Long glass fiber reinforced polypropylene material with high weld mark strength and preparation method thereof

Abstract

The invention provides a preparation method of a long glass fiber reinforced polypropylene material with high weld mark strength. The long glass fiber reinforced polypropylene comprises the following components in percentage by mass: 5-50% of continuous long glass fiber, 5-10% of chopped flat glass fiber, 40-90% of polypropylene, 0-8% of compatilizer and 0.5-1.5% of antioxidant. The chopped flat glass fibers are introduced, so that the weld mark strength of the long glass fiber reinforced polypropylene is improved, the long glass fiber reinforced polypropylene material is suitable for various application scenes such as automobile interior and exterior decoration and household appliances, and powerful help is provided for improving the external force resisting capacity and the environment temperature and humidity alternating resisting capacity of a product in the actual use process.

Description

Technical Field

[0001] The invention relates to a method for improving the performance of a modified polypropylene material, in particular to a long glass fiber reinforced polypropylene material with high weld mark strength and a preparation method thereof. Background Art

[0002] As the concept of replacing steel with plastic deepens in the automotive industry, many types of parts, such as tailgate inner panels, front end frames, sunroof components, etc., are beginning to use glass fiber reinforced polypropylene materials to replace or partially replace the original metal parts. The reliability and durability of product performance are one of the key evaluation indicators.

[0003] However, glass fiber reinforced polypropylene materials are more likely to produce a large number of weld marks during the injection molding process. The main reasons include: uneven fiber orientation, residual stress, microstructural differences in the weld line area, and stress concentration. Compared with the melt temperature, the mold temperature is lower, and the melt in different directions flows forward while cooling. The melt at the front end of the injection molding has cooled when multiple strands meet and cannot be completely fused. Because the mold cannot be completely replicated, the weld mark is formed. The location of the weld mark will become a weak link in the part structure, with a greater risk of cracking / deformation, and there are also obvious defects in appearance, morphology, color, etc.

[0004] By optimizing the injection molding process parameters and mold design, the generation of weld marks can be effectively reduced or eliminated:

[0005] 1. Increase mold temperature: Increasing mold temperature can promote the mutual diffusion of polymers at the weld, thereby increasing weld strength;

[0006] 2. Optimize injection molding process parameters: Adjusting process parameters such as injection speed, holding pressure and cooling time can minimize welding defects and improve the overall part quality;

[0007] 3. Mold defects: The weld mark position has poor exhaust, and the residual air squeezed by the melt in the mold cavity cannot be discharged in time, which aggravates the weld mark. An exhaust port or dirty edge can be set to make the melt more fully integrated and enhance the weld strength; the mold process length will also affect the structure and performance of the weld, and an optimized design is required.

[0008] However, this reduction or elimination is often only effective for welding parts with simple structures. For parts with complex structures, such as places with many holes or where inserts are located, it is difficult to improve them simply through process or structure, and the material end also needs to cooperate. Summary of the invention

[0009] In view of the above problems, the present invention proposes a new method for improving the weld mark strength of long glass fiber reinforced polypropylene. This method effectively enhances the strength of the welded part by introducing short chopped flat glass fibers into long glass fiber reinforced polypropylene, thereby improving the overall structure's ability to resist external forces and adapt to environmental changes. The present invention provides a long glass fiber reinforced polypropylene material with high weld mark strength and a preparation method thereof, which is applied to various application scenarios such as automotive interior and exterior decoration, home appliances, etc., and provides strong help for improving the product's tolerance to environmental temperature and humidity changes during actual use.

[0010] The technical solution adopted by the present invention to solve its technical problem is:

[0011] A long glass fiber reinforced polypropylene material with high weld mark strength, the composition of which is as follows in terms of mass percentage:

[0012]

[0013] The method for improving the weld mark strength of long glass fiber reinforced polypropylene is characterized in that the melt flow rate of the polypropylene resin is relatively high, 30 to 150 g / 10 min, and the test conditions are 230° C.*2.16 kg.

[0014] The method for improving the weld mark strength of long glass fiber reinforced polypropylene is characterized in that the continuous long glass fiber is: long glass fiber direct untwisted roving for LFT, with a specification of 500-3000tex; the short chopped flat glass fiber is: alkali-free short chopped flat glass fiber treated with a silane coupling agent, with a flatness of 2-5%, and the length of the short chopped glass fiber is 2-5mm.

[0015] The method for improving the weld mark strength of long glass fiber reinforced polypropylene is characterized in that: the compatibilizer is maleic anhydride grafted polypropylene, and its function is to improve the compatibility between glass fiber and polypropylene;

[0016] The method for improving the weld mark strength of long glass fiber reinforced polypropylene is characterized in that: the antioxidant includes a main antioxidant of hindered phenol and hindered amine, and a secondary antioxidant formed by a combination of one or more of phosphites, thiodipropionates and thiols, so as to enhance the thermal stability of the modified material during the production process and subsequent use;

[0017] The above-mentioned long glass fiber reinforced polypropylene material with high weld mark strength and a preparation method thereof include the following steps:

[0018] (1) Weigh polypropylene, compatibilizer, and antioxidant according to weight ratio, put them into a high-speed mixer, and stir them at room temperature for 10 to 30 minutes.

[0019] (2) adding the mixed material in step (1) to the main feed port of a twin-screw extruder, adding the short chopped flat glass fibers weighed according to the weight ratio to the side feed port of the twin-screw extruder of the long glass fiber reinforced polypropylene production line, mixing at 190-280° C. to fully impregnate the long glass fiber bundles, and then extruding and granulating to obtain the long glass fiber reinforced polypropylene material with high weld mark strength of the present invention.

[0020] Compared with the prior art, the main innovations of the present invention are as follows:

[0021] 1. The introduction of short chopped flat glass fibers effectively enhances the strength of the welded parts of glass fiber reinforced polypropylene materials. Due to the orientation and brittleness of long glass fibers, such materials are prone to microcracks at the welded interface, reducing the overall strength. However, the present invention can hinder the expansion of microcracks and improve the tensile strength, shear strength and other key performance indicators of the welded parts by adding short chopped flat glass fibers.

[0022] 2. Improve the service life of glass fiber reinforced polypropylene materials in harsh environments. In actual use, glass fiber reinforced polypropylene materials often encounter harsh environments such as alternating temperature and humidity, which leads to a decrease in the strength of the welded parts and affects the overall structural performance. The present invention effectively enhances the environmental resistance of the welded parts by introducing short chopped flat glass fibers, greatly improving the service life of glass fiber reinforced polypropylene materials in harsh environments.

[0023] 3. Applicable to a variety of industrial application scenarios. Glass fiber reinforced polypropylene materials are widely used in the fields of automotive interior and exterior decoration, home appliances, etc., and have high requirements for structural strength and environmental adaptability. The method proposed in the present invention can effectively improve the welding performance of glass fiber reinforced polypropylene materials, providing strong support for the above application scenarios, and also providing ideas for solving other material-related problems.

[0024] Compared with the prior art, the present invention has the following improvement effects:

[0025] (1) The long glass fiber reinforced polypropylene material of the present invention adopts a high melt index polypropylene resin base material, so that the filled glass fibers are oriented along the flow direction as much as possible, and can intersect and interweave at the weld mark to form an interlaced state, thereby enhancing the interface bonding between the glass fibers and the polypropylene between the two melts. At the same time, the hot melt is allowed to arrive before the cold material at the front end of the injection molding as soon as possible, thereby avoiding obvious weld marks as much as possible;

[0026] (2) The long glass fiber reinforced polypropylene material of the present invention introduces short chopped flat glass fibers. The two melts solidify while flowing. When they collide with each other at the weld mark, they will not fuse. The long glass fibers are longer and flow slower, so this characteristic is more obvious. The introduction of short chopped flat glass fibers allows the glass fibers at the weld mark to intersect with the other's matrix along with the melt. The polypropylene is oriented and crystallized on the surface of the glass fibers, generating a certain interface bonding force. The flat glass fibers play a certain connecting and supporting role at the weld, hindering the expansion of cracks and enhancing the weld mark strength at the weld.

[0027] (3) The present invention introduces short-cut flat glass fibers with a relatively low content, thereby preserving the overall performance of the material to the greatest extent possible without causing very significant losses. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further illustrated by examples and comparative examples below. Without violating the purpose of the present invention, the present invention should not be limited to the specific contents of the following experimental examples.

[0029] Raw materials used in the embodiments of the present invention:

[0030] Polypropylene PP-1: a commercially available polypropylene resin having a melt flow rate of 60 g / 10 min;

[0031] Polypropylene PP-2: a commercially available polypropylene resin having a melt flow rate of 70 g / 10 min;

[0032] Compatibilizer: Maleic anhydride grafted polypropylene MAH-g-PP, commercially available.

[0033] Antioxidants: Hindered phenol antioxidant 1010, phosphite antioxidant 619F, distearate thiodipropionate DSTP.

[0034] Continuous long glass fiber: specification is 1200tex, commercially available;

[0035] Chopped flat glass fiber: flatness 3%, length 3mm, commercially available.

[0036] Product performance test method:

[0037] Density: According to ISO 1183 method, sample specification 10*10*4mm, test condition method A;

[0038] Impact strength: According to ISO 179 method, sample size 80*10*4mm;

[0039] Notched impact strength: According to ISO 179 method, sample size 80*10*4mm;

[0040] Bending strength: According to ISO 178 method, the sample specification is 80*10*4mm, the test speed is 2mm / min, and the span is 64mm;

[0041] Flexural modulus: According to ISO 178 method, the sample size is 80*10*4mm, the test speed is 2mm / min, and the span is 64mm;

[0042] Tensile strength: According to ISO 527 method, 1A specimen, tensile speed 5mm / min;

[0043] Weld mark strength: Cut samples from the weld mark mold plate, according to ISO 527 method, 1A sample, tensile speed 5mm / min;

[0044] Examples 1-5

[0045] Polypropylene, compatibilizer, antioxidant and glass fiber were weighed according to the weight percentages of Examples 1 to 5 described in Table 1.

[0046] Preparation method:

[0047] (1) Weigh polypropylene, compatibilizer, and antioxidant according to weight ratio, put them into a high-speed mixer, and stir them at room temperature for 10 to 30 minutes.

[0048] (2) adding the mixed material in step (1) to the main feed port of a twin-screw extruder, adding the short chopped flat glass fibers weighed according to the weight ratio to the side feed port of the twin-screw extruder of the long glass fiber reinforced polypropylene production line, mixing at 190-280° C. to fully impregnate the long glass fiber bundles, and then extruding and granulating to obtain the long glass fiber reinforced polypropylene material with high weld mark strength of the present invention.

[0049] Comparative Examples 1-3

[0050] (1) Weigh polypropylene, compatibilizer, and antioxidant according to weight ratio, put them into a high-speed mixer, and stir them at room temperature for 10 to 30 minutes.

[0051] (2) adding the mixed material in step (1) to the main feed port of a twin-screw extruder, adding the short chopped flat glass fibers weighed according to the weight ratio to the side feed port of the twin-screw extruder of the long glass fiber reinforced polypropylene production line, mixing at 190-280° C. to fully impregnate the long glass fiber bundles, and then extruding and granulating to obtain the long glass fiber reinforced polypropylene material with high weld mark strength of the present invention.

[0052] The standard test specimens were prepared by injection molding machine. The test results are shown in Table 1.

[0053] Table 1 Performance test results

[0054]

[0055]

[0056] It can be seen from Examples 1-5 and the comparative example in Table 1 that when short-cut flat glass fibers are introduced into long glass fiber reinforced polypropylene materials, certain negative effects will be brought to the material properties. When the addition ratio is higher than 4%, this effect is more obvious, but when the addition ratio is 2-4%, the degree of influence is small, and the amount of short-cut glass fibers introduced should not reach more than 4%. In addition, the introduction of short-cut glass fibers has a certain effect on the weld mark strength of long glass fiber reinforced polypropylene materials. When the introduction amount is within 4%, this effect is positive. When the introduction amount is more than 6%, the overall performance loss of the material is more obvious, but the effect of improving the weld mark strength is large.

[0057] It can be seen from Examples 1-5 and Comparative Examples 1-3 in Table 1 that when the filling amount of long glass fiber reinforced polypropylene material is high, the introduction of short chopped flat glass fibers brings less loss to the overall performance of the material within a certain range (within 4%). If the filling amount of the material itself is low, the introduction of short chopped glass fibers will bring obvious performance loss. Therefore, this solution is more suitable for long glass fiber reinforced polypropylene materials with high filling amount.

[0058] The present invention obtains a long glass fiber reinforced polypropylene material with high weld mark strength by introducing short chopped flat glass fibers. The long glass fiber reinforced polypropylene material is suitable for various application scenarios such as automotive interior and exterior decoration, home appliances, etc., and improves the ability of the overall structure of the material to resist external forces. It also provides strong help for improving the product's tolerance to alternating environmental temperature and humidity during actual use.

Claims

1. A long glass fiber reinforced polypropylene material with high weld mark strength, characterized in that: Made from the following raw materials in proportion by mass:

2. The long glass fiber reinforced polypropylene material with high weld mark strength according to claim 1, characterized in that: The melt flow rate of the polypropylene resin is relatively high, which is 30-150 g / 10 min, and the test conditions are 230° C.*2.16 kg.

3. The long glass fiber reinforced polypropylene material with high weld mark strength according to claim 1, characterized in that: The continuous long glass fiber is: long glass fiber direct untwisted roving for LFT, with a specification of 500-3000tex.

4. The long glass fiber reinforced polypropylene material with high weld mark strength according to claim 1, characterized in that: The short chopped flat glass fiber is: an alkali-free short chopped flat glass fiber treated with a silane coupling agent, with a flatness of 2-5%, and a length of 2-5 mm.

5. The long glass fiber reinforced polypropylene material with high weld mark strength according to claim 1, characterized in that: The compatibilizer is maleic anhydride grafted polypropylene, which plays a role in improving the compatibility between glass fiber and polypropylene.

6. The long glass fiber reinforced polypropylene material with high weld mark strength according to claim 1, characterized in that: The antioxidant includes hindered amine and hindered phenol as main antioxidants, and auxiliary antioxidants formed by compounding one or more combinations of thiodipropionate, phosphite and thiol, which are used to enhance the thermal stability of modified polypropylene materials during the production process and subsequent use.

7. The method for preparing the long glass fiber reinforced polypropylene material with high weld mark strength according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Weigh polypropylene, compatibilizer, and antioxidant according to weight ratio, put them into a high-speed mixer, and stir them at room temperature for 10 to 30 minutes; (2) adding the mixed material in step (1) to the main feed port of a twin-screw extruder, adding the short chopped flat glass fibers weighed according to the weight ratio to the side feed port of the twin-screw extruder of the long glass fiber reinforced polypropylene production line, mixing at 190-280° C. to fully impregnate the long glass fiber bundles, and then extruding and granulating to obtain the long glass fiber reinforced polypropylene material with high weld mark strength of the present invention.

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