A method for evaluating the quality of polyethylene raw material for electronic protection film

Abstract

The application discloses a quality evaluation method for polyethylene raw material of electronic protection film, which comprises the following steps: step 1, forming polyethylene raw material into a sheet with a thickness of 0.02-0.1 mm; step 2, testing the crystal point of the sheet, and determining that the polyethylene raw material is unqualified product when the diameter of the crystal point particle on the sheet is greater than or equal to 0.5 mm or the number of crystal points is greater than 0.5 / m 2 ; step 3, determining the melt strength of the polyethylene raw material of the non-unqualified product obtained in step 2, and determining whether the melt strength and the number of crystal points satisfy the following relationship: y<=0.19335+2.3796x-3.73523x 2 ; wherein y is the number of crystal points, and the unit is piece / m 2 ; x is the melt strength, and the unit is N; and the polyethylene raw material is qualified product when the melt strength and the number of crystal points satisfy the above relationship. The evaluation method can quickly determine whether the raw material is qualified.

Description

Technical Field

[0001] This invention relates to a rapid evaluation method for polymer materials, specifically a quality evaluation method for polyethylene raw materials used in electronic protective films. Background Technology

[0002] With the rapid development of the information industry and the widespread application of high-end optical devices, electronic protective films have become one of the key materials in the fields of high-end electronics and optics. During transportation, storage, processing, or assembly, it is often necessary to protect the surface of materials and components to prevent dust contamination or scratches caused by mechanical abrasions. One common method is to apply a protective film to the surface of the object to be protected. After transportation, storage, processing, or assembly is completed, the protective film is removed to protect the surface of the material. There is also surface protection for finished products, such as the protection of optical lenses in high-end cameras, and the surface protection of tablet computers and light guide plates.

[0003] The evaluation cycle for low-density polyethylene (LDPE) electronic protective films is relatively long. Currently, the only methods for judging the quality of LDPE film materials are fisheyes and streaks. Fisheyes are spherical blocks formed by transparent or translucent resin in the film, with a size range of 0.3mm to 2mm and a magnification of 0.1mm. Streaks are linear, hammer-shaped, fine protrusions and continuous fisheyes in the film, with a size range of ≥1.0cm and a ruler accuracy of 1.0cm. However, the existing size range and accuracy cannot meet the quality evaluation requirements of LDPE raw materials for electronic protective films. The quality of the raw materials can only be determined after downstream users use them. Poor performance can lead to significant losses for both manufacturers and downstream users.

[0004] Crystal points in LDPE resin are the main reason for substandard quality of LDPE protective films. Crystal points are transparent, hard microparticles, clearly visible to the naked eye in transparent or semi-transparent plastic films, that are not fully integrated with the surrounding material and have no size limitation. The main reasons for crystal points during polyethylene film production are: Firstly, the polymer at the crystal point has a higher molecular weight than the surrounding polymer. Due to its higher molecular weight, the polymer at the crystal point has a higher melting point and higher viscosity during melting. When blown into a film, the polymer at the crystal point cannot be evenly dispersed / mixed with the surrounding polymer and solidifies before the surrounding polymer after the melt is blown into a film, thus forming "arrowhead"-shaped or spherical overpolymer and solidified solids. Secondly, the resin may undergo cross-linking or form long branches during production and post-processing, resulting in microscopic gelation. Thirdly, additives, low molecular weight resins, and dust in the raw materials may condense on the die during processing. Accumulated amounts are then carried away by the film, also forming crystal points.

[0005] The main methods for controlling the crystal point of polyethylene raw materials in existing technologies are:

[0006] (1) Improvement through polymerization process and additives

[0007] The literature "Formation and Countermeasures of Fish Eyes in LDPE Film" (Synthetic Resins and Plastics, 2010, 27(4):56-58) addresses the problem of excessive "fish eyes" in high-transparency low-density polyethylene (LDPE) resin 2436H film, exploring the causes of "fish eyes" formation from the perspectives of the production reaction system and the additive addition system. By adjusting the reaction process technology, the order of grade switching, and screening the types of additives, the number of "fish eyes" in the first three batches of each production was reduced to less than 6 per 1200cm. 2 .

[0008] The literature "Analysis of the Causes and Countermeasures for Fish Eyes in LDPE Products" (Plastics Technology, 2002:33) analyzed the formation of fish eyes in film products and found that the main cause was the low quality of the film material. Improvements were made to the high-pressure reaction process for LDPE production, including reducing wall adhesion, shortening residence time, and strictly controlling the amount of recycled material injected. These measures improved the quality of the film material and significantly reduced the number of fish eyes in the film products.

[0009] The literature "Analysis and Prevention of Fish-Eye Formation in Blown Film Resin" (Heilongjiang Petrochemical Industry, 1996:12) discusses the causes of fish-eye formation during blown film resin production based on the production process of high-pressure low-density polyethylene, and proposes ideas to reduce the number of fish-eyes in blown film resin based on current production conditions. During the production of blown film resin, ensuring high reaction pressure, relatively low reaction temperature, and adding additives such as antioxidants can effectively inhibit the formation of fish-eyes in the resin.

[0010] Patent CN105855765 A discloses a low-density polyethylene resin for manufacturing high-transparency films and its preparation method. The low-density polyethylene resin for manufacturing high-transparency films has a number-average molecular weight of 10,000 to 20,000, a molecular weight distribution index of 4 to 6, a haze range of 4% to 9%, and a melt flow rate of 1.0 to 5.0 g / 10 min under the conditions of 190°C and 2.16 kg weight pressure. Its preparation method includes the following steps: (1) Fresh ethylene and unreacted recycled ethylene in the reactor are pressurized to 250-280 MPa by the front and rear compressors, and then heated to 170-190°C by the preheater before entering the reactor. In the reactor, air and organic peroxides are used as mixed initiators for polymerization. During the polymerization process, the ratio of 1-butene to propionaldehyde is adjusted. The polyethylene raw material product is obtained by separation by high and low pressure product separators. The unreacted ethylene gas is returned to the compressor for recycling. (2) Antioxidant 1010 and opening agent are mixed and dry granulated to obtain masterbatch, which is then extruded and granulated with the separated polyethylene raw material product to obtain low-density polyethylene resin for high-transparency film manufacturing.

[0011] CN105585766 A discloses a low-density polyethylene resin for pharmaceutical films and its preparation method: The resin has a number-average molecular weight of 10,000 to 20,000, a molecular weight distribution index of 4 to 6, a haze range of 4% to 9%, a hexane extract content of 0.5 to 2 g / 100 g, and a melt flow rate of 1.0 to 5.0 g / 10 min at 190℃ and a pressure of 2.16 kg weight. This product uses ethylene as raw material and air and organic peroxides as mixed initiators for polymerization. By adjusting the ratio of 1-butene to propionaldehyde, a polyethylene raw material product is first obtained. This product is then mixed with antioxidants and an opening agent, and a masterbatch obtained by dry granulation is extruded and granulated to obtain a low-density polyethylene resin specifically for the manufacture of high-transparency films.

[0012] Methods to control the crystal point of raw materials by improving polymerization processes and additives aim to control the crystal point through the structural properties of the raw materials. However, there is a lack of rapid and effective crystal point detection methods, and the effectiveness of structural property control can only be determined after downstream users have used the materials, which is a significant lag. Poor performance can lead to substantial losses for both the manufacturer and downstream users.

[0013] (2) Evaluate or test the crystal point of the raw materials and deal with any unqualified materials in a timely manner.

[0014] Currently, the only methods for judging the quality of LDPE film materials are fisheyes and streaks. Fisheyes are spherical blocks formed by transparent or translucent resin in the film, with a size range of 0.3mm-2mm and a magnification of 0.1mm. Streaks are linear, hammer-shaped, and continuous fisheye-like protrusions in the film, with a size range of ≥1.0cm and a ruler accuracy of 1.0cm. Different raw materials have quantitative indicators, and materials exceeding the standards are considered unqualified. These can be handled promptly, but the size range and accuracy cannot meet the quality requirements of LDPE raw materials for electronic protective films.

[0015] (3) Methods to reduce crystal point through post-processing:

[0016] The main methods for adjusting the crystal point during blown film processing are: a. After a certain period, increase the screw speed and melt extrusion pressure to remove precipitates. b. Clean the die head regularly. c. Appropriately increase the melt temperature to fully plasticize the melt. These methods are well known in the art.

[0017] Surface protective films, also known as masking films, are typically used to provide a physical barrier to prevent damage, contamination, scratches, abrasions, or other damage to the substrate to which they are adhered. Surface protective films can be used to provide this protection during manufacturing, transportation, or storage before the substrate is used. Substrates used as optical components in televisions, computer monitors, and other displays require surface protective films that adhere to the substrate surface and are then removed without damaging the substrate or leaving residues, contaminating the substrate surface, or causing other defects.

[0018] US2018 / 9993954 provides a method for preparing a surface protective film, wherein the surface protective film is free from rolling defects such as blockage or wrinkling when rolled into a roll, and after the film is bonded to the substrate, it is rolled into a roll and stored for a long time without transferring unevenness or fisheyes.

[0019] In summary, post-processing techniques can appropriately reduce the crystal point of thin films, but cannot fundamentally eliminate the crystal point caused by the raw material itself. Therefore, rapid determination of the crystal point during the raw material production process is of great significance in production, especially the combination of the crystal point of the raw material and the evaluation method.

[0020] CN105922689A discloses a high-viscosity self-adhesive surface protective film and its manufacturing method. The surface protective film includes a self-adhesive layer, an intermediate layer, and an anti-adhesive layer. The self-adhesive layer comprises ultra-low density polyethylene and flexible polypropylene. The intermediate layer comprises one or a mixture of low-crystal-point ethylene-propylene copolymer and polyethylene. The anti-adhesive layer is made of block copolymer polypropylene. This invention also discloses a method for manufacturing a high-transparency self-adhesive surface protective film, which involves sequentially performing raw material dust removal, automatic weighing and metering of raw materials, heated extrusion, high-efficiency filtration, co-extrusion film formation, cooling and shaping, automatic thickness control, defect detection, edge trimming and winding, aging treatment, and slitting and packaging. This patent controls product quality by controlling the number and size of crystal points in the film.

[0021]

[0022] JB / T 1043 7-2 004, "Cross-linkable Polyethylene Insulation Material for Wires and Cables," discloses a method for detecting the impurity content of YJ-35 and YJG-35 type cross-linkable polyethylene insulation materials. The detection principle involves placing the sample strip under a light beam. Impurity particles, due to their light-blocking properties, are detected by an electronic camera under a constant, continuous, and adjustable light source. The size and quantity of the transmitted and blocked light beams are detected by the impurity particle detector. The resolution of the impurity particle detector should be better than 100 μm. The sample is a strip-shaped sheet with a thickness of (0.5–0.8) mm, a width of (50 ± 3) mm, and a weight of approximately 1000 g. The sample is prepared using a small extruder, and the surface of the strip-shaped sheet is made smooth, clean, and free of contaminants by guide rollers and calendering rollers.

[0023] The literature "Performance of LLDPE Resin for High-Speed ​​Automatic Packaging Film" (Synthetic Resins and Plastics, 2010(5): 79-81) has reported on the relationship between melt strength and the ease of blown film production: When blown film is produced from electronic protective film raw materials, the rheological processes involved include both shearing action in the extruder and tensile action at the die exit and during traction. High melt tension is particularly important for film formation and high blow-up ratio blown film processes. Too low a melt tension makes film formation difficult, while higher melt tension results in better film formation, but higher melt strength also leads to more crystal points.

[0024] Currently, the quality of LDPE electronic protective film raw materials produced by manufacturers can only be determined by downstream users, resulting in long lead times and significant losses if the performance is unsatisfactory. Therefore, there is an urgent need for a simple and rapid evaluation method for LDPE electronic protective film raw materials, enabling raw material manufacturers to control the quality of their materials. Summary of the Invention

[0025] The main objective of this invention is to provide a quality evaluation method for polyethylene raw materials used in electronic protective films, so as to overcome the shortcomings of existing technologies, such as the lag in quality evaluation of protective film raw materials and the difficulty in meeting the quality requirements of electronic protective films under evaluation conditions.

[0026] To achieve the above objectives, the present invention provides a method for quality evaluation of polyethylene raw materials used in electronic protective films, comprising:

[0027] Step 1: Form the polyethylene raw material into thin sheets with a thickness of 0.02–0.1 mm;

[0028] Step 2: Test the crystal points of the thin film. When the diameter of the crystal point particles on the thin film is ≥0.5mm, or the number of crystal points is >0.5 / m. 2 At that time, the polyethylene raw material was determined to be a substandard product;

[0029] Step 3: Measure the melt strength of the polyethylene raw material obtained from the non-defective product in Step 2, and determine whether the obtained melt strength and the number of crystal points satisfy the following relationship:

[0030] y≤0.19335+2.3796x-3.73523x 2

[0031] Where y represents the number of crystal points, in units of points / m. 2 x represents the melt strength, in N.

[0032] When the melt strength and the number of crystal points satisfy the above relationship, the polyethylene raw material is a qualified product;

[0033] The apparatus for forming thin sheets from polyethylene raw materials includes:

[0034] An extrusion device for extruding the polyethylene raw material into sheets;

[0035] Winding device, including a rotating shaft;

[0036] The positioning sleeve is detachably mounted on the rotating shaft and rotates under the drive of the rotating shaft;

[0037] The thin sheet is wound around the positioning sleeve, and the thin sheet is tightened as the positioning sleeve rotates.

[0038] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention, wherein the rotation speed of the extrusion device is 10-60 rpm.

[0039] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention includes a method for testing the crystal points of the sheet as follows: the sheet is irradiated under a light beam generated by a constant, continuous, and adjustable light source; an electronic camera is used to receive the light beams that are transmitted and blocked; and an impurity particle detector is used to detect the particle size and number of crystal points with a resolution greater than 20 μm.

[0040] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention includes the following method for determining melt strength: testing is performed using a Goettfert RT-2000 melt tensile rheometer at a temperature of 190°C, with a capillary aspect ratio of any one of 20 / 2, 10 / 1, 20 / 1, or 30 / 1, and a shear rate of 45 s⁻¹. -1 The traction roller spacing is 0.4mm to 1mm, and the traction acceleration is 6mm / s². 2 .

[0041] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention, wherein the positioning sleeve is sleeved on the rotating shaft.

[0042] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention, wherein the positioning sleeve is made of flexible material and the positioning sleeve is fixed to the rotating shaft by fasteners.

[0043] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention, wherein when the testing and evaluation are stopped, the positioning sleeve is disassembled along with the sheet on the rotating shaft.

[0044] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention further includes: visually inspecting the polyethylene raw materials before forming them into sheets; if the polyethylene raw materials do not contain black and / or yellow granules, then forming the polyethylene raw materials into sheets.

[0045] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention, wherein when counting the number of crystal points, the diameter of the crystal points is greater than or equal to 0.02 mm.

[0046] The method for quality evaluation of polyethylene raw materials for electronic protective films according to the present invention includes, when counting the number of crystal points, counting the number of crystal points with diameters ranging from (0.02 to 0.1) mm, (0.1 to 0.2) mm, (0.2 to 0.3) mm, (0.3 to 0.5) mm, and ≥0.5 mm respectively.

[0047] The beneficial effects of this invention are:

[0048] This invention discloses a rapid evaluation method for polyethylene raw materials used in electronic protective films. By controlling the sample processing method and crystal point testing conditions, and establishing the relationship between the crystal point and melt strength of the extruded sheet, the method enables rapid judgment of the raw material's quality. Compared with existing technologies, it is particularly faster and more accurate than existing post-testing methods. When using the preferred extrusion temperature and thickness, the crystal point test results are more accurate and the effect is better due to the raw material properties and the surface condition of the sheet.

[0049] Furthermore, this invention employs a specific winding device to place the positioning sleeve onto the rotating shaft, with the thin sheet wound around the positioning sleeve. This tightens the thin sheet, facilitating the detection of crystal points. After testing, the thin sheet and positioning sleeve are disassembled together on the rotating shaft. This prevents the film from deforming or breaking due to excessive force during disassembly, and avoids delays caused by the inability to disassemble the film properly, allowing for continuous testing and improving work efficiency. It also prevents film deformation or damage during disassembly, thus avoiding impacts on subsequent product production. The thickness of the positioning sleeve in this invention is selected based on the specific equipment. Because the positioning sleeve is relatively thin, it does not affect the original operating parameters of the equipment and can be used for process parameters when the equipment does not use a positioning sleeve, making it very convenient to use. Attached Figure Description

[0050] Figure 1 This is a partial cross-sectional view of the apparatus for forming thin sheets from polyethylene raw materials according to the present invention.

[0051] In the attached figures, the following labels are used:

[0052] 1 Fasteners

[0053] 2. Positioning sleeve

[0054] 4. Rotation axis Detailed Implementation

[0055] The technical solution of the present invention will be described in detail below. The following embodiments are implemented under the premise of the technical solution of the present invention and a detailed implementation process is given. However, the protection scope of the present invention is not limited to the following embodiments. Structures or experimental methods that do not specify specific conditions in the following embodiments are generally performed under conventional conditions.

[0056] This invention provides a method for quality evaluation of polyethylene raw materials used in electronic protective films, comprising:

[0057] Step 1: Form the polyethylene raw material into thin sheets with a thickness of 0.02–0.1 mm;

[0058] Step 2: Test the crystal points of the thin film. When the diameter of the crystal point particles on the thin film is ≥0.5mm, or the number of crystal points is >0.5 / m. 2 At that time, the polyethylene raw material was determined to be a substandard product;

[0059] Step 3: Measure the melt strength of the polyethylene raw material obtained in Step 2 that does not belong to the unqualified products, and determine whether the obtained melt strength and the number of crystal points satisfy the following relationship:

[0060] y≤0.19335+2.3796x-3.73523x 2

[0061] Where y represents the number of crystal points, in units of points / m. 2 x represents the melt strength, in N.

[0062] When the melt strength and the number of crystal points satisfy the above relationship, the polyethylene raw material is a qualified product;

[0063] The apparatus for forming thin sheets from polyethylene raw materials includes:

[0064] An extrusion device for extruding the polyethylene raw material into sheets;

[0065] Winding device, including a rotating shaft;

[0066] The positioning sleeve is detachably mounted on the rotating shaft and rotates under the drive of the rotating shaft;

[0067] The polyethylene sheet is wound around the positioning sleeve, and the sheet is tightened as the positioning sleeve rotates.

[0068] This invention does not specifically limit the electronic protective film, such as a protective film for optical components of televisions, computer monitors, and other display devices. The electronic protective film of this invention is generally formed from polyethylene raw material through a film-forming process. This invention does not specifically limit the film-forming process. In one embodiment, the polyethylene raw material of this invention is low-density polyethylene raw material (LDPE raw material).

[0069] The melt strength of polyethylene raw materials is related to properties such as molecular weight and branched structure, which affect product quality, including blown film stability and appearance. Crystal points are influenced by external factors, product structure, transportation, and processing. Based on extensive testing, a specific relationship has been found between melt strength and the number of crystal points, as described in the formula above. Within a certain range, as melt strength decreases, the number of crystal points decreases because the content of long-chain branches and molecular weight decreases, resulting in a reduction in the number of crystal points. When the melt strength decreases to a certain extent, it becomes too low, leading to easy film breakage and severely impacting product quality. Conversely, as melt strength increases, the number of crystal points increases because the content of long-chain branches and molecular weight increases, resulting in an increase in the number of crystal points. However, if the melt strength is too high, the film becomes hard and prone to breakage, severely affecting product quality. Therefore, the melt strength should not be too high or too low, with a range of 0.07–0.18, preferably 0.08–0.15.

[0070] The present invention provides a method for evaluating the quality of polyethylene raw materials. By controlling the processing method of polyethylene raw materials, the relationship between the crystal point of the extruded sheet and the melt strength is established. This allows for a rapid judgment on whether the raw materials are qualified. Compared with existing technologies, this method is particularly faster and more accurate than existing post-testing methods.

[0071] In one embodiment, the present invention involves extruding polyethylene raw material into a sheet and winding the sheet onto a specific device. Figure 1 This is a partial cross-sectional view of the apparatus for forming thin sheets from polyethylene raw materials according to the present invention, as shown below. Figure 1 As shown, the device includes an extrusion device (not shown), a winding device, and a positioning sleeve 2.

[0072] In one embodiment, the extrusion device rotates at a speed of 10 to 60 rpm.

[0073] This invention does not specifically limit the winding device; any winding device used in the art for forming thin sheets from polyethylene raw materials is acceptable. This invention improves upon existing winding devices by including a rotating shaft 4. In the prior art, the polyethylene raw material used for testing is wound onto the rotating shaft to form a film. This invention further includes a positioning sleeve 2, detachably mounted on the rotating shaft 4. More specifically, the positioning sleeve is a hollow cylindrical structure corresponding to the rotating shaft, sleeved on the rotating shaft 4, and can rotate under the drive of the rotating shaft 4. That is, the positioning sleeve 2 rotates together with the rotating shaft 4, and as the positioning sleeve 2 rotates, the polyethylene sheet is wound onto the positioning sleeve 2.

[0074] Since the positioning sleeve 2 of the present invention is detachably mounted on the rotating shaft 4, when the test evaluation is stopped, the positioning sleeve 2 can be removed along with the sheet on the rotating shaft 2. This can prevent the sheet formed by polyethylene raw material from deforming or breaking due to excessive force during disassembly caused by the tight winding.

[0075] In one embodiment, the positioning sleeve 2 of the present invention is mounted on the rotating shaft 4 by a fastener 1. Before testing, the positioning sleeve 2 is fixed to the rotating shaft 4 by the fastener 1, and the polyethylene sheet is fixed to the positioning sleeve 2. As the positioning sleeve 2 rotates, the sheet tightens, which improves the accuracy of the testing equipment in detecting crystal points. When the polyethylene sheet has wrapped around the positioning sleeve 2 to a certain thickness and the test needs to be stopped, the fastener 1 is loosened, and the positioning sleeve 2 and the sheet are removed together from the rotating shaft 2. In another embodiment, the fastener can be a threaded fastener, preferably a screw.

[0076] In one embodiment, the positioning sleeve 2 is made of a flexible material. When the film formed from polyethylene raw material is collided during transportation or storage, the positioning sleeve 2 can undergo a certain deformation, thereby ensuring that the film is not damaged.

[0077] Meanwhile, the present invention adds a positioning sleeve 2 to the device used for evaluating the quality of polyethylene raw materials, which can prevent the working time from being delayed due to the inability to properly disassemble the film layer used for polyethylene raw materials, thereby improving work efficiency.

[0078] In one embodiment, the thickness of the sheet formed from the polyethylene raw material of the present invention is (0.04-0.06) mm. Appropriately reducing the thickness of the sheet can improve the accuracy of the test and evaluation.

[0079] This invention does not impose any particular limitation on the testing method for thin-film crystal points. Conventional testing methods in the field can be used, such as the method specified in JB / T 1043 7-2004 "Cross-linkable polyethylene insulation material for wires and cables" for detecting the impurity content of YJ-35 and YJG-35 type cross-linkable polyethylene insulation materials. The process described in Appendix B, "Impurity content detection method", is sufficient. Specifically, "the test sample is irradiated by a beam of light generated by a constant, continuous, and adjustable light source. The light beams that are transmitted and blocked are received by an electronic camera, and the size and number of crystal point particles are detected." Currently, there are also ready-made devices for this.

[0080] In one embodiment, the crystal point testing conditions of the present invention are as follows: under the illumination of a light beam generated by a constant, continuous, and adjustable light source, the light-transmitting and light-blocking beams are received by an electronic camera, and an impurity particle detector detects the size and number of crystal point particles with a resolution greater than 20 μm. The light source, electronic camera, and impurity particle detector constitute a crystal point testing device. This device can be a commercially available device or can be assembled independently. The crystal point testing device only needs to be installed after the extrusion device to test the sheet, preferably between the extrusion device and the winding device.

[0081] In this invention, when the diameter of the crystal particles is ≥0.5mm, or the number of crystal points is >0.5 per m 2 The polyethylene raw material was found to be substandard. Electronic protective films have very high requirements for film appearance, and because they are low-viscosity, the amount of adhesive applied is limited. If the crystal point diameter is greater than 0.5mm, or the number is greater than 0.5 per m, it is considered substandard. 2 This could easily cause damage to the object being covered during the covering or stacking process. Therefore, the diameter of the crystal dots must not be ≥0.5mm and the number of crystal dots must not exceed 0.5 per m. 2 .

[0082] When counting the number of crystal points, this invention uses an impurity particle detector with a resolution greater than 20 μm. At this time, the diameter of the crystal points that can be detected is greater than or equal to 0.02 mm.

[0083] Because electronic protective films have very high requirements for film appearance, the fewer crystal spots the better. Since they are low-viscosity and require less adhesive, the smaller the crystal spot size, the less impact it has on the protected object when the number of crystal spots is the same. Therefore, in one embodiment, the number of crystal spots with sizes ranging from (0.02 to 0.1) mm, (0.1 to 0.2) mm, (0.2 to 0.3) mm, 0.3 to 0.5) mm, and ≥0.5 mm are statistically analyzed. This allows for a more accurate comparison of the quality of polyethylene raw materials used in electronic protective films.

[0084] When the diameter of the crystal point particles on the thin plate is ≥0.5mm, or the number of crystal points is >0.5 / m 2 If the diameter of the crystal particles on the sheet is less than 0.5 mm and the number of crystal points is less than 0.5 per m, then the polyethylene raw material is considered a substandard product. Otherwise, if the diameter of the crystal particles on the sheet is less than 0.5 mm and the number of crystal points is less than 0.5 per m, then the polyethylene raw material is considered a substandard product. 2 Then, proceed to the next quality assessment.

[0085] Step 3 involves determining the melt strength of the polyethylene raw material from the non-conforming product obtained in Step 2. Specifically, this involves determining that the diameter of the crystal particles on the sheet obtained in Step 2 is <0.5 mm, and the number of crystal particles is ≤0.5 per m. 2 The melt strength of polyethylene raw materials.

[0086] This invention does not impose any particular limitation on the determination of melt strength; conventional methods in the art are sufficient. In one embodiment, the melt strength of this invention is measured using a direct measurement method in the art, which is common knowledge in the field. Wu Chunshuang described the direct measurement method of polyethylene melt strength in "Rheological Characterization of Long-Branched Chain Polymer for PERT Pipes" (Shanghai Plastics, 2017, 177(1):31-36) and "Methods for Testing Polyethylene Melt Strength and Its Influencing Factors" (Shanghai Plastics, 2015, (3):55-60), CN201180013377.5, regarding the method for preparing polyethylene with high melt strength. The melt strength testing conditions recommended by this invention are as follows: testing is performed using a Goettfert RT-2000 melt tensile rheometer at a temperature of 190°C, with a capillary aspect ratio of any one of 20 / 2, 10 / 1, 20 / 1, or 30 / 1, preferably 20 / 2, and a shear rate of 45 s. -1 The traction roller spacing is 0.4mm to 1mm, preferably 0.5mm to 0.7mm, and the traction acceleration is 6mm / s². 2 .

[0087] Determine whether the measured melt strength and number of crystal points satisfy the following relationship:

[0088] y≤0.19335+2.3796x-3.73523x 2

[0089] Where y represents the number of crystal points measured above, in units of points / m. 2 x represents the melt strength in N, specifically the melt strength tested at 190°C, typically ranging from 0.07 to 0.18 N.

[0090] When the melt strength and the number of crystal points satisfy the above relationship, the polyethylene raw material is a qualified product. Otherwise, the polyethylene raw material is an unqualified product.

[0091] The present invention tests the melt strength of polyethylene raw materials. The tests of the number and diameter of crystal points on thin sheets generally need to be performed in parallel multiple times, for example, 3-5 times. For the above parameters of the same raw material, multiple samples of the raw material are generally taken, and then the average value of the test data is taken, which can effectively eliminate errors.

[0092] In one embodiment, before forming the polyethylene raw material into sheets, the appearance of the polyethylene raw material is preferably visually inspected. If the polyethylene raw material does not have black and / or yellow granules, then the sheets are formed and subsequent tests are performed. If the polyethylene raw material has black and / or yellow granules, it is judged to be a substandard product.

[0093] In one specific embodiment, the method for quality evaluation of polyethylene raw materials for electronic protective films of the present invention is formed by the following steps:

[0094] (1) Fix the positioning sleeve 2 on the rotating shaft 4 of the winding device; form a thin sheet from polyethylene raw material through the extrusion device, fix the thin sheet on the positioning sleeve 2, and when the rotating shaft 4 drives the positioning sleeve 2 to rotate together, the polyethylene sheet can be wound on the positioning sleeve 2, thus achieving the tightening of the sheet; the rotation speed of the extrusion device is 10 to 60 rpm, and the thickness of the sheet is 0.02 to 0.1 mm;

[0095] (2) Perform crystal point testing on the thin film obtained in step (1):

[0096] Under the illumination of a constant, continuous, and adjustable light source, the transmitted and blocked light beams of the test sample were received by an electronic camera. An impurity particle detector, with a resolution greater than 20 μm, detected the size and number of crystal particles. When the diameter of a crystal particle was ≥0.5 mm, or the number of crystal particles was >0.5 particles / m... 2 The raw material was found to be substandard; further evaluation will be conducted on the initially qualified products.

[0097] (3) Determine the melt strength of the polyethylene raw material and determine whether the melt strength and the number of crystal points satisfy the following relationship:

[0098] y≤0.19335+2.3796x-3.73523x 2

[0099] y - number of crystal points, x - melt strength;

[0100] Among them, melt strength x is a value calculated in Newtons based on a test at 190°C, with a value range of 0.07 to 0.18; the number of crystal points is the value of the total number of crystal points per square meter of thin film.

[0101] (4) Loosen the fastener 1 and remove the electronic protective film and positioning sleeve 2 together.

[0102] Thus, the present invention provides a rapid and convenient method for evaluating the quality of electronic protective film raw materials, which correlates the melt strength of polyethylene raw materials with the number of crystal points in the thin film formed by polyethylene raw materials. Polyethylene raw materials that meet the evaluation conditions of the present invention can basically meet the subsequent film formation requirements.

[0103] The technical solution of the present invention will be further described below through specific embodiments, but should not be construed as limiting the present invention.

[0104] Raw material sources: LDPE electronic protective film special material from a Sinopec company, and imported LDPE electronic protective film special material, both commercially available products. The electronic protective film special material from a PetroChina company includes trial production sample 1, trial production sample 2, trial production sample 3, trial production sample 4, and trial production sample 5.

[0105] Analysis method:

[0106] Melt strength was tested using a Goettfert RT-2000 melt tensile rheometer at a temperature of 190℃.

[0107] Crystal point: Tested using a Harpo SCD-50 impurity analyzer.

[0108] Example 1

[0109] For pilot production sample 1, a sheet was extruded at an extruder die head temperature of 190℃, a rotation speed of 10 rpm, and a thickness of 20 μm. The sheet was then tightened using a winding device. A crystal point detector was placed between the extrusion and winding devices. The detector measured the number and diameter of crystal points on a 250g sample sheet. The test was performed in triplicate, and the average value was taken. The area of ​​the sheet formed by the sample was 33.6 μm. 2 The crystal point test results are shown in Table 1.

[0110] Table 1

[0111]

[0112] The melt strength test result of the trial production sample 1 was 0.141 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2 The calculated result is 0.455, and the crystal point test result is 0.44, which satisfies the condition y≤0.19335+2.3796x-3.73523x. 2 The product was deemed qualified. When blown into thin films by downstream electronic protective film manufacturers, the number of crystal points was low, and the film bubbles remained stable during the blown film process. Application results indicate that the product meets the requirements for electronic protective film use.

[0113] Example 2

[0114] For pilot production sample 2, extrusion was performed at an extruder die head temperature of 180℃, a speed of 20 rpm, and a thickness of 40 μm. A crystal point detector was used to measure the thickness of 250 g of sample (sheet area 33.6 μm). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 2.

[0115] Table 2

[0116]

[0117] The melt strength test result of the trial production sample 2 was 0.137 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2 The calculated result is 0.449, and the crystal point test result is 0.42, which satisfies y≤0.19335+2.3796x-3.73523x. 2 The product was deemed qualified and was used by downstream electronic protective film manufacturers to blow-dry films. It had a small number of crystal points and the film bubbles were stable during the blowing process. The application results showed that it could meet the requirements for electronic protective film use.

[0118] Example 3

[0119] For pilot production sample 3, extrusion was performed at an extruder die head temperature of 160℃, a speed of 30 rpm, and a thickness of 60 μm. A crystal point detector was used to analyze 250 g of the sample (sheet area 33.6 μm). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 3.

[0120] Table 3

[0121]

[0122] The melt strength test result of the trial production sample 3 was 0.126 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2 The calculated result is 0.434, and the test result is 0.40, which satisfies the condition y≤0.19335+2.3796x-3.73523x. 2, The product was deemed qualified and blown into thin films by downstream electronic protective film manufacturers. It exhibited a low number of crystal points, stable film bubbles during the blown film process, and consistent product quality. Application results indicate that it meets the requirements for electronic protective film use.

[0123] Example 4

[0124] For pilot production sample 4, extrusion was performed at an extruder die head temperature of 150℃, a speed of 50 rpm, and a thickness of 100 μm. A crystal point detector was used to analyze 250 g of the sample (sheet area 33.6 μm). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 4.

[0125] Table 4

[0126]

[0127] The melt strength test result of trial production sample 4 was 0.130 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2The calculated result is 0.440, and the test result is 0.43, which satisfies the condition y≤0.19335+2.3796x-3.73523x. 2 The product was deemed qualified. When blown into thin films by downstream electronic protective film manufacturers, the number of crystal points was low, and the film bubbles remained stable during the blown film process, resulting in consistent product quality. Application results indicate that the product meets the requirements for electronic protective film use.

[0128] Example 5

[0129] A special material for electronic protective film from a Sinopec company was extruded into thin sheets at an extruder die head temperature of 190℃, a speed of 40 rpm, and a thickness of 80 μm. A crystal point detector was used to analyze a 250g sample sheet (sheet area 33.6 μm). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 5.

[0130] Table 5

[0131]

[0132] The melt strength test result of the electronic protective film raw material was 0.154 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2 The calculated result is 0.471, and the crystal point test result is 0.46, which conforms to y≤0.19335+2.3796x-3.73523x. 2 The product was deemed qualified. When blown into thin films by downstream electronic protective film manufacturers, the number of crystal points was low, and the film bubbles remained stable during the blown film process, resulting in consistent product quality. Application results indicate that the product meets the requirements for electronic protective film use.

[0133] Example 6

[0134] Imported LDPE electronic protective film material was extruded into thin sheets at an extruder die head temperature of 190℃, a speed of 35 rpm, and a thickness of 70 μm. A crystal point detector was used to analyze a 250g sample sheet (sheet area 33.6 μm). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 6.

[0135] Table 6

[0136]

[0137] The melt strength test result of the electronic protective film raw material was 0.170 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2 The calculated result is 0.490, and the test result is 0.47, which satisfies the condition y≤0.19335+2.3796x-3.73523x. 2The product was deemed qualified. When blown into thin films by downstream electronic protective film manufacturers, the number of crystal points was low, and the film bubbles remained stable during the blown film process, demonstrating good quality stability. Application results indicate that it meets the requirements for electronic protective film use.

[0138] Example 7

[0139] For pilot production sample 5, extrusion was performed at an extruder die head temperature of 190℃, a speed of 10 rpm, and a thickness of 20 μm. A crystal point detector was used to analyze the 250g sample (sheet area 33.6 μm). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 7.

[0140] Table 7

[0141]

[0142] The melt strength test result of trial production sample 5 was 0.150 N, calculated using the formula 0.19335 + 2.3796x - 3.73523x. 2 The calculated result is 0.466, and the crystal point test result is 0.49, which does not meet the condition y≤0.19335+2.3796x-3.73523x. 2 The product was deemed substandard. When used by downstream electronic protective film manufacturers, poor quality stability was observed during the blown film process, with inconsistent crystal density, failing to meet the requirements for electronic protective film applications.

[0143] Comparative Example 1

[0144] For trial production sample 5, extrusion was performed at an extruder die head temperature of 190℃, a speed of 10 rpm, and a thickness of 20 μm. According to the crystal point range specified in CN105922689A, a crystal point detector was used to measure the crystal point area of ​​a 250g sample (33.6 μm²). 2 The number of crystal points on the surface was determined by conducting three parallel tests and taking the average value. The results are shown in Table 8.

[0145] Table 8

[0146]

[0147] The test was conducted within the specified range and met the required index. However, the results of Example 7 show that the test did not meet the manufacturer's requirements because many small crystal points were overlooked.

[0148] Comparative Example 2

[0149] For the trial production sample 5, extrusion was carried out at an extruder die head temperature of 190℃ to form a sheet with a thickness of 0.5mm. According to the crystal point range of JB / T10437-2004, the number of impurities on a 1KG sample belt was tested. The test was performed in parallel for 3 times, and the average value was taken. The results are shown in Table 9.

[0150] Table 9

[0151]

[0152] The test was conducted within the specified range and met the required index. However, the results of Example 7 show that the test did not meet the manufacturer's requirements because many small crystal points were ignored and the sample was too thick, resulting in low test accuracy.

[0153] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the quality of a polyethylene raw material for an electronic protection film, characterized by, The application relates to a method for testing the quality of polyethylene raw materials, comprising the following steps: Step 1: forming a polyethylene raw material into a sheet, wherein the thickness of the sheet is 0.02-0.1 mm; Step 2, test the crystal point of the sheet, when the diameter of the crystal point particle on the sheet is ≥0.5mm, or the number of crystal points is >0.5 / m 2 , determine that the polyethylene raw material is unqualified product; Step 3: testing the melt strength of the polyethylene raw material of the non-substandard product obtained in step 2, and determining whether the melt strength and the number of crystal points satisfy the following relationship: y < 0.19335 + 2.3796x - 3.73523x2 2 wherein y is the number of crystal points, in units of pieces / m 2 ; x is the melt strength, in units of N; When the melt strength and the number of crystal points satisfy the above relationship, the polyethylene raw material is a qualified product; The device for forming the polyethylene raw material into a sheet comprises: An extrusion device for extruding the polyethylene raw material into a sheet; A winding device comprising a rotating shaft; A positioning sleeve which is detachably arranged on the rotating shaft and rotates under the driving of the rotating shaft; The sheet is wound on the positioning sleeve, and the sheet is tightened along with the rotation of the positioning sleeve.

2. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, The rotating speed of the extrusion device is 10-60 rpm.

3. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, The method for testing the crystal points of the sheet is as follows: the sheet is irradiated under a light beam generated by a constant, continuous and controllable light source, an electronic camera is used to receive the light beam which is transparent and blocked, and an impurity particle detector is used to detect the particle size and the number of crystal points under the condition that the resolution is greater than 20 um.

4. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, The method for measuring the melt strength is as follows: using a melt tensile rheometer RT-2000 of Goettfert Company to test, the temperature is 190℃, the capillary mouth film length-diameter ratio is any one of 20 / 2, 10 / 1, 20 / 1, 30 / 1, the shearing rate is 45s -1 , the traction roller distance is 0.4mm-1mm, and the traction acceleration is 6mm / s 2 .

5. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, The positioning sleeve is sleeved on the rotating shaft.

6. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 5, characterized by, The positioning sleeve is made of flexible material, and the positioning sleeve is fixed on the rotating shaft by a fastener.

7. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, When the testing and evaluation are stopped, the positioning sleeve is detached from the rotating shaft together with the sheet.

8. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, The application further comprises the following steps: Before the polyethylene raw material is formed into a sheet, the polyethylene raw material is visually inspected, and if the polyethylene raw material does not contain black and / or yellow particle materials, the polyethylene raw material is formed into a sheet.

9. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 1, characterized by, When the number of crystal points is counted, the diameter of the crystal points is greater than or equal to 0.02 mm.

10. The method for evaluating the quality of polyethylene raw material for electronic protection films according to claim 9, characterized in that, When the number of crystal points is counted, the number of crystal points with a diameter in the range of (0.02-0.1) mm, (0.1-0.2) mm, (0.2-0.3) mm, (0.3-0.5) mm and greater than or equal to 0.5 mm is counted respectively.

Images