Method for uniformly optimizing foaming of polyurethane thermal insulation product
By dynamically adjusting the mixing ratio of recycled polyols and fresh polyols, the foaming process of polyurethane insulation products is optimized, solving the problem of high scrap rate caused by a fixed ratio, and achieving more efficient resource utilization and production efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HENAN SANJIE THERMOELECTRIC TECH
- Filing Date
- 2026-01-15
- Publication Date
- 2026-04-21
AI Technical Summary
In the existing technology, during the production of polyurethane insulation products, the fixed mixing ratio of recycled polyols and fresh polyols cannot adapt to the fluctuations in hydroxyl value and viscosity between batches, resulting in a high scrap rate and an inability to effectively cope with fluctuations in raw material properties.
By collecting the hydroxyl value, viscosity, and additive concentration of recycled and fresh polyols, the compatibility index is calculated, the mixing ratio is dynamically adjusted, and the mixing ratio is optimized through viscosity and temperature correction factors during the mixing process to ensure that the isocyanate and polyol have synchronous reactivity and optimize foaming uniformity.
It improves the utilization rate of recycled polyols, reduces density deviation and cell size differences, significantly reduces scrap rate, and improves production efficiency and resource utilization.
Smart Images
Figure CN121893450A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of plastic recycling technology, specifically to a method for optimizing the uniformity of foaming in polyurethane insulation products. Background Technology
[0002] Polyurethane (PU), a high-performance material, is widely used in building insulation, automobiles, furniture, and other fields. However, waste polyurethane is difficult to degrade naturally, and long-term accumulation can cause soil and water pollution. Furthermore, incineration releases toxic gases. In addition, polyurethane production relies on petroleum-based raw materials; recycling waste polyurethane can reduce dependence on fossil resources and lower energy consumption. Currently, the most common method for polyurethane recycling is alcoholysis, which decomposes polyurethane into recycled polyols. While recycled polyols can be reused, they need to be mixed with fresh polyols when producing polyurethane insulation products. Due to reduced functionality, residual impurities, or uneven molecular weight distribution, the reactivity of recycled polyols decreases. Mixing them with fresh polyols can improve the overall reaction rate and crosslinking density of the system, ensuring foam strength and reducing costs.
[0003] Existing technologies typically use a fixed mixing ratio, determining the optimal ratio of recycled polyols to fresh polyols based on orthogonal experiments and range analysis. However, due to differences in the alcoholysis process, recycled polyols exhibit batch-to-batch fluctuations in hydroxyl value and viscosity, leading to changes in the optimal mixing ratio of the system. A fixed ratio cannot accommodate these fluctuations, resulting in a high scrap rate for polyurethane boards. Summary of the Invention
[0004] To address the technical problem of high scrap rates caused by fixed mixing, this application provides a method for optimizing the uniformity of polyurethane insulation product foaming. The specific technical solution adopted is as follows: This application proposes a method for optimizing the uniformity of foaming in polyurethane insulation products, which includes the following steps: For polyurethane, alcoholysis is used to recycle plastics and obtain recycled polyols. Before the recycled polyol, fresh polyol and additives are mixed and foamed, data are collected on the recycled polyol and fresh polyol to obtain their hydroxyl value and viscosity, as well as the concentration of the additives. The compatibility index between recycled and fresh polyols is obtained based on the difference in hydroxyl values between recycled and fresh polyols, the viscosity of recycled polyols, and the concentration of surfactants in the additives. A standard hydroxyl value is preset, and the basic mixing ratio of recycled polyols is obtained based on the difference in hydroxyl values between fresh and recycled polyols and the difference between fresh and standard hydroxyl values. The initial mixing ratio of recycled polyols is obtained by comparing the basic mixing ratio with the upper and lower limits of the recycled polyol mixing ratio using the compatibility index as a threshold. The raw materials and additives are added and stirred to obtain a mixture by initial mixing ratio; the hydroxyl value, viscosity and temperature of the mixture are collected; the viscosity of the mixture is compared with the target viscosity range or the hydroxyl value is compared with the target hydroxyl value to determine whether the mixing ratio needs to be corrected, and the mixture with the adjusted ratio is obtained. Methods for correcting the mixing ratio include: A viscosity correction factor is obtained based on the difference between the viscosity of the mixture and the target viscosity range of the mixture; a temperature compensation value for the viscosity correction factor is obtained by performing temperature compensation on the viscosity correction factor based on the difference between the temperature of the mixture and the reference temperature; and a correction ratio is obtained based on the temperature compensation value of the viscosity correction factor and the initial mixing ratio. The adjusted mixture is injected into the foaming machine, and foaming agent and isocyanate are added at once. The model is cured and trimmed to obtain polyurethane insulation products.
[0005] In the above scheme, this application calculates the initial mixing ratio by hydroxyl value balance, and adjusts the mixing ratio by calculating correction factors by collecting the viscosity and temperature of the mixture during the mixing process. This allows the mixing ratio of recycled polyol and fresh polyol to be adaptively adjusted, thereby ensuring that the reactivity of isocyanate and polyol is synchronized, optimizing the foaming uniformity of polyurethane insulation products, and improving the utilization rate of recycled polyol. It can better cope with the fluctuation of raw material properties, reduce density deviation, cell size difference and defective products, improve foaming quality, significantly reduce scrap rate, and significantly improve production efficiency and resource utilization.
[0006] In one embodiment, the compatibility index is negatively correlated with the difference in hydroxyl value between the recycled polyol and the fresh polyol, and with the viscosity of the recycled polyol, and positively correlated with the concentration of the surfactant.
[0007] In one embodiment, the method for obtaining the basic mixing ratio of the regenerated polyol based on the difference in hydroxyl values between fresh and regenerated polyols and the difference in hydroxyl values between fresh and standard polyols is as follows: , The standard hydroxyl value, This is the basic mixing ratio for recycled polyols. According to industry standards... Indicates the hydroxyl value of fresh polyols. This indicates the hydroxyl value of the regenerated polyol.
[0008] In one embodiment, the method for obtaining the initial mixing ratio is as follows: Compare the base mixing ratio with 20% and 60% respectively. If it is less than 20%, the base mixing ratio is 20%; if it is greater than 60%, the base mixing ratio is 60%; otherwise, the base mixing ratio remains unchanged. When the compatibility index is greater than 0.5, the basic mixing ratio remains unchanged; when the compatibility index is less than or equal to 0.5, the basic mixing ratio is the minimum of the compatibility index and 40%; the basic mixing ratio after the compatibility index is determined is recorded as the initial mixing ratio.
[0009] In one embodiment, the raw materials in the mixture are recycled polyol and fresh polyol, with their mass fractions ranging from 12% to 36% and 24% to 48%, respectively; the surfactant in the additives is a silane foam stabilizer, the catalyst is triethylamine and dibutyltin dilaurate, and the antioxidant is di-tert-butyl-p-cresol.
[0010] In one embodiment, the method for obtaining the viscosity correction factor based on the difference between the viscosity of the mixture and the target viscosity range of the mixture is as follows: ,in This represents the correction factor. Indicates the viscosity of the mixture. This represents the median value of the target viscosity range for the mixture. This represents the viscosity correction factor.
[0011] In one embodiment, the method for obtaining the temperature compensation value of the viscosity correction factor by temperature compensation based on the difference between the mixture temperature and the reference temperature is as follows: ,in This represents the correction factor. This indicates the temperature of the mixture, where T represents the reference temperature. Indicates viscosity correction factor, The temperature compensation value represents the viscosity correction factor; the reference temperature is a preset value.
[0012] In one embodiment, the correction ratio is the product of the temperature compensation value of the viscosity correction factor and the initial mixing ratio.
[0013] In one embodiment, the method for determining whether to correct the mixing ratio by comparing the viscosity and hydroxyl value of the mixture with the target viscosity range and target hydroxyl value is as follows: When the deviation between the hydroxyl value of the mixture and the target hydroxyl value is greater than 5%, or when the viscosity of the mixture exceeds the target range of 500~1500 mPa·s, the mixing ratio correction is triggered.
[0014] In one embodiment, the deviation between the hydroxyl value of the mixture and the target hydroxyl value is the ratio of the absolute value of the difference between the hydroxyl value of the mixture and the target hydroxyl value to the target hydroxyl value.
[0015] The beneficial effects of this application are as follows: This application calculates the initial mixing ratio by hydroxyl value balance and adjusts the mixing ratio by calculating correction factors based on the viscosity and temperature of the mixture during the mixing process. This allows the mixing ratio of recycled polyol and fresh polyol to be adaptively adjusted, thereby ensuring that the reactivity of isocyanate and polyol is synchronized, optimizing the foaming uniformity of polyurethane insulation products, and improving the utilization rate of recycled polyol. It can better cope with fluctuations in raw material properties, reduce density deviation, cell size differences and defective products, improve foaming quality, significantly reduce scrap rate, and significantly improve production efficiency and resource utilization. Attached Figure Description
[0016] To more clearly illustrate the technical solutions and advantages 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.
[0017] Figure 1 This is a flowchart illustrating a method for optimizing the uniformity of foaming in a polyurethane insulation product according to an embodiment of this application. Detailed Implementation
[0018] To further illustrate the technical means and effects adopted by this application to achieve the intended purpose of the invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of the method for optimizing the uniform foaming of polyurethane insulation products according to this application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.
[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.
[0020] Example of a method to optimize the uniformity of polyurethane insulation product foaming: The following, in conjunction with the accompanying drawings, details the specific scheme of the method for optimizing the uniform foaming of polyurethane insulation products provided in this application.
[0021] Please see Figure 1 The document illustrates a flowchart of a method for optimizing the uniformity of polyurethane insulation product foaming according to an embodiment of this application. The method includes the following steps: Step S001: Recycle and obtain regenerated polyols.
[0022] Recycled polyols can be obtained by using alcoholysis to recycle polyurethane plastics. To reduce environmental impact, recycled polyols are now widely used in production. However, when producing polyurethane insulation products, the properties of recycled polyols vary from batch to batch. To ensure that the recycled polyols meet standardized production processes, it is necessary to mix fresh polyols with the recycled polyols to adjust some product indicators. This embodiment uses the production of insulation boards as an example for illustration.
[0023] Recycled polyols may contain fillers, cross-linked polymer fragments introduced during the recycling process, or oxidation products generated during long-term storage, requiring multi-stage filtration for removal. This is because solid impurities can clog foaming machine nozzles, wear down equipment, and easily lead to cell rupture or structural defects. Furthermore, because recycled polyols are exposed to air or contain residual water-based release agents during the recycling process, their moisture content is usually high, necessitating dehydration. Moisture is a key variable in the foaming reaction; in polyurethane systems, water reacts with isocyanates (-NCO) to generate CO2 and urea bonds. Excessive moisture can lead to uncontrolled foaming (excessive CO2 causes cell rupture), uneven foam density, and increased urea bonds, resulting in increased foam brittleness.
[0024] Therefore, pretreatment of the regenerated polyols is necessary.
[0025] In this embodiment, the pretreatment method is as follows: first, the material is passed through a 100-200 mesh stainless steel filter (primary filtration), and then through a 5-10 μm precision filter (fine filtration) to remove solid particles (such as filler calcium carbonate, glass fiber fragments, and metal shavings). For regenerated polyols containing impurities with density differences (such as sediment), the material is separated by centrifugation at 3000-5000 rpm for 10-15 minutes; subsequently, the regenerated polyol is heated to 50-80°C in a vacuum chamber under vacuum. Stirring at 0.09 MPa for 30-60 minutes, the boiling point of water is lowered by reducing the gas pressure, thus removing it through vaporization. The water content after dehydration is... 0.1%.
[0026] Thus, the pretreated regenerated polyol was obtained.
[0027] Step S002: Collect data on regenerated polyols, fresh polyols, and additives.
[0028] When producing polyurethane insulation boards, polyurethane foaming is required. The principle of polyurethane foaming is based on the chemical reaction between polyols (containing hydroxyl groups, -OH) and isocyanates (containing isocyanate groups, -NCO), while a foaming agent is introduced to generate a bubble structure.
[0029] Isocyanates undergo an addition reaction with the hydroxyl groups in polyols to generate urethane segments, forming linear or three-dimensional polymers. Next, water in the system acts as a chemical blowing agent, reacting with isocyanates to form urea bonds and release carbon dioxide (CO2), or a physical blowing agent (such as a low-boiling-point halogenated hydrocarbon) is added and vaporized upon heating, generating bubble nuclei. As the reaction proceeds, the polymer viscosity increases, surfactants (such as silicone oil) stabilize the bubble interface, and catalysts (such as organotin compounds and amines) regulate the reaction rate, ultimately forming a porous foam structure supported by a polymer skeleton and with uniformly distributed bubbles. The system incorporates surfactants, catalysts, antioxidants, and blowing agents.
[0030] The hydroxyl value of a polyol reflects the content of active hydroxyl groups in the polyol, directly affecting the rate and extent of cross-linking reaction with isocyanates. Collecting the hydroxyl value ensures that the reactivity of recycled polyols matches that of fresh polyols, avoiding incomplete curing, insufficient foam strength, or excessive cross-linking due to fluctuations in the hydroxyl value; it also controls the amount of isocyanate in the formulation to ensure chemical reaction balance during foaming. Viscosity reflects the flowability of a polyol and is affected by molecular weight, temperature, and impurities (such as water and residual catalysts). Recycled polyols may experience greater viscosity fluctuations due to impurities or molecular chain breakage introduced during the recycling process. Collecting viscosity ensures that the polyol is uniformly dispersed with other raw materials (such as foaming agents and catalysts) during mixing, avoiding insufficient stirring or increased energy consumption due to excessively high viscosity; it also controls the flowability during foaming machine injection, preventing foam collapse due to excessively low viscosity or injection difficulties due to excessively high viscosity. Surfactants play a crucial role in stabilizing foam structure and regulating interfacial tension in polyol foaming systems. Their compatibility with polyols and isocyanates directly affects the uniformity of the foaming process and the performance of the final product. If surfactants are not compatible with other components, it may lead to phase separation, decreased foam stability, or fluctuations in process parameters.
[0031] Therefore, it is necessary to collect the hydroxyl values of the regenerated polyol and the fresh polyol before mixing using an automatic potentiometric titrator; collect the viscosity of the regenerated polyol and the fresh polyol before mixing using a rotational viscometer; and collect the concentration of the auxiliaries using high performance liquid chromatography.
[0032] Thus, the hydroxyl values and viscosities of the regenerated and fresh polyols, as well as the concentrations of the additives, were obtained.
[0033] Step S003: Calculate the compatibility index of the regenerated polyol and the fresh polyol based on their data, and obtain the basic mixing ratio by giving the difference between the hydroxyl value and the standard hydroxyl value; determine the initial mixing ratio by combining the compatibility index.
[0034] When mixing recycled and fresh polyols, their compatibility directly affects the mechanical properties and structural uniformity of the foamed material. Surfactants, by reducing interfacial tension and enhancing intermolecular interactions, can improve the system's compatibility, ensuring the stable reaction of the mixture during foaming and forming a high-quality finished product. Compatibility refers to the ability of two or more substances to form a homogeneous and stable system without phase separation after mixing; its essence is microscopic uniform dispersion driven by intermolecular forces.
[0035] Therefore, it is necessary to quantify compatibility risks to avoid foaming defects and performance degradation caused by poor compatibility. The difference in hydroxyl value between recycled and fresh polyols reflects the reactivity and molecular weight of the polyols; excessive differences can lead to uneven crosslinking reactions with isocyanates, affecting the mechanical strength and dimensional stability of the foam. Furthermore, excessively high viscosity of recycled polyols can cause uneven mixing, exacerbate phase separation, and reduce compatibility. Surfactants improve the compatibility of different components by reducing the interfacial tension between the two phases, thus indirectly reflecting the strength of intermolecular forces.
[0036] Based on the above analysis, the compatibility index between regenerated polyols and fresh polyols is obtained according to the difference in hydroxyl value between regenerated polyols and fresh polyols, the viscosity of regenerated polyols, and the concentration of surfactants.
[0037] The compatibility index is negatively correlated with the difference in hydroxyl value between recycled polyol and fresh polyol, and with the viscosity of recycled polyol, and positively correlated with the concentration of surfactant.
[0038] It should be noted that positive correlation means that when one variable increases, the other variable also increases, and the two variables change in the same direction. When one variable changes from large to small or from small to large, the other variable also changes from large to small or from small to large. The specific relationship is determined by the actual application, and this application does not impose any special restrictions.
[0039] It should be noted that negative correlation means that when one variable increases, the other variable decreases accordingly, and the two variables change in opposite directions. When one variable changes from large to small or from small to large, the other variable also changes from small to large or from large to small. The specific relationship is determined by practical application, and this application does not impose any special restrictions.
[0040] Preferably, in this embodiment, the expression for the compatibility index is: , Indicates the hydroxyl value of fresh polyols. Indicates the hydroxyl value of the recycled polyol. Indicates the viscosity of the recycled polyol. Indicates the concentration of surfactant. Represents the normalization function. This indicates the compatibility index between regenerated polyols and fresh polyols.
[0041] The greater the difference in hydroxyl values, the greater the difference in reaction rate and cross-linking degree between the polyol and isocyanate, resulting in a higher compatibility risk and a lower upper limit for the proportion of recycled polyol, and vice versa. Since the hydroxyl value of recycled polyol is generally lower than that of fresh polyol, the hydroxyl value difference will never be zero. Higher surfactant concentrations result in lower interfacial tension, less interfacial resistance during mixing, more sufficient intermolecular contact and interaction, and better intermolecular compatibility, allowing for a higher upper limit for the proportion of recycled polyol, and vice versa. Higher viscosity of recycled polyol should also result in a lower upper limit for its proportion, and vice versa.
[0042] A higher compatibility index indicates better compatibility between recycled and fresh polyols, allowing for a higher upper limit on the mixing ratio of recycled polyols. When the compatibility index is greater than 0.5, the upper limit for the mixing ratio of recycled polyols is 40% to 60%; otherwise, the upper limit is 20% to 40%. In this embodiment, when the compatibility index is greater than 0.5, the upper limit for the mixing ratio of recycled polyols is 60%; otherwise, the upper limit is 40%.
[0043] The basic mixing ratio is calculated based on the hydroxyl value balance principle, and the expression for the basic mixing ratio is: , The standard hydroxyl value, The basic mixing ratio is as follows. According to industry standards, the hydroxyl value of flexible polyurethane foam is 200~400 mgKOH / g, and the hydroxyl value of rigid polyurethane foam is 400~800 mgKOH / g. In this embodiment, the target hydroxyl value is 300 mgKOH / g.
[0044] Excessive differences in the hydroxyl values of the mixed raw materials may lead to phase separation. By performing linear weighted balancing of the hydroxyl value difference between the two raw materials, the mixing ratio that satisfies the target hydroxyl value is determined, thereby ensuring that the two raw materials are uniformly dispersed at the molecular level and avoiding foam structure defects and uneven foaming.
[0045] Considering batch-to-batch variations in recycled polyols, when the hydroxyl values of recycled polyols and fresh polyols are close, The ratio may approach 0 or 1, leading to an excessively high proportion of a certain component, which could cause uneven foaming. Therefore, it is necessary to limit the basic mixing ratio.
[0046] Since the mixing ratio of regenerated polyols is between 20% and 60%, the calculated basic mixing ratio is compared with 20% and 60%. If it is less than 20%, the basic mixing ratio is 20%; if it is greater than 60%, the basic mixing ratio is 60%; otherwise, the basic mixing ratio remains unchanged.
[0047] Furthermore, since the upper limit of the mixing ratio varies depending on the compatibility index, the basic mixing ratio is adjusted based on the compatibility index.
[0048] When the compatibility index is greater than 0.5, the basic mixing ratio remains unchanged; when the compatibility index is less than or equal to 0.5, the basic mixing ratio is the minimum of the two values and 40%.
[0049] The adjusted base mixing ratio is recorded as the initial mixing ratio.
[0050] At this point, the initial mixing ratio has been obtained.
[0051] Step S004: Collect data of the mixture; compare the relevant data of the mixture with the target data to determine whether the mixing ratio needs to be corrected, and obtain the mixture with the adjusted ratio.
[0052] The raw materials and additives are added to a mixing tank according to the initial mixing ratio, and the mixture is stirred to obtain a solution. The stirring speed is 200 rpm, each stirring premixing lasts 30 seconds, and the stirring temperature is 25~35℃.
[0053] The raw materials consist of 12%–36% recycled polyol, providing hydroxyl groups to participate in the cross-linking reaction, and 24%–48% fresh polyol, supplementing the reactivity and stabilizing the hydroxyl value of the system. The surfactant is a silane-based foam stabilizer (0.5%–1.0%), stabilizing the bubble nuclei and promoting uniform dispersion. The catalyst is triethylamine (tertiary amine) (0.15%–0.25%), catalyzing the reaction of hydroxyl groups with NCO and regulating the reaction rate, and dibutyltin dilaurate (organotin) (0.05%–0.1%), catalyzing the cross-linking reaction and optimizing the cell structure. The antioxidant is di-tert-butyl-p-cresol (BHT) (0.1%–0.2%), which can prevent high-temperature oxidation, thereby improving the durability of the polyurethane insulation board. It should be noted that the above percentages are by weight (wt%), which differs from the mixing ratio.
[0054] The hydroxyl value, viscosity, and temperature of the mixture were then collected using an automatic potentiometric titrator, a rotational viscometer, and a temperature sensor, respectively. A mixing ratio correction was triggered when the deviation between the hydroxyl value of the mixture and the target hydroxyl value exceeded 5%, or when the viscosity of the mixture exceeded the target range of 500~1500 mPa·s.
[0055] The deviation between the hydroxyl value of the mixture and the target hydroxyl value is the ratio of the absolute value of the difference between the hydroxyl value of the mixture and the target hydroxyl value to the target hydroxyl value.
[0056] During the recycling process, the polymer chains of recycled polyols break down, leading to a decrease in average molecular weight. Liquid viscosity is directly related to molecular chain length (molecular weight); the lower the molecular weight, the weaker the intermolecular forces, the better the flowability, and the lower the viscosity. Therefore, the viscosity of recycled polyols is usually lower than that of fresh polyols. Furthermore, recycled polyols may contain incompletely separated small-molecule byproducts (such as ethylene glycol and propylene glycol) or catalyst residues. These low-molecular-weight substances dilute the system, further reducing viscosity.
[0057] The expression for the viscosity correction factor is: ,in This represents the correction factor. Indicates the viscosity of the mixture. This represents the median value of the target viscosity range for the mixture. This represents the viscosity correction factor.
[0058] Preferably, in this embodiment, the correction coefficient The value range is 0.1 to 0.2, and the value in this embodiment is 0.1. The target range of viscosity of the mixture is 500-1500 mPa·s, and the median value in this embodiment is 1000.
[0059] When the viscosity of the mixture is too high, it indicates that there is too much fresh polyol. The proportion of recycled polyol needs to be increased to reduce the viscosity of the mixture, and vice versa. By adjusting the proportion of recycled material through viscosity feedback, the viscosity of the mixture is brought closer to the target value, avoiding dispersibility issues caused by batch-to-batch viscosity differences that could affect foaming uniformity.
[0060] Furthermore, the viscosity of the mixture is also temperature-dependent; the viscosity of polyols decreases with increasing temperature. Therefore, temperature compensation is needed to avoid the influence of temperature on the viscosity of the mixture. Thus, a temperature compensation is applied to the viscosity correction factor based on temperature differences. Its expression is: ,in This represents the correction factor. This indicates the temperature of the mixture, where T represents the reference temperature. Indicates viscosity correction factor, This represents the temperature compensation value of the viscosity correction factor.
[0061] Preferably, in this embodiment, the correction coefficient The value range is 0.01~0.05, and the value in this embodiment is 0.02; the reference temperature is 30℃.
[0062] The product of the temperature compensation value of the viscosity correction factor and the initial mixing ratio is used as the correction ratio.
[0063] Regenerated or fresh polyols are added to the mixing tank using a metering pump to change the current mixing ratio to a corrected ratio.
[0064] After stirring and mixing thoroughly, the viscosity and temperature of the mixture are measured again. If the difference between the hydroxyl value and the target hydroxyl value, as well as the viscosity of the mixture, still do not meet the requirements, the mixing ratio is adjusted until the requirements are met.
[0065] At this point, the adjusted mixture was obtained.
[0066] Step S005: Inject the adjusted mixture into the foaming machine, and add foaming agent and isocyanate at once. After curing and trimming, polyurethane insulation board is obtained.
[0067] The foaming agent is a physical foaming agent, cyclopentane (8%~10%), which vaporizes to form cell nuclei and reduce density, and a chemical foaming agent, deionized water (0.3%~0.5%), which reacts with NCO to generate CO2, assisting in foaming. The isocyanate is diphenylmethane diisocyanate (MDI) (28%~32%), which provides isocyanate groups and reacts with hydroxyl groups to generate polyurethane.
[0068] The mixture is injected using a foaming machine, followed by the foaming agent, and finally the isocyanate. The mixture is then stirred and foamed to obtain the foam slurry.
[0069] The foam slurry is then injected into the preheated mold and cured. After demolding, the four sides of the board are trimmed to remove burrs and excess material, resulting in a polyurethane insulation board.
[0070] Preferably, when the final mixture viscosity is greater than or equal to 1000 mPa·s, the stirring speed of the foaming machine is set to 1200~1500 rpm; otherwise, it is set to 800~1000 rpm. The working pressure of the foaming machine cavity is set to 0.3~0.6 MPa, and the outlet back pressure valve is controlled at 0.1~0.2 MPa to prevent foam collapse and ensure uniform thickening of the cell walls. The foaming machine first injects the mixture, then the foaming agent, and finally the isocyanate, with a stirring time of 5~10 seconds; the mold preheating temperature is 40~50℃, and the curing time is 2~4 hours.
[0071] To verify the validity of this application, several comparative examples are provided below, as follows: Comparative Example 1: The mixing ratio of the regenerated polyols was fixed at 30%.
[0072] Comparative Example 2: The mixing ratio of the regenerated polyols was fixed at 40%.
[0073] Comparative Example 3: The mixing ratio of the regenerated polyols was fixed at 50%.
[0074] Unless otherwise stated, the process flow and parameters of Comparative Examples 1, 2, and 3 are consistent with those of this embodiment.
[0075] Table 1 shows a comparison between the traditional fixed mixing ratio and that of this embodiment: Table 1 Comparison of Mixing Ratios Density standard deviation refers to the dispersion of density values in different areas of a polyurethane insulation board, and is a core indicator for measuring the overall density uniformity of the material. A smaller density standard deviation indicates a more consistent density distribution within the material, and stronger controllability in material mixing, reaction processes, and cell growth during foaming. The measurement method is as follows: 10-20 test points are evenly selected on the molded insulation board using a grid method. The density of each sample is measured using the drainage method (according to GB / T 6343) or an electronic densitometer, and the standard deviation is calculated.
[0076] The coefficient of variation (CVA) is the ratio of the standard deviation to the mean of cell size (diameter or chord length), used to quantify the uniformity of cell size. A smaller CVA indicates a more concentrated cell size distribution and higher consistency in cell nucleation and growth during the foaming process. The measurement method is as follows: The insulation board is cut into 5mm thick slices, subjected to liquid nitrogen brittle fracture, and the flat cross-section is obtained. Gold sputtering is applied to enhance the contrast under scanning electron microscopy (SEM) or optical microscopy. At 100-200x magnification, 5-10 fields of view are randomly selected. Image analysis software is used to label the equivalent diameter of each cell. The average cell diameter and standard deviation for each field of view are calculated, and the weighted average of all field-view data is taken as the final CVA.
[0077] The comparison in the table shows that the insulation board in this solution precisely balances the hydroxyl value of the system by dynamically adjusting the mixing ratio of recycled polyol and fresh polyol, ensuring synchronous isocyanate reaction and effectively optimizing foaming uniformity. Compared with the comparative solution with a fixed ratio, this solution can better cope with fluctuations in raw material properties, reduce density deviation, cell size differences, and defective products, significantly reduce scrap rate while improving foaming quality, and significantly improve production efficiency and resource utilization.
[0078] 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 of the technical features. 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, and should all be included within the protection scope of this application.
[0079] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.
Claims
1. A method for optimizing the uniform foaming of polyurethane insulation products, characterized in that, The method includes the following steps: For polyurethane, alcoholysis is used to recycle plastics and obtain recycled polyols. Before the recycled polyol, fresh polyol and additives are mixed and foamed, data are collected on the recycled polyol and fresh polyol to obtain their hydroxyl value and viscosity, as well as the concentration of the additives. The compatibility index between recycled and fresh polyols is obtained based on the difference in hydroxyl values between recycled and fresh polyols, the viscosity of recycled polyols, and the concentration of surfactants in the additives. A standard hydroxyl value is preset, and the basic mixing ratio of recycled polyols is obtained based on the difference in hydroxyl values between fresh and recycled polyols and the difference between fresh and standard hydroxyl values. The initial mixing ratio of recycled polyols is obtained by comparing the basic mixing ratio with the upper and lower limits of the recycled polyol mixing ratio using the compatibility index as a threshold. The raw materials and additives are added and stirred to obtain a mixture by initial mixing ratio; the hydroxyl value, viscosity and temperature of the mixture are collected; the viscosity of the mixture is compared with the target viscosity range or the hydroxyl value is compared with the target hydroxyl value to determine whether the mixing ratio needs to be corrected, and a mixture with the adjusted ratio is obtained. Methods for correcting the mixing ratio include: A viscosity correction factor is obtained based on the difference between the viscosity of the mixture and the target viscosity range of the mixture; a temperature compensation value for the viscosity correction factor is obtained by performing temperature compensation on the viscosity correction factor based on the difference between the temperature of the mixture and the reference temperature; and a correction ratio is obtained based on the temperature compensation value of the viscosity correction factor and the initial mixing ratio. The adjusted mixture is injected into the foaming machine, and foaming agent, isocyanate mold is added at once, cured, and trimmed to obtain polyurethane insulation products.
2. The method for optimizing the uniformity of polyurethane insulation product foaming as described in claim 1, characterized in that, The compatibility index is negatively correlated with the difference in hydroxyl value between recycled polyol and fresh polyol, and with the viscosity of recycled polyol, and positively correlated with the concentration of surfactant.
3. The method for optimizing the uniformity of polyurethane insulation product foaming as described in claim 1, characterized in that, The method for obtaining the basic mixing ratio of regenerated polyols based on the difference in hydroxyl values between fresh and regenerated polyols, and the difference in hydroxyl values between fresh and standard polyols, is as follows: , The standard hydroxyl value, This is the basic mixing ratio for regenerated polyols; Indicates the hydroxyl value of fresh polyols. This indicates the hydroxyl value of the regenerated polyol.
4. The method for optimizing the uniformity of foaming in polyurethane insulation products as described in claim 1, characterized in that, The method for obtaining the initial mixing ratio is as follows: Compare the base mixing ratio with 20% and 60% respectively. If it is less than 20%, the base mixing ratio is 20%; if it is greater than 60%, the base mixing ratio is 60%; otherwise, the base mixing ratio remains unchanged. When the compatibility index is greater than 0.5, the basic mixing ratio remains unchanged; when the compatibility index is less than or equal to 0.5, the basic mixing ratio is the minimum of the compatibility index and 40%; the basic mixing ratio after the compatibility index is determined is recorded as the initial mixing ratio.
5. The method for optimizing the uniformity of foaming in polyurethane insulation products as described in claim 1, characterized in that, The raw materials in the mixture are recycled polyol and fresh polyol, with mass fractions ranging from 12% to 36% and 24% to 48%, respectively; the surfactant in the additives is a silane foam stabilizer, the catalyst is triethylamine and dibutyltin dilaurate, and the antioxidant is di-tert-butyl-p-cresol.
6. The method for optimizing the uniformity of polyurethane insulation product foaming as described in claim 1, characterized in that, The method for obtaining the viscosity correction factor based on the difference between the viscosity of the mixture and the target viscosity range of the mixture is as follows: ,in This represents the correction factor. Indicates the viscosity of the mixture. This represents the median value of the target viscosity range for the mixture. This represents the viscosity correction factor.
7. The method for optimizing the uniformity of foaming in polyurethane insulation products as described in claim 1, characterized in that, The method for obtaining the temperature compensation value of the viscosity correction factor based on the difference between the temperature of the mixture and the reference temperature is as follows: ,in This represents the correction factor. This indicates the temperature of the mixture, where T represents the reference temperature. Indicates viscosity correction factor, The temperature compensation value represents the viscosity correction factor; the reference temperature is a preset value.
8. The method for optimizing the uniformity of foaming in polyurethane insulation products as described in claim 1, characterized in that, The correction ratio is the product of the temperature compensation value of the viscosity correction factor and the initial mixing ratio.
9. The method for optimizing the uniformity of foaming in polyurethane insulation products as described in claim 1, characterized in that, The method for determining whether to correct the mixing ratio by comparing the viscosity and hydroxyl value of the mixture with the target viscosity range and target hydroxyl value is as follows: When the deviation between the hydroxyl value of the mixture and the target hydroxyl value is greater than 5%, or when the viscosity of the mixture exceeds the target range of 500~1500 mPa·s, the mixing ratio correction is triggered.
10. The method for optimizing the uniformity of polyurethane insulation product foaming as described in claim 9, characterized in that, The deviation between the hydroxyl value of the mixture and the target hydroxyl value is the ratio of the absolute value of the difference between the hydroxyl value of the mixture and the target hydroxyl value to the target hydroxyl value.