High-fluidity modified injection molding material for thin-wall injection molding and preparation method thereof

Abstract

The invention discloses a high-fluidity modified injection molding material for thin-wall injection molding and a preparation method of the high-fluidity modified injection molding material for thin-wall injection molding. 2-8 parts of a hyperbranched rheology modifier; 5 to 15 parts of a nano synergistic toughening agent; 0.5-2 parts of a composite nucleating agent; 0.2 to 1 part of an antioxidant; 0.3 to 1.5 parts of a lubricating dispersant; wherein the base resin matrix is co-polypropylene resin with a high melt flow rate, the hyperbranched rheological modifier is hydroxyl-terminated hyperbranched polyester with a spherical three-dimensional structure, and the base resin matrix and the hyperbranched rheological modifier form a microscopic phase structure with the base resin matrix as a continuous phase and the hyperbranched rheological modifier as a dispersed phase in a molten state; the material prepared by the invention can still keep the notch impact strength at 10 kJ / m or above and the bending modulus at 1400 MPa or above under the ultrahigh fluidity that the MFR reaches 65-80 g / 10 min. In a spiral flow test with the wall thickness of 0.5 mm, the flow length is increased by more than 30% compared with that of traditional modified PP, and the contradiction of'difficult mold filling 'and'easy brittle rupture' of thin-wall injection molding is solved.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, specifically to high-flowability modified injection molding materials for thin-wall injection molding and their preparation methods. Background Technology

[0002] With the increasing demand for lightweighting and material conservation in the packaging, consumer electronics, and automotive industries, thin-wall injection molding (TWIM) technology has become a mainstream trend. Thin-wall design (typically referring to a wall thickness of less than 0.8 mm, or even 0.4 mm) significantly shortens the molding cycle and reduces raw material costs, but it also places extremely stringent and contradictory requirements on the rheological and mechanical properties of the injection molding material.

[0003] In existing technologies, to meet the extremely high filling requirements of thin-walled molds, polypropylene (PP) with ultra-high melt flow rate (MFR>60g / 10min) is typically used as the base material, either through a degradation method or by directly selecting such material. However, according to the basic principles of polymer physics, the flowability of a polymer is inversely proportional to its molecular weight, while mechanical properties such as impact strength and resistance to environmental stress cracking are directly proportional to molecular weight. Therefore, simply pursuing high flowability often leads to a sharp decrease in the material's impact toughness, making the product brittle and prone to breakage during demolding, transportation, or drops.

[0004] To improve toughness, the conventional approach is to add elastomers such as ethylene-octene copolymer (POE) or ethylene propylene diene monomer (EPDM). However, elastomers themselves have high viscosity, and their addition will significantly "drag down" the flowability of the base resin, causing the melt viscosity to rise, which in turn leads to problems such as short shots (insufficient glue) and internal stress warping caused by high injection pressure during thin-wall injection molding.

[0005] Furthermore, commonly used viscosity reducers such as peroxides (DCP, etc.) can trigger resin degradation, produce irritating odors, and cause yellowing of materials, making it difficult to meet the hygiene requirements for food contact or medical grades. On the other hand, excessive amounts of low molecular weight lubricants (such as EBS and PE wax) can easily precipitate onto the surface of the product, affecting printing and adhesion performance. Therefore, this paper proposes a high-flowability modified injection molding material for thin-wall injection molding and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a high-flowability modified injection molding material for thin-walled injection molding and a method for preparing the same. This addresses one of the shortcomings of existing thin-walled injection molding materials, as mentioned in the background section, in achieving a balance between "high flowability" and "high toughness."

[0007] Firstly, to solve the aforementioned technical problems, this application adopts the following technical solution: a high-flowability modified injection molding material for thin-walled injection molding, comprising, by weight, the following components: 60-90 parts of base resin matrix; 2-8 parts of hyperbranched rheology modifier; 5-15 parts of nano-synergistic toughening agent; 0.5-2 parts of composite nucleating agent; 0.2-1 part of antioxidant; and 0.3-1.5 parts of lubricating dispersant. The base resin matrix is ​​a copolymer polypropylene resin with a high melt flow rate, and the hyperbranched rheology modifier is a terminal hydroxyl hyperbranched polyester with a spherical three-dimensional structure. The two form a microstructure in the molten state with the base resin matrix as the continuous phase and the hyperbranched rheology modifier as the dispersed phase.

[0008] More preferably, the melt flow rate (230℃ / 2.16kg) of the base resin matrix is ​​40-80g / 10min, and its molecular weight distribution index (PDI) is controlled between 3.5 and 5.5; The ethylene monomer content in the base resin matrix is ​​4wt%-8wt%, and it exists in the form of random copolymer or block copolymer.

[0009] More preferably, the hyperbranched rheology modifier has a weight-average molecular weight of 1500-4000 g / mol and its molecular structure contains 16-64 active hydroxyl terminal groups; the hyperbranched rheology modifier has a dispersion particle size of 50-200 nm in the base resin matrix, which is used to reduce the entanglement density between molecular chains and provide internal lubrication.

[0010] More preferably, the nano-synergistic toughening agent is composed of maleic anhydride-grafted ethylene-octene copolymer (POE-g-MAH) with a grafting rate of 0.8%-1.2% and stearic acid-modified nano-calcium carbonate, with a mass ratio of 3:1 to 5:1; when subjected to impact load, the nano-synergistic toughening agent initiates crazing and shear bands through the debonding of nanoparticles, and the crazing propagation is terminated by the elastomer component.

[0011] More preferably, the composite nucleating agent is a compound of sorbitol acetal α-nucleating agent and calcium pimecrolate β-nucleating agent, with a mass ratio of 1:0.1 to 1:0.3; the composite nucleating agent induces the base resin matrix to form a crystal structure with a high crystallization rate, so that the heat distortion temperature of the material is ≥105℃.

[0012] Further preferred, the material has a melt flow rate (230℃ / 2.16kg) ≥65g / 10min, a cantilever beam notched impact strength (23℃) ≥10kJ / m², and a flexural modulus ≥1400MPa; in an Archimedes spiral flow test with a wall thickness of 0.5mm, its flow length is greater than 45cm.

[0013] Secondly, the present invention provides a method for preparing a high-flowability modified injection molding material for thin-walled injection molding, comprising the following steps: S1. Liquid-phase coating premix: The base resin matrix is ​​put into a high-speed mixer. Under low-speed stirring, the preheated liquid hyperbranched rheology modifier is sprayed onto the resin surface in the form of a spray. Then, the composite nucleating agent, antioxidant and lubricating dispersant are added. The mixture is mixed at high speed until the material temperature reaches 40-50℃ to obtain the primary premix. S2, Side-feed compounding: The primary premix is ​​added to the main feed port of the twin-screw extruder, and the nano-synergistic toughening agent is added through the side feed port; S3. Reactive extrusion and granulation: The product is obtained by melt blending under the shear field of a twin-screw extruder, followed by extrusion, water cooling, pelletizing, and drying.

[0014] More preferably, the length-to-diameter ratio (L / D) of the twin-screw extruder is 44:1 to 52:1, and the screw assembly includes at least three sets of kneading block assemblies; in the screw section downstream of the side feed port, two sets of reverse kneading elements and one set of toothed disc elements are provided to enhance the dispersion and shearing of the nano-synergistic toughening agent.

[0015] More preferably, the barrel temperature of the twin-screw extruder is set in a saddle shape, with the following temperature distribution from the feed port to the die head: Zone 1 160-170℃, Zones 2 to 4 180-200℃, Zones 5 to 8 210-230℃, Zones 9 to 11 190-200℃, and the die head 190-200℃; the screw speed is controlled at 350-550 rpm, and the material residence time in the barrel is 25-45 seconds.

[0016] More preferably, in step S1, the preheating temperature of the spraying of the hyperbranched rheology modifier is 80-95℃, and the spraying pressure is controlled at 0.2-0.4MPa, so as to ensure that the modifier is uniformly coated on the surface of the solid base resin matrix particles in a micro-mist form.

[0017] Thirdly: The present invention provides a thin-walled injection molded product prepared by application material, characterized in that the wall thickness of the product is 0.3mm-0.8mm, and the product is a thin-walled food packaging container, a disposable medical consumable, or a precision structural component of an electronic product.

[0018] Advantages of this invention: The material prepared by this invention maintains a notched impact strength of over 10 kJ / m² and a flexural modulus of over 1400 MPa even with an MFR of 65-80 g / 10 min, despite its ultra-high fluidity. In a spiral flow test with a wall thickness of 0.5 mm, the flow length is increased by more than 30% compared to traditional modified PP, thus resolving the contradiction between "difficulty in mold filling" and "easily brittle" in thin-walled injection molding.

[0019] This invention utilizes a non-peroxide degradation process, resulting in materials with no irritating odor and low VOC content. The introduction of hyperbranched polymers eliminates the precipitation and frosting phenomena of traditional lubricants, leading to thin-walled products with high surface gloss, free of flow marks and loose fibers.

[0020] The extremely low melt viscosity of this invention reduces injection molding pressure by 15%-20%, effectively reducing mold wear and internal stress warping of the product. It is particularly suitable for the manufacture of thin-walled food containers with large projected areas and precision electronic structural components. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the preparation process of a high-flowability modified injection molding material for thin-walled injection molding according to the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Figure 1 This is a schematic flowchart of a high-flowability modified injection molding material for thin-walled injection molding according to an embodiment of the present invention. It should be noted that if substantially the same result is achieved, the method of this application is not necessarily the same. Figure 1 The sequence of processes shown is limited. Example 1

[0025] like Figure 1 The high-flowability modified injection molding material for thin-walled injection molding shown comprises, by weight, 60-90 parts of base resin matrix; 2-8 parts of hyperbranched rheology modifier; 5-15 parts of nano-synergistic toughening agent; 0.5-2 parts of composite nucleating agent; 0.2-1 parts of antioxidant; and 0.3-1.5 parts of lubricating dispersant.

[0026] A method for preparing a high-flowability modified injection molding material for thin-walled injection molding includes the following steps: S1. Liquid-phase coating premix: The base resin matrix is ​​put into a high-speed mixer. Under low-speed stirring, the preheated liquid hyperbranched rheology modifier is sprayed onto the resin surface in the form of a spray. Then, the composite nucleating agent, antioxidant and lubricating dispersant are added. The mixture is mixed at high speed until the material temperature reaches 40-50℃ to obtain the primary premix. S2, Side-feed compounding: The primary premix is ​​added to the main feed port of the twin-screw extruder, and the nano-synergistic toughening agent is added through the side feed port; S3. Reactive extrusion and granulation: The product is obtained by melt blending under the shear field of a twin-screw extruder, followed by extrusion, water cooling, pelletizing, and drying.

[0027] In this embodiment of the invention, specifically, the length-to-diameter ratio (L / D) of the twin-screw extruder is 44:1 to 52:1, and the screw assembly includes at least three sets of kneading block assemblies; in the screw section downstream of the side feed port, two sets of reverse kneading elements and one set of toothed disc elements are provided to enhance the dispersion and shearing of the nano-synergistic toughening agent.

[0028] In this embodiment of the invention, specifically, the barrel temperature of the twin-screw extruder is set in a saddle shape, with the following temperature distribution from the feed port to the die head: Zone 1 160-170℃, Zones 2 to 4 180-200℃, Zones 5 to 8 210-230℃, Zones 9 to 11 190-200℃, and the die head 190-200℃; the screw speed is controlled at 350-550 rpm, and the material residence time in the barrel is 25-45 seconds.

[0029] In this embodiment of the invention, specifically in step S1, the preheating temperature for spraying the hyperbranched rheology modifier is 80-95°C, and the spraying pressure is controlled at 0.2-0.4 MPa to ensure that the modifier is uniformly coated on the surface of the solid base resin matrix particles in a micro-mist form. This invention abandons the traditional peroxide degradation method and innovatively introduces terminal hydroxyl hyperbranched polyester with a spherical three-dimensional structure as a rheology modifier. Unlike the entanglement mechanism of linear polymer chains, hyperbranched molecules exhibit a "nanoball" effect in the melt, which can significantly increase the free volume between polymer chains and reduce the friction coefficient between molecular chains, thereby greatly improving the melt fluidity without reducing the molecular weight of the matrix.

[0030] The numerous active hydroxyl groups at the ends of the hyperbranched polyester undergo in-situ physical / chemical interactions with the anhydride groups in POE-g-MAH and the polar groups on the surface of nano-calcium carbonate. This interaction not only prevents the precipitation of small molecules but, more importantly, forms a robust "soft-hard" interface layer between the matrix and the toughening agent. When the material is subjected to impact, the nanoparticles induce crazes, the elastomer passivates the crazes, and the hyperbranched structure dissipates energy. The synergistic effect of these three factors achieves highly efficient toughening in a highly fluid matrix.

[0031] By introducing α / β composite nucleating agents, the crystallization temperature is increased and the molding cycle is shortened. On the other hand, the formation of β crystals with better toughness is induced, which further compensates for the brittle defects caused by the high-flow matrix.

[0032] Preferably, the base resin matrix is ​​a highly crystalline copolymer polypropylene with an MFR of 40-80 g / 10 min and a PDI controlled at 3.5-5.5 to ensure a wide processing window. Preferably, the ratio of POE-g-MAH to nano-calcium carbonate in the nano-synergistic toughening agent is controlled at 3:1 to 5:1, as this ratio results in the highest toughening efficiency and the least negative impact on modulus.

[0033] This invention also provides a method for preparing the above-mentioned material, particularly employing a specific process of "liquid phase coating premixing + side feeding composite". By pre-coating the surface of PP particles with liquid hyperbranched polymer by spraying, its preferential distribution in the early stage of melting is ensured; by adding toughening agents through side feeding, the problem of screw slippage or degradation caused by premature melting of the elastomer at the main feed port is avoided. Example 2

[0034] A high-flowability modified injection molding material for thin-walled injection molding, with the following formulation: High melt flow index copolymer PP (MFR=65g / 10min, PDI=4.2): 80 parts; Hydroxyl-terminated hyperbranched polyester (3rd generation, Boltorn H20): 4 parts; POE-g-MAH (grafting rate 1.0%): 9 copies; Stearic acid modified nano-calcium carbonate (particle size 60nm): 3 parts; Composite nucleating agent (Millad3988 + calcium pimecronate, mass ratio 1:0.2): 0.8 parts; Antioxidant (1010 / 168 compound): 0.4 parts; Slip agent (erucamide): 0.5 parts; Preparation process: Pretreatment: The hyperbranched polyester is heated to 90°C and melted into a low-viscosity liquid.

[0035] S1 Mixing: Add PP resin to a high-speed mixer, start low-speed stirring, spray liquid hyperbranched polyester onto the surface of PP particles through a high-pressure nozzle, and stir for 3 minutes; then add nucleating agent and antioxidant, and mix at high speed to 45°C.

[0036] S2 Extrusion: The premixed material is added to the main feed port of the twin-screw extruder (L / D=48:1). POE-g-MAH and nano-calcium carbonate are premixed and then added through the side feed port in the middle of the barrel.

[0037] Process parameters: Barrel temperature set at 170℃-190℃-210℃-220℃-200℃ (head). Screw speed 450rpm. A combination of "reverse kneading + toothed disc" is used to enhance shearing.

[0038] Post-processing: Extrusion into strands, water cooling, pelletizing, and drying at 80℃ for 4 hours.

[0039] Examples 3-4 and Comparative Examples 1-2 (adjustments and test data for each component are shown in Table 1) Comparative Example 1: No hyperbranched rheology modifier was added, but an equal amount of PP matrix was added. Comparative Example 2: Conventional EBS wax was used instead of the hyperbranched rheology modifier, and the rest was the same as in Example 2.

[0040]

[0041] Table 1: Performance test results of each embodiment and comparative example.

[0042] Comparing Example 1 with Comparative Example 1, it can be seen that after adding the hyperbranched rheology modifier, the MFR increased from 58 to 72.5, the helical flow length increased significantly, and the impact strength did not decrease but increased slightly (from 11.2 to 12.8), which proves the effectiveness of the "ball effect" and "synergistic toughening".

[0043] Comparing Example 2 and Comparative Example 3, it can be seen that although ordinary lubricant (EBS) can also improve fluidity, it leads to a sharp drop in impact strength (down to 6.2) and surface precipitation problems. This further confirms the necessity of using a specific hyperbranched structure modifier in this invention.

[0044] In summary, this invention has successfully prepared high-performance materials that meet the requirements of ultra-thin wall injection molding through a unique formulation system and process control.

[0045] For a detailed description of this embodiment, please refer to the corresponding descriptions in the foregoing embodiments, which will not be repeated here.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-flowability modified injection molding material for thin-walled injection molding, characterized in that, By weight, the material comprises the following components: 60-90 parts of base resin matrix; 2-8 parts of hyperbranched rheology modifier; 5-15 parts of nano-synergistic toughening agent; 0.5-2 parts of composite nucleating agent; 0.2-1 part of antioxidant; 0.3-1.5 parts of lubricating dispersant; The base resin matrix is ​​a copolymer polypropylene resin with a high melt flow rate, and the hyperbranched rheology modifier is a terminal hydroxyl hyperbranched polyester with a spherical three-dimensional structure. The two form a microstructure in the molten state with the base resin matrix as the continuous phase and the hyperbranched rheology modifier as the dispersed phase.

2. The high-flowability modified injection molding material for thin-walled injection molding according to claim 1, characterized in that, The melt flow rate of the base resin matrix is ​​40-80 g / 10 min, and its molecular weight distribution index is controlled between 3.5 and 5.

5. The ethylene monomer content in the base resin matrix is ​​4wt%-8wt%, and it exists in the form of random copolymer or block copolymer.

3. The high-flowability modified injection molding material for thin-walled injection molding according to claim 1, characterized in that, The hyperbranched rheology modifier has a weight-average molecular weight of 1500-4000 g / mol and its molecular structure contains 16-64 active hydroxyl terminal groups. The hyperbranched rheology modifier has a dispersion particle size of 50-200 nm in the base resin matrix, which is used to reduce the entanglement density between molecular chains and provide internal lubrication.

4. The high-flowability modified injection molding material for thin-walled injection molding according to claim 1, characterized in that, The nano-synergistic toughening agent is composed of maleic anhydride-grafted ethylene-octene copolymer with a grafting rate of 0.8%-1.2% and stearic acid-modified nano-calcium carbonate, with a mass ratio of 3:1 to 5:

1.

5. The high-flowability modified injection molding material for thin-walled injection molding according to claim 1, characterized in that, The composite nucleating agent is composed of a sorbitol acetal α-nucleating agent and a calcium pimecrolate β-nucleating agent in a mass ratio of 1:0.1 to 1:0.

3.

6. The high-flowability modified injection molding material for thin-walled injection molding according to claim 1, characterized in that, The material has a melt flow rate ≥65g / 10min, a notched cantilever beam impact strength ≥10kJ / m², and a flexural modulus ≥1400MPa.

7. A method for preparing a high-flowability modified injection molding material for thin-walled injection molding as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. The base resin matrix is ​​put into a high-speed mixer. Under low-speed stirring, the preheated liquid hyperbranched rheology modifier is sprayed onto the resin surface in the form of a spray. Then, the composite nucleating agent, antioxidant and lubricating dispersant are added. The mixture is mixed at high speed until the material temperature reaches 40-50°C to obtain a primary premix. S2. Add the primary premix to the main feed port of the twin-screw extruder, and add the nano-synergistic toughening agent through the side feed port; S3. The product is obtained by melt blending under the shear field of a twin-screw extruder, followed by extrusion, water cooling, pelletizing and drying.

8. The preparation method according to claim 7, characterized in that, The twin-screw extruder has a length-to-diameter ratio of 44:1 to 52:1, and the screw assembly includes at least three sets of kneading block assemblies; in the screw section downstream of the side feed port, two sets of reverse kneading elements and one set of toothed disc elements are provided.

9. The preparation method according to claim 7, characterized in that, The barrel temperature settings of the twin-screw extruder are arranged in a saddle shape, with the following sequence from the feed port to the die head: Zone 1: 160-170℃; Zones 2-4: 180-200℃; Zones 5-8: 210-230℃; Zones 9-11: 190-200℃; Head unit: 190-200℃. The screw speed is controlled at 350-550 rpm, and the material residence time in the barrel is 25-45 seconds.

10. The preparation method according to claim 7, characterized in that, In step S1, the spray preheating temperature of the hyperbranched rheology modifier is 80-95℃, and the spray pressure is controlled at 0.2-0.4MPa.

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