Liquid crystal pigment, identification element and preparation method thereof

Abstract

The present invention relates to the field of liquid crystal pigments, and specifically to C09K19 / 50. More specifically, the present invention relates to a liquid crystal pigment, an identification element, and a preparation method thereof. The liquid crystal pigment comprises a first component and a second component, wherein the first component comprises a composite pigment composed of a cholesteric liquid crystal reflective layer and a nematic liquid crystal layer, and the cholesteric liquid crystal reflective layer and the nematic liquid crystal layer in the composite pigment are stacked and distributed; the second component comprises a cholesteric liquid crystal layer pigment. The liquid crystal pigment provided by the present invention is used for identification elements, can be identified by irradiation of a mobile phone screen, and can undergo dynamic color changes when the mobile phone screen is rotated.

Description

Technical Field

[0001] The present invention relates to the field of liquid crystal pigments, in particular to C09K19 / 50, and more particularly to a liquid crystal pigment, an identification element and a preparation method thereof. Background Art

[0002] Using the light from a mobile phone screen as an authenticity identification tool has the advantages of being easy to identify and difficult to forge. In recent years, it has been widely used in the protection of high-security and high-end goods.

[0003] Patent CN110018589A discloses an anti-counterfeiting film based on photo-alignment and polymerizable liquid crystal technology. The film cannot be observed with naked eyes, but can present information under the light of a mobile phone screen. However, the invention also has significant shortcomings, namely: the invention can only exist in the form of a film, which limits the application scenarios of the invention.

[0004] In order to solve this problem, the present invention proposes a liquid crystal pigment. Summary of the invention

[0005] In response to some problems existing in the prior art, the first aspect of the present invention provides a liquid crystal pigment, including a first component and a second component, wherein the first component includes a composite pigment composed of a cholesteric liquid crystal reflective layer and a nematic liquid crystal layer, and the cholesteric liquid crystal reflective layer and the nematic liquid crystal layer in the composite pigment are stacked and distributed; the second component includes a cholesteric liquid crystal layer pigment.

[0006] In one embodiment, the phase delay of the nematic liquid crystal layer is 75-200nm, preferably 100-170nm, and more preferably 135nm. In the present application, the nematic liquid crystal layer can change the polarization state of the light reflected by the liquid crystal layer, and its phase delay is controlled within the scope of the present application, which can maximize the conversion of the circularly polarized reflected light of the liquid crystal layer into linearly polarized light.

[0007] The arrangement of the nematic liquid crystal layer in the present application enables the first component and the second component to produce different actions and effects on the incident linearly polarized light. The nematic liquid crystal layer of the first component can periodically convert the incident linearly polarized light into left-handed circularly polarized light, linearly polarized light, right-handed circularly polarized light, and linearly polarized light, depending on the different angles between the polarization direction of the incident linearly polarized light and the optical axis direction of the nematic liquid crystal layer. Among them, the circularly polarized light with the same rotation direction as the cholesteric liquid crystal layer is reflected, the circularly polarized light with the opposite rotation direction is transmitted, and the linear polarized light is partially transmitted and partially reflected. Therefore, the intensity of the reflected light of the first component changes accordingly for the linearly polarized light with a constantly changing direction. The second component indiscriminately reflects linearly polarized light of any polarization direction, and the intensity of the reflected light does not change.

[0008] In one embodiment, the first component includes a composite pigment consisting of a stacked N1 nematic liquid crystal layer, an N2 cholesteric liquid crystal reflective layer, and an N3 nematic liquid crystal layer, wherein N1≥0, N2≥1, N3≥0, and N1 and N3 are not 0 at the same time. In the present application, the nematic liquid crystal layer is located on the upper surface of the cholesteric liquid crystal reflective layer, close to the incident direction of the linearly polarized light, in order to produce the above-mentioned polarized light modulation effect. If the nematic liquid crystal layer is located on the lower surface of the cholesteric liquid crystal layer, its effect is equivalent to that of the second component. Therefore, the second component described in the present invention may also be the first component after flipping. When the upper and lower surfaces of the first component have phase difference layers, a symmetrical structure is formed, and there is no need to consider the flipping problem.

[0009] Preferably, the first component includes a composite pigment formed by stacking at least one cholesteric liquid crystal reflective layer located in the middle and at least two nematic liquid crystal layers located on the upper surface and the lower surface of the cholesteric liquid crystal reflective layer, respectively.

[0010] Preferably, the first component includes a composite pigment formed by stacking at least two cholesteric liquid crystal reflective layers with different handedness and at least one nematic liquid crystal layer located on the surface of the cholesteric liquid crystal reflective layer.

[0011] Preferably, the first component includes a composite pigment formed by stacking at least two layers of cholesteric liquid crystal reflective layers with different rotation directions located in the middle and at least two layers of nematic liquid crystal layers located on the upper surface and the lower surface of the cholesteric liquid crystal reflective layer respectively.

[0012] For the first component, according to the different angles between the polarization direction of the incident linear polarized light and the optical axis direction of the nematic phase liquid crystal layer, the nematic phase liquid crystal layer can periodically convert the incident linear polarized light into left-handed circularly polarized light, linear polarized light, right-handed circularly polarized light, and linear polarized light. Among them, the circularly polarized light with the same rotation direction as the cholesteric liquid crystal reflective layer is reflected, and the circularly polarized light with the opposite rotation direction is transmitted. When the first component includes cholesteric liquid crystal reflective layers with different rotation directions, for the incident linear polarized light with continuously changing polarization directions, after passing through the nematic phase liquid crystal layer, it will be periodically reflected by the left-handed liquid crystal layer and the right-handed liquid crystal layer, so that the intensity and color of the reflected light will change accordingly.

[0013] Preferably, the diameter of the liquid crystal pigment is 5-150 μm, more preferably 10-120 μm, and even more preferably 25-100 μm.

[0014] Preferably, the thickness of the liquid crystal pigment is 3-8 μm.

[0015] In one embodiment, the color difference value ΔE ≥ 6.5 between the colors of the cholesteric liquid crystal reflective layers of different rotation directions, preferably ΔE ≥ 13, and more preferably ΔE ≥ 25. When the first component includes cholesteric liquid crystal reflective layers of different rotation directions, for incident linear polarized light with a continuously changing polarization direction, it will be periodically reflected by the left-handed liquid crystal layer and the right-handed liquid crystal layer after passing through the nematic phase liquid crystal layer, so that the intensity and color of the reflected light will change accordingly. If the color contrast of the cholesteric liquid crystal reflective layers of different rotation directions is greater, the color change is more obvious. The inventors have found that when the color difference value ΔE ≥ 6.5 between the colors of the cholesteric liquid crystal reflective layers of different rotation directions, a slightly obvious color difference can be distinguished, when ΔE ≥ 13, a more obvious color difference can be distinguished, and when ΔE ≥ 25, a very obvious color difference can be distinguished.

[0016] In one embodiment, in the second component, the number of cholesteric liquid crystal layers is greater than or equal to 1. Preferably, the second component includes a pigment composed of at least two overlapping cholesteric liquid crystal reflective layers with the same or opposite rotation directions. In the present application, the second component does not contain a phase difference layer, and produces a reflection independent of the polarization direction of the incident linearly polarized light, that is, the intensity and color of the reflected light do not change. Therefore, the rotation directions of the two layers of cholesteric liquid crystal constituting the second component are not limited.

[0017] Preferably, the color difference value ΔE between the first component and the second component is ≤6.5, preferably ΔE≤3.2, and more preferably ΔE≤1.6. The color of the second component should be as close as possible to the color of the first component, so that the naked eye cannot distinguish the difference between the first component and the second component without using an identification tool. The inventors found that when the color difference ΔE between the first component and the second component is ≤6.5, an inconspicuous color difference can be distinguished, when ΔE≤3.2, the color difference cannot be distinguished unless professionally trained, and when ΔE≤1.6, the color difference cannot be distinguished.

[0018] The mass ratio of the first component and the second component has a significant effect on the recognition effect. Since the surface, position and direction of the pigment are randomly distributed, from a macroscopic point of view, when illuminated by linear polarized light, a large number of first component individuals each reflect different colors and intensities, so that they tend to be averaged and cancel each other out. Therefore, the second component is required to disperse the first component, and the dispersed first component can be identified under the constant background of the second component. Preferably, the mass ratio of the first component to the second component is 10:1-1:100, and the preferred weight ratio is 1:1-1:50. The inventors have found that when the mass ratio of the first component to the second component is 10:1-1:100, preferably 1:1-1:50, the optimal recognition effect can be obtained.

[0019] The first component in the present application is set so that the incident linear polarized light is reflected in a manner related to the incident polarization direction, such as a corresponding change in the reflected color and / or intensity. The second component causes the incident linear polarized light to be reflected independently of the incident polarization direction, such as a constant reflected color and intensity. The two components in the present application are fully mixed, and under the irradiation of linear polarized light with a continuously changing polarization direction (such as a rotating mobile phone screen), the second component maintains a constant color and intensity, and the first component undergoes a periodic change in reflected color and / or intensity, thereby producing an effect that can be identified with the help of a mobile phone.

[0020] The second aspect of the present invention provides a method for preparing the liquid crystal pigment, comprising: mixing a first component and a second component to obtain.

[0021] The mixing method of the first component and the second component in the present application can be conventionally selected by those skilled in the art, for example, various mixers such as resonance mixer, ball mill, V-type, barrel-type, cone-type or spiral mixer, etc.

[0022] The preparation method of the liquid crystal pigment of the present invention is not particularly limited, and those skilled in the art can make conventional selections. For example, the first component can be prepared according to the raw materials and methods described in patent US5942030A, and the second component can be prepared according to the raw materials and methods described in US20080291389.

[0023] In one embodiment, the method for preparing the first component comprises the following steps:

[0024] 1) applying a first polymerizable cholesteric liquid crystal to a surface of a substrate;

[0025] 2) aligning the liquid crystal;

[0026] 3) polymerizing the liquid crystal;

[0027] 4) Repeat steps 1-3 to complete the preparation of the second cholesteric liquid crystal layer;

[0028] 5) Optionally, continue to repeat steps 1-3 to complete the production of more cholesteric liquid crystal layers;

[0029] 6) The nematic liquid crystal phase difference layer is prepared according to the raw materials and preparation method described in patent US20080291389;

[0030] 7) Separating the polymer film from the substrate surface and pulverizing the polymer film to form pigment particles.

[0031] In one embodiment, the method for preparing the second component comprises the following steps:

[0032] 1) applying a first polymerizable cholesteric liquid crystal to a surface of a substrate;

[0033] 2) aligning the liquid crystal;

[0034] 3) polymerizing the liquid crystal;

[0035] 4) Repeat steps 1-3 to complete the preparation of the second cholesteric liquid crystal layer;

[0036] 5) Optionally, continue to repeat steps 1-3 to complete the production of more cholesteric liquid crystal layers;

[0037] 6) Separating the polymer film from the substrate surface and pulverizing the polymer film to form pigment particles.

[0038] The third aspect of the present invention provides an identification element containing the liquid crystal pigment.

[0039] In the present invention, the liquid crystal pigment is printed in the form of ink and attached to the substrate to form an identification element.

[0040] The specific preparation method of the identification element in the present invention can be conventionally selected by those skilled in the art. For example, according to the formula and method described in patent US9840632B2, the liquid crystal pigment is prepared into liquid crystal ink, and the liquid crystal ink is printed on the substrate by screen printing, offset printing, gravure printing, relief printing and inkjet printing to form the identification element.

[0041] A fourth aspect of the present invention provides an identification method, comprising: lighting a device capable of emitting linearly polarized light, irradiating an identification element, rotating a device such as a mobile phone or rotating the identification element, and observing changes in the appearance color and / or brightness of the identification element.

[0042] like Figure 1 When the identification element printed with the article of the present invention is observed with the naked eye, the color cannot be distinguished. When a device capable of emitting linearly polarized light (such as a mobile phone screen) is used to illuminate the substrate printed with the article of the present invention, colored spots appear, and as the mobile phone screen rotates, the color and / or brightness of the spots change.

[0043] Beneficial Effects

[0044] 1. The liquid crystal pigment provided by the present invention is used for identification elements, can be identified by irradiation of a mobile phone screen, and can undergo dynamic color changes when the mobile phone screen is rotated.

[0045] 2. The arrangement of the nematic liquid crystal layer in the present invention can maximize the conversion of the circularly polarized reflected light of the liquid crystal layer into linearly polarized light.

[0046] 3. The present invention sets cholesteric liquid crystal reflective layers with different rotation directions. For incident linear polarized light with a continuously changing polarization direction, it will be periodically reflected by the left-handed liquid crystal layer and the right-handed liquid crystal layer, so that the intensity and color of the reflected light will change accordingly.

[0047] 4. The present invention controls the mass ratio of the first component and the second component to obtain the best recognition effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Rendering of the identification element for naked eyes and devices capable of emitting linearly polarized light. DETAILED DESCRIPTION

[0049] Example 1

[0050] The preparation method of liquid crystal pigment is as follows:

[0051] The gravure coating method was used to coat the surface of the PET substrate with a left-handed cholesteric liquid crystal coating liquid (green) with a wet coating amount of 10-12 g / sqm; after drying and orientation at 80°C, cross-linking and curing were carried out under a high-pressure mercury lamp with a curing energy of 0.6 J / cm 2 ; Continue to apply right-handed cholesteric liquid crystal coating liquid (red), the wet coating amount is 10-12g / sqm; after drying and orientation at 80℃, cross-linking and curing are carried out under a high-pressure mercury lamp, and the curing energy is 1J / cm 2 The above steps obtain a liquid crystal film. Then the liquid crystal film is peeled off from the PET surface, ground and pulverized using a grinder, and sieved through a 400-mesh sieve to obtain a second component of a liquid crystal pigment with an average particle size of about 50 μm. The color difference value ΔE between the colors of the cholesteric liquid crystal reflective layers of different rotation directions is ≥6.5.

[0052] The gravure coating method was used to coat the surface of the PET substrate with a left-handed cholesteric liquid crystal coating liquid (green) with a wet coating amount of 10-12 g / sqm; after drying and orientation at 80°C, cross-linking and curing were carried out under a high-pressure mercury lamp with a curing energy of 0.6 J / cm 2 ; Continue to apply right-handed cholesteric liquid crystal coating liquid (red), the wet coating amount is 10-12g / sqm; after drying and orientation at 80℃, cross-linking and curing are carried out under a high-pressure mercury lamp, and the curing energy is 1J / cm 2 ; Continue to apply the photo-alignment coating liquid (used to orient the nematic phase liquid crystal liquid behind), the wet coating amount is 5g / sqm; after drying and orientation at 80℃, expose at 0° under a linear polarized high-pressure mercury lamp, and the exposure energy is 0.1J / cm 2 ; Continue to apply nematic liquid crystal coating liquid, wet coating amount is 5g / sqm, dry coating amount is 1.15g / sqm, after drying and orientation at 80℃, cross-linking and curing are carried out under high pressure mercury lamp, and curing energy is 0.6J / cm 2 The above process yielded a liquid crystal film. The phase delay of the nematic liquid crystal layer was 125 nm as measured by Axoscan. The liquid crystal film was peeled off the PET surface, ground and pulverized using a grinder, and sieved through a 400-mesh sieve to obtain a first component of liquid crystal pigment with an average particle size of about 50 μm. The color difference between the first component and the second component was ΔE≤6.5

[0053] The first component and the second component are mixed thoroughly in proportion to obtain the product.

[0054] Embodiment 2-5 Liquid crystal ink production and printing

[0055] According to Table 1 (mass ratio), the liquid crystal pigment is added to part of the solvent containing the dispersant and the reactive diluent, and the mixture is fully mixed and dispersed to obtain the UV-curable liquid crystal screen ink of the present invention. A screen printer with an overprint function and a UV curing unit is used for printing, the substrate is 120g / sqm black coated paper, and the printed pattern is the word "5". The printed product is rapidly UV-cured after passing through the drying unit, and the dry film thickness is 15 microns. Examples 2-5 and Comparative Examples 1-2 are obtained.

[0056] Table 1

[0057]

[0058] Example 6 Identification

[0059] The printed materials obtained in Examples 2-5 and Comparative Examples 1-2 were identified using a smartphone. When observed with the naked eye, the number 5 was golden yellow, and turned light green when observed at an angle, and the color consistency of the number 5 was good. When the mobile phone screen was turned on to illuminate the identification element, red and green bright spots of varying shades could be observed in the number 5; then the mobile phone was rotated continuously, and the color spots in the number 5 gradually changed in color and brightness. The printed materials were evaluated according to the following evaluation method, and the results are shown in Table 2.

[0060] Evaluation of recognition effect

[0061] 1) Color consistency for naked eyes

[0062] The substrate size is set to 50mm×50mm square, placed in a D65 / 10° standard light box, 25cm in front of the human eye, and the surface color difference is observed with the naked eye. The color consistency is divided into the following levels:

[0063] A: No difference

[0064] B: Very slight difference

[0065] C: identifiable difference

[0066] D: Significant difference

[0067] 2) Color effect under polarized light

[0068] The substrate size is set to 50mm×50mm square, placed in a dark room, 25cm away from the human eye, and 45° above the sample, with a light table loaded with polarizer to illuminate the substrate, the light table luminance is 300 nits. Observe the color and / or brightness difference of the identification element when the polarizer is 0° and 45°, and classify the color effect according to the following levels:

[0069] A: Can be clearly identified

[0070] B: Able to identify

[0071] C: Difficult to identify

[0072] D: Unable to distinguish

[0073] Table 2

[0074]

[0075] From the test results in Table 2, it can be seen that the liquid crystal pigment provided by the present invention is used for identification elements and can be identified by irradiation of a mobile phone screen. Moreover, the liquid crystal pigment of the present invention exists in the form of pigment and has a relatively broad application prospect.

Claims

1. A liquid crystal pigment, characterized in that: The invention comprises a first component and a second component, wherein the first component comprises a composite pigment composed of a cholesteric liquid crystal reflective layer and a nematic liquid crystal layer, and the cholesteric liquid crystal reflective layer and the nematic liquid crystal layer in the composite pigment are stacked and distributed; the second component comprises a cholesteric liquid crystal layer pigment; and the phase delay of the nematic liquid crystal layer is 75-200nm; The color difference value ΔE between the first component and the second component is ≤6.5; The mass ratio of the first component to the second component is 10:1-1:

100.

2. The liquid crystal pigment according to claim 1, characterized in that: The first component includes a composite pigment consisting of a stacked N1 nematic liquid crystal layer, an N2 cholesteric liquid crystal reflective layer, and an N3 nematic liquid crystal layer, wherein N1≥0, N2≥1, N3≥0, and N1 and N3 are not 0 at the same time.

3. The liquid crystal pigment according to claim 1 or 2, characterized in that: The first component includes a composite pigment formed by stacking at least two cholesteric liquid crystal reflective layers with different rotation directions and at least one nematic liquid crystal layer located on the surface of the cholesteric liquid crystal reflective layer.

4. The liquid crystal pigment according to claim 1 or 2, characterized in that: The first component includes a composite pigment formed by stacking at least two cholesteric liquid crystal reflective layers with different rotation directions in the middle and at least two nematic liquid crystal layers respectively located on the upper surface and the lower surface of the cholesteric liquid crystal reflective layer. 5 . The liquid crystal pigment according to claim 1 , wherein the color difference between the colors of the cholesteric liquid crystal reflective layers of different rotation directions in the first component is ΔE≥6.

5. 6 . The liquid crystal pigment according to claim 1 , wherein the color difference between the colors of the cholesteric liquid crystal reflective layers of different handedness in the first component is ΔE≥13. 7 . The liquid crystal pigment according to claim 1 , wherein the color difference between the colors of the cholesteric liquid crystal reflective layers of different handedness in the first component is ΔE≥25.

8. The liquid crystal pigment according to claim 1, wherein the second component is composed of at least two overlapping cholesteric liquid crystal reflective layers having the same or opposite handedness. 9 . The liquid crystal pigment according to claim 1 , wherein the color difference between the first component and the second component is ΔE≤3.

2. 10 . The liquid crystal pigment according to claim 1 , wherein the color difference between the first component and the second component is ΔE≤1.

6.

11. An identification element comprising the liquid crystal pigment according to any one of claims 1 to 10.

12. A recognition method, characterized in that: include: Light up a device capable of emitting linearly polarized light, illuminate the identification element according to claim 11, rotate the device or the identification element, and observe changes in the appearance color and / or brightness of the identification element.

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