A method for judging the curing degree of UV ink

Abstract

The present invention discloses a method for determining the degree of curing of UV ink, comprising the following steps: preparing a UV ink sample and detecting the double bond conversion rate of the UV ink sample after curing; then, obtaining the highest degree of curing under different process conditions based on the double bond conversion rate; then, rubbing the UV ink sample with a solvent-soaked friction head until the ink layer falls off, and recording the number of frictions; and then, determining the curing level of the UV ink based on the number of frictions. The present invention uses monomer conversion as a bridge to establish a corresponding relationship between the degree of curing of UV ink and its wet abrasion resistance. Using ink layer shedding as a basis for judgment, the number of frictions used to indirectly evaluate the degree of curing of UV ink can be used as a method for detecting the curing performance of incoming UV ink and can also achieve the purpose of monitoring the curing status of UV ink during the printing process.

Description

Technical Field

[0001] The present invention relates to the field of printing technology, in particular to a method for judging the curing degree of UV ink. Background Art

[0002] UV inks are widely used in high-end printing and packaging due to their high quality, high efficiency, and environmental friendliness. To meet the growing demand for fast, multi-color printing, the curing performance of UV inks is crucial, directly impacting production efficiency and product quality. Poor curing can lead to problems such as poor adhesion, poor abrasion and scratch resistance, and sticking and deinking. Overcuring can cause dullness and color bleeding on printed products. Therefore, developing an accurate and intuitive method for determining the curing degree of UV inks is crucial for improving product quality and production efficiency.

[0003] Currently, the main methods used to qualitatively determine the degree of UV ink curing are finger touch (scratching), scratching, and anti-blocking methods, which rely on the technician's naked eye and operational experience. These methods are simple and easy to operate, but are too subjective and have low accuracy. Researchers usually use infrared spectroscopy, Raman spectroscopy, and optical differential thermal analysis as methods for evaluating the degree of curing. These methods are highly accurate, but have drawbacks such as difficult sample preparation, high technical barriers, and expensive instruments. In addition, they cannot intuitively determine the curing level of UV inks, making them difficult to promote and popularize.

[0004] Recently, the industry has proposed indirectly evaluating the curing degree of UV inks through the characterization of other properties. The indirect method is simple to operate, easy to implement, and the test results are relatively intuitive, but it also has certain limitations. For example, the pencil hardness test method and the pressure method are not suitable for UV ink systems with good flexibility and low hardness. They are usually used to determine whether they are completely cured and cannot distinguish the curing level. The friction coefficient is related to the properties of the sample surface (such as roughness) and cannot characterize the curing degree of deep-layer UV inks. In the solvent wiping method, the same solvent cannot cope with different types of UV inks. Manual wiping, the amount of solvent dipped, etc. will affect the test results. In addition, judging the curing degree by ink discoloration is too subjective.

[0005] CN109283131A discloses an optical fiber coloring and curing detection device and method, which aims to replace manual wiping and qualitatively judge whether the optical fiber coloring and curing degree is qualified by whether the coloring layer fades. However, different pigments have obvious differences in solvent resistance, and the fading of the coloring layer is not enough to characterize the curing degree of the deep ink. In addition, this method does not classify the curing degree, so it is impossible to accurately and qualitatively judge the curing degree of UV ink. CN110940606A discloses a method for judging the curing degree of pure glue of flexible circuit boards. By immersing the glue in an organic solvent, the weight loss before and after is measured, and the difference before and after the pure glue is laminarized is compared to quantitatively characterize the curing degree. This method requires baking the pure glue sample. Heating will accelerate the curing of UV ink, so it is not suitable for judging the curing degree of UV ink.

[0006] Therefore existing technology still needs to be improved and improved. Summary of the Invention

[0007] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a method for judging the curing degree of UV ink, which can intuitively judge the curing degree of UV ink.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A method for determining the curing degree of UV ink comprises the following steps:

[0010] Prepare UV ink samples and test the double bond conversion rate after curing of UV ink samples;

[0011] According to the double bond conversion rate, the highest degree of curing under different process conditions is obtained;

[0012] Use a friction head soaked in solvent to rub the UV ink sample until the ink layer falls off, and record the number of frictions;

[0013] Determine the curing level of UV ink according to the number of frictions;

[0014] The method of obtaining the highest degree of curing under different process conditions includes:

[0015] Adjust the curing conditions to obtain UV ink samples with different curing degrees;

[0016] Calculate the double bond conversion rate at different curing degrees. When the double bond conversion rate reaches the maximum value and tends to be stable, the highest curing degree is reached. The process conditions at this time are recorded as T 100 , before curing is recorded as T0;

[0017] The step of determining the curing level of the UV ink according to the number of frictions includes:

[0018] For UV inks of the same system, set T0 and T 100 The curing grades under the conditions are 1 and 5 respectively;

[0019] Determine T0-T according to the number of frictions 100 The curing level within the conditions, the curing level is 5 levels;

[0020] The five curing levels are: Level 1 has a wear resistance of 0-5 times, Level 2 has a wear resistance of 6-15 times, Level 3 has a wear resistance of 16-25 times, Level 4 has a wear resistance of 26-35 times, and Level 5 has a wear resistance of 36 times.

[0021] A curing degree of 1 indicates that the ink is severely undercured; a curing degree of 2 indicates that the ink is undercured; a curing degree of 3 indicates that the ink is normally cured; a curing degree of 4 indicates that the ink is well cured; and a curing degree of 5 indicates that the ink is overcured.

[0022] The steps of preparing a UV ink sample and detecting the double bond conversion rate of the UV ink sample after curing specifically include:

[0023] According to the designed solid color blocks, print the required color blocks on the substrate and prepare UV ink samples;

[0024] Fourier transform infrared spectroscopy was used to detect the characteristic band 810 cm-1 of UV ink samples before and after curing. -1 Strength A 810 and the characteristic band at 1720 cm -1 Peak intensity A 1720 Used as a reference to calculate the double bond conversion rate.

[0025] The double bond conversion is obtained by the following method:

[0026]

[0027] Among them, A 810 The characteristic band (810 cm -1 ) strength, A 1720 The characteristic band is 1720 cm -1 The intensity at , t is 0-100, indicating the double bond conversion state.

[0028] The solvent includes any one or more of distilled water, ethanol, N,N-dimethylformamide, acetone, ethyl acetate, and cyclohexane. The friction head is pure wool felt, and the pressure is 1-5 N / cm 2 ; The amount of the solvent used is 1~2 mL.

[0029] The curing conditions include light source power, printing speed, lamp distance and / or lamp pass times.

[0030] After the step of obtaining the highest degree of curing under different process conditions according to the double bond conversion rate and before rubbing the UV ink sample with a rubbing head soaked in solvent until the ink layer falls off and recording the number of rubbings, the method further includes:

[0031] Cut the UV ink sample into strips with a specification of 25mm×200mm.

[0032] Compared with the existing technology, the present invention adopts a combination of microscopic (FTIR) and macroscopic (solvent-loaded friction) methods, using monomer conversion rate as a bridge to establish a matching relationship between the degree of UV ink curing and wet abrasion resistance, thereby replacing manual operation and empirical judgment. The multifunctional friction tester required by the present invention is easy to obtain and has low testing costs. In addition, the detection equipment has a simple structure, is easy to operate, and has high efficiency. The technical threshold of the required detection personnel is low, and it is suitable for production line operation, which is easy to promote and popularize. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of the method for determining the curing degree of UV ink provided by the present invention.

[0034] Figure 2 This is a graph showing the relationship between the curing degree of UV ink and actual power obtained in Example 1 of the present invention.

[0035] Figure 3 This is a graph showing the relationship between the curing degree of UV ink and actual power obtained in Example 2 of the present invention.

[0036] Figure 4 This is a graph showing the relationship between the curing degree of UV ink and actual power obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] It should be noted that when a component is referred to as being “mounted on,” “fixed on,” or “disposed on” another component, it may be directly on the other component or there may be an intermediate component. When a component is referred to as being “connected to” another component, it may be directly connected to the other component or there may be an intermediate component.

[0039] It should also be noted that the directional terms such as left, right, up, and down in the embodiments of the present invention are merely relative concepts or are based on the normal use status of the product and should not be considered as restrictive.

[0040] Poor UV ink curing can easily lead to problems such as poor adhesion, poor abrasion resistance, poor scratch resistance, and sticking and de-inking. Over-curing can lead to dullness and color bleed on the printed surface. However, conventional scientific research methods such as Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and photo-differential thermal analysis (Photo-DSC) alone cannot cope with complex actual production conditions. They suffer from problems such as poor repeatability of test results and high technical barriers, and cannot easily and intuitively quantify the difference in the degree of UV ink curing before and after printing. The present invention proposes a method for determining the degree of UV ink curing. Specifically, the method uses monomer conversion rate as a bridge to establish a corresponding relationship between the degree of UV ink curing and wet abrasion resistance. The method uses ink layer shedding as a basis for judgment and the number of abrasion resistance tests to indirectly evaluate the degree of UV ink curing. This method can not only serve as a method for detecting the curing properties of incoming UV ink, but also achieve the purpose of monitoring the curing status of UV ink during the printing process.

[0041] See also Figure 1 The method for determining the curing degree of UV ink provided by the present invention comprises the following steps:

[0042] S10, preparing a UV ink sample, and detecting a double bond conversion rate of the UV ink sample after curing;

[0043] S20, obtaining the highest degree of curing under different process conditions according to the double bond conversion rate;

[0044] S30, rubbing the UV ink sample with a friction head soaked in solvent until the ink layer falls off, and recording the number of frictions;

[0045] S40: Determine the curing level of the UV ink according to the number of frictions.

[0046] The present invention adopts a combination of microscopic (FTIR) and macroscopic (solvent-loaded friction) methods, using monomer conversion rate as a bridge to establish a matching relationship between the curing degree of UV ink and wear resistance, thereby replacing manual operation and empirical judgment. The multifunctional friction testing machine required for the present invention (such as the application number: 201811495311.4, and the name: A UV ink curing degree detection device, offset printing machine and detection method thereof) is easy to obtain, with low testing cost, and the detection equipment has a simple structure, is easy to operate, and has high efficiency. The technical threshold of the required detection personnel is low, and it is suitable for production line operation, which is convenient for promotion and popularization.

[0047] Specifically, step S10 includes:

[0048] S101. Print the required color blocks on the substrate according to the designed solid color blocks to prepare UV ink samples;

[0049] S102, Fourier transform infrared spectroscopy was used to detect the characteristic band 810 cm-1 of UV ink samples before and after curing. -1 Strength A 810 and the characteristic band at 1720 cm -1 Peak intensity A 1720 Used as a reference to calculate the double bond conversion rate.

[0050] In step S101, when creating a UV ink sample, a solid color block is designed. The UV ink is transferred to a substrate using offset printing, flexographic printing, gravure printing, screen printing, inkjet printing, or coating to produce the desired color block. A solid color block refers to a full-screen print, i.e., a 100% dot area ratio. In this embodiment, a color block, or color bar, is designed, rather than text, lines, or patterns. The substrate can be any of paper, film, or composite paper. All parts of the UV ink sample have the same ink layer thickness.

[0051] In step S102, the double bond conversion rate is obtained by:

[0052] (1)

[0053] Among them, A 810 The characteristic band (810 cm -1 ) strength, A 1720 The characteristic band is 1720 cm -1 The intensity at , t is 0-100.

[0054] For example, UV ink samples were irradiated and cured using an ultraviolet mercury lamp, and the FTIR (Fourier transform infrared spectroscopy) was used to test the samples before curing (state 0) and after curing (state t) at 810 cm -1 The intensity A 810 , and with A 1720 (1720 cm -1 The double bond conversion rate Ct is calculated according to formula (1), where t is 0-100, "t" represents the double bond conversion state, T0 and T 100 They represent the states before curing and fully cured respectively. The intermediate state can be normalized to a value between 0 and 100 according to the conversion rate. In the present invention, T is measured three times (i.e., three test points are taken on the same spline or sample) and the average value is taken to obtain the final double bond conversion rate. This embodiment is mainly used to measure the double bond conversion rate under the same curing conditions.

[0055] Furthermore, the step S20 includes:

[0056] S201, adjusting curing conditions to obtain UV ink samples with different curing degrees;

[0057] S202. Calculate the double bond conversion rate at different curing degrees. When the double bond conversion rate reaches a maximum value and tends to be stable, the highest curing degree is reached. The process condition at this time is recorded as T 100 , before curing is recorded as T0.

[0058] When adjusting the curing conditions, the curing conditions are adjusted from low to high to obtain UV ink samples with different degrees of curing. In this embodiment, the curing conditions include light source power, printing speed, lamp distance, and / or number of lamp passes. Adjusting the curing conditions from low to high includes adjusting the light source power or printing speed from low to high, the UV lamp distance from far to near, and the number of lamp passes from few to many.

[0059] In addition, when calculating the double bond conversion rate of different curing degrees, no less than 50 groups are calculated. When the monomer conversion rate reaches 90% and tends to be stable, the highest curing degree under the actual process conditions is reached. The process conditions at this time are recorded as T 100 , before curing is recorded as T0.

[0060] The curing process of ink is actually the process of addition reaction of monomers in ink, which can be measured by the conversion ratio of C=C double bond to CC single bond. The conversion rate ranges from 0-100%, and the double bond conversion rate cannot actually reach 100% (complete curing). Therefore, when the curing conditions (energy density) continue to improve, the double bond conversion rate first increases and then tends to stabilize, and the maximum value is reached when it stabilizes.

[0061] In step S30, when rubbing the ink layer, the solvent includes any one or more of distilled water, ethanol, N,N-dimethylformamide, acetone, ethyl acetate, and cyclohexane, the rubbing head is pure wool felt, and the pressure is 1-5 N / cm 2 ; The amount of the solvent used is 1~2 mL.

[0062] Ink layer shedding is manifested as de-inking areas with a scale of not less than 0.3mm on the surface of the spline. Film grids, magnifying glasses, etc. are used as auxiliary tools for judgment. By taking photos or scanning, when at least three exposed areas with a scale of not less than 0.2mm appear in the spline test area, it is determined to be ink layer shedding.

[0063] Furthermore, after step S20 and before step S30, the process further includes cutting the UV ink sample into strips measuring 25 mm x 200 mm and securing them to the sample stage. This secures the strips to the sample stage to facilitate subsequent friction with the friction head. Of course, the test strip preparation step can also be performed simultaneously with step S20, as long as it does not affect solvent penetration and load friction.

[0064] In step S40, during the wear resistance test, the test temperature is 20-25°C and the humidity is 45-55%. The step of determining the curing level of the UV ink according to the number of frictions includes:

[0065] S401, for the same system of UV ink, set T0 and T 100 The curing grades under the conditions are 1 and 5 respectively;

[0066] S402, determine T0-T according to the number of frictions 100 There are 5 levels of curing grades within the conditions.

[0067] The five curing levels are: Level 1 (0-5 abrasion resistance times), Level 2 (6-15 abrasion resistance times), Level 3 (16-25 abrasion resistance times), Level 4 (26-35 abrasion resistance times), and Level 5 (36 abrasion resistance times). Specifically, Level 1 indicates that the ink is severely undercured and tacky; Level 2 indicates that the ink is undercured and has poor adhesion; Level 3 indicates that the ink is properly cured; Level 4 indicates that the ink is well cured; and Level 5 indicates that the ink is overcured, with the ink surface losing gloss or easily cracking.

[0068] Furthermore, the steps S30 and S40 are repeated three to five times under the same process conditions to improve the accuracy of the determination. If the determination results are different after the steps S30 to S40 are repeated five times, the lowest curing level is selected.

[0069] In a first preferred embodiment of the present invention, step S10 can be performed by offset printing to transfer the UV ink onto transfer paper, printing the desired color blocks, and ensuring that the ink layer thickness of the UV ink sample is approximately 2 μm. The UV ink can be a flexible four-color blue supplied by Shenzhen Haizhonghui Ink Products Co., Ltd. During curing, radiation curing is performed using either a UV mercury lamp or an LED lamp, either singly or in combination.

[0070] In the first preferred embodiment of the present invention, step S30 may use a mixed solvent of ethanol and water (m 乙醇 :m 水 =3:2) soaked with 100% pure wool felt friction head, and then rubbed with solvent load using a multifunctional friction tester. When a deinking area with a size of not less than 0.3 mm appears on the surface of the specimen, stop the machine and record the number of frictions; the load weight is 2 N / cm 2 The amount of the solvent used was 1.3 mL, and the relationship between the degree of UV ink curing and the actual power of the curing lamp was finally obtained. Figure 2 shown.

[0071] The second preferred embodiment of the present invention is different from the first preferred embodiment in that: in step S10, when preparing the UV ink sample, the UV ink is transferred to the white cardboard by coating, and the ink layer thickness of the sample is about 5 μ m; wherein, the UV ink used is UV-3162 hot stamping varnish provided by Guangzhou Longzhu Chemical Co., Ltd. In step S30, the solvent is a mixed solvent of ethanol and ethyl acetate (m 乙醇 :m 乙酸乙酯 =3:1) Soak the friction head and adjust the load weight of the friction head to 5N / cm 2 Finally, the relationship between the curing degree of UV ink and the actual power of the curing lamp is obtained as shown in the figure below: Figure 3 shown.

[0072] In the third preferred embodiment of the present invention, the difference from the first preferred embodiment is that: during curing, the UV ink sample is irradiated and cured using an LED lamp with a wavelength of 385 nm. In step S30, the solvent is a mixed solvent of ethanol and water (m 乙醇 :m 水 =2:3) Soak the friction head and adjust the load weight of the friction head to 1N / cm 2 Finally, the relationship between the curing degree of UV ink and the actual power of the curing lamp is obtained as shown in the figure below: Figure 4 shown.

[0073] In summary, the present invention uses FTIR to detect the double bond conversion rate of UV ink to obtain the maximum degree of curing under actual process conditions. Then, a solvent-impregnated load friction method is used to record the number of frictions when the ink layer falls off, thereby judging the degree of curing of the UV ink. The method has high accuracy, good repeatability, intuitiveness, and is easy to implement. It can be used as a method for detecting the curing performance of UV ink incoming materials and can also achieve the purpose of monitoring the curing status of UV ink during the printing process.

[0074] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for judging the curing degree of UV ink, characterized in that: The following steps are involved: Prepare UV ink samples and test the double bond conversion rate after curing of UV ink samples; According to the double bond conversion rate, the highest degree of curing under different process conditions is obtained; Use a friction head soaked in solvent to rub the UV ink sample until the ink layer falls off, and record the number of frictions; Determine the curing level of UV ink according to the number of frictions; The method of obtaining the highest degree of curing under different process conditions includes: Adjust the curing conditions to obtain UV ink samples with different curing degrees; Calculate the double bond conversion rate at different curing degrees. When the double bond conversion rate reaches the maximum value and tends to be stable, the highest curing degree is reached. The process conditions at this time are recorded as T 100 , before curing is recorded as T0; The step of determining the curing level of the UV ink according to the number of frictions includes: For UV inks of the same system, set T0 and T 100 The curing grades under the conditions are 1 and 5 respectively; Determine T0-T according to the number of frictions 100 The curing level within the conditions, the curing level is 5 levels; The five curing levels are: Level 1 has a wear resistance of 0-5 times, Level 2 has a wear resistance of 6-15 times, Level 3 has a wear resistance of 16-25 times, Level 4 has a wear resistance of 26-35 times, and Level 5 has a wear resistance of 36 times. A curing degree of 1 indicates that the ink is severely undercured; a curing degree of 2 indicates that the ink is undercured; a curing degree of 3 indicates that the ink is normally cured; a curing degree of 4 indicates that the ink is well cured; and a curing degree of 5 indicates that the ink is overcured.

2. The method for determining the curing degree of UV ink according to claim 1, wherein: The steps of preparing a UV ink sample and detecting the double bond conversion rate of the UV ink sample after curing specifically include: According to the designed solid color blocks, print the required color blocks on the substrate and prepare UV ink samples; Fourier transform infrared spectroscopy was used to detect the characteristic band 810 cm-1 of UV ink samples before and after curing. -1 The intensity A 810 and the characteristic band at 1720 cm -1 Peak intensity A 1720 Used as a reference to calculate the double bond conversion rate.

3. The method for determining the curing degree of UV ink according to claim 2, characterized in that: The double bond conversion is obtained by the following method: Among them, A 810 Characteristic band at 810 cm -1 The intensity at A 1720 The characteristic band is 1720 cm -1 The intensity at , t is 0-100, indicating the double bond conversion state.

4. The method for determining the curing degree of UV ink according to claim 2, wherein: The solvent includes any one or more of distilled water, ethanol, N,N-dimethylformamide, acetone, ethyl acetate, and cyclohexane. The friction head is pure wool felt, and the pressure is 1-5 N / cm 2 ; The amount of the solvent used is 1~2 mL.

5. The method for determining the curing degree of UV ink according to claim 1, wherein: The curing conditions include light source power, printing speed, lamp distance and / or lamp pass times.

6. The method for determining the curing degree of UV ink according to claim 1, wherein: After the step of obtaining the highest degree of curing under different process conditions according to the double bond conversion rate and before rubbing the UV ink sample with a rubbing head soaked in solvent until the ink layer falls off and recording the number of rubbings, the method further includes: Cut the UV ink sample into strips with a specification of 25mm×200mm.

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