Method for evaluating polyethylene raw material for optical protective film

Abstract

The application relates to an evaluation method of a polyethylene raw material for an optical protective film, which can quickly judge whether the raw material is qualified by controlling the processing method of a test sample, the crystal point test condition, and establishing the relationship between the crystal point of the raw material extruded sheet and the melt strength, and compared with the prior art, especially the existing post-test, the method can be faster and more accurate.

Description

Technical Field

[0001] This invention relates to the field of polymer resin evaluation, and more specifically to a method for evaluating polyethylene raw materials used in optical protective films. Background Technology

[0002] High-pressure polyethylene resin possesses excellent flexibility, extensibility, electrical insulation, transparency, processability, and a certain degree of air permeability. Its good chemical stability, resistance to alkalis, and resistance to common organic solvents make it widely used in medical, foaming, profile, and film industries. With the rapid development of the electronics industry, the demand for optical protective films is increasing. Polyethylene optical protective films, made from PE film as the base material, are widely used in instruments, meters, and electronics industries. These protective films have very strict requirements for the production and processing environment, generally produced in GMP cleanrooms to ensure film cleanliness. Furthermore, strict control over various physicochemical indicators such as transparency and crystal points is essential for product quality, resulting in high added value.

[0003] In 2020, my country's demand for low-density polyethylene (LDPE) optical protective films reached 50,000 tons, entirely reliant on imports. While some domestic companies have attempted to develop such products, the evaluation cycle is lengthy. Optical protective films have very high requirements for crystal point density; high crystal point density can cause scratches on the surface of the protected object. Therefore, crystal point density is a major cause of substandard optical protective film quality. Different literatures offer varying opinions on the sources of crystal point density, but most consider long-chain branching and macromolecular gelation to be the main factors. Existing technologies include methods to control raw material crystal point density through optimized polymerization processes and methods to reduce film crystal point density through post-processing. The former controls product crystal point density by controlling the raw material structure, but lacks rapid and effective crystal point detection methods. The effectiveness of structural performance control can only be determined after downstream user testing, resulting in significant delays. Poor performance can lead to substantial losses for both manufacturers and downstream users. The latter, through post-processing, can appropriately reduce film crystal point density, but cannot fundamentally eliminate crystal point density caused by raw material factors. Therefore, rapid determination of crystal point density during raw material production is crucial, especially combining raw material crystal point density with evaluation methods.

[0004] The existing methods for evaluating thin film crystal points are as follows:

[0005] 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.

[0006]

[0007] As can be seen from the table above, crystal points smaller than 0.2mm were not included in the statistics, but these crystal points have a significant impact on the quality of optical protective films, and their size range cannot meet the quality requirements of LDPE raw materials for optical protective films.

[0008] JB / T10437-2004, "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. When the sample strip is irradiated by a light beam, the impurity particles are light-blocking. A constant, continuous, and adjustable light source is used. Under this light beam, the transmitted and blocked light beams of the sample strip are received by an electronic camera, and the impurity particle detector detects the size and number of particles. The resolution of the impurity particle detector should be better than 100 μm. The sample is a strip-shaped sheet material 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 method, and the surface of the strip-shaped sheet material is made smooth, clean, and free of contamination by guide rollers and calendering rollers. The number of impurity particles (0.175–0.250) mm on a 1 kg sample strip should not exceed 5, and the number of impurity particles larger than 0.250 mm should be zero. This method does not include statistics on crystal points smaller than 0.175 mm. These crystal points have a significant impact on the quality of optical protective films, and their dimensional accuracy cannot meet the quality requirements of LDPE raw materials for optical protective films.

[0009] CN112710669A discloses a method for rapidly evaluating the crystal points of homopolymer polypropylene lithium-ion battery rigid elastic separators, specifically involving a method for evaluating the crystal points of homopolymer polypropylene lithium-ion battery rigid elastic separators. The method includes: using a twin-screw extruder to extrude lithium-ion battery separator material through casting rollers; before winding the rigid elastic film, installing an online defect detector at a position after extrusion; before traction winding, stretching and extending the cast film through multiple layers, then flattening it between the last two sets of casting rollers to form a rigid elastic film; using the online defect detector to detect the crystal points of the lithium-ion battery rigid elastic separator, collecting crystal point data, and estimating product quality based on the number of crystal point classifications. This invention uses an online defect detector to obtain the relationship between product crystal points and ash content, resilience, and filter permeability, shortening product evaluation time. It allows for a preliminary judgment of the performance of lithium-ion battery separator material during the preparation of the rigid elastic film, greatly improving evaluation efficiency. The defect judgment criteria are classified as follows:

[0010] Superior grade: Total number of defects less than 600 per 100m 2 Furthermore, the total number of small crystals and small black dots is ≤300;

[0011] Qualified products: Grade 1 qualified products: 600 < total quantity ≤ 1000 pieces / 100m 2 And 300 / 100m 2 <Total number of small crystals and black dots ≤ 500 / 100m 2 Level 2 qualified products: 1000 < total quantity ≤ 2000 pieces / 100m 2 And 500 / 100m 2 <Total number of small crystals and black dots ≤ 1000 per 100m 2 Level 3 qualified products: 2000 < total quantity ≤ 3000 pieces / 100m 2 And 1000 / 100m 2 <Total number of small crystals and black dots ≤ 1500 / 100m 2 Non-conforming products: Total number > 3000 pieces / 100m 2 Furthermore, the total number of small crystals and small black dots is greater than 1500 per 100m. 2 .

[0012] It can be seen that this method includes the number of black dots, which is not allowed in optical protective films. Furthermore, it does not specify the crystal size, only the quantity requirement, which cannot meet the requirements of optical protective films.

[0013] GB / T11115-2009 specifies only fisheyes and streaks as the appearance criteria for LDPE film materials. Fisheyes are spherical lumps 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.

[0014] It can be seen that the existing crystal point evaluation can enable the timely handling of unqualified products, but the size range and accuracy cannot meet the quality requirements of LDPE raw materials for optical protective films.

[0015] To date, publicly reported technologies regarding optical protective films primarily focus on improvements in raw material production processes, coating, and formulation. While some testing involves the range of crystal point sizes, the precision required for these measurements is insufficient to meet the raw material requirements of optical protective films. Furthermore, meeting only the crystal point specification may result in insufficient melt strength, affecting film formation stability during blown film production. Currently, the suitability of optical protective film raw materials from manufacturers can only be determined through application by downstream users. This leads to lengthy evaluation cycles, and poor performance can result in significant losses for both manufacturers and downstream users. Therefore, a simple and rapid evaluation method for LDPE optical protective film resin is urgently needed to facilitate resin quality assessment by production units. Summary of the Invention

[0016] The purpose of this invention is to provide a method for evaluating polyethylene raw materials used in optical protective films, which can quickly and conveniently evaluate the quality of optical protective film raw materials.

[0017] To achieve the above objectives, the present invention provides a method for evaluating polyethylene raw materials for optical protective films, comprising the following steps:

[0018] (1) Extruding LDPE raw material into sheets of 0.03 to 0.09 mm on an extrusion device;

[0019] (2) The thin film is irradiated by a light beam generated by a constant, continuous, and adjustable light source. The light beams that are transmitted and blocked are received by an optical camera. The crystal particle detector detects the size and number of crystal particles with a size greater than or equal to 0.02 mm at a resolution greater than or equal to 20 μm. When the diameter of the crystal particles is ≥0.4 mm, or the number of crystal particles is >0.4 particles / m 2 If the product is unqualified, it is considered a substandard product; otherwise, it is considered a preliminarily qualified product.

[0020] (3) The number of crystal points and the melt strength of the LDPE resin raw material of the obtained preliminary qualified product are calculated. The relationship between the two satisfies the following formula and can be used as a raw material for optical protective films:

[0021] y≤6.9616x-27.78413x 2 -0.02853

[0022] Where x is the melt strength, calculated in Newtons based on a test at 190℃, with a value ranging from 0.04 to 0.15.

[0023] y represents the number of crystal points, expressed as the total number of crystal points per square meter of thin film.

[0024] The evaluation method for polyethylene raw materials used in optical protective films according to the present invention has a melt strength value of 0.06 to 0.14.

[0025] The melt strength is measured using a direct measurement method known in the art. This method is common knowledge in the field. Wu Chunshuang described the direct measurement method of polyethylene melt strength in "Rheological Characterization of Long-Chain Branched Materials for PERT Pipes" (Shanghai Plastics, 2017, 177(1):31-36) and "Test Method and Influencing Factors of Polyethylene Melt Strength" (Shanghai Plastics, 2015, (3):55-60), CN201180013377.5: Method for Preparing Polyethylene with High Melt Strength. The melt strength testing conditions recommended in this invention are as follows: testing is performed using a Goettfert RT-2000 melt tensile rheometer at a temperature of 190℃, capillary orifice aspect ratio of any one of 20 / 2, 10 / 1, 20 / 1, or 30 / 1 (preferably 20 / 2), and shear rate of 45s. -1 The traction roller spacing is 0.4mm to 1mm, preferably 0.5mm to 0.7mm, and the traction acceleration is 6mm / s². 2 .

[0026] The method described in step (2) is a well-known technique in the field. For example, the method of detecting the impurity content of YJ-35 and YJG-35 crosslinkable polyethylene insulation materials can be used, as specified in JB / T1043 7-2004 "Crosslinkable polyethylene insulation material for wires and cables". The method described is: "Under the illumination of the light beam generated by the constant, continuous and adjustable light source, the light beam transmitted and blocked by the light is received by the optical camera, and the crystal particle detector detects the size and number of crystal particles with a crystal particle size greater than or equal to 0.02 mm with a resolution greater than 20 μm". For example, the method described in Appendix B is sufficient to detect the impurity content of YJ-35 and YJG-35 crosslinkable polyethylene insulation materials. This application can perform crystal particle detection by meeting the requirements of the thickness in step (1) and the resolution in step (2) of the sample preparation.

[0027] In the evaluation method for polyethylene raw materials used in optical protective films according to the present invention, the number of crystal points in step (3) is the average value of 3 to 5 parallel tests on the same thin film. Using the average value can effectively eliminate errors.

[0028] The evaluation method for polyethylene raw materials used in optical protective films according to the present invention refers to LDPE raw materials that are granular materials without powder, black particles, and / or yellow particles in appearance. Before the LDPE raw materials are extruded into sheets on the extrusion device, the appearance of the LDPE raw material granules is visually inspected first. Only when the LDPE raw materials are free of powder, black particles, and / or yellow particles can the extrusion into sheets operation and subsequent testing be carried out; if the LDPE raw materials have powder, black particles, and / or yellow particles in appearance, they are judged to be unqualified raw materials.

[0029] In the evaluation method for polyethylene raw materials used in optical protective films according to the present invention, step (2) involves statistically analyzing the number of crystal points 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 0.4 mm, and ≥0.4 mm. Since optical protective films have very high requirements for film appearance, fewer crystal points are preferable. Because they are low-viscosity, given the same number of crystal points, smaller crystal point sizes are better, as they have less impact on the protected object.

[0030] The evaluation method for polyethylene raw materials used in optical protective films according to the present invention uses an extrusion device that is a single-screw extruder or a twin-screw extruder, and the extruder nozzle temperature is 140℃~180℃.

[0031] The evaluation method for polyethylene raw materials used in optical protective films according to the present invention has an extruder nozzle temperature of 150℃~170℃.

[0032] The evaluation method for polyethylene raw materials used in optical protective films according to the present invention uses an extrusion device with a rotation speed of 15 to 45 rpm.

[0033] The present invention describes an evaluation method for polyethylene raw materials used in optical protective films, wherein the extrusion apparatus is equipped with a winding device. The winding device ensures that the extruded sheet can be stretched without wrinkles and is not deformed, as both stretching deformation and wrinkles will lead to inaccurate crystal point test results. This technique is common knowledge in the field and is referred to as effective synergy. Specifically, the extrusion process involves placing the LDPE resin raw material in the extrusion apparatus for plasticizing and extruding, directly extruding a sheet with a thickness of 0.03–0.09 mm. This method is simple, uses less raw material, and allows for faster evaluation of the raw material's crystal points.

[0034] A crystal point testing device consists of a light source, an optical camera, and a crystal point particle detector. This device can be a commercially available one or assembled by the user. It only needs to be installed after the extrusion unit to test the sheet, and preferably between the extrusion unit and the winding unit.

[0035] The beneficial effects of this invention are:

[0036] This invention discloses an evaluation method for polyethylene raw materials used in optical protective films. By controlling the sample processing method and crystal point testing conditions, and establishing the relationship between the crystal points and melt strength of the extruded sheet, it enables rapid judgment of the raw material's qualification. 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 may be more accurate and the effect better due to the raw material properties and the surface condition of the sheet. This invention is applicable to the rapid evaluation of optical protective film raw materials. Detailed Implementation

[0037] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0038] Raw material source: Imported LDPE optical protective film special material is a commercially available product. Optical protective film resin from a PetroChina company, trial production samples 1, 2, 3, 4, 5, 6, 7, and 8.

[0039] Analysis method:

[0040] Melt strength was tested using a Goettfert RT-2000 melt tensile rheometer at a temperature of 190℃.

[0041] Crystal points: Detected using a HAP SCD-50 crystal point detector.

[0042] Example 1

[0043] For pilot production sample 1, extrusion was performed at an extruder die head temperature of 170℃, a speed of 20 rpm, and a thickness of 40 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 1.

[0044] Table 1

[0045]

[0046] The melt strength test result of the trial production sample 1 was 0.051 N, which is calculated using the formula 6.9616x - 27.78413x. 2 The calculated value of -0.02853 is 0.2542, and the crystal point test result is 0.22, which satisfies the condition y ≤ 6.9616x - 27.78413x. 2 -0.02853 indicates the product is qualified. It was applied at the optical protective film manufacturer, and the results show that it meets the requirements for use as an optical protective film.

[0047] Example 2

[0048] For pilot production sample 2, extrusion was performed at an extruder die head temperature of 180℃, a speed of 15 rpm, and a thickness of 30 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 2.

[0049] Table 2

[0050]

[0051] The melt strength test result of the trial production sample 2 was 0.04 N, according to the formula 6.9616x - 27.78413x 2 The calculated value of -0.02853 is 0.2055, and the crystal point test result is 0.19, which satisfies the condition y≤6.9616x-27.78413x. 2 -0.02853 indicates the product is qualified. Application results from optical protective film manufacturers show that it meets the requirements for use as an optical protective film.

[0052] Example 3

[0053] 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 measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 3.

[0054] Table 3

[0055]

[0056] The melt strength test result of the trial production sample 3 was 0.06 N, according to the formula 6.9616x - 27.78413x 2 The calculated value of -0.02853 is 0.289, and the test result is 0.27, which satisfies the condition y ≤ 6.9616x - 27.78413x. 2-0.02853 indicates the product is qualified. It was applied at the optical protective film manufacturer, and the results show that it meets the requirements for use as an optical protective film.

[0057] Example 4

[0058] For pilot production sample 4, extrusion was performed at an extruder die head temperature of 140℃, a speed of 45 rpm, and a thickness of 90 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 4.

[0059] Table 4

[0060]

[0061] The melt strength test result of trial production sample 4 was 0.07 N, according to the formula 6.9616x - 27.78413x 2 The calculated value of -0.02853 is 0.320, and the test result is 0.31, which satisfies the condition y ≤ 6.9616x - 27.78413x. 2 -0.02853 indicates the product is qualified. It was applied at the optical protective film manufacturer, and the results show that it meets the requirements for use as an optical protective film.

[0062] Example 5

[0063] For pilot production sample 5, extrusion was performed at an extruder die head temperature of 175℃, a speed of 40 rpm, and a thickness of 80 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 5.

[0064] Table 5

[0065]

[0066]

[0067] The melt strength test result of trial production sample 5 was 0.075 N, calculated according to the formula 6.9616x - 27.78413x. 2 The calculated value of -0.02853 is 0.337, and the crystal point test result is 0.32, which conforms to the formula y≤6.9616x-27.78413x. 2 -0.02853 indicates the product is qualified. It was applied at the optical protective film manufacturer, and the results show that it meets the requirements for use as an optical protective film.

[0068] Example 6

[0069] Imported LDPE optical protective film material was extruded into thin sheets at an extruder die temperature of 180℃, a speed of 35 rpm, and a thickness of 70 μm. A crystal point detector was used to measure a thickness of 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 6.

[0070] Table 6

[0071]

[0072] The melt strength test result of the raw material for the optical protective film was 0.068 N, according to the formula 6.9616x - 27.78413x. 2 The calculated value of -0.02853 is 0.316, and the test result is 0.30, which satisfies the condition y≤6.9616x-27.78413x. 2 -0.02853 indicates the product is qualified. It was applied at the optical protective film manufacturer, and the results show that it can meet the requirements for use of optical protective films.

[0073] Example 7

[0074] For pilot production sample 6, extrusion was performed at an extruder die head temperature of 180℃, a speed of 25 rpm, and a thickness of 50 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 7.

[0075] Table 7

[0076]

[0077] The melt strength test result of trial production sample 6 was 0.150 N, calculated according to the formula 6.9616x - 27.78413x. 2 The calculated value of -0.02853 is 0.391, and the crystal point test result is 0.37, which conforms to the formula y≤6.9616x-27.78413x. 2 -0.02853 indicates the product is qualified. Its application in the optical protective film manufacturer shows that it meets the requirements for use of optical protective films.

[0078] Example 8

[0079] For pilot production sample 7, extrusion was performed at an extruder die head temperature of 150℃, a speed of 33 rpm, and a thickness of 66 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 8.

[0080] Table 8

[0081]

[0082] The melt strength test result of trial production sample 7 was 0.0651 N, calculated according to the formula 6.9616x - 27.78413x. 2 The calculated value of -0.02853 is 0.307, and the crystal point test result is 0.24, which conforms to y≤6.9616x-27.78413x. 2 -0.02853 indicates the product is qualified. Its application in the optical protective film manufacturer shows that it meets the requirements for use of optical protective films.

[0083] Example 9

[0084] For pilot production sample 8, extrusion was performed at an extruder die head temperature of 150℃, a speed of 33 rpm, and a thickness of 66 μm. A crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 9.

[0085] Table 9

[0086]

[0087] The melt strength test result of trial production sample 8 was 0.08 N, according to the formula 6.9616x - 27.78413x 2 The calculated value of -0.02853 is 0.351, while the crystal point test result is 0.40, which does not meet the requirement of y≤6.9616x-27.78413x. 2 -0.02853 indicates the product is unqualified. This sample was used by the optical protective film manufacturer, and the results showed that the number of crystal points varied, the film quality stability was poor, and it could not meet the requirements for use as an optical protective film.

[0088] Comparative Example 1

[0089] For trial production sample 8, extrusion was performed at an extruder die head temperature of 150℃, a speed of 33 rpm, and a thickness of 66 μm. According to the crystal point range in CN105922689A, a crystal point detector was used to measure 33.6 μm at a resolution of 20 μm. 2 The number of crystal points on the sample was measured in three parallel tests, and the average value was taken. The results are shown in Table 10.

[0090] Table 10

[0091]

[0092] The test was conducted within the specified range and met the required specifications. However, as can be seen from Example 9, it did not meet the manufacturer's requirements because many small crystal points smaller than 0.2 mm were ignored.

[0093] Comparative Example 2

[0094] For the trial production sample 8, extrusion was performed at an extruder die head temperature of 150℃, a speed of 25 rpm, and a thickness of 0.5 mm. According to the crystal point range of JB / T10437-2004, the number of impurities on a 1 kg sample strip was tested with a crystal point detector at a resolution of 20 μm. The test was performed in parallel for 3 times, and the average value was taken. The results are shown in Table 11.

[0095] Table 11

[0096]

[0097] The test was conducted within the specified range and met the required specifications. However, as can be seen from Example 9, it did not meet the manufacturer's requirements because many small crystal points were overlooked.

[0098] Comparative Example 3

[0099] The trial production sample 8 was extruded into a thin sheet at an extruder die head temperature of 150℃, a rotation speed of 33 rpm, and a thickness of 66 μm. A crystal point detector was used to measure the thickness at 33.6 μm with a resolution of 20 μm. 2 The samples were statistically analyzed according to the crystal point classification method in CN112710669A. The tests were performed in parallel three times, and the average value was taken. The results are shown in Table 12.

[0100] Table 12

[0101]

[0102] As can be seen from Table 12, it far meets the indicators of superior grade products, but as can be seen from Example 8, it cannot meet the manufacturer's requirements because its crystal point requirements are relatively low and cannot meet the requirements of optical protective film.

[0103] 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 polyethylene raw materials used in optical protective films, characterized in that, Includes the following steps: (1) Extruding LDPE raw material into sheets of 0.03 to 0.09 mm on an extrusion device; (2) When the thin film is irradiated by a light beam generated by a constant, continuous, and adjustable light source, the light-transmitting and light-blocking light beams are received by an optical camera. The crystal particle detector detects the size and number of crystal particles with a size greater than or equal to 0.02 mm at a resolution greater than or equal to 20 μm. When the diameter of the crystal particles is ≥0.4 mm, or the number of crystal particles is >0.4 / m 2 If the product is unqualified, it is considered a substandard product; otherwise, it is considered a preliminarily qualified product. (3) The number of crystal points and the melt strength of the LDPE resin raw material of the obtained preliminary qualified product are calculated. The relationship between the two satisfies the following formula and can be used as a raw material for optical protective films: y≤6.9616x-27.78413x 2 -0.02853 Where x is the melt strength, calculated in Newtons based on a test at 190°C, with a value ranging from 0.04 to 0.

15. y represents the number of crystal points, expressed as the total number of crystal points per square meter of thin film.

2. The evaluation method for polyethylene raw materials used in optical protective films according to claim 1, characterized in that, The melt strength value is 0.06 to 0.

14.

3. The evaluation method for polyethylene raw materials used in optical protective films according to claim 1, characterized in that, The number of crystal points in step (3) is the average value of 3 to 5 parallel tests on the same thin slice.

4. The evaluation method for polyethylene raw materials used in optical protective films according to claim 1, characterized in that, The LDPE raw material is a granular material with no powder, black particles and / or yellow particles in appearance.

5. The evaluation method for polyethylene raw materials used in optical protective films according to claim 1, characterized in that, In step (2), the number of crystal points with crystal point sizes ranging from 0.02 to 0.1 mm, 0.1 to 0.2 mm, 0.2 to 0.3 mm, 0.3 to 0.4 mm, and ≥0.4 mm are counted respectively.

6. The method for evaluating polyethylene raw materials for optical protective films according to claim 1, characterized in that, The extrusion device is a single-screw extruder or a twin-screw extruder, and the extruder nozzle temperature is 140℃~180℃.

7. The method for evaluating polyethylene raw materials for optical protective films according to claim 6, characterized in that, The extruder nozzle temperature is 150℃~170℃.

8. The method for evaluating polyethylene raw materials for optical protective films according to claim 1, characterized in that, The extrusion unit rotates at 15–45 rpm.

9. The method for evaluating polyethylene raw materials for optical protective films according to claim 1, characterized in that, The extrusion device is equipped with a winding device.

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