Laminated paper for packaging and preparation method thereof

Abstract

The invention provides a coated paper for packaging and a preparation method thereof. The coated paper comprises the following raw material components: 20-25 parts of modified corn starch citrate, 75-80 parts of alginic acid, 20-25 parts of polypropylene carbonate, 20-25 parts of polylactic acid, 1-3 parts of glycerol, 1-3 parts of polyhydroxystearic acid and 2-2.5 parts of carboxymethyl cellulose. The preparation method of the modified corn starch citrate comprises the following steps: in a reaction kettle, preparing a citric acid solution with a mass percentage of 0.8-1.2% by using distilled water, and heating the solution to 35-38 DEG C; starting stirring; adding corn starch to the citric acid solution while stirring, and reacting for 2.5-3 hours; then, adjusting the pH value of the solution in the reaction kettle to be alkaline with sodium hydroxide, cooling the solution to 26-28 DEG C, adding octenyl succinic anhydride and sodium alginate, and continuing stirring and reacting for 30-50 minutes; after the reaction, standing and filtering; drying and grinding the filtered solid to 80-100 meshes. The coated paper prepared by the invention is environmentally friendly, safe and easily degradable.

Description

Technical Field

[0001] The present invention relates to the technical field of coated paper and its production, and particularly relates to a coated paper for packaging and a preparation method thereof. Background Art

[0002] Coated paper refers to a composite material formed by coating and bonding plastic particles on the surface of paper through a casting method. Its main feature is that, by virtue of the properties of plastic particles, the paper has excellent waterproof and oil-proof properties.

[0003] With the increasing awareness of people's safety and environmental protection, recycled or degradable products in packaging are becoming more and more popular. Therefore, it is very necessary to provide a coated paper that is safe, environmentally friendly and highly degradable.

[0004] In the prior art, the invention patent with the application number 202011418161.4: a degradable food packaging laminated paper and its preparation method and application. This technology includes: taking dissolving pulp and an N-methylmorpholine-N-oxide aqueous solution, mixing and dissolving them, and then washing with water to obtain a regenerated cellulose suspension; sequentially adding citric acid ester starch, glycerol, citric acid, regenerated cellulose, defoaming agent, and dispersant into water in proportion, continuously stirring, heating to 80-90°C for dissolution and gelatinization for 30-60 minutes, diluting to a concentration of 5-10%, then feeding it into the hopper of a laminating machine, spraying it onto the surface of the base paper, and drying to obtain a degradable food packaging laminated paper. This degradable food packaging laminated paper has good waterproof performance, oil-proof performance, and physical properties, etc. Although this technology improves the waterproof, oil-proof, and physical properties of the laminated paper, its low-temperature tolerance is poor and it is not suitable for packaging materials with fresh-keeping requirements. The invention patent with the application number 201811546090.9: a photo-oxidative degradable polyethylene laminated paper and its preparation method and application. The polyethylene laminated paper of this technology includes a base paper and a laminating material. Its characteristic lies in that the laminating material includes the following components by weight percentage: 75-85% of polyethylene, 0.5-1.5% of photo-oxidative degradation masterbatch, 10-20% of water-soluble glue, 0.2-1% of degradation promoter, and 1-3% of nano-organic montmorillonite. The paper-plastic separation effect of the polyethylene laminated paper of the present invention is good, the degradation is sufficient and rapid, and the residues after degradation will not have any impact on animals, plants, and soil; and its mechanical properties are better, it is convenient for processing and use, non-toxic, green and environmentally friendly, and has high use safety. Although this technology significantly improves its mechanical properties, the degree of microbial decomposition is poor. The invention patent with the application number 202010138716.3: a fully biodegradable laminated paper and its preparation method. Among them, it is composed of a special laminating paper and a biodegradable film. The biodegradable film is laminated by a special resin for biodegradable laminated paper. The provided fully biodegradable laminated paper has a simple structure and is only composed of a special laminating paper and a biodegradable film. At the same time, the raw material of the provided biodegradable film overcomes the problem of low heat distortion temperature of PBAT, and there is no need to blend and modify with PLA, which greatly reduces the production cost and improves the production efficiency at the same time. But the product of this technology is not resistant to low temperature and its mechanical properties are not ideal.

[0005] In summary, the laminated papers of the prior art have the following technical defects: poor biodegradability, low biodegradation rate, and not resistant to low temperature. Summary of the Invention

[0006] In view of the above technical problems, the present invention provides a preparation method for a laminated paper for packaging, and aims to achieve the following invention purposes: having excellent degradability and low-temperature resistance, and being non-toxic and having high use safety.

[0007] To achieve the above invention purposes, the following technical solutions are adopted:

[0008] A preparation method of a coated paper for packaging, the specific steps are as follows:

[0009] Step 1: Prepare modified corn starch citrate

[0010] In a reaction kettle, citric acid is prepared into a citric acid solution with a mass percentage of 0.8 - 1.2% using distilled water. The prepared citric acid solution is heated to 35 - 38 °C, stirring is started, and the stirring rate is 120 - 150 rpm. While stirring, corn starch is added to the citric acid solution, and the reaction lasts for 2.5 - 3 h. Then, the pH value of the solution in the reaction kettle is adjusted to 8.2 with sodium hydroxide, the temperature is lowered to 26 - 28 °C, octenyl succinic anhydride and sodium alginate are added, and stirring and reaction continue for 30 - 50 min.

[0011] After the reaction, it is left to stand at room temperature for 16 h and filtered; the filtered solid is dried at 60 °C for 6 - 9 h and ground to 80 - 100 meshes to obtain modified corn starch citrate.

[0012] The dosages of the citric acid, corn starch, octenyl succinic anhydride, and sodium alginate, in parts by weight, are: 20 - 27 parts of citric acid, 50 - 62 parts of corn starch, 5.5 - 7.5 parts of octenyl succinic anhydride, and 0.8 - 1.2 parts of sodium alginate.

[0013] Step 2: Prepare the coating material

[0014] The coating raw materials (in parts by weight) include 20 - 25 parts of modified corn starch citrate, 75 - 80 parts of alginic acid, 20 - 25 parts of poly(propylene carbonate), 20 - 25 parts of polylactic acid, 1 - 3 parts of glycerol, 1 - 3 parts of polyhydroxystearic acid, and 2 - 2.5 parts of carboxymethyl cellulose.

[0015] Prepare the coating raw materials, place the coating raw materials in a mixer and heat and mix them, the heating temperature is 120 - 128 °C, and the heating time is 60 - 100 min to obtain the coating material.

[0016] Step 3: Select the base paper

[0017] Select bamboo pulp paper with a water content of 1% - 5% and a thickness of 30 - 100 as the base paper.

[0018] Step 4: Primary coating

[0019] Put the coating material prepared in Step 2 into the feed hopper of the coating machine, spray it onto both sides of the base paper, and the single - side coating amount is 4 - 8 g / , to obtain the primary coated paper.

[0020] Step 5: Secondary coating

[0021] Re-introduce the primary coated paper into the coating machine for secondary coating. The coating method is the same as that of the primary coating, and the single-sided coating amount is 5-10 g / , and the coated paper is obtained.

[0022] Step 6, drying and winding

[0023] Place the coated paper obtained in Step 5 in a drying oven for drying. The drying temperature is 60-90 °C, and the drying time is 3-5 min; let the dried coated paper stand still to cool and then wind it to obtain the finished product.

[0024] Adopting the above technical solutions, the present invention achieves the following beneficial effects:

[0025] 1. The coated paper prepared by the method of the present invention is easily biodegradable, with a biodegradation rate of over 84% in 45 days and a maximum biodegradation rate of over 93%.

[0026] 2. The coated paper prepared by the method of the present invention has excellent freshness preservation effect, with an oxygen transmission rate lower than 7 cm 3 / (m 2 ·24 h·0.1 MPa), and a water vapor transmission rate lower than 8 g / (m 2 ·24 h).

[0027] 3. The coated paper prepared by the method of the present invention has good grease resistance and permeability, and has good low-temperature tolerance.

[0028] 4. The coated paper prepared by the method of the present invention uses safe and environmentally friendly materials, and the finished product is easily degradable, which is suitable for market promotion and use. Specific embodiments

[0029] Example 1 A preparation method of coated paper for packaging

[0030] The specific steps are as follows:

[0031] Step 1, prepare modified corn starch citrate

[0032] In a reaction kettle, prepare a citric acid solution with a mass percentage of 1% by mixing citric acid with distilled water. Heat the prepared citric acid solution to 35 °C, start stirring, and the stirring rate is 120 rpm. While stirring, add corn starch to the citric acid solution and react for 2.5 h. Then, adjust the pH value of the solution in the reaction kettle to 8.2 with sodium hydroxide, cool down to 28 °C, add octenyl succinic anhydride and sodium alginate, and continue stirring and reacting for 50 min.

[0033] After the reaction, let it stand still at room temperature for 16 h and filter; dry the filtered solid at 60 °C for 9 h and grind it to 80 mesh to obtain modified corn starch citrate.

[0034] The dosages of the citric acid, corn starch, octenyl succinic anhydride, and sodium alginate are, by weight, as follows: 20 parts of citric acid, 50 parts of corn starch, 5.5 parts of octenyl succinic anhydride, and 1.2 parts of sodium alginate.

[0035] Step 2: Prepare the coating material

[0036] The coating raw materials, by weight, have the following composition ratio: 20 parts of modified corn starch citrate, 80 parts of alginic acid, 25 parts of poly(propylene carbonate), 20 parts of polylactic acid, 1 part of glycerol, 3 parts of polyhydroxystearic acid, and 2 parts of carboxymethyl cellulose.

[0037] Prepare the coating raw materials, place the coating raw materials in a mixer and heat and mix them. The heating temperature is 128 °C and the heating time is 60 min to obtain the coating material.

[0038] Step 3: Select the base paper

[0039] Select bamboo pulp paper with a water content of 5% and a thickness of 80 as the base paper.

[0040] Step 4: Primary coating

[0041] Put the coating material prepared in Step 2 into the feed hopper of the coater, spray it onto both sides of the base paper, and the single-sided coating amount is 6 g / to obtain the primary coated paper.

[0042] Step 5: Secondary coating

[0043] Put the primary coated paper into the coater again for secondary coating, and the single-sided coating amount is 8 g / to obtain the coated paper.

[0044] Step 6: Drying and winding

[0045] Put the coated paper obtained in Step 5 into a drying oven for drying. The drying temperature is 75 °C and the drying time is 3 min; let the dried coated paper stand for 2 h and then wind it to obtain the finished product.

[0046] Example 2 A method for preparing a coated paper for packaging

[0047] The specific steps are as follows:

[0048] Step 1: Prepare modified corn starch citrate

[0049] In a reaction kettle, citric acid is prepared into a citric acid solution with a mass percentage of 1% using distilled water. The prepared citric acid solution is heated to 36 °C, and stirring is started at a stirring rate of 120 rpm. While stirring, corn starch is added to the citric acid solution, and the reaction proceeds for 2.5 h. Then, the pH value of the solution in the reaction kettle is adjusted to 8.2 with sodium hydroxide, the temperature is lowered to 28 °C, and octenyl succinic anhydride and sodium alginate are added, and stirring and reaction continue for 30 min.

[0050] After the reaction, it is left standing at room temperature for 16 h and then filtered; the filtered solid is dried at 60 °C for 9 h and ground to 100 mesh to obtain modified corn starch citrate.

[0051] The dosages of the citric acid, corn starch, octenyl succinic anhydride, and sodium alginate are, by weight: 24 parts of citric acid, 60 parts of corn starch, 7.5 parts of octenyl succinic anhydride, and 0.8 part of sodium alginate.

[0052] Step 2: Prepare the coating material

[0053] The coating raw materials, by weight, have the following composition ratio: 20 parts of modified corn starch citrate, 75 parts of alginic acid, 25 parts of poly(propylene carbonate), 25 parts of polylactic acid, 3 parts of glycerol, 3 parts of polyhydroxystearic acid, and 2 parts of carboxymethyl cellulose.

[0054] Prepare the coating raw materials, place the coating raw materials in a mixer and heat and mix them at a heating temperature of 120 °C for 100 min to obtain the coating material.

[0055] Step 3: Select the base paper

[0056] Select bamboo pulp paper with a water content of 5% and a thickness of 80 as the base paper.

[0057] Step 4: Primary coating

[0058] Put the coating material prepared in Step 2 into the feed hopper of the coating machine and spray it onto both sides of the base paper, with a single-sided coating amount of 6 g / to obtain the primary coated paper.

[0059] Step 5: Secondary coating

[0060] Re-introduce the primary coated paper into the coating machine for secondary coating, with a single-sided coating amount of 8 g / to obtain the coated paper.

[0061] Step 6: Drying and winding

[0062] Place the coated paper obtained in Step 5 in a drying oven for drying at a drying temperature of 75 °C for 3 min; let the dried coated paper stand for 2 h and then wind it to obtain the finished product.

[0063] Example 3 Preparation method of a coated paper for packaging

[0064] The specific steps are as follows:

[0065] Step 1: Prepare modified corn starch citrate

[0066] In a reaction kettle, citric acid is formulated into a citric acid solution with a mass percentage content of 1% using distilled water. The prepared citric acid solution is heated to 38 °C, and stirring is started at a stirring rate of 140 rpm. While stirring, corn starch is added to the citric acid solution, and the reaction is carried out for 3 h. Then, the pH value of the solution in the reaction kettle is adjusted to 8.2 with sodium hydroxide, cooled to 26 °C, and octenyl succinic anhydride and sodium alginate are added, and stirring and reaction are continued for 40 min.

[0067] After the reaction, it is left to stand at room temperature for 16 h and filtered; the filtered solid is dried at 60 °C for 7 h and ground to 80 mesh to obtain modified corn starch citrate.

[0068] The dosages of the citric acid, corn starch, octenyl succinic anhydride, and sodium alginate are, by weight: 27 parts of citric acid, 55 parts of corn starch, 7.5 parts of octenyl succinic anhydride, and 1 part of sodium alginate.

[0069] Step 2: Prepare the coating material

[0070] The coating raw materials, by weight, have a composition ratio of: 25 parts of modified corn starch citrate, 78 parts of alginic acid, 24 parts of poly(propylene carbonate), 20 parts of polylactic acid, 2 parts of glycerol, 1.5 parts of polyhydroxystearic acid, and 2.5 parts of carboxymethyl cellulose.

[0071] Prepare the coating raw materials, place the coating raw materials in a mixer and heat and mix them at a heating temperature of 122 °C for 90 min to obtain the coating material.

[0072] Step 3: Select the base paper

[0073] Select bamboo pulp paper with a water content of 5% and a thickness of 80 as the base paper.

[0074] Step 4: Primary coating

[0075] Load the coating material prepared in Step 2 into the feed hopper of the coating machine and spray it onto both sides of the base paper, with a single-sided coating amount of 6 g / to obtain the primary coated paper.

[0076] Step 5: Secondary coating

[0077] Re-introduce the primary coated paper into the coating machine for secondary coating, with a single-sided coating amount of 8 g / , a coated paper is obtained.

[0078] Step 6, drying and winding

[0079] Place the coated paper obtained in Step 5 in a drying oven for drying. The drying temperature is 75 °C and the drying time is 3 min; let the dried coated paper stand for 2 h and then wind it to obtain the finished product.

[0080] Comparative Example 1

[0081] On the basis of Example 3, do not perform Step 1 to prepare modified corn starch citrate. In the preparation of the coating material in Step 2, replace modified corn starch citrate with corn starch citrate. The specific operation is as follows:

[0082] Do not perform Step 1 to prepare modified corn starch citrate;

[0083] Step 2, prepare the coating material

[0084] The coating raw materials, in parts by weight, have the following composition ratio: 25 parts of corn starch citrate, 78 parts of alginic acid, 24 parts of poly(propylene carbonate), 20 parts of polylactic acid, 2 parts of glycerol, 1.5 parts of polyhydroxystearic acid, and 2.5 parts of carboxymethyl cellulose.

[0085] Prepare the coating raw materials, place the coating raw materials in a mixer for heating and mixing. The heating temperature is 122 °C and the heating time is 90 min to obtain the coating material.

[0086] Step 3, select the base paper, which is the same as in Example 3.

[0087] Step 4, primary coating, which is the same as in Example 3.

[0088] Step 5, secondary coating, which is the same as in Example 3.

[0089] Step 6, drying and winding, which is the same as in Example 3.

[0090] Comparative Example 2

[0091] On the basis of Example 3, do not add sodium alginate in the preparation of modified corn starch citrate in Step 1, and keep other steps unchanged. The specific operation is as follows:

[0092] Step 1, prepare modified corn starch citrate

[0093] In the reaction kettle, citric acid is prepared into a citric acid solution with a mass percentage of 1% using distilled water. The prepared citric acid solution is heated to 38 °C, and stirring is started at a stirring rate of 140 rpm. While stirring, corn starch is added to the citric acid solution, and the reaction proceeds for 3 h. Then, the pH value of the solution in the reaction kettle is adjusted to 8.2 with sodium hydroxide, the temperature is lowered to 26 °C, and octenyl succinic anhydride is added, and stirring and reaction continue for 40 min.

[0094] After the reaction, it is left to stand at room temperature for 16 h and then filtered; the filtered solid is dried at 60 °C for 7 h and ground to 80 mesh to obtain modified corn starch citrate.

[0095] The dosages of the citric acid, corn starch, and octenyl succinic anhydride, in parts by weight, are as follows: 27 parts of citric acid, 55 parts of corn starch, and 7.5 parts of octenyl succinic anhydride.

[0096] Step 2: Preparation of the coating material is the same as in Example 3.

[0097] Step 3: Selection of the base paper is the same as in Example 3.

[0098] Step 4: Primary coating is the same as in Example 3.

[0099] Step 5: Secondary coating is the same as in Example 3.

[0100] Step 6: Drying and winding are the same as in Example 3.

[0101] Comparative Example 3

[0102] Based on Example 3, alginic acid in the preparation of the coating material in Step 2 is replaced with citric acid, and other steps remain unchanged. The specific operations are as follows:

[0103] Step 1: Preparation of modified corn starch citrate is the same as in Example 3.

[0104] Step 2: Preparation of the coating material

[0105] The coating raw materials, in parts by weight, have the following composition ratio: 25 parts of modified corn starch citrate, 78 parts of citric acid, 24 parts of poly(propylene carbonate), 20 parts of polylactic acid, 2 parts of glycerol, 1.5 parts of polyhydroxystearic acid, and 2.5 parts of carboxymethyl cellulose.

[0106] Prepare the coating raw materials, place the coating raw materials in a mixer and heat and mix them at a heating temperature of 122 °C for 90 min to obtain the coating material.

[0107] Step 3: Selection of the base paper is the same as in Example 3.

[0108] Step 4: Primary coating is the same as in Example 3.

[0109] Step 5: Secondary coating is the same as in Example 3.

[0110] Step 6: Drying and winding are the same as in Example 3.

[0111] Comparative Example 4

[0112] On the basis of Example 3, carboxymethyl cellulose is not added to the coating material prepared in Step 2, and other steps remain unchanged. The specific operations are as follows:

[0113] Step 1: Preparation of modified corn starch citrate is the same as in Example 3.

[0114] Step 2: Preparation of coating material

[0115] The coating raw materials, by weight, have the following composition ratio: 25 parts of modified corn starch citrate, 78 parts of alginic acid, 24 parts of poly(propylene carbonate), 20 parts of polylactic acid, 2 parts of glycerol, and 1.5 parts of polyhydroxystearic acid.

[0116] Prepare the coating raw materials, place the coating raw materials in a mixer for heating and mixing, the heating temperature is 122 °C, and the heating time is 90 min to obtain the coating material.

[0117] Step 3: Selection of base paper is the same as in Example 3.

[0118] Step 4: Primary coating is the same as in Example 3.

[0119] Step 5: Secondary coating is the same as in Example 3.

[0120] Step 6: Drying and winding are the same as in Example 3.

[0121] Comparative Example 5

[0122] On the basis of Example 3, polyhydroxystearic acid is not added to the coating material prepared in Step 2, and other steps remain unchanged. The specific operations are as follows:

[0123] Step 1: Preparation of modified corn starch citrate is the same as in Example 3.

[0124] Step 2: Preparation of coating material

[0125] The coating raw materials, by weight, have the following composition ratio: 25 parts of modified corn starch citrate, 78 parts of alginic acid, 24 parts of poly(propylene carbonate), 20 parts of polylactic acid, 2 parts of glycerol, and 2.5 parts of carboxymethyl cellulose.

[0126] Prepare the coating raw materials, place the coating raw materials in a mixer for heating and mixing, the heating temperature is 122 °C, and the heating time is 90 min to obtain the coating material.

[0127] Step 3: Select the base paper, which is the same as in Example 3.

[0128] Step 4: Primary coating, which is the same as in Example 3.

[0129] Step 5: Secondary coating, which is the same as in Example 3.

[0130] Step 6: Drying and winding, which is the same as in Example 3.

[0131] Example 4 Performance Test

[0132] Performance test on the coated papers prepared in Examples 1-3 and Comparative Examples 1-5:

[0133] 1. The sampling of the specimens is carried out according to GB / T 450, the treatment of the specimens and the standard atmospheric conditions for the tests are carried out according to GB / T 10739. According to GB / T 36392-2018 Coated Papers and Boards for Food Packaging, the following indexes of the coated papers are detected: grease resistance and permeability. The bursting strength of the coated paper is detected according to GB / T 454-2002. After the coated paper is stored at -40 °C for 48 h, its bursting strength is detected again (detected at normal temperature and normal pressure, and the coated paper is detected after it returns to normal temperature). The ink absorbency of the coated paper is detected according to GB / T 12911-1991.

[0134] The test results are shown in Table 1.

[0135]

[0136] As can be seen from Table 1, the coated paper of the present invention has excellent grease resistance and permeability, high bursting strength, and is resistant to low-temperature storage. The ink absorption value is 18-20%, the printed characters are clear, the printed oil film is smooth, uniform, and has high gloss, and it saves ink.

[0137] 2. The oxygen transmission rate and water vapor transmission rate of the coated papers prepared in Examples 1-3 and Comparative Examples 1-5 are detected according to the method (differential pressure method) of GB / T 1038.1-2022, and the test results are shown in Table 2.

[0138] Table 2

[0139]

[0140] Analyzing the data in Table 2, it can be seen that the oxygen transmission rate and water vapor transmission rate of the coated papers in Examples 1-3 are significantly lower than those in Comparative Examples 1-5, indicating that the fresh-keeping effect of the coated papers in Examples 1-3 is significantly higher than that in Comparative Examples 1-5.

[0141] 3. The degradation performance of the coated papers prepared in Examples 1-3 and Comparative Examples 1-5 is detected according to the method of GB / T 39951-2021, and the test results are shown in Table 3.

[0142] Table 3

[0143]

[0144] As can be seen from Table 3, the coated paper prepared by the present invention is easily biodegradable, with a biodegradation rate of over 84% after 45 days and a maximum biodegradation rate of over 93%.

[0145] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A laminated paper for packaging, characterized in that: The raw material components include, by weight: 20-25 parts of modified corn starch citrate, 75-80 parts of alginic acid, 20-25 parts of polypropylene carbonate, 20-25 parts of polylactic acid, 1-3 parts of glycerol, 1-3 parts of polyhydroxystearic acid, and 2-2.5 parts of carboxymethyl cellulose; The preparation method of the modified corn starch citrate ester is as follows: in a reaction kettle, citric acid is prepared into a citric acid solution with a mass percentage of 0.8-1.2% by using distilled water, and the solution is heated to 35-38° C.; stirring is started; corn starch is added to the citric acid solution while stirring, and the reaction is carried out for 2.5-3 hours; then, the pH value of the solution in the reaction kettle is adjusted to be alkaline with sodium hydroxide, the temperature is lowered to 26-28° C., octenyl succinic anhydride and sodium alginate are added, and the stirring reaction is continued for 30-50 minutes; after the reaction, the solution is allowed to stand and filtered; the filtered solid is dried and ground to 80-100 meshes.

2. The laminated paper for packaging according to claim 1, characterized in that: The dosage of the citric acid, corn starch, octenyl succinic anhydride and sodium alginate is, by weight, 20 to 27 parts of citric acid, 50 to 62 parts of corn starch, 5.5 to 7.5 parts of octenyl succinic anhydride and 0.8 to 1.2 parts of sodium alginate.

3. The method for preparing a laminated paper for packaging according to claim 1, characterized in that: The coating raw materials are placed in a mixer for heating and mixing, and then sprayed onto both sides of the base paper for primary coating to obtain primary coating paper; the primary coating paper is introduced into the coating machine again for secondary coating to obtain coating paper, which is then dried and rolled up.

4. The method for preparing a laminated paper for packaging according to claim 3, characterized in that: The base paper has a moisture content of 1% to 5% and a thickness of 30 ~100 .

5. The method for preparing a laminated paper for packaging according to claim 3, characterized in that: The first coating: the coating amount on one side is 4 to 8 g / The secondary coating: the coating amount on one side is 5-10g / .

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