Double-coated copperplate paperboard capable of being contacted with food as well as preparation method and application of double-coated copperplate paperboard

Abstract

The invention belongs to the technical field of papermaking, and provides a double-coated copperplate paperboard capable of being in contact with food as well as a preparation method and application of the double-coated copperplate paperboard. The double-coated copperplate paperboard capable of being in contact with the food comprises a front surface coating, a front surface bottom coating, body paper, a back surface bottom coating and a back surface coating which are sequentially stacked from the front surface to the back surface, the body paper comprises a surface layer, a core layer and a bottom layer which are sequentially stacked from the front surface to the back surface, and the front surface bottom coating and the back surface bottom coating are obtained by coating a first coating; the front surface coating and the back surface coating are obtained by coating a second coating, the first coating comprises the following components: 65-grade ground calcium carbonate, first latex and a starch acrylate grafted copolymer, and the second coating comprises the following components: 95-grade ground calcium carbonate, second latex and a starch acrylate grafted copolymer. The double-coated copperplate paperboard provided by the invention has the advantages of high printing surface strength, high glossiness, low surface roughness, low two-side difference and low heavy metal content.

Description

Technical Field

[0001] The present invention relates to the technical field of papermaking, and more particularly to a food-contactable double-coated copperplate cardboard, a preparation method thereof, and an application thereof. Background Art

[0002] Coated cardboard, also known as printed coated cardboard, is made by coating the surface of base paper. As a commonly used printing paper material, it is often used as a base material for high-end printed products such as books, product nameplates, exquisite cards, playing cards, etc. It not only has the characteristics of high quantitative (quantity ≥ 200g / m 2 ), and also requires both the front and back sides to have high gloss and high surface flatness (both the front and back sides are required to meet the following requirements: gloss ≥ 60%, and surface roughness ≤ 1.40μm), and the difference in smoothness, gloss and other indicators between the front and back sides of the paper is required to be low (the difference in gloss and surface roughness of the two sides is ≤ 3%), that is, low difference between the two sides. Common coated cardboard products on the market are usually produced from recycled waste paper pulp to produce base paper, and then coated on both sides of the base paper to produce coated cardboard. It is often necessary to add fluorescent brighteners to the recycled wood pulp and coating to improve the whiteness of the product and the coating quality of both sides of the base paper, and add porcelain clay to the coating formula to improve the gloss of the product.

[0003] With the emergence of market demand for double-coated copperplate cardboard for food contact, the copperplate cardboard currently on the market is difficult to meet the requirements for food contact because the waste paper recycled pulp and fluorescent brighteners used in it do not meet the requirements for food contact. In addition, the coating mass accounts for a large proportion, and the kaolin content in the coating is high, which can easily lead to excessive heavy metal content in the finished paper. It obviously cannot meet the requirements of "GB 4806.8-2022 Food Contact Paper and Paperboard Materials and Products" (in the finished paper, arsenic is required to be ≤1.0mg / kg and lead ≤5.0mg / kg), and cannot be used as food contact materials. In addition, during the papermaking process of printed coated paper, during the dehydration and forming process of the mesh, as the paper web runs, the vacuum degree gradually changes from low to high, and the fine fibers in the pulp follow the water to transfer to the side in contact with the forming mesh, resulting in differences in flatness, smoothness, and surface roughness between the contact surface and non-contact surface of each layer of pulp and the forming mesh. The contact surface of the surface layer pulp and the forming mesh is compounded with the core layer, and the non-contact surface of the bottom layer pulp and the forming mesh is compounded with the core layer, resulting in a large difference in gloss and surface roughness between the front and back sides of the paper. The difference between the two sides is large, which will cause different acceptance and absorption of ink on both sides of the coated cardboard during the printing process, resulting in different depths of ink on both sides of the printed product and low printing quality.

[0004] Therefore, there is an urgent need to develop a double-coated copperplate cardboard that can be used for food contact, has high gloss, low surface roughness and low two-sidedness difference, and meets high printing quality requirements. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a double-coated copperplate cardboard that can be in contact with food, and its preparation method and application. The double-coated copperplate cardboard provided by the present invention has the characteristics of high printing surface strength (printing surface strength ≥1.3m / s), high gloss (front gloss reaches ≥60%, back gloss reaches ≥60%), low surface roughness (front surface roughness ≤1.40μm, back surface roughness ≤1.40μm), low two-sided difference (the difference in gloss between the front and back is ≤1%, the difference in surface roughness between the front and back is ≤0.03μm), low heavy metal content (lead content is as low as 2.1-2.2mg / kg, arsenic content is as low as 0.6-0.7mg / kg) and high safety, and meets the requirements of food contact paper (that is, it meets the national food safety standard GB 4806.8-2022 "Food contact paper and paperboard materials and products").

[0006] A first aspect of the present invention provides a food contact double-coated copperplate paperboard.

[0007] Specifically, a double-coated copperplate cardboard comprises, from the front to the back, a front topcoat layer, a front primer layer, a base paper, a back primer layer, and a back topcoat layer stacked in sequence, wherein the base paper comprises, from the front to the back, a top layer, a core layer, and a bottom layer stacked in sequence, wherein the front primer layer and the back primer layer are coated with a first coating, and the front topcoat layer and the back topcoat layer are coated with a second coating;

[0008] The first coating comprises the following components: 65-grade ground calcium carbonate, a first latex, and a starch acrylate graft copolymer;

[0009] The second coating comprises the following components: 95-grade ground calcium carbonate, a second latex, and a starch acrylate graft copolymer.

[0010] The two-side difference mentioned in the present invention refers to the difference in properties between the front and back sides of paper, mainly including the difference in smoothness and glossiness.

[0011] The present invention adds a starch acrylate graft copolymer to both the first and second coatings, i.e., both the front and back coatings contain the starch acrylate graft copolymer. The starch acrylate graft copolymer has good water absorption, swells to form a gel after absorbing water, and is not easily dehydrated under external forces. During the coating dispersion process, the hydrophilic carboxyl and hydroxyl groups in the starch acrylate graft copolymer can form hydrogen bonds with water molecules. The starch chain structure in the starch acrylate graft copolymer has many spaces that can accommodate water molecules, and the presence of osmotic pressure allows it to absorb a large amount of water. During the coating process, water is not easily migrated out of the coating, reducing the evaporation rate of the coating water and effectively improving the water retention of the coating. In addition, hydrogen bonding between the starch acrylate graft copolymer and the various components in the coating reduces the evaporation rate of water, which also helps to improve the water retention of the coating. The high water retention allows the coating to remain moist for a long time after application, slowly releasing water, improving the leveling and permeability of the coating, thereby improving the gloss and smoothness of the coating. At the same time, due to the repulsive effect of ions, the polymer expands and the structure stretches. The swollen and hydrated high molecular polymer occupies the space of the solution, and the hydrophobic groups on the polymer associate with each other, which increases the viscosity. In addition, the starch acrylate graft copolymer has a high affinity for calcium carbonate particles. Its polar functional groups are attracted by the polar surface of the pigment (the pigment of the present invention refers to inorganic mineral pigment particles such as china clay and calcium carbonate in the coating, which can usually improve the whiteness of paper and cover the fiber base color). They are combined together by a bridging mechanism, so that the entire system has a high degree of cross-linking, which associates to form a strong network structure, which helps the pigment particles to stick to each other. As the coating wetting, penetration, bonding and curing process on the surface of the base paper fiber, the combination between the particles gradually becomes tighter, thereby enhancing the strength of the coating. The general paper coating amount is about 30g / m 2 The coating amount of conventionally produced coated cardboard (the sum of the total coating amount on the front and the total coating amount on the back) is as high as about 60g / m 2, and the present invention can effectively improve the printing surface strength and reduce the coating powder shedding phenomenon under the high coating amount requirements of coated paper. Therefore, the use of starch acrylate graft copolymer solves the problem of low coating strength caused by large coating amount. In addition, the acrylic polymer component in the starch acrylate graft copolymer has high thermoplasticity and can well adapt to calendering treatment. After calendering, the roughness and microscopic flatness of the coating are excellently improved, which is conducive to improving the gloss and smoothness of the finished paper. Therefore, the present invention utilizes starch acrylate graft copolymer to achieve the effect of improving the water retention, glossiness and printing surface strength of the coating. 95 grade ground calcium carbonate is also added to the second coating of the present invention. When the second coating contacts the base paper, the largest pigment particles and particles close to the boundary layer are first fixed to the boundary layer between the coating and the base paper. Liquid and smaller particles may still move in the porous network composed of fixed particles. As the coating dries, the smaller particles fill the porous network structure and simultaneously form a dense particle layer on the coating surface, improving the glossiness. The front primer layer and the back primer layer of the present invention are both coated with the first coating, and the front topcoat layer and the back topcoat layer are both coated with the second coating, thereby further reducing the difference between the two sides of the paper and making the glossiness and roughness of the two sides closer.

[0012] Preferably, the base paper comprises a surface sizing layer, a surface layer, a core layer, a bottom layer and a surface sizing layer of the bottom layer which are stacked in sequence from the front side to the back side.

[0013] Preferably, the food contact double-coated copper plate cardboard has a basis weight of ≥200g / m 2 .

[0014] More preferably, the food contactable double-coated copper plate paper has a basis weight of 300-400 g / m 2 .

[0015] More preferably, the basis weight of the food contact double-coated copper plate cardboard is 345-355g / m 2 .

[0016] Preferably, the first coating comprises the following components in parts by weight: 100 parts of 65-grade ground calcium carbonate, 10-20 parts of the first latex, and 0.1-2 parts of the starch acrylate graft copolymer.

[0017] Further preferably, the first coating comprises the following components in parts by weight: 100 parts of 65-grade ground calcium carbonate, 10-15 parts of the first latex, and 0.1-1 part of the starch acrylate graft copolymer.

[0018] More preferably, the first coating comprises the following components in parts by weight: 100 parts of 65-grade ground calcium carbonate, 12-14 parts of the first latex, and 0.1-0.6 parts of the starch acrylate graft copolymer.

[0019] Preferably, the second coating comprises the following components in parts by weight: 50-80 parts of 95-grade ground calcium carbonate, 10-20 parts of the second latex, and 0.1-2 parts of the starch acrylate graft copolymer.

[0020] Further preferably, the second coating comprises the following components in parts by weight: 60-80 parts of 95-grade ground calcium carbonate, 15-20 parts of the second latex, and 0.5-2 parts of starch acrylate graft copolymer.

[0021] More preferably, the second coating comprises the following components in parts by weight: 70-75 parts of 95-grade ground calcium carbonate, 17-20 parts of the second latex, and 0.5-1.5 parts of starch acrylate graft copolymer.

[0022] Preferably, the second coating further comprises grade 99 calcium carbonate.

[0023] Preferably, the second coating further comprises 20-50 parts by weight of 99 grade ground calcium carbonate.

[0024] Further preferably, the second coating further comprises 20-40 parts by weight of 99 grade ground calcium carbonate.

[0025] More preferably, the second coating further comprises 30-40 parts by weight of 99 grade ground calcium carbonate.

[0026] The second coating of the present invention also contains grade 99 calcium carbonate. The heavy metal content of grade 99 calcium carbonate is much lower than that of china clay (the lead content in grade 99 calcium carbonate is ≤4.0 mg / kg, while the lead content in china clay is ≤70.0 mg / kg), thus solving the problem of excessive heavy metal content in the coating. Furthermore, grade 99 calcium carbonate has a small particle size and a narrow particle size distribution (with a concentrated distribution of 2 μm and 1 μm particle sizes), which can provide a good stacking effect, better fill pits on the paper surface, improve the microscopic smoothness of the coating, reduce the roughness of the paper surface, and reduce the diffusion ratio of reflected light from the coating, thereby improving the glossiness and compensating for the loss of gloss due to the lack of china clay.

[0027] Preferably, the ISO whiteness of the grade 65 ground calcium carbonate is 93%-95%, and / or the particles of the grade 65 ground calcium carbonate having a particle size less than 2 μm account for 60-65%.

[0028] Preferably, the ISO whiteness of the 95-grade ground calcium carbonate is 92%-94%, and / or the particles of the 95-grade ground calcium carbonate have a particle size of less than 2 μm accounting for 93-96%, and / or the particles of the 95-grade ground calcium carbonate have a particle size of less than 1 μm accounting for 72-76%.

[0029] Preferably, the ISO whiteness of the 99-grade ground calcium carbonate is 91%-93%, and / or the particles of the 99-grade ground calcium carbonate with a particle size of less than 2 μm account for 97-99.5%, and / or the particles of the 99-grade ground calcium carbonate with a particle size of less than 1 μm account for 82-84%.

[0030] Preferably, the first coating further comprises an additive I, and / or the second coating further comprises an additive II, and / or the additives I and II are independently selected from at least one of a dispersant, a water repellent, a lubricant, and a rheological agent.

[0031] Preferably, the auxiliary agent I comprises the following components in parts by weight: 0.05-0.2 parts of dispersant, 0.5-1.0 parts of water repellent, 0.5-1.5 parts of lubricant, and 0.15-0.5 parts of rheological agent.

[0032] Preferably, the auxiliary agent II includes the following components in parts by weight: 0.1-0.25 parts of a dispersant, 0.5-1.0 parts of a water repellent, 1.0-2.0 parts of a lubricant, and 0.15-0.5 parts of a rheological agent.

[0033] Preferably, the first latex is styrene-butadiene latex and / or styrene-acrylate latex, and / or the second latex is styrene-butadiene latex and / or styrene-acrylate latex.

[0034] Preferably, the dispersant is at least one of sodium polycarboxylate dispersant, polyacrylate, and polyphosphate.

[0035] Preferably, the water repellent is a zirconium carbonate salt water repellent and / or a polyamide polyurea water repellent.

[0036] Preferably, the lubricant is calcium stearate lubricant and / or polyoxyethylene wax.

[0037] Preferably, the rheological agent is a modified carboxylic acid terpolymer rheological agent and / or polyacrylate.

[0038] Preferably, the viscosity of the first coating at 35° C. is 1500-1800 cps, and / or the solids content of the first coating is 67-70%, and / or the viscosity of the second coating at 35° C. is 1500-1800 cps, and / or the solids content of the second coating is 67-70%. Solids content refers to the weight percentage of solid components contained in a substance.

[0039] Preferably, the raw materials for preparing the surface layer include: bleached softwood kraft pulp and bleached hardwood kraft pulp.

[0040] Further preferably, the raw materials for preparing the surface layer include, by weight percentage, 10%-30% bleached softwood kraft pulp and 70%-90% bleached hardwood kraft pulp.

[0041] Preferably, the raw materials for preparing the core layer include: bleached chemical thermomechanical pulp, bleached hardwood kraft pulp and bleached softwood kraft pulp.

[0042] Further preferably, the raw materials for preparing the core layer include, by weight percentage: 30%-50% bleached chemical thermomechanical pulp, 20%-40% bleached hardwood kraft pulp, and 10%-30% bleached softwood kraft pulp.

[0043] Preferably, the raw materials for preparing the core layer further include process recycled paper (process recycled paper refers to broken paper generated during the production process, including trimmed paper webs, broken paper obtained by recycling unqualified products, etc.).

[0044] Further preferably, the raw materials for preparing the core layer further comprise 10%-30% of recycled paper according to weight percentage.

[0045] Preferably, the raw materials for preparing the bottom layer include: bleached softwood kraft pulp and bleached hardwood kraft pulp.

[0046] Further preferably, the raw materials for preparing the bottom layer include, by weight percentage, 10%-30% bleached softwood kraft pulp and 70%-90% bleached hardwood kraft pulp.

[0047] Preferably, the ISO brightness of the bleached softwood kraft pulp is 88-90%, and / or the ISO brightness of the bleached hardwood kraft pulp is 90-92%, and / or the ISO brightness of the bleached chemithermomechanical pulp is 78-80%, and / or the ISO brightness of the process recycled paper is 84-86%.

[0048] Preferably, the wood pulp raw materials (i.e., white softwood kraft pulp, bleached hardwood kraft pulp, or bleached chemical thermomechanical pulp) used for the surface layer, core layer, and bottom layer are all 100% water-refined pulp. The present invention uses 100% water-refined pulp as the raw material, and no alkali is added during the pulping process to avoid a decrease in the whiteness of the raw materials during production. The addition of fluorescent brighteners during the pulping process also avoids the use of recycled waste paper pulp with high heavy metal content and uncontrollable microorganisms, thereby reducing food safety risks and improving the safety of the paper products of the present invention.

[0049] Preferably, the starch acrylate graft copolymer is prepared by a preparation method comprising the following steps: preparing starch glue using starch, then mixing the starch glue, emulsifier, initiator, crosslinking agent and acrylate monomer, and preparing the starch acrylate graft copolymer through free radical emulsion polymerization.

[0050] Preferably, the method for preparing the starch glue comprises the following steps: mixing starch and water, and cooking at 90-100° C. to obtain the starch glue.

[0051] Preferably, the starch is at least one of tapioca starch, corn starch and wheat starch.

[0052] Preferably, the temperature of the free radical emulsion polymerization reaction is 70-90° C., and / or the time of the free radical emulsion polymerization reaction is 3-8 hours.

[0053] Preferably, the raw materials of the starch acrylate graft copolymer include, by weight, 100 parts of starch, 5-10 parts of emulsifier, 2-3 parts of initiator, 1-3 parts of cross-linking agent and 35-40 parts of acrylate monomer.

[0054] Preferably, the acrylic acid ester monomer is at least one of acrylic acid, methacrylic acid, and methyl methacrylate.

[0055] More preferably, the acrylic acid ester monomers are acrylic acid, methacrylic acid and methyl methacrylate.

[0056] More preferably, the weight ratio of acrylic acid, methacrylic acid and methyl methacrylate is 0.5-1.5:0.5-1.5:0.5-1.5.

[0057] More preferably, the weight ratio of acrylic acid, methacrylic acid and methyl methacrylate is 1-1.5:1-1.5:1-1.5.

[0058] More preferably, the weight ratio of acrylic acid, methacrylic acid and methyl methacrylate is 1:1:1.

[0059] Preferably, the emulsifier is sodium lauryl sulfate and / or polyvinyl alcohol.

[0060] Preferably, the initiator is at least one of ammonium persulfate, potassium persulfate, and sodium thiosulfate.

[0061] Preferably, the cross-linking agent is N,N-methylenebisacrylamide and / or N-hydroxymethylacrylamide.

[0062] A second aspect of the present invention provides a method for preparing food-contact double-coated copperplate cardboard.

[0063] A method for preparing food-contact double-coated copperplate cardboard comprises the following steps:

[0064] (1) respectively mixing the raw materials for the surface layer, the core layer, and the bottom layer to obtain surface layer slurry, core layer slurry, and bottom layer slurry, respectively; and respectively shaping the surface layer slurry, the core layer slurry, and the bottom layer slurry to obtain the surface layer, the core layer, and the bottom layer;

[0065] (2) compounding the surface layer, the core layer, and the bottom layer in the order of surface layer, core layer, and bottom layer from the front to the back to obtain a wet paper sheet;

[0066] (3) sizing and drying the wet paper sheet to obtain base paper, and then sequentially hard calendering, coating, and soft calendering the base paper to obtain the double-coated copperplate cardboard;

[0067] In step (3), the coating is performed by sequentially applying a first coating and a second coating on the front side of the base paper, respectively, to obtain a front primer and a front topcoat, and by sequentially applying a first coating and a second coating on the back side of the base paper, respectively, to obtain a back primer and a back topcoat.

[0068] Preferably, in step (1), before forming, the surface layer slurry, the core layer slurry and the bottom layer slurry are respectively crushed, ground, mixed, screened and deslagging, and then enter the triple mesh forming to obtain the surface layer, core layer and bottom layer respectively.

[0069] Preferably, in step (3), the drying includes pre-drying and post-drying.

[0070] Further preferably, in step (3), the wet paper sheet is sequentially subjected to pressing, pre-drying, surface sizing and post-drying to obtain base paper.

[0071] Preferably, in step (3), the coating amount of the front primer layer is 14-15 g / m 2 , and / or, the coating amount of the front surface coating is 14-15g / m 2 , and / or, the coating amount of the back primer layer is 16-17g / m 2 , and / or, the coating amount of the back surface coating is 16-17g / m 2 , and / or, the total coating amount of the front side of the double-coated copper plate cardboard is 28-30g / m 2 , and / or, the total coating amount on the back of the double-coated copper plate cardboard is 32-34g / m 2 The total coating amount on the front side is the sum of the coating amounts of the front primer and the front topcoat, and the total coating amount on the back side is the sum of the coating amounts of the back primer and the back topcoat.

[0072] Preferably, in step (3), the temperature of the hot roller for hard calendering is 150-180° C., and / or the linear pressure of the hard calendering is 30-50 kN / m.

[0073] The present invention controls the pressure and temperature of hard calendering to perform a strong pressurization treatment on the surface of the base paper, so that the thickness between the base paper fiber layers is adjusted, the density and strength of the paper are increased, and at the same time, the protrusions and irregular parts of the surface are trimmed, the smoothness of the paper surface is improved, the cross-section thickness difference is reduced, the flatness of the paper surface is optimized, and the uniformity of the paper surface coating in the subsequent stage is improved, so that the surface flatness and thickness uniformity of the base paper can be improved.

[0074] Preferably, in step (3), the number of soft calendering is 2 times, including the first soft calendering and the second soft calendering in sequence, the upper roller of the first soft calendering is a hot roller, and / or, the lower roller of the first soft calendering is a soft roller, and / or, the temperature of the hot roller of the first soft calendering is 150-180°C, and / or, the pressure of the first soft calendering is 30-50 kN / m, and / or, the lower roller of the second soft calendering is a hot roller, and / or, the upper roller of the second soft calendering is a soft roller, and / or, the temperature of the hot roller of the second soft calendering is 150-180°C, and / or, the pressure of the second soft calendering is 50-70 kN / m.

[0075] The first soft calendering is mainly to improve the gloss and smoothness of the front side; the second soft calendering is mainly to improve the gloss and smoothness of the back side. The two soft calenderings are helpful to reduce the difference between the two sides of the paper.

[0076] The present invention cleverly solves the problem of large difference in coating effect between the front and back sides of coated cardboard by setting different total coating amounts on the front and back sides and adjusting the temperature and pressure of the first soft calendering and the second soft calendering, thereby reducing the difference between the two sides.

[0077] Preferably, in step (3), after the soft calendering is completed, the temperature is lowered to 40-50° C. and then coiled.

[0078] A third aspect of the present invention provides an application of food contact double-coated copperplate cardboard.

[0079] The invention discloses an application of food contact double-coated copperplate cardboard in the preparation of packaging materials, decorative materials or printing materials.

[0080] A fourth aspect of the present invention provides a food packaging material.

[0081] A food packaging material is made from the double-coated copperplate cardboard.

[0082] Compared with the prior art, the present invention has the following beneficial effects:

[0083] The food-contact double-coated copperplate cardboard provided by the present invention comprises, from the front to the back, a front topcoat layer, a front basecoat layer, base paper, a back basecoat layer, and a back topcoat layer which are sequentially stacked. The base paper comprises, from the front to the back, a top layer, a core layer, and a bottom layer which are sequentially stacked. The front basecoat layer and the back basecoat layer are obtained by coating with a first coating, and the front topcoat layer and the back topcoat layer are obtained by coating with a second coating, wherein the first coating layer comprises the following components: 65-grade ground calcium carbonate, a first latex, and a starch acrylate graft copolymer; and the second coating layer comprises the following components: 95-grade ground calcium carbonate, a second latex, and a starch acrylate graft copolymer. The present invention adds a starch acrylate graft copolymer to a first coating and a second coating, so that the graft copolymer forms a strong network structure in the coating system, reducing the migration of the starch acrylate graft copolymer in the wet coating. The starch acrylate graft copolymer forms a thin film upon drying, reducing the air permeability of the finished paper surface. At the same time, the formed thin film is insensitive to moisture and is not prone to swelling due to water absorption, thereby having little effect on the smoothness and glossiness of the coating. The double-coated copperplate cardboard provided by the present invention has the advantages of high printing surface strength (printing surface strength as high as 1.4-1.7 m / s), high gloss (front gloss reaches 60-65%, back gloss reaches 60-64%), low surface roughness (front surface roughness 0.98-1.22 μm, back surface roughness 0.99-1.21 μm), and low two-sidedness difference (the difference in gloss between the front and back is ≤1%, and the difference in surface roughness between the front and back is ≤0.03 μm). Moreover, the raw materials selected in the present invention are of safe origin and have a low heavy metal content. The whiteness of the product is improved by optimizing the production process, and no fluorescent whitening agent is added. The present invention meets the requirements of the national food safety standard GB 4806.8-2022 "Food Contact Paper and Paperboard Materials and Products" (the lead content is as low as 2.1-2.2 mg / kg, and the arsenic content is as low as 0.6-0.7 mg / kg), and can be used to prepare food contact paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 This is a schematic structural diagram of the double-coated copper plate cardboard prepared in Example 1 of the present invention;

[0085] Figure 2 This is a production process flow chart of the double-coated copperplate cardboard of Example 1 of the present invention. DETAILED DESCRIPTION

[0086] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0087] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0088] The main raw materials used in the examples and comparative examples of the present invention are as follows:

[0089] Starch acrylate graft copolymer: 100 parts of cassava starch and water were used to prepare a starch solution with a solute mass percentage of 20%. The solution was cooked and gelatinized at 95°C to obtain a starch glue. A free radical emulsion polymerization method was then used to add 5 parts of sodium lauryl sulfate (emulsifier), 3 parts of ammonium persulfate (initiator), and 3 parts of N,N-methylenebisacrylamide (cross-linker). 35 parts of an acrylate monomer (acrylic acid, methacrylic acid, and methyl methacrylate in a weight ratio of 1:1:1) were added dropwise at a constant pressure to the starch glue to allow polymerization to proceed. The product was reacted at 80°C with stirring at 300 rpm for 5 hours to obtain a product, designated as starch acrylate graft copolymer A.

[0090] Grade 65 ground calcium carbonate: ISO whiteness is 93.9%, and particles with a size of less than 2μm account for 63.5%.

[0091] Grade 95 ground calcium carbonate: ISO whiteness is 93.7%, and particles with a size less than 2μm account for 94.2%.

[0092] Grade 99 ground calcium carbonate: ISO whiteness is 92%, particles with a size of less than 2μm account for 99%, and particles with a size of less than 1μm account for 83%.

[0093] China clay: ISO whiteness is 89.2%, particles with a particle size of less than 2μm account for 98.6%, and particles with a particle size of less than 1μm account for 94.7%.

[0094] Bleached softwood kraft pulp: ISO brightness is 89.8%.

[0095] Bleached hardwood kraft pulp: ISO brightness is 91.6%.

[0096] Bleached chemical thermomechanical pulp: ISO brightness is 79.5%.

[0097] Process return paper (broken paper): ISO brightness is 85.2%.

[0098] Example 1

[0099] A double-coated copperplate cardboard, which comprises, from the front to the back, a front topcoat, a front basecoat, a top surface sizing layer, base paper, a bottom surface sizing layer, a back basecoat, and a back topcoat which are stacked in sequence; the base paper comprises, from the front to the back, a top layer, a core layer, and a bottom layer which are stacked in sequence; the front basecoat and the back basecoat are obtained by coating with a first coating, and the front topcoat and the back topcoat are obtained by coating with a second coating.

[0100] The preparation method of the above-mentioned double-coated copper plate cardboard that can contact food (such as Figure 2 ), including the following steps:

[0101] 1. Preparation of surface pulp: The raw materials include 30wt% bleached softwood kraft pulp and 70wt% bleached hardwood kraft pulp. After being crushed with clean water and beaten in a disc mill, the pulp is mixed and screened in the flow section to remove slag. The pulp is then evenly sprayed onto the surface screen through the headbox to form the surface layer. The surface layer weight is 36g / m 2 .

[0102] 2. Preparation of core layer pulp: The raw materials include 50wt% bleached chemical thermomechanical pulp, 20wt% bleached hardwood kraft pulp, 10wt% bleached softwood kraft pulp and 20wt% recycled paper. After shredding and beating in a disc mill, the pulp is mixed and screened in the flow section to remove slag. The pulp is then evenly sprayed onto the core mesh through the headbox to form the core layer. The basis weight of the core layer is 198g / m 2 .

[0103] 3. Preparation of bottom stock: The raw materials include 30wt% bleached softwood kraft pulp and 70wt% bleached hardwood kraft pulp. After water pulping and disc grinding, the pulp is mixed and screened in the flow section to remove slag. The pulp is then evenly sprayed onto the bottom screen through the headbox to form the bottom stock. The base weight is 44g / m 2 .

[0104] 4. Preparation of base paper: The three layers of paper web, namely the face, core and bottom, are compounded to produce a wet paper sheet with the face, core and bottom layers. The wet paper sheet is pressed, pre-dried, surface sizing and post-dried to obtain base paper. The surface sizing is applied using a double-roller film transfer sizing machine to evenly spread the glue on the paper surface. The solid content of the surface layer feeding trough is 15%, and the surface sizing amount is 3.0g / m 2 The solid content of the bottom feed trough is 15%, and the glue amount of the bottom surface is 3.0g / m 2 .

[0105] The pressing process uses a combination of double shoe presses and a single light press, which increases fiber bonding, improves paper density and strength, eliminates web marks, improves smoothness, and reduces discrepancies between the two sides. Surface sizing uses cassava surface sizing starch, which has better film-forming properties than native cassava starch, improving the smoothness of the base paper.

[0106] 5. Hard calendering

[0107] The line pressure of hard calendering is 40kN / m, the upper roller is a hot roller, the lower roller is a normal temperature roller, and the surface temperature of the hot roller is 180℃.

[0108] 6. Coating

[0109] After hard calendering, the two sides of the paper are coated twice, that is, the first coating is firstly applied to the front side and the back side of the base paper once, respectively, to obtain the front base coating and the back base coating; then the second coating is applied to the front side and the back side of the base paper twice, respectively, to obtain the front top coating and the back top coating. The total coating amount of the front base coating and the front top coating is 30g / m 2 The total coating weight of the back primer and the back top coating is 32g / m 2 The total weight of the paper is 350g / m 2 ,in:

[0110] The coating amount on the front side is 15g / m 2 , the back coating amount is 16g / m 2 The first coating, calculated by weight, includes: 100 parts grade 65 ground calcium carbonate, 14 parts styrene-butadiene latex, 0.6 parts starch acrylate graft copolymer A, 0.2 parts sodium polycarboxylate dispersant, 1.0 parts potassium zirconium carbonate water repellent, 1.0 parts calcium stearate lubricant, and 0.5 parts modified carboxylic acid terpolymer rheological agent. The first coating has a solids content of 68%, and the pH is adjusted to 9.5-10.5 using 10% sodium hydroxide solution.

[0111] Secondary coating amount on the front side: 15g / m 2 , secondary coating amount on the back side 16g / m 2 The second coating comprises, by weight, 70 parts grade 95 ground calcium carbonate, 30 parts grade 99 ground calcium carbonate, 17 parts styrene-butadiene latex, 0.6 parts starch acrylate graft copolymer A, 0.2 parts sodium polycarboxylate dispersant, 1.0 parts potassium zirconium carbonate water repellent, 1.5 parts calcium stearate lubricant, and 0.5 parts modified carboxylic acid terpolymer rheological agent. The second coating has a solids content of 67%, and the pH is adjusted to 9.5-10.5 using 10% sodium hydroxide solution.

[0112] 7. Soft calendering

[0113] The first soft calendering line pressure was 40 kN / m, the hot roller surface temperature was 180°C, and the second soft calendering line pressure was 60 kN / m. The first soft calendering line pressure was a hot roller, and the lower roller was a soft roller. The second soft calendering line pressure was a hot roller, and the upper roller was a soft roller.

[0114] 8. Coiling

[0115] After soft calendering, the paper enters the cold air box for cooling, and the paper temperature is cooled to 48°C. It is then rolled into large rolls in the winding process, which is convenient for subsequent handling and slitting.

[0116] The structure of each layer of the food contact double-coated copper plate cardboard prepared in Example 1 is as follows: Figure 1As shown, from front to back, they are the front top coating (the main components of the second coating: 95 grade calcium carbonate, 99 grade calcium carbonate and the second latex), the front primer (the main components of the first coating: 65 grade calcium carbonate and the first latex), the surface sizing layer (the main component is starch), the surface layer (the main component is fiber), the core layer (the main component is fiber), the bottom layer (the main component is fiber), the bottom layer surface sizing layer (the main component is starch), the back primer (the main components of the first coating: 65 grade calcium carbonate and the first latex) and the back top coating (the main components of the second coating: 95 grade calcium carbonate, 99 grade calcium carbonate and the second latex).

[0117] Example 2

[0118] A double-coated copperplate cardboard suitable for food contact, which differs from Example 1 in that the starch acrylate graft copolymer A in the first and second coating formulations is increased from 0.6 parts to 0.8 parts.

[0119] Example 3

[0120] A double-coated copperplate cardboard suitable for food contact, which differs from Example 1 in that the starch acrylate graft copolymer A in the first and second coating formulations is increased from 0.6 part to 1.0 part.

[0121] Example 4

[0122] A double-coated copperplate cardboard suitable for food contact, which differs from Example 1 in that the starch acrylate graft copolymer A in the first and second coating formulations is increased from 0.6 parts to 1.5 parts.

[0123] Examples 5-7

[0124] The food contactable double-coated copper plate cardboard provided in Examples 5-7 differs from that in Example 1 in that the coating amounts on the front and back sides and the linear pressures of the primary and secondary soft calendering in the preparation methods of Examples 4-6 are different, as shown in the following table:

[0125] Table 1: Coating amount on the front and back sides of Examples 5-7, and the pressure of two soft calendering lines

[0126]

[0127] Examples 8-13

[0128] Examples 8-13 provide food-contact double-coated copperplate paperboard. The difference from Example 3 is that the starch acrylate graft copolymer A in the first and second coating formulations is different. Specifically, the weight ratios of the acrylate monomers used to prepare the starch acrylate graft copolymer A are different, as shown in the following table:

[0129] Table 2 Acrylate monomers and their weight ratios of starch acrylate graft copolymers A of Examples 8-13

[0130]

[0131] Comparative Example 1

[0132] A double-coated copperplate cardboard is different from Example 1 in that 0.6 parts of starch acrylate graft copolymer in the first coating is replaced by an equal part by weight of sodium carboxymethyl cellulose.

[0133] Comparative Example 2

[0134] A double-coated copperplate cardboard is different from Example 1 in that 0.6 parts of starch acrylate graft copolymer in the second coating is replaced by an equal part by weight of sodium carboxymethyl cellulose.

[0135] Comparative Example 3

[0136] A double-coated copperplate cardboard is different from Example 1 in that 0.6 parts of starch acrylate graft copolymer in the first and second coatings are replaced by equal parts by weight of sodium carboxymethyl cellulose.

[0137] Comparative Example 4

[0138] A double-coated copperplate cardboard is different from Example 1 in that 30 parts by weight of 99-grade ground calcium carbonate in the second coating are replaced by equal parts by weight of porcelain clay.

[0139] Product effect testing

[0140] 1. Test method

[0141] Quantitative determination: GB / T 451.2-2023 Paper and paperboard - Determination of quantitative determination.

[0142] Thickness: GB / T 451.3-2023 Paper and paperboard - Determination of thickness.

[0143] Printing surface strength: GB / T 22365-2008 Paper and board — Determination of printed surface strength. Printing surface strength evaluates the bond strength between fibers, fillers, and sizing materials on the paper surface, between coating particles on the paper surface, and between the coating and the paper base. It indicates the paper's ability to resist ink splitting during the printing process. Greater printing surface strength indicates greater resistance to ink splitting.

[0144] Gloss: GB-T8941-2013 Paper and paperboard - Determination of specular gloss.

[0145] Surface roughness: GB / T 22363-2008 Paper and board — Determination of roughness (air leakage method) — Bendtsen method and printed surface method. Surface roughness is an indicator of the degree of surface roughness of paper and board. A greater surface roughness indicates a rougher surface, and a less smooth surface.

[0146] Heavy metal content: "GB 31604.49-2023 National Food Safety Standard Food Contact Materials and Articles - Determination of Multi-Elements and Determination of Multi-Element Migration".

[0147] Smoothness: GB / T 456-2002 Paper and paperboard - Determination of smoothness (Buick method).

[0148] 2. Test results

[0149] The performance test results of the double-coated copper plate cardboard prepared in Examples 5-7 are as follows:

[0150] Table 3: Conditions on both sides of double-coated copperplate paperboards of Examples 5-7

[0151]

[0152] As can be seen from the table above, when comparing Example 5 with Example 6, the front and back coating amounts of Example 5 were the same, while the front and back coating amounts of Example 6 were different. The results show that the difference between the two sides of Example 6 was significantly reduced. When comparing Example 6 with Example 7, the two soft calendering line pressures of Example 6 were the same, while the two soft calendering line pressures of Example 7 were different. The results show that the difference between the two sides of Example 7 was further reduced. This shows that the present invention significantly reduces the difference in coating effect between the front and back sides of coated cardboard by setting different total front and back coating amounts and different two soft calendering line pressures.

[0153] The performance test results of the double-coated copper plate paperboards prepared in each embodiment and comparative example are as follows:

[0154] Table 4 Performance test results of double-coated copper plate paperboard of each embodiment and comparative example

[0155]

[0156]

[0157] As can be seen from the above table, the double-coated copper plate cardboard provided by the present invention has a printing surface strength of up to 1.4-1.7 m / s, a front gloss of 60-65%, a back gloss of 60-64%, a gloss difference between the front and back sides of ≤1%, a front surface roughness of 0.98-1.22 μm, a back surface roughness of 0.98-1.21 μm, a front and back surface roughness difference of ≤0.02 μm, a heavy metal lead content as low as 2.1-2.2 mg / kg, and a heavy metal arsenic content as low as 0.6-0.7 mg / kg. This shows that the double-coated copper plate cardboard provided by the present invention has the characteristics of high printing surface strength, high gloss, low surface roughness, low two-sidedness difference, low heavy metal content, and high safety. The second coating of the present invention contains a starch acrylate graft copolymer, which utilizes a bridging mechanism to form a high degree of crosslinking in the entire coating system, forming a strong network structure by association, which helps the pigment particles to adhere to each other. As the coating wetting, penetrating, bonding and curing process on the surface of the base paper fiber, the bonding between the particles gradually becomes tighter, thereby enhancing the strength of the coating, forming a tight coating, and improving the gloss and surface roughness of both sides of the finished paper. At the same time, the acrylic polymer component has high thermoplasticity and is more adaptable to calendering than thermosetting films formed from natural products such as sodium carboxymethyl cellulose. This makes the roughness and microscopic flatness of the coating after calendering more significantly improved, further improving gloss and reducing surface roughness. In addition, the coatings applied on the front and back sides are both two layers, and the same coating is used (i.e., the front and back base coats are both applied using the first coating, and the front and back top coats are both applied using the second coating), which reduces the difference between the two sides.

[0158] Compared with Example 1, Example 2 increases the amount of starch acrylate graft copolymer from 0.6 parts to 0.8 parts, further enhancing the coating strength and improving the gloss and surface roughness on both sides of the paper. The surface strength increases to 1.5 m / s, the gloss increases to 63 / 63% on the front / back side, and the surface roughness decreases to 1.10 / 1.12 μm on the front / back side.

[0159] Compared with Example 2, Example 3 further increases the amount of starch acrylate graft copolymer to 1.0 part, further enhancing the strength of the coating and improving the gloss and surface roughness of both sides of the paper. The surface strength increases to 1.7 m / s, the gloss increases to 65 / 64% on the front / back side, and the surface roughness decreases to 0.98 / 0.99 μm on the front / back side.

[0160] Compared to Example 3, Example 4 further increased the amount of starch acrylate graft copolymer to 1.5 parts, but the overall paper-forming performance was slightly reduced. This indicates that the improvement in paper-forming performance does not necessarily increase with the amount of starch acrylate graft copolymer used. Excessive amounts can lead to overly dense crosslinking of the coating components, excessively high coating viscosity, and reduced fluidity, affecting the overall leveling of the coating and, in turn, affecting paper-forming performance.

[0161] Compared to Example 3, Examples 8-10 adjusted the types of acrylic acid ester monomers in the starch acrylate graft copolymers in the first and second coating formulations. Compared to Example 3, the printed surface strength, glossiness, and surface roughness indicators of Examples 8-13 decreased. Among them, acrylic acid monomers can improve the water solubility and dispersibility of starch, which is beneficial for the cross-linking of the starch acrylate graft copolymer and pigment particles; methacrylic acid monomers can improve the rigidity of the copolymer; and methyl methacrylate monomers can reduce the hygroscopicity of starch and improve the moisture resistance of the copolymer. Examples 11-13 adjusted the ratio of acrylic acid ester monomers in the starch acrylate graft copolymers in the first and second coating formulations. Among them, the increased amount of acrylic acid monomer in Example 11 resulted in too tight cross-linking with the pigment particles, excessively high coating viscosity, and reduced fluidity, affecting the overall leveling effect of the coating, and thus affecting the paper quality indicators. The increased amount of methacrylic acid monomer in Example 12 improved the rigidity of the overall coating, which had a better calendering and finishing effect on the coating, but had a slightly negative impact on the printed surface strength of the coating. In Example 13, the increased amount of methyl methacrylate monomer improves starch flexibility and reduces moisture absorption, but the overall calendering effect of the coating is slightly weakened. Example 3 utilizes three acrylate monomers and their specific ratios to achieve a synergistic effect, resulting in the best improvement in paper quality.

[0162] Compared to Example 1, Comparative Example 1 replaced 0.6 parts of the starch acrylate graft copolymer in the first coating with an equal weight of sodium carboxymethyl cellulose. This resulted in a decrease in both the gloss and surface roughness of the finished paper, as well as reduced printed surface strength. The surface strength dropped to 1.3 m / s, the gloss dropped to 58 / 57% on the front / back sides, and the surface roughness increased to 1.42 / 1.45 μm on the front / back sides.

[0163] Compared to Example 1, in Comparative Example 2, replacing the starch acrylate graft copolymer with an equal weight of sodium carboxymethyl cellulose in the second coating, the gloss and surface roughness of the finished paper deteriorated, and the printed surface strength also decreased. The surface strength dropped to 1.2 m / s, the gloss dropped to 56 / 56% for the front / back sides, and the surface roughness increased to 1.57 / 1.56 μm for the front / back sides.

[0164] Compared to Example 2, in Comparative Example 3, replacing the starch acrylate graft copolymer with equal parts by weight of sodium carboxymethyl cellulose in both the first and second coatings resulted in poorer gloss and surface roughness of the finished paper, as well as reduced printed surface strength. Surface strength dropped to 1.0 m / s, gloss dropped to 54 / 53% front / back, and surface roughness increased to 1.65 / 1.68 μm front / back.

[0165] Compared with Example 1, Comparative Example 4 replaced 30 parts of grade 99 ground calcium carbonate in the second coating with an equal weight of porcelain clay. Although the gloss, roughness and surface strength of the product met the requirements, the lead content increased to 3.6 mg / kg and the arsenic content increased to 1.5 mg / kg (increased by approximately 71% and 150% respectively relative to Example 1). The heavy metal content seriously exceeded the standard, did not meet food safety requirements, and could not be used as a food contact material.

[0166] As can be seen from Comparative Examples 1-3 above, the double-coated copperplate paperboard provided by the present invention uses a starch acrylate graft copolymer in the coating instead of the conventional sodium carboxymethyl cellulose. This copolymer can associate to form a strong network structure in the coating system, reducing its migration in the wet coating. Furthermore, the starch acrylate graft copolymer forms a thin film upon drying, reducing the surface air permeability of the finished paper. Furthermore, the formed film is insensitive to moisture and is less likely to swell due to water absorption, thereby improving the water retention of the coating and having a minimal impact on the smoothness and gloss of the coating. Therefore, the finished paper can achieve high gloss and low surface roughness, thereby ensuring coating quality. Furthermore, the second coating of the present invention also contains 99-grade ground calcium carbonate instead of china clay, significantly reducing the heavy metal content (the finished paper contains only 2.1-2.2 mg / kg of heavy metal lead and 0.6-0.7 mg / kg of heavy metal arsenic). Furthermore, the base paper is made of 100% wood pulp, which is more environmentally friendly and ensures the application of the double-coated copperplate paperboard in food contact paper.

Claims

1. A double-coated copperplate cardboard, characterized in that: The front side includes a front topcoat, a front basecoat, a base paper, a back basecoat, and a back topcoat, which are sequentially stacked from the front side to the back side. The base paper includes a top layer, a core layer, and a bottom layer, which are sequentially stacked from the front side to the back side. The front basecoat and the back basecoat are coated with a first coating, and the front topcoat and the back topcoat are coated with a second coating. The first coating comprises the following components: 65-grade ground calcium carbonate, a first latex, and a starch acrylate graft copolymer; The second coating comprises the following components: 95-grade ground calcium carbonate, a second latex, and a starch acrylate graft copolymer.

2. The double-coated copper plate paperboard according to claim 1, characterized in that: The first coating comprises the following components in parts by weight: 100 parts of 65-grade ground calcium carbonate, 10-20 parts of a first latex, and 0.1-2 parts of a starch acrylate graft copolymer.

3. The double-coated copper plate paperboard according to claim 1, characterized in that: The second coating comprises the following components in parts by weight: 50-80 parts of 95-grade ground calcium carbonate, 10-20 parts of a second latex, and 0.1-2 parts of a starch acrylate graft copolymer.

4. The double-coated copper plate paperboard according to claim 3, characterized in that: The second coating also includes grade 99 calcium carbonate.

5. The double-coated copper plate paperboard according to claim 4, characterized in that: The second coating further comprises 20-50 parts by weight of 99-grade ground calcium carbonate.

6. The double-coated copper plate paperboard according to claim 1, characterized in that: The first coating further includes an additive I, and / or the second coating further includes an additive II, and / or the additive I and additive II are independently selected from at least one of a dispersant, a water repellent, a lubricant, and a rheological agent.

7. The double-coated copper plate paperboard according to claim 1, characterized in that: The first latex is styrene-butadiene latex, and / or the second latex is styrene-butadiene latex.

8. The double-coated copper plate paperboard according to claim 1, characterized in that: The viscosity of the first coating at 35° C. is 1500-1800 cps, and / or the solid content of the first coating is 67-70%, and / or the viscosity of the second coating at 35° C. is 1500-1800 cps, and / or the solid content of the second coating is 67-70%.

9. The method for preparing the food contactable double-coated copper plate cardboard according to any one of claims 1 to 8, characterized in that: The steps include: (1) respectively mixing the raw materials for the surface layer, the core layer, and the bottom layer to obtain surface layer slurry, core layer slurry, and bottom layer slurry, respectively; and respectively shaping the surface layer slurry, the core layer slurry, and the bottom layer slurry to obtain the surface layer, the core layer, and the bottom layer; (2) compounding the surface layer, the core layer, and the bottom layer in the order of surface layer, core layer, and bottom layer from the front to the back to obtain a wet paper sheet; (3) sizing and drying the wet paper sheet to obtain base paper, and then sequentially hard calendering, coating, and soft calendering the base paper to obtain the double-coated copperplate cardboard; In step (3), the coating is performed by sequentially applying a first coating and a second coating on the front side of the base paper, respectively, to obtain a front primer and a front topcoat, and by sequentially applying a first coating and a second coating on the back side of the base paper, respectively, to obtain a back primer and a back topcoat.

10. The preparation method according to claim 9, characterized in that The coating amount of the front primer layer is 14-15g / m 2 , and / or, the coating amount of the front surface coating is 14-15g / m 2 , and / or, the coating amount of the back primer layer is 16-17g / m 2 , and / or, the coating amount of the back surface coating is 16-17g / m 2 , and / or, the total coating amount of the front side of the double-coated copper plate cardboard is 28-30g / m 2 , and / or, the total coating amount on the back of the double-coated copper plate cardboard is 32-34g / m 2 The total coating amount on the front side is the sum of the coating amounts of the front primer and the front topcoat, and the total coating amount on the back side is the sum of the coating amounts of the back primer and the back topcoat.

11. The preparation method according to claim 9, characterized in that The temperature of the hot roller of the hard calendering is 150-180° C., and / or the linear pressure of the hard calendering is 30-50 kN / m.

12. The preparation method according to claim 9, characterized in that The number of soft calendering is 2 times, including the first soft calendering and the second soft calendering in sequence, the upper roller of the first soft calendering is a hot roller, and / or, the lower roller of the first soft calendering is a soft roller, and / or, the temperature of the hot roller of the first soft calendering is 150-180°C, and / or, the pressure of the first soft calendering is 30-50 kN / m, and / or, the lower roller of the second soft calendering is a hot roller, and / or, the upper roller of the second soft calendering is a soft roller, and / or, the temperature of the hot roller of the second soft calendering is 150-180°C, and / or, the pressure of the second soft calendering is 50-70 kN / m.

13. Use of the double-coated copper plate paperboard according to any one of claims 1 to 8 in the preparation of packaging materials, decorative materials or printing materials.

14. A food packaging material, characterized in that: The double-coated copper plate cardboard is made from the double-coated copper plate cardboard according to any one of claims 1 to 8.

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