A method and apparatus for preparing formaldehyde-free decorative paper impregnated with water-based polyacrylate.

Abstract

This application discloses a method and apparatus for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate, belonging to the field of decorative paper production technology. The method includes: providing continuously running formaldehyde-free decorative paper; establishing an asymmetric pulsed electric field within a reactor impregnated with an aqueous polyacrylate emulsion along the path of the formaldehyde-free decorative paper; and controlling the formaldehyde-free decorative paper to pass through the reactor, so that negatively charged polymer micelles in the aqueous polyacrylate emulsion, under the action of the asymmetric pulsed electric field, overcome electrostatic repulsion and surface tension, and are forcibly and rapidly penetrate and fill the internal fiber network of the formaldehyde-free decorative paper. This application fundamentally solves the technical problem of the difficulty in deeply and uniformly impregnating the base paper with environmentally friendly aqueous resin under high-speed production conditions by introducing an electrodynamic forced penetration mechanism.

Description

Technical Field

[0001] This application relates to the field of decorative paper production technology, and more specifically, to a method and apparatus for preparing formaldehyde-free decorative paper impregnated with water-based polyacrylate. Background Technology

[0002] In the modern home furnishing and building materials industry, the environmental and physical properties of decorative paper, as a surface finishing material, are of paramount importance. Traditional decorative paper often uses urea-formaldehyde resin or melamine-formaldehyde resin containing formaldehyde for impregnation, resulting in serious formaldehyde release problems that endanger human health. Therefore, the development and use of formaldehyde-free waterborne polyacrylate (PAA) emulsions as impregnation resins has become a key direction for technological upgrading in the industry. However, the inherent high dynamic surface tension of waterborne polyacrylate emulsions, and the fact that both their polymer micelles and wood pulp cellulose exhibit negative charge in water, lead to a significant electrostatic double-layer repulsion effect between them. This fundamental physicochemical contradiction makes it extremely difficult for waterborne resins to spontaneously and uniformly penetrate deep into the dense fiber network of the base paper in a short time, often resulting in insufficient glue in the paper core, uneven impregnation inside and outside, and ultimately fatal defects such as delamination and bubbling during hot pressing. Existing technologies either add chemical additives to improve permeability (undermining the original intention of being purely non-toxic) or significantly reduce production line speed (sacrificing economic benefits), creating a vicious cycle in which environmental protection, quality, and efficiency are difficult to balance. Summary of the Invention

[0003] The first aspect of this application provides a method for preparing formaldehyde-free decorative paper impregnated with water-based polyacrylate, which aims to solve the technical problem in the prior art that environmentally friendly water-based resins have poor permeability and are prone to product delamination under high-speed production conditions due to the limitations of their physicochemical properties.

[0004] To solve the above-mentioned technical problems, the technical solution provided in this application is as follows:

[0005] A method for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate includes: providing continuously running formaldehyde-free decorative paper; establishing an asymmetric pulsed electric field in a reactor impregnated with an aqueous polyacrylate emulsion along the travel path of the formaldehyde-free decorative paper; and controlling the formaldehyde-free decorative paper to pass through the reactor such that the aqueous polyacrylate emulsion penetrates into the interior of the formaldehyde-free decorative paper under the action of the asymmetric pulsed electric field.

[0006] Specifically, the formaldehyde-free decorative paper is controlled to pass through the electrodynamic impregnation reactor. The negatively charged polymer micelles in the aqueous polyacrylate emulsion are driven by the positive driving pulse to penetrate into the fiber network of the formaldehyde-free decorative paper. The polarization layer and the closed water film are destroyed by the reverse depolarization pulse, thereby completing the impregnation.

[0007] Optionally, establishing an asymmetric pulsed electric field includes: setting a guide roller attached to the formaldehyde-free decorative paper as an anode and setting a tank component of the reactor as a cathode; and applying an alternating voltage waveform comprising a forward drive pulse and a reverse depolarization pulse between the anode and the cathode, wherein the voltage amplitude of the forward drive pulse is greater than the voltage amplitude of the reverse depolarization pulse.

[0008] Optionally, the method further includes: real-time monitoring of the conductivity of the aqueous polyacrylate emulsion in the reactor; and dynamically adjusting the duty cycle of the alternating voltage waveform based on the monitoring results of the conductivity to suppress the electrolytic polarization effect.

[0009] Optionally, after the formaldehyde-free decorative paper leaves the reactor, the method further includes applying a dynamically varying linear pressure to the formaldehyde-free decorative paper via an extrusion assembly to control the amount of residual adhesive on its surface.

[0010] Optionally, the method further includes: detecting the amount of dry adhesive downstream of the formaldehyde-free decorative paper and generating a dry adhesive amount deviation; and performing closed-loop feedback regulation on the dynamically changing linear pressure based on the dry adhesive amount deviation and in conjunction with a control algorithm for compensating for physical transmission lag.

[0011] Optionally, after the formaldehyde-free decorative paper is permeated with the aqueous polyacrylate emulsion, the method further includes: using dielectric heating, by applying a high-frequency alternating electromagnetic field, to cause the polar water molecules inside the formaldehyde-free decorative paper to generate heat through friction, thereby achieving gradient drying from the inside out.

[0012] A second aspect of this application provides an apparatus for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate, which aims to provide a physical entity capable of efficiently implementing the aforementioned method.

[0013] An apparatus for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate includes: a spreading module for providing continuously running formaldehyde-free decorative paper; an electrodynamic impregnation reactor disposed in the travel path of the formaldehyde-free decorative paper, wherein the interior is impregnated with an aqueous polyacrylate emulsion and configured with an electrode system for establishing an asymmetric pulsed electric field within the reactor; and a control system for controlling the formaldehyde-free decorative paper to pass through the electrodynamic impregnation reactor and controlling the electrode system to establish the asymmetric pulsed electric field to drive the aqueous polyacrylate emulsion to penetrate into the interior of the formaldehyde-free decorative paper.

[0014] Optionally, the electrode system includes: a guide roller serving as an anode, the surface of which is adhered to the formaldehyde-free decorative paper; a tank component serving as a cathode; and a pulsed power supply connected to the anode and the cathode, the pulsed power supply being used to generate an alternating voltage waveform comprising a forward drive pulse and a reverse depolarization pulse, wherein the voltage amplitude of the forward drive pulse is greater than the voltage amplitude of the reverse depolarization pulse.

[0015] Optionally, the electrodynamic impregnation reactor further includes a conductivity sensor, and the control system is further configured to: receive monitoring data from the conductivity sensor; and dynamically adjust the duty cycle of the alternating voltage waveform output by the pulse power supply based on the monitoring data.

[0016] Optionally, the apparatus further includes: an extrusion assembly disposed downstream of the electrodynamic impregnation reactor for applying a dynamically varying linear pressure to the formaldehyde-free decorative paper; and an online detection module disposed downstream of the extrusion assembly for detecting the dry glue content of the formaldehyde-free decorative paper and generating a dry glue content deviation; wherein the control system is further configured to perform closed-loop feedback regulation of the dynamically varying linear pressure applied by the extrusion assembly based on the dry glue content deviation and in conjunction with a control algorithm for compensating for physical transmission lag.

[0017] Optionally, the pulse power supply includes: a front-end dual-channel DC regulated rectifier unit for independently outputting a forward high-voltage DC bus voltage and a reverse low-voltage DC bus voltage; an asymmetric full-bridge solid-state switch matrix connected between the front-end dual-channel DC regulated rectifier unit and the anode and the cathode, for alternately switching the forward high-voltage DC bus voltage and the reverse low-voltage DC bus voltage to the anode and the cathode according to the received switching timing signal; and a timing controller for generating the switching timing signal with a dead time to control the asymmetric full-bridge solid-state switch matrix to output the asymmetric pulse electric field.

[0018] The beneficial effects of this application are as follows:

[0019] This application constructs a non-contact electrodynamic forced impregnation architecture, utilizing an asymmetric pulsed electric field to directly impart kinetic energy to waterborne polyacrylate micelles to overcome physicochemical barriers. This transforms the original impregnation resistance into a core driving force, thereby achieving deep, rapid, and uniform impregnation of formaldehyde-free decorative paper without relying on any chemical additives or sacrificing the speed of industrial production lines. This method fundamentally decouples the strong constraint relationship between impregnation efficiency and the inherent physicochemical properties of materials, breaking the impossible triangle between environmental protection, quality, and efficiency in existing waterborne impregnation technologies. It significantly improves the physical properties of the final product (such as internal bond strength) and eliminates delamination defects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the overall structure of the preparation apparatus according to one embodiment of this application.

[0022] Figure 2 This is a schematic cross-sectional view of an electrodynamic impregnation reactor according to an embodiment of this application.

[0023] Figure 3 This is an overall flowchart of the preparation method according to one embodiment of this application.

[0024] Figure 4 This is a timing diagram of the voltage waveform of an asymmetric pulsed electric field according to an embodiment of this application.

[0025] Figure 5 This is a system control logic and data flow block diagram according to one embodiment of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0028] Example 1

[0029] This embodiment provides a method and apparatus for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate. In a specific implementation, this method and apparatus employ a non-contact electrodynamic forced penetration architecture, thereby utilizing a dynamically constructed asymmetric pulsed electric field to provide directional, high-intensity kinetic energy to the negatively charged polymer micelles in the aqueous polyacrylate emulsion, enabling them to actively and rapidly penetrate and fill the micropores of the equally negatively charged base paper fiber network. This method and apparatus solve the core technical problems in the prior art, namely, low impregnation efficiency, uneven penetration, and easy delamination of the finished product under high-speed production conditions caused by the two major physical bottlenecks of electrostatic repulsion and high surface tension between aqueous resin and paper fibers. It achieves the beneficial effect of formaldehyde-free environmentally friendly impregnation with high interfacial bonding strength at industrial-grade linear speeds without using any volatile organic chemical additives.

[0030] Reference Figure 1 The diagram illustrates the overall structure of the preparation apparatus described in the embodiments of this application. The apparatus mainly includes a constant tension continuous spreading module 100, an electrodynamic impregnation reactor 200, a dynamic dielectric heating and gradient drying module 300, and a winding and online detection module 400.

[0031] The constant tension continuous unwinding module 100 is used to provide a stable, flat, and tension-constant formaldehyde-free base paper substrate for the entire continuous production process. In a specific implementation, the constant tension continuous unwinding module 100 internally includes an unwinding shaft for carrying large-diameter base paper, a magnetic powder brake coaxially connected to the unwinding shaft, and a high-frequency tension sensor located downstream of the paper path. The magnetic powder brake generates a controllable braking torque independent of the paper roll speed by adjusting its internal excitation current. The high-frequency tension sensor non-contactly measures the instantaneous tension value of the paper belt during operation. A central programmable logic controller (PLC) receives the feedback signal from the tension sensor and compares it with a preset target tension value (e.g., 150 Newtons). Through a standard proportional-integral-derivative (PID) control algorithm, it dynamically adjusts the excitation current output to the magnetic powder brake, thereby forming a high-precision closed-loop tension control system. The function of this system is to ensure that the formaldehyde-free base paper is always kept in an optimal micro-tension state before entering the subsequent core impregnation process. This state can effectively eliminate wrinkles that may be caused by uneven tension inside and outside the paper roll, and can also moderately open the macroscopic inter-fiber pores, creating favorable physical conditions for subsequent resin penetration.

[0032] The electrodynamic impregnation reactor 200 is used to replace the traditional passive impregnation tank, creating an electric field-driven forced permeation environment. (Refer to...) Figure 2In a preferred embodiment, the tank of the reactor 200 is integrally molded using a material with high insulation strength and excellent chemical corrosion resistance, such as polytetrafluoroethylene (PTFE) or engineering ceramics. At the bottom of the tank, one or more titanium-based ruthenium-coated cathode array plates 201 serve as the system cathodes. The titanium-based ruthenium-coated material is a size-stable anode (DSA) material with extremely low hydrogen evolution overpotential, and in this application, it is used as the cathode in reverse. Its purpose is to greatly suppress the side reaction of hydrogen bubbles generated on the electrode surface due to water electrolysis, even at higher current densities, thus maintaining the stability of the immersion environment. At the center or top of the reactor 200, a rotatable central anode guide roller 202 serves as the system anode, and the formaldehyde-free decorative paper 203 adheres tightly to the surface of this guide roller during its movement.

[0033] To further improve penetration efficiency, the surface of the central anode guide roller 202 can be machined with a micron-level porous structure or fine guide grooves to enhance mechanical engagement with the paper and the uniformity of the electric field distribution. The roller substrate is preferably a titanium alloy with good conductivity and corrosion resistance, and the surface is coated with a layer of ruthenium oxide-iridium oxide (RuO₂) with a thickness between 3 and 10 microns using advanced processes such as magnetron sputtering. A mixed noble metal oxide coating is used. This coating not only possesses excellent electrocatalytic activity, effectively preventing anode passivation at high potentials, but its high hardness and wear resistance also ensure a long service life under prolonged contact with high-speed paper. The reactor 200 is also connected to a high-frequency programmable bipolar pulse power supply assembly, which can generate an asymmetric pulse electric field with a specific waveform and adjustable voltage and frequency between the central anode guide roller 202 and the bottom cathode array plate 201.

[0034] The dynamic dielectric heating and gradient drying module 300 aims to achieve rapid, uniform, and inside-out drying of the impregnated wet paper to match the high-speed impregnation rhythm at the front end, and fundamentally avoid the problem of surface skin formation and internal moisture residue that is easily caused by traditional hot air drying.

[0035] In one specific embodiment, the module 300 mainly consists of a microwave radio frequency (RF) generator and a coupled metal resonant cavity through which the wet impregnated paper continuously passes. The RF generator operates in an Industrial, Scientific, and Medical (ISM) band, such as 27.12 MHz. When a high-frequency alternating electromagnetic field acts on the wet paper, the highly polar water molecules inside the paper, acting as dielectrics, undergo intense dipole reversal and friction under the high-speed alternation of the electric field, efficiently converting electromagnetic energy into heat energy. This heating method is essentially volumetric heating; heat is generated directly inside the wet paper, creating a reverse temperature gradient along the paper's thickness direction—higher inside and lower outside. This gradient generates a water vapor partial pressure gradient from the inside out, driving internal moisture to migrate and overflow to the paper surface in gaseous form, thus achieving a uniform drying effect and ensuring sufficient cross-linking and curing of the waterborne polyacrylate resin during dehydration.

[0036] The winding and online inspection module 400, located at the end of the production process, is responsible for quality monitoring and neat winding of the finished product. This module includes a set of cooling rollers for cooling and shaping the dried decorative paper, a near-infrared (NIR) online inspection instrument for real-time, non-destructive monitoring of key indicators of the finished product, and a winding unit driven by a servo motor with tapered tension control. The NIR online inspection instrument can analyze the absorption spectrum of infrared light at specific wavelengths to deduce core quality parameters of the finished product in real time, such as resin solids content, moisture content, and basis weight. This data is not only used for final product quality assessment, but more importantly, some key data (such as dry glue content) will be fed back to the upstream control system as the data basis for achieving high-precision closed-loop control.

[0037] The preparation apparatus described in this application's embodiments constitutes a highly coordinated intelligent control system through its internal data flow and control logic. (Refer to...) Figure 5 A central PLC serves as the control core, connected to the sensors and actuators of each module via a high-speed industrial fieldbus (such as EtherCAT). The PLC collects real-time data on the production line speed from the constant tension continuous unfolding module 100. and the width of the original paper Real-time emulsion conductivity was collected from an immersion probe in the electrodynamic impregnation reactor 200. With temperature .

[0038] The PLC, based on the pulsed electroosmotic and electrophoretic coupled permeation physical model (PEPM), issues voltage amplitude matrix and frequency commands to the high-frequency programmable bipolar pulse power supply component. In a specific embodiment, the PEPM model is internalized into the following set of coupled empirical equations for real-time calculation of optimal control parameters:

[0039] Equation for calculating the amplitude of the forward drive pulse voltage:

[0040]

[0041] in, for The forward voltage amplitude calculated at any given time (unit: volts); The nominal voltage amplitude under reference operating conditions (e.g., 80 volts); and These are the real-time linear velocity and the emulsion conductivity, respectively. and The baseline linear velocity (e.g., 25 m / min) and baseline conductivity (e.g., 2.0 mS / cm) are used. A velocity sensitivity index (e.g., 0.5) is used to compensate for the shortened permeation time at high speeds; The conductivity compensation index (e.g., 0.8) is used to maintain a constant electrophoretic driving force when the emulsion ion concentration changes.

[0042] Pulse frequency calculation equation:

[0043]

[0044] in, for The pulse frequency calculated at each moment (unit: Hertz); Real-time linear velocity (unit: meters per second); The optimal number of pulses required per unit length of paper (unit: meter) -1 This parameter, considered a key process parameter, was calibrated experimentally (e.g., 400 pulses / meter). This ensures that at any linear speed, a unit length of paper receives the same number of electric field pulses, thus guaranteeing consistent impregnation results.

[0045] Meanwhile, the PLC also runs a PI control algorithm, based on real-time conductivity. To compensate for deviations from the reference value, the voltage duty cycle is fine-tuned to mitigate the impact of ion concentration variations. For extrusion pressure control, the PLC receives dry adhesive quantity deviation signals from the downstream winding and online detection module 400, and, combined with a pure hysteresis compensation algorithm featuring a Smith predictor, outputs a precise dynamic linear pressure command to the upstream extrusion assembly. For controlling the drying power, the PLC employs a feedforward control strategy. Based on the moisture content of the wet paper measured before entering the drying module and the current linear velocity, it directly calculates the required matching radio frequency output power according to the thermodynamic law of conservation of energy. This enables lag-free and energy-efficient control of the drying process.

[0046] The following will combine Figure 3 This application provides a detailed description of a method for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate, as provided in the embodiments of this application. The method mainly includes the following steps:

[0047] S100 provides formaldehyde-free decorative paper for continuous operation.

[0048] In one embodiment, a roll of formaldehyde-free decorative paper that meets quality requirements is mounted on the unwinding shaft of the constant tension continuous unwinding module 100. At production start-up, the end of the paper strip is guided through a series of guide rollers and tension detection rollers. The operator inputs the target tension value for this batch of production at the central control console; for example, for solid-color decorative paper with a basis weight of 70 g / m², the target tension can be set to 150 Newtons. Subsequently, the closed-loop tension control system of the constant tension continuous unwinding module 100 is activated. A high-frequency tension sensor in the system continuously measures the actual tension of the paper path at a frequency of hundreds of times per second. This value is then transmitted to the central PLC. The PID controller inside the PLC compares this actual value with the set value. The comparison generates a deviation signal.

[0049] Based on the deviation signal, the PID controller performs calculations according to its internally set proportional, integral, and derivative parameters to obtain a control output. This output is converted into an analog voltage or digital signal, which is used to adjust the excitation current of the magnetic powder brake connected to the unwinding shaft. When the actual tension is greater than the set value, the controller reduces the excitation current, thereby reducing the braking torque and loosening the paper belt; conversely, it increases the excitation current, increasing the braking torque and tightening the paper belt. Through such a continuous and rapid dynamic adjustment process, it is ensured that throughout the entire production process, regardless of changes in the paper roll diameter or fluctuations in the production line speed, the raw paper entering the subsequent electrodynamic impregnation reactor 200 is always maintained at a constant, optimal tension.

[0050] For example, assume the target tension The actual tension detected by the sensor at a certain moment is 150 Newtons. The current is 155 Newtons, with a deviation of -5 Newtons. The PID controller is based on its internal parameters (e.g., ...). , , The system performs calculations and outputs a negative adjustment command. This command, via a digital-to-analog converter (DAC), acts on the drive circuit of the magnetic powder brake, reducing its excitation current from the current 2.5 amps to 2.45 amps. This slight decrease in current results in a corresponding reduction in braking torque, decreasing the rotational resistance of the unwinding shaft and thus lowering the paper tape tension. In the next control cycle (e.g., after 10 milliseconds), the new tension value is measured and compared again, and this process is repeated to ensure that the actual tension remains within a very small range around 150 Newtons (e.g., ...). This tension control not only prevents physical wrinkling but also creates unobstructed entry channels for the subsequent electrodynamically driven resin microjets by maintaining appropriate fiber separation, which is a prerequisite for deep penetration.

[0051] S200, along the path of the formaldehyde-free decorative paper, an asymmetric pulsed electric field is established in a reactor impregnated with an aqueous polyacrylate emulsion.

[0052] The purpose of this step is to create a strong, unidirectional physical driving field to overcome the physicochemical barriers between the water-based resin and the paper fibers. In one specific embodiment, this step is further subdivided into several collaboratively executed sub-steps.

[0053] S210, in one specific embodiment, firstly, before production begins, a pre-prepared aqueous polyacrylate (PAA) emulsion is pumped into the tank of the electrodynamic impregnation reactor 200 until the liquid level reaches the working height, completely submerging the bottom cathode array plate 201 and the lower half of the central anode guide roller 202. Subsequently, the high-frequency programmable bipolar pulse power supply assembly is activated. The power supply assembly, according to waveform parameters preset by the central PLC, begins to apply a high-frequency, asymmetrical alternating voltage between the anode and cathode. (Refer to...) Figure 4 The voltage waveform is not a standard sine wave or square wave, but a specially designed combination waveform that includes a high-amplitude, wide-pulse forward drive pulse 401 and a low-amplitude, narrow-pulse reverse depolarization pulse 402.

[0054] In a preferred embodiment, during the positive drive pulse 401, the potential of the central anode guide roller 202 is positive (e.g., +80 volts), while the potential of the bottom cathode array plate 201 is negative (or grounded), and the duration of this pulse... The time is relatively long (e.g., 5 milliseconds). Because the polymer micelles in aqueous PAA emulsions typically have functional groups such as carboxyl groups on their surface, they become negatively charged after dissociation in water (their zeta potential can be measured experimentally, typically between -30 and -50 millivolts). Therefore, under the influence of this strong positive electric field, these negatively charged micelles are driven by a powerful Coulomb force (electrophoretic force) pointing towards the anode (i.e., the guide roller attached to the base paper). This force is much stronger than the electrostatic repulsion between the micelles and fibers and the viscous resistance of the fluid passing through the porous medium, thus allowing the PAA micelles to be forcibly and rapidly injected into the micropores of the fiber network inside the base paper in a manner similar to micro-electrophoretic jetting.

[0055] Immediately following the positive drive pulse, the power supply outputs a reverse depolarization pulse 402. During this period, the polarity of the electrodes is instantaneously reversed; the potential of the central anode guide roller 202 becomes negative (e.g., -20 volts), while the potential of the bottom cathode array plate 201 becomes positive. The duration of this pulse is... The reverse pulse is relatively short (e.g., 1 millisecond). This reverse pulse serves two purposes: first, to effectively disrupt the polarization layer and concentration polarization that may form on the electrode surface during the forward pulse, preventing a decrease in electric field efficiency and electrode passivation due to ion enrichment; second, and more importantly, the brief reverse electric field can instantly break down and disturb microbubbles or closed water films that may form in the fiber pores due to surface tension, creating an electrocavitation effect that further clears the permeation channels and improves the microscopic uniformity of impregnation. Because the amplitude of the reverse pulse is much smaller than that of the forward pulse and its duration is short, the resulting reverse electrophoretic force is insufficient to pull out micelles that have already penetrated deep into the paper, thus ensuring that the entire process achieves net, unidirectional forced permeation on a macroscopic scale. The entire forward and reverse pulse cycle is repeated continuously at a high frequency (e.g., 100 to 500 Hz) to ensure sufficient and saturated impregnation is completed in the extremely short time it takes for the paper to pass through the reactor at high speed.

[0056] For example, assuming a production line speed of 25 meters per minute and a length of 0.8 meters for the impregnation zone (i.e., the arc segment where the paper contacts the anode guide roller and is submerged in the liquid), then the total time for the paper to pass through the impregnation zone is only... Seconds. If the pulse period is (5ms + 1ms) = 6ms, then within these 1.92 seconds, each area of ​​the paper will experience... This involves multiple forward injection and reverse defoaming cycles. Such a high frequency of physical action ensures that even within such an extreme time window, the resin can still fully and saturately penetrate into the deepest core of the paper, something that traditional passive impregnation methods cannot achieve.

[0057] Meanwhile, to address potential fluctuations in emulsion ion concentration during production due to water evaporation or emulsion replenishment, and thus maintain a constant electric field efficiency, the system also includes a dynamic adjustment mechanism. An immersion-type conductivity sensor monitors the conductivity of the emulsion in the tank in real time. The central PLC compares this real-time value with the reference conductivity calibrated before production begins. Comparison. When When drift occurs, a built-in PI (proportional-integral) controller is activated. This controller calculates a duty cycle correction based on the magnitude and duration of the drift. For example, when conductivity increases, it means current will increase. To prevent overheating or over-electrolysis, the controller will appropriately reduce the width of the positive drive pulse. That is, reduce the duty cycle, and vice versa. Its governing equation can be expressed as: .in, and The proportional and integral gains are obtained through system identification or empirical tuning. In this way, the system can automatically adapt to slow changes in the electrical properties of the adhesive, ensuring that the effect of electrodynamic forced penetration is always optimal.

[0058] S300, control the formaldehyde-free decorative paper to pass through the reactor, so that the aqueous polyacrylate emulsion penetrates into the interior of the formaldehyde-free decorative paper under the action of the asymmetric pulsed electric field.

[0059] This step describes the completion of the physical transport and impregnation process of the base paper in the established electric field environment, as well as the subsequent glue control and drying process.

[0060] In a specific embodiment, S310, formaldehyde-free decorative paper is continuously fed into the electrodynamic impregnation reactor 200 at a set linear velocity (e.g., 25 m / min) under the traction of the constant tension continuous spreading module 100. The paper strip first passes through a set of guide rollers, then adheres tightly to the surface of the central anode guide roller 202, which serves as the anode, and is subsequently immersed in the aqueous PAA emulsion. During the arc-length region where the paper contacts the guide roller and is immersed in the liquid, the strong asymmetric pulsed electric field established in step S200 continues to act. Negatively charged PAA micelles are forcibly injected into the paper's fiber network under the drive of hundreds of high-frequency pulses. Simultaneously, due to the porous structure of the paper itself, an electroosmotic effect occurs under the electric field, where cations in the liquid (such as hydrated hydrogen ions) carry some water molecules towards the cathode, which objectively plays an auxiliary role in squeezing out excess free water and increasing the relative solid content of the resin. When the paper leaves the impregnation zone and passes the anode guide roller, its internal fiber network has reached a highly saturated impregnation state.

[0061] Next, to control the amount of adhesive applied to the final product, the wet impregnated paper needs to pass through an extrusion assembly. This assembly typically consists of a pair of rubber or stainless steel rollers with precisely adjustable spacing and pressure. The pressure applied here is not a constant value, but a dynamic variable precisely controlled by a central PLC. This control loop is a large time-delay closed-loop feedback system with significant time lag. Specifically, in the winding and online inspection module 400 at the end of the production line, a near-infrared online detector measures the dry adhesive amount and areal density of the final dried product in real time. This value is related to the target dry adhesive amount set in the process. By comparison, a deviation value is obtained. However, due to the long physical distance (e.g., several meters to tens of meters) between the extrusion point and the detection point, there is a pure lag time related to the linear velocity in acquiring this deviation signal. If this delayed signal is used directly to adjust the extrusion pressure, it will inevitably cause the system to oscillate violently, making stable production impossible.

[0062] To address this issue, the control system of this application incorporates the classic Smith predictor-compensator algorithm from the field of process control. The core idea of ​​this algorithm is to establish a mathematical model within the controller that matches the characteristics of the actual production process (gain, time constant, pure time delay).

[0063] To implement this algorithm, a mathematical model matching the characteristics of the actual physical process must be pre-established within the controller. In one specific embodiment, this internal model uses a first-order inertial plus pure time-delay (FOPDT) transfer function to describe the linear pressure from the extrusion assembly. The change is measured by the dry adhesive amount and areal density detected at the online detection module (400). Dynamic response relationships between changes:

[0064]

[0065] in, For the Laplace operator; The system static gain (unit: This characterizes the steady-state change in the dry adhesive amount and areal density caused by a change in unit linear pressure. The system inertial time constant (unit: seconds) characterizes the hysteresis characteristics of the mechanical response and fluid redistribution of the extrusion system; The pure time delay (in seconds) is the physical distance from the extrusion point to the detection point. With current line speed Precise calculation yields, that is These model parameters ( , All systems were identified and calibrated through offline step response experiments conducted during the production preparation phase.

[0066] The controller uses this internal model to predict the system's output under the current adjustment action, assuming no lag, and uses this predicted value to replace the actual, lagging measurement for feedback control. Simultaneously, it continuously compares the actual measurement with the model's prediction, using the error between the two to correct the model and ensure the accuracy of the prediction. In this way, the system achieves closed-loop control of the final product quality while overcoming the instability caused by significant lag.

[0067] Instantaneous command line pressure of the extrusion roller Determined by a multivariate compensation equation: .in, At baseline speed The first is the base pressure that produces the target amount of adhesive; the second is based on the current linear speed. The first term is feedforward compensation, used to overcome changes in fluid dynamic pressure; the third term is based on the equivalent bias after phase lag has been eliminated, processed by the Smith predictor. Feedback corrections were made. This is the hydrodynamic compensation coefficient, and its unit is _____. ; This is the lag equivalent compensation coefficient, and its unit of measurement is... .

[0068] For example, assume the physical distance from the extrusion point to the detection point The current linear speed is 10 meters. If the speed is 25 m / min (approximately 0.417 m / s), then the pure time delay is... for Seconds. At a certain moment, the controller issues a command to increase the extrusion pressure. Without a Smith predictor, the controller would need to wait... The effect of this command will be visible after a few seconds (i.e., ...). The changes in the controller (such as the Smith predictor) can easily lead to overshoot. However, by introducing the Smith predictor, the controller... At the same time the command is issued, its internal model immediately calculates a prediction. Changes are observed, and this estimated value is used to stabilize the current control loop. When Seconds, the real When the measured value arrives, the controller compares it with the model. The predicted values ​​at different times are compared. If there is a difference, it means that the model is inaccurate or there is an unmodeled disturbance. The controller will use this difference to correct its internal model, thereby making more accurate predictions in subsequent control.

[0069] After precise control of the sizing amount, the wet impregnated paper is fed into the dynamic dielectric heating and gradient drying module 300. As mentioned earlier, through the action of a 27.12 MHz high-frequency electromagnetic field, the moisture inside the wet paper is instantly and uniformly heated and vaporized and discharged. The energy control here also employs an advanced feedforward control strategy. Before entering the drying chamber, another near-infrared moisture meter is installed to measure the total areal density of the wet paper in real time. The central PLC uses this real-time measurement value and the current line speed... Paper width and the preset target surface density after drying. Based on the first law of thermodynamics, the excess water ( The theoretical power required for complete gasification. Its calculation formula is: .in, It is the latent heat of vaporization of water (approximately (joules / kg) It is the overall RF energy conversion efficiency (a constant calibrated experimentally, such as 0.65) that takes into account cavity losses and power supply efficiency. The advantage of this feedforward control method is that it can adjust the drying power without lag according to changes in the state of the inlet material (e.g., small fluctuations in the upstream extrusion rollers causing changes in moisture content), ensuring that the moisture content of the outlet product is always accurately maintained at the target value, which greatly improves the stability of product quality and energy utilization efficiency.

[0070] Finally, the formaldehyde-free decorative paper, after thorough drying and curing, is cooled and shaped using cooling rollers, and then finally wound into a roll by the online inspection module 400. Throughout the process, the online inspection instrument continuously monitors product quality, providing data support for the entire intelligent control system and forming a complete automated production closed loop.

[0071] Example 2

[0072] This embodiment provides an apparatus for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate, which serves as the physical carrier for the method described in Embodiment 1. (Refer to...) Figures 1 to 5 The structure and working principle of the device are basically the same as those described in Embodiment 1. Here, we will focus on providing supplementary explanations on the physical implementation and security mechanisms of some of its core components.

[0073] In one specific embodiment, the pulsed power supply configured in the electrodynamic impregnation reactor 200 is a hardware system integrating a multi-stage power electronic converter and a digital logic controller. The pulsed power supply is configured to stably output a high-frequency, asymmetric current of several hundred amperes within an extremely short electrode spacing.

[0074] The internal architecture of this pulse power supply can include a front-end dual-channel DC regulated rectifier unit. This rectifier unit is connected to industrial three-phase AC power and, through two physically isolated insulated-gate bipolar transistor active front-end (AFE) rectifier bridges, converts it into two independently adjustable DC bus voltages: a positive high-voltage DC bus voltage. and a reverse low-voltage DC bus voltage Both buses are equipped with high-capacity metallized thin-film capacitor banks to absorb reactive ripple energy generated during high-frequency pulse switching.

[0075] Following this is an asymmetric full-bridge solid-state switching matrix. This matrix consists of four high-power silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors forming an "H-bridge" topology. Unlike traditional H-bridges that flip the polarity of the same bus voltage, in this matrix, when the upper transistor of the left half-bridge and the lower transistor of the right half-bridge are conducting, the load (i.e., the conductive emulsion between the anode guide roller and the cathode tank) is connected to the positive high-voltage DC bus voltage; when the lower transistor of the left half-bridge and the upper transistor of the right half-bridge are conducting, the load is connected to the reverse low-voltage DC bus voltage.

[0076] The switching matrix is ​​controlled by a timing controller. This timing controller is built on a field-programmable gate array (FPGA). The timing controller receives macroscopic instructions (i.e., frequency and duty cycle parameters) from the central controller via a high-speed industrial Ethernet bus (such as EtherCAT) and converts them into a sequence of physical gate drive pulses with nanosecond precision.

[0077] For example, the front-end dual-channel DC voltage regulator and rectifier unit forward-biases the high-voltage DC bus voltage. The stable output is +120V, which will reverse the low-voltage DC bus voltage. The stable output is -30 V. The rated maximum output current of the pulse power supply is... It is set to 500 A. When generating the switching timing signals for switching the positive and negative buses, the timing controller forcibly inserts a dead time. The dead time The value is set to 1.5 for example. (microseconds). The introduction of this dead time ensures that the two solid-state switches on the same bridge arm will never simultaneously conduct due to a short-circuit fault at the moment of polarity reversal, thus guaranteeing the safe and accurate generation of high-frequency asymmetric pulse waveforms (such as 166 Hz) at the hardware physical level.

[0078] In one specific embodiment, the control system inside the electrodynamic impregnation reactor 200 integrates a mandatory disaster prevention and safety mechanism based on a three-dimensional electric field distribution topology matrix (EFTM) to address the risk of localized arc breakdown that may occur under a high-voltage, high-frequency electric field. This mechanism is implemented as follows: The central PLC's controller memory is virtually divided into a fine three-dimensional mesh according to the reactor tank's geometry. The PLC maintains a real-time updated data matrix, EFTM, in memory that corresponds one-to-one with this physical spatial mesh. Each element of this matrix stores the electric field intensity vector of the corresponding spatial mesh point at the current moment. and current density vector The estimated values ​​are based on a simplified electric field model designed to accommodate the microsecond-level fast computation of PLCs. This model bypasses the complex solution of finite element partial differential equations and employs an approximate calculation method based on geometric weights and real-time electrical parameter correction. For any node in the 3D mesh... Its electric field strength modulus exist The equation for estimating time is as follows:

[0079]

[0080] in, This refers to the real-time voltage difference between the anode and cathode measured by the sensor. For nodes The effective weighted distance to the anode and cathode surfaces is pre-calculated offline based on the reactor geometry and stored as a static lookup table. , which is a dimensionless current distortion correction factor (e.g., 0.3) used to simulate the local distortion effect of electric field lines under high current density; To be based on the total current and effective electrode area The calculated real-time average current density ; This represents the nominal average current density under baseline operating conditions. Using this equation, the PLC can rapidly estimate the approximate distribution of the electric field strength across the entire field within each scan cycle, thereby enabling rapid early warning of potential electrical breakdown risks.

[0081] The core operating logic of this safety mechanism is as follows: In each control clock cycle (e.g., less than 1 millisecond), a high-priority interrupt service routine inside the PLC will check the electric field intensity magnitude of all grid points in the entire EFTM matrix. Perform a high-speed extreme value scan. The system has a preset, absolutely safe dielectric breakdown threshold. The threshold is determined based on the critical breakdown field strength of the aqueous PAA emulsion under standard conditions (e.g., approximately...). (Volts / meter), and multiplied by a safety factor (e.g., 0.8) to obtain an operational safety threshold, for example... Volts per meter. During the scan, if the field strength modulus of any node in the matrix exceeds this preset threshold, it means that an electric arc flashover may be imminent at that physical location. At this time, the interrupt service routine will immediately trigger a hardware interrupt instruction with the highest priority. This instruction bypasses all conventional control logic and acts directly on the underlying drive circuit of the pulse power supply, forcibly clearing the gate drive signal of the IGBT (Insulated Gate Bipolar Transistor) responsible for generating the high-voltage pulse. This action can instantly cut off the currently output high-voltage pulse within microseconds, thereby blocking the energy supply at its source before an arc actually forms and causes equipment damage or a fire.

[0082] For example, suppose that at a certain moment, a tiny metal shaving impurity is accidentally introduced into the adhesive, causing severe distortion of the electric field lines around it. The electric field strength value of the node corresponding to the impurity location in the EFTM matrix instantly changes from normal... Volts / meter jump to Volts per meter. This value exceeds... A preset threshold of volts per meter is set. The PLC's scan program detects this anomaly within the next clock cycle (e.g., within 500 microseconds). A hardware interrupt is immediately triggered, forcibly turning off the conducting IGBTs and instantly reducing the high-voltage output to zero. Simultaneously, the central control system illuminates an alarm light and sounds an alarm, prompting operators to check and troubleshoot the fault. In this way, the mechanism provides reliable safety assurance for the entire high-voltage electrodynamic impregnation process.

[0083] It should be noted that, in specific embodiments of this application, the preferred physicochemical parameters of the aqueous polyacrylate (PAA) emulsion are: a solid content of 35% to 55%, a dynamic viscosity of 50 to 200 mPa·s at 25°C, and a pH value of 7.0 to 8.5.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0085] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit described above can be implemented in hardware.

[0086] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A process for the preparation of a formaldehyde-free decorative paper for waterborne polyacrylate impregnation, characterized in that, include: Provide formaldehyde-free decorative paper for continuous operation; An asymmetric pulsed electric field is established in a reactor impregnated with an aqueous polyacrylate emulsion along the travel path of the formaldehyde-free decorative paper. as well as The formaldehyde-free decorative paper is controlled to pass through the reactor, so that the aqueous polyacrylate emulsion penetrates into the interior of the formaldehyde-free decorative paper under the action of the asymmetric pulsed electric field.

2. The method of claim 1, wherein, The establishment of an asymmetric pulsed electric field includes: A guide roller bonded to the formaldehyde-free decorative paper is designated as the anode, and a tank component of the reactor is designated as the cathode; and An alternating voltage waveform comprising a forward drive pulse and a reverse depolarization pulse is applied between the anode and the cathode, wherein the voltage amplitude of the forward drive pulse is greater than the voltage amplitude of the reverse depolarization pulse.

3. The method of claim 2, wherein, The method further includes: Real-time monitoring of the conductivity of the aqueous polyacrylate emulsion within the reactor; and Based on the monitoring results of the conductivity, the duty cycle of the alternating voltage waveform is dynamically adjusted to suppress the electrolytic polarization effect.

4. The method of claim 1, wherein, After the formaldehyde-free decorative paper leaves the reactor, the method further includes: A dynamically varying linear pressure is applied to the formaldehyde-free decorative paper using an extrusion assembly to control the amount of residual adhesive on its surface.

5. The method according to claim 4, characterized in that, The method further includes: Downstream of the formaldehyde-free decorative paper, its dry adhesive content is measured, and a dry adhesive content deviation is generated; and Based on the dry adhesive quantity deviation and combined with a control algorithm for compensating for physical transmission lag, the dynamically changing linear pressure is adjusted using closed-loop feedback.

6. The method according to claim 1, characterized in that, After the formaldehyde-free decorative paper is impregnated with the aqueous polyacrylate emulsion, the method further includes: The method employs dielectric heating, which involves applying a high-frequency alternating electromagnetic field to generate heat through friction between polar water molecules inside the formaldehyde-free decorative paper, thereby achieving gradient drying from the inside out.

7. An apparatus for preparing formaldehyde-free decorative paper impregnated with aqueous polyacrylate, characterized in that, include: One deployment module is used to provide formaldehyde-free decorative paper for continuous operation; An electrodynamic impregnation reactor is disposed on the travel path of the formaldehyde-free decorative paper, the interior of which is impregnated with an aqueous polyacrylate emulsion and is equipped with an electrode system for establishing an asymmetric pulsed electric field within the reactor. as well as A control system is used to control the formaldehyde-free decorative paper to pass through the electrodynamic impregnation reactor and to control the electrode system to establish the asymmetric pulsed electric field to drive the aqueous polyacrylate emulsion to penetrate into the interior of the formaldehyde-free decorative paper.

8. The apparatus according to claim 7, characterized in that, The electrode system includes: A guide roller serving as an anode, the surface of which is adhered to the formaldehyde-free decorative paper; One is the tank component used as the cathode; and A pulsed power supply connected to the anode and the cathode, the pulsed power supply being used to generate an alternating voltage waveform comprising a forward drive pulse and a reverse depolarization pulse, wherein the voltage amplitude of the forward drive pulse is greater than the voltage amplitude of the reverse depolarization pulse.

9. The apparatus according to claim 8, characterized in that, The electrodynamic impregnation reactor also includes a conductivity sensor, and the control system is further used for: Receive monitoring data from the conductivity sensor; and Based on the monitoring data, the duty cycle of the alternating voltage waveform output by the pulse power supply is dynamically adjusted.

10. The apparatus according to claim 7, characterized in that, The device further includes: An extrusion assembly, located downstream of the electrodynamic impregnation reactor, is used to apply a dynamically varying linear pressure to the formaldehyde-free decorative paper; An online detection module is located downstream of the extrusion assembly to detect the amount of dry adhesive in the formaldehyde-free decorative paper and generate a dry adhesive deviation. The control system is further configured to perform closed-loop feedback adjustment of the dynamically changing linear pressure applied by the extrusion assembly based on the dry glue quantity deviation and in conjunction with a control algorithm for compensating for physical transmission lag.

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