Low density polyethylene resin, method for producing the same, and coated article

Abstract

The application provides a low-density polyethylene resin, a preparation method thereof and a coated product. The preparation method comprises mixing a flexible monomer oligomer, ethylene, a first initiator and a chain transfer agent, and performing a polymerization reaction at a pressure of 100-400 MPa to obtain the low-density polyethylene resin. The application further provides the low-density polyethylene resin obtained by the above preparation method. The application further provides a coated product, which comprises a product body and a film layer coated on the surface of the product body, and the film layer comprises the low-density polyethylene resin. By adding the flexible monomer oligomer in the preparation process of the low-density polyethylene resin, the adhesion of the low-density polyethylene resin as the coated product can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of coating products with high adhesion performance, and more particularly to a low-density polyethylene resin, its preparation method, and the coating product thereof. Background Technology

[0002] Coating-grade low-density polyethylene (LDPE) resin features good toughness, strong adhesion, uniform film formation, and good hygiene, and is widely used in the outer packaging of food, chemical, and textile products. With the development of the packaging industry, the scope and amount of use of specialized materials will gradually expand, and market demand will increase daily.

[0003] The current state of research in this field is as follows:

[0004] For paper-plastic composite products, the strength between the coating and the base paper is crucial; this is the meaning of "composite." "Peeling" refers to the process of separating two bonded layers. Peel force differs from tensile and shear forces; it is not applied simultaneously across the entire bonded surface but only along a single line. Therefore, peel strength is not defined as the maximum stress that can be withstood per unit area, but rather as the maximum peel force that can be withstood per unit width to cause the bond to fail. The unit of peel strength is Newton-meter (N / m).

[0005] Currently, the performance of coated LDPE resins in the industry is usually controlled by MFR and density. However, peel strength, as one of the important parameters of coated LDPE resins, is only slightly affected by changes in MFR and density.

[0006] There is a current need for a coating material with high peel strength and strong adhesion. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a low-density polyethylene resin, its preparation method, and coated products. By adding flexible monomeric oligomers during the preparation of low-density polyethylene resin, the present invention effectively improves the adhesive strength of low-density polyethylene resin as a coated product.

[0008] To achieve the above objectives, the present invention provides a method for preparing low-density polyethylene resin, wherein the method comprises: mixing a flexible monomer oligomer, ethylene, a first initiator, and a chain transfer agent, and carrying out a polymerization reaction to obtain the low-density polyethylene resin; wherein the mass ratio of the flexible monomer oligomer to the ethylene is 1:10-1:500, and the pressure of the polymerization reaction is 100-400 MPa; the flexible monomer oligomer is obtained by polymerizing a flexible monomer, the degree of polymerization of the flexible monomer oligomer is 50-800, and the flexible monomer includes an acrylate and / or a diene.

[0009] In the above preparation method, by inserting flexible monomer oligomers into ethylene polymerization segments, amorphous elastic segments can be formed in polyethylene resin, thereby improving the adhesion of low-density polyethylene resin coated products. The preparation method provided by this invention involves a macromolecular polymerization reaction occurring through intermolecular transfer of initiator molecules during the polymerization of ethylene into polyethylene; that is, the connection between the flexible monomer oligomers and ethylene occurs at the molecular level. Therefore, compared to conventional methods for modifying polyethylene, the preparation method provided by this invention can effectively improve dispersion effect and dispersion degree.

[0010] According to a specific embodiment of the present invention, the degree of polymerization of the flexible monomer oligomer can be 100-400.

[0011] According to a specific embodiment of the present invention, the preparation method of the flexible monomer oligomer may include: initiating a prepolymerization reaction of the flexible monomer using a second initiator to obtain the flexible monomer oligomer.

[0012] In the above-mentioned method for preparing flexible monomer oligomers, the flexible monomer generally includes acrylates and / or dienes. The acrylates may include one or more combinations of methyl methacrylate, ethyl acrylate, acrylates, vinyl acetate, etc. The dienes may include one or more combinations of butadiene, 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, etc.

[0013] In the above-mentioned method for preparing flexible monomer oligomers, the flexible monomer oligomers are preferably formed by polymerization of a flexible monomer.

[0014] In the above-mentioned method for preparing flexible monomer oligomers, the temperature of the prepolymerization reaction can be 50-200℃, for example, 80-150℃.

[0015] In the above method for preparing flexible monomer oligomers, the pressure of the prepolymerization reaction can be 5-100 MPa, for example, 10-50 MPa.

[0016] In the above-described method for preparing flexible monomer oligomers, the time of the prepolymerization reaction is not particularly limited and is generally adjusted according to the degree of polymerization, prepolymerization temperature, and pressure of the flexible monomer oligomer. In the above-described method for preparing flexible monomer oligomers, the second initiator generally includes dialkyl peroxides and / or diacyl peroxides. The dialkyl peroxide can be di-tert-butyl peroxide, etc., and the diacyl peroxide can be benzoyl peroxide, etc.

[0017] In the above-mentioned method for preparing flexible monomer oligomers, the mass ratio of the second initiator to the flexible monomer is generally controlled to be 1:100-1:1000, for example, 1:200-1:600.

[0018] In the above-mentioned method for preparing low-density polyethylene resin, the mass ratio of the flexible monomer oligomer to the ethylene can be controlled to be 1:50-1:200.

[0019] In the above-described method for preparing low-density polyethylene resin, the chain transfer agent generally includes one or more of the following: olefins, aldehydes, ketones, alcohols, saturated hydrocarbons, ethers, etc. For example, the chain transfer agent may include one or more of the following: propionaldehyde, butene, diethyl ether, propane, ethanol, etc.

[0020] In the above-mentioned method for preparing low-density polyethylene resin, the mass ratio of the chain transfer agent to the ethylene is generally controlled to be 1:200-1:2000, for example, 1:200-1:1000.

[0021] In the above-mentioned method for preparing low-density polyethylene resin, the first initiator generally includes a peroxide ester. The peroxide ester may include one or a combination of two or more of the following: tert-butyl peroxypentanoate, 2-ethylhexanoate peroxide, and tert-butyl peroxy-3,5,5-trimethylhexanoate.

[0022] In the above-mentioned method for preparing low-density polyethylene resin, the mass ratio of the first initiator to the ethylene is generally controlled to be 1:500-1:5000.

[0023] In the above-described method for preparing low-density polyethylene resin, the polymerization temperature is generally controlled at 100-400℃, for example, 300-400℃. In a specific embodiment, the polymerization reaction is generally carried out in a reactor, and the polymerization reaction temperature in each region of the reactor can be correspondingly controlled at 100-400℃, for example, 300-400℃.

[0024] In the above-described method for preparing low-density polyethylene resin, the pressure of the polymerization reaction is generally controlled at 100-400 MPa, for example, 150-300 MPa. In a specific embodiment, the polymerization reaction is generally carried out in a reactor, and the polymerization reaction pressure in each region of the reactor can be correspondingly controlled at 100-400 MPa, for example, 150-300 MPa.

[0025] In the above-mentioned method for preparing low-density polyethylene resin, the polymerization reaction time is generally controlled to be 10-120 min, for example, 30-100 min.

[0026] In a specific embodiment of the present invention, the reactor for the above-mentioned polymerization reaction can be a single tubular reactor or a batch reactor, or a combination of both, with a single tubular reactor being preferred.

[0027] In specific embodiments of the present invention, the processes for producing low-density polyethylene resin using tubular reactors and batch reactors are largely the same; the structures of tubular reactors and batch reactors are also quite similar, typically consisting of five parts: an ethylene compression system, which uses a set of compressors with interstage coolers to compress purified ethylene; an initiator preparation and injection system, used to add free radical initiators (peroxides or oxygen) and chain transfer agents, which are added in the compression stage in some processes and directly injected into the reactor in others; a polymerization reactor, used to carry out the polymerization reaction, in which the conversion rate of the polymerization reaction can reach 15%-30%; a separation system, used to separate the generated polymer from the unreacted ethylene; and an extrusion granulation system, used to extrude the molten polymer, granulate it, and then cool, degas, blend, store, and package it.

[0028] According to a specific embodiment of the present invention, the method for preparing the above-mentioned low-density polyethylene resin may include:

[0029] 1. A second initiator is used to initiate the prepolymerization of flexible monomers to obtain flexible monomer oligomers with a degree of polymerization of 50-800; preferably, the temperature of the prepolymerization reaction is 50-200℃ and the pressure of the prepolymerization reaction is 5-100MPa.

[0030] 2. The above-mentioned flexible monomer oligomer, ethylene, first initiator and chain transfer agent are mixed and polymerized at a temperature of 100-400℃ and a pressure of 100-400MPa to obtain the low-density polyethylene resin.

[0031] The present invention also provides a low-density polyethylene resin obtained by the above-described preparation method. This low-density polyethylene resin can be considered as a reaction product based on ethylene and can be used as a coating-grade low-density polyethylene resin.

[0032] In a specific embodiment of the present invention, density can characterize the degree of branching of low-density polyethylene resin molecules. The lower the density, the better the toughness, the lower the heat-sealing temperature, and the smaller the deformation of low-density polyethylene resin products. The present invention can adjust the density of low-density polyethylene resin molecules by controlling the reaction pressure and temperature. Specifically, the density of low-density polyethylene resin can be reduced by decreasing the pressure and increasing the temperature, thereby reducing the toughness and heat-sealing temperature of the resin, and thus reducing the deformation of low-density polyethylene resin products.

[0033] In a specific embodiment of the present invention, the density of the aforementioned low-density polyethylene resin is generally 0.915-0.925 g / cm³. 3 .

[0034] In a specific embodiment of this invention, SR reflects the Mw / Mn ratio and the degree of long-chain branching of low-density polyethylene resin. A larger SR indicates a wider Mw / Mn ratio and a greater degree of long-chain branching. For resins, higher crystallinity results in higher mechanical properties (such as rigidity and hardness) and thermal properties (such as melting point, crystallization temperature, and Vicat softening temperature). Mw / Mn is an important indicator for testing the polydispersity of polymers. In coating processes, when MFRs are similar, a wide molecular weight distribution indicates a high content of both high-molecular-weight and low-molecular-weight fractions. A high content of high-molecular-weight fractions leads to significant macromolecular entanglement, which can easily cause uneven flowability and breakage during casting; a high content of low-molecular-weight fractions results in low melt strength and poor coating film strength. By changing different types of reactors and operating conditions, products with different degrees of long-chain branching can be obtained.

[0035] In a specific embodiment of the present invention, the Mw / Mn ratio of the aforementioned low-density polyethylene resin is 4-12.

[0036] In a specific embodiment of the present invention, the long-chain branching degree of the above-mentioned low-density polyethylene resin is 5-25 carbon atoms per 1000 carbon atoms.

[0037] In a specific embodiment of the present invention, by controlling the melt flow rate of low-density polyethylene resin, the casting traction stress of low-density polyethylene resin as a coating material can be guaranteed, and the problem of resin Mw / Mn widening caused by process control fluctuations can be overcome.

[0038] The melt flow rate of low-density polyethylene (LDPE) resin can be controlled by adjusting temperature, pressure, and the amount of chain transfer agent added. In some specific embodiments, by controlling the reaction pressure and maintaining a certain relative molecular weight, the branching degree of both long and short chains in the LDPE resin can be reduced, increasing its density. By controlling the reaction temperature, the melt flow rate can be increased, thereby improving the processing performance of the LDPE resin. In some specific embodiments, the melt flow rate of the LDPE can reach a high level (e.g., 7-8 g / 10 min) with good stability, making it suitable as a coating layer for films, woven fabrics, and paper surfaces.

[0039] In a specific embodiment of the present invention, the melt flow rate of the above-mentioned low-density polyethylene resin was measured to be 1g / 10min-10g / 10min using a 2.16Kg weight.

[0040] The present invention further provides a coated article comprising a main body and a film layer coated on the surface of the main body, the film layer comprising the aforementioned low-density polyethylene resin. Preferably, the peel strength between the main body and the film layer can reach 1N / 15mm-10N / 15mm, for example 4.1N / 15mm-6.8N / 15mm.

[0041] The above-mentioned coated products can be obtained by laminating low-density polyethylene with base paper (i.e., the main body of the product, which can be film, tarpaulin, woven fabric, paper, coated paper, etc.). Specifically, the low-density polyethylene resin can form a smooth sealing film on the paper surface through a paper-plastic composite processing technology, thereby obtaining a coated product with high peel strength.

[0042] In a specific embodiment of the present invention, the processing temperature of the above-mentioned paper-plastic composite processing technology can be controlled at 330±5℃, the coating speed can be controlled at 200±10m / min, the coating thickness can be controlled at 20±0.5μm, and the paper width is generally controlled at 2000±50mm.

[0043] The beneficial effects of this invention are as follows:

[0044] This invention improves the adhesion of coated products made from low-density polyethylene resin by adding flexible monomer oligomers during the preparation process of low-density polyethylene resin. Detailed Implementation

[0045] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0046] In the following examples and comparative examples, the method for preparing coated articles using low-density polyethylene resin and coated paper includes: extruding low-density polyethylene resin through a T-die and then laminating it with coated paper to form a smooth and sealed film on the surface of the coated paper, thereby obtaining the coated article.

[0047] The parameters for the paper-plastic composite processing technology are as follows: processing temperature 330±5℃, coating speed 200±10m / min, coating thickness 20±0.5μm, and paper width 2000±50mm.

[0048] In the following examples and comparative examples, the melt flow rate was tested according to GB / T3682-2000 Determination of melt mass flow rate and melt volume flow rate of thermoplastics, and the density was tested according to GB / T 1033.2-2010 Determination of density of non-foamed plastics - Part 2: Density gradient column method.

[0049] In the following examples and comparative examples, the peel strength of paper-plastic products was tested according to Method A of GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The specific operating method is as follows:

[0050] (1) Sample preparation: Take two samples each in the warp and weft directions, each 15.0±0.1mm wide and 200mm long. Use your hands or adhesive tape to peel the film and paper apart by 50mm beforehand, ensuring that the peeled part is not obviously damaged.

[0051] (2) After sampling, the sample needs to be stabilized at 23±2℃ for 4 hours at room temperature.

[0052] (3) Test: Clamp the two ends of the peeled part of the sample onto the upper and lower clamps of the electronic tensile testing machine (material testing machine), so that the longitudinal axis of the peeled part of the sample coincides with the line connecting the centers of the upper and lower clamps, and the tightness is appropriate.

[0053] (4) During the test, the unpeeled part is T-shaped with the stretching direction.

[0054] (5) Set the test parameters, where the speed is 300 mm / min.

[0055] (6) Record the peel strength parameters.

[0056] Example 1

[0057] This embodiment provides a low-density polyethylene resin, the preparation method of which includes:

[0058] 1. Methyl methacrylate (MMA) was used as a flexible monomer, and di-tert-butyl peroxide (DPBS) was used as an initiator to initiate the self-polymerization reaction of the flexible monomer in a prepolymerization reactor at 120°C and 10 MPa, to obtain polymethyl methacrylate oligomers, i.e., flexible monomer oligomers, with a degree of polymerization of 217. The mass ratio of initiator to flexible monomer was 1:250.

[0059] 2. Flexible monomer oligomers, ethylene, tert-butyl peroxypentanoate, and propionaldehyde are simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor is controlled at 300℃ and the polymerization pressure at 200MPa for high-pressure polymerization to obtain low-density polyethylene resin. The mass ratio of flexible monomer oligomers to ethylene is 1:150, the mass ratio of propionaldehyde to ethylene is 1:200, and the mass ratio of tert-butyl peroxypentanoate to ethylene is 1:1000.

[0060] The density of the aforementioned low-density polyethylene product was measured to be 0.919 g / cm³. 3 The Mw / Mn ratio is 8, and the long-chain branching degree is 25 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 1.2 g / 10 min using a 2.16 kg weight.

[0061] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 4.1 N / 15 mm.

[0062] Comparative Example 1

[0063] This comparative example provides a low-density polyethylene resin, the preparation method of which differs from the preparation method of the low-density polyethylene resin in Example 1 in that: the low-density polyethylene resin of this comparative example is directly prepared by high-pressure polymerization reaction of ethylene, initiator and chain transfer agent, without the participation of flexible monomer oligomers in the reaction.

[0064] Specifically, the preparation method of the low-density polyethylene resin in this comparative example includes:

[0065] Ethylene, tert-butyl peroxypentanoate, and propionaldehyde were simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor was controlled at 300℃ and the polymerization pressure at 200MPa to carry out a high-pressure polymerization reaction, yielding low-density polyethylene resin. The mass ratio of propionaldehyde to ethylene was 1:200, and the mass ratio of tert-butyl peroxypentanoate to ethylene was 1:1000.

[0066] The density of the aforementioned low-density polyethylene product was measured to be 0.918 g / cm³. 3 The Mw / Mn ratio is 5, and the long-chain branching degree is 22 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 1.0 g / 10 min using a 2.16 kg weight.

[0067] The above-mentioned low-density polyethylene product was combined with coated paper to obtain a coated product. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 1.3 N / 15 mm.

[0068] Example 2

[0069] This embodiment provides a low-density polyethylene resin, the preparation method of which includes:

[0070] 1. Vinyl acetate was used as a flexible monomer, and benzoyl peroxide was used as an initiator to initiate the self-polymerization reaction of the flexible monomer in a prepolymerization reactor at 150℃ and 50MPa to obtain polyvinyl acetate oligomers, i.e., flexible monomer oligomers, with a degree of polymerization of 386. The mass ratio of initiator to flexible monomer was 1:500.

[0071] 2. Flexible monomer oligomers, ethylene, 2-ethylhexanoate peroxide, and butene are simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor is controlled at 350℃, and the polymerization pressure is 280MPa for high-pressure polymerization to obtain low-density polyethylene resin. The mass ratio of flexible monomer oligomers to ethylene is 1:50, the mass ratio of butene to ethylene is 1:1000, and the mass ratio of 2-ethylhexanoate peroxide to ethylene is 1:500.

[0072] The density of the aforementioned low-density polyethylene product was measured to be 0.924 g / cm³. 3 The Mw / Mn ratio is 10, and the long-chain branching degree is 12 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 9.4 g / 10 min using a 2.16 kg weight.

[0073] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated product. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 6.8 N / 15 mm.

[0074] Comparative Example 2

[0075] This comparative example provides a low-density polyethylene resin, the preparation method of which differs from the preparation method of the low-density polyethylene resin in Example 1 in that: the low-density polyethylene resin of this comparative example is directly prepared by high-pressure polymerization reaction of ethylene, initiator and chain transfer agent, without the participation of flexible monomer oligomers in the reaction.

[0076] Specifically, the preparation method of the low-density polyethylene resin in this comparative example includes:

[0077] Ethylene, 2-ethylhexanoate peroxide, and butene were simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor was controlled at 350℃ and the polymerization pressure at 280MPa to carry out a high-pressure polymerization reaction, yielding low-density polyethylene resin. The mass ratio of butene to ethylene was 1:1000, and the mass ratio of 2-ethylhexanoate peroxide to ethylene was 1:500.

[0078] The density of the aforementioned low-density polyethylene product was measured to be 0.923 g / cm³. 3 The Mw / Mn ratio is 8, and the long-chain branching degree is 10 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 8.9 g / 10 min using a 2.16 kg weight.

[0079] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 1.9 N / 15 mm.

[0080] Example 3

[0081] This embodiment provides a low-density polyethylene resin, the preparation method of which includes:

[0082] 1. Butadiene was used as a flexible monomer, and di-tert-butyl peroxide and benzoyl peroxide (mass ratio 1:1) were used as initiators to initiate the self-polymerization reaction of the flexible monomer in a prepolymerization reactor at 90℃ and 20MPa, yielding polybutadiene oligomers, i.e., flexible monomer oligomers, with a degree of polymerization of 282. The mass ratio of initiator to flexible monomer was 1:400.

[0083] 2. Flexible monomer oligomers, ethylene, tert-butyl peroxide-3,5,5-trimethylhexanoate, and diethyl ether are simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor is controlled at 310℃ and the polymerization pressure at 150MPa for high-pressure polymerization to obtain low-density polyethylene resin. The mass ratio of flexible monomer oligomers to ethylene is 1:200, the mass ratio of diethyl ether to ethylene is 1:700, and the mass ratio of tert-butyl peroxide-3,5,5-trimethylhexanoate to ethylene is 1:2000.

[0084] The density of the aforementioned low-density polyethylene product was measured to be 0.916 g / cm³. 3 The Mw / Mn ratio is 12, and the long-chain branching degree is 18 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 6.7 g / 10 min using a 2.16 kg weight.

[0085] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 4.9 N / 15 mm.

[0086] Comparative Example 3

[0087] This comparative example provides a low-density polyethylene resin, the preparation method of which differs from the preparation method of the low-density polyethylene resin in Example 1 in that: the low-density polyethylene resin of this comparative example is directly prepared by high-pressure polymerization reaction of ethylene, initiator and chain transfer agent, without the participation of flexible monomer oligomers in the reaction.

[0088] Specifically, the preparation method of the low-density polyethylene resin in this comparative example includes:

[0089] Ethylene, tert-butyl peroxide-3,5,5-trimethylhexanoate, and diethyl ether were simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor was controlled at 310℃, and the polymerization pressure at 150 MPa, to conduct a high-pressure polymerization reaction, yielding low-density polyethylene resin. The mass ratio of diethyl ether to ethylene was 1:700, and the mass ratio of tert-butyl peroxide-3,5,5-trimethylhexanoate to ethylene was 1:2000.

[0090] The density of the aforementioned low-density polyethylene product was measured to be 0.915 g / cm³. 3 The Mw / Mn ratio is 9, and the long-chain branching degree is 15 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 6.4 g / 10 min using a 2.16 kg weight.

[0091] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 1.6 N / 15 mm.

[0092] Example 4

[0093] This embodiment provides a low-density polyethylene resin, the preparation method of which includes:

[0094] 1. Acrylic acid ester was used as a flexible monomer, and di-tert-butyl peroxide was used as an initiator to initiate the self-polymerization reaction of the flexible monomer in a prepolymerization reactor at 80°C and 30 MPa to obtain polyacrylate oligomers, i.e., flexible monomer oligomers, with a degree of polymerization of 127. The mass ratio of initiator to flexible monomer was 1:350.

[0095] 2. Flexible monomer oligomers, ethylene, tert-butyl peroxide-3,5,5-trimethylhexanoate, and propane are simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor is controlled at 330℃ and the polymerization pressure at 240MPa for high-pressure polymerization to obtain low-density polyethylene resin. The mass ratio of flexible monomer oligomers to ethylene is 1:90, the mass ratio of propane to ethylene is 1:900, and the mass ratio of tert-butyl peroxide-3,5,5-trimethylhexanoate to ethylene is 1:3000.

[0096] The density of the aforementioned low-density polyethylene product was measured to be 0.921 g / cm³. 3 The Mw / Mn ratio is 4, and the long-chain branching degree is 6 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 2.6 g / 10 min using a 2.16 kg weight.

[0097] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated product. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 5.7 N / 15 mm.

[0098] Comparative Example 4

[0099] This comparative example provides a low-density polyethylene resin, the preparation method of which differs from the preparation method of the low-density polyethylene resin in Example 1 in that: the low-density polyethylene resin of this comparative example is directly prepared by high-pressure polymerization reaction of ethylene, initiator and chain transfer agent, without the participation of flexible monomer oligomers in the reaction.

[0100] Specifically, the preparation method of the low-density polyethylene resin in this comparative example includes:

[0101] Ethylene, tert-butyl peroxide (3,5,5-trimethylhexanoate), and propane were simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor was controlled at 330°C, and the polymerization pressure at 240 MPa, to conduct a high-pressure polymerization reaction, yielding low-density polyethylene resin. The mass ratio of propane to ethylene was 1:900, and the mass ratio of tert-butyl peroxide (3,5,5-trimethylhexanoate) to ethylene was 1:3000.

[0102] The density of the aforementioned low-density polyethylene product was measured to be 0.919 g / cm³. 3 The Mw / Mn ratio is 3.5, and the long-chain branching degree is 5 per 1000 carbons. The melt flow rate of the above low-density polyethylene resin was measured to be 2.1 g / 10 min using a 2.16 kg weight.

[0103] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 1.7 N / 15 mm.

[0104] Example 5

[0105] This embodiment provides a low-density polyethylene resin, the preparation method of which includes:

[0106] 1. Using 1,5-hexadiene as a flexible monomer, benzoyl peroxide was used as an initiator to initiate the self-polymerization reaction of the flexible monomer in a prepolymerization reactor at 150℃ and 50MPa, to obtain poly(1,5-hexadiene) oligomer, i.e., flexible monomer oligomer, with a degree of polymerization of 394. The mass ratio of initiator to flexible monomer was 1:350.

[0107] 2. Flexible monomer oligomers, ethylene, tert-butyl peroxypentanoate, and ethanol are simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor is controlled at 400℃ and the polymerization pressure at 300MPa for high-pressure polymerization to obtain low-density polyethylene resin. The mass ratio of flexible monomer oligomers to ethylene is 1:75, the mass ratio of ethanol to ethylene is 1:900, and the mass ratio of tert-butyl peroxypentanoate to ethylene is 1:1500.

[0108] The density of the aforementioned low-density polyethylene product was measured to be 0.925 g / cm³. 3 The Mw / Mn ratio is 6, and the long-chain branching degree is 10 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 6.1 g / 10 min using a 2.16 kg weight.

[0109] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 4.2 N / 15 mm.

[0110] Comparative Example 5

[0111] This comparative example provides a low-density polyethylene resin, the preparation method of which differs from the preparation method of the low-density polyethylene resin in Example 1 in that: the low-density polyethylene resin of this comparative example is directly prepared by high-pressure polymerization reaction of ethylene, initiator and chain transfer agent, without the participation of flexible monomer oligomers in the reaction.

[0112] Specifically, the preparation method of the low-density polyethylene resin in this comparative example includes:

[0113] Ethylene, tert-butyl peroxypentanoate, and ethanol were simultaneously fed into a tubular reactor. The polymerization temperature in each zone of the reactor was controlled at 400℃ and the polymerization pressure at 300MPa to carry out a high-pressure polymerization reaction, yielding low-density polyethylene resin. The mass ratio of ethanol to ethylene was 1:900, and the mass ratio of tert-butyl peroxypentanoate to ethylene was 1:1500.

[0114] The density of the aforementioned low-density polyethylene product was measured to be 0.924 g / cm³. 3 The Mw / Mn ratio is 5, and the long-chain branching degree is 8 / 1000 carbons; the melt flow rate of the above low-density polyethylene resin was measured to be 3.8 g / 10 min using a 2.16 kg weight.

[0115] The above-mentioned low-density polyethylene product was processed into paper-plastic composite with coated paper to obtain coated products. The peel strength was tested according to Method A in GB / T8808 "Peel Test Method for Flexible Composite Plastic Materials". The test result was 1.4 N / 15 mm.

[0116] Comparing the test results of each embodiment with the corresponding comparative examples, it can be seen that by adding flexible monomer oligomer components during the preparation of low-density polyethylene resin, the present invention can enable flexible monomer oligomers to be inserted into ethylene polymerization segments, forming amorphous elastic segments in low-density polyethylene resin, thereby improving the adhesion of coated products prepared from low-density polyethylene resin.

Claims

1. A method for preparing low-density polyethylene resin, the method comprising: The low-density polyethylene resin is obtained by mixing a flexible monomer oligomer, ethylene, a first initiator and a chain transfer agent and carrying out a polymerization reaction. The mass ratio of the flexible monomer oligomer to the ethylene is 1:10-1:500; the polymerization reaction pressure is 150-300 MPa; the polymerization reaction time is 10-120 min; and the polymerization reaction temperature is 300-400 °C. The flexible monomer oligomer is obtained by polymerizing a flexible monomer, the degree of polymerization of the flexible monomer oligomer is 50-800, and the flexible monomer includes acrylate and / or diene; the acrylate includes one or more of acrylate and vinyl acetate; the diene includes one or more of butadiene, 1,4-pentadiene, 1,5-hexadiene, and 1,6-heptadiene; the flexible monomer oligomer is formed by polymerizing one flexible monomer. The Mw / Mn ratio of the low-density polyethylene resin is 4-12; the degree of branching of the long chain of the low-density polyethylene resin is 5-25 carbon atoms per 1000 carbon atoms.

2. The preparation method according to claim 1, wherein, The degree of polymerization of flexible monomer oligomers is 100-400.

3. The preparation method according to claim 1 or 2, wherein, The method for preparing the flexible monomer oligomer includes: using a second initiator to initiate a prepolymerization reaction of the flexible monomer to obtain the flexible monomer oligomer.

4. The preparation method according to claim 1, wherein, The acrylate includes one or more of methyl methacrylate and ethyl acrylate.

5. The preparation method according to claim 3, wherein, The temperature of the prepolymerization reaction is 50-200℃; The pressure of the prepolymerization reaction is 5-100 MPa.

6. The preparation method according to claim 3, wherein, The temperature of the prepolymerization reaction is 80-150℃.

7. The preparation method according to claim 3, wherein, The pressure of the prepolymerization reaction is 10-50 MPa.

8. The preparation method according to claim 3, wherein, The second initiator includes dialkyl peroxide and / or diacyl peroxide.

9. The preparation method according to claim 8, wherein, The dialkyl peroxide includes di-tert-butyl peroxide, and the diacyl peroxide includes dibenzoyl peroxide.

10. The preparation method according to claim 8, wherein, The mass ratio of the second initiator to the flexible monomer is 1:100-1:1000.

11. The preparation method according to claim 8, wherein, The mass ratio of the second initiator to the flexible monomer is 1:200-1:

600.

12. The preparation method according to claim 1, wherein, The mass ratio of the flexible monomer oligomer to the ethylene is 1:50 to 1:

200.

13. The preparation method according to claim 1, wherein, The chain transfer agent includes one or more of the following: olefins, aldehydes, ketones, alcohols, saturated hydrocarbons, and ethers.

14. The preparation method according to claim 13, wherein, The chain transfer agent includes one or more of the following: propionaldehyde, butene, diethyl ether, propane, and ethanol.

15. The preparation method according to any one of claims 1, 13-14, wherein, The mass ratio of the chain transfer agent to the ethylene is 1:200 to 1:2000.

16. The preparation method according to claim 15, wherein, The mass ratio of the chain transfer agent to the ethylene is 1:200 to 1:1000.

17. The preparation method according to claim 1, wherein, The first initiator includes a peroxide ester.

18. The preparation method according to claim 17, wherein, The peroxide ester includes one or more of the following: tert-butyl peroxypentanoate, 2-ethylhexanoate peroxide, and tert-butyl peroxy-3,5,5-trimethylhexanoate.

19. The preparation method according to any one of claims 1 and 17-18, wherein, The mass ratio of the first initiator to the ethylene is 1:500 to 1:5000.

20. The preparation method according to claim 1, wherein, The polymerization reaction takes 30-100 minutes.

21. A low-density polyethylene resin, which is obtained by the preparation method according to any one of claims 1-20.

22. The low-density polyethylene resin according to claim 21, wherein, The density of the low-density polyethylene resin is 0.915-0.925 g / cm³. 3 .

23. The low-density polyethylene resin according to claim 22, wherein, The melt flow rate of the low-density polyethylene resin is 1 g / 10 min to 10 g / 10 min.

24. A coated article comprising an article body and a film coating the surface of the article body, the film comprising the low-density polyethylene resin as described in any one of claims 21-23.

25. The coated article according to claim 24, wherein, The peel strength between the main body and the film layer is 1-10 N / 15 mm.