Paper, modified corn starch adhesive and method of making same

Abstract

The application provides a paper product, modified corn starch glue and a preparation method thereof. The preparation method comprises the following steps: mixing and stirring corn starch, glycerol and deionized water to obtain a mixed solution; adding alpha-amylase into the mixed solution and reacting for a first preset time; inactivating the enzyme and cooking to obtain enzyme conversion starch paste; adding a starch enhancer into the enzyme conversion starch paste and stirring; adding an alkali solution to adjust the pH value to 7.5-8.0 and reacting for a second preset time. A four-step synergistic process of "glycerol premixing-precise enzymolysis-starch enhancer crosslinking-pH regulation" is constructed: the dispersion of starch paste is improved through glycerol pre-mixing, the molecular chain length is controlled through precise enzymolysis, crosslinking sites are provided through the introduction of a starch enhancer, and finally a stable three-dimensional network structure is formed through crosslinking reaction, so that the glue solution still has good fluidity and bonding performance during long-term storage, the sieve residue content of the glue solution is greatly reduced, and the uniformity and purity of the glue solution are improved.

Description

Technical Field

[0001] This application relates to the technical field of papermaking, specifically to a paper product, a modified corn starch slurry, and a method for preparing the same. Background Technology

[0002] In the papermaking industry, coating adhesives are the core components that determine the surface properties and performance of coated paper. Enzymatically converted starch has become one of the mainstream raw materials for coating adhesives due to its advantages such as mild enzymatic hydrolysis conditions (can be carried out at 70-80℃ and normal pressure), low raw material cost (starch is widely available), and good biodegradability (meeting environmental requirements). However, its industrial application mainly uses cassava starch, which has better strength and stability, while corn starch faces three major technical bottlenecks in the paper coating field, severely limiting its application scope and product quality: 1. Poor storage stability of corn starch gel (prone to aging): After corn starch is hydrolyzed by enzymes such as α-amylase, the starch molecular chains break down, generating a large amount of short-chain starch and dextrin. These short-chain polymers have weak intermolecular forces and a loose molecular arrangement. During storage, the starch molecular chains, especially amylose, are prone to recordination and crystallization, resulting in a sharp increase in gel viscosity, decreased fluidity, and the formation of gel clumps (i.e., "starch aging"). The higher the proportion of amylose in corn starch (approximately 27%) compared to cassava starch (approximately 17%), the worse the storage stability of the corn starch gel, causing significant inconvenience to continuous production.

[0003] 2. High residue levels in the adhesive and coating: Residue mainly originates from three sources: First, uneven enzymatic hydrolysis results in some corn starch granules not being fully gelatinized and degraded, forming solid residues. Second, short-chain starch molecules produced by enzymatic hydrolysis, due to their high surface energy, are prone to secondary aggregation, forming micron-sized aggregates. Third, small amounts of impurities such as alcohol-soluble proteins and gluten remain in the corn starch raw material. Conventional cooking processes lack specific control methods, preventing the complete dissolution and dispersion of proteins in the starch. These proteins easily precipitate during adhesive storage, forming flocculent or particulate matter, ultimately resulting in a large amount of residue. In existing processes, the residue content on a 200-mesh sieve of enzymatically converted corn starch adhesive is generally ≥1.5%-3%. When mixed with pigments such as calcium carbonate to prepare coatings, the residue content further increases, easily clogging coating screens and scrapers, causing coating interruptions, paper surface particle defects, uneven coating, and other production problems, significantly increasing equipment cleaning frequency and production losses.

[0004] 3. Insufficient system fluidity and compatibility: The corn starch adhesive modified by single cooking and enzymatic hydrolysis is brittle, has poor flexibility, and poor compatibility with coating pigments and fillers. After coating and molding, the coating has insufficient flexibility and poor paper coating strength.

[0005] Current industry solutions to these problems have significant limitations and cannot address the aging issue at the molecular structure level. Increasing enzyme dosage or extending enzymatic hydrolysis time to reduce residue leads to excessive degradation of starch molecular chains, further accelerating aging and creating a technical contradiction: reducing residue inevitably accelerates aging and reduces the strength of the adhesive. Therefore, developing an enzyme-modified corn starch conversion technology that can simultaneously solve both stability and residue issues through molecular design and process optimization has become an urgent need for the paper coating industry. Summary of the Invention

[0006] The first aspect of this application provides a method for preparing modified corn starch adhesive, the method comprising: Corn starch, glycerin, and deionized water were mixed and stirred to obtain a mixture; Add α-amylase to the mixture and react for the first preset time; Enzyme inactivation and cooking yield enzyme-converted starch paste; Add starch enhancer to the enzyme-converted starch paste and stir; Add an alkaline solution to adjust the pH value to 7.5-8.0 and react for the second preset time.

[0007] In some optional embodiments, in the step of mixing and stirring corn starch, glycerol and deionized water to obtain a mixture, the corn starch is 100 parts by weight, the glycerol is 6-8 parts by weight, and the deionized water is 170-180 parts by weight.

[0008] In some optional embodiments, in the step of adding α-amylase to the mixture and reacting for a first preset time, the amount of α-amylase added is 0.02-0.03 parts by weight.

[0009] In some optional embodiments, in the step of adding α-amylase to the mixture and reacting for a first preset time, the pH value is adjusted to 5.5-7.0 and the temperature is 85-95°C.

[0010] In some optional embodiments, in the step of adding starch enhancer to the enzyme-converted starch paste and stirring, the amount of starch enhancer added is 10-12 parts by weight.

[0011] In some optional embodiments, the starch reinforcing agent includes any one or a mixture of multiple of the following: acrylic acid and its esters, acrylamide, methacrylic acid and its esters, olefin monomers, phenolic resin, polyamide polyamine epichlorohydrin resin, silane coupling agent, and urea-formaldehyde resin.

[0012] In some optional embodiments, the first preset time is 15-30 minutes, and the second preset time is 30-90 minutes.

[0013] In some optional embodiments, in the step of inactivating enzymes and cooking to obtain enzyme-converted starch paste, the enzyme inactivation temperature is 138-145°C, and the enzyme-converted starch paste obtained after cooking is cooled to 90-95°C and transferred to the finished product storage tank.

[0014] Secondly, this application provides a modified corn starch adhesive solution, which is prepared using the preparation method described in the above embodiments.

[0015] Thirdly, embodiments of this application provide a paper product coated with the modified corn starch slurry described in the above embodiments.

[0016] The modified corn starch adhesive preparation method provided in this application constructs a four-step synergistic process: "glycerol premixing - precise enzymatic hydrolysis - starch enhancer crosslinking - pH adjustment". Premixing with glycerol improves starch gelatinization and dispersibility; precise enzymatic hydrolysis controls molecular chain length; the introduction of a starch enhancer provides crosslinking sites; and finally, a stable three-dimensional network structure is formed through crosslinking reaction. This simultaneously improves the storage stability of the corn starch adhesive and enhances protein solubility and reduces protein precipitation by adjusting the pH of the adhesive to 7.5-8.0. This allows the adhesive to maintain good flowability and bonding properties during long-term storage, significantly reduces the residue content on sieves, and improves the uniformity and purity of the adhesive. This method can then be applied to paper coating processing. This reduces equipment clogging during coating, ensures the uniformity and stability of the coating, and improves product quality and production efficiency. Furthermore, the method of this invention should have good environmental friendliness and cost-effectiveness, meeting the requirements of sustainable development, and providing a new and superior solution for the development of corn starch in the coating adhesive industry. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0018] Figure 1 This is a schematic flowchart of an embodiment of the preparation method of the modified corn starch adhesive of this application. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0020] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] To address the technical shortcomings of existing corn starch coating adhesive preparation processes, such as low protein solubility, high levels of sieve residue and impurities, poor storage stability, large viscosity fluctuations, and weaker coating strength compared to cassava starch, this invention provides a green and efficient method for modifying corn starch adhesive. This method solves the following core technical problems by optimizing the process system and additive combinations, combined with precise pH control technology: 1. Solves the problems of insufficient dissolution and easy precipitation of endogenous proteins in corn starch in traditional processes, and large amount of solid impurities, significantly reduces the content of adhesive residue on the screen, and eliminates coating particle defects and equipment blockage. 2. This invention addresses the problems of easy aging, large viscosity fluctuations, and short shelf life of conventional enzyme-converted starch gel during storage, extending the effective use time of the gel and improving its long-term storage stability and system homogeneity. 3. Break through the technical bottleneck of "the contradiction between reducing sieve residue and improving anti-aging performance" and achieve synergistic optimization of the two; 4. To solve the problem of protein precipitation and colloidal instability caused by disordered pH fluctuations in starch solution, the system's modification effect is maximized and the physicochemical properties of the solution are stabilized through precise pH range control. 5. Improve the basic adhesion properties of modified corn starch adhesive, realize the compatibility and binding force of pigments (such as calcium carbonate) in the coating system, and improve the key properties of coated paper such as surface strength and smoothness.

[0023] This application provides a method for preparing a modified corn starch adhesive solution. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the preparation method of the modified corn starch adhesive of this application, which includes, but is not limited to, the following steps.

[0024] Step S100: Mix corn starch, glycerin and deionized water and stir to obtain a mixture.

[0025] In this step, the corn starch is industrial grade, with a moisture content ≤14%, amylopectin content ≥65%, and protein content ≤0.40%; it provides the basic adhesive framework. Glycerin is food grade, with a purity ≥99.5%; it is added pre-added to improve starch dispersibility and provide anti-aging groups. Deionized water is used to prepare the starch solution and adjust the solid content of the solution to 39±1.0%, controlling the final viscosity to 300±25 cps.

[0026] Optionally, in this embodiment, the corn starch comprises 100 parts by weight, glycerol comprises 6-8 parts by weight, and deionized water comprises 170-180 parts by weight. In a specific embodiment, the glycerol may be 6.5-7.5 parts by weight.

[0027] In an optional embodiment, 100 parts corn starch, 6.5-7.5 parts glycerol, and 170-180 parts deionized water are added to a starch slurry preparation tank. The stirring device is turned on (250-300 rpm), and the mixture is stirred at room temperature for 20 minutes to allow the glycerol to be evenly dispersed and penetrate into the gaps between the starch particles, resulting in a homogeneous glycerol-starch premix emulsion. Adding glycerol at this stage allows it to pre-penetrate into the starch particles, acting as an internal plasticizer and preparing for subsequent reactions.

[0028] Step S200: Add α-amylase to the mixture and react for a first preset time.

[0029] In step S200, the amount of α-amylase added can be 0.02-0.03 parts by mass, the enzyme activity of α-amylase is required to be 25000-30000 U / g, the temperature resistance is ≥90℃, and it catalyzes the breaking of starch molecular chains.

[0030] Specifically, 0.02-0.03 parts of α-amylase can be added to the glycerol-containing starch slurry and stirred evenly. The pH and temperature are adjusted to the optimal operating conditions of the α-amylase used (e.g., mesophilic α-amylase), with a pH of 5.5-7.0 and a temperature of 85-95°C. The mixture is then transferred to an enzyme reaction tank for a first preset reaction time of 15-30 minutes, such as 20 minutes, until the desired degree of conversion is achieved (usually measured by the viscosity after cooking).

[0031] Step S300: Inactivate the enzyme and cook to obtain enzyme-converted starch paste.

[0032] In this step, the enzyme inactivation temperature is 138-145℃. After the enzyme-converted starch liquid is cooked, it is fully gelatinized to obtain a transparent and uniform enzyme-converted starch paste. The enzyme-converted starch paste obtained after cooking is cooled to 90-95℃ and transferred to a finished product storage tank for heat preservation and later use.

[0033] Step S400: Add starch enhancer to the enzyme-converted starch paste and stir.

[0034] In step S400, the amount of starch enhancer added is 10-12 parts by mass, specifically 10 parts by mass, 10.5 parts by mass, 10.8 parts by mass, 11 parts by mass, 11.5 parts by mass, 12 parts by mass, etc.

[0035] The starch reinforcing agent includes any one or a mixture of several of the following: acrylic acid and its esters, acrylamide, methacrylic acid and its esters, olefin monomers, phenolic resin, polyamide polyamine epichlorohydrin resin, silane coupling agent, and urea-formaldehyde resin.

[0036] After enzymatic hydrolysis and glycerol modification, the starch solution is transferred to a storage tank. Under constant temperature and static conditions, 10-12 parts of starch enhancer are added, and the mixture is stirred at low speed for 30 minutes to ensure complete reaction and homogeneity of the solution system.

[0037] In step S500, an alkaline solution is added to adjust the pH value to 7.5-8.0 and the reaction is carried out for a second preset time.

[0038] In this step, a 2% sodium hydroxide solution is added to adjust the pH to 7.5-8.0. The adhesive solution is slowly stirred in the finished product storage tank, and the second preset time for the cross-linking reaction is 30-90 minutes, generally requiring more than 30 minutes. During this process, the starch enhancer undergoes complex cross-linking, esterification, and graft copolymerization reactions with the enzyme-pretreated starch molecules and the pre-added glycerol, forming a three-dimensional cross-linked network of starch and starch enhancer.

[0039] After the reaction is complete, the adhesive solution is cooled to 60±1℃ and the viscosity is tested to be 300±25cps (25℃, 100rpm). If the viscosity of the adhesive solution is not within the above control range, the adhesive solution is boiled again.

[0040] The reaction mechanism of the modified corn starch solution preparation method in this application embodiment lies in the synergistic effect of glycerol and bio-based starch enhancer, and the pH regulation of corn starch solution, the specific effects of which are as follows.

[0041] The role of glycerol: As a small-molecule plasticizer and penetrant, adding 6-8 parts of glycerol before enzymatic hydrolysis allows it to fully penetrate into the starch granules and embed itself between the starch molecular chains, providing internal plasticization for the starch molecules. Simultaneously, it weakens interchain hydrogen bonds, playing a protective role during enzymatic hydrolysis and initially preventing the tight arrangement of starch molecules, laying the foundation for the stability of the final product. More importantly, it creates a more relaxed molecular environment for subsequent cross-linking reactions.

[0042] 2. Starch Reinforcing Agent: The main components are acrylic acid and its esters, acrylamide, methacrylic acid and its esters, olefin monomers, phenolic resin, polyamide-polyamine epichlorohydrin resin, silane coupling agent, and urea-formaldehyde resin. The olefin monomers contain highly active double bonds, carboxyl groups, and amide groups, which can graft copolymerize with starch hydroxyl groups and residual protein active groups in the system, activating and encapsulating residual proteins and preventing protein aggregation and precipitation. Phenolic and urea-formaldehyde resins provide a rigid cross-linking framework, improving the film strength and temperature stability of the adhesive. Polyamide-polyamine epichlorohydrin resin provides cationic active groups, strengthening the adhesion between the adhesive and paper fibers and coating pigments. Silane coupling agents achieve interfacial coupling between the organic starch system and inorganic pigments and paper substrates, eliminating interfacial defects and comprehensively improving the storage stability and coating performance of the adhesive.

[0043] 3. pH Control of the Sediment: Corn starch protein mainly consists of glutenin and glucomannan, with small amounts of albumin and globulin, all of which are alkali-soluble proteins. They dissolve when the pH of the sediment is greater than the pI (isoelectric point), and the higher the pH, the greater the solubility. The pI of the four proteins generally ranges from 4.5 to 7.5. Therefore, raising the pH of the corn starch sediment to above 7.5 improves protein solubility and avoids residue buildup that could affect processing and quality (proteins are sticky). Considering the impact of pH on protein solubility, the formation of free fatty acid and amylose complex particles during storage and gelatinization, and the darkening of the sediment color and the development of a caramel flavor when the pH is 8.5 or higher, the planned pH control for the corn starch sediment is a weakly alkaline stable range of 7.5-8.0. This pH range significantly increases the electrostatic negative charge density of residual proteins in the system, enhances the electrostatic repulsion between protein molecules, achieves efficient protein dissolution, and fundamentally prevents protein aggregation, precipitation, and residue buildup.

[0044] The modified corn starch adhesive preparation method provided in this application constructs a four-step synergistic process: "glycerol premixing - precise enzymatic hydrolysis - starch enhancer crosslinking - pH adjustment". Premixing with glycerol improves starch gelatinization and dispersibility; precise enzymatic hydrolysis controls molecular chain length; the introduction of a starch enhancer provides crosslinking sites; and finally, a stable three-dimensional network structure is formed through crosslinking reaction. This simultaneously improves the storage stability of the corn starch adhesive and enhances protein solubility and reduces protein precipitation by adjusting the pH of the adhesive to 7.5-8.0. This allows the adhesive to maintain good flowability and bonding properties during long-term storage, significantly reduces the residue content on sieves, and improves the uniformity and purity of the adhesive. This method can then be applied to paper coating processing. This reduces equipment clogging during coating, ensures the uniformity and stability of the coating, and improves product quality and production efficiency. Furthermore, the method of this invention should have good environmental friendliness and cost-effectiveness, meeting the requirements of sustainable development, and providing a new and superior solution for the development of corn starch in the coating adhesive industry.

[0045] Example verification 1. Experimental Design Control group: The traditional 100% cassava starch enzyme conversion coating starch cooking process was used.

[0046] Experimental group: 50% and 100% corn starch were used to replace cassava starch, and the process of this invention was carried out (5.0 parts glycerol, 11 parts starch enhancer, and the pH of the coating starch solution was adjusted to a weakly alkaline range of 7.5-8.0).

[0047]

[0048] The raw material quality testing is shown in the table below.

[0049]

[0050] Raw material quality: Compared with cassava starch, corn starch has a higher protein content and a higher initial paste temperature.

[0051] The performance test results are shown in the table below.

[0052]

[0053] Summary: ① Amylase dosage at the same viscosity: Corn starch required more amylase than cassava starch. ② Solubility: Corn starch had lower solubility after adding glycerol and starch enhancer. ③ Anti-aging test: Corn starch solutions were generally worse than cassava starch solutions, with worse aging occurring with increasing dosage; stability improved significantly after adding glycerol and starch enhancer. ④ Sieve residue: Corn starch had much higher residue than cassava starch, with residue increasing with dosage; stability improved significantly after adding glycerol and starch enhancer; pH adjustment in Scheme 2 (7.5-8.0) significantly reduced residue compared to Scheme 3 (pH 6.62).

[0054] In terms of film-forming properties of the adhesive, the film-forming effect of the adhesive was ranked from best to worst as follows: corn starch scheme 1 > corn starch scheme 2 > control group (cassava starch).

[0055] Mechanism: In aqueous solutions, hydrophobic groups aggregate due to hydrophobic-lipophilic interactions, behaving similarly to the clustering of small organic molecules. This clustering is constrained by the water-soluble polymers, hence the term "hydrophobic association." Hydrophobic association can occur both intermolecularly and intramolecularly. Starch is a hydrophilic polymer. The introduction of hydrophobic groups causes these groups to associate in aqueous solutions, forming hydrophobic microlayers that spread across the membrane surface during film formation, thus improving film-forming properties. Simultaneously, the introduction of alkyl groups hinders the association of hydroxyl groups between starch molecules, acting as an internal plasticizer and significantly enhancing the tensile strength of the membrane.

[0056] The physical properties of the coating are shown in the table below.

[0057]

[0058] Summary: 1. Static & Dynamic Water Retention: Static water retention refers to water between molecules and within the molecular network, while dynamic water retention refers to water bound to molecules. Corn starch has lower solubility than cassava starch, reflecting its weaker hydrophilicity. The addition of glycerol and water-resistant groups from starch enhancers to corn starch adhesives results in generally lower water retention compared to cassava starch adhesives. 2. High Shear Viscosity: The high shear viscosity of corn starch adhesive coatings is reduced in all cases.

[0059] The physical properties of the coated paper are shown in the table below.

[0060]

[0061] Summary: ① Gloss & Printing Gloss: Corn starch adhesive improved gloss by 1.5%. ② K&N: Compared with the control group, the CBC of corn starch was slightly lower. ③ Ink Drying Speed, IGT, TV-16, and Cold Adhesion: All three adhesives were similar. ④ Printing Splashing: With the latex content unchanged, increasing the corn starch ratio worsened the splashing problem. Using a coating adhesive prepared with corn starch and tapioca starch in a 1:1 ratio resulted in slightly better paper coating strength compared to the control group using pure tapioca starch. Adding glycerin and starch enhancers to the corn starch adhesive can improve the plasticizing effect and strength of the adhesive, thus helping to improve paper gloss.

[0062] in conclusion A four-step synergistic process involving glycerol premixing, precise enzymatic hydrolysis, starch enhancer crosslinking, and pH adjustment was employed to crosslink corn starch with glycerol and starch enhancers. This process, combined with pH adjustment, improved the protein solubility in corn starch, resulting in significantly enhanced anti-aging properties of the modified corn starch adhesive, reduced sieve residue, and greatly improved overall colloidal stability. When a coating adhesive prepared from corn starch and cassava starch in a 1:1 ratio was applied to paper coating, the coating strength was superior to that of samples coated with pure cassava starch, while the paper gloss and K&N absorbance were also significantly improved.

[0063] Currently, cassava starch raw materials mainly rely on imports, while domestic corn starch supplies are plentiful, resulting in a significant price difference between the two types of raw materials. This modified process effectively improves the coating compatibility of corn starch, demonstrating good industrialization promotion and market application value and prospects.

[0064] The method for preparing modified corn starch adhesive in this application embodiment is based on a highly stable starch adhesive preparation method using corn starch cooked by enzymatic conversion modification, compound additive control, and precise pH optimization. The application process of this corn starch adhesive in paper coating production is applicable to surface coating processing of various machine-made papers such as coated paper and coated white cardboard. It has the following advantages.

[0065] 1. Significantly improves protein solubility and completely reduces residue precipitation. This invention precisely controls the pH of the adhesive solution within the weakly alkaline range of 7.5-8.0, completely eliminating the isoelectric point of corn starch protein, significantly enhancing the electrostatic repulsion of protein molecules, increasing protein solubility by more than 40%, completely solving the problems of protein agglomeration, impurity precipitation, and excessive residue on the sieve in traditional processes, eliminating clogging of the coating screen and particle defects on the paper surface, and greatly improving the smoothness and cleanliness of the coated paper surface.

[0066] 2. Comprehensive improvement of starch gelatin storage stability Glycerol is embedded in the starch molecular chain to inhibit starch retrogradation. The starch enhancer constructs a stable colloidal system through graft copolymerization and three-dimensional cross-linking, which effectively avoids flocculation and aging failure during the storage of the adhesive solution, improves the stability of the adhesive solution, and is fully compatible with the continuous, large-scale, high-speed coating production of paper mills.

[0067] 3. Avoids the defects of traditional processes and technologies; parameters are precise and controllable. The corn starch adhesive solution has a precise weakly alkaline pH range of 7.5-8.0, which solves the problem of protein precipitation in neutral / acidic environments and avoids the drawbacks of excessive starch hydrolysis and loss of adhesive strength caused by strong alkaline environments. The process parameters are precise and stable, and the product quality is highly consistent, making it suitable for industrialized and standardized mass production.

[0068] 4. Optimize the rheological properties of the adhesive to adapt to high-speed coating processes. Enzymatic hydrolysis reduces the viscosity of starch macromolecules, while glycerol plasticization enhances the fluidity and flexibility of the adhesive. The adhesive exhibits stable rheological properties and excellent coating uniformity, with no sagging or accumulation. It is perfectly suited for high-speed coating operations, significantly improving production efficiency and reducing downtime due to production failures.

[0069] 5. Enhance the overall performance of the coating and improve the quality of finished paper products. The cross-linking resin and silane coupling agent in the starch reinforcing agent can improve the film strength, water resistance and interfacial adhesion of the starch adhesive. After coating, the paper coating is dense and uniform, with strong adhesion and excellent abrasion resistance, effectively improving the smoothness, gloss and printability of the paper, and significantly improving the grade of the finished paper.

[0070] 6. The process is green and environmentally friendly, with controllable costs and wide adaptability. All additives in this invention are environmentally friendly and compliant raw materials for papermaking, free of formaldehyde and toxic residues, and meet green papermaking production standards. They can be achieved by modifying conventional starch gluing equipment without the need for new large-scale equipment. The process is simple, the operation is controllable, and the production cost is low. It can be widely adapted to the production of various coated papers and has extremely high versatility and industrialization value.

[0071] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or directly or indirectly applied to other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A method for preparing a modified corn starch adhesive, characterized in that, The preparation method includes: Corn starch, glycerin, and deionized water were mixed and stirred to obtain a mixture; Add α-amylase to the mixture and react for the first preset time; Enzyme inactivation and cooking yield enzyme-converted starch paste; Add starch enhancer to the enzyme-converted starch paste and stir; Add an alkaline solution to adjust the pH value to 7.5-8.0 and react for the second preset time.

2. The preparation method according to claim 1, characterized in that, In the step of mixing and stirring corn starch, glycerin and deionized water to obtain a mixture, the corn starch is 100 parts by weight, the glycerin is 6-8 parts by weight, and the deionized water is 170-180 parts by weight.

3. The preparation method according to claim 2, characterized in that, In the step of adding α-amylase to the mixture and reacting for a first preset time, the amount of α-amylase added is 0.02-0.03 parts by mass.

4. The preparation method according to claim 3, characterized in that, In the step of adding α-amylase to the mixture and reacting for a first preset time, the pH value is adjusted to 5.5-7.0 and the temperature is 85-95℃.

5. The preparation method according to claim 4, characterized in that, In the step of adding starch enhancer to the enzyme-converted starch paste and stirring, the amount of starch enhancer added is 10-12 parts by weight.

6. The preparation method according to claim 1, characterized in that, The starch reinforcing agent includes any one or a mixture of multiple of the following: acrylic acid and its esters, acrylamide, methacrylic acid and its esters, olefin monomers, phenolic resin, polyamide polyamine epichlorohydrin resin, silane coupling agent, and urea-formaldehyde resin.

7. The preparation method according to claim 1, characterized in that, The first preset time is 15-30 minutes, and the second preset time is 30-90 minutes.

8. The preparation method according to claim 1, characterized in that, In the step of inactivating enzymes and cooking to obtain enzyme-converted starch paste, the enzyme inactivation temperature is 138-145℃, and the enzyme-converted starch paste obtained after cooking is cooled to 90-95℃ and transferred to the finished product storage tank.

9. A modified corn starch adhesive, characterized in that, The modified corn starch solution was prepared using the preparation method described in any one of claims 1-8.

10. A paper product, characterized in that, The paper product is coated with the modified corn starch slurry as described in claim 9.

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