Preparation method of anti-aging white cardboard

Abstract

The invention belongs to the technical field of white cardboard preparation, and particularly relates to an anti-aging white cardboard preparation method, which is characterized in that the anti-aging white cardboard comprises raw paper and a coating layer covering the surface of the raw paper, the raw paper comprises a surface paper layer, a core paper layer and a bottom paper layer, the coating layer comprises a pre-coating layer, a surface coating layer and a back coating layer, the eucalyptus paper is characterized in that paper pulp of the body paper comprises bleached eucalyptus pulp, coatings of the pre-coating layer, the surface coating layer and the back coating layer comprise pigments, coating layer adhesives and filler, the coating layer adhesives are starch-based adhesives, and the eucalyptus paper has the effects of aging resistance and high strength.

Description

Technical Field

[0001] This invention belongs to the field of white cardboard preparation technology, and specifically relates to a method for preparing aging-resistant white cardboard. Background Technology

[0002] In the packaging and printing industry, white cardboard occupies an important position due to its superior properties. White cardboard is a type of paper made primarily from bleached chemical pulp, fully sizing it, with a basis weight typically above 150g / m². It features high smoothness, good stiffness, a clean appearance, and excellent uniformity, and can be further subdivided into blue-white single- and double-sided coated cardboard, white-backed coated cardboard, and gray-backed coated cardboard, among others. This type of paper is widely used in business cards, menus, certificates, trademarks, and packaging for various high-end products, and is ubiquitous in people's daily lives and business activities.

[0003] However, existing technologies for producing white cardboard have aging problems. Under the combined influence of environmental and time factors, the performance of white cardboard gradually declines. Internally, the main components of paper—cellulose, hemicellulose, and lignin—undergo various chemical reactions under external conditions. Lignin, containing numerous reactive groups, has the worst stability and is prone to oxidation and photolysis. Hemicellulose also undergoes hydrolysis, oxidation, and photolysis. While cellulose has relatively better stability, it still experiences hydrolysis, oxidative degradation, and photolysis. The photo-oxidation reaction of lignin, cellulose, and hemicellulose is the main cause of paper yellowing. Furthermore, harmful substances such as acids, oxidants, and metal ions remaining from the paper production process also accelerate the aging process of white cardboard. Natural starch adhesives have poor bonding performance, poor stability, high viscosity, and poor hydrophobicity, failing to meet the needs of industrial applications. Therefore, natural starch is often modified to improve the overall performance of starch adhesives.

[0004] From an external perspective, environmental factors such as temperature, humidity, light, acids, oxidants, harmful gases, and harmful microorganisms can all cause or accelerate hydrolysis, oxidation, and photolysis reactions in the main components of white cardboard. For example, ultraviolet radiation can cause cellulose in white cardboard to degrade and discolor; free radicals generated by photo-oxidation reactions can rapidly degrade cellulose, causing the paper to yellow and become brittle, reducing its strength; high temperatures can accelerate cellulose degradation, causing the paper to yellow, become brittle, and lose strength and durability; acidic substances can react with cellulose, leading to cellulose degradation and reducing the paper's strength and durability.

[0005] To address the aging problem of white cardboard, the industry has explored various approaches. Some studies have attempted to suppress yellowing by optimizing pulping processes and bleaching methods, but these methods are difficult to implement and costly. Other studies have added yellowing inhibitors to the pulp and coatings, which can suppress yellowing to some extent, but significantly reduce the initial whiteness of the paper and cannot guarantee its stability. Therefore, developing a preparation method that can effectively improve the aging resistance of white cardboard while preserving its original excellent properties, and is also cost-effective, has become a key issue that urgently needs to be addressed in the current white cardboard production field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing aging-resistant white cardboard, which has the effects of aging resistance and high strength.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for preparing aging-resistant white cardboard, characterized in that: it includes base paper and a coating layer covering its surface, wherein the base paper includes a face paper layer, a core paper layer and a back paper layer, and the coating layer includes a pre-coating layer, a top coating layer and a back coating layer, characterized in that: the pulp of the base paper includes bleached eucalyptus pulp, and the coatings of the pre-coating layer, the top coating layer and the back coating layer all include pigments, coating adhesives and fillers, wherein the coating adhesive is a starch-based adhesive.

[0008] The starch-based adhesive is prepared by the following steps:

[0009] S1: Preparation of dialdehyde corn starch: Corn starch, sodium periodate and water in a mass ratio of 6-7:1:15-2 were stirred for 10 min, and then the pH was adjusted to 3 with sulfuric acid solution. The reaction was carried out in a 40℃ water bath in the dark for 4-5 h. After the reaction was completed, the mixture was filtered, washed, dried and ground to obtain dialdehyde corn starch.

[0010] S2: Dissolve dialdehyde corn starch in water, add appropriate amount of anti-agglomeration agent, 35%-55% polyethylene glycol and 55%-65% urea, stir and mix, and stir and react in a water bath at 30-45℃ for 4-5 hours. Then filter, wash, dry and grind to obtain powdered starch-based adhesive.

[0011] S3: Add the powdered starch-based adhesive to water and stir. Then stir in a water bath at 93-96℃ for 0.5-0.8 hours to make it completely gelatinized. Then gradually lower it to room temperature to obtain the starch-based adhesive.

[0012] By adopting the above technical solution, this invention prepares dialdehyde starch using corn starch as raw material and sodium periodate as an oxidant, and then uses polyethylene glycol and urea to graft and modify it to prepare a dialdehyde starch-grafted polyethylene glycol / urea adhesive. Sodium periodate is an oxidant that can selectively bind the C-terminal molecules of starch glucose units.２ -C ３ The ortho-hydroxyl group on the starch is oxidized to two acid groups, yielding dialdehyde starch. Substituting the hydroxyl group can enhance the hydrophobicity of starch adhesives and provide active aldehyde sites for subsequent modification. The reaction of polyethylene glycol with polyacrylate and dialdehyde-modified nanocellulose can prepare formaldehyde-free adhesives, which can significantly improve the surface properties of impregnated decorative paper.

[0013] A further provision of the present invention is that the anti-agglomeration agent in step S2 is modified nano-silica.

[0014] A further provision of the present invention is that the modified nano-silica is prepared by the following steps: a certain mass of nano-silica is added to an ethanol solution, ultrasonicated for 2 hours, a silane coupling agent is added, the mixture is stirred at room temperature for 24 hours, then an oxalic acid solution is added, the mixture is stirred in a water bath at 75°C for 4 hours, then centrifuged, and the solid is ultrasonically cleaned and dried to obtain the modified nano-silica.

[0015] A further provision of the present invention is that the modified nano-silica accounts for 0.5-1.5% of the total mass fraction of the starch-based adhesive.

[0016] After hydrolysis, the silane coupling agent forms hydrogen bonds with the -OH groups on the surface of nano-SiO2. Heating and dehydration then generate partial covalent bonds, covering the surface of the nano-SiO2 particles. This allows the small molecules of the coupling agent with specific functional groups to be successfully grafted onto the surface of the nano-SiO2 particles, improving the compatibility between the nano-SiO2 particles and the organic phase. Furthermore, a flexible interfacial layer is formed between the two phases, resulting in more uniform stress transfer at the interface. During the hydrolysis of the silane coupling agent KH-570, the Si-OH groups generated condense with the -OH groups on the SiO2 surface to form Si-O-Si, chemically bonding KH-570 to the surface of the nano-SiO2. This changes the surface of the nano-SiO2 from hydrophilic to hydrophobic, and the coupling agent on the nano-SiO2 also prevents particle aggregation.

[0017] A further provision of the present invention is that the pigment comprises ground calcium carbonate and kaolin, in a mass ratio of 85-95 parts of ground calcium carbonate and 5-15 parts of kaolin.

[0018] The present invention is further configured to include the following preparation steps: S1: Take the raw material of dye by mass, add water and mix, wherein the mass of water is 6-8 times the mass of dye;

[0019] S2: Take the face paper layer pulp, core paper layer pulp and bottom paper layer pulp, and adjust the pH value of the face paper layer pulp, core paper layer pulp and bottom paper layer pulp to between 6.5 and 7.5;

[0020] S3: The face paper layer pulp, core paper layer pulp and bottom paper layer pulp are dewatered and formed through the corresponding forming wires, and the anti-counterfeiting dye in S1 is sprayed onto the core paper layer during the dewatering and forming process of the core paper layer.

[0021] S4: Lay the face paper layer, core paper layer and bottom paper layer together;

[0022] S5: The composite layer in S4 is sequentially pressed, dried for the first time, sizing, dried for the second time, hard calendered, coated, soft calendered, and wound to obtain the finished product; the temperature of the first drying and the second drying is both below 50℃.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention uses corn starch as raw material and sodium periodate as an oxidant to prepare dialdehyde starch. Polyethylene glycol and urea are then used to graft and modify it to prepare a dialdehyde starch-grafted polyethylene glycol / urea adhesive. Sodium periodate is an oxidant that can selectively bind the C-terminal molecules of the starch glucose units. ２ -C ３ The ortho-hydroxyl group on the starch is oxidized to two acid groups, yielding dialdehyde starch. Substituting the hydroxyl group can enhance the hydrophobicity of starch adhesives and provide active aldehyde sites for subsequent modification. The reaction of polyethylene glycol with polyacrylate and dialdehyde-modified nanocellulose can prepare formaldehyde-free adhesives, which can significantly improve the surface properties of impregnated decorative paper.

[0025] 2. After hydrolysis, the silane coupling agent forms hydrogen bonds with the -OH groups on the surface of nano-SiO2. Heating and dehydration produce partial covalent bonds, thus covering the surface of the nano-SiO2 with the silane coupling agent. This allows the small molecules of the coupling agent, possessing special functional groups, to be successfully grafted onto the surface of the nano-SiO2 particles, improving the compatibility between the nano-SiO2 particles and the organic phase. Furthermore, a flexible interface layer is formed between the two phases, resulting in more uniform stress transfer at the interface. During the hydrolysis of the silane coupling agent KH-570, the Si-OH groups generated condense with the -OH groups on the SiO2 surface to form Si-O-Si, chemically bonding KH-570 to the surface of the nano-SiO2. This changes the surface of the nano-SiO2 from hydrophilic to hydrophobic, and the coupling agent on the nano-SiO2 also prevents particle aggregation. Detailed Implementation

[0026] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] Powdered starch-based adhesives are prepared through the following steps:

[0029] S1: Preparation of dialdehyde corn starch: Corn starch, sodium periodate and water in a mass ratio of 6-7:1:15-2 were stirred for 10 min, and then the pH was adjusted to 3 with sulfuric acid solution. The reaction was carried out in a 40℃ water bath in the dark for 4-5 h. After the reaction was completed, the mixture was filtered, washed, dried and ground to obtain dialdehyde corn starch.

[0030] S2: Dissolve 15g of dialdehyde corn starch in 80mL of water, add appropriate amount of modified nano silica, 35%-55% of polyethylene glycol and 55%-65% of urea, stir and mix, and react in a water bath at 30-45℃ for 4-5 hours. Then filter, wash, dry and grind to obtain powdered starch-based adhesive; the modified nano silica accounts for 0.5-1.5% of the total mass fraction of starch-based adhesive.

[0031] S3: Add 15g of powdered starch-based adhesive to 35ml of water and stir. The mass ratio of powdered starch-based adhesive to water is: Then stir in a water bath at 93-96℃ for 0.5-0.8h to make it completely gelatinized, and then gradually lower it to room temperature to obtain starch-based adhesive.

[0032] Example 2

[0033] Powdered starch-based adhesives are prepared through the following steps:

[0034] S1: Preparation of dialdehyde corn starch: Corn starch, sodium periodate and water in a mass ratio of 6-7:1:15-2 were stirred for 10 min, and then the pH was adjusted to 3 with sulfuric acid solution. The reaction was carried out in a 40℃ water bath in the dark for 4-5 h. After the reaction was completed, the mixture was filtered, washed, dried and ground to obtain dialdehyde corn starch.

[0035] S2: Dissolve 15g of dialdehyde corn starch in 80mL of water, add 35%-55% polyethylene glycol and 55%-65% urea, stir and mix, and stir and react in a water bath at 30-45℃ for 4-5 hours. Then filter, wash, dry and grind to obtain powdered starch-based adhesive.

[0036] S3: Add 15g of powdered starch-based adhesive to 35ml of water and stir. The mass ratio of powdered starch-based adhesive to water is: Then stir in a water bath at 93-96℃ for 0.5-0.8h to make it completely gelatinized, and then gradually lower it to room temperature to obtain starch-based adhesive.

[0037] Example 3

[0038] Powdered starch-based adhesives are prepared through the following steps:

[0039] S1: Preparation of dialdehyde corn starch: Corn starch, sodium periodate and water in a mass ratio of 6-7:1:15-2 were stirred for 10 min, and then the pH was adjusted to 3 with sulfuric acid solution. The reaction was carried out in a 40℃ water bath in the dark for 4-5 h. After the reaction was completed, the mixture was filtered, washed, dried and ground to obtain dialdehyde corn starch.

[0040] S2: Dissolve 15g of dialdehyde corn starch in 80mL of water, add 55%-65% urea, stir and mix, and react in a water bath at 30-45℃ for 4-5 hours. Then filter, wash, dry and grind to obtain powdered starch-based adhesive.

[0041] S3: Add 15g of powdered starch-based adhesive to 35ml of water and stir. The mass ratio of powdered starch-based adhesive to water is: Then stir in a water bath at 93-96℃ for 0.5-0.8h to make it completely gelatinized, and then gradually lower it to room temperature to obtain starch-based adhesive.

[0042] Example 4

[0043] Powdered starch-based adhesives are prepared through the following steps:

[0044] S1: Preparation of dialdehyde corn starch: Corn starch, sodium periodate and water in a mass ratio of 6-7:1:15-2 were stirred for 10 min, and then the pH was adjusted to 3 with sulfuric acid solution. The reaction was carried out in a 40℃ water bath in the dark for 4-5 h. After the reaction was completed, the mixture was filtered, washed, dried and ground to obtain dialdehyde corn starch.

[0045] S2: Dissolve 15g of dialdehyde corn starch in 80mL of water, stir and mix, and react in a water bath at 30-45℃ for 4-5 hours. Then filter, wash, dry and grind to obtain powdered starch-based adhesive.

[0046] S3: Add 15g of powdered starch-based adhesive to 35ml of water and stir. The mass ratio of powdered starch-based adhesive to water is: Then stir in a water bath at 93-96℃ for 0.5-0.8h to make it completely gelatinized, and then gradually lower it to room temperature to obtain starch-based adhesive.

[0047] The adhesives obtained in Examples 1-4 were used in the preparation of white cardboard.

[0048] The preparation steps include: S1: Take the raw materials of the dye according to the mass ratio, add water and mix, wherein the mass of water is 6-8 times the mass of the dye;

[0049] S2: Take the face paper layer pulp, core paper layer pulp and bottom paper layer pulp, and adjust the pH value of the face paper layer pulp, core paper layer pulp and bottom paper layer pulp to between 6.5 and 7.5;

[0050] S3: The face paper layer pulp, core paper layer pulp and bottom paper layer pulp are dewatered and formed through the corresponding forming wires, and the anti-counterfeiting dye in S1 is sprayed onto the core paper layer during the dewatering and forming process of the core paper layer.

[0051] S4: Lay the face paper layer, core paper layer and bottom paper layer together;

[0052] S5: The composite layer in S4 is sequentially subjected to pressing, first drying, application of adhesive, second drying, hard calendering, coating, soft calendering, and winding to obtain the finished product; wherein the temperature of the first and second drying is below 50℃.

[0053] The starch-based adhesives obtained in Examples 1-4 were subjected to performance tests. The dry shear strength of the adhesive samples was determined according to the national standard GB / T17657-2013, and the viscosity was tested according to the method of national standard GBAT2794-2013. The results are shown in Table 1.

[0054] Example 1 Example 2 Example 3 Example 4 Dry shear strength (MPa) 2.9 2.5 2.3 2.1 Viscosity (MPa·s) 6847 6354 5943 5483

[0055] As shown in Table 1, the increased probability of collision between the amino groups of urea and the aldehyde groups on dialdehyde starch, meaning an increase in the amount of urea grafted onto dialdehyde starch, strengthens the polymerization force between urea and dialdehyde starch, thereby increasing the dry shear strength of the adhesive. Simultaneously, the increased probability of collision between the hydroxyl groups of polyethylene glycol and the aldehyde groups on dialdehyde starch, meaning an increase in the amount of polyethylene glycol grafted onto dialdehyde starch, and the inherent adhesive properties of polyethylene glycol further enhance the dry shear strength of the adhesive.

[0056] The adhesives obtained in Examples 1-4 were used in the preparation of white cardboard, and the performance of the white cardboard was tested, as shown in Table 2.

[0057] Prepare 2.5cm wide paper / plastic (white cardboard / PET) and plastic / plastic laminated tapes. Then, according to GB / T 2791-1995 standard, apply the prepared adhesive to the paper / plastic and plastic / plastic tapes, dry them, and bond the tapes together. Test them using an electronic universal testing machine.

[0058] The coated aging-resistant cardboard was placed in an aging chamber (light temperature 50℃, light intensity 500w / m²). 2 The paper was aged for 4 hours in the heat-aged medium, and then the performance of the paper before and after heat aging was tested.

[0059] Example 1 Example 2 Example 3 Example 4 <![CDATA[Peeling strength [N·(2.5 cm) -1 > 11.45 7.54 6.54 6.22 Tensile strength before heat aging / MPa 268.4 243.4 214.8 174.7 Tensile strength after heat aging / MPa 259.6 238.7 208.3 142.1 Appearance after heat aging No change No change Slight yellowing Serious anti-pornography

Claims

1. A method for preparing aging-resistant white cardboard, characterized in that: The invention comprises a base paper and a coating layer covering its surface. The base paper includes a face paper layer, a core paper layer, and a back paper layer. The coating layer includes a pre-coating layer, a top coating layer, and a back coating layer. The invention is characterized in that the pulp of the base paper includes bleached eucalyptus pulp, and the coatings of the pre-coating layer, the top coating layer, and the back coating layer all include pigments, coating adhesives, and fillers.

2. The method for preparing aging-resistant white cardboard according to claim 1, characterized in that: The coating adhesive is a starch-based adhesive.

3. The method for preparing aging-resistant white cardboard according to claim 2, characterized in that: The starch-based adhesive is prepared by the following steps: S1: Preparation of dialdehyde corn starch: Corn starch, sodium periodate and water in a mass ratio of 6-7:1:15-2 were stirred for 10 min, and then the pH was adjusted to 3 with sulfuric acid solution. The reaction was carried out in a 40℃ water bath in the dark for 4-5 h. After the reaction was completed, the mixture was filtered, washed, dried and ground to obtain dialdehyde corn starch. S2: Dissolve dialdehyde corn starch in water, add appropriate amount of anti-agglomeration agent, 35%-55% polyethylene glycol and 55%-65% urea, stir and mix, and stir and react in a water bath at 30-45℃ for 4-5 hours. Then filter, wash, dry and grind to obtain powdered starch-based adhesive. S3: Add the powdered starch-based adhesive to water and stir. Then stir in a water bath at 93-96℃ for 0.5-0.8 hours to make it completely gelatinized. Then gradually lower it to room temperature to obtain the starch-based adhesive.

4. The method for preparing aging-resistant white cardboard according to claim 3, characterized in that: The anti-agglomeration agent in step S2 is modified nano-silica.

5. The method for preparing aging-resistant white cardboard according to claim 4, characterized in that: The modified nano-silica is prepared by the following steps: a certain mass of nano-silica is added to an ethanol solution, ultrasonicated for 2 hours, a silane coupling agent is added, and the mixture is stirred at room temperature for 24 hours. Then, an oxalic acid solution is added, and the mixture is stirred in a water bath at 75°C for 4 hours. After centrifugation, the solid is ultrasonically cleaned and dried to obtain the modified nano-silica.

6. The method for preparing aging-resistant white cardboard according to claim 4, characterized in that: The modified nano-silica accounts for 0.5-1.5% of the total mass fraction of all starch-based adhesives.

7. The method for preparing aging-resistant white cardboard according to claim 1, characterized in that: The pigment comprises ground calcium carbonate and kaolin, in a mass ratio of 85-95 parts of ground calcium carbonate and 5-15 parts of kaolin.

8. The method for preparing aging-resistant white cardboard according to claim 1, characterized in that: The preparation steps include: S1: Take the raw materials of the dye according to the mass ratio, add water and mix, wherein the mass of water is 6-8 times the mass of the dye; S2: Take the face paper layer pulp, core paper layer pulp and bottom paper layer pulp, and adjust the pH value of the face paper layer pulp, core paper layer pulp and bottom paper layer pulp to between 6.5 and 7.5; S3: The face paper layer pulp, core paper layer pulp and bottom paper layer pulp are dewatered and formed through the corresponding forming wires, and the anti-counterfeiting dye in S1 is sprayed onto the core paper layer during the dewatering and forming process of the core paper layer. S4: Lay the face paper layer, core paper layer and bottom paper layer together; S5: The composite layer in S4 is sequentially pressed, dried for the first time, sizing, dried for the second time, hard calendered, coated, soft calendered, and wound to obtain the finished product; the temperature of the first drying and the second drying is both below 50℃.