LDPE resin for coating products, preparation method and application thereof

Abstract

The present invention relates to an LDPE resin for coating products. It primarily addresses the problem of poor adhesion during the coating process of existing low-density polyethylene for coating products. The resin is characterized in that the raw material components and proportions are as follows by mass: prepolymerization raw material: prepolymerization initiator: flexible monomer in a ratio of 1:100-1:1000; polymerization raw material: prepolymerization product: ethylene in a ratio of 1:10-1:500; polymerization initiator: ethylene in a ratio of 1:500-1:5000; chain transfer agent: ethylene in a ratio of 1:200-1:2000; and a preparation method comprising: S1, in a prepolymerization kettle, using a prepolymerization initiator to initiate self-polymerization of the flexible monomer to produce a flexible monomer oligomer; S2, simultaneously adding the produced flexible monomer oligomer, ethylene, polymerization initiator, and chain transfer agent to a reactor operating under high-pressure polymerization conditions to obtain a final product. The LDPE resin for coating products improves the peel strength of the product by adding the flexible monomer oligomer to participate in the reaction, fully meeting the requirements of paper and plastic products.

Description

Technical field:

[0001] The present invention relates to the technical field of coating products with high adhesive properties, in particular to an LDPE resin for coating products and a preparation method and application thereof. Background technology:

[0002] Coating-grade LDPE features excellent toughness, strong adhesion, uniform film formation, and good hygiene, making it widely used in the outer packaging of food, chemicals, textiles, and other products. With the development of the domestic packaging industry, the scope and amount of specialized materials will gradually expand, and market demand will continue to increase.

[0003] Currently, coating-grade LDPE is prepared using a single high-pressure reactor. Since EVA or EMA is added during the coating process, the uneven mixing of resins will affect the coating effect under high-speed lamination conditions. In addition, physical mixing has a poor effect on enhancing the adhesion of the coating. Summary of the invention:

[0004] The present invention aims to overcome the problem of poor adhesion of LDPE resins for coating products during the coating process, as previously mentioned. The present invention provides an LDPE resin for coating products. By incorporating flexible monomers and oligomers into the reaction, the LDPE resin improves the adhesion and peel strength of the product, fully meeting the requirements for paper and plastic products. The present invention also provides a method for preparing and applying the LDPE resin for coating products.

[0005] The present invention solves the problem by the following technical solution: an LDPE resin for coating products, the raw material components and proportions thereof are as follows by mass:

[0006] Prepolymerization reaction raw materials: prepolymerization initiator, flexible monomer; the mass ratio of prepolymerization initiator: flexible monomer is 1:100-1:1000;

[0007] Polymerization reaction raw materials: prepolymerization product, ethylene, polymerization initiator, chain transfer agent;

[0008] The mass ratio of prepolymerization product to ethylene is 1:10-1:500;

[0009] The mass ratio of polymerization initiator: ethylene is 1:500-1:5000;

[0010] The mass ratio of chain transfer agent: ethylene is 1:200-1:2000.

[0011] Preferably, the flexible monomer is one or a combination of methyl methacrylate, ethyl acrylate, acrylic acid ester, vinyl acetate, butadiene, 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, preferably a single flexible monomer self-polymerizes; the prepolymerization initiator is one or a combination of dialkyl peroxide (ROOR') or diacyl peroxide (RCOOOOCR').

[0012] Preferably, the polymerization initiator is one or a combination of peroxy esters (RCOOOR'); and the chain transfer agent is one of olefins, aldehydes, ketones, alcohols, saturated hydrocarbons, and ethers.

[0013] Preferably, the prepolymerization initiator is di-tert-butyl peroxide, dibenzoyl peroxide or a combination thereof; the polymerization initiator is tert-butyl peroxypivalate, peroxy-2-ethylhexanoate, or peroxy-3,5,5-trimethylhexanoate.

[0014] The present invention also provides a method for preparing LDPE resin for coating products, comprising the following steps:

[0015] S1. First, a prepolymerization initiator is used in a prepolymerization reactor to initiate self-polymerization of the flexible monomer to produce a flexible monomer oligomer;

[0016] S2. Adding the produced flexible monomer oligomer, ethylene, a polymerization initiator, and a chain transfer agent simultaneously into a reactor operated under high-pressure polymerization conditions, and obtaining the final product after polymerization reaction.

[0017] Preferably, the temperature in the prepolymerization kettle is 50-200° C., preferably 80-150° C.; the pressure in the prepolymerization kettle is 5-100 MPa, preferably 10-50 MPa.

[0018] Preferably, the degree of polymerization of the flexible monomer oligomer is 50-800, preferably 100-400.

[0019] Preferably, the polymerization temperature in each zone of the reactor is 100-400° C., preferably 300-400° C.; the polymerization pressure in each zone of the reactor is 100-400 MPa, preferably 150-300 MPa.

[0020] Preferably, the reactor operated under high pressure polymerization conditions is a tubular reactor or a tank reactor, or a combination of the two, preferably a single tubular process; the reaction product prepared is an ethylene-based polymer.

[0021] The present invention also provides an application of a final product of an LDPE resin for coating products in the coating field.

[0022] The functions of the various components of an LDPE resin for coating products are as follows: a prepolymerization initiator initiates preliminary polymerization of a flexible monomer and ethylene; after entering the reactor, the flexible monomer oligomers participate in inter- and intramolecular chain transfer of ethylene, promote the formation of macromolecular chain segments between the flexible monomer and ethylene, enhance the polarity of the copolymer, and thereby enhance its adhesion to the substrate.

[0023] In the present invention's process for preparing LDPE resin for coated articles, a flexible monomer is first autopolymerized using an initiator in a prepolymerization reactor to produce a flexible monomer oligomer. The resulting flexible monomer oligomer is then simultaneously introduced into a reactor operating under high-pressure polymerization conditions containing ethylene, an initiator, and a chain transfer agent to produce a reaction product. The flexible monomer oligomer produced through prepolymerization can be incorporated into ethylene polymer segments to form amorphous elastic segments, thereby enhancing the adhesive strength of the coated article.

[0024] For coating grade LDPE resins, the industry controls product properties by controlling melt flow rate (MFR) and density.

[0025] MFR decreases with decreasing temperature and increasing pressure. Under most industrial operating conditions, a small amount of chain transfer agent is used to control MFR, allowing for increased reactor pressure within industrial limits while maintaining a certain relative molecular weight. This reduces long and short chain branching and increases density. In free radical polymerization, higher reaction temperatures increase product conversion. Therefore, the temperature must be controlled to avoid excessively high temperatures, as excessively high temperatures increase chain transfer reactions, increase relative molecular weight, and decrease MFR. Furthermore, high temperatures can produce large molecular gels, impairing processing performance.

[0026] Density is related to the degree of branching. Density increases with increasing pressure and decreases with increasing temperature. The degree of long-chain branching increases with increasing temperature and conversion rate, and decreases with increasing pressure. By changing different reactor types and operating conditions, products with different degrees of long-chain branching can be obtained.

[0027] However, peel strength, a key parameter of coating-grade LDPE resin, is limitedly affected by changes in MFR and density. Generally speaking, the higher the melt index (MI) of a resin, the better its fluidity, the lower the viscosity of the molten film, and the greater its adhesion. A resin with a lower MI and a higher molecular weight exhibits poorer fusion properties and poor adhesion to the coated substrate, resulting in decreased peel strength. Density is also a key factor. Lower resin density and a higher branched chain content make the surface more easily activated, leading to greater adhesion and a greater improvement in peel strength. However, changes in these two factors have very limited impact on peel strength.

[0028] For paper-plastic composite products, the strength between the coating and the base paper is crucial; this is the very meaning of "composite." "Peeling" can be described figuratively as peeling the two bonded layers apart, like skinning cattle or sheep. Peel force, unlike tensile or shear force, is applied not simultaneously across the entire bond surface but only along a single line. Therefore, peel strength is not defined as the maximum stress per unit area, but rather as the maximum peel force per unit width that can withstand failure. The unit of measurement is Newtons per meter (N / m).

[0029] Compared with the above background technology, the present invention has the following beneficial effects:

[0030] The final product of the present invention is extruded through a T-die and then laminated with base paper to form a smooth, sealed film on its surface to form a coated product. The peel strength between the paper and the film was then tested. The LDPE resin for coated products prepared using the present invention significantly improves the adhesiveness of the product. Compared to LDPE resins prepared using existing methods, peel strength tests show a more than two-fold improvement. This improved adhesiveness makes the film less likely to fall off, resulting in superior performance in the paper-plastic composite product. Specific implementation method:

[0031] The present invention will be further described below in conjunction with embodiment:

[0032] The final product of the present invention is extruded through a T-die and then compounded with base paper to form a smooth and sealed film on the surface of the coated product. The peel strength between the paper and the film is tested.

[0033] The test conditions for paper-plastic composite processing are shown in Table 1:

[0034] Table 1

[0035]

[0036] The paper-plastic products prepared under the above processing conditions were tested for peel strength according to Method A of GB / T 8808 Peel Test Method for Soft Composite Plastic Materials. The specific operation method is as follows:

[0037] (1) Sample preparation: Take two specimens with a width of 15.0 ± 0.1 mm and a length of 200 mm in each of the warp and weft directions. Peel the film and paper apart by hand or with adhesive tape for 50 mm. The peeled apart parts must not show any obvious damage.

[0038] (2) After sampling, the sample must be stabilized at room temperature of 23±2℃ for 4 hours.

[0039] (3) Test: Clamp the two ends of the peeled portion of the specimen on the upper and lower clamps of the electronic tensile testing machine (material testing machine) so that the longitudinal axis of the peeled portion of the specimen coincides with the center line of the upper and lower clamps, and the tightness is appropriate.

[0040] (4) During the test, the unpeeled portion is in a T-shape with the stretching direction.

[0041] (5) Set the test parameters, with the speed being 300 mm / min.

[0042] (6) Record the peel strength parameters.

[0043] After testing, the peeling strength fully meets the requirements of paper-plastic products.

[0044] Example 1:

[0045] In a prepolymerization reactor, di-tert-butyl peroxide was used to initiate the autopolymerization of the flexible monomer methyl methacrylate. The mass ratio of initiator to flexible monomer in the prepolymerization reactor was 1:250. The temperature was 120°C and the pressure was 10 MPa. The flexible monomer oligomer was produced, and the degree of polymerization of the flexible monomer oligomer was 217.

[0046] The produced flexible monomer oligomers are fed simultaneously with the polymerization feedstock containing ethylene, tert-butyl peroxypivalate, and propionaldehyde into a tubular reactor operated under high pressure polymerization conditions. The reaction conditions are as follows:

[0047] The mass ratio of polymethyl methacrylate oligomer to ethylene is 1:150;

[0048] The mass ratio of propionaldehyde to ethylene is 1:200;

[0049] The mass ratio of tert-butyl peroxypivalate to ethylene is 1:1000;

[0050] The polymerization temperature in each zone of the reactor was 300°C;

[0051] The polymerization pressure in each zone of the reactor was 200 MPa;

[0052] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 1.2 g / 10 min and a density of 0.919 g / cm 3 .

[0053] The above product was processed into paper-plastic composite with coated paper, and the peeling strength of the obtained product was tested according to Method A of "GB / T8808 Peeling Test Method for Soft Composite Plastic Materials", and the test result was 4.1N / 15mm.

[0054] Example 2:

[0055] Dibenzoyl peroxide was used in a prepolymerization reactor to initiate the autopolymerization of the flexible monomer vinyl acetate. The mass ratio of initiator to flexible monomer in the prepolymerization reactor was 1:500. The temperature was 150°C and the pressure was 50 MPa. Vinyl acetate oligomers were produced with a degree of polymerization of 386.

[0056] The produced vinyl acetate oligomers are fed simultaneously with a polymerization feedstock comprising ethylene, 2-ethylhexanoate, and butene into a tubular reactor operated under high pressure polymerization conditions. The reaction conditions are as follows:

[0057] The mass ratio of polyvinyl acetate oligomer to ethylene is 1:50

[0058] The mass ratio of butene to ethylene is 1:1000;

[0059] The mass ratio of 2-ethylhexanoate peroxide to ethylene is 1:500

[0060] The polymerization temperature in each zone of the reactor was 350°C;

[0061] The polymerization pressure in each zone of the reactor was 280 MPa;

[0062] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 9.4 g / 10 min and a density of 0.924 g / cm 3 .

[0063] The above product was processed into paper-plastic composite with coated paper, and the peeling strength of the obtained product was tested according to Method A of "GB / T8808 Peeling Test Method for Soft Composite Plastic Materials", and the test result was 6.8N / 15mm.

[0064] Example 3:

[0065] In a prepolymerization reactor, di-tert-butyl peroxide and dibenzoyl peroxide (mass ratio 1:1) were used to initiate the autopolymerization of the flexible monomer butadiene. The mass ratio of initiator to flexible monomer in the prepolymerization reactor was 1:400. The temperature was 90°C and the pressure was 20 MPa. The degree of polymerization of the butadiene oligomer produced was 282.

[0066] The produced butadiene oligomers and the polymerization feed containing ethylene, tert-butyl peroxy-3,5,5-trimethylhexanoate and diethyl ether are simultaneously fed into a tubular reactor operated under high pressure polymerization conditions. The reaction conditions are as follows:

[0067] The mass ratio of polybutadiene oligomer to ethylene is 1:200;

[0068] The mass ratio of ether to ethylene is 1:700;

[0069] The mass ratio of tert-butyl peroxy-3,5,5-trimethylhexanoate to ethylene is 1:2000

[0070] The polymerization temperature in each zone of the reactor was 310°C;

[0071] The polymerization pressure in each zone of the reactor was 150 MPa;

[0072] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 6.7 g / 10 min and a density of 0.916 g / cm 3 .

[0073] The above product was processed into paper-plastic composite with coated paper, and the peeling strength of the obtained product was tested according to Method A of "GB / T8808 Peeling Test Method for Soft Composite Plastic Materials", and the test result was 4.9N / 15mm.

[0074] Example 4:

[0075] Di-tert-butyl peroxide was used to initiate the autopolymerization of acrylate in a prepolymerization kettle. The mass ratio of initiator to flexible monomer in the prepolymerization kettle was 1:350. The temperature was 80°C and the pressure was 30 MPa. The degree of polymerization of the produced acrylate oligomer was 127.

[0076] The produced acrylate oligomers are fed simultaneously with a polymerization feedstock containing ethylene, tert-butyl peroxy-3,5,5-trimethylhexanoate, and propane into a tubular reactor operated under high-pressure polymerization conditions. The reaction conditions are as follows:

[0077] The mass ratio of polyacrylate oligomer to ethylene is 1:90;

[0078] The mass ratio of propane to ethylene is 1:900;

[0079] The mass ratio of tert-butyl peroxy-3,5,5-trimethylhexanoate to ethylene is 1:3000

[0080] The polymerization temperature in each zone of the reactor was 330°C;

[0081] The polymerization pressure in each zone of the reactor was 240 MPa;

[0082] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 2.6 g / 10 min and a density of 0.921 g / cm 3 .

[0083] The above product was processed into paper-plastic composite with coated paper, and the peeling strength of the obtained product was tested according to Method A of "GB / T8808 Peeling Test Method for Soft Composite Plastic Materials", and the test result was 5.7N / 15mm.

[0084] Example 5:

[0085] Dibenzoyl peroxide was used in a prepolymerization reactor to initiate the autopolymerization of the flexible monomer 1,5-hexadiene. The mass ratio of initiator to flexible monomer in the prepolymerization reactor was 1:350. The temperature was 150°C and the pressure was 50 MPa to produce a flexible monomer oligomer with a degree of polymerization of 394.

[0086] The produced flexible monomer oligomers are fed simultaneously with a polymerization feedstock containing ethylene, initiator tert-butyl peroxypivalate, and ethanol into a tubular reactor operated under high-pressure polymerization conditions. The reaction conditions are as follows:

[0087] The mass ratio of poly 1,5-hexadiene oligomer to ethylene is 1:75;

[0088] The mass ratio of ethanol to ethylene is 1:900;

[0089] The mass ratio of tert-butyl peroxypivalate to ethylene is 1:1500

[0090] The polymerization temperature in each zone of the reactor was 400°C;

[0091] The polymerization pressure in each zone of the reactor was 300 MPa;

[0092] The final product of the reaction has a melt flow rate of 6.1 g / 10 min and a density of 0.925 g / cm 3 .

[0093] The above product was processed into paper-plastic composite with coated paper, and the peeling strength of the obtained product was tested according to Method A of "GB / T8808 Peeling Test Method for Soft Composite Plastic Materials", and the test result was 4.2N / 15mm.

[0094] Comparative Example 1:

[0095] The difference from Example 1 is that the coated product is prepared by directly introducing ethylene, initiator and chain transfer agent into a reactor operated under high pressure polymerization conditions, without any flexible monomer or oligomer participating in the reaction.

[0096] Ethylene, tert-butyl peroxypivalate, and propionaldehyde are simultaneously fed into a tubular reactor operating under high pressure polymerization conditions. The reaction conditions are as follows:

[0097] The mass ratio of propionaldehyde to ethylene is 1:200;

[0098] The mass ratio of tert-butyl peroxypivalate to ethylene is 1:1000;

[0099] The polymerization temperature in each zone of the reactor was 300°C;

[0100] The polymerization pressure in each zone of the reactor was 200 MPa;

[0101] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 1.0 g / 10 min and a density of 0.918 g / cm 3 .

[0102] The above product was composited with coated paper to obtain a product having a peel strength of 1.3 N / 15 mm according to Method A of GB / T 8808 Peel Test Method for Soft Composite Plastic Materials.

[0103] Comparative Example 2:

[0104] The difference from Example 2 is that the low-density polyethylene resin of the coated product is directly prepared by introducing ethylene, initiator and chain transfer agent into a reactor operating under high-pressure polymerization conditions, without any flexible monomer or oligomer participating in the reaction.

[0105] Ethylene, 2-ethylhexanoate and butene are simultaneously fed into a tubular reactor operated under high pressure polymerization conditions. The reaction conditions are as follows:

[0106] The mass ratio of butene to ethylene is 1:500;

[0107] The mass ratio of 2-ethylhexanoate peroxide to ethylene is 1:500

[0108] The polymerization temperature in each zone of the reactor was 350°C;

[0109] The polymerization pressure in each zone of the reactor was 280 MPa;

[0110] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 8.9 g / 10 min and a density of 0.923 g / cm 3 .

[0111] The above product was processed into paper-plastic composite with coated paper, and the peeling strength of the obtained product was tested according to Method A of "GB / T8808 Peeling Test Method for Soft Composite Plastic Materials", and the test result was 1.9N / 15mm.

[0112] Comparative Example 3:

[0113] The difference from Example 3 is that the low-density polyethylene resin of the coated product is directly prepared by introducing ethylene, initiator and chain transfer agent into a reactor operating under high-pressure polymerization conditions, and no flexible monomer oligomer participates in the reaction.

[0114] Ethylene, tert-butyl peroxy-3,5,5-trimethylhexanoate and diethyl ether are simultaneously fed into a tubular reactor operating under high pressure polymerization conditions. The reaction conditions are as follows:

[0115] The mass ratio of ether to ethylene is 1:700;

[0116] The mass ratio of tert-butyl peroxy-3,5,5-trimethylhexanoate to ethylene is 1:2000

[0117] The polymerization temperature in each zone of the reactor was 310°C;

[0118] The polymerization pressure in each zone of the reactor was 150 MPa;

[0119] The final product of the reaction has a melt flow rate of 6.4 g / 10 min and a density of 0.915 g / cm 3 .

[0120] The above product was composited with coated paper to obtain a product having a peel strength of 1.6 N / 15 mm according to Method A of GB / T 8808 Peel Test Method for Soft Composite Plastic Materials.

[0121] Comparative Example 4:

[0122] The difference from Example 4 is that the low-density polyethylene resin of the coated product is directly prepared by feeding ethylene, initiator and chain transfer agent into a reactor operating under high-pressure polymerization conditions, without flexible monomers and oligomers participating in the reaction.

[0123] Ethylene, tert-butyl peroxy-3,5,5-trimethylhexanoate and propane are simultaneously fed into a tubular reactor operated under high pressure polymerization conditions. The reaction conditions are as follows:

[0124] The mass ratio of propane to ethylene is 1:900;

[0125] The mass ratio of tert-butyl peroxy-3,5,5-trimethylhexanoate to ethylene is 1:3000

[0126] The polymerization temperature in each zone of the reactor was 330°C;

[0127] The polymerization pressure in each zone of the reactor was 240 MPa;

[0128] The final product of the reaction has a melt flow rate of 2.1 g / 10 min and a density of 0.919 g / cm 3 .

[0129] The above product was composited with coated paper to obtain a product having a peel strength of 1.7 N / 15 mm according to Method A of GB / T 8808 Peel Test Method for Soft Composite Plastic Materials.

[0130] Comparative Example 5:

[0131] The difference from Example 5 is that the low-density polyethylene resin of the coated product is directly prepared by feeding ethylene, initiator and chain transfer agent into a reactor operating under high-pressure polymerization conditions, without any flexible monomer or oligomer participating in the reaction.

[0132] Ethylene, initiator tert-butyl peroxypivalate, and ethanol are simultaneously fed into a tubular reactor operating under high pressure polymerization conditions. The reaction conditions are as follows:

[0133] The mass ratio of ethanol to ethylene is 1:900;

[0134] The mass ratio of tert-butyl peroxypivalate to ethylene is 1:1500

[0135] The polymerization temperature in each zone of the reactor was 400°C;

[0136] The polymerization pressure in each zone of the reactor was 300 MPa;

[0137] The final product of the reaction is a 2.16 kg weight with a melt flow rate of 3.8 g / 10 min and a density of 0.924 g / cm 3 .

[0138] The above product was composited with coated paper to obtain a product having a peel strength of 1.4 N / 15 mm according to Method A of GB / T 8808 Peel Test Method for Soft Composite Plastic Materials.

[0139] The final reaction products prepared in Examples 1-5 were composited with coated paper to produce paper-plastic products. Testing revealed that the peel strength of the products fully met the requirements for paper-plastic products. However, the peel strength of Comparative Examples 1-5 was only 20-30% of that of the products of the present invention, affecting the adhesion and usability of the products.

Claims

1. An LDPE resin for coating products, the raw material components and proportions thereof are as follows by mass: Prepolymerization reaction raw materials: prepolymerization initiator, flexible monomer; the mass ratio of prepolymerization initiator: flexible monomer is 1:100-1:1000; Polymerization reaction raw materials: prepolymerization product, ethylene, polymerization initiator, chain transfer agent; The mass ratio of prepolymerization product to ethylene is 1:10-1:500; The mass ratio of polymerization initiator: ethylene is 1:500-1:5000; The mass ratio of chain transfer agent: ethylene is 1:200-1:2000; The flexible monomer is one of methyl methacrylate, ethyl acrylate, acrylic acid ester, vinyl acetate, butadiene, 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, or a combination of the two or more thereof.

2. The LDPE resin for coating products according to claim 1, wherein: The prepolymerization initiator is one or a combination of dialkyl peroxide ROOR' or diacyl peroxide RCOOOOCR'.

3. The LDPE resin for coating products according to claim 1, wherein: The polymerization initiator is one or a combination of peroxyesters RCOOOR'; the chain transfer agent is one of olefins, aldehydes, ketones, alcohols, saturated hydrocarbons, and ethers.

4. The LDPE resin for coating products according to claim 1 or 3, characterized in that: The prepolymerization initiator is di-tert-butyl peroxide, dibenzoyl peroxide or a combination of the two; the polymerization initiator is tert-butyl peroxypivalate, peroxy-2-ethylhexanoate, or peroxy-3,5,5-trimethylhexanoate.

5. A method for preparing the LDPE resin for coating products according to claim 1, comprising the following steps: S1. First, a prepolymerization initiator is used in a prepolymerization reactor to initiate self-polymerization of the flexible monomer to produce a flexible monomer oligomer; S2. Adding the produced flexible monomer oligomer, ethylene, a polymerization initiator, and a chain transfer agent simultaneously into a reactor operated under high-pressure polymerization conditions, and obtaining the final product after polymerization reaction.

6. The method for preparing LDPE resin for coating products according to claim 5, characterized in that: The temperature in the prepolymerization kettle is 50-200° C.; the pressure in the prepolymerization kettle is 5-100 MPa; and the polymerization degree of the flexible monomer oligomer is 50-800.

7. The method for preparing LDPE resin for coating products according to claim 6, wherein: The temperature in the prepolymerization kettle is 80-150° C.; the pressure in the prepolymerization kettle is 10-50 MPa; and the polymerization degree of the flexible monomer and oligomer is 100-400.

8. The method for preparing LDPE resin for coating products according to claim 5, wherein: The polymerization temperature in each zone of the reactor is 100-400° C.; the polymerization pressure in each zone of the reactor is 100-400 MPa.

9. The method for preparing LDPE resin for coating products according to claim 8, wherein: The polymerization temperature in each zone of the reactor is 300-400° C.; the polymerization pressure in each zone of the reactor is 150-300 MPa.

10. The method for preparing LDPE resin for coating products according to claim 5, characterized in that: The reactor operated under high-pressure polymerization conditions is a tubular reactor or a tank reactor, or a combination of the two; the reaction product prepared is an ethylene-based polymer.

11. Use of the LDPE resin for coating products obtained by the preparation method according to any one of claims 1 to 4 or any one of claims 5 to 10 in the field of coating.

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