magnetic thin film materials, they are generally applied to the multi-layer color-changing film structure using methods such as vacuum evaporation or sputtering. For example, the magnetic color-changing ink prepared by the existing literature method is prepared by mixing the above-mentioned color-changing film powder and colorless ink. During the packaging and printing process, it is difficult to directly print using the printing process of general ink. If printing is forced according to the general process, especially when the ordinary silk screen printing process is used to print the anti-counterfeiting layer with the above-mentioned magnetic color-changing ink on the existing offset printing layer, the pattern and the expected effect will produce obvious color differences and a larger graininess. , unable to achieve the expected magnetochromic effect.

The applicant has proposed a magnetic color-changing ink and its preparation method with publication number CN112778839A. The ink comprises, by weight, 17-20 parts of petroleum hydrogenation light fraction, 3-4 parts of melamine resin, 0.5-2 parts of magnetic particles, 20-35 parts of ink binder, 0.5-1.5 parts of phenol-modified urea-formaldehyde resin, 2-5 parts of photoinitiator, 5-10 parts of diluent, 0.1-1 parts of aluminate, 0.05-0.2 parts of defoamer, 0.05-0.5 parts of anti-gelling agent and 25-35 parts of active monomer; the particle size of the magnetic particles is 10-450nm. The color-changing principle of this ink is that "when an external magnetic field is applied to the color-changing ink of the present application, the magnetic particles therein are magnetically polarized, and the distance between the particles is kept constant, reflecting light with a wavelength corresponding to the distance between the particles; when the intensity or direction of the external magnetic field changes, the wavelength of the reflected light and the displayed color change accordingly." This ink is mainly used on "white cardboard, coated paper and cast-coated paper commonly used in cigarette box packaging" and is not suitable for printing an anti-counterfeiting layer with a magnetic color-changing ink on an existing offset layer using ordinary silk-screen printing technology.

Contents of the invention

The present invention aims to solve the above problems and provide a magnetic color-changing ink for offset printing color packaging and a preparation method thereof.

The technical solution of the present invention to solve the problem is to first provide a magnetic color-changing ink for offset printing color packaging, which according to the mass parts includes 17-20 parts of petroleum hydrogenation light fraction, 3-4 parts of melamine resin, and 20-35 parts of ink binder parts, photoinitiator 2-5 parts, diluent 5-10 parts, aluminate 0.1-1 part, defoaming agent 0.05-0.2 parts, degelling agent 0.05-0.5 parts, active monomer 25-35 parts;

It also includes 5-10 parts of magnetic color-changing pigments. The magnetic color-changing pigments include a pigment core and a coating layer covering the pigment core; the coating layer includes a colorless transparent medium and a magnetochromic medium. The magnetochromic medium is nano-superparamagnetic ferroferric oxide hydrosol, and the light transmittance of the coating layer changes under the action of a magnetic field.

The present application sets a coating layer to coat the core of the magnetic color-changing pigment, so that it can be applied on the offset printing layer. And the magnetic color-changing pigment with such a coating structure is different from the color-changing principle of the magnetic color-changing ink previously proposed by the applicant. The present application is: when an external magnetic field is applied to the magnetic color-changing ink of the present application, the spacing between the particles in the magnetic color-changing pigment changes, and light of a specific frequency range is reflected; therefore, the coating layer in the magnetic color-changing pigment changes from colorless and transparent to a specific color under the action of the magnetic field; when the intensity or direction of the external magnetic field changes, the wavelength of the reflected light and the displayed color change accordingly.

Preferably, the pigment core is a reducible oxide of Fe, Ni or Co.

Preferably, the colorless transparent medium is selected from the group consisting of methanol, ethanol, toluene, benzene, chloroform, melamine formaldehyde, gelatin, ethyl cellulose, polyamide, methyl methacrylate, and propylene carbonate. Or several.

As a preferred option of the present invention, the mass ratio of the colorless transparent medium and the magnetochromic medium is (0.5-2):1.

As a preferred option of the present invention, the mass ratio of the pigment core and the coating layer is 1: (2-9).

As a preferred embodiment of the present invention, the composition includes, by mass, 18 parts of petroleum hydrogenation light fraction, 4 parts of melamine resin, 1 part of pigment core, 30 parts of ink binder, 3 parts of photoinitiator, 8 parts of diluent, 0.5 parts of aluminate, 0.1 parts of defoaming agent, 0.3 parts of anti-gelling agent and 30 parts of active monomer.

As preferred in the present invention, the reactive monomer is composed of ethoxyethoxyethyl acrylate, 2-phenoxyethyl acrylate, isobornyl methacrylate, ethoxylated bisphenol A acrylate, Propoxylated glyceryl triacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, trimethylolpropane trimethacrylate, ethoxy It is prepared by mixing at least two of trimethylolpropane triacrylate, pentaerythritol triacrylate and 3-(2,3-epoxypropoxy)propyltrimethoxysilane in any mass ratio.

As preferred embodiment of the present invention, the photoinitiator is selected from one or more of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 1-(4-morpholinophenyl)-2-(dimethylamino)-2-benzyl-1-butanone, 2-benzoylbenzoic acid methyl ester, 4-phenylbenzophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone and 1-hydroxy-cyclohexyl-phenyl ketone.

As a preferred embodiment of the present invention, the ink binder is selected from one or more of alkyd resin, polyamide resin, vinyl resin, epoxy resin, polyphenylene ether resin, polyurethane resin and acrylate oligomer resin.

Another object of the present invention is to provide a preparation method of magnetic color-changing ink for offset printing color packaging, which includes the following steps:

a. After the pigment core is immersed in the solution of the material used in the coating layer, it is spray-dried to obtain the magnetic color-changing pigment;

b. The light fraction of petroleum hydrogenation is divided into two parts, one part is mixed with melamine resin, ink binder, diluent, aluminate, defoamer, anti-gelling agent, and active monomer, stirred evenly, and filtered to obtain liquid 1; the other part is mixed with a photoinitiator, stirred evenly, and filtered to obtain liquid 2;

c. Add the magnetic color-changing pigment to the material liquid one, stir evenly at a speed of less than 300r/min, then raise the temperature to 50-70°C and stir for 40-60 minutes to obtain the material liquid three;

d. Mix material liquid three and material liquid two, stir evenly to obtain a mixture;

e. Bake the mixture in an oven at a temperature lower than the boiling point of the hydrogenated petroleum light fraction until it is dry;

f. After pulverizing the dried mixture, grind it to powder while cooling to obtain a magnetic color-changing ink product.

As a preferred embodiment of the present invention, the grinding is performed to a fineness of less than 10 microns.

Another object of the present invention is to provide an application of magnetic color-changing ink for offset-printed color packaging, which is used to print an anti-counterfeiting layer on the offset-printed bottom layer.

Beneficial effects of the present invention:

1. When an external magnetic field is applied to the magnetic color-changing ink of the present application, the distance between the particles in the magnetic color-changing pigment changes, reflecting light in a specific range of frequencies; therefore, the coating layer in the magnetic color-changing pigment changes from colorless to transparent under the action of the magnetic field. It is a specific color; when the strength or direction of the external magnetic field changes, the wavelength of the reflected light and the displayed color change accordingly.

2. By controlling the particle size of the raw material and the preparation process, the magnetic color-changing ink in the present invention can use ordinary screen printing technology to print an anti-counterfeiting layer with the above-mentioned magnetic color-changing ink on the existing offset printing layer. It shows a better magnetochromic effect on the underlying pattern without affecting the pattern of the formed graphics, which can provide more diverse choices for the design of actual packaging styles and the selection of printing processes.

3. The magnetic color-changing ink in the present invention is colorless and transparent under normal conditions, showing the underlying pattern of the offset printing below. In a strong magnetic field, its light transmittance changes to a translucent light-changing strip, thereby showing different anti-counterfeiting patterns. ; Because when the anti-counterfeiting pattern appears, the intensity of the magnetic field can be adjusted to cause the wavelength of the reflected light of the anti-counterfeiting pattern to change within the visible light range. The discoloration range is wide and the discoloration effect is obvious. It is unique and stronger than the existing magnetic color-changing inks on the market. anti-counterfeiting effect.

4. The preparation method of the magnetic color-changing ink in the present invention can use the magnetic color-changing ink for printing in a manner similar to the general cigarette box packaging printing process, and can further directly use the magnetic color-changing ink to print special anti-counterfeiting patterns. In general scenes, the transparent pattern is covered by the background color and does not appear. In the magnetic field, due to the change in the light transmittance of the color-changing ink and its own color development, a pattern or font that looks different from the background color appears, thereby achieving a corresponding anti-counterfeiting effect.

Detailed ways

The following are specific embodiments of the present invention, and further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

Example 1

A magnetic color-changing ink for offset printing color packaging, including, in parts by mass, 18 parts of petroleum hydrogenated light fractions, 4 parts of melamine resin, 30 parts of ink binder, 3 parts of photoinitiator, 8 parts of diluent, and 0.5 aluminate 0.1 part of defoaming agent, 0.3 part of degelling agent, 30 parts of active monomer, and 8 parts of magnetic color-changing pigment.

Among them, the magnetic color-changing pigment includes a pigment core and a coating layer covering the pigment core. The pigment core is 1 part and the coating layer is 7 parts. The pigment core is made of iron ferric oxide. The coating layer is an equal mass ratio mixture of a colorless transparent medium and a magnetochromic medium. The magnetochromic medium is nano-superparamagnetic iron tetroxide hydrosol, and methanol is used as the colorless transparent medium.

The active monomer is an equal mass ratio mixture of ethoxyethoxyethyl acrylate and isobornyl methacrylate.

The photoinitiator was phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

The ink binder is alkyd resin.

The preparation method of this magnetic color-changing ink for offset printing color packaging includes the following steps:

a. After the pigment core is immersed in the solution of the material used in the coating layer, it is spray-dried to obtain the magnetic color-changing pigment.

b. Divide the petroleum hydrogenated light fraction into two parts according to the mass ratio of 8:2, the larger part is mixed with melamine resin, ink binder, diluent, aluminate, defoaming agent, degelling agent, The active monomers are mixed, stirred evenly, and filtered to obtain material liquid one; another smaller portion is mixed with the photoinitiator, stirred evenly, and filtered to obtain material liquid two.

c. Add the magnetic color-changing pigment to material liquid one, stir evenly at a speed of 200r/min, then raise the temperature to 60°C and stir for another 50 minutes to obtain material liquid three.

d. Mix material liquid three and material liquid two on a high-speed disperser and stir evenly to obtain a mixture.

e. Bake the mixture in an oven at a temperature lower than the boiling point of the hydrogenated petroleum light fraction until it is dry.

f. After pulverizing the dried mixture, grind it to a fineness of 8 μm while cooling to obtain a magnetic color-changing ink product.

Example 2

A kind of magnetic color-changing ink for offset printing color packaging, including 17 parts of petroleum hydrogenated light fraction, 3 parts of melamine resin, 20 parts of ink binder, 2 parts of photoinitiator, 5 parts of diluent, and 0.1 aluminate in parts by mass. parts, 0.05 parts of defoaming agent, 0.05 parts of degelling agent, 25 parts of active monomers, and 5 parts of magnetic color-changing pigments.

Among them, the magnetic color-changing pigment includes a pigment core and a coating layer covering the pigment core. The pigment core is 0.5 parts and the coating layer is 4.5 parts. The pigment core is made of cobalt trioxide. The coating layer is a mixture of a colorless transparent medium and a magnetochromic medium at a mass ratio of 2:1. The magnetochromic medium is nano-superparamagnetic iron tetroxide aqueous sol, and the colorless and transparent medium is ethanol.

The active monomer is composed of propoxylated glycerol triacrylate, tripropylene glycol diacrylate, and 1,6-hexanediol diacrylate in a mass ratio of 3:1:2.

The photoinitiator is a mixture of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 4-phenylbenzophenone in an equal weight ratio.

The ink binder is an equal mass ratio mixture of alkyd resin and polyamide resin.

The preparation method of this magnetic color-changing ink for offset printing color packaging includes the following steps:

a. After the pigment core is immersed in a solution of the material used for the coating layer, it is spray-dried to obtain a magnetic color-changing pigment.

b. Divide the petroleum hydrogenated light fraction into two parts according to the mass ratio of 9:1. The larger part is mixed with melamine resin, ink binder, diluent, aluminate, defoaming agent, degelling agent, The active monomers are mixed, stirred evenly, and filtered to obtain material liquid one; another smaller portion is mixed with the photoinitiator, stirred evenly, and filtered to obtain material liquid two.

c. Add the magnetic color-changing pigment to the material liquid one, stir evenly at a speed of 180r/min, then raise the temperature to 50°C and stir for another 60 minutes to obtain the material liquid three.

d. Mix material liquid three and material liquid two on a high-speed disperser and stir evenly to obtain a mixture.

e. Bake the mixture in an oven at a temperature lower than the boiling point of the hydrogenated petroleum light fraction until it is dry;

f. After pulverizing the dried mixture, grind it to a fineness of 9 μm while cooling to obtain a magnetic color-changing ink product.

Example 3

A magnetic color-changing ink for offset printing color packaging comprises, in parts by mass, 20 parts of petroleum hydrogenation light fraction, 3.5 parts of melamine resin, 35 parts of ink vehicle, 5 parts of photoinitiator, 10 parts of diluent, 1 part of aluminate, 0.2 parts of defoamer, 0.5 parts of anti-gelling agent, 35 parts of active monomer and 10 parts of magnetic color-changing pigment.

The magnetic color-changing pigment includes a pigment core and a coating layer covering the pigment core, wherein the pigment core is 3 parts and the coating layer is 7 parts. The pigment core is made of nickel oxide. The coating layer is a mixture of a colorless transparent medium and a magnetochromic medium in a mass ratio of 1:2, the magnetochromic medium is a nano superparamagnetic ferroferric oxide hydrosol, and the colorless transparent medium is a mixture of ethanol and polyamide in an equal mass ratio.

The active monomer is pentaerythritol triacrylate.

The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone. The ink binder is an equal mass ratio mixture of polyurethane resin and acrylic oligomer resin.

The ink vehicle is a mixture of alkyd resin and epoxy resin in equal weight ratio.

The preparation method of this magnetic color-changing ink for offset printing color packaging includes the following steps:

a. After the pigment core is immersed in the solution of the material used in the coating layer, it is spray-dried to obtain the magnetic color-changing pigment.

b. Divide the petroleum hydrogenated light fraction into two parts according to the mass ratio of 7:3, and the larger part is mixed with melamine resin, ink binder, diluent, aluminate, defoaming agent, degelling agent, The active monomers are mixed, stirred evenly, and filtered to obtain material liquid one; another smaller portion is mixed with the photoinitiator, stirred evenly, and filtered to obtain material liquid two.

c. Add the magnetic color-changing pigment to the material liquid one, stir evenly at a speed of 100r/min, then raise the temperature to 70°C and stir for another 40 minutes to obtain the material liquid three;

d. Mix material liquid three and material liquid two on a high-speed disperser and stir evenly to obtain a mixture.

e. Bake the mixture in an oven at a temperature lower than the boiling point of the hydrogenated petroleum light fraction until it is dry;

f. After pulverizing the dried mixture, grind it to a fineness of 7 μm while cooling to obtain a magnetic color-changing ink product.

Comparative example 1

Using the method disclosed in the prior art CN1088239, the magnetic color-changing film is obtained by following the steps of coating a release layer on a flexible film, plating a multi-layer color-changing film, plating a magnetic film, stripping, crushing, surface treatment, mixing with transparent ink, etc. Fragments of magnetic color-changing ink.

Comparative example 2

This comparative example is basically the same as Example 1, except that the magnetic color-changing pigment used therein does not include a coating layer.

Comparative example 3

This comparative example is substantially the same as Example 1, except that the coating layer does not contain a magnetochromic medium.

After the finished product is produced, the performance test of the magnetic color-changing ink obtained in the embodiments and comparative examples of the present invention is carried out. The relevant performance test items and test methods are as follows:

Printing detection on the offset printing layer: Use ordinary screen printing technology to print an anti-counterfeiting layer on the existing offset printing layer.

Magnetic color-changing ink and cigarette box packaging tinting strength test: According to the GB/T 14624.2 ink tinting strength testing method, weigh 2g of white ink and 0.2g of magnetic color-changing ink on a glass piece, and use an ink mixing knife to take about 0.5g of the standard sample that has been mixed thoroughly. Apply the ink to the upper right and upper left of the sample paper of the material to be tested. Use a scraper to scrape the ink into a thin layer on the sample paper. After forming a standard pattern, calculate the tinting strength of the sample within 30 seconds.

Color difference test: Use an ink color and color difference automatic tester to measure and obtain the color deviation between the printed product of each embodiment and the standard color sample.

Drying performance test: initial drying property. Place a small amount of ink at 100 microns of the groove of the scraper, scrape it off quickly, immediately turn on the stopwatch, and after 30 seconds, use a piece of ink, align the lower end with the zero mark, place it flat against the groove, press it quickly with the palm of your hand, and remove the ink. Remove the paper and measure the length of the unsticky ink, expressed in millimeters, which is the initial drying property (mm. 25°C, relative humidity 65±5°C).

Fineness test: Use the method specified in GB/T1724-2019 for the determination of grinding fineness of paints, varnishes and printing inks to conduct the ink fineness test.

The test results of the products of each embodiment and comparative example are shown in Table 1.

Table 1.

Compared with Comparative Example 1, it can be seen that when the magnetic color-changing ink of the present invention is printed on the existing offset printing layer using ordinary screen printing technology, it has the effect of significantly reducing the color difference of the pattern and greatly reducing the particle size.

Compared with Comparative Examples 2 and 3, it can be seen that the magnetic color-changing ink of the present invention has a correlation by limiting the magnetic color-changing pigment used to include a coating layer covering the pigment core, and the magnetochromic medium contained in the coating layer. The synergistic effect can achieve the effect that the transparency is covered by the background color and does not appear in normal scenes. In the magnetic field, due to the change in light transmittance of the color-changing ink and its own color development, patterns or fonts that appear to be different colors than the background color appear. If the coating layer is missing in Comparative Example 2, or if the magnetochromic medium included in the coating layer is missing in Comparative Example 3, it is difficult to achieve the above effect, and the required discoloration effect cannot be achieved.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or additions to the described specific embodiments or substitute them in similar ways, but this will not deviate from the spirit of the present invention or exceed the definition of the appended claims. range.

Claims (10)

1. The magnetic color-changing ink for offset printing color-changing packaging comprises, by mass, 17-20 parts of petroleum hydrogenation light fraction, 3-4 parts of melamine resin, 20-35 parts of ink binder, 2-5 parts of photoinitiator, 5-10 parts of diluent, 0.1-1 part of aluminate, 0.05-0.2 part of defoamer, 0.05-0.5 part of anti-gelling agent and 25-35 parts of active monomer;

the method is characterized in that:

the color-changing pigment comprises a pigment core body and a coating layer coating the pigment core body, wherein the pigment core body comprises 5-10 parts of magnetic color-changing pigment; the coating layer comprises a colorless transparent medium and a magneto-chromic medium, wherein the magneto-chromic medium is nano superparamagnetic ferroferric oxide hydrosol, and the light permeability of the coating layer is changed under the action of a magnetic field.

2. The magnetic color-changing ink for offset color packaging according to claim 1, wherein: the pigment core body is made of reducible oxide of Fe, ni or Co.

3. The magnetic color-changing ink for offset color packaging according to claim 1, wherein: the colorless transparent medium is one or more selected from methanol, ethanol, toluene, benzene, chloroform, melamine formaldehyde, gelatin, ethyl cellulose, polyamide, methyl methacrylate and propylene carbonate.

4. The magnetic color-changing ink for offset color packaging according to claim 1, wherein: the mass ratio of the colorless transparent medium to the magnetochromic medium is (0.5-2): 1.

5. the magnetic color-changing ink for offset color packaging according to claim 1, wherein: the mass ratio of the pigment core body to the coating layer is 1: (2-9).

6. The magnetic color-changing ink for offset color packaging according to claim 1, wherein: the active monomer is formed by mixing at least two of ethoxyethoxy ethyl acrylate, 2-phenoxyethyl acrylate, isobornyl methacrylate, ethoxylated bisphenol A acrylate, propoxylated glycerol triacrylate, tripropylene glycol diacrylate, 1, 6-hexanediol diacrylate, neopentyl glycol diacrylate, trimethylolpropane trimethacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate and 3- (2, 3-epoxypropoxy) propyl trimethoxysilane according to any mass ratio.

7. The magnetic color-changing ink for offset color packaging according to claim 1, wherein: the photoinitiator is selected from one or more of phenyl bis (2, 4, 6-trimethylbenzoyl) phosphine oxide, 1- (4-morpholinophenyl) -2- (dimethylamino) -2-benzyl-1-butanone, 2-benzoyl methyl benzoate, 4-phenylbenzophenone, 2,4, 6-trimethylbenzoyl-diphenyl phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-acetone and 1-hydroxy-cyclohexyl-phenyl ketone.

8. The magnetic color-changing ink for offset color packaging according to claim 1, wherein: the ink binder is one or more selected from alkyd resin, polyamide resin, vinyl resin, epoxy resin, polyphenyl ether resin, polyurethane resin and acrylate oligomer resin.

9. A method for preparing the magnetic color-changing ink for offset color packaging according to any one of claims 1 to 8, characterized in that: the method comprises the following steps:

a. dipping the pigment core body in a solution of a material used for the coating layer, and then spray-drying to obtain the magnetic color-changing pigment;

b. dividing petroleum hydrogenation light fraction into two parts, mixing one part with melamine resin, ink binder, diluent, aluminate, defoamer, anti-gelling agent and active monomer, stirring uniformly, and filtering to obtain feed liquid I; mixing the other part with a photoinitiator, uniformly stirring, and filtering to obtain a second feed liquid;

c. adding a magnetic color-changing pigment into the feed liquid I, uniformly stirring at a speed of less than 300r/min, heating to 50-70 ℃, and stirring for 40-60min to obtain a feed liquid III;

d. mixing the material liquid III with the material liquid II, and uniformly stirring to obtain a mixture;

e. baking the mixture in a baking oven under the temperature condition lower than the boiling point of the petroleum hydrogenation light fraction until the mixture is dried;

f. and (3) crushing the dried mixture, and grinding the mixture into powder while cooling to obtain the magnetic color-changing ink product.

10. Use of a magnetically variable ink for offset color packaging according to any one of claims 1 to 8, characterized in that: for overprinting the security layer on the offset-printed substrate.