A method for real-time monitoring of ink viscosity for carton printing equipment

Abstract

This invention relates to the field of monitoring technology for corrugated box printing equipment, and more particularly to a method for real-time monitoring of ink viscosity in corrugated box printing equipment. This method is based on the capillary flow characteristics of nanochannels, introduces a non-Newtonian fluid shear rate correction coefficient, and combines shear rate with ink base parameters for coupled calculation to accurately offset measurement errors caused by the non-Newtonian characteristics of the ink. By establishing a surface tension evaporation attenuation model, it dynamically corrects for surface tension changes caused by solvent evaporation during printing, achieving a high degree of consistency with actual working conditions. The method employs a binary function of temperature and ink type for the basic fitting parameters, adapting to various inks such as water-based, oil-based, and UV-curable inks through correction factors. Simultaneously, it corrects for environmental fluctuations through temperature difference, meeting the needs of multiple scenarios without requiring device replacement. It achieves high-precision monitoring by real-time acquisition of flow data and fitting the slope to inversely deduce viscosity, exhibiting strong versatility, requiring no frequent cleaning, and adapting to continuous corrugated box printing production.

Description

Technical Field

[0001] This invention relates to the field of monitoring technology for corrugated box printing equipment, and in particular to a method for real-time monitoring of ink viscosity for corrugated box printing equipment. Background Technology

[0002] In the corrugated box printing process, ink viscosity is a key parameter affecting print quality—high viscosity leads to uneven ink transfer, blurred printed patterns, and dot gain; low viscosity, on the other hand, easily causes ink penetration and misregistration. Therefore, real-time and accurate monitoring of ink viscosity is a core requirement for ensuring the stability of corrugated box printing quality. Existing ink viscosity monitoring methods include traditional offline monitoring and emerging online monitoring: Traditional offline monitoring methods, such as rotational viscometer and capillary viscometer methods, require manual sampling and testing, which is cumbersome and time-consuming (a single test can take several minutes). They cannot achieve real-time monitoring and are difficult to adapt to the continuous production rhythm of printing equipment. Furthermore, the ink cannot be recycled after testing, resulting in waste. In addition, the sampling process is easily affected by the environment, leading to measurement errors.

[0003] Emerging online monitoring methods, some of which employ micron-level channels based on capillary flow principles, fail to consider the non-Newtonian fluid characteristics of inks, relying solely on Newtonian fluid models for calculations, leading to significant viscosity measurement deviations. They also neglect the dynamic changes in surface tension caused by ink solvent evaporation, assuming a constant surface tension value, which contradicts the continuous evaporation conditions in actual printing scenarios, further introducing errors. Furthermore, many channels are reusable, allowing pigments and fillers from the ink to easily adhere and contaminate subsequent monitored inks, affecting measurement accuracy. They are only compatible with a single type of ink, failing to meet the universal monitoring needs of various inks, including water-based, oil-based, and UV-curable inks, in carton printing. Temperature correction and ink type correction are independent, failing to consider their coupling effect, resulting in a significant decrease in monitoring accuracy under different temperature and ink type switching scenarios.

[0004] Chinese patent document CN107389502B discloses a liquid viscosity measurement method and system based on micro / nanochannel capillary flow. Its core is to establish a model of the relationship between liquid flow length and time, and determine unknown parameters a and b by fitting the ratio of the slope to the theoretical slope, thereby inferring the liquid viscosity. While this method solves the problems of large liquid volume and complex operation required by traditional capillary methods, it still has the following technical points that need improvement for monitoring inks used in cardboard printing: First, it does not adapt to non-Newtonian fluid characteristics: the method assumes that the measurement object is a Newtonian fluid, without considering the shear thinning or shear thickening characteristics of non-Newtonian fluids such as inks, and directly applying the model will lead to significant deviations in viscosity calculation; second, it ignores dynamic changes in surface tension: the model uses a constant surface tension parameter, without considering the surface tension decay caused by ink solvent evaporation in the printing scenario, which is inconsistent with actual working conditions; third, the parameter correction dimension is singular: the unknown parameters a and b are only... The existing technology suffers from several shortcomings. First, it lacks a channel depth-dependent, temperature- and ink-type-dependent coupling correction, making it unsuitable for various inks used in carton printing, including water-based, oil-based, and UV-curable inks. Furthermore, its measurement accuracy decreases under fluctuating temperatures. Second, the channel design is not optimized for ink characteristics: while mentioning disposable channels, key parameters such as channel depth range and aspect ratio are not clearly defined, and the impact of pigment residue in the ink on the measurement is not fully considered, resulting in insufficient accuracy. Third, its real-time performance is not adapted to printing production needs: the data acquisition time interval is not limited, and it is not optimized for the real-time monitoring requirements of continuous carton printing production, making it difficult to meet the needs of online, dynamically adjusted production schedules. Therefore, a method for monitoring ink viscosity that combines real-time performance, high accuracy, multi-ink compatibility, and avoids residual contamination is urgently needed to address the problems of existing technologies. Summary of the Invention

[0005] Technical Objective: To overcome the shortcomings of existing technologies, and addressing issues such as insufficient adaptation to non-Newtonian characteristics, neglect of dynamic changes in surface tension, single-dimensional parameter correction, unoptimized channel design, and lack of real-time performance in the monitoring of ink viscosity for carton printing, this invention provides a real-time ink viscosity monitoring method for carton printing equipment. By optimizing the channel structure design and establishing a multi-factor coupling correction model, real-time, accurate, and universal monitoring of ink viscosity can be achieved.

[0006] This invention provides a method for real-time monitoring of ink viscosity in cardboard box printing equipment, comprising: S1. Establishing an ink flow calculation model: A model is established to demonstrate the actual relationship between the flow length and time of ink in nanochannels during capillary flow in cardboard printing equipment, as shown in Formula 1. Formula 1: ; in, express The distance the ink flows at any given moment. and For unknown parameters related to channel depth, ink temperature, and ink type, For the real-time temperature of the ink, For ink type correction factor, The surface tension of the ink changes over time. The balanced contact angle between the ink and the channel wall. For ink dynamic viscosity, For the channel height, This is the correction factor for the shear rate of non-Newtonian fluids. This refers to the shear rate during ink flow. This represents the actual fitted slope; S2 Determines the relationship model between ink viscosity and the fitted slope: Based on the actual relationship model described in step S1, the relationship model between ink dynamic viscosity and the actual fitted slope is determined, as shown in Formula 2: Formula 2: ; S3: Introduce an iterative model with unknown parameters: as described in step S1 , It is a binary function of temperature and ink type, as shown in Formulas 3 and 4: Formula 3: ; Formula 4: ; in: , , , , , These are the basic fitting parameters calculated based on experimental data using multiple linear regression. The standard calibration temperature is 25℃. The value is determined based on the ink type: water-based ink Oil-based inks UV-curable inks ; S4: Ink viscosity calculation: based on the fitting slope of the actual capillary flow process of the ink used in carton printing equipment. Substitute the binary function of temperature and ink type described in step S3 into the relationship model between ink dynamic viscosity and actual fitting slope described in step S2 to calculate the ink viscosity.

[0007] Further, the shear rate described in step S1 satisfy: ,in This is the shear rate calibration constant. for The first derivative, i.e., the ink flow rate; the non-Newtonian fluid shear rate correction coefficient. satisfy: ,in and These are fitting parameters related to the ink base type.

[0008] Furthermore, the surface tension of the ink as a function of time described in step S1... Satisfies the evaporation decay model: ,in The initial surface tension of the ink. The volatile coefficient of the ink is determined by the type of ink solvent and the ambient humidity.

[0009] Furthermore, the method for determining the basic fitting parameters in step S3 includes: S3.1 Basic fitting parameter calibration: Select N kinds of commonly used standard inks for carton printing with known dynamic viscosity, where N is an integer greater than 2. The standard inks cover at least three types: water-based, oil-based, and UV-curable. S3.2 Collect data and calculate the actual fitting slope, and control the ink temperature to... N sets of experiments were conducted using the N standard inks, according to the formula. Obtain the fitting slope for each group of experiments. ,in The known dynamic viscosity of the standard ink in the i-th group of experiments is... Let be the shear rate of the ink in the i-th group of experiments; S3.3 Based on the theoretical model formula Obtain the theoretical slope for each experimental group. ; S3.4 Calculate the ratio of the fitted slope to the corresponding theoretical slope for each experimental group, and obtain: ,in This is the type correction factor for the standard ink in the i-th group of experiments; S3.5 Based on N sets of experimental data, the basic fitting parameters are determined through multiple linear regression fitting. , , , , , And thus obtain and The complete expression.

[0010] Furthermore, step S3.5 also includes: selecting M groups of nanochannels at different depths, where M is an integer greater than 1, repeating steps S3.1 to S3.4 to obtain the basic fitting parameters at different channel depths, and establishing the channel depth. Relationship function with basic fitting parameters This enables rapid parameter calibration at different channel depths.

[0011] Further, the actual fitted slope described in step S4 It is obtained by fitting at least three sets of ink flow distance and corresponding time data collected in real time, with a data collection time interval of no more than 0.5 seconds, which is suitable for the real-time monitoring needs of carton printing equipment.

[0012] Furthermore, the depth range of the nanochannels described in step S1 is 100-500 nanometers, and the channel width to depth ratio satisfies... Furthermore, the channel is designed for single use, avoiding measurement errors caused by ink residue contamination.

[0013] The beneficial effects of this invention are: 1. The real-time ink viscosity monitoring method for carton printing equipment provided by the present invention introduces a non-Newtonian fluid shear rate correction coefficient. Through the coupling calculation of shear rate and ink base material type related parameters, the error caused by the non-Newtonian characteristics of ink is accurately corrected, and the measurement accuracy is greatly improved. 2. The real-time ink viscosity monitoring method for carton printing equipment provided by the present invention establishes a surface tension evaporation attenuation model and corrects the surface tension changes caused by solvent evaporation in real time, so that the model is highly consistent with the actual working conditions of continuous ink evaporation in carton printing and accurately matches the actual printing conditions. 3. The real-time ink viscosity monitoring method for carton printing equipment provided by the present invention designs the basic fitting parameters as a binary function of temperature and ink type, adapts to various inks such as water-based, oil-based, and UV-curable inks through correction factors, and corrects the influence of ambient temperature through temperature difference. It can meet the needs of multiple scenarios without replacing the monitoring device, effectively improving the technical versatility. 4. The method for real-time monitoring of ink viscosity for carton printing equipment provided by the present invention ensures capillary flow stability by limiting the depth and aspect ratio of the nanochannels. At the same time, it adopts a disposable structure to avoid the adhesion of pigments and fillers in the ink, ensuring the independence and accuracy of each monitoring and eliminating the need for frequent channel cleaning. Attached Figure Description

[0014] Figure 1 This is a flowchart of a method for real-time monitoring of ink viscosity in cardboard box printing equipment. Detailed Implementation

[0015] The following is in conjunction with the appendix Figure 1 The principles and features of this invention are described herein, and the examples given are for illustrative purposes only and are not intended to limit the scope of the invention. To distinguish between letters representing variables and letters representing units, the letters representing variables in this invention use italicized Cambria Math font, for example: For ink type correction factors, water-based inks The letters representing units in this invention are in regular Song typeface, for example: ink dynamic viscosity unit: mPa·s.

[0016] like Figure 1 As shown, a method for real-time monitoring of ink viscosity in cardboard box printing equipment includes: S1: Establishing an ink flow calculation model: Establishing a model of the actual relationship between the flow length and time of ink in the capillary flow of carton printing equipment in nanochannels, as shown in Formula 1: Formula 1: ; The parameters are defined as follows: : The distance the ink flows at any given time (unit: μm); 、 Unknown parameters related to channel depth, ink temperature, and ink type will be solved iteratively using a binary function. Real-time ink temperature (unit: °C); Ink type correction factor, water-based ink Oil-based inks UV-curable inks ; The surface tension of the ink as a function of time (unit: mN / m) satisfies ,in The initial surface tension of the ink (unit: mN / m). The volatile coefficient of ink is determined by the type of ink solvent and the ambient humidity. For example, for water-based inks, the volatile coefficient is determined by the humidity at 50%. ; The equilibrium contact angle (unit: °) between the ink and the channel wall is determined by the channel material and the ink properties, and can be determined through preliminary experiments (e.g., when using a quartz channel, the water-based ink...). (Approximately 30-45°) : Ink dynamic viscosity (unit: mPa·s), which is the target parameter to be monitored; Channel height (unit: nm), i.e., the depth of the nanochannel; Shear rate during ink flow (unit: s) -1 ),satisfy ,in This is a shear rate calibration constant (determined experimentally, with a value ranging from 1.2 to 1.5). for The first derivative, i.e., the ink flow rate; : Non-Newtonian fluid shear rate correction factor, used to correct the influence of the non-Newtonian properties of ink on flow, to meet the requirements. ,in and Fitting parameters related to ink base type (e.g., water-based inks) 、 Oil-based inks , (It can be calibrated through preliminary experiments). The actual fitting slope is obtained by fitting the ink flow distance and time data collected in real time. Nanochannel parameters: depth range of 100-500 nanometers, channel width to depth ratio meets the following requirements. (Ensuring capillary flow dominates), and the channel is a single-use structure to avoid measurement errors caused by ink residue contamination.

[0017] S2: Determine the relationship model between ink viscosity and fitted slope: Based on the actual relationship model in step S1, derive the dynamic viscosity of the ink. Slope of the actual fit The relationship model is shown in Equation 2: Formula 2: ; This model provides the core basis for subsequent inference of viscosity by fitting the slope, and can be transformed algebraically... As the dependent variable, the solution is obtained based on the known parameters.

[0018] S3: Introducing an iterative model with unknown parameters: (from step S1) , As a bivariate function of temperature and ink type, an iterative model is established through linear fitting, as shown in Equations 3 and 4: Formula 3: ; Formula 4: ; The parameters are defined as follows: 、 、 、 、 、 The basic fitting parameters are obtained by fitting experimental data using multiple linear regression. The standard calibration temperature is fixed at 25℃. The difference between the real-time temperature of the ink and the standard temperature is used to correct the influence of temperature on the basic fitting parameters. Ink type correction factor, the value rules are the same as in step S1.

[0019] The methods for determining the basic fitting parameters specifically include: S3.1 Selection kind( (Integers greater than 2) Commonly used standard inks for carton printing with known dynamic viscosity, covering at least three types: water-based, oil-based, and UV-curable, to ensure parameter compatibility; S3.2 Control the ink temperature to (25℃), using Corresponding standard ink Group experiments, according to the formula Obtain the fitting slope for each group of experiments. ,in For the first The known dynamic viscosity of the standard ink in the group experiment, For the first The shear rate of the ink in the group experiment, The initial surface tension of the ink; S3.3 Calculate the theoretical slope according to the Lucas-Washburn theoretical model formula. Obtain the theoretical slope for each experimental group. ; S3.4 Calculate the ratio, shear rate, and correction coefficient. Calculate the ratio of the fitted slope to the theoretical slope for each experimental group, and obtain: ,in For the first Correction factor for the type of standard ink in the group experiment; S3.5 Multiple linear regression calculates basic parameters based on Using a set of experimental data, the basic fit parameters were determined through multiple linear regression fitting. 、 、 、 、 、 And thus obtain and The complete expression.

[0020] Furthermore, to adapt to different channel depths, step S3.5 can also select... Group( For nanochannels at different depths (integers greater than 1), repeat steps S3.1 to S3.4 to obtain the basic fitting parameters at different channel depths, and establish the channel depth. Relationship function with basic fitting parameters This enables rapid parameter calibration at different channel depths.

[0021] S4: Ink viscosity calculation, based on the fitting slope of the actual capillary flow process of the ink used in carton printing equipment. Substitute the bivariate functions of temperature and ink type obtained in step S3 (Equations 3 and 4) into the relationship model of step S2 (Equation 2), and obtain the dynamic viscosity of the ink through algebraic solution. .

[0022] Among them, the actual fitted slope The data is obtained by fitting at least three sets of ink flow distance data with corresponding time data collected in real time, with a data collection time interval of no more than 0.5 seconds, to ensure that the real-time monitoring requirements of the carton printing equipment are met.

[0023] The present invention will be further described in detail below with reference to specific data. Example 1: I. Summary of basic experimental parameters, S3.1 Calibration of basic fitting parameters; Material preparation: Select 5 standard inks ( ), covering water-based ( Known viscosity mPa·s), oily ( , mPa·s), UV-curable type ( , mPa·s), high viscosity water-based ( , mPa·s), low viscosity oily ( , mPa·s); Three groups of nanochannels at different depths were selected ( ): 100nm, 300nm, 500nm, all with a channel width of 3μm (meeting the requirements) ); Temperature environment: temperature ℃, humidity 50%.

[0024] Preset parameters: Balanced contact angle (Measured values ​​of quartz channel and ink); initial surface tension mN / m (average initial surface tension of 5 inks); Shear rate calibration constant ; Non-Newton correction parameter , (Compatible with experimental ink base materials); Volatility coefficient s -1 (Measured values ​​under experimental conditions).

[0025] II. 100nm channel ( The stepwise calculation data (nm) is obtained in S3.2, and the actual fitting slope is calculated. For each type of ink, collect Flow length of s ,based on and linear relationship ( The fitting yielded As shown in Table 1: Table 1: Summary table of fitted slope data; , S3.3 Calculation of theoretical slope According to the Lucas-Washburn model: As shown in Table 2: Table 2: Summary of Theoretical Slope Data; , S3.4 Calculate the ratio, shear rate, and correction factor: ratio: Shear rate: ( ,Pick s); correction factor: As shown in Table 3: Table 3: Summary of Ratios, Shear Rates and Correction Factors; , S3.5 Multiple linear regression calculates basic parameters based on the formula. The parameters for the 100nm channel were obtained by fitting: , , ; , , ; III. Basic parameter results for the 300 / 500nm channels: Repeat the above steps to obtain two more sets of channel parameters, as shown in Table 4: Table 4: Summary table of parameters for the other two sets of channels; , IV. The relationship function between channel depth and basic parameters, based on channel depth. and , The linear relationship, fitted, yields: ( ); ( ); Therefore, establish channel depth The relationship function with the basic fitting parameters: , ( Unit: nm), used for rapid calibration of channels at different depths.

[0026] Example 2: Real-time monitoring of ink viscosity; Monitoring object: Water-based ink used in a certain cardboard box printing production line ( ); Monitoring conditions: Nanochannels: 300nm depth, 3μm width (single-use); Real-time temperature ; Ambient humidity 50%, volatility coefficient s -1 ; Monitoring process: collection s、 s、 Ink flow distance at time s: μm, μm, μm; The actual fitting slope was obtained based on fitting three sets of data. ; Calculate the temperature difference ℃, substituting into formulas 3 and 4, we get: ; ; Calculate real-time surface tension mN / m; Calculate the shear rate ,in Depend on The derivative of the fitted curve is obtained μm / s, then s -1 ; Calculate the non-Newton correction factor ; Substituting the above parameters into Formula 2, the dynamic viscosity of the ink is obtained. mPa·s; Results verification: The same ink sample was tested offline using a standard rotational viscometer, and the viscosity was measured to be 22.1 mPa·s. The measurement error of the method of this invention was 0.9%, which is significantly better than the error performance of the prior art in the measurement of similar non-Newtonian fluids (the error of the prior art is usually ≥5% when measuring non-Newtonian fluids).

[0027] Example 3: Compatibility verification of different types of inks; Select UV-curable inks ( The temperature was monitored in real time in the 300nm channel calibrated in Example 1. ℃, 3 groups were collected Data fitting yielded Calculated according to the steps of Example 2 The standard rotational viscometer reading is 41.2 mPa·s, with an error of 0.7%. Comparative studies require channel changes or parameter recalibration to adapt to different types of inks, while this invention provides accurate monitoring without additional steps, demonstrating significant versatility.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for real-time monitoring of ink viscosity in cardboard box printing equipment, characterized in that, include: S1. Establishing an ink flow calculation model: A model is established to demonstrate the actual relationship between the flow length and time of ink in nanochannels during capillary flow in cardboard printing equipment, as shown in Formula 1. Official 1: ; in, express The distance the ink flows at any given moment. and For unknown parameters related to channel depth, ink temperature, and ink type, For the real-time temperature of the ink, For ink type correction factor, The surface tension of the ink changes over time. The balanced contact angle between the ink and the channel wall. For ink dynamic viscosity, For the channel height, This is the correction factor for the shear rate of non-Newtonian fluids. This refers to the shear rate during ink flow. This represents the actual fitted slope; S2 Determines the relationship model between ink viscosity and the fitted slope: Based on the actual relationship model described in step S1, the relationship model between ink dynamic viscosity and the actual fitted slope is determined, as shown in Formula 2: Formula 2: Official 2: ; S3: Introduce an iterative model with unknown parameters: as described in step S1 , It is a binary function of temperature and ink type, as shown in Formulas 3 and 4: Official 3: ; Official 4: ; in: , , , , , These are the basic fitting parameters calculated based on experimental data using multiple linear regression. The standard calibration temperature is 25℃. The value is determined based on the ink type: water-based ink Oil-based inks UV-curable inks ; S4: Ink viscosity calculation: based on the fitting slope of the actual capillary flow process of the ink used in carton printing equipment. Substitute the binary function of temperature and ink type described in step S3 into the relationship model between ink dynamic viscosity and actual fitting slope described in step S2 to calculate the ink viscosity.

2. The method for measuring ink viscosity in cardboard printing equipment according to claim 1, characterized in that, The shear rate described in step S1 satisfy: ,in This is the shear rate calibration constant. for The first derivative, i.e., the ink flow rate; the non-Newtonian fluid shear rate correction coefficient. satisfy: ,in and These are fitting parameters related to the ink base type.

3. The method for measuring ink viscosity in cardboard printing equipment according to claim 1, characterized in that, The surface tension of the ink as a function of time described in step S1 Satisfies the evaporation decay model: ,in The initial surface tension of the ink, The volatile coefficient of the ink is determined by the type of ink solvent and the ambient humidity.

4. The method for measuring ink viscosity in cardboard printing equipment according to claim 1, characterized in that, The method for determining the basic fitting parameters in step S3 includes: S3.1 Basic fitting parameter calibration: Select N kinds of commonly used standard inks for carton printing with known dynamic viscosity, where N is an integer greater than 2. The standard inks cover at least three types: water-based, oil-based, and UV-curable. S3.2 Collect data and calculate the actual fitting slope, and control the ink temperature to... N sets of experiments were conducted using the N standard inks, according to the formula. Obtain the fitting slope for each group of experiments. ,in The known dynamic viscosity of the standard ink in the i-th group of experiments is given. Let be the shear rate of the ink in the i-th group of experiments; S3.3 Based on the theoretical model formula Obtain the theoretical slope for each experimental group. ; S3.4 Calculate the ratio of the fitted slope to the corresponding theoretical slope for each experimental group, and obtain: ,in This is the type correction factor for the standard ink in the i-th group of experiments; S3.5 Based on N sets of experimental data, the basic fitting parameters are determined through multiple linear regression fitting. , , , , , And thus obtain and The complete expression.

5. The method for measuring ink viscosity in cardboard printing equipment according to claim 4, characterized in that, Step S3.5 also includes: selecting M groups of nanochannels at different depths, where M is an integer greater than 1, repeating steps S3.1 to S3.4 to obtain the basic fitting parameters at different channel depths, and establishing the channel depth. Relationship function with basic fitting parameters This enables rapid parameter calibration at different channel depths.

6. The method for measuring ink viscosity in cardboard printing equipment according to claim 1, characterized in that, The actual fitted slope described in step S4 It is obtained by fitting at least three sets of ink flow distance and corresponding time data collected in real time, with a data collection time interval of no more than 0.5 seconds, which is suitable for the real-time monitoring needs of carton printing equipment.

7. The method for measuring ink viscosity in carton printing equipment according to claim 1, characterized in that, The depth range of the nanochannels described in step S1 is 100-500 nanometers, and the channel width to depth ratio satisfies the following conditions: Furthermore, the channel is designed for single use, avoiding measurement errors caused by ink residue contamination.

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