Multi-angle color-changing cold stamping foil and preparation process thereof

Abstract

The invention discloses a multi-angle color-changing cold stamping foil and a preparation process thereof, and relates to the technical field of package printing and anti-counterfeiting. The cold stamping foil comprises a base film layer, a separation layer, a first aluminum plating layer, a dielectric layer, a second aluminum plating layer and an adhesive layer which are sequentially stacked, the thickness of the dielectric layer is 100-500 nm, and the second aluminum plating layer is a semitransparent layer with the thickness of 5-20 nm. The preparation process comprises the following steps: preparing the cold stamping foil, coating an adhesive on a printing stock, pressing and transferring, and stripping a base film. According to the invention, the Fabry-Perot interference structure is formed by controlling the thicknesses of the two aluminized layers and the middle dielectric layer, so that the final hot stamping pattern presents a smooth and bright dynamic color changing effect at different observation angles. The technology is compatible with standard cold stamping equipment, the cost is low, the efficiency is high, and the manufactured product has the excellent visual effect and the high anti-fake performance and is suitable for the fields of high-end packaging, anti-fake certificates and the like.

Description

Technical Field

[0001] This invention relates to the fields of packaging printing and anti-counterfeiting technology, specifically to a multi-angle color-changing cold foil and its preparation process. It is an innovative method and product that achieves a multi-angle dynamic color-changing effect of a pattern through secondary aluminum plating and dielectric layer structure design. Background Technology

[0002] Cold foil stamping is a printing finishing process that transfers the metal or pattern layer from aluminum foil to the surface of a substrate (such as paper, plastic, or fabric) using a cold foil adhesive at room temperature or under pressure. Compared to traditional hot foil stamping, it eliminates the need for heated printing plates, offering significant advantages such as high production efficiency, low energy consumption, a wide range of applicable substrates, and high line precision. Therefore, cold foil stamping technology has been widely used in high-end luxury packaging, anti-counterfeiting labels, trademarks, publication covers, and security documents.

[0003] As the market's demands for product aesthetics and anti-counterfeiting features continue to rise, simple metallic luster or static holographic effects are no longer sufficient. Optical color-changing effects, which can dynamically change color depending on the viewing angle, have become a cutting-edge technological goal pursued by the industry due to their strong visual appeal and excellent anti-counterfeiting properties.

[0004] Currently, the main technologies for achieving similar visual effects are optically variable film transfer technology, multi-laser holography technology, and optically variable ink and printing overlay technology. Optically variable films, based on complex optical interference or diffraction structures, can produce vibrant and continuously changing dynamic colors. However, applying them to products typically requires specialized composite, molding, or hot stamping transfer processes. These processes have poor compatibility with mainstream cold stamping production lines, resulting in high equipment modification costs. Furthermore, the manufacturing cost of optically variable films is extremely high, limiting their application to a very limited range of fields such as currency and high-security documents, making widespread adoption in commercial packaging difficult. Multi-laser holography technology generates a sense of depth and color changes by recording complex fringes formed by the interference of multiple laser beams. While it can be combined with hot stamping to form laser holographic hot stamping foil, the equipment for producing laser holographic masters and molding workpieces is extremely expensive and technically complex. The resulting color changes are usually discrete rainbow spectra, lacking smoothness and naturalness, resulting in a somewhat harsh visual effect. Additionally, the complex holographic patterns can sometimes interfere with the legibility of text or the main image. The optically variable ink and printing overlay technology typically involves first performing ordinary hot stamping on the substrate, and then partially overprinting an optically variable ink layer onto the hot stamped pattern. This results in a disjointed visual effect; the static metallic base color and the overlaid color-changing ink layer fail to create a unified optical effect, leading to visual disharmony. The metallic texture is partially obscured by the ink layer. Furthermore, the pigment particles in the ink scatter and absorb light, causing the color saturation, brightness, and purity to be far lower than the "structural color" produced purely by thin-film interference, resulting in an overall dull visual effect. This technology requires two independent processes: hot stamping and precise overprinting. In high-speed production, extremely high registration accuracy is required, leading to a high rate of defective products and low production efficiency. Moreover, the surface ink layer typically has lower abrasion and scratch resistance than a metal plating layer, making it susceptible to damage over long-term use, affecting aesthetics and anti-counterfeiting lifespan.

[0005] Therefore, this invention proposes a cold foil stamping method that can be directly integrated into the structure of cold foil stamping. It utilizes mature cold foil stamping technology to form the foil in one step, maintaining the advantages of high efficiency and low cost while producing a smooth and vibrant dynamic color-changing effect comparable to optical color changing. This provides a truly high-performance, aesthetically pleasing and practical technical means for high-end packaging and anti-counterfeiting applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a cold foil stamping method that is simple in process, cost-controllable, easy to industrialize, and can produce a strong multi-angle color-changing effect. This method aims to form a nanostructure with optical interference effect after cold foil transfer through two independent aluminum plating processes and a specific interlayer dielectric design, thereby achieving a color effect that dynamically changes with the viewing angle.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In one aspect, the present invention provides a multi-angle color-changing cold foil, comprising, from bottom to top: Base film layer; Release layer coated on the base film layer; The first aluminum plating layer formed on the release layer serves as a reflective layer. A dielectric layer coated on the first aluminum plating layer, wherein the thickness of the dielectric layer is 100nm-500nm; The second aluminum plating layer formed on the dielectric layer serves as a semi-reflective layer with a thickness of 5 nm-20 nm. And an adhesive layer applied to the second aluminum plating layer.

[0008] Furthermore, the dielectric layer is made of a transparent or translucent polymer resin, selected from acrylic resin, polyurethane resin, epoxy acrylate, or blends thereof, with a refractive index of 1.45–1.65; the base film layer is a 12–25 µm PET, BOPP, or PI film; the release layer is a wax-based or silicone-based peelable coating with a dry film weight of 0.5–1.5 g / m³. 2 .

[0009] Furthermore, the first aluminum plating layer has a thickness of 20nm-50nm and is a continuous and dense high-reflectivity aluminum layer; the second aluminum plating layer is a semi-transparent aluminum layer with an optical density of 0.2-0.6, which causes the incident light to be partially reflected and partially transmitted.

[0010] Furthermore, the interlayer peel force of the cold foil is 0.08–0.25 N / cm, achieving 100% transfer during cold foil peeling with no aluminum layer residue.

[0011] On the one hand, the present invention provides a preparation process for multi-angle color-changing cold foil stamping products, including the following steps: S1: Sequentially deposit a release layer, a first aluminum plating layer, a dielectric layer with a thickness of 100nm–500 nm, a second aluminum plating layer with a thickness of 5nm–20 nm, and an adhesive layer on a base film to obtain a cold hot stamping foil. S2: Apply cold foil stamping adhesive to the predetermined pattern area of ​​the substrate; S3: Align and bond the adhesive layer of the cold foil with the cold foil adhesive on the substrate, and complete the cold foil transfer at room temperature and pressure. The cold foil transfer pressure is 0.3–1.2 MPa, the transfer temperature is 15–40℃, and the transfer speed is 20–120 m / min. S4: Peel off the base film layer to transfer the structure above the release layer onto the substrate, forming a pattern with a multi-angle color-changing effect.

[0012] Furthermore, in step S1, both the first and second aluminum plating layers of the cold foil are formed by vacuum evaporation.

[0013] Furthermore, in step S1, the medium layer of the cold foil is formed by gravure coating or a similar coating method, and by controlling the coating parameters to adjust the thickness of the medium layer by ±5 nm, the color-changing sequence can be switched arbitrarily between gold-green, green-blue, purple-blue, and red-gold.

[0014] Furthermore, the cold-stamping adhesive mentioned in step S2 is a UV-curing adhesive or a water-based acrylic adhesive, with a dry film weight of 2.0-4.0 g / m³. 2 After step S4 peels off the base film layer, the process also includes a step of curing the adhesive by UV light.

[0015] On the other hand, the present invention provides a multi-angle color-changing cold foil stamping product, wherein the product forms a stacked structure including a first aluminum plating layer, a dielectric layer and a second aluminum plating layer on the surface of the substrate, which makes the pattern color change smoothly and dynamically with different viewing angles.

[0016] Furthermore, by adjusting the thickness of the dielectric layer, different color change sequences can be achieved, including gold changing to green or purple changing to blue.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. This invention constructs a stacked structure of "high reflectivity layer - optical spacer layer - second aluminum-plated semi-reflective layer" in cold foil, forming a microscopic "Fabry-Perot" type interference cavity. Light undergoes multiple reflections and interferences within this structure, with the interference conditions changing with the viewing angle. This results in a continuous and smooth shift in the dominant wavelength of the reflected light, producing a physical color-changing effect. It perfectly integrates dynamic color changes with a metallic texture, and its color purity and optical effects far surpass those of traditional ink-layering printing methods.

[0018] 2. The cold foil structure design and cold foil printing process of the present invention do not require any modification to the existing expensive cold foil printing equipment or the addition of complex optical processing equipment. They can utilize the existing production line to achieve the production of high-end dynamic color-changing effects, which is conducive to rapid industrialization.

[0019] 3. Compared to relying on special optical thin films or complex laser holographic technology to achieve similar effects, this invention mainly adopts vacuum evaporation and coating processes, resulting in low raw material costs and strong controllability of the production process. Furthermore, the entire color-changing effect can be completed in a single cold foil transfer process, completely avoiding the problems of low efficiency, low precision, and high scrap rate caused by multiple processes in traditional cold foil stamping and overprinting color-changing ink solutions, significantly improving production efficiency and product qualification rate.

[0020] 4. By adjusting the thickness of nanoscale film layers such as the dielectric layer and the semi-transparent aluminum layer, this invention creates a dynamic color-changing effect that is intuitive, eye-catching, and cannot be reproduced by ordinary scanning or copying. This provides dual anti-counterfeiting protection for products, allowing for easy identification of authenticity by observing color changes with the naked eye, and also enabling authentication by testing the film structure with professional equipment. It is suitable for high-end product packaging, brand anti-counterfeiting, securities, and security documents.

[0021] 5. This invention allows for color-changing patterns by adjusting the thickness and refractive index of the dielectric layer, thereby meeting the anti-counterfeiting requirements of different brands and products. Furthermore, the outermost layer of the pattern finally transferred to the substrate surface consists of a second aluminum plating layer and a dielectric layer, which possess excellent wear resistance, scratch resistance, and chemical stability, a smooth feel, and can maintain a vibrant visual effect for a long time, resulting in a long product lifespan. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: Gold-green color-changing cold foil stamping label for high-end cosmetic packaging (1) Preparation of multi-angle color-changing cold foil: A transparent biaxially oriented polyethylene terephthalate film with a thickness of 16 μm was selected as the base film layer; a layer of wax was coated on the base film layer by gravure coating, and the dry film coating amount was controlled at 1.0 g / m 2 The material is dried in an 80°C oven to form a release layer. Using a vacuum roll-to-roll evaporation machine, aluminum is deposited onto the surface of the release layer to obtain a first aluminum layer with a thickness of 30 nm, forming a continuous and dense high-reflectivity layer. A transparent acrylic resin solution with a solid content of 30% and a refractive index of approximately 1.48 is prepared. Using a precision gravure coating machine, this solution is applied to the first aluminum layer and dried at 100°C to form a dielectric layer with a dry film thickness of 180 nm, producing interference light with a green center wavelength. A second aluminum layer is deposited onto the dielectric layer using vacuum evaporation equipment to obtain a second aluminum layer with a thickness of 10 nm. This layer is uniformly translucent with an optical density of 0.4, constituting a semi-reflective layer. A layer of ultraviolet (UV)-curable acrylic adhesive is coated onto the second aluminum layer, with a dry film coating weight of 3.0 g / m². 2 This forms an adhesive layer; (2) Pretreatment of substrate: with 250 g / m 2High-grade white cardboard was used as the printing substrate. A flexographic printing press was used to print UV-curable cold foil stamping adhesive on the predetermined logo area of ​​the cardboard. The dry film weight was 3.5 g / m². 2 ; (3) Cold foil transfer and post-processing: Align the cold foil with the substrate, ensuring the adhesive layer is in contact with the adhesive. At room temperature, apply a pressure of 0.8 MPa using a cold foil press machine. Set the transfer speed to 60 m / min. Immediately after pressing, peel off the PET base film layer. The remaining first aluminized layer, dielectric layer, second aluminized layer, and adhesive layer are completely transferred to the substrate. Use a UV curing system at 80 mJ / cm². 2 The adhesive is completely cured by the radiation energy.

[0024] This embodiment creates a logo on a cosmetic box with a dynamic visual effect that changes from gold to green, enhancing the product's perceived quality and anti-counterfeiting capabilities. When viewed from a vertical angle (nearly 90°), the logo appears as a bright gold. When the box is tilted, reducing the viewing angle to approximately 45°, the logo smoothly and continuously transitions to a vibrant green. The color-changing effect is striking, visually impactful, and possesses a rich metallic texture.

[0025] Example 2: Purple-blue color-changing pattern for document anti-counterfeiting (1) Preparation of cold foil: Preparation of multi-angle color-changing cold foil: A transparent biaxially oriented polyethylene terephthalate film with a thickness of 16 μm was selected as the base film layer; a layer of wax was coated on the base film layer by gravure coating, and the dry film coating amount was controlled at 1.0 g / m 2 The material is dried in an 80°C oven to form a release layer. Using a vacuum roll-to-roll evaporation machine, aluminum is deposited on the surface of the release layer to obtain a first aluminum layer with a thickness of 30 nm, forming a continuous and dense high-reflectivity layer. A transparent acrylic resin solution with a solid content of 30% and a refractive index of approximately 1.48 is prepared. Using a precision gravure coating machine, this solution is applied to the first aluminum layer and dried at 100°C to form a dielectric layer with a dry film thickness of 250 nm, causing the reflected light from the interference structure to be biased towards the purplish-red band at a vertical viewing angle. A second aluminum layer is deposited on the dielectric layer using vacuum evaporation equipment to obtain a second aluminum layer with a thickness of 8 nm and an optical density of 0.3, to optimize the interference contrast in this band. A layer of ultraviolet (UV)-curable acrylic adhesive is coated on the second aluminum layer, with a dry film coating weight of 3.0 g / m². 2 This forms an adhesive layer; (2) Substrate pretreatment: Passport-grade security paper was used as the substrate, and UV cold foil was applied by high-precision screen printing. The dry film weight was 3.5 g / m³. 2 ; (3) Cold foil transfer and post-processing: Align the cold foil with the substrate, ensuring the adhesive layer is in contact with the adhesive. At room temperature, apply a cold foil transfer pressure of 0.6 MPa, a temperature of 30°C, and a speed of 40 m / min using a cold foil press. Immediately after pressing, peel off the PET base film layer. The remaining first aluminized layer, dielectric layer, second aluminized layer, and adhesive layer are completely transferred to the substrate. Use a UV curing system at 80 mJ / cm². 2 The adhesive is completely cured by the radiation energy.

[0026] This embodiment creates a unique, color-changing security pattern on the passport's personal information page, making it difficult to forge. The resulting security pattern appears as a deep purplish-red when viewed vertically. As the document is tilted, the pattern gradually changes to a deep blue. This effect cannot be achieved through ordinary printing or traditional hot stamping techniques, providing extremely strong anti-counterfeiting identification.

[0027] Comparative Example: Traditional single-layer aluminum plating cold foil stamping combined with color-changing ink printing (1) Preparation of conventional single-layer aluminized cold hot stamping aluminum foil: The base film layer uses a PET film with a thickness of 19 μm; a conventional wax release layer is coated on the PET base film, and the dry film weight is about 1.2 g / m 2 An aluminum layer with a thickness of approximately 35 nm is formed on the release layer using vacuum evaporation. A UV-cured acrylic adhesive is then applied to the aluminum layer, resulting in a dry film weight of approximately 3.0 g / m². 2 ; (2) Pretreatment of substrate and first cold foil transfer: The substrate used is the same as that in the embodiment of the present invention, with a density of 250 g / m². 2 White cardstock is printed with UV-curable cold foil using a flexographic printing press on a predetermined pattern area. A conventional single-layer aluminized cold foil is then aligned with the substrate and pressed together at room temperature and 0.7 MPa pressure. The PET base film is then peeled off, transferring the aluminized layer and adhesive layer onto the substrate to form a static silver metallic pattern. UV curing is then performed. (3) Preparation of optical color-changing ink: Use optical color-changing inks available on the market that can be used for screen printing. Select an optical color-changing ink that is purple when viewed vertically and turns blue when tilted. Adjust the ink to achieve a viscosity suitable for screen printing. (4) Precision overprinting of optical color-changing ink: A high-precision screen printing machine is used, and a screen printing plate that is completely matched with the cold foil pattern in step (1) is used. The mesh number is selected according to the characteristics of the ink. The substrate that has been cold foil printed is put back on the machine for a second printing.

[0028] Examples 1 and 2 utilize the multiple reflections and interferences of light between the two aluminum films to generate color by adjusting the nanoscale thickness of the dielectric layer and the extremely thin thickness of the translucent aluminum layer. The contrast ratio depends on the material superposition. First, a static silver total reflection aluminum layer is formed on the substrate, and then a layer of ink containing optical color-changing pigment is covered on its surface. The color change originates from the optical properties of the pigment particles in the ink. The aluminum layer only acts as a reflective background.

[0029] The processes in Examples 1 and 2 are completed in a single step, while the comparative example requires a cumbersome, two-stage process involving separate printing. First, a standard cold foil stamping process is needed to obtain the metallic base. Then, equipment, consumables, and processes must be changed for a second, high-precision overprinting to add the color-changing ink. This process is highly susceptible to defects due to misalignment, resulting in a complex, inefficient, and costly process.

[0030] Performance testing Test the adhesion of hot stamping: Apply 3M test tape to the hot stamping pattern, roll it horizontally back and forth 3 times with a 2kg roller, then peel off the test tape and observe the hot stamping pattern that is still left on the substrate. The adhesion is expressed as the percentage of the remaining pattern area (100% means that the tape did not remove any hot stamping pattern, which is the best adhesion; 0% means that the tape removed all the hot stamping pattern, which is the worst adhesion).

[0031] Scratch resistance testing: The scratch resistance of the hot-stamped pattern surface was tested using a friction testing machine. This invention utilizes a steel wool abrasion testing machine (model ZJ-339-GSR) from Shenzhen Zhijia Instrument Equipment Co., Ltd. The friction pressure of the slider was set to 20N, and the friction frequency to 40 times / minute. The slider was rubbed back and forth on the hot-stamped pattern surface, and the number of back-and-forth strokes at which scratches began to appear on each surface was recorded.

[0032]

[0033] The multi-angle color-changing cold foil stamped products prepared in Examples 1 and 2 of this invention are significantly superior to those produced by the traditional comparative process. In the foil stamping adhesion test, both examples achieved a high level of 90-95%, indicating strong interlayer bonding, complete functional layer transfer, and excellent adhesion to the substrate. In the scratch resistance test, the examples withstood 70-75 cycles of friction before scratches appeared, demonstrating excellent surface abrasion resistance. In contrast, the comparative product using the traditional "cold foil stamping + overprinting color-changing ink" process had an adhesion strength of only 65-75% and a scratch resistance of only 50-55 cycles, both significantly lower than the traditional methods. Therefore, this invention, through its "reflective layer-medium layer-semi-reflective layer" structure, not only achieves dynamic optical effects but also significantly improves the mechanical durability and reliability of the product, overcoming the inherent defects of insufficient adhesion and abrasion resistance in traditional overlay processes.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A multi-angle color-changing cold foil, characterized in that, From bottom to top, they include: Base film layer; Release layer coated on the base film layer; The first aluminum plating layer formed on the release layer serves as a reflective layer. A dielectric layer coated on the first aluminum plating layer, wherein the thickness of the dielectric layer is 100nm-500nm; The second aluminum plating layer formed on the dielectric layer serves as a semi-reflective layer with a thickness of 5 nm-20 nm. And an adhesive layer applied to the second aluminum plating layer.

2. The multi-angle color-changing cold foil according to claim 1, characterized in that, The dielectric layer is made of a transparent or translucent polymer resin, selected from acrylic resin, polyurethane resin, epoxy acrylate, or blends thereof, with a refractive index of 1.45–1.65; the base film layer is a 12–25 µm PET, BOPP, or PI film; the release layer is a wax-based or silicone-based peelable coating with a dry film weight of 0.5–1.5 g / m³. 2 .

3. The multi-angle color-changing cold foil according to claim 1, characterized in that, The first aluminum plating layer has a thickness of 20nm-50nm and is a continuous and dense high-reflectivity aluminum layer; the second aluminum plating layer is a semi-transparent aluminum layer with an optical density of 0.2-0.6, which causes the incident light to be partially reflected and partially transmitted.

4. The multi-angle color-changing cold foil according to claim 1, characterized in that, The cold foil has an interlayer peel force of 0.08–0.25 N / cm, achieving 100% transfer during cold foil peeling with no aluminum layer residue.

5. A preparation process for multi-angle color-changing cold foil stamping products, characterized in that, Includes the following steps: S1: Sequentially deposit a release layer, a first aluminum plating layer, a dielectric layer with a thickness of 100nm–500 nm, a second aluminum plating layer with a thickness of 5nm–20nm, and an adhesive layer on a base film to obtain a cold hot stamping foil. S2: Apply cold foil stamping adhesive to the predetermined pattern area of ​​the substrate; S3: Align and bond the adhesive layer of the cold foil with the cold foil adhesive on the substrate, and complete the cold foil transfer at room temperature and pressure. The cold foil transfer pressure is 0.3–1.2 MPa, the transfer temperature is 15–40℃, and the transfer speed is 20–120 m / min. S4: Peel off the base film layer to transfer the structure above the release layer onto the substrate, forming a pattern with a multi-angle color-changing effect.

6. The preparation process of a multi-angle color-changing cold foil stamped product according to claim 5, characterized in that, In step S1, the first and second aluminum plating layers of the cold foil are both formed by vacuum evaporation.

7. The preparation process of a multi-angle color-changing cold foil stamped product according to claim 5, characterized in that, In step S1, the medium layer of the cold foil is formed by gravure coating or a similar coating method. By controlling the coating parameters to adjust the thickness of the medium layer by ±5 nm, the color-changing sequence can be switched arbitrarily between gold-green, green-blue, purple-blue, and red-gold.

8. The preparation process of a multi-angle color-changing cold foil stamped product according to claim 5, characterized in that, The cold stamping adhesive mentioned in step S2 is a UV-curing adhesive or a water-based acrylic adhesive, with a dry film weight of 2.0-4.0 g / m³. 2 After step S4 peels off the base film layer, the process also includes a step of curing the adhesive by UV light.

9. A multi-angle color-changing cold foil stamped product prepared by the preparation process according to any one of claims 5-8, characterized in that, The article forms a laminated structure on the surface of the substrate, including a first aluminum plating layer, a dielectric layer and a second aluminum plating layer. This structure allows the pattern color to change smoothly and dynamically depending on the viewing angle.

10. A multi-angle color-changing cold foil stamped product according to claim 9, characterized in that, By adjusting the thickness of the dielectric layer, different color change sequences can be achieved, including gold turning into green or purple turning into blue.

Images