Photosensitive polyurethane film with surface relief grating pattern as well as preparation method and application of photosensitive polyurethane film

Abstract

The invention relates to the technical field of optical encryption, and discloses a photosensitive polyurethane film with a surface relief grating pattern and a preparation method and application thereof.The method comprises the steps that in an ice bath and inert atmosphere, toluene diisocynate and a dihydropyridine photosensitizer monomer are added into N, N-dimethylformamide, and a mixture is obtained; the preparation method comprises the following steps: adding the raw materials into a mixed solvent of N, N-diethyl formamide and dimethyl sulfoxide, and then dropwise adding 1, 4-dibutanol; removing the ice bath, and reacting at the temperature of room temperature to 60 DEG C to obtain a photosensitive polyurethane solution; spin-coating the photosensitive polyurethane solution on a substrate, and drying to obtain a photosensitive polyurethane film; and exposing the designed mask plate on the surface of the photosensitive polyurethane film. According to the invention, the non-covalent interaction difference of the polymer-dihydropyridine / pyridine part can be constructed to realize effective surface patterning, and the generation of a two-dimensional ordered grating-shaped wrinkle structure with a sinusoidal phase is realized on the surface of the polyurethane film in a wrinkling manner in combination with an optical anti-counterfeiting technology, so that pattern anti-counterfeiting is realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical encryption, and in particular to a photosensitive polyurethane film with a surface relief grating pattern, and a preparation method and application thereof. Background Art

[0002] Photoinduced surface structuring of films containing dihydropyridine units allows the creation of complex surface relief patterns with varying heights that are difficult to form using conventional photolithography tools. Multiple grating patterns can be combined to create pixels with wide gamut structural colors as well as bright grating structures on the film surface. As long as the material behavior is linear, any Fourier optical surface can be created using this multiple patterning approach, with the potential to create complex 3D surface reliefs with nanometer precision.

[0003] Research so far has focused on constructing supramolecular hierarchical structures. Chinese patent CN111845148A discloses an optical anti-counterfeiting element and a method for making the same, and Chinese patent CN103576216A discloses an optical anti-counterfeiting element and an anti-counterfeiting product using the optical anti-counterfeiting element, and the preparation of the surface relief requires multiple surfaces (substrate, coating, and absorption layer) to achieve iridescent structural colors. Although there are currently a variety of technologies and methods for producing wrinkled structures with different morphologies, it is still a major challenge to develop a technology that can produce orderly and controllable one-dimensional or two-dimensional wrinkled structures on a large area of ​​a polymer surface. Among them, controlling the stress distribution state on the surface of the film during the wrinkling process, that is, the magnitude and direction of the stress, is particularly important for the final wrinkle structure morphology. Summary of the invention

[0004] The present invention aims at the problems existing in the current research field of polymer surface wrinkling phenomenon, such as narrow selection of polymer types, single method for manufacturing wrinkled structure, difficulty in controlling stress distribution state (size and direction) during polymer surface wrinkling, difficulty in manufacturing large-area ordered structure, and narrow application scope of wrinkled structure in the field of information recording and signal transmission. Based on the development direction of new polymer materials and new technologies for manufacturing wrinkled structure, the present invention proposes a strategy of combining photolithography technology and residual solvent directional diffusion technology to construct a periodic wrinkle pattern (grating pattern) with precise aspect ratio wrinkling on a photosensitive polyurethane film by controlling the stress distribution state. This strategy can be regarded as a method for realizing a new type of micro-patterning on the surface of a film. The present invention can freely encode the surface properties of a polymer film at room temperature. The present invention combines optical anti-counterfeiting technology to realize the generation of a two-dimensional ordered grating-like wrinkle structure with a sinusoidal phase on the surface of a polyurethane film by wrinkling, and can successfully write specific encrypted information (such as text, graphics, letters, etc.) in the visible light range using simple optical diffraction principles.

[0005] To achieve the above object, the present invention provides a method for preparing a photosensitive polyurethane film with a surface relief grating pattern, which comprises the following steps:

[0006] S1. In an ice-water bath and inert atmosphere, first add toluene diisocyanate and the dihydropyridine photosensitizer monomer of formula (1) into a mixed solvent of N,N-diethylformamide and dimethyl sulfoxide (DMF:DMSO=1:0-4:1, v / v), mix well, stir for reaction (preferably for 0.5-3 h), and then dropwise add 1,4-dibutanol;

[0007]

[0008] S2, removing the ice water bath in step S1, and reacting the reaction system at a temperature between room temperature and 60° C. to obtain a photosensitive polyurethane solution;

[0009] S3, spin coating the photosensitive polyurethane solution on the substrate, and drying to obtain a photosensitive polyurethane film with a thickness of 3 to 30 μm;

[0010] S4. Using an ultraviolet exposure machine, expose a mask having a preset grating pattern on the surface of the photosensitive polyurethane film, and then immerse the exposed photosensitive polyurethane film in an ethanol solution for development operation, so that the exposure area forms a relief grating pattern having a grating structure corresponding to the preset grating pattern, that is, a photosensitive polyurethane film with a surface relief grating pattern is obtained.

[0011] As a further preferred technical solution of the present invention, in step S1, the molar ratio of toluene diisocyanate to dihydropyridine photosensitizer monomer is 10-20:1, and the molar ratio of the amount of 1,4-dibutanol added dropwise to the dihydropyridine photosensitizer monomer is 10-20:1.

[0012] As a further preferred technical solution of the present invention, in step S2, the reaction is first stirred at room temperature for 8 to 24 hours, then heated at 40° C. for 8 to 24 hours, and finally heated at 60° C. for 8 to 24 hours.

[0013] As a further preferred technical solution of the present invention, in step S3, the spin coating procedure is 500-3500r for 10-30s.

[0014] As a further preferred technical solution of the present invention, in step S4, a direct writing exposure mode is adopted to expose the mask to the surface of the photosensitive polyurethane film, and the exposure parameters are: the exposure wavelength is 365nm, the exposure time is 15 to 300s, and the power is 3-30w.

[0015] As a further preferred technical solution of the present invention, the relief grating pattern is composed of a grating line group consisting of periodically arranged grating lines with a line width of 1 to 10 μm and a period of 2 to 20 μm.

[0016] As a further preferred technical solution of the present invention, the grating line group consists of a convex grating line and a concave grating line, the line widths of the convex grating line and the concave grating line are both 1 to 10 μm, and adjacent convex grating lines and concave grating lines form a grating line group with a two-dimensional concave-convex structure with a depth difference of less than or equal to 100 nm.

[0017] According to another aspect of the present invention, the present invention also provides a photosensitive polyurethane film with a surface relief grating pattern, which is prepared by the above method.

[0018] According to another aspect of the present invention, the present invention also provides a photosensitive polyurethane film with a surface relief grating pattern for use as an anti-counterfeiting label in pattern anti-counterfeiting.

[0019] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0020] 1) The present invention effectively expands the photoinduced surface relief grating (SRG) materials. Research so far has focused on constructing supramolecular hierarchical structures, while the present invention can construct the non-covalent interaction difference between polymer-dihydropyridine / pyridine parts to achieve effective surface patterning;

[0021] 2) The film of the present invention has a grating pattern on its surface, and the film surface is made into a specific pattern for anti-counterfeiting, which can achieve anti-counterfeiting specificity and easy reading. In addition, the development method adopts immersion in non-toxic and low-harm anhydrous ethanol, which is green and environmentally friendly, and the immersion time is only 3 to 30 seconds, which is simple to operate and highly efficient;

[0022] 3) The present invention can achieve a better SRG formation ratio by regulating the content of photosensitive monomer and chain extender. These irreversible mechanical changes of polymers in photosensitive polyurethane have been further utilized in many studies on hardness, stiffness, creep elastic modulus and creep coefficient.

[0023] 4) The present invention can freely encode the surface properties of the polyurethane film at room temperature, and combines optical anti-counterfeiting technology to achieve the generation of a two-dimensional ordered grating-like wrinkle structure with a sinusoidal phase on the surface of the polyurethane film by wrinkling. In the visible light range, it uses a simple optical diffraction principle to successfully write specific encrypted information (such as text, graphics, letters, etc.), thereby realizing relief grating patterning for pattern anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 It is the mass spectrometry diagram of the pyridine structure formed after the dehydration of the dihydropyridine photosensitizer monomer (DHPDO) under ultraviolet light irradiation.

[0026] Figure 2 It is the POM diagram of the surface relief grating of a part of the thin film sample obtained in Example 1.

[0027] Figure 3 It is the AFM diagram of the surface relief grating formed on the thin film sample obtained in Example 1, where (a) is the two-dimensional plan view of AFM, (b) is the three-dimensional stereogram of AFM, and (c) is the concave-convex grating diagram of AFM.

[0028] Figure 4 It is the physical display diagram of the thin film sample obtained in Example 1. (a) is the iridescent diagram of the inner frame of the Chinese character "回" in the anti-counterfeiting pattern, and (b) is the iridescent diagram of the outer frame of the Chinese character "回" in the anti-counterfeiting pattern.

[0029] The realization of the object, functional features, and advantages of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific Embodiments

[0030] The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0031] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0032] The dihydropyridine photosensitizer monomer provided by the present invention has the following molecular structural formula:

[0033]

[0034] This photosensitizer monomer can be synthesized through the following route:

[0035]

[0036] In a specific embodiment, its synthesis method is as follows:

[0037] (1) Synthesis of the compound dihydropyridine photosensitizer monomer (NDHP)

[0038] A1. Weigh 16.712 g (10 mmol, 1 eq) of 5-hydroxy-2-nitrobenzaldehyde and dissolve it in an appropriate amount of ethanol to form a uniform solution. Then, add an appropriate amount of trifluoroacetic acid (27 ml) (3.5 mmol, 3 eq) while stirring in an ice-water bath at 0°C;

[0039] A2. Dissolve 34.54 g (30 mmol, 3 eq) of 3-amino methyl crotonate in 150 ml of anhydrous ethanol, gradually add anhydrous ethanol solution (150 ml) of 3-amino methyl crotonate to the solution of A1 in an ice-water bath at 0°C, and react in an ice-water bath at 0°C for 8 h;

[0040] A3. After the reaction, a large amount of deionized water was added to precipitate, filtered, and the intercepted material was heated and dissolved with a small amount of ethanol, and recrystallized to obtain the purified target product NDHP, which was weighed after drying (the yield was 70%).

[0041] (2) Synthesis of intermediate A

[0042] B1. 3,5-dibromophenol (10.00 g, 39.70 mmol) and 1,4-dihalobutane (3 eq, 59.55 mmol) were dissolved in 100 mL of acetone, and K2CO3 (16.46 g, 119.09 mmol) was added. The mixture was refluxed at 80°C for 48 h under an inert atmosphere. The halogen atom of 1,4-dihalobutane is Br, but it can also be Cl or I.

[0043] B2. After the reaction was completed, the reaction solution was cooled to room temperature, washed with petroleum ether, and purified by silica gel column chromatography under reduced pressure to obtain a colorless transparent liquid intermediate A (x is Br) (yield 90%).

[0044] (3) Synthesis of intermediate B

[0045] C1. NDHP (3.15 g, 8.70 mmol) was dissolved in acetone (150 mL), and K2CO3 (10.81 g, 78.33 mmol) was added. Intermediate A (1 eq, 26.11 mmol) was added to the reaction system under an inert gas atmosphere at 80°C; the mixture was refluxed and stirred for 36 h under an inert gas atmosphere;

[0046] C2. After the reaction was completed, the mixture was washed with petroleum ether and purified by silica gel column chromatography to obtain intermediate B (x is Br) as a light yellow solid (yield: 60%).

[0047] (4) Synthesis of dihydropyridine photosensitizer monomer (DHPDO)

[0048] D1. In an inert atmosphere glove box, tetrahydrofuran (100 mL) was added to a 500 mL flask to dissolve intermediate B (1 eq, 19.83 mmol) to obtain a homogeneous mixed solution, and then 2M K2CO3 aqueous solution (70 mL) and 4-hydroxymethylphenylboronic acid (5.71 g, 49.58 mmol) were added;

[0049] D2. Rapidly add tetrakis(triphenylphosphine)palladium(0)(Pd[P(C6H5)3]4))(0.02eq, 0.397mmol) of catalyst to the above mixed solution, stir and reflux for 72h under an inert gas atmosphere;

[0050] D3. After the reaction, the oily substance washed with petroleum ether was dissolved in a small amount of methanol solution, and a large amount of deionized water was used for precipitation and purification of the product to obtain a novel hydroxyl-containing dihydropyridine photosensitizer (DHPDO) (yield 76%).

[0051] The dihydropyridine photosensitizer monomer is based on the sensitivity of the dihydropyridine unit to ultraviolet light. Under ultraviolet light, its structure can undergo intramolecular dehydration reaction, thereby achieving its photosensitivity. The photosensitivity of DHPDO can be verified by mass spectrometry characterization, such as Figure 1 As shown. Based on this characteristic, the present invention proposes a photosensitive polyurethane film with a surface relief grating pattern prepared by using the dihydropyridine photosensitizer monomer as a raw material, which can be used as an anti-counterfeiting label to achieve pattern anti-counterfeiting. In order to allow those skilled in the art to further understand the technical solution of the present invention, the technical solution of the present invention is further described in detail below through specific embodiments.

[0052] Embodiment 1:

[0053] (1) In a magnetically stirred inert gas atmosphere container, toluene diisocyanate (TDI) (16.8 mmol) was injected and stirred in an ice-water bath at 0°C for 10 to 60 min;

[0054] (2) In an inert atmosphere glove box, the weighed dihydropyridine photosensitizer monomer DHPDO (1 mmol) was dissolved in an anhydrous N,N-diethylformamide (DMF) and dimethyl sulfoxide (DMSO) mixed solvent (DMF:DMSO = 4:1, v / v);

[0055] (3) In the toluene diisocyanate solution of step (1), the solution containing the dihydropyridine photosensitizer monomer DHPDO is dropwise injected into the solution of step (2) under 0° C. ice-water bath conditions, and stirred in the ice-water bath for 0.5 to 3.5 h;

[0056] (4) Inject 15 mmol of 1,4-dibutanol BDO dropwise under ice bath conditions, then remove the ice bath, stir and react at room temperature for 8 to 24 hours, heat at 40° C. for 8 to 24 hours, and heat at 60° C. for 8 to 24 hours to obtain a photosensitive polyurethane solution;

[0057] (5) After UV treatment for 15 min, a 2.5×2.5 glass substrate was placed on a spin coater, and 50 μL of the photosensitive polyurethane solution was spin-coated on the glass substrate at 3500 r for 30 s. The solution was then dried to obtain a photosensitive polyurethane film with a thickness of 30 μm.

[0058] (5) A direct-write exposure mode is used to expose the mask template to the surface of the photosensitive polyurethane film. The exposure parameters are as follows: an exposure wavelength of 365 nm, an exposure time of 15 to 100 s, and a power of 3 to 30 W. A template with a U-shaped grating stripe pattern is used. The U-shaped grating stripe pattern includes an inner frame grating line group and an outer frame grating line group. The stripes of the inner frame grating line group and the stripes of the outer frame grating line group are inclined at an angle of 15 degrees. The inner frame grating line group and the outer frame grating line group are both composed of periodically arranged grating lines with a line width of 5 μm and a period of 10 μm.

[0059] (6) The exposed photosensitive polyurethane film is immersed in an ethanol solution for development, and after drying, the surface relief rasterized encrypted "Hu"-shaped pattern is formed, that is, the film with the rasterized encrypted pattern on the surface is obtained. Since the inner and outer frame stripes have a certain inclination angle, different pattern effects can be achieved at different observation angles.

[0060] Figure 2 This is a POM image of the surface relief grating of the film sample obtained in Example 1. It can be seen from the image that a group of grating lines arranged in a periodic manner is formed on the surface of the film substrate.

[0061] Figure 3 This is an AFM image of the surface relief grating formed on the thin film sample obtained in Example 1. It can be seen from the figure that the height of the protrusion, i.e. the peak height, is 15.7nm, and the groove part, i.e. the peak to valley, is 13.7nm, forming a grating with a total height difference of 29.4nm. These gratings can form iridescent structural colors visible under natural light.

[0062] Figure 4 This is a physical display picture of the photosensitive polyurethane film of this embodiment at different viewing angles. By adjusting the angle, the inner frame of the "U"-shaped pattern can be cleaned and displayed, and then by adjusting the inclination angle of the film to one side by about 15 degrees, the outer frame of the "U"-shaped pattern can be cleaned and displayed, while the inner frame is hidden.

[0063] In the present invention, when the stress generated by hydrogen bond formation in the ultraviolet irradiation area on the photosensitive polyurethane film reaches a certain critical value, it will cause mechanical instability on the film surface, thereby inducing the film to buckle and deform. For a film that has only been subjected to ultraviolet exposure treatment in a local area, the irradiated area will shrink in volume due to the generation of new intermolecular forces, which will cause the surrounding unexposed parts to expand in volume to a certain extent. This result will correspondingly cause the shrunken exposed area to have a larger modulus than the unexposed area in an expanded state, which can be derived from the modulus difference in the AFM test. It can be applied to anti-counterfeiting signatures in banknotes to achieve iridescent structural colors that can be observed visually under natural light.

[0064] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a photosensitive polyurethane film with a surface relief grating pattern, characterized in that: The following steps are involved: S1. In an ice-water bath and inert atmosphere, toluene diisocyanate and a dihydropyridine photosensitizer monomer having the structure of the following formula (1) are first added to a mixed solvent of N,N-diethylformamide and dimethyl sulfoxide. After the reaction is completed by stirring, 1,4-dibutanol is added dropwise; S2, removing the ice water bath in step S1, and reacting the reaction system at a temperature between room temperature and 60° C. to obtain a photosensitive polyurethane solution; S3, spin coating the photosensitive polyurethane solution on the substrate, and drying to obtain a photosensitive polyurethane film; S4. Using an ultraviolet exposure machine, expose a mask having a preset grating pattern on the surface of the photosensitive polyurethane film, and then immerse the exposed photosensitive polyurethane film in an ethanol solution for development operation, so that the exposure area forms a relief grating pattern having a grating structure corresponding to the preset grating pattern, that is, a photosensitive polyurethane film with a surface relief grating pattern is obtained.

2. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to claim 1, characterized in that: In step S1, the molar ratio of toluene diisocyanate to dihydropyridine photosensitizer monomer is 10-20:1, and the molar ratio of the amount of 1,4-dibutanol added dropwise to the dihydropyridine photosensitizer monomer is 10-20:

1.

3. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to claim 1, characterized in that: In step S2, the reaction is first stirred at room temperature for 8 to 24 hours, then heated at 40° C. for 8 to 24 hours, and finally heated at 60° C. for 8 to 24 hours.

4. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to claim 1, characterized in that: In step S3, the spin coating procedure is 500-3500r for 10-30s.

5. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to claim 1, characterized in that: In step S3, a glass substrate is used, and the glass substrate is irradiated with ultraviolet light for 15 minutes before spin coating.

6. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to claim 1, characterized in that: In step S4, a direct writing exposure mode is adopted to expose the mask to the surface of the photosensitive polyurethane film, and the exposure parameters are as follows: the exposure wavelength is 365nm, the exposure time is 15-300s, and the power is 3-30w.

7. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to any one of claims 1 to 6, characterized in that: The relief grating pattern is composed of a grating line group consisting of periodically arranged grating lines with a line width of 1 to 10 μm and a period of 2 to 20 μm.

8. The method for preparing a photosensitive polyurethane film with a surface relief grating pattern according to claim 7, characterized in that: The grating line group consists of a convex grating line and a concave grating line. The line widths of the convex grating line and the concave grating line are both 1-10 μm. Adjacent convex grating lines and concave grating lines form a grating line group with a two-dimensional concave-convex structure with a depth difference of less than or equal to 100 nm.

9. A photosensitive polyurethane film with a surface relief grating pattern, prepared by the method according to any one of claims 1 to 7.

10. Use of the photosensitive polyurethane film with a surface relief grating pattern as claimed in claim 9 as an anti-counterfeiting label in pattern anti-counterfeiting.

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