Manufacturing method of composite plastic-substituted flexible packaging paper

Abstract

The invention discloses a manufacturing method of composite plastic-substituted flexible packaging paper, and belongs to the technical field of papermaking, and the manufacturing method comprises the following steps: S1, removing surface impurities from needle-leaved wood and broad-leaved wood, cutting the needle-leaved wood and the broad-leaved wood into wood chips, cooking the wood chips, soaking the wood chips in a sulfite solution, and grinding the soaked wood chips by a disc to obtain sulfite paper pulp; s2, adding toughening paper pulp into the sulfite paper pulp, performing pulping treatment to obtain mixed paper pulp, adding a wet strength agent and a fiber dispersing agent into the mixed paper pulp, and performing pulping treatment to obtain papermaking primary pulp; s3, performing papermaking and drying on the papermaking raw pulp to obtain coarse base paper; s4, coating the surface of the coarse base paper with the isolation slurry, drying, and carrying out calendering treatment to obtain the packaging paper; the packaging paper prepared by the invention has higher strength in a wet state.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a method for making composite plastic-substitute soft packaging paper. Background Art

[0002] At present, the outer packaging bags of most products in our lives are made of non-degradable plastic materials, which are prone to cause a series of microplastic hazards. Microplastics are plastic debris and particles with a diameter of less than 5mm, which can further turn into micron plastics, submicron plastics, and nanoplastics. Due to their tiny size and difficult to degrade properties, microplastics can easily enter the human body through the food chain in nature, posing potential hazards to human health. Some of the outer packaging currently on the market is made of degradable plastics such as polylactic acid, polycaprolactone, and polypropylene succinate, but the production cost of these materials is high, which makes it difficult for them to widely replace difficult-to-degrade plastics and be used to make product outer packaging.

[0003] Wood pulp paper, as a product made of natural raw materials, is completely biodegradable, making it an ideal packaging material. It can be processed into wrapping paper for packaging products. However, the barrier and protective properties of current wrapping paper and plastic packaging materials are quite different. Wrapping paper is easily penetrated by moisture in a humid environment for a long time. When moisture penetrates into the interior of the wrapping paper, the strength of the wrapping paper will be reduced, and the wrapping paper will not be able to protect the internal products well.

[0004] Based on the above situation, a Chinese patent with announcement number CN104674608A discloses a method for preparing environmentally friendly packaging paper, including the following steps: Step 1, completing the preparation of a surface coating in a container, the surface coating is composed of varnish, water and an anti-scratch agent, the varnish is a polyacrylate resin or a polyurethane resin, and the anti-scratch agent is a trifunctional cross-linking agent; Step 2, placing embossed paper in an air knife coater, using a feeding roller to apply the surface coating filtered by a screen onto the paper surface, and using an air knife to blow out excess coating to form a coating, and then using a drying room to dry the moisture of the paper after the surface coating is completed to form environmentally friendly packaging paper, and then rolling it up for storage.

[0005] The above patent document discloses a kind of wrapping paper with good water resistance. The wrapping paper prevents moisture from penetrating into the inside of the wrapping paper by applying glue on the surface of the wrapping paper, and improves the strength of the wrapping paper in a wet state by using a reinforcing agent. However, applying glue on the surface of the wrapping paper can usually only delay the entry of moisture into the inside. If the moisture on the surface of the wrapping paper cannot be cleaned in time, the moisture will penetrate into the inside of the wrapping paper and reduce the strength of the wrapping paper. In addition, the reinforcing agent can usually only make the wrapping paper in a wet state maintain 20% to 30% of the strength when it is dry, and it still cannot protect the products inside well. Therefore, the technical solution in the above patent document still has room for improvement. Summary of the invention

[0006] In view of the technical defects existing in the background technology, the present invention proposes a method for making a composite plastic-substitute flexible packaging paper, which solves the above technical problems and meets the actual needs. The specific technical solution is as follows: A method for making composite plastic-substitute flexible packaging paper comprises the following steps: S1. After removing surface impurities from coniferous wood and hardwood, the wood chips are cut into wood chips, the wood chips are placed in a cooking container and steam is introduced to cook the wood chips, the cooked wood chips are immersed in a sulfite solution, the immersed wood chips are taken out and excess water is removed by squeezing, and the squeezed wood chips are subjected to disc grinding to obtain sulfite pulp; S2, adding toughening pulp to sulfite pulp and beating the pulp to obtain mixed pulp, adding wet strength agent and fiber dispersant to the mixed pulp and beating the pulp to obtain papermaking stock pulp; S3, spreading the papermaking pulp on the surface of the mesh curtain through a headbox and shaping the paper prototype through a finishing roller, then squeezing the paper prototype to remove excess water and dry it to obtain a coarse base paper; S4, coating the release slurry on the surface of the coarse base paper, drying it, and then calendering it to obtain the packaging paper.

[0007] As a further technical solution of the present invention, the toughened pulp is selected from rattan pulp, straw pulp or a mixture of rattan pulp and straw pulp.

[0008] As a further technical solution of the present invention, the rattan pulp is made by the following method: soaking dry rattan in water and then peeling off the rattan bark, cutting the rattan bark into sections and mixing it with wood ash and crushing it to obtain rattan bark scraps, adding an appropriate amount of water to soak the rattan bark scraps to soften the fibers therein, then washing and filtering the rattan bark mixture to obtain rattan bark fibers, mixing the rattan bark fibers with a sulfite solution for steaming, washing the steamed rattan bark fibers, mixing them with an appropriate amount of water and stirring them evenly to obtain rattan pulp.

[0009] As a further technical solution of the present invention, the straw pulp is prepared by the following method: cutting dry straw into segments and then soaking them in water, mixing the straw segments with wood ash and crushing them to obtain straw fragments, soaking the straw fragments in a sodium hydroxide solution, washing and filtering the straw fragments after the fibers in the straw fragments are softened to obtain straw fibers, mixing the straw fibers with a sulfite solution and steaming them, washing the steamed straw fibers and mixing them with an appropriate amount of water and stirring them uniformly to obtain straw pulp.

[0010] As a further technical solution of the present invention, the toughened pulp also needs to be treated as follows: adding a cross-linking agent and a catalyst to the toughened pulp and stirring evenly, heating the toughened pulp and adding an auxiliary cross-linking agent to react during the stirring process, filtering after the reaction is completed and washing the filtered fibers, adding an appropriate amount of water to the washed fibers again and stirring evenly to obtain the modified toughened pulp.

[0011] As a further technical solution of the present invention, the cross-linking agent is selected from one of glyoxal and amino resin; the catalyst is selected from one of zinc chloride, zinc sulfate, aluminum chloride and aluminum sulfate; the auxiliary cross-linking agent is selected from one of polyvinyl alcohol, polyethylene glycol, glycerol and sorbitol.

[0012] As a further technical solution of the present invention, in step S2, the dry weight ratio of sulfite pulp to toughened pulp in the mixed pulp is 1:(0.5~2), the concentration of the papermaking stock pulp is 3%~6%, and the beating degree is 40~60°SR.

[0013] As a further technical solution of the present invention, the papermaking raw pulp contains 0.1%~1% of a wet strength agent and 0.05%~0.2% of a fiber dispersant calculated by the dry weight of the mixed pulp; the wet strength agent is selected from one of polyamide polyepichlorohydrin resin, polyethyleneimine, polyacrylamide, and polyacrylamide derivatives; and the fiber dispersant is selected from one of polyethylene oxide, methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose.

[0014] As a further technical solution of the present invention, the isolation slurry includes the following components in percentage by mass: 4% to 8% oxidized cassava starch, 0.5% to 2% starch enhancer, 0.2% to 0.5% sodium carboxymethyl cellulose, and the balance is water; in step S4, the coating dry weight of the isolation slurry is 1 to 2 gsm.

[0015] The beneficial effects of the present invention are: The present invention is based on the sulfite method for making wrapping paper. The strength of the wrapping paper in a wet state is improved by adding toughening pulp into papermaking raw pulp. The fibers in the toughening pulp have the characteristic of increased toughness in a completely wet state, so that the wrapping paper can maintain more than 50% of its strength in a dry state in a completely wet state. In addition, the toughening pulp improves the hydrophilicity of the fibers through cross-linking modification, so that the fibers have greater interaction force in a wet state, and these fibers can preferentially absorb moisture when the wrapping paper is not completely wet, so that the wrapping paper maintains a higher strength. DETAILED DESCRIPTION

[0016] The implementation mode of the present invention is described below in conjunction with relevant embodiments. The implementation mode of the present invention is not limited to the following embodiments, and the present invention relates to relevant necessary components in the technical field, which should be regarded as the known technology in the technical field and can be known and mastered by the technical personnel in the technical field.

[0017] A method for making composite plastic-substitute flexible packaging paper comprises the following steps: S1. After removing surface impurities from coniferous wood and hardwood, the wood chips are cut into wood chips, the wood chips are placed in a cooking container and steam is introduced to cook the wood chips, the cooked wood chips are immersed in a sulfite solution, the immersed wood chips are taken out and excess water is removed by squeezing, and the squeezed wood chips are subjected to disc grinding to obtain sulfite pulp; S2, adding toughening pulp to sulfite pulp and beating the pulp to obtain mixed pulp, adding wet strength agent and fiber dispersant to the mixed pulp and beating the pulp to obtain papermaking stock pulp; S3, spreading the papermaking pulp on the surface of the mesh curtain through a headbox and shaping the paper prototype through a finishing roller, then squeezing the paper prototype to remove excess water and dry it to obtain a coarse base paper; S4, coating the release slurry on the surface of the coarse base paper, drying it, and then calendering it to obtain the packaging paper.

[0018] The present invention mainly processes coniferous wood and hardwood as raw materials into sulfite pulp and then makes packaging paper through subsequent processing flow. In step S1, the coniferous wood and hardwood need to remove bark and leaves before cutting. This is because the bark and leaves contain more impurities such as resin, which can easily affect the purity of pulp. The fiber structure of pulp can be optimized and the quality of the final paper obtained can be better. The coniferous wood and hardwood are cut into wood chips with uniform thickness and then steamed. During the steaming process, the fiber structure inside the wood chips will be softened and the connection structure between the fibers will be destroyed, so that the fibers inside the wood chips are flexible and plastic. Steaming can also kill the impurities in the wood chips. The wood chips are immersed in a sulfite solution, and the pH of the sulfite solution is controlled within the range of 6 to 9. The wood chips are heated and boiled to effectively remove impurities such as lignin in the wood chips. The wood chips are then taken out and cleaned, and excess water is removed by a screw extruder and then refined by a disc grinder. The disc grinder exerts a strong mechanical action on the wood chips through a high-speed rotating grinding disc, so that the fibers are further refined and dispersed into single fibers or fiber bundles. An appropriate amount of water is added during the disc grinding process to refine the fibers and improve the disc grinding efficiency. The wood chips are disc ground to obtain sulfite pulp.

[0019] In steps S2 and S3, after the sulfite pulp and the toughening pulp are mixed to obtain a mixed pulp, the toughening pulp is selected from rattan pulp, straw pulp or a mixture of rattan pulp and straw pulp, the toughening pulp is preferably a mixture of rattan pulp and straw pulp, the dry weight ratio of the sulfite pulp to the toughening pulp in the mixed pulp is 1:(0.5-2), the concentration of the papermaking stock pulp is 3%-6%, and the beating degree is 40-60°SR; in addition to wood fiber, the mixed pulp also contains one or two of rattan fiber and straw fiber, and the fiber content in the mixed pulp is 1:(0.5-2). The fiber serves as the skeleton structure of the coarse base paper formed in the subsequent papermaking process. The dry coarse base paper is mainly composed of dry wood fiber, rattan fiber and straw fiber. When the coarse base paper is processed into packaging paper and used, when water penetrates into the fibers inside the packaging paper, the wood fiber, rattan fiber and straw fiber inside will be moistened, and the toughness of the rattan fiber and the straw fiber will be significantly improved in the moistened state, which is beneficial to improve the toughness and strength of the packaging paper in the moistened state, so that the packaging paper can still better protect the internal packaged products in the moistened state.

[0020] Furthermore, the papermaking stock contains 0.1% to 1% of a wet strength agent and 0.05% to 0.2% of a fiber dispersant calculated by the dry weight of the mixed pulp. The wet strength agent is selected from one of polyamide polyepichlorohydrin resin, polyethyleneimine, polyacrylamide, and polyacrylamide derivatives. The wet strength agent can improve the strength of the paper in a wet state. The higher the beating degree of the papermaking stock, the larger the fiber surface area in the papermaking stock, the greater the adsorption capacity for the wet strength agent, and the wet strength of the paper finally obtained is correspondingly improved. In addition, the wet strength agent has obvious retention and filtration effects on the fibers during the papermaking process, but the wet strength agent can only be added in an appropriate amount. Excessive addition of the wet strength agent will reduce the air permeability and water absorption of the paper, and reduce the elongation at break of the paper; the fiber dispersant is selected from one of polyethylene oxide, methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose. The fiber dispersant can shorten the beating time and improve the softness and strength of the paper after papermaking. The fiber dispersant can also form a network and interact with the suspended solids present in the papermaking stock to improve the retention rate of the fiber.

[0021] In step S4, the isolation slurry includes the following components in percentage by mass: 4% to 8% oxidized cassava starch, 0.5% to 2% starch enhancer, 0.2% to 0.5% sodium carboxymethyl cellulose, and the balance is water; the coating dry weight of the isolation slurry is 1 to 2 gsm; the oxidized cassava starch has good adhesion and film-forming properties, so that the isolation slurry can evenly form an isolation film layer on the surface of the coarse base paper, improve the tear resistance of the paper and make the paper smoother and flatter, the starch enhancer can enhance the adhesion, film-forming properties and other properties of the oxidized cassava starch, thereby achieving better coating and film-forming effects at a lower dosage, the sodium carboxymethyl cellulose can improve the water resistance of the paper and make the surface of the paper smooth and delicate, and the sodium carboxymethyl cellulose can enhance the inter-fiber bonding of the paper, thereby improving the mechanical strength of the paper such as tear resistance and folding resistance.

[0022] Furthermore, the isolation slurry is prepared as follows: water is poured into a suitable container, and then the oxidized cassava starch and the starch enhancer are dispersed in the water, and heated to a liquid while stirring to gelatinize the oxidized cassava starch, and after the liquid is fully gelatinized, sodium carboxymethyl cellulose is added and stirred evenly to obtain the isolation slurry.

[0023] As one of the preferred embodiments of the present invention, rattan pulp is made by the following method: soaking dry rattan in water and then peeling off the rattan bark, cutting the rattan bark into sections and mixing it with wood ash to obtain rattan bark scraps, soaking the rattan bark scraps in an appropriate amount of water to soften the fibers therein, then washing and filtering the rattan bark mixture to obtain rattan bark fibers, mixing the rattan bark fibers with a sulfite solution for steaming, washing the steamed rattan bark fibers and mixing them with an appropriate amount of water and stirring them evenly to obtain rattan pulp; the rattan of the present invention can be made of wisteria, green rattan, black rattan, yellow rattan, etc. as raw materials, and rattan Rattan fibers usually have longer fiber lengths and better fiber bonding, which helps to improve the strength and toughness of paper. Rattan fibers have a unique fiber structure, with cell walls rich in cellulose, forming a tight network structure that increases compressive and tensile strengths. Based on this special fiber structure and under the wetting effect of water molecules, water molecules can penetrate into the fibers to lubricate, reduce friction and resistance between fibers, and make the fibers easier to bend and stretch, thereby enhancing the toughness of rattan fibers in a wet state and increasing the strength of the packaging paper in a wet state.

[0024] As one of the preferred embodiments of the present invention, straw pulp is made by the following method: dry straw is cut into segments and then soaked in water, the straw segments are mixed with wood ash and pounded to obtain straw fragments, the straw fragments are soaked in a sodium hydroxide solution, the straw fragments are washed and filtered to obtain straw fibers after the fibers in the straw fragments are softened, the straw fibers are mixed with a sulfite solution and steamed, the steamed straw fibers are washed and mixed with an appropriate amount of water and stirred to obtain straw pulp; the straw fibers have moderate fiber fineness and strong toughness and wear resistance. Based on the toughness of the straw fibers, water molecules can penetrate into the fibers under the wetting effect of water molecules, play a lubricating role, reduce friction and resistance between fibers, thereby making the fibers easier to bend and stretch, enhancing the toughness of the straw fibers in a wet state, and thus increasing the strength of the packaging paper in a wet state.

[0025] As one of the preferred embodiments of the present invention, the toughened pulp also needs to be treated as follows: adding a cross-linking agent and a catalyst to the toughened pulp and stirring evenly, heating the toughened pulp and adding an auxiliary cross-linking agent to react during the stirring process, filtering after the reaction is completed and washing the filtered fibers, adding an appropriate amount of water to the washed fibers again and stirring evenly to obtain the modified toughened pulp; the cross-linking agent is selected from one of glyoxal and amino resin; the catalyst is selected from one of zinc chloride, zinc sulfate, aluminum chloride, and aluminum sulfate; the auxiliary cross-linking agent is selected from one of polyvinyl alcohol, polyethylene glycol, glycerol, and sorbitol.

[0026] The above-mentioned treatment operation can improve the hydrophilicity of the fibers in the toughened pulp. During the above-mentioned treatment process, the cross-linking agent reacts with functional groups such as hydroxyl and carboxyl in the fibers under the catalytic action of the catalyst to form a cross-linked structure, and a hydrophilic substance such as a co-cross-linking agent is introduced during the cross-linking reaction. These hydrophilic substances can be combined with the fibers by chemical bonding or physical adsorption, thereby making the rattan fibers and straw fibers in the toughened pulp have higher hydrophilicity. In the process of the packaging paper being infiltrated with water, the rattan fibers and straw fibers can absorb water first. When the water content is low and the packaging paper is not completely infiltrated, most of the water will be distributed in the rattan fibers and straw fibers. The water content will not have a significant effect on the structure of the wood fibers in the packaging paper. In addition, the toughness of the rattan fibers and straw fibers increases when wet, so the packaging paper can maintain a higher strength at this time.

[0027] Furthermore, for the rattan fibers and straw fibers in the toughened pulp, after the cross-linking reaction, the internal structure of the fibers can be made tighter, so the fibers may be more easily combined with other materials in a wet state, and due to the increased hydrophilicity, water films may be more easily formed on the fiber surface, thereby increasing the contact area and interaction force between the fibers and other materials, which helps to enhance the bonding force between the fibers in the wrapping paper, so that the wrapping paper can still maintain a high strength in a wet state.

[0028] In summary, the present invention is based on the sulfite method to produce packaging paper. The strength of the packaging paper in a wet state is improved by adding toughening pulp to the papermaking raw pulp. The fibers in the toughening pulp have the characteristic of increased toughness in a completely wet state, so that the packaging paper can maintain more than 50% of its strength in a dry state in a completely wet state. In addition, the toughening pulp improves the hydrophilicity of the fibers through cross-linking modification, so that the fibers have greater interaction force in a wet state, and these fibers can preferentially absorb moisture when the packaging paper is not completely wet to enable the packaging paper to maintain a higher strength.

[0029] The present invention is further described below by way of examples and comparative examples.

[0030] Example 1

[0031] S1. After removing surface impurities from coniferous wood and hardwood, the wood chips are cut into wood chips, the wood chips are placed in a cooking container and steam is introduced for cooking, the cooked wood chips are immersed in a sulfite solution with a concentration of 2.5, the immersed wood chips are taken out and excess water is removed by squeezing, and the squeezed wood chips are subjected to disc grinding to obtain sulfite pulp; S2, soaking dried wisteria canes in water and then peeling off the rattan bark, cutting the rattan bark into sections and mixing with plant ash to obtain rattan bark scraps, soaking the rattan bark scraps in an appropriate amount of water to soften the fibers therein, then washing and filtering the rattan bark mixture to obtain rattan bark fibers, mixing the rattan bark fibers with a sulfite solution for steaming, washing the steamed rattan bark fibers, mixing with an appropriate amount of water, and stirring to obtain rattan paper pulp; S3, cutting dry rice straw into segments and soaking them in water, mixing the rice straw segments with plant ash and crushing them to obtain rice straw fragments, soaking the rice straw fragments in a sodium hydroxide solution, washing and filtering the rice straw fragments after the fibers in the rice straw fragments are softened to obtain rice straw fibers, mixing the rice straw fibers with a sulfite solution and steaming them, washing the steamed rice straw fibers and mixing them with an appropriate amount of water and stirring them to obtain rice straw pulp; S4, mixing rattan pulp and straw pulp in a dry weight ratio of 1:1 to obtain toughened pulp, mixing the toughened pulp and sulfite pulp in a dry weight ratio of 1:1 and beating the mixture to obtain mixed pulp, adding 0.5% polyamide polyepichlorohydrin resin and 0.1% polyethylene oxide based on the dry weight of the mixed pulp to the mixed pulp, and then beating the mixture to obtain papermaking stock pulp, wherein the concentration of the papermaking stock pulp is 5% and the beating degree is 50°SR; S5, spreading the papermaking pulp on the surface of the mesh curtain through a headbox and shaping the paper prototype through a finishing roller, then squeezing the paper prototype to remove excess water and shape it, and then drying it to obtain a coarse base paper with a gram weight of 100 gsm; S6. Prepare an isolation slurry with 6% oxidized cassava starch, 1.2% starch enhancer, 0.3% sodium carboxymethyl cellulose and 92.5% water by mass percentage, apply the isolation slurry on the surface of coarse base paper with a coating dry weight of 1.5 gsm, dry it, and then obtain packaging paper by calendering.

[0032] Example 2

[0033] S1. After removing surface impurities from coniferous wood and hardwood, the wood chips are cut into wood chips, the wood chips are placed in a cooking container and steam is introduced for cooking, the cooked wood chips are immersed in a sulfite solution with a concentration of 2.5, the immersed wood chips are taken out and excess water is removed by squeezing, and the squeezed wood chips are subjected to disc grinding to obtain sulfite pulp; S2, soaking dried wisteria canes in water and then peeling off the rattan bark, cutting the rattan bark into sections and mixing with plant ash to obtain rattan bark scraps, soaking the rattan bark scraps in an appropriate amount of water to soften the fibers therein, then washing and filtering the rattan bark mixture to obtain rattan bark fibers, mixing the rattan bark fibers with a sulfite solution for steaming, washing the steamed rattan bark fibers, mixing with an appropriate amount of water, and stirring to obtain rattan paper pulp; S3, cutting dry rice straw into segments and soaking them in water, mixing the rice straw segments with plant ash and crushing them to obtain rice straw fragments, soaking the rice straw fragments in a sodium hydroxide solution, washing and filtering the rice straw fragments after the fibers in the rice straw fragments are softened to obtain rice straw fibers, mixing the rice straw fibers with a sulfite solution and steaming them, washing the steamed rice straw fibers and mixing them with an appropriate amount of water and stirring them to obtain rice straw pulp; S4, mixing rattan pulp and straw pulp in a dry weight ratio of 1:1 to obtain toughened pulp, adding 4% ethylene glycol and 0.5% zinc chloride based on the dry weight of the toughened pulp to the toughened pulp and stirring evenly, heating the toughened pulp to 80° C. and adding 2% polyvinyl alcohol based on the dry weight of the toughened pulp to react during the stirring process, filtering after the reaction is completed and washing the filtered fibers, adding an appropriate amount of water to the washed fibers again and stirring evenly to obtain the modified toughened pulp; S5, mixing the modified toughened pulp and sulfite pulp in a dry weight ratio of 1:1 and beating the mixture to obtain a mixed pulp, adding 0.5% polyamide polyepichlorohydrin resin and 0.1% polyethylene oxide based on the dry weight of the mixed pulp to the mixed pulp, and then beating the mixture to obtain a papermaking stock pulp, wherein the concentration of the papermaking stock pulp is 5% and the beating degree is 50°SR; S6, spreading the papermaking pulp on the surface of the mesh curtain through a headbox and shaping the paper prototype through a finishing roller, then squeezing the paper prototype to remove excess water and shape it, and then drying it to obtain a coarse base paper with a gram weight of 100 gsm; S7. Prepare an isolation slurry with 6% oxidized cassava starch, 1.2% starch enhancer, 0.3% sodium carboxymethyl cellulose and 92.5% water by mass percentage, apply the isolation slurry on the surface of coarse base paper with a coating dry weight of 1.5 gsm, dry it, and then obtain packaging paper by calendering.

[0034] Comparative Example 1 S1. After removing surface impurities from coniferous wood and hardwood, the wood chips are cut into wood chips, the wood chips are placed in a cooking container and steam is introduced for cooking, the cooked wood chips are immersed in a sulfite solution with a concentration of 2.5, the immersed wood chips are taken out and excess water is removed by squeezing, and the squeezed wood chips are subjected to disc grinding to obtain sulfite pulp; S2, adding 0.5% polyamide polyepichlorohydrin resin and 0.1% polyethylene oxide based on the dry weight of sulfite pulp to sulfite pulp, and then beating the pulp to obtain papermaking stock pulp, wherein the concentration of the papermaking stock pulp is 5% and the beating degree is 50°SR; S3, spreading the papermaking pulp on the surface of the mesh curtain through a headbox and shaping the paper prototype through a finishing roller, then squeezing the paper prototype to remove excess water and shape it, and then drying it to obtain a coarse base paper with a gram weight of 100 gsm; S4. Prepare an isolation slurry with 6% cassava oxidized starch, 1.2% starch enhancer, 0.3% sodium carboxymethyl cellulose and 92.5% water by mass percentage, apply the isolation slurry on the surface of coarse base paper with a coating dry weight of 1.5 gsm, dry it, and then obtain packaging paper by calendering.

[0035] Comparative Example 2 The packaging paper prepared by referring to the specific implementation method of a method for preparing environmentally friendly packaging paper in Chinese patent literature (Announcement No.: CN104674608A) has the same gram weight as the packaging paper prepared in the above-mentioned Example 1, Example 2, and Comparative Example 1.

[0036] The wrapping papers of all the above embodiments and comparative examples are cut into 300mm×15mm wrapping paper strips, and the mass of the wrapping paper strips in a dry state is weighed. Then, the wrapping paper strips are soaked in water, and the wrapping paper is taken out immediately after the water completely soaks the wrapping paper strips. When the wrapping paper strips are free of water and dripping downward, the weight of the wrapping paper strips is weighed, and the maximum water absorption Xg of the wrapping paper strips is calculated according to the weight of the wrapping paper strips after soaking and the weight of the wrapping paper strips in a dry state. In addition, several wrapping paper strips of the same size are cut, and the tensile index and elongation at break of the wrapping paper strips are tested in a dry state and after absorbing 0.25Xg, 0.5Xg, 0.75Xg, and Xg of water, respectively. The tensile index and elongation at break are tested according to the standard document GBT12914-2008, and the test results are shown in Table 1 below.

[0037]

[0038] Table 1 According to the data in Table 1, the packaging paper strips in Example 1 and Example 2 can maintain more than 70% of the strength in a dry state when absorbing less than 0.75Xg of moisture, and can maintain more than 50% of the strength in a dry state even if they are completely soaked with moisture; the packaging paper strip of Comparative Example 1 can only maintain about 20% of the strength in a dry state after being completely soaked with moisture, and the packaging paper strip of Comparative Example 2 can only maintain about 350% of the strength in a dry state; through comprehensive comparison, the packaging paper obtained in Example 1 and Example 2 based on the technical solution of the present invention has relatively high strength whether in a dry state or a wet state, and when the packaging paper is used as an outer packaging of a product, the packaging paper can better protect the product packaged inside.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for making composite plastic-substitute flexible packaging paper, characterized in that: The following steps are involved: S1. After removing surface impurities from coniferous wood and hardwood, the wood chips are cut into wood chips, the wood chips are placed in a cooking container and steam is introduced to cook the wood chips, the cooked wood chips are immersed in a sulfite solution, the immersed wood chips are taken out and excess water is removed by squeezing, and the squeezed wood chips are subjected to disc grinding to obtain sulfite pulp; S2, adding toughening pulp to sulfite pulp and beating the pulp to obtain mixed pulp, adding wet strength agent and fiber dispersant to the mixed pulp and beating the pulp to obtain papermaking stock pulp; S3, spreading the papermaking pulp on the surface of the mesh curtain through a headbox and shaping the paper prototype through a finishing roller, then squeezing the paper prototype to remove excess water and dry it to obtain a coarse base paper; S4, coating the release slurry on the surface of the coarse base paper, drying it, and then calendering it to obtain the packaging paper.

2. The method for making composite plastic-substitute flexible packaging paper according to claim 1, characterized in that: The toughened pulp is selected from rattan pulp, straw pulp or a mixture of rattan pulp and straw pulp.

3. The method for making composite plastic-substitute flexible packaging paper according to claim 2, characterized in that: The rattan pulp is prepared by the following method: soaking dry rattan in water and then peeling off the rattan bark, cutting the rattan bark into sections and mixing it with wood ash to obtain rattan bark scraps, soaking the rattan bark scraps in a proper amount of water to soften the fibers therein, then washing and filtering the rattan bark mixture to obtain rattan bark fibers, mixing the rattan bark fibers with a sulfite solution to steam, washing the steamed rattan bark fibers, mixing them with a proper amount of water and stirring them evenly to obtain rattan pulp.

4. The method for making composite plastic-substitute flexible packaging paper according to claim 2, characterized in that: The straw pulp is prepared by the following method: cutting dry straw into segments and then soaking them in water, mixing the straw segments with plant ash and crushing them to obtain straw fragments, soaking the straw fragments in a sodium hydroxide solution, washing and filtering the straw fragments after the fibers in the straw fragments are softened to obtain straw fibers, mixing the straw fibers with a sulfite solution and steaming them, washing the steamed straw fibers and mixing them with a proper amount of water and stirring them uniformly to obtain straw pulp.

5. The method for making composite plastic-substitute flexible packaging paper according to claim 1, characterized in that: The toughened pulp also needs to be treated as follows: adding a crosslinking agent and a catalyst to the toughened pulp and stirring evenly, heating the toughened pulp and adding an auxiliary crosslinking agent to react during the stirring process, filtering after the reaction is completed and washing the filtered fibers, adding an appropriate amount of water to the washed fibers and stirring evenly to obtain the modified toughened pulp.

6. The method for making composite plastic-substitute flexible packaging paper according to claim 5, characterized in that: The cross-linking agent is selected from one of glyoxal and amino resin; the catalyst is selected from one of zinc chloride, zinc sulfate, aluminum chloride and aluminum sulfate; the auxiliary cross-linking agent is selected from one of polyvinyl alcohol, polyethylene glycol, glycerol and sorbitol.

7. The method for making composite plastic-substitute flexible packaging paper according to claim 1, characterized in that: In step S2, the dry weight ratio of sulfite pulp to toughened pulp in the mixed pulp is 1:(0.5-2), the concentration of the papermaking stock pulp is 3%-6%, and the beating degree is 40-60°SR.

8. The method for making composite plastic-substitute flexible packaging paper according to claim 1, characterized in that: The papermaking raw pulp contains 0.1%-1% of a wet strength agent and 0.05%-0.2% of a fiber dispersant, calculated based on the dry weight of the mixed pulp; the wet strength agent is selected from one of polyamide polyepichlorohydrin resin, polyethyleneimine, polyacrylamide, and polyacrylamide derivatives; and the fiber dispersant is selected from one of polyethylene oxide, methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose.

9. The method for making composite plastic-substitute flexible packaging paper according to claim 1, characterized in that: The isolation slurry comprises the following components by mass percentage: 4% to 8% oxidized cassava starch, 0.5% to 2% starch enhancer, 0.2% to 0.5% sodium carboxymethyl cellulose, and the balance is water; in step S4, the coating dry weight of the isolation slurry is 1 to 2 gsm.

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