Process for improving blister fastness of blister card

Abstract

The invention belongs to the technical field of papermaking, and particularly relates to a process for improving blister fastness of a blister card. Comprising the following steps: treating needle and hardwood pulp with compound enzyme, adding light magnesium oxide, grinding to obtain compound modified pulp, preparing three layers of pulp, diluting and purifying, adding auxiliaries into a three-layer slushing pump before purifying, and adding core layer auxiliaries containing hydroxymethyl urea modified cationic polysaccharide and the like into a core layer pump; the three layers of pulp are compounded into a wet paper web layer by layer through an upper net of a headbox, gradient pre-drying is performed after multiple times of squeezing dehydration, and then surface sizing, post-drying, hard calendaring, front and back coating and soft calendaring are performed in sequence to obtain a finished blister card product. The process effectively solves the problems of infirm blister and shelling in narrow-edge blister processing, realizes standardized control of slurry quality, greatly reduces batch-to-batch difference of blister effects, remarkably improves the binding force of a narrow-edge blister area, optimizes the surface performance of paper, reduces the phenomena of linting and powdering during printing, and improves the printing quality of the narrow-edge blister blister. And the printing adaptability is improved.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, specifically relating to a process for improving the blister pack strength of blister cards. Background Technology

[0002] Blister cards, as an environmentally friendly paper-based packaging material, have been widely used in packaging scenarios across various industries, including food, pharmaceuticals, electronics, toys, cosmetics, and machinery hardware, thanks to their excellent forming performance and environmentally friendly characteristics. They are particularly suitable for forming narrow-edge blister packs and can be used to produce various non-thermoformed blister products such as folded, bi-folded, cylindrical, and top-and-bottom boxes, holding an important position in the packaging field. This product belongs to the field of paper-based packaging material preparation technology, and its core requirement is to balance printability and blister strength to meet the packaging requirements of different scenarios.

[0003] Currently, existing blister card manufacturing processes mostly use PVC, PP, PET, and recyclable paper as base materials. The paper strength is improved by adding reinforcing chemicals such as cationic starch and dry strength agents to the pulp, and blister forming is achieved through a blister oil coating process. However, existing technologies still have many defects and shortcomings that urgently need to be addressed in practical applications, seriously affecting the product quality and application expansion of blister cards. Firstly, there is a fundamental contradiction between paper strength and blister pack adhesion. Current technologies typically improve paper strength by increasing the amount of reinforcing agents and enhancing the fine fiberization of the pulp. However, excessive fiber hydrogen bonding leads to a dense paper structure, hindering the full penetration of the blister pack oil. This is especially problematic for narrow-edge blister packs (where the processing area is limited), where the blister pack oil cannot effectively bond with the paper fibers, easily resulting in poor adhesion and detachment, making it difficult to meet the processing requirements of specialized blister products.

[0004] Secondly, insufficient control over the stability of raw materials leads to poor product consistency. Some existing processes do not fix the specific types and proportions of softwood and hardwood pulps, and lack targeted technical modification treatments, resulting in fluctuations in pulp quality and consequently unstable paper strength. This instability indirectly exacerbates the volatility of thermoforming effects, leading to significant batch-to-batch differences and making it difficult to adapt to the needs of large-scale production, thus limiting the company's capacity expansion and market development.

[0005] Third, it has poor adaptability to narrow-edge blister packaging. Existing blister card manufacturing processes are mostly designed based on the needs of wide-edge conventional blister products, without optimizing paper structure and chemical formulas to address the limited processing area of ​​narrow-edge blister packs. This results in insufficient blister strength when blister cards are used in narrow-edge packaging scenarios, failing to meet the requirements of high-end precision packaging and hindering the application and promotion of blister cards in the high-end market.

[0006] Therefore, developing a blister card manufacturing process that can resolve the contradiction between strength and blister fastness, ensure product consistency, and adapt to narrow-edge blister packaging has become an urgent technical problem to be solved in the current paper-based packaging materials field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a process for improving the blister card's blister strength. This process can synergistically enhance both paper strength and blister strength, effectively solving the problems of weak blistering and detachment in narrow-edge blister packaging. It also enables standardized control of pulp quality, significantly reducing batch-to-batch variations in blistering effects, adapting to the needs of large-scale production. Simultaneously, it can significantly improve the bonding strength of the narrow-edge blister area, making blister cards suitable for high-end precision packaging scenarios. Furthermore, it can optimize paper surface properties, reduce printing lint and powdering, and improve printability.

[0008] The technical solution adopted in this invention is as follows: The process for improving the blister card's blister adhesion includes the following steps: S1. Pulping: White water produced by the forming section of the paper machine is used as pulping water; S2. Pulping: The softwood pulp and hardwood pulp are enzymatically treated with a combination of cellulase and laccase, respectively, and then mixed to obtain a composite modified pulp. Light magnesium oxide is then added to the composite modified pulp, the concentration is adjusted, and then the pulp is sent to a disc mill for pulping. S3. Slurry preparation: Prepare the surface layer slurry, bottom layer slurry and core layer slurry separately; S4. Dilution: The surface slurry, bottom slurry, and core slurry are diluted separately and then transported by three-layer slurry pumps to a pressure screen for purification. Dry powder additives are added to all three slurry pumps, and core layer additives are added to the slurry pump corresponding to the core layer slurry. The core layer additives include AKD, GCC 60, silica sol, hydroxymethylurea-modified cationic polysaccharide, and cationic starch-PAE composite dry strength agent. The hydroxymethylurea-modified cationic polysaccharide is obtained by grafting cationic starch with hydroxymethylurea. The cationic starch-PAE composite dry strength agent is obtained by chemically reacting cationic starch with polyamide epichlorohydrin resin. S5. Forming the web: The purified surface slurry, bottom slurry and core slurry are respectively transported to the three-layer headbox for slurry distribution. The slurry flows of each layer are sprayed onto the surface of the forming wire from the lip of the headbox in sequence, and the layers are compounded to form a wet paper web. S6. Pressing: The wet paper web is fed into the press section and dewatered by passing through a first boot press and a second boot press in sequence. Then, it passes through a third gloss press to remove wire marks and felt marks. S7. Pre-drying: After the wet paper web is dewatered by pressing, it enters the pre-drying section and is pre-dried using a gradient temperature increase method. S8. Surface sizing: Apply surface sizing to the pre-dried paper web; S9. Post-drying: Post-drying is performed on the paper web after surface sizing to allow the surface sizing solution to mature. S10, Hard Calendering: Hard calendering is performed on the paper web after it has been dried. S11. Coating: Coating the front and back sides of the hardened calendered paper web; S12, Soft calendering: The front and back sides of the coated paper web are calendered separately to obtain the finished blister card.

[0009] In step S1, the pulp concentration is 5%.

[0010] In step S2, the softwood pulp is Yinxing brand bleached sulfate softwood pulp, and the hardwood pulp is Chilean Star brand bleached sulfate hardwood pulp. During the enzyme treatment, the softwood pulp is treated with a compound enzyme for 20-30 minutes, with the compound enzyme added at 0.08-0.12 wt.% of the softwood pulp, at a hydrolysis temperature of 55-60℃, and the pH is controlled at 4.8-5.2 using an acetate buffer solution. The hardwood pulp is treated with a compound enzyme for 15-20 minutes, with the compound enzyme added at 0.05-0.08 wt.% of the hardwood pulp, at a hydrolysis temperature of 50-55℃, and the pH is 5.0-5.4. Enzyme-treated softwood pulp and hardwood pulp were mixed at a mass ratio of (28-32):(68-72) to obtain a composite modified pulp. Light magnesium oxide was added to the composite modified pulp at a mass ratio of 1.5-2.5 wt.% to adjust the concentration to 3.0-3.5% before being fed into a disc mill for pulping. The pulping energy consumption was controlled to be ≥90 kWh / t, the disc gap was 0.12-0.16 mm, the pulping current was 300-340 A, the pulping reflux ratio was 10-15%, and the freeness of the pulp after pulping was 34-38°SR, with a wet weight of 6.3-6.7 g.

[0011] In step S3, the surface layer quantitative amount is 35g / m³. 2 The bottom layer quantitative amount is 37g / m 2 The surface pulp consists of 70-75% bleached sulfate hardwood pulp and 25-30% bleached sulfate softwood pulp; the bottom pulp consists of 70-75% bleached sulfate hardwood pulp and 25-30% bleached sulfate softwood pulp; the core pulp consists of 57-65% bleached chemithermomechanical pulp and 35-43% waste pulp; the waste pulp is the pulp obtained after the unqualified paper produced during the production process is pulped by a pulper; the bleached chemithermomechanical pulp is prepared from poplar and pine wood as raw materials, and is obtained by sequentially pre-impregnating with NaOH, primary refining, bleaching, secondary refining and concentration. Preferably, the method for preparing the bleached chemithermomechanical pulp includes the following steps: Using 90 wt.% poplar and 10 wt.% pine as raw materials, the raw wood chips were fed at a mass ratio of 1.1:1 to the pulp. After washing, the raw wood chips were pre-impregnated with NaOH at a mass ratio of 2.5-3.5 wt.% of the raw wood chips. Following pre-impregnation, the pulp underwent primary refining, bleaching, secondary refining, and concentration to obtain a bleached chemithermomechanical pulp. During the bleaching stage, a mixture of NaOH, H₂O₂, chelating agent CH-1636 (purchased from Guangdong Liangshi Industrial Materials Co., Ltd.), and stabilizer WT-3066 (purchased from Guangdong Liangshi Industrial Materials Co., Ltd.) at a mass ratio of 1.5:3:0.2:1 was added at a mass ratio of 4.5-5.5 wt.% of the pulp. The resulting bleached chemithermomechanical pulp had a brightness of 74-78% and a bulk of 2.45-2.65 cm. 3 / g, tensile index is 21-24N m / g, and the process methods used are all conventional methods in this field; In step S4, the concentration of the diluted back layer slurry and the bottom layer slurry is 0.25-0.35%, and the concentration of the core layer slurry is 0.8-1.2%; the amount of dry powder additive (purchased from Yingde Askemo Chemical Co., Ltd.) added is 200-500 ppm of the total amount of each layer slurry.

[0012] The dosage of AKD in the core layer additives is 4.5-7 kg / t slurry, the dosage of GCC 60 is 20-60 kg / t slurry, the dosage of silica sol is 2-7 kg / t slurry, the dosage of hydroxymethyl urea modified cationic polysaccharide is 4-8 kg / t slurry, and the dosage of cationic starch-PAE composite dry strength agent is 6-9 kg / t slurry.

[0013] The preparation method of the hydroxymethylurea-modified cationic polysaccharide includes: adding cationic starch to deionized water to prepare a polysaccharide suspension, heating to 60-65℃, stirring until completely gelatinized, adjusting the pH of the system to 4.8-5.2 with 0.1mol / L hydrochloric acid solution, then adding ammonium chloride and hydroxymethylurea, heating to 75-80℃, and stirring at a constant temperature for 40-60 min, maintaining the pH of the system at 4.8-5.2 with 0.1mol / L hydrochloric acid solution during the reaction, adjusting the pH of the system to 6.8-7.2 with 0.1mol / L sodium hydroxide solution after the reaction, and drying for later use. The concentration of the polysaccharide suspension is 8-12 wt.%; the amount of ammonium chloride added is 0.05-0.1 wt.% of the total amount of the polysaccharide suspension; and the mass ratio of the polysaccharide suspension to hydroxymethylurea is (4-6):1.

[0014] The preparation method of the cationic starch-PAE composite dry strength agent includes: mixing cationic starch and PAE at a mass ratio of (3-5):1, adding them to water to prepare a mixed solution with a concentration of 10-15 wt.%, stirring and reacting at 70-75℃ for 30-40 min, and then cooling to obtain the final product.

[0015] In the GCC 60, the content of particles with a diameter ≤2μm accounts for 59-61%. The preparation method is as follows: calcium carbonate ore is crushed into coarse particles with a diameter of less than 5cm, and then transferred to a ball mill for pre-grinding to obtain an intermediate product with a diameter of less than 500μm. Then, a dispersant is added and zirconium beads are wet-ground. After wet grinding, the ground product is dried to obtain a product with the target particle size. The dispersant is ZH-671 (purchased from Changshu Juhe Chemical Co., Ltd.), and the amount of dispersant added is 0.2-0.3% of the dry basis mass of the intermediate product.

[0016] In step S5, the core layer is first laminated with the surface layer. Before lamination, tapioca starch (purchased from Thailand's ETC Group) is sprayed onto the bonding surface of the surface layer, and then laminated with the bottom layer.

[0017] In step S6, the dryness of the base paper after pressing is 45-48%.

[0018] In step S7, the gradient heating method specifically involves controlling the drying temperature in three segments: 100℃, 110℃, and 105℃, corresponding to drying completion rates of 30%, 70%, and 100%, respectively. In step S9, the post-drying temperature is 100-120℃ to ensure that the adhesive can be fully cured, increase the surface strength of the paper, and reduce lint and powder shedding during the printing process.

[0019] In step S8, a mixture of cassava starch and AKD is used as the sizing agent, with AKD accounting for 0.9-1.3 wt.% of the cassava starch. The prepared sizing agent has a viscosity of 200-220 cps and a solid content of 27-29%. The machine temperature is 72-78℃, the machine viscosity is 30-40 cps, the machine solid content is 10-14%, and the application rate on the front side is 0.8-1.2 g / m². 2 The amount of adhesive applied on the reverse side is 3-4 g / m². 2 .

[0020] In step S10, the hard calendering temperature is 110-130℃ and the pressure is 5-20kN / m. The paper surface is modified by high temperature and high pressure to reduce the roughness of the base paper. In step S12, the front soft calendering temperature is 110-130℃ and the pressure is 15-25kN / m. The coated surface is finished to improve gloss and smoothness and reduce roughness. The back soft calendering temperature is ≤55℃ and the pressure is 0kN / m. The coated surface is finished to improve gloss and smoothness and reduce roughness. Using soft calendering on both the front and back can reduce the difference between the two sides.

[0021] In step S11, a hard doctor blade is used for front-side coating, and the coating amount is 24.5-26.5 g / m². 2 For back-side coating, use a soft scraper with a coating amount of 21-23 g / m². 2 .

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention fixes the types of softwood pulp and hardwood pulp, uses a specially formulated cellulase-laccase composite enzyme for differentiated enzymatic modification, and optimizes the pulping parameters. While ensuring a pulp freeness of 34-38°SR and a wet weight of 6.3-6.7g to improve paper strength, it avoids excessive fiber fragmentation and overly dense hydrogen bonding. At the same time, by reasonably controlling the amount of reinforcing agent, the paper structure density is reduced, providing sufficient channels for blister oil penetration, effectively solving the problems of weak blister forming and shell detachment in narrow-edge blister processing, and achieving synergistic optimization of strength and blister forming firmness. (2) This invention clearly defines the categories of softwood pulp and hardwood pulp, and achieves standardized control of pulp quality through composite enzymatic modification and other technical means; at the same time, it optimizes the pulp preparation scheme and chemical formulation, eliminating the influence of anionic waste on pulp performance. The above improvements effectively avoid the problem of unstable paper strength caused by raw material fluctuations, greatly reduce the batch-to-batch differences in thermoforming effect, and fully adapt to the needs of large-scale production; (3) This invention specifically optimizes the paper structure, surface sizing process, and calendering and coating parameters. By controlling the temperature curves of the three stages of pre-drying, the sizing agent is uniformly cured to form a dense hydrophobic layer. Combined with differentiated soft calendering treatment, the difference between the two sides of the paper and its roughness are reduced, significantly improving the blister bonding force in the narrow edge blister area. This improvement enables blister cards to be successfully adapted to high-end precision packaging scenarios, breaking the limitations of existing processes on application scenarios and enhancing the market competitiveness of the product. (4) This invention does not require modification of existing paper machine hardware. It can be achieved simply by optimizing the process, adjusting the raw material ratio and chemical formula. The modification investment is small and the production cost is controllable. At the same time, the process flow is clear, the parameters are well-defined, and the operation is simple, making it easy for enterprises to implement quickly and with significant industrial application value. (5) By optimizing the pulp modification process and surface treatment technology, this invention improves the blister fastness while ensuring the surface strength and smoothness of the paper, reduces the shedding and powdering during the printing process, and improves the printability. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments, but these embodiments do not limit the implementation of the present invention.

[0024] Unless otherwise specified, the raw materials used in the examples and comparative examples are all commercially available materials, and the process methods used in the examples and comparative examples are all conventional methods in the art.

[0025] The following is a description of some of the raw materials used in the examples and comparative examples: Silver Star brand bleached sulfate softwood pulp, purchased from ARAUCO, Chile.

[0026] Chilean Star brand bleached sulfate hardwood pulp, purchased from ARAUCO, Chile.

[0027] The method for preparing the bleached chemithermomechanical pulp includes the following steps: Using 90 wt.% poplar and 10 wt.% pine as raw materials, the raw wood chips were fed at a mass ratio of 1.1:1 to pulp. After washing, the raw wood chips were pre-impregnated with NaOH at a mass ratio of 3 wt.% of the raw wood chips. Following pre-impregnation, the pulp underwent primary refining, bleaching, secondary refining, and concentration to obtain a bleached chemithermomechanical pulp. During the bleaching stage, a mixture of NaOH, H₂O₂, chelating agent CH-1636 (purchased from Guangdong Liangshi Industrial Materials Co., Ltd.), and stabilizer WT-3066 (purchased from Guangdong Liangshi Industrial Materials Co., Ltd.) at a mass ratio of 1.5:3:0.2:1 was added at a mass ratio of 5 wt.% of the pulp. The resulting bleached chemithermomechanical pulp had a brightness of 76% and a bulk of 2.55 ± 0.1 cm. 3 / g, with a tensile index of 22.0±1.0 N·m / g, and the process methods used are all conventional methods in this field.

[0028] The aforementioned waste pulp refers to the pulp obtained after the unqualified finished paper produced during the production process is broken down by a pulper.

[0029] In the GCC 60, the content of particles with a diameter ≤2μm is 60±1%. The preparation method is as follows: calcium carbonate ore is crushed into coarse particles with a diameter of less than 5cm, and then transferred to a ball mill for pre-grinding to obtain an intermediate product with a diameter of less than 500μm. Then, a dispersant is added and zirconium beads are wet-ground. After wet grinding, the ground product is dried to obtain a product with the target particle size. The dispersant is ZH-671 (purchased from Changshu Juhe Chemical Co., Ltd.), and the amount of dispersant added is 0.25% of the dry basis mass of the intermediate product.

[0030] The preparation method of the hydroxymethylurea-modified cationic polysaccharide includes: adding cationic starch to deionized water to prepare a polysaccharide suspension, heating to 65°C, stirring until completely gelatinized, adjusting the pH of the system to 5.0 with 0.1 mol / L hydrochloric acid solution, then adding ammonium chloride and hydroxymethylurea, heating to 78°C, and stirring at a constant temperature for 50 min, maintaining the pH of the system at 5.0 with 0.1 mol / L hydrochloric acid solution during the reaction, adjusting the pH of the system to 7.0 with 0.1 mol / L sodium hydroxide solution after the reaction, and drying for later use. The concentration of the polysaccharide suspension is 10 wt.%; the amount of ammonium chloride added is 0.07 wt.% of the total amount of the polysaccharide suspension; and the mass ratio of the polysaccharide suspension to hydroxymethylurea is 5:1.

[0031] The preparation method of the cationic starch-PAE composite dry strength agent includes: mixing cationic starch and PAE at a mass ratio of 3:1, adding them to water to prepare a mixed solution with a concentration of 12wt.%, stirring and reacting at 75℃ for 35min, and then cooling to obtain the final product.

[0032] Example 1 The process for improving the blister card's blister adhesion includes the following steps: S1. Pulping: White water produced by the forming section of the paper machine is used as pulping water, and the pulp concentration is 5%; S2. Pulping: A composite enzyme of cellulase and laccase at a mass ratio of 1:2 was used to enzymatically treat Yinxing brand bleached sulfate softwood pulp and Chilean Mingxing brand bleached sulfate hardwood pulp, respectively. The enzymatic treatment process was as follows: Yinxing brand bleached sulfate softwood pulp was treated with the composite enzyme for 25 minutes, with the amount of composite enzyme added being 0.10 wt.% of the softwood pulp, the enzymatic hydrolysis temperature being 58℃, and the pH value being controlled at 5.0 using acetate buffer; hardwood pulp was treated with the composite enzyme for 18 minutes, with the amount of composite enzyme added being 0.065 wt.% of the hardwood pulp, and the enzymatic hydrolysis temperature being 58℃. The temperature was 53℃ and the pH was 5.0. Enzyme-treated softwood pulp and hardwood pulp were mixed at a mass ratio of 30:70 to obtain a composite modified pulp. Light magnesium oxide was then added to the composite modified pulp at a concentration of 2.0 wt.% of the composite modified pulp. After adjusting the concentration to 3.2%, the pulp was sent to a disc mill for grinding. The grinding energy consumption was controlled at 92 kWh / t, the disc gap was 0.14 mm, the grinding current was 320 A, the grinding reflux ratio was 12%, and the freeness of the pulp after grinding was 36°SR and the wet weight was 6.5 g. S3. Slurry Preparation: Prepare the surface layer slurry, bottom layer slurry, and core layer slurry separately, with the surface layer having a basis weight of 35 g / m³. 2 The bottom layer quantitative amount is 37g / m 2 The core layer quantification was 251 g / m³. 2 The surface pulp consists of 70% bleached sulfate hardwood pulp and 30% bleached sulfate softwood pulp; the bottom pulp consists of 70% bleached sulfate hardwood pulp and 30% bleached sulfate softwood pulp; the core pulp consists of 62% bleached chemithermomechanical pulp and 38% waste pulp. S4. Dilution: The top layer slurry, bottom layer slurry, and core layer slurry are diluted separately. After dilution, the concentration of the top layer slurry and bottom layer slurry is 0.30%, and the concentration of the core layer slurry is 1.0%. The diluted slurry is transported by the three-layer slurry pumps and then enters the pressure screen for purification. Dry powder additives are added to each of the three slurry pumps at a rate of 350 ppm of the total amount of each layer slurry. At the same time, core layer additives are added to the slurry pump corresponding to the core layer slurry. The core layer additives include AKD at a rate of 6 kg / t slurry, GCC 60 at a rate of 40 kg / t slurry, silica sol at a rate of 6 kg / t slurry, hydroxymethylurea-modified cationic polysaccharide at a rate of 6 kg / t slurry, and cationic starch-PAE composite dry strength agent at a rate of 8 kg / t slurry. S5. Web forming: The purified surface slurry, bottom slurry and core slurry are respectively transported to the three-layer headbox for slurry distribution. Each layer of slurry is sprayed onto the surface of the forming wire from the lip of the headbox, and the layers are laminated to form a wet paper web. The core layer is laminated with the surface layer first. Before lamination, cassava starch is sprayed onto the bonding surface of the surface layer, and then laminated with the bottom layer. S6. Pressing: The wet paper web is fed into the press section and dewatered by passing through a first shoe press and a second shoe press. Then, it passes through a third gloss press to remove wire marks and felt marks. The dryness of the base paper after pressing is 47%. S7. Pre-drying: After the wet paper web is dewatered by pressing, it enters the pre-drying section, where a gradient temperature increase method is adopted for pre-drying. Specifically, the drying temperature is controlled in three stages: 100℃, 110℃ and 105℃, corresponding to drying completion rates of 30%, 70% and 100% respectively. S8. Surface Sizing: Surface sizing is performed on the pre-dried paper web using a mixture of tapioca starch and AKD as the sizing solution. The amount of AKD used is 1.1 wt.% of the tapioca starch. The prepared viscosity of the sizing solution is 210 cps, the prepared solid content is 28%, the machine temperature is 76℃, the machine viscosity is 35 cps, the machine solid content is 12%, and the sizing amount on the front side is 1.0 g / m². 2 The amount of adhesive applied on the reverse side is 3.5 g / m². 2 ; S9. Post-drying: The paper web after surface sizing is post-dried at a temperature of 110℃. S10, Hard Calendering: Hard calendering is performed on the paper web after drying. The hard calendering temperature is 120℃ and the pressure is 15kN / m. S11. Coating: Apply front and back coatings to the hard-calendered paper web. Front coating uses a hard doctor blade, with a coating amount of 25.5 g / m². 2 The back coating was applied using a soft scraper, with a coating amount of 22 g / m². 2 ; S12, Soft calendering: The front and back sides of the coated paper web are subjected to soft calendering treatment respectively. The temperature of the front soft calendering is 120℃ and the pressure is 20kN / m, while the temperature of the back soft calendering is ≤55℃ and the pressure is 0kN / m. After treatment, the finished blister card is obtained.

[0033] Example 2 The process for improving the blister card's blister adhesion includes the following steps: S1. Pulping: White water produced by the forming section of the paper machine is used as pulping water, and the pulp concentration is 5%; S2. Pulping: A composite enzyme of cellulase and laccase at a mass ratio of 1:2 was used to enzymatically treat Yinxing brand bleached sulfate softwood pulp and Chilean Mingxing brand bleached sulfate hardwood pulp, respectively. The enzymatic treatment process was as follows: Yinxing brand bleached sulfate softwood pulp was treated with the composite enzyme for 25 minutes, with the amount of composite enzyme added being 0.10 wt.% of the softwood pulp, the enzymatic hydrolysis temperature being 60℃, and the pH value being controlled at 5.2 using acetate buffer; hardwood pulp was treated with the composite enzyme for 20 minutes, with the amount of composite enzyme added being 0.065 wt.% of the hardwood pulp, and the enzymatic hydrolysis temperature being 60℃. The temperature was 55℃ and the pH value was 5.4. Enzyme-treated softwood pulp and hardwood pulp were mixed at a mass ratio of 30:70 to obtain a composite modified pulp. Light magnesium oxide was then added to the composite modified pulp at a concentration of 2.0 wt.% of the composite modified pulp. After adjusting the concentration to 3.2%, the pulp was sent to a disc mill for grinding. The grinding energy consumption was controlled at 92 kWh / t, the disc gap was 0.14 mm, the grinding current was 320 A, the grinding reflux ratio was 12%, and the freeness of the pulp after grinding was 36°SR and the wet weight was 6.5 g. S3. Slurry Preparation: Prepare the surface layer slurry, bottom layer slurry, and core layer slurry separately, with the surface layer having a basis weight of 35 g / m³. 2 The bottom layer quantitative amount is 37g / m 2 The core layer quantification was 249 g / m³. 2 The surface pulp consists of 70% bleached sulfate hardwood pulp and 30% bleached sulfate softwood pulp; the bottom pulp consists of 70% bleached sulfate hardwood pulp and 30% bleached sulfate softwood pulp; the core pulp consists of 62% bleached chemithermomechanical pulp and 38% waste pulp. S4. Dilution: The top layer slurry, bottom layer slurry, and core layer slurry are diluted separately. After dilution, the concentration of the top layer slurry and bottom layer slurry is 0.30%, and the concentration of the core layer slurry is 1.0%. The diluted slurry is transported by the three-layer slurry pumps and then enters the pressure screen for purification. Dry powder additives are added to each of the three slurry pumps at a rate of 350 ppm of the total amount of each layer slurry. At the same time, core layer additives are added to the slurry pump corresponding to the core layer slurry. The core layer additives include AKD at a rate of 6 kg / t slurry, GCC 60 at a rate of 40 kg / t slurry, silica sol at a rate of 6 kg / t slurry, hydroxymethylurea-modified cationic polysaccharide at a rate of 6 kg / t slurry, and cationic starch-PAE composite dry strength agent at a rate of 8 kg / t slurry. S5. Web forming: The purified surface slurry, bottom slurry and core slurry are respectively transported to the three-layer headbox for slurry distribution. Each layer of slurry is sprayed onto the surface of the forming wire from the lip of the headbox, and the layers are laminated to form a wet paper web. The core layer is laminated with the surface layer first. Before lamination, cassava starch is sprayed onto the bonding surface of the surface layer, and then laminated with the bottom layer. S6. Pressing: The wet paper web is fed into the press section and dewatered by passing through a first shoe press and a second shoe press. Then, it passes through a third gloss press to remove wire marks and felt marks. The dryness of the base paper after pressing is 48%. S7. Pre-drying: After the wet paper web is dewatered by pressing, it enters the pre-drying section, where a gradient temperature increase method is adopted for pre-drying. Specifically, the drying temperature is controlled in three stages: 100℃, 110℃ and 105℃, corresponding to drying completion rates of 30%, 70% and 100% respectively. S8. Surface Sizing: Surface sizing is performed on the pre-dried paper web using a mixture of cassava starch and AKD as the sizing solution. The amount of AKD used is 1.2 wt.% of the cassava starch. The prepared viscosity of the sizing solution is 220 cps, the prepared solid content is 29%, the machine temperature is 78℃, the machine viscosity is 40 cps, the machine solid content is 14%, and the sizing amount on the front side is 1.2 g / m². 2 The amount of adhesive applied on the reverse side is 4g / m². 2 ; S9. Post-drying: The paper web after surface sizing is post-dried at a temperature of 120℃. S10, Hard Calendering: Hard calendering is performed on the paper web after drying. The hard calendering temperature is 130℃ and the pressure is 20kN / m. S11. Coating: Apply front and back coatings to the hard-calendered paper web. The front coating uses a hard doctor blade, and the coating amount is 26.5 g / m². 2 The back coating was applied using a soft scraper, with a coating amount of 23 g / m². 2 ; S12, Soft calendering: The front and back sides of the coated paper web are subjected to soft calendering treatment respectively. The temperature of the front soft calendering is 130℃ and the pressure is 25kN / m, while the temperature of the back soft calendering is ≤55℃ and the pressure is 0kN / m. After treatment, the finished blister card is obtained.

[0034] Example 3 The process for improving the blister card's blister adhesion includes the following steps: S1. Pulping: White water produced by the forming section of the paper machine is used as pulping water, and the pulp concentration is 5%; S2. Pulping: A composite enzyme of cellulase and laccase at a mass ratio of 1:2 was used to enzymatically treat Yinxing brand bleached sulfate softwood pulp and Chilean Mingxing brand bleached sulfate hardwood pulp, respectively. The enzymatic treatment process was as follows: Yinxing brand bleached sulfate softwood pulp was treated with the composite enzyme for 25 minutes, with the amount of composite enzyme added being 0.10 wt.% of the softwood pulp, the enzymatic hydrolysis temperature being 60℃, and the pH value being controlled at 5.2 using acetate buffer; hardwood pulp was treated with the composite enzyme for 20 minutes, with the amount of composite enzyme added being 0.065 wt.% of the hardwood pulp, and the enzymatic hydrolysis temperature being 60℃. The temperature was 55℃ and the pH value was 5.4. Enzyme-treated softwood pulp and hardwood pulp were mixed at a mass ratio of 30:70 to obtain a composite modified pulp. Light magnesium oxide was then added to the composite modified pulp at a concentration of 1.5 wt.% of the composite modified pulp. After adjusting the concentration to 3.5%, the pulp was sent to a disc mill for grinding. The grinding energy consumption was controlled at 92 kWh / t, the disc gap was 0.16 mm, the grinding current was 340 A, the grinding reflux ratio was 15%, and the freeness of the pulp after grinding was 38°SR and the wet weight was 6.7 g. S3. Slurry Preparation: Prepare the surface layer slurry, bottom layer slurry, and core layer slurry separately, with the surface layer having a basis weight of 35 g / m³. 2 The bottom layer quantitative amount is 37g / m 2 The core layer quantitative density is 250 g / m³. 2 The surface pulp consists of 70% bleached sulfate hardwood pulp and 30% bleached sulfate softwood pulp; the bottom pulp consists of 70% bleached sulfate hardwood pulp and 30% bleached sulfate softwood pulp; the core pulp consists of 62% bleached chemithermomechanical pulp and 38% waste pulp. S4. Dilution: The top layer slurry, bottom layer slurry, and core layer slurry are diluted separately. After dilution, the concentration of the top layer slurry and bottom layer slurry is 0.30%, and the concentration of the core layer slurry is 1.0%. The diluted slurry is transported by the three-layer slurry pumps and then enters the pressure screen for purification. Dry powder additives are added to each of the three slurry pumps at a rate of 350 ppm of the total amount of each layer slurry. At the same time, core layer additives are added to the slurry pump corresponding to the core layer slurry. The core layer additives include AKD at a rate of 6 kg / t slurry, GCC 60 at a rate of 40 kg / t slurry, silica sol at a rate of 6 kg / t slurry, hydroxymethylurea-modified cationic polysaccharide at a rate of 6 kg / t slurry, and cationic starch-PAE composite dry strength agent at a rate of 8 kg / t slurry. S5. Web forming: The purified surface slurry, bottom slurry and core slurry are respectively transported to the three-layer headbox for slurry distribution. Each layer of slurry is sprayed onto the surface of the forming wire from the lip of the headbox, and the layers are laminated to form a wet paper web. The core layer is laminated with the surface layer first. Before lamination, cassava starch is sprayed onto the bonding surface of the surface layer, and then laminated with the bottom layer. S6. Pressing: The wet paper web is fed into the press section and dewatered by passing through a first shoe press and a second shoe press. Then, it passes through a third gloss press to remove wire marks and felt marks. The dryness of the base paper after pressing is 48%. S7. Pre-drying: After the wet paper web is dewatered by pressing, it enters the pre-drying section, where a gradient temperature increase method is adopted for pre-drying. Specifically, the drying temperature is controlled in three stages: 100℃, 110℃ and 105℃, corresponding to drying completion rates of 30%, 70% and 100% respectively. S8. Surface Sizing: Surface sizing is performed on the pre-dried paper web using a mixture of cassava starch and AKD as the sizing solution. The amount of AKD used is 0.9 wt.% of the cassava starch. The prepared viscosity of the sizing solution is 200 cps, the prepared solid content is 27%, the machine temperature is 72℃, the machine viscosity is 30 cps, the machine solid content is 10%, and the sizing amount on the front side is 0.8 g / m². 2 The amount of adhesive applied on the reverse side is 3g / m². 2 ; S9. Post-drying: The paper web after surface sizing is post-dried at a temperature of 100℃. S10, Hard Calendering: Hard calendering is performed on the paper web after drying. The hard calendering temperature is 110℃ and the pressure is 5kN / m. S11. Coating: Apply front and back coatings to the hard-calendered paper web. The front coating uses a hard doctor blade, and the coating amount is 24.5 g / m². 2 The back coating was applied using a soft scraper, with a coating amount of 21 g / m². 2 ; S12, Soft calendering: The front and back sides of the coated paper web are subjected to soft calendering treatment respectively. The temperature of the front soft calendering is 110℃ and the pressure is 15kN / m, while the temperature of the back soft calendering is ≤55℃ and the pressure is 0kN / m. After treatment, the finished blister card is obtained.

[0035] Comparative Example 1 The difference from Example 1 is that the amount of hydroxymethylurea-modified cationic polysaccharide in the core layer additive is 2 kg / t slurry, and other conditions are the same as in Example 1.

[0036] Comparative Example 2 The difference from Example 1 is that the core layer additive does not use hydroxymethylurea-modified cationic polysaccharide, but instead uses an equal amount of cationic starch, while other conditions are the same as in Example 1.

[0037] The performance of the blister cards prepared in the examples and comparative examples was tested respectively, and the test methods are as follows: Paper basis weight (g / m 2 (The test shall be conducted in accordance with GB / T 451.2-2023;) Thickness (μm): Tested according to GB / T 451.3-2002; Moisture content (%): Tested according to GB / T 462-2023; Surface roughness (μm): Tested according to GB / T 22363-2008; Flexural endurance (cycles): Tested according to GB / T 2679.5-1995; Interlayer bond strength (J / m) 2 (The test shall be conducted in accordance with GB / T 26203-2023;) Gloss (%): Tested according to GB / T 8941-2007; Whiteness (%): Tested according to GB / T 7974-2013; Printed surface strength (m / s): Tested according to GB / T 22365-2008; Ash content of finished paper (%): Tested according to GB / T 742-2018; The test results are shown in Table 1.

[0038] Table 1 Performance Test Results

[0039] As can be seen from the test data in Table 1, the blister cards prepared in Examples 1-3 exhibit excellent and stable performance across all indicators. In particular, the interlayer bonding strength, folding endurance, and printing surface strength remain at high levels, while the surface roughness is maintained at a low level. This indicates that the process described in this invention (including specific pulp modification, core layer additive formulation, and calendering coating process) can effectively synergistically improve the internal bonding strength and surface quality of the paper, solving the problem of insufficient blister adhesion for narrow edges.

[0040] In Comparative Example 1, reducing the amount of hydroxymethylurea-modified cationic polysaccharide to 2 kg / t pulp resulted in a decrease in paper strength (interlayer bonding strength, folding endurance, and printing surface strength), which in turn led to a corresponding decrease in blister fastness. This indicates that when the amount of hydroxymethylurea-modified cationic polysaccharide is insufficient, it cannot adequately promote the bonding between fibers, thereby weakening the internal structure and surface strength of the paper.

[0041] In Comparative Example 2, the use of an equal amount of cationic starch to replace the hydroxymethylurea-modified cationic polysaccharide resulted in a decrease in paper strength (interlayer bond strength, folding endurance, and printing surface strength), and a corresponding decrease in blister packing strength. This indicates that the hydroxymethylurea-modified cationic polysaccharide has a unique reinforcing effect compared to ordinary cationic starch, possibly because the grafted hydroxymethylurea groups can provide more active sites, thereby enhancing the cross-linking effect with fibers and auxiliaries such as AKD.

Claims

1. A process for improving the blister card forming strength, characterized in that, Includes the following steps: S1. Pulping: White water produced by the forming section of the paper machine is used as pulping water; S2. Pulping: The softwood pulp and hardwood pulp are enzymatically treated with a combination of cellulase and laccase, respectively, and then mixed to obtain a composite modified pulp. Light magnesium oxide is then added to the composite modified pulp, the concentration is adjusted, and then the pulp is sent to a disc mill for pulping. S3. Slurry preparation: Prepare the surface layer slurry, bottom layer slurry and core layer slurry separately; S4. Dilution: The surface slurry, bottom slurry, and core slurry are diluted separately and then transported by three-layer slurry pumps to a pressure screen for purification. Dry powder additives are added to all three slurry pumps, and core layer additives are added to the slurry pump corresponding to the core layer slurry. The core layer additives include AKD, GCC 60, silica sol, hydroxymethylurea-modified cationic polysaccharide, and cationic starch-PAE composite dry strength agent. The hydroxymethylurea-modified cationic polysaccharide is obtained by grafting cationic starch with hydroxymethylurea. The cationic starch-PAE composite dry strength agent is obtained by chemically reacting cationic starch with polyamide epichlorohydrin resin. S5. Forming the web: The purified surface slurry, bottom slurry and core slurry are respectively transported to the three-layer headbox for slurry distribution. The slurry flows of each layer are sprayed onto the surface of the forming wire from the lip of the headbox in sequence, and the layers are compounded to form a wet paper web. S6. Pressing: The wet paper web is fed into the press section and dewatered by passing through a first boot press and a second boot press in sequence. Then, it passes through a third gloss press to remove wire marks and felt marks. S7. Pre-drying: After the wet paper web is dewatered by pressing, it enters the pre-drying section and is pre-dried using a gradient temperature increase method. S8. Surface sizing: Apply surface sizing to the pre-dried paper web; S9. Post-drying: Post-drying is performed on the paper web after surface sizing to allow the surface sizing solution to mature. S10, Hard Calendering: Hard calendering is performed on the paper web after it has been dried. S11. Coating: Coating the front and back sides of the hardened calendered paper web; S12, Soft calendering: The front and back sides of the coated paper web are calendered separately to obtain the finished blister card.

2. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S1, the pulp concentration is 5%; In step S2, the softwood pulp is Silver Star brand bleached sulfate softwood pulp, and the hardwood pulp is Chile Star brand bleached sulfate hardwood pulp. During the enzyme treatment, the softwood pulp is treated with a compound enzyme for 20-30 minutes, with the compound enzyme added at 0.08-0.12 wt.% of the softwood pulp, at a hydrolysis temperature of 55-60℃, and a pH of 4.8-5.

2. The hardwood pulp is treated with a compound enzyme for 15-20 minutes, with the compound enzyme added at 0.05-0.08 wt.% of the hardwood pulp, at a hydrolysis temperature of 50-55℃, and a pH of 5.0-5.

4. The softwood pulp and hardwood pulp were mixed at a mass ratio of (28-32):(68-72) to obtain a composite modified pulp. Light magnesium oxide was added to the composite modified pulp at a mass ratio of 1.5-2.5 wt.% and the concentration was adjusted to 3.0-3.5%. The pulp was then fed into a disc mill for grinding. The grinding energy consumption was controlled to be ≥90 kWh / t, the disc gap was 0.12-0.16 mm, the grinding current was 300-340 A, the grinding reflux ratio was 10-15%, and the freeness of the pulp after grinding was 34-38°SR and the wet weight was 6.3-6.7 g.

3. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S3, the surface pulp consists of 70-75% bleached sulfate hardwood pulp and 25-30% bleached sulfate softwood pulp; the bottom pulp consists of 70-75% bleached sulfate hardwood pulp and 25-30% bleached sulfate softwood pulp; the core pulp consists of 57-65% bleached chemithermomechanical pulp and 35-43% waste pulp; the waste pulp is the pulp obtained after the unqualified paper produced in the production process is pulped by a pulper; the bleached chemithermomechanical pulp is prepared from poplar and pine wood as raw materials, and is obtained by NaOH pre-impregnation, primary refining, bleaching, secondary refining and concentration in sequence.

4. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S4, the concentration of the diluted layer slurry and the bottom layer slurry is 0.25-0.35%, and the concentration of the core layer slurry is 0.8-1.2%; the amount of dry powder additive added is 200-500 ppm of the total amount of each layer slurry. The dosage of AKD in the core layer additives is 4.5-7 kg / t slurry, the dosage of GCC 60 is 20-60 kg / t slurry, the dosage of silica sol is 2-7 kg / t slurry, the dosage of hydroxymethyl urea modified cationic polysaccharide is 4-8 kg / t slurry, and the dosage of cationic starch-PAE composite dry strength agent is 6-9 kg / t slurry. The preparation method of the hydroxymethylurea-modified cationic polysaccharide includes: adding cationic starch to deionized water to prepare a polysaccharide suspension, heating to 60-65℃, stirring until completely gelatinized, adjusting the pH of the system to 4.8-5.2 with hydrochloric acid solution, then adding ammonium chloride and hydroxymethylurea, heating to 75-80℃, stirring at a constant temperature for 40-60 minutes, maintaining the pH of the system at 4.8-5.2 with hydrochloric acid solution during the reaction, adjusting the pH of the system to 6.8-7.2 with sodium hydroxide solution after the reaction, and drying for later use; wherein, the concentration of the polysaccharide suspension is 8-12 wt.%; the amount of ammonium chloride added is 0.05-0.1 wt.% of the total amount of the polysaccharide suspension; the mass ratio of the polysaccharide suspension to hydroxymethylurea is (4-6):1; The preparation method of the cationic starch-PAE composite dry strength agent includes: mixing cationic starch and PAE at a mass ratio of (3-5):1, adding them to water to prepare a mixed solution with a concentration of 10-15 wt.%, stirring and reacting at 70-75℃ for 30-40 min, and then cooling to obtain the final product.

5. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S5, the core layer is first bonded to the surface layer. Before bonding, tapioca starch is sprayed onto the bonding surface of the surface layer, and then it is bonded to the bottom layer.

6. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S6, the dryness of the base paper after pressing is 45-48%.

7. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S7, the gradient heating method specifically involves dividing the drying temperature into three segments: 100℃, 110℃, and 105℃, corresponding to drying completion rates of 30%, 70%, and 100%, respectively. In step S9, the final drying temperature is 100-120℃.

8. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S8, a mixture of cassava starch and AKD is used as the sizing agent, with AKD accounting for 0.9-1.3 wt.% of the cassava starch. The prepared sizing agent has a viscosity of 200-220 cps and a solid content of 27-29%. The machine temperature is 72-78℃, the machine viscosity is 30-40 cps, the machine solid content is 10-14%, and the application rate on the front side is 0.8-1.2 g / m². 2 The amount of adhesive applied on the reverse side is 3-4 g / m². 2 .

9. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S10, the temperature of hard calendering is 110-130℃ and the pressure is 5-20kN / m; in step S12, the temperature of soft calendering on the front side is 110-130℃ and the pressure is 15-25kN / m; the temperature of soft calendering on the back side is ≤55℃ and the pressure is 0kN / m.

10. The process for improving the blister card forming strength according to claim 1, characterized in that, In step S11, a hard doctor blade is used for front-side coating, and the coating amount is 24.5-26.5 g / m². 2 For back-side coating, use a soft scraper with a coating amount of 21-23 g / m². 2 .

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