Low density polyethylene, process for its preparation and film

Abstract

This invention relates to the field of polymer materials technology, specifically to a low-density polyethylene (LDPE), its preparation method, and a film thereof. The LPE has a weight-average molecular weight of 500,000-650,000 and a methyl branching degree of 2.2-2.7 CH3 / 100C. Starting from the film material itself, the LPE provided by this invention requires no special treatment as a film material. A simple casting process can achieve a high haze, meeting the requirements for high-haze protective films. The film prepared from this LPE has high mechanical properties and few crystal points. The film prepared using this LPE as a film material has high light transmittance and high haze. The film prepared using this LPE has a high processing speed, which can meet the process requirements of different film-making equipment, achieving good technical results.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a low-density polyethylene, its preparation method, and a film thereof. Background Technology

[0002] With changing societal aesthetic standards, people's demands for packaging materials are constantly evolving. In recent years, high-haze (matte, de-gloss, etc.) films have increasingly attracted the attention of businesses and consumers. High-haze films offer numerous advantages, including a comfortable feel, a serene and elegant appearance, and realistic color reproduction during printing, gradually becoming a new development trend in the film industry.

[0003] High-haze film-grade LDPE is mainly used in two fields: matte and matte films, and surface protective films. Currently, the high-haze effect is mostly achieved by improving the surface roughness of the film or changing the layer structure of the film through special treatment during the casting process, which places high demands on the casting equipment and processes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high-haze low-density polyethylene (LDPE) with high mechanical properties and few crystal points; the film prepared by the LDPE has high light transmittance and high haze; the film prepared by the LDPE has a high processing speed and can meet the process requirements of different film-making equipment.

[0005] Unlike existing technologies, this invention starts with the resin itself and achieves high haze through a simple casting process without special treatment, thus meeting the requirements of high haze protective films.

[0006] According to a first aspect of the present invention, the present invention provides a low-density polyethylene with a weight-average molecular weight of 500,000 to 650,000 and a methyl branching degree of 2.2 to 2.7 CH3 / 100C.

[0007] According to a second aspect of the present invention, the present invention provides a method for preparing the aforementioned low-density polyethylene, the method comprising:

[0008] In the presence of a catalyst, ethylene monomers undergo addition polymerization, and a molecular weight regulator is used to adjust the molecular weight. The polymerization conditions include: temperature of 240-250℃; pressure of 160-180 MPa; and flow rate of the molecular weight regulator of 40-45 kg / h.

[0009] According to a third aspect of the present invention, the present invention provides a film prepared from the aforementioned low-density polyethylene.

[0010] Compared with the prior art, the present invention starts from the film material itself. The low-density polyethylene provided by the present invention does not require special treatment as a film material. A simple casting process can make the film achieve a high haze, which meets the requirements of a high-haze protective film. The film prepared by the low-density polyethylene has high mechanical properties and few crystal points. The film prepared by using the low-density polyethylene as a film material has high light transmittance and high haze. The film prepared by using the low-density polyethylene has a high processing speed, which can meet the process requirements of different film-making equipment and achieve better technical results. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] This invention provides a low-density polyethylene (LDPE) with a weight-average molecular weight of 500,000-650,000 and a methyl branching degree of 2.2-2.7 CH3 / 100C. LDPE possessing the aforementioned properties exhibits high mechanical properties and few crystal points. As a film material, it requires no special treatment; a simple casting process can achieve high haze, meeting the requirements for high-haze protective films.

[0013] According to a preferred embodiment of the present invention, the low-density polyethylene (LDPE) has a weight-average molecular weight of 550,000-600,000 and a methyl branching degree of 2.4-2.6 CH3 / 100C. Using this low-density polyethylene as a film material is beneficial to improving the mechanical properties of the film. Moreover, the low-density polyethylene does not require special treatment, and the film can achieve high haze and transparency through a simple casting process, thus meeting the requirements of high-haze protective film.

[0014] According to a preferred embodiment of the present invention, the melt mass flow rate of the low-density polyethylene at 190°C / 2.16kg is 4-9g / 10min, preferably 5-7g / 10min; using this low-density polyethylene as a film material is beneficial to improving the mechanical properties of the film, and the low-density polyethylene does not require special treatment, and the film can achieve high haze and transparency through a simple casting process, meeting the requirements of high haze protective film.

[0015] According to a preferred embodiment of the present invention, the low-density polyethylene has a molecular weight distribution of 23-35, preferably 27-30; using low-density polyethylene as a film material is beneficial to improving the mechanical properties of the film, and the low-density polyethylene does not require special treatment, and the film can achieve high haze and transparency through a simple casting process, thus meeting the requirements of high haze protective film.

[0016] Low-density polyethylene (LDPE) possessing the aforementioned features of this invention can achieve the objectives of this invention, and there are no special requirements for its preparation method. According to a preferred embodiment of this invention, this invention provides a method for preparing the aforementioned low-density polyethylene, the method comprising:

[0017] In the presence of a catalyst, ethylene monomers undergo addition polymerization, with the molecular weight adjusted using a molecular weight regulator. The polymerization conditions include a temperature of 240-250℃, a pressure of 160-180 MPa, and a flow rate of 40-45 kg / h for the molecular weight regulator. Low-density polyethylene prepared using this method, when used as a film material, improves the mechanical properties of the film. Furthermore, this low-density polyethylene requires no special treatment; a simple casting process can achieve high haze and transparency, meeting the requirements for high-haze protective films.

[0018] According to a preferred embodiment of the present invention, the aforementioned preparation method is carried out in a reactor. Optionally, the reactor is a batch reactor, which can be one, two or more reactors, preferably two batch reactors connected in series. This is beneficial to improving the mechanical properties and processing performance of the film. Moreover, the low-density polyethylene does not require special treatment, and the film can achieve high haze and transparency through a simple casting process, thus meeting the requirements of high haze protective film.

[0019] According to the present invention, the catalyst is a conventional catalyst in the art. Optionally, the catalyst includes an organic peroxide, preferably one or more of tert-butyl peroxide (TBPIN), tert-butyl peroxide, tert-butyl peroxybenzoate, tert-butyl pervalerate, and tert-butyl peracetate. Using the low-density polyethylene prepared by the aforementioned catalyst as a film material is beneficial to improving the mechanical properties of the film, and the film does not require special surface treatment. A simple casting process can achieve high haze and light transmittance, meeting the requirements of high haze protective film.

[0020] According to a preferred embodiment of the present invention, the molecular weight regulator is one or both of propylene and ethane; using the aforementioned molecular weight regulator to prepare low-density polyethylene as a film material is beneficial to improving the mechanical properties of the film, and the low-density polyethylene does not require special treatment, and the film can achieve high haze and transparency through a simple casting process, thus meeting the requirements of high haze protective film.

[0021] The present invention provides a film, wherein at least one layer of the film is formed of the aforementioned low-density polyethylene.

[0022] According to the present invention, the low-density polyethylene film-forming method is relatively broad. Optionally, the film-forming method is one of single-layer or multi-layer co-extrusion blow molding or single-layer or multi-layer co-extrusion casting molding.

[0023] According to a preferred embodiment of the present invention, the haze of the film is ≥40%; more preferably ≥45%.

[0024] According to a preferred embodiment of the present invention, the light transmittance of the film is ≥90%.

[0025] The present invention will be described in detail below through embodiments, but it should be understood that the scope of protection of the present invention is not limited to the embodiments.

[0026] The test methods for the following embodiments and comparative examples include:

[0027] 1. Melt mass flow rate: determined according to the method specified in GB / T 3682-2000; test temperature is 190℃, load is 2.16 kg.

[0028] 2. The method for determining tensile properties is GB / T 1040.3-2006, and the test speed is 500 mm / min.

[0029] 3. The test method for methyl branching degree is GB / T 6040-2002, and the test is conducted using an infrared spectrometer.

[0030] 4. Molecular weight was determined by gel permeation chromatography, according to the method specified in Q / SZSY.07.16-2008, using trichlorobenzene as the solvent.

[0031] 5. The methods for determining haze and transmittance are GB / T 2410-2008, and the film thickness is 30 μm.

[0032] 6. Crystal point testing was performed using an online OCS detection system on a cast film machine with a film thickness of 30µm. The test method was Q / SZSY.07.10-2008.

[0033] 7. The method for determining melt tensile tension and melt tensile fracture rate is Q / SZSY.07.23-2008, and the test temperature is 190℃.

[0034] The reactor used in the following embodiments of the present invention is a dual-reactor series reactor based on the gas-phase free radical polymerization process introduced from Sumitomo Chemical Co., Ltd. of Japan.

[0035] Example 1

[0036] 1) Preparation of LDPE granules: Ethylene was fed into a dual-reactor series reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 245℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 45kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0037] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0038] Example 2

[0039] 1) Preparation of LDPE granules: Ethylene was fed into a dual-reactor series reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 245℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 40kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0040] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0041] Example 3

[0042] 1) Preparation of LDPE granules: Ethylene was fed into a dual-reactor series reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 245℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 43kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0043] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0044] Example 4

[0045] 1) Preparation of LDPE granules: Ethylene was fed into a dual-reactor series reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 250℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 45kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0046] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0047] Example 5

[0048] 1) Preparation of LDPE granules: Ethylene was fed into a dual-reactor series reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 240℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 45kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0049] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0050] Example 6

[0051] 1) Preparation of LDPE granules: Ethylene was fed into a single-stage reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 245℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 45kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0052] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0053] Comparative Example 1

[0054] 1) Preparation of LDPE granules: Ethylene was fed into a double-reactor series reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 245℃ and the pressure at 140MPa. Propylene, a molecular weight regulator, was added at a flow rate of 45kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0055] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0056] Comparative Example 2

[0057] 1) Preparation of LDPE granules: Ethylene was fed into a batch reactor, and TBPIN catalyst was added. The reactor temperature was controlled at 230℃ and the pressure at 165MPa. Propylene, a molecular weight regulator, was added at a flow rate of 45kg / h to obtain LDPE granules. The melt mass flow rate, degree of methyl branching, molecular weight, crystal point, melt tensile tension, and melt tensile fracture velocity were tested. The test results of the LDPE granules are shown in Table 1.

[0058] 2) Thin film preparation: Using the granules prepared in step (1) as the raw material for the three-layer co-extrusion cast film, a three-layer cast film with a total thickness of 30 μm was prepared, and the mechanical and optical properties of the film were tested. The test results of the film are shown in Table 2.

[0059] Table 1

[0060]

[0061]

[0062] Table 2

[0063]

[0064] As can be seen from the results of Examples 1-5, the films prepared using the low-density polyethylene provided by this invention have very high haze, exceeding 45% and even reaching over 50%. This is because the present invention, through process adjustment, enables the low-density polyethylene resin to have a high weight-average molecular weight and a large number of long-chain branched structures, thereby resulting in an undulating film surface and producing high haze. The films prepared using the low-density polyethylene of this invention possess excellent mechanical properties and low crystal point density while exhibiting high haze, thus meeting the requirements for high-haze film applications.

[0065] In Comparative Example 1, the pressure in the reactor was too low, which caused the polymer molecular weight to decrease, the melt index to increase, and the long branches to decrease, resulting in very low haze.

[0066] In Comparative Example 2, the reaction temperature was low, resulting in a high molecular weight but few branches. The film orientation was severe, and the film haze, transmittance and tensile strain were all low. The high macromolecular content led to severe gelation and a large number of large crystal points in the film.

[0067] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A low-density polyethylene, characterized in that, The low-density polyethylene has a weight-average molecular weight of 500,000-650,000 and a methyl branching degree of 2.2-2.7 CH3 / 100C.

2. The low-density polyethylene according to claim 1, wherein, The low-density polyethylene has a weight-average molecular weight of 550,000-600,000 and a methyl branching degree of 2.4-2.6 CH3 / 100C.

3. The low-density polyethylene according to claim 1 or 2, wherein, The low-density polyethylene has a molecular weight distribution of 23-35.

4. The low-density polyethylene according to claim 3, wherein, The low-density polyethylene has a molecular weight distribution of 27-30.

5. The low-density polyethylene according to claim 1 or 2, wherein, The low-density polyethylene has a melt flow rate of 4-9 g / 10 min at 190℃ / 2.16 kg.

6. The low-density polyethylene according to claim 5, wherein, The low-density polyethylene has a melt flow rate of 5-7 g / 10 min at 190℃ / 2.16 kg.

7. A method for preparing low-density polyethylene according to any one of claims 1-6, characterized in that, The method includes: In the presence of a catalyst, ethylene monomers undergo addition polymerization, and a molecular weight regulator is used to adjust the molecular weight. The polymerization conditions include: a temperature of 240-250℃, a pressure of 160-180 MPa, and a flow rate of 40-45 kg / h for the molecular weight regulator.

8. The preparation method according to claim 7, wherein, The molecular weight regulator is one or both of propylene and ethane.

9. The preparation method according to claim 7, wherein, The catalyst includes organic peroxides.

10. The preparation method according to claim 9, wherein, The organic peroxide is one or more selected from tert-butyl peroxide (3,5,5-trimethylhexanoate), tert-butyl peroxide (3,5,5-trimethylhexanoate), tert-butyl peroxide (benzoate), tert-butyl peroxypentanoate, and tert-butyl peracetate.

11. A thin film, characterized in that, The film has at least one layer formed of low-density polyethylene as described in any one of claims 1-6.

12. The thin film according to claim 11, wherein, The haze of the film is ≥40%.

13. The thin film according to claim 11, wherein, The haze of the film is ≥45; and / or Light transmittance is ≥90%.

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