A method for integrated production of decorative wrapping paper based on multi-net cage grading sizing

Abstract

This invention discloses an integrated production method for decorative packaging paper based on multi-cage graded sizing, comprising four steps: base layer forming, wet implantation of decorative materials, surface coating and sealing, and drying and paper output. The first cage forms the base fiber layer by sizing at a pulp-to-water ratio of 2:8. The second cage is modified into a flooded sizing tank, and a cationic starch-grafted silane coupling agent is used to wet-implant metal sheets, dried flower and plant fragments, and colored fiber filaments modified with nano-silica into the base fiber layer. The third cage is sizing and sealing at a pulp-to-water ratio of 2:5 and coated with a self-crosslinking waterborne polyurethane-acrylate hybrid emulsion. After drying in multiple cylinders, the finished product is obtained. This invention realizes integrated continuous production from pulp to decorative packaging paper, with strong adhesion of the decorative layer and a realistic three-dimensional texture.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, specifically relating to an integrated production method for decorative packaging paper based on multi-cage graded sizing, and particularly to a process method for integrated continuous production of base layer forming, wet in-situ implantation of decorative materials, and surface film encapsulation using multi-level cylindrical cages. Background Technology

[0002] Decorative packaging paper, as an important category of high-value-added paper products, is widely used in gift packaging, cultural and creative products, and high-end consumer goods packaging. Traditional decorative packaging paper production typically involves first making the base paper, and then achieving the decorative effect through secondary processing steps such as printing, hot stamping, embossing, and lamination. This multi-process, separate production model faces numerous technical bottlenecks.

[0003] First, traditional processes separate papermaking and decoration into two independent production stages, resulting in numerous process connections, long production cycles, and large equipment investments. After the base paper is made, it needs to be rewound, stored, and transferred to the printing or post-processing workshop before undergoing each decoration process. Each transfer step may introduce quality risks such as paper surface damage and moisture content fluctuations.

[0004] Secondly, in terms of decorative effect, traditional hot stamping printing is essentially a surface-adhesive decoration method. The decorative material only stays on the surface of the paper, lacking effective physical interlocking and chemical bonding with the paper base. During use, the decorative layer is prone to problems such as peeling, fading, and bubbling, especially in humid environments or under conditions of repeated folding.

[0005] Furthermore, the current market demands increasingly higher levels of three-dimensionality and realistic texture from decorative packaging paper. Consumers expect to see authentic plant fiber textures and the natural distribution of metallic sheen in the sheets, rather than flat, printed patterns. However, in traditional cylinder papermaking, multi-cylinder paper machines are primarily used for producing multi-layered paperboard. Each wire cage has a single function: fiber deposition and forming. They do not simultaneously incorporate decorative materials or apply surface functional layers during the papermaking process.

[0006] Chinese patent CN102154930A discloses a method for preparing high-gloss furniture veneer impregnated paper. This method involves impregnating and roller-coating printing roll paper with modified melamine-formaldehyde resin, followed by drying to obtain the impregnated paper. Although this method relates to the field of decorative paper, its technical approach is a post-processing method of printing first and then impregnating, essentially still belonging to the category of secondary processing. It cannot integrate decorative materials into the papermaking process, and its product is positioned as a veneer material for engineered wood panels rather than packaging paper.

[0007] Chinese patent CN105603827A discloses a method for producing environmentally friendly high-barrier food packaging paper, involving surface sizing and coating technologies. It utilizes existing sizing and coating equipment in paper mills to add barrier functions. This patent focuses on improving barrier performance and does not address the embedding of decorative materials. Furthermore, its lamination operation is a separate process after paper forming, not integrated with the papermaking process.

[0008] Chinese patent CN102966004A discloses a method for producing impregnated paper, which involves immersing the base paper in a resin solution to achieve impregnation. This method is a single-layer impregnation process, lacking the characteristics of multi-cage graded sizing, and does not address the dispersion and implantation of solid decorative materials such as metal sheets and plant fragments in the sizing solution.

[0009] Furthermore, in terms of sizing and laminating materials, existing technologies mostly use general-purpose starch adhesives or polyvinyl alcohol as sizing agents and polyethylene film as laminating materials. These general-purpose materials have significant shortcomings when used for decorative packaging paper. General-purpose sizing agents have weak anchoring ability for heterogeneous decorative materials such as metal sheets and plant fragments, and the adhesion between the laminating layer and the paper surface containing raised decorative materials is poor, easily causing bubbles and curling at the edges of the decorative materials.

[0010] Therefore, there is an urgent need to develop a new production method that can integrate base layer forming, decorative material implantation, and surface film encapsulation during the paper forming process. This would simplify the process flow, reduce production costs, minimize quality losses in intermediate stages, and achieve deep integration of decorative materials with the paper base through wet in-situ implantation technology, resulting in high-quality decorative packaging paper products with a realistic three-dimensional texture and a durable and stable decorative effect. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of existing decorative packaging paper production technologies, such as process separation, weak bonding of decorative layers, and insufficient three-dimensional texture, and to provide an integrated production method for decorative packaging paper based on multi-cage graded sizing. This method differentiates the functions of each cage in a multi-cylinder paper machine, simultaneously completing base layer fiber forming, wet-laid in-situ implantation of decorative materials, and surface coating and encapsulation in a single continuous papermaking process, thus achieving integrated continuous production from pulp to finished decorative packaging paper.

[0012] To achieve the above objectives, the present invention adopts the following technical solution.

[0013] An integrated production method for decorative packaging paper based on multi-cage grading and sizing includes the following steps.

[0014] Step 1, base layer formation. Softwood pulp and hardwood pulp are mixed at a mass ratio of 6:4 to 7:3 to prepare a base slurry. The base slurry is then beaten to a freeness of 35 to 45°SR and adjusted to a mass ratio of slurry to water of 2:8. The mixture is then fed into the mesh trough of the first mesh cage for slurry application and forming to create the base fiber layer.

[0015] Step Two: Wet Implantation of Decorative Materials. The mesh trough of the second mesh cage is modified into a flooded sizing tank. A decorative sizing solution is prepared, comprising surface-modified decorative materials and a modified sizing agent. The decorative materials are selected from one or more of dried flower and plant fragments, gold foil, silver foil, and colored fiber filaments. The modified sizing agent is a cationic starch-grafted silane coupling agent modifier. The decorative sizing solution is added to the flooded sizing tank, and the concentration of the flooded sizing solution is controlled at 0.3% to 0.8%. The base fiber layer is then flooded and sizing in the tank. During the flooding process, the decorative material is uniformly deposited and embedded into the upper surface of the base fiber layer, forming a decorative composite layer.

[0016] Step 3, surface coating and encapsulation. In the third mesh cage, slurry is applied at a mass ratio of 2:5 to water to form a surface fiber encapsulation layer. At the same time, a coating and gluing device is installed at the outlet of the third mesh cage to uniformly coat the surface fiber encapsulation layer with a self-crosslinking waterborne polyurethane-acrylate hybrid emulsion at a coating amount of 8 to 20 g / m to form a protective coating layer.

[0017] Step four, drying and paper output. The paper web processed in step three is sent to a multi-cylinder drying section and dried at 105 to 120°C until the moisture content is 5% to 8%, thus obtaining the finished decorative packaging paper.

[0018] This invention also provides a method for preparing the modified sizing agent, specifically, by gelatinizing cationic starch at 75 to 85°C for 30 to 45 min, cooling it to 55 to 65°C, adding 3% to 8% of gamma-aminopropyltriethoxysilane by dry weight of the cationic starch, and reacting under stirring for 2 to 3 h to obtain a cationic starch-grafted silane coupling agent modified sizing agent. In this modified sizing agent, the amino group of the silane coupling agent undergoes a condensation reaction with the hydroxyl group of the cationic starch to form a Si-OC covalent bond, and the silanol group retained at the molecular end can further condense with the hydroxyl group on the surface of the metal oxide, thereby establishing a chemical bridge between the surface of the decorative material and the fiber matrix.

[0019] This invention also provides a method for surface modification of the decorative material, specifically, immersing gold or silver foil sheets in an ethanol solution containing tetraethyl orthosilicate and ammonia, and stirring the solution at 30 to 40°C for 4 to 6 hours to form a nano-silica coating layer with a thickness of 50 to 200 nm on the surface of the metal sheet. The coating is then filtered, washed, and dried to obtain a surface-modified metal decorative sheet. The nano-silica coating layer significantly improves the dispersion stability of the metal sheet in aqueous slurry and the interfacial bonding strength with the fiber matrix.

[0020] The beneficial effects of this invention are as follows.

[0021] First, by differentiating the functions of each wire cage in a multi-circular wire paper machine, the present invention can simultaneously complete the three functions of substrate forming, decorative implantation and film sealing in a single continuous papermaking process, eliminating the multiple transfer and independent processing links in the traditional process, increasing production efficiency by more than 40% and reducing overall costs by 25% to 35%.

[0022] Secondly, the decorative material is deposited and embedded in situ on the surface of the wet fiber layer through the wetting effect of the water slurry. The decorative material is wrapped and anchored by the fiber, forming a physical interlocking structure. Combined with the chemical bridging effect provided by the modified sizing agent, the bonding strength of the decorative layer reaches a dry peel strength greater than 2.5 N / 15 mm and a wet peel strength greater than 1.2 N / 15 mm, which is far superior to traditional surface-printed decorative paper.

[0023] Third, the water-based sizing process allows the decorative material to flow and distribute naturally in the sizing liquid, forming random and uniform decorative patterns. This results in a natural three-dimensional texture and an unreplicable visual effect, with a realism and artistry significantly superior to printing simulations.

[0024] Fourth, the self-crosslinking waterborne polyurethane-acrylate hybrid emulsion coating layer has excellent flexibility and adhesion, and can tightly wrap irregular paper surfaces containing raised decorative materials. After coating, the paper surface gloss reaches 45 to 65 GU, the folding endurance is greater than or equal to 80 times, and the waterproof performance Cobb value is less than 30 g / m. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the integrated production process of multi-cage graded sizing and decorative packaging paper according to the present invention.

[0026] Figure 2 This is a schematic cross-sectional view of the multi-layer structure of the decorative packaging paper of the present invention.

[0027] Figure 3 This is a schematic diagram illustrating the chemical bridging mechanism between the modified sizing agent of this invention and the fiber matrix.

[0028] Figure 4Microscopic morphology of the surface of gold foil coated with nano-silica.

[0029] Figure 5 This is a schematic diagram of the ketone-hydrazide crosslinking and microphase separation structure of a self-crosslinking waterborne polyurethane-acrylate hybrid emulsion coating layer.

[0030] Figure 6 The figures show a comparison of the dry and wet peel strength of Examples 1 to 3 and Comparative Examples 1 to 4.

[0031] Figure 7 This is a comparison chart of the overall performance of folding endurance, gloss and Cobb value between Examples 1 to 3 and Comparative Examples 1 to 4. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Example 1

[0033] This embodiment provides an integrated production method for decorative packaging paper based on multi-mesh cage grading and sizing, such as... Figure 1 As shown, a three-cage cylinder paper machine is used. The pulp passes through the first, second and third cages in sequence to complete the three functional stages of substrate forming, decorative implantation and film sealing. The specific steps are as follows.

[0034] Step 1: Preparation of the modified sizing agent. Take 100 parts of cationic starch and add 400 parts of deionized water. Stir and gelatinize at 80°C for 40 min to form a uniform and transparent starch paste. Cool the paste to 60°C and slowly add 5 parts of gamma-aminopropyltriethoxysilane. Continue the reaction for 2.5 h with stirring at 300 r / min. During the reaction, the ethoxy group of the silane coupling agent undergoes a hydrolytic condensation reaction with the hydroxyl group on the starch chain to form a Si-OC covalent bond. After the reaction, allow it to cool naturally to room temperature to obtain a modified sizing agent with a solid content of approximately 20%. The viscosity of this modified sizing agent is 850 to 1200 mPa·s, and the pH value is 6.5 to 7.5.

[0035] Step 2: Surface Modification Treatment of Decorative Materials. Take 100 parts of gold foil (thickness 0.1 to 0.3 mm, area 3 to 8 mm x 3 to 8 mm) and place it in a mixed solution containing 15 parts of tetraethyl orthosilicate, 200 parts of anhydrous ethanol, and 10 parts of ammonia (25% by mass). Stir and react in a 35°C constant temperature water bath for 5 hours. Tetraethyl orthosilicate hydrolyzes under the catalysis of ammonia to generate a silanol intermediate. The silanol further condenses and deposits on the surface of the gold foil to form a nano-silica coating layer with a thickness of approximately 100 nm. Figure 4As shown, the coating layer exhibits a uniform and dense granular morphology, with nanoparticles of approximately 15 to 30 nm in diameter, tightly packed and covering the surface of the metal substrate. After the reaction, the modified gold foil was filtered, washed three times with anhydrous ethanol, and dried at 60°C for 2 h for later use. Dried flower and plant fragments (2 to 5 mm x 2 to 5 mm in area) and colored fibers (5 to 15 mm in length) require no surface modification treatment and can be used directly.

[0036] Step 3: Substrate Layer Formation (First Wire Mesh Cage). Bleached softwood sulfate pulp and bleached hardwood sulfate pulp are mixed at a mass ratio of 65:35, diluted with deionized water, and pulped using a disc mill to a freeness of 40°SR and a wet weight of 8.5 g. The pulp concentration is adjusted to a pulp-to-water mass ratio of 2:8, i.e., a pulp concentration of approximately 20% (octane-dry fiber concentration of approximately 0.8% to 1.2%). The prepared pulp is fed into the co-current mesh trough of the first wire mesh cage at a rotation speed of 20 m / min. Conventional filtration and dewatering are performed on the mesh surface, forming a substrate fiber layer with a basis weight of 60 to 80 g / m.

[0037] Step 4: Wet Implantation of Decorative Materials (Second Mesh Cage). The mesh trough of the second mesh cage is modified into a submerged slurry tank. A slurry circulation pump and a stirring paddle are installed at the bottom of the tank to ensure uniform slurry flow. The composition of the decorative slurry is as follows: 1000 parts deionized water, 30 parts modified sizing agent (obtained in Step 1), 5 parts surface-modified gold foil (obtained in Step 2), 8 parts dried flower and plant fragments, and 3 parts colored fiber filaments. The above components are added to the submerged slurry tank. The circulation pump and stirring paddle are turned on, and the stirring speed is 60 to 100 r / min to ensure uniform dispersion of the decorative materials in the slurry. The slurry concentration is controlled at 0.5%. The base fiber layer from the first mesh cage (with a moisture content of approximately 75% to 80%) is transferred by a roller and enters the submerged slurry tank of the second mesh cage, with the upper surface of the base fiber layer immersed in the decorative slurry. During the flooding process, the decorative material settles naturally and is evenly distributed on the upper surface of the base fiber layer under the combined action of gravity and slurry flow. The silanol groups in the modified sizing agent undergo a condensation reaction with the nano-silica layer on the surface of the decorative material and the hydroxyl groups of the cellulose fibers, establishing a ternary chemical bridging network of decorative material-sizing agent-fiber. The flooding time is 3 to 8 seconds, depending on the rotation speed of the mesh cage and the arc length of the flooding section.

[0038] Step 5: Surface Coating and Sealing (Third Cage). In the third cage, the sealing slurry is prepared. The slurry composition is the same as that of the first cage, but the slurry-to-water mass ratio is adjusted to 2:5, i.e., the slurry concentration is approximately 28.6% (octane-dry fiber concentration is approximately 1.5% to 2.0%). The decorative composite layer from the second cage enters the third cage for sizing. A thin layer of fibers is deposited and covers the surface of the decorative material, forming a surface fiber sealing layer with a basis weight of 15 to 30 g / m. Simultaneously, a roll-coating and sizing device is installed behind the couch roll at the exit of the third cage. A self-crosslinking waterborne polyurethane-acrylate hybrid emulsion (solid content 40%, viscosity 500 to 800 mPa·s) is used to roll-coat the paper web surface, with the coating amount controlled at 12 g / m. The preparation method of this coating adhesive is as follows: 100 parts of isophorone diisocyanate (IPDI), 200 parts of polytetrahydrofuran diol (PTMG, molecular weight 2000), and 15 parts of dimethylolpropionic acid (DMPA) are reacted at 80°C for 3 h to obtain a polyurethane prepolymer. After neutralization with triethylamine, it is dispersed in water, and then emulsion polymerized with 50 parts of butyl acrylate, 30 parts of methyl methacrylate, and 8 parts of diacetone acrylamide (DAAM) under potassium persulfate initiation. Finally, 6 parts of adipic acid dihydrazide (ADH) are added as a crosslinking agent to obtain a self-crosslinking waterborne polyurethane-acrylate hybrid emulsion. During the film formation process, the ketone carbonyl group of DAAM and the hydrazide group of ADH undergo a ketone-hydrazide crosslinking reaction to form a dense three-dimensional network coating layer.

[0039] Step Six: Drying and Paper Output. The paper web treated by the third wire mesh is sequentially passed through a multi-cylinder drying section (10 drying cylinders in total). The temperature of the first 4 drying cylinders is set at 105°C, the temperature of the middle 4 drying cylinders is set at 115°C, and the temperature of the last 2 drying cylinders is set at 110°C. The total drying time is approximately 45 to 60 seconds. After drying, the moisture content of the paper web is 6% to 7%. After cooling in the cold cylinder, it is wound up to obtain the finished decorative packaging paper.

[0040] The total basis weight of the decorative packaging paper prepared in this embodiment is 120 g / m². Figure 2 As shown, its multi-layered structure, from bottom to top, consists of a base fiber layer (70 g / m basis weight), a decorative material embedding layer (approximately 20 g / m basis weight), a surface fiber encapsulation layer (20 g / m basis weight), and a protective coating layer (approximately 10 g / m basis weight). The paper clearly displays the naturally distributed shimmering effect of gold foil flakes, the natural texture of dried flower and plant fragments, and the striped patterns of colored fibers, giving the decorative pattern a unique random aesthetic and a realistic three-dimensional feel. Example 2

[0041] The difference between this embodiment and Embodiment 1 lies in the composition of the decorative slurry and the adjustment of the slurry ratio of the first mesh cage; the remaining steps are the same.

[0042] Step 1: Preparation of modified sizing agent. Take 100 parts of cationic starch, add 350 parts of deionized water, and stir to gelatinize at 85°C for 30 min. After cooling to 55°C, add 8 parts of gamma-aminopropyltriethoxysilane, and react for 3 h under stirring at 350 r / min to obtain a modified sizing agent with a solid content of about 22%.

[0043] Step 2: Surface modification treatment of decorative materials. Take 80 parts of silver foil (thickness 0.1 to 0.2 mm, area 2 to 6 mm x 2 to 6 mm) and coat it with nano-silica according to the method in Example 1, except that the amount of tetraethyl orthosilicate is adjusted to 20 parts and the reaction time is extended to 6 hours, so that the coating thickness is increased to about 150 nm. 120 parts of dried flower plant fragments (a mixture of dried flower fragments of lavender, baby's breath and daisies) are used; colored fibers are not used.

[0044] Step 3: Base Layer Forming (First Wire Mesh Cage). Bleached coniferous sulfate pulp and bleached hardwood sulfate pulp are mixed at a mass ratio of 60:40, beaten to a freeness of 45°SR, and the pulp-to-water mass ratio is adjusted to 2:8. The mixture is then fed into the first wire mesh cage for forming. Since this embodiment uses dried flower fragments as the main decorative material, the area and thickness of the plant fragments are relatively large, and the base layer quantity is increased to 80 g / m² to provide stronger load-bearing capacity.

[0045] Step 4: Wet Installation of Decorative Materials (Second Net Cage). The decorative slurry consists of: 1000 parts deionized water, 35 parts modified sizing agent, 80 parts surface-modified silver foil, and 120 parts dried flower and plant fragments. The slurry concentration is controlled at 0.8%. Due to the increased amount of dried flower fragments, the stirring speed is reduced to 50 r / min to avoid excessive fragment breakage. During the flooding process, a large number of plant fragments are deposited on the surface of the base fiber layer, forming a dense plant fiber decorative layer, interspersed with silver foil, presenting a visual effect where silver specks and natural floral textures complement each other.

[0046] Step 5: Surface Coating and Encapsulation (Third Mesh Cage). The encapsulation slurry to water mass ratio is 2:5, and the encapsulation layer basis weight is 25 g / m. The coating adhesive application amount is increased to 18 g / m to ensure sufficient coverage of the thicker dried flower fragments. The coating adhesive formulation is the same as in Example 1, but the DAAM amount is increased to 10 parts, and the ADH amount is correspondingly increased to 7.5 parts to improve the crosslinking density and the hardness of the coating layer, preventing the dried flower fragments from falling off during use.

[0047] Step 6: Drying and paper output. The temperature of the first 4 drying cylinders is 105°C, the temperature of the middle 4 drying cylinders is 110°C (the temperature is lowered to protect the color of the dried flower fragments), and the temperature of the last 2 drying cylinders is 105°C, with the moisture content controlled at 7% to 8%.

[0048] The decorative packaging paper prepared in this embodiment has a total basis weight of 160 g / m². The paper surface presents a rich natural floral style, and the natural colors and textures of the dried flower fragments are well preserved. The metallic luster of the silver foil adds a touch of sophistication. It is suitable for high-end floral gift packaging and cultural and creative product packaging. Example 3

[0049] This embodiment is a lightweight decorative packaging paper solution, suitable for applications requiring low basis weight, such as envelopes and book wrapping paper.

[0050] Step 1: Preparation of the modified sizing agent. Take 100 parts of cationic starch and add 450 parts of deionized water. Stir and gelatinize at 75°C for 45 min. After cooling to 65°C, add 3 parts of gamma-aminopropyltriethoxysilane and react at 250 r / min for 2 h to obtain a modified sizing agent with a solid content of approximately 18%. The relatively low amount of silane coupling agent is sufficient to meet the anchoring requirements of fewer decorative materials in lightweight solutions.

[0051] Step 2: Surface modification treatment of decorative materials. Take 50 parts of gold foil (thickness 0.05 to 0.15 mm, area 1 to 3 mm x 1 to 3 mm, using thinner and smaller gold foil to suit the lightweight design) and perform nano-silica coating treatment according to the method in Example 1, shortening the reaction time to 4 hours, and achieving a coating layer thickness of approximately 50 nm. Take 20 parts of colored fiber filaments (length 3 to 8 mm), excluding dried flower and plant fragments.

[0052] Step 3: Base Layer Forming (First Wire Cage). Bleached softwood sulfate pulp and bleached hardwood sulfate pulp are mixed at a mass ratio of 70:30 and beaten to a freeness of 35°SR (a lower freeness is beneficial for improving paper bulk and stiffness). The pulp and water mass ratio is adjusted to 2:8. The pulp is then fed into the first wire cage for sizing and forming. The basis weight of the base layer is 45 g / m.

[0053] Step 4: Wet Implantation of Decorative Materials (Second Net Cage). The decorative slurry consists of: 1000 parts deionized water, 20 parts modified sizing agent, 50 parts surface-modified gold foil, and 20 parts colored fiber filaments. The slurry concentration is controlled at 0.3%. The lower slurry concentration and less decorative material usage result in a sparse distribution of gold foil and colored fiber filaments on the paper surface, creating a simple yet refined decorative style.

[0054] Step 5: Surface Coating and Encapsulation (Third Mesh Cage). The encapsulation slurry to water mass ratio is 2:5, and the encapsulation layer basis weight is 10 g / m. The coating adhesive application amount is 8 g / m. The coating adhesive formulation contains 6 parts DAAM and 4.5 parts ADH. The lower crosslinking density gives the coating layer better flexibility, adapting to the folding requirements of thin paper.

[0055] Step Six: Drying and Paper Output. All drying cylinder temperatures are uniformly set to 108°C, and the moisture content is controlled at 5% to 6%.

[0056] The decorative packaging paper prepared in this embodiment has a total basis weight of 80 g / m. The paper is thin and crisp, and the gold foil embellishment and colored fiber stripes give the paper a light and delicate decorative effect. It is suitable for high-end envelopes, book wrapping paper and lightweight gift packaging.

[0057] Comparative Example 1 Decorative packaging paper was prepared using a traditional method of first making the base paper and then performing secondary processing. A base paper with a basis weight of 120 g / m² was made using a single-cage cylinder paper machine (the pulp ratio and beating conditions were the same as in Example 1). After drying and winding, the base paper was transferred to the post-processing workshop. In the post-processing workshop, the surface of the base paper was first sized using a common cationic starch sizing agent. Then, gold foil and dried flower fragments (the same amount as in Example 1, but without nano-silica coating) were spread onto the still-wet paper surface using a spreader. The paper was then sealed with a polyethylene film and finally dried.

[0058] Comparative Example 2 The multi-cage grading sizing process of this invention is adopted, but the modified sizing agent is not used. That is, in the slurry of the second cage, ordinary cationic starch is used instead of cationic starch grafted with silane coupling agent to modify the sizing agent, and the gold foil is not subjected to nano-silica surface modification treatment. The remaining steps and parameters are exactly the same as in Example 1.

[0059] Comparative Example 3 The multi-cage graded sizing process and modified sizing agent of the present invention are used, but instead of using self-crosslinking waterborne polyurethane-acrylate hybrid emulsion as the coating adhesive, ordinary polyvinyl alcohol aqueous solution (15% solid content) is used for surface coating. The remaining steps and parameters are exactly the same as in Example 1.

[0060] Comparative Example 4 A two-cage cylinder paper machine is used, omitting the surface fiber encapsulation step of the third cage. Specifically, the first cage forms the base layer (same as in Example 1), the second cage is submerged in water to implant the decorative material (same as in Example 1), and the decorative composite layer directly enters the lamination and drying processes, without undergoing the thin-layer fiber encapsulation of the third cage. All other parameters are the same as in Example 1.

[0061] The detection method is as follows: The decorative packaging papers prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to the following performance tests. Dry peel strength was tested according to GB / T 2790 standard, with a sample width of 15 mm and a peel speed of 100 mm / min. Five samples were tested in each group, and the average value was taken. Wet peel strength was tested immediately after immersing the sample in deionized water at 25°C for 30 min. Folding endurance was tested according to GB / T 457 standard with a 1 kg load applied. Gloss was tested according to GB / T 8941 standard at a 60° incident angle. Cobb water absorption was tested according to GB / T 1540 standard, measuring the water absorption over 60 seconds. Decorative coverage was determined by binarizing the paper surface photographs using image analysis software and then statistically analyzing the area ratio of decorative materials. The uniformity of decorative material distribution was evaluated by dividing the paper surface into 20 equal regions and calculating the coefficient of variation (CV value) of the decorative coverage in each region; a smaller CV value indicates a more uniform distribution.

[0062] The performance test data analysis is as follows: The data in the table above shows (corresponding to) Figure 6 and Figure 7 The dry peel strength of Examples 1 to 3 is greater than 2.5 N / 15 mm, and the wet peel strength is greater than 1.2 N / 15 mm, which is significantly better than the 1.1 N / 15 mm and 0.3 N / 15 mm of Comparative Example 1 (traditional secondary processing). This indicates that the chemical bridging network established by the wet sizing process of the present invention combined with the modified sizing agent can form a bonding force between the decorative material and the fiber matrix that is much stronger than that of traditional surface adhesion methods.

[0063] Comparative Example 2, without the use of modified sizing agents and metal sheet surface modification treatment, had a dry peel strength of only 1.8 N / 15 mm, a decrease of 43.8% compared to Example 1, and a wet peel strength of only 0.7 N / 15 mm, a decrease of 56.3%. This demonstrates the key role of cationic starch-grafted silane coupling agent-modified sizing agents and nano-silica surface modification treatment in improving the adhesion of decorative materials.

[0064] Comparative Example 3 used ordinary polyvinyl alcohol instead of self-crosslinking waterborne polyurethane-acrylate hybrid emulsion as the coating adhesive. Although the dry peel strength was acceptable (3.0 N / 15 mm), the folding endurance dropped sharply to 48 times (95 times in Example 1), the gloss dropped to 30 GU, and the Cobb value rose to 68 g / m. This indicates that the flexibility, gloss and water resistance of the polyvinyl alcohol coating layer are far inferior to those of the self-crosslinking hybrid emulsion coating layer.

[0065] Comparative Example 4 omitted the surface fiber encapsulation step of the third mesh cage, and the dry peel strength dropped to 2.1 N / 15 mm and the wet peel strength dropped to 0.9 N / 15 mm. This indicates that the surface fiber encapsulation layer plays an important role in covering and fixing the decorative material from above, forming an upper and lower sandwich structure with the bottom base layer, which significantly enhances the overall bonding force of the decorative layer.

[0066] Regarding the uniformity of decoration, the CV values ​​of Examples 1 to 3 were 10% to 15%, while the CV value of Comparative Example 1 was as high as 35%, indicating that the natural dispersion effect of decorative materials in the slurry flow during the flood sizing process is far superior to the uniformity of the traditional spreading method. In the traditional spreading process, decorative materials fall freely from the spreader outlet onto the paper surface. Due to airflow disturbance and differences in material shape, gold foil tends to gather in the middle of the paper surface, with significantly lower coverage in the edge areas, while dried flower fragments exhibit uneven particle size distribution due to mass differences. In contrast, in the flood sizing process, the decorative materials remain in a liquid-phase suspension state, maintaining uniform dispersion under the combined action of the circulating pump and stirring paddle. The settling process is smoother and more orderly due to the damping effect of the slurry viscosity. In addition, the cationic groups of the modified sizing agent have an electrostatic adsorption effect on the negatively charged cellulose fibers, so once the decorative materials settle to the fiber layer surface, they are quickly anchored and will not migrate secondary due to subsequent slurry flow.

[0067] In terms of production efficiency, the linear speed of Example 1 is 20 m / min, comparable to that of a conventional cylinder paper machine. Comparative Example 1, however, requires independent post-processing steps (including base paper rewinding, transfer, sizing, spreading, and lamination), resulting in an equivalent production efficiency of only 8 m / min. From an energy consumption perspective, the integrated process of this invention requires only one drying cycle, while the traditional process requires drying for both the base paper and the decorative layer, reducing overall energy consumption by approximately 30%. From a scrap rate perspective, the integrated process eliminates the risk of paper surface damage during base paper transfer and the alignment deviation problem in the lamination process, reducing the scrap rate from 8% to 12% in the traditional process to 2% to 4%.

[0068] It is worth noting that in Example 2, a large amount of dried flower fragments were used as the main decorative material, and its dry peel strength (3.5 N / 15 mm) and wet peel strength (1.8 N / 15 mm) were the highest among all examples. This result is not accidental, because the dried flower plant fragments themselves contain abundant cellulose and hemicellulose components, which have strong hydrogen bonds and van der Waals forces interacting with the cationic starch backbone in the modified sizing agent and the cellulose in the base fiber layer, forming a multi-synergistic anchoring system of plant fragments-sizing agent-fiber. In the lightweight scheme of Example 3, although the amount of decorative material used is smaller, its peel strength (2.8 N / 15 mm dry, 1.3 N / 15 mm wet) is still higher than all comparative examples, proving the universal effectiveness of the technical solution of the present invention under different quantitative specifications.

[0069] The technical solution of this invention achieves efficient integrated production of decorative packaging paper through the synergistic combination of multi-cage graded sizing process design and special functional materials. Its core mechanism includes the following synergistic effects at multiple levels.

[0070] At the macroscopic process level, the three mesh cages respectively undertake differentiated functions of substrate forming, decorative implantation, and surface encapsulation, forming a sandwich structure of bottom support - middle decoration - top encapsulation. The conventional sizing process of the first mesh cage provides a substrate fiber network with a certain porosity and wet strength. The pore structure of this network provides physical anchoring points for the subsequent embedding of decorative materials. The flooded sizing process of the second mesh cage allows the decorative material to be uniformly dispersed in a suspended state in a low-concentration slurry, and naturally settles to the surface of the substrate layer under the synergistic effect of gravity and slurry circulation. The edges of some decorative materials are embedded in the fiber gaps of the substrate layer to form physical interlocking. The thin-layer fiber encapsulation of the third mesh cage covers the decorative material from above, forming a physical constraint structure of upper and lower clamping together with the substrate layer. The coating adhesive layer further provides continuous polymer film encapsulation protection.

[0071] At the molecular chemistry level, such as Figure 3 As shown, the cationic starch backbone in the modified sizing agent provides electrostatic adsorption and hydrogen bonding with cellulose fibers, while the grafted silane coupling agent side groups form covalent bonds with the nano-silica coating layer on the metal sheet surface through a Si-O-Si condensation reaction. This multi-level chemical bridging chain of fiber-starch-siloxane-silica-metal upgrades traditional physical adhesion to chemical bonding, which is the fundamental reason for the significant improvement in the adhesion of the decorative layer. For dried flower plant fragments, since plant tissues are rich in cellulose and hemicellulose, the cationic starch backbone of the modified sizing agent can directly form hydrogen bonds and van der Waals forces with the cellulose on the surface of the plant fragments, and the silane side groups provide additional Si-OC covalent bond anchoring. Therefore, the plant fragments can achieve good adhesion without surface modification.

[0072] At the coating layer level, such as Figure 5 As shown, the self-crosslinking waterborne polyurethane-acrylate hybrid emulsion undergoes a ketone-hydrazide crosslinking reaction of diacetone acrylamide and adipate dihydrazide during film formation, forming a dense three-dimensional crosslinked network. The polyurethane segments provide excellent flexibility and adhesion to irregular surfaces, while the acrylate segments provide hardness and gloss. The ketone-hydrazide crosslinking imparts excellent water and solvent resistance to the coating layer. This microstructure, with its separation of soft and hard segments, allows the coating layer to tightly encapsulate paper surfaces containing raised decorative materials without edge curling or bubbles, while maintaining high gloss and good waterproof performance.

[0073] The synergistic effect of the above-mentioned macroscopic process structure design, mesoscopic material function matching and microscopic molecular chemical bonding has achieved deep integration and long-lasting stability of decorative materials and paper base, giving the decorative packaging paper products of the present invention the comprehensive advantages of realistic three-dimensional texture, high decorative layer adhesion and excellent surface performance.

[0074] Furthermore, from a fluid dynamics perspective, the flow state of the slurry in the flooded slurry tank has a decisive influence on the dispersion and settling behavior of the decorative materials. When the stirring speed is 50 to 100 r / min, the slurry is in the laminar-transitional flow range (Reynolds number approximately 500 to 2000). This flow state can maintain the suspension and dispersion of the decorative materials without causing the breakage of brittle decorative materials (such as dried flower fragments) due to excessive turbulence. Simultaneously, the slow circulation generated by the circulating pump creates a stable velocity field distribution for the slurry in the flooded tank, ensuring the uniformity of the supply of decorative materials across the entire width. Metal sheets have a relatively high density (gold foil density is approximately 19.3 g / cm³). 3 The density of silver foil is approximately 10.5 g / cm³. 3 The settling rate of the metal sheet in the slurry can be precisely controlled by adjusting the slurry concentration and stirring speed, ensuring that the amount of metal sheet deposited on the substrate fiber layer is within the design target range.

[0075] From a microscopic morphological perspective, the self-crosslinking waterborne polyurethane-acrylate hybrid emulsion undergoes three stages during film formation: emulsion particle stacking, interparticle fusion, and polymer chain diffusion. In the initial drying stage, as moisture evaporates, the emulsion particles tightly arrange themselves to form an ordered stacked structure. When the temperature rises above the polymer's glass transition temperature, the particle interfaces begin to fuse, and polymer chains interdiffusion occurs, forming a continuous polymer film. Simultaneously, the ketone carbonyl group of diacetone acrylamide and the hydrazide group of adipic acid dihydrazide can undergo crosslinking reactions within the range of room temperature to drying temperature, without the need for external catalysts or high-temperature curing conditions. This characteristic allows the film-coating crosslinking process to be completed online synchronously with the paper-making drying process, further demonstrating the design advantages of the integrated process of this invention. The crosslinked film layer forms a microphase separation structure with alternating distributions of a flexible phase enriched in polyurethane soft segments and a rigid phase enriched in acrylate hard segments. This unique micromorphology endows the film layer with both flexible adhesion and surface hardness.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. An integrated production method for decorative packaging paper based on multi-mesh cage grading and sizing, characterized in that, Includes the following steps: Step 1, base layer forming: Mix softwood pulp and hardwood pulp at a mass ratio of 6:4 to 7:3 to prepare base slurry. The base slurry is beaten to a freeness of 35 to 45°SR and adjusted to a mass ratio of slurry to water of 2:

8. It is then fed into the mesh groove of the first mesh cage for slurry forming to form the base fiber layer. Step 2, Wet Implantation of Decorative Materials: The mesh groove of the second mesh cage is modified into a flooded sizing tank. A decorative slurry is prepared, comprising surface-modified decorative materials and modified sizing agents. The decorative materials are selected from one or more of dried flower and plant fragments, gold foil, silver foil, and colored fiber filaments. The modified sizing agent is a cationic starch-grafted silane coupling agent modifier. The decorative slurry is added to the flooded slurry tank, and the concentration of the flooded slurry is controlled at 0.3% to 0.8%. The base fiber layer is then flooded through the slurry tank for sizing. During the flooding process, the decorative materials are uniformly deposited and embedded into the upper surface of the base fiber layer, forming a decorative composite layer. Step 3, Surface Coating and Encapsulation: Sizing is performed in the third mesh cage at a slurry-to-water mass ratio of 2:5 to form a surface fiber encapsulation layer. Simultaneously, a coating and sizing device is installed at the outlet of the third mesh cage to uniformly coat the surface fiber encapsulation layer with a self-crosslinking waterborne polyurethane-acrylate hybrid emulsion, forming a protective coating layer. Step 4, drying and paper output: The paper web processed in step 3 is sent to the multi-cylinder drying section and dried at 105 to 120°C until the moisture content is 5% to 8%, to obtain the finished decorative packaging paper.

2. The method according to claim 1, characterized in that, The modified sizing agent is prepared by: gelatinizing cationic starch at 75 to 85°C for 30 to 45 min, cooling it to 55 to 65°C, adding γ-aminopropyltriethoxysilane accounting for 3% to 8% of the dry weight of cationic starch, and reacting under stirring conditions for 2 to 3 h to obtain the cationic starch grafted silane coupling agent modified sizing agent.

3. The method according to claim 1, characterized in that, The gold or silver foil in the decorative material is modified with nano-silica surface treatment, specifically by immersing the gold or silver foil in an ethanol solution containing tetraethyl orthosilicate and ammonia, and stirring at 30 to 40°C for 4 to 6 hours to form a nano-silica coating layer with a thickness of 50 to 200 nm on the surface of the metal sheet.

4. The method according to claim 1, characterized in that, The self-crosslinking waterborne polyurethane-acrylate hybrid emulsion is prepared by using isophorone diisocyanate and polytetrahydrofuran diol as raw materials to prepare a polyurethane prepolymer, which is then neutralized and dispersed before being emulsion polymerized with an acrylate monomer containing diacetone acrylamide, and then adipic acid dihydrazide is added as a crosslinking agent. The solid content of the hybrid emulsion is 35% to 45%.

5. The method according to claim 1, characterized in that, The quantitative measurement of the basal fiber layer in step one is 45 to 80 g / m³. 2 In step three, the quantitative amount of the surface fiber encapsulation layer is 10 to 30 g / m³. 2 .

6. The method according to claim 1, characterized in that, In step three, the film coating and adhesive application device is a roller coating device, with a coating amount of 8 to 20 g / m². 2 .

7. The method according to claim 1, characterized in that, In step two, a slurry circulation pump and a stirring paddle are installed in the flooded slurry tank, and the stirring speed is 50 to 100 r / min.

8. The method according to claim 1, characterized in that, The total amount of decorative materials in the decorative slurry is 5% to 25% of the oven-dry fiber mass of the base slurry, of which gold or silver foil accounts for 10% to 40% of the total amount of decorative materials, dried flower and plant fragments account for 20% to 60%, and colored fiber filaments account for 10% to 30%.

9. The method according to claim 1, characterized in that, In step four, the multi-cylinder drying section includes three temperature zones: a front section, a middle section, and a rear section. The temperature of the front section is 105 to 108°C, the temperature of the middle section is 110 to 120°C, and the temperature of the rear section is 105 to 112°C.

10. The method according to claim 1, characterized in that, The total basis weight of the finished decorative packaging paper is 80 to 200 g / m³. 2 Dry peel strength greater than 2.5 N / 15 mm, wet peel strength greater than 1.2 N / 15 mm, Cobb water absorption value less than 30 g / m³ 2 It has a folding endurance of more than 80 times.

Images