A PP-based standard sample for testing ball indentation hardness and its preparation method

Abstract

This invention relates to a PP-based standard sample for testing ball indentation hardness and its preparation method, belonging to the field of plastic physical testing technology. The PP-based standard sample for testing ball indentation hardness of this invention comprises the following components by weight: 50-80 parts polypropylene resin, 10-50 parts polystyrene resin, 5-40 parts filler, 1-10 parts compatibilizer, 0.1-5 parts antioxidant, and 0.1-1 parts processing aid; the polypropylene resin has a melt flow rate of 14-16 g / 10 min under test conditions of 200℃ and 5 kg; the filler is at least one of nano-calcium carbonate, barium sulfate, or a mixture of nylon and glass fiber. This invention uses polypropylene resin as the base material and selects specific types and contents of fillers and compatibilizers to ensure that the prepared PP-based standard sample for testing ball indentation hardness has good uniformity and stability, a wide range of applications, and can meet the requirements of the two load (132N and 358N) test conditions in the standard.

Description

Technical Field

[0001] This invention belongs to the field of plastic physical testing technology, specifically relating to a PP-based standard sample for testing ball indentation hardness and its preparation method. Background Technology

[0002] Ball indentation hardness testing is a metrological standard used to assess the hardness of plastics. Under the sequential application of an initial test force and a main test force, a steel ball indenter of a certain diameter is pressed into the surface of the plastic sample. After holding the sample for a certain period, the depth of the indentation is measured to determine the entire process of sample hardness. Ball indentation hardness testing is primarily used for research and development, quality control, and providing data for acceptance and rejection according to product standards. It provides a reliable metrological standard for assessing the hardness of plastics in my country's chemical, light industrial, aerospace, and automotive industries, and also provides an authoritative arbitration basis for trade settlement and quality certification. Ball indentation hardness testers are devices used to evaluate the hardness performance of materials. To obtain accurate test results, ensuring the accuracy of the testing machine is crucial. Therefore, it is necessary not only to regularly calibrate and verify the testing machine, but also to continuously monitor and evaluate the equipment's condition and standardize personnel operation. To improve the accuracy of test results, laboratories often optimize testing equipment or operating procedures, but this cannot fully evaluate the accuracy of the test results and has certain limitations.

[0003] Currently, metals are commonly used as standard materials for ball indentation hardness testing. For example, the patent "Manufacturing Process of Plastic Ball Indentation Hardness Standard Block" provides a manufacturing process for plastic ball indentation hardness standard blocks that can be effectively used for testing the hardness and mechanical properties of polymer materials. It selects industrial pure aluminum plates that meet relevant conditions as the base material, and then obtains more homogeneous metal ball indentation hardness standard blocks through melting and casting. This type of metal standard material has high requirements for its storage environment, is only suitable for one test load, has a high purchase cost, and has a service life of one year.

[0004] The ball indentation hardness test process requires verification of equipment status and personnel operation to ensure the accuracy of test results. Currently, laboratories cannot identify anomalies in advance; verification is only carried out step by step by checking various parts of the equipment and personnel operations after an anomaly complaint occurs. This process is cumbersome and labor-intensive. However, by periodically testing samples to verify the equipment and standardize personnel operation, the process is simple. It not only allows for the timely detection of equipment problems and human error but also helps to trace the causes of test anomalies, serving as an effective means of daily equipment status and personnel supervision. However, there is a lack of standard samples for ball indentation hardness in the market for plastic materials. Standard samples for metal materials have drawbacks such as high storage requirements and high costs. Furthermore, current market offerings only have standard samples for one load condition, lacking a standard sample that can be used for pre-testing inspection and calibration of equipment under two load conditions, as well as for evaluating the consistency of test results between laboratories. Therefore, a target-uniform and stable standard sample is needed for inter-laboratory proficiency testing comparisons, internal laboratory verification of the accuracy of testing methods, verification of the stability of testing instruments, quality control management, uncertainty assessment, and competency evaluation of testing personnel. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PP-based standard sample for detecting the hardness of ball indentation and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a PP-based standard sample for testing the hardness of ball indentation, comprising the following components by weight: 50-80 parts of polypropylene resin, 10-50 parts of polystyrene resin, 5-40 parts of filler, 1-10 parts of compatibilizer, 0.1-5 parts of antioxidant, and 0.1-1 parts of processing aid; the polypropylene resin has a melt flow rate of 14-16 g / 10 min under test conditions of 200°C and 5 kg; the filler is at least one of calcium carbonate, barium sulfate, or a mixture of nylon and glass fiber. Preferably, the polystyrene resin has a melt flow rate of 4.4-9.8 g / 10 min under a load of 5 kg and 200°C. Polypropylene resin has a high cost-performance ratio and is abundant in supply. This invention uses polypropylene resin as the base material, and obtains standard samples with different hardness steps by compounding other resins and adding different fillers. More preferably, the average particle size of the calcium carbonate and barium sulfate is 0.01-0.1 μm. Fillers are one of the main factors affecting the ball indentation hardness of PP. Therefore, when selecting fillers, it is necessary to consider the influence of the material's own characteristics on the sample, aiming to improve the sample's ball indentation hardness, heat resistance, weather resistance, and water resistance, achieving a more optimized effect for the required performance. Nano-calcium carbonate has an oleophilic and hydrophobic surface, good compatibility with resin, improves the sample's dimensional stability and heat resistance, and also plays a role in stabilizing the filler and enhancing the ball indentation hardness. Nylon resin with glass fiber restricts the mutual movement of plastic polymer chains, reduces the shrinkage rate of standard samples, increases the ball indentation hardness of standard samples, and improves the thermal stability of standard samples.

[0007] In a preferred embodiment of the PP-based standard sample for testing the hardness of ball indentation according to the present invention, the polypropylene resin is a copolymer polypropylene resin. Polypropylene resin is inexpensive, readily available, and easy to prepare samples, but its performance is greatly affected by temperature and its weather resistance is poor.

[0008] In a preferred embodiment of the PP-based standard sample for testing ball indentation hardness according to the present invention, the number-average molecular weight of the nylon resin in the nylon-glass fiber mixture is 15,000-36,000, and the average length of the glass fiber is 0.2-0.6 mm. The average length of the glass fiber in the PP-based standard sample for testing ball indentation hardness obtained by the present invention is not significantly different from the average length of the glass fiber in the nylon-glass fiber mixture. The inventors of this application have found that the addition of the nylon-glass fiber mixture within the above parameter range can improve the thermal stability of the standard sample. Preferably, the nylon resin is at least one of PA6, PA66, or PA12.

[0009] In a preferred embodiment of the PP-based standard sample for testing ball indentation hardness according to the present invention, the weight ratio of nylon resin to glass fiber in the nylon-glass fiber mixture is 2–4:1. The inventors of this application have discovered that when the weight ratio of nylon resin to glass fiber in the nylon-glass fiber mixture is 2–4:1, the prepared standard sample exhibits high ball indentation hardness and stability.

[0010] In a preferred embodiment of the PP-based standard sample for testing ball indentation hardness according to the present invention, the compatibilizer is maleic anhydride multi-monomer-grafted polypropylene. The inventors of this application have discovered that using maleic anhydride multi-monomer-grafted polypropylene as a compatibilizer can increase the compatibility between the components and can chemically react with nylon molecules, improving the barrier effect against water penetration and reducing the water absorption of nylon.

[0011] In a preferred embodiment of the PP-based standard sample for testing the hardness of ball indentation according to the present invention, the antioxidant is at least one of hindered phenolic antioxidants or phosphite antioxidants. The addition of antioxidants can prevent significant natural aging of the standard material during routine storage. More preferably, the antioxidant is a mixture of 1010 and antioxidant 168 in a weight ratio of 1:(1-2).

[0012] In a preferred embodiment of the PP-based standard sample for testing the hardness of ball indentation according to the present invention, the processing aid includes a dispersant and a lubricant.

[0013] The present invention also provides a method for preparing the PP-based standard sample for detecting ball indentation hardness, comprising the following steps:

[0014] (1) Polypropylene resin, styrene resin, filler, compatibilizer, antioxidant and processing aid are sequentially fed into a high-speed mixer for mixing and stirring. After melting and mixing, the mixture is extruded and granulated, and then dried to obtain PP granules.

[0015] (2) The PP granules are injection molded to obtain the PP-based standard sample for testing the hardness of the ball indentation.

[0016] In a preferred embodiment of the method for preparing PP-based standard samples for detecting ball indentation hardness according to the present invention, the apparatus for extrusion granulation after melt mixing is a twin-screw extruder; the twin-screw extruder has a length-to-diameter ratio of 25-50:1, a main extruder speed of 300-600 rpm, and a barrel temperature of 170-260℃; the injection molding temperature is 190-260℃, the pressure is 55-60 Bar, and the speed is 25-30%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a PP-based standard sample for testing ball indentation hardness. The present invention uses polypropylene resin as the base material, and by selecting the specific types and contents of fillers and compatibilizers, the prepared PP-based standard sample for testing ball indentation hardness has good molding ability and stability, a wide range of applications, and can meet the requirements of different test conditions in the standard. The PP-based standard sample for testing ball indentation hardness of the present invention fills the gap in the current market where there are no standard samples of plastic ball indentation hardness, and makes up for the deficiency of metal ball indentation hardness standard blocks which are only applicable to one load condition. It can be used for proficiency testing comparisons of plastic ball indentation hardness testing projects between laboratories, accuracy verification of internal laboratory testing methods, stability verification of testing instruments, internal laboratory quality control management, uncertainty assessment, and competency assessment of testing personnel. Detailed Implementation

[0018] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0019] The raw materials used in the embodiments and comparative examples of the present invention are described below, but are not limited to these materials:

[0020] PP resin 1: PP K9017, Formosa Plastics Co., Ltd., melt flow rate at 230℃ and 2.16kg load is 16g / 10min;

[0021] PP resin 2: PP K8009, SK Chemicals International Trading (Shanghai) Co., Ltd., melt flow rate of 7 g / 10 min at 230℃ and 2.16 kg load.

[0022] PP resin 3: PP 320 powder, Sinopec Hunan Petrochemical Co., Ltd., melt flow rate at 230℃ and 2.16kg load is 32g / 10min;

[0023] PP resin 4: PP-K8003, Hengli Petrochemical (Dalian) Chemical Co., Ltd., melt flow rate of 3g / 10min at 230℃ and 2.16kg load;

[0024] PS Resin 1: PS MA5210, Yashide Chemical (Jiangsu) Co., Ltd., melt flow rate at 200℃ and 5kg load is 4.4g / 10min;

[0025] PS resin 2: GPPS123, Shanghai SECCO Petrochemical Co., Ltd., melt flow rate at 200℃ and 5kg load is 9.8g / 10min;

[0026] Filler 1: Nano calcium carbonate, average particle size 0.05μm, commercially available;

[0027] Filler 2: PA6 + 30% GF, density 1.36 g / cm³ 3 Commercially available; the glass fiber is 0.4 mm in length and the nylon resin has a number-average molecular weight of 16,000.

[0028] Filler 3: PA66 + 30% GF, density 1.45 g / cm³ 3 Commercially available; the glass fiber is 0.4 mm in length and the nylon resin has a number-average molecular weight of 16,000.

[0029] Filler 4: PA12 + 50% GF, density 1.45 g / cm³ 3 Commercially available; the glass fiber is 0.2 mm in length and the nylon resin has a number-average molecular weight of 15,000.

[0030] Filler 5: PA6 + 50% GF, density 1.50 g / cm³ 3 Commercially available; the glass fiber is 0.4 mm in length and the nylon resin has a number-average molecular weight of 16,000.

[0031] Filler 6: PA66 + 25% GF, density 1.24 g / cm³ 3 Commercially available; the glass fiber is 0.4 mm in length and the nylon resin has a number-average molecular weight of 16,000.

[0032] Compatibilizer 1: Maleic anhydride multimonomer grafted polypropylene, LyondellBasell, melt flow rate of 5.4 g / 10 min at 230°C and 2.16 kg load;

[0033] Compatibilizer 2: EMA1609AC compatibilizer, commercially available;

[0034] Antioxidant: A mixture of hindered phenolic antioxidants and commercially available phosphite antioxidants, wherein the mass ratio of hindered phenolic antioxidants to phosphite antioxidants is 1:1, and the mixture is commercially available;

[0035] Processing aids: lubricant oxidized polyethylene wax and dispersant OW-2 (white oil), wherein the mass ratio of the dispersant to the lubricant is 1:1, commercially available.

[0036] Examples 1-10, Comparative Examples 1-3

[0037] The composition of the PP-based standard samples for testing the hardness of ball indentation in Examples 1-10 and Comparative Examples 1-3 of this invention is shown in Table 1 below.

[0038] The preparation method of PP-based standard samples for testing ball indentation hardness in Examples 1-10 and Comparative Examples 1-3 of this invention is as follows: Resin, filler, compatibilizer, antioxidant, and processing aid are weighed according to the specified proportions and sequentially added to a high-speed mixer for mixing and stirring. After uniform mixing, a premix is ​​obtained. The premix is ​​added to a twin-screw extruder, where the materials are fully melted and fused under the shearing and mixing action of the screws. After extrusion, granulation, and drying, PP granules are obtained. The obtained PP granules are then added to an injection molding machine to process the ball indentation hardness standard samples. The extruder processing conditions are as follows: twin-screw extruder length-to-diameter ratio 25-50:1, main extruder speed 300-600 rpm, barrel temperature 170-260℃; injection molding conditions are: injection temperature 190-260℃, pressure 55-60 Bar, and speed 25-30%.

[0039] Table 1. Composition of PP-based standard samples used for testing ball indentation hardness in Examples 1-10 and Comparative Examples 1-3.

[0040]

[0041]

[0042] The uniformity and stability of the PP-based standard samples used for testing the ball indentation hardness in Examples 1-10 and Comparative Examples 1-3 were tested respectively.

[0043] Performance testing methods:

[0044] (1) Homogeneity test: According to CNAS-GL003-2018 "Guidelines for evaluating the homogeneity and stability of proficiency testing samples", one-way ANOVA was used to test the homogeneity among the test samples. Taking the product of Example 1 as an example, 10 groups of prepared Example 1 samples were randomly selected, and two standard samples were taken from each group. The standard samples were conditioned in a constant temperature and humidity chamber at (23±2)℃ and (50±5)%RH for 24 hours, and then tested according to the requirements of 132N load and 358N load in GB / T 3398.1-2008. Other examples and comparative samples were tested using the same method. According to the degree of freedom and significance level, the critical value of uniformity for each product was F0.05(9,10)=3.02. If the statistical value F<F0.05(9,10)=3.02, it was considered that there was no significant difference between groups and within groups, which meant that the sample was uniform. The smaller the value, the more uniform the product. If the F value ≥ the critical value F0.05(9,10)=3.02, it meant that the product was not uniform enough.

[0045] (2) Stability Test: According to CNAS-GL003:2018 "Guidelines for Evaluation of Homogeneity and Stability of Proficiency Testing Samples", the stability of the samples was tested using the t-test method, specifically the consistency between two average values. The homogeneity test data was used as one average value. Twenty prepared samples were randomly selected at 15-day intervals. The standard samples were conditioned in a constant temperature and humidity chamber at (23±2)℃ and (50±5)%RH for 24 hours before testing. The average value of this test data was used as the average value of another parallel group. The stability of the samples was tested using the t-test method, specifically the consistency between two average values. The homogeneity test data was used as one average value. The t-values ​​of each example product were calculated using the two average value samples. If the t-value was less than the critical value t... 0.05 If (38) = 2.024, it means that there is no significant difference between the two groups of products and the product has ideal stability; the smaller the t value, the higher the product stability; if the t value is greater than the critical value t0.05(38) = 2.024, it means that the product does not have ideal stability.

[0046] The test results are shown in Tables 2 and 3.

[0047] Table 2

[0048]

[0049] Table 3

[0050]

[0051]

[0052] As can be seen from the tables above, the PP-based standard samples for testing ball indentation hardness described in this invention exhibit good uniformity (F values ​​did not exceed the critical value) and stability. According to the data from Example 3 and Comparative Examples 1-2, products prepared using polypropylene resin at 200℃ and a melt flow rate of 14-16 g / 10 min or less under test conditions of 5 kg showed poor uniformity, and the standard deviation in the stability test was much higher than that of Example 3. Data from Examples 3, 9, and 10 show that the uniformity and stability of the standard products are related to the weight ratio of nylon resin to glass fiber in the nylon-glass fiber mixture. When the weight ratio of nylon resin to glass fiber in the nylon-glass fiber mixture is within the preferred range, the obtained standard products exhibit better uniformity and stability.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A PP-based standard sample for testing the hardness of ball indentation, characterized in that, The product comprises the following components by weight: 50-80 parts polypropylene resin, 10-50 parts polystyrene resin, 5-40 parts filler, 1-10 parts compatibilizer, 0.1-5 parts antioxidant, and 0.1-1 parts processing aid; the polypropylene resin has a melt flow rate of 14-16 g / 10 min under test conditions of 200°C and 5 kg; the filler is at least one of nano-calcium carbonate, barium sulfate, or a mixture of nylon and glass fiber; the polystyrene resin has a melt flow rate of 4.4-9.8 g / 10 min under test conditions of 200°C and 5 kg load.

2. The PP-based standard sample for testing the hardness of ball indentation according to claim 1, characterized in that, The polypropylene resin is a copolymer polypropylene resin.

3. The PP-based standard sample for testing the hardness of ball indentation according to claim 1, characterized in that, The nylon-glass fiber blend comprises nylon resin and glass fiber, wherein the number average molecular weight of the nylon resin in the nylon-glass fiber blend is 15,000-36,000, and the average length of the glass fiber is 0.2-0.6 mm.

4. The PP-based standard sample for testing the hardness of ball indentation according to claim 3, characterized in that, The weight ratio of nylon resin to glass fiber in the nylon-glass fiber mixture is 2 to 4:

1.

5. The PP-based standard sample for testing the hardness of ball indentation according to claim 1, characterized in that, The compatibilizer is maleic anhydride multi-monomer grafted polypropylene.

6. The PP-based standard sample for testing the hardness of ball indentation according to claim 1, characterized in that, The antioxidant is at least one of hindered phenolic antioxidants or phosphite antioxidants.

7. The PP-based standard sample for testing the hardness of ball indentation according to claim 1, characterized in that, The processing aids include dispersants and lubricants.

8. The method for preparing PP-based standard samples for testing ball indentation hardness according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Polypropylene resin, polystyrene resin, filler, compatibilizer, antioxidant and processing aid are sequentially fed into a high-speed mixer for mixing and stirring. After melting and mixing, the mixture is extruded and granulated, and then dried to obtain PP granules. (2) The PP granules are injection molded to obtain the PP-based standard sample for testing the hardness of the ball indentation.

9. The method for preparing PP-based standard samples for detecting ball indentation hardness according to claim 8, characterized in that, The device for extruding and granulating after melt mixing is a twin-screw extruder; the twin-screw extruder has a length-to-diameter ratio of 25-50:1, a main extruder speed of 300-600 rpm, and a barrel temperature of 170-260℃; the injection molding temperature is 190-260℃, the pressure is 55-60 Bar, and the speed is 25-30%.

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