Modified elastomer injection molding process

Abstract

The invention discloses a modified elastomer injection molding process which comprises the following steps: by taking a hydrogenated styrene-butadiene-styrene block copolymer (SEBS) as a matrix, adding maleic anhydride grafted polypropylene (PP-g-MAH), an ethylene-octylene copolymer (POE) and an inorganic fine filler, and carrying out melt blending to prepare modified elastomer particles; carrying out temperature-controlled drying treatment on the granules, feeding the granules into an injection molding machine, plasticizing under the condition of stepped charging barrel temperature, and injecting the granules into a mold cavity under the conditions of controlled injection speed, injection pressure and dwell pressure; and shaping under low-pressure delay and pressure maintaining conditions, and cooling and demolding the mold to obtain an injection molding product. Through the process, the PP-g-MAH improves the interfacial compatibility among the components, and the flow rate of the POE melt is higher than that of SEBS, so that uniform flow of the melt is facilitated, the internal stress is reduced, and the size consistency and the molding stability of the product are improved. The process is suitable for preparation of high-performance modified elastomer injection molding products, and has good mechanical properties, elasticity and injection molding operability.

Description

Technical Field

[0001] This invention relates to the field of elastic materials, and more particularly to a modified elastomer injection molding process. Background Technology

[0002] In the field of elastomer material molding, thermoplastic elastomers are widely used in shock-absorbing and buffer components because they combine the elastic properties of rubber with the processability of thermoplastic materials.

[0003] Among them, elastomeric materials, represented by styrene block copolymers, have good elastic recovery properties and molding adaptability, making them suitable for large-scale production using injection molding processes.

[0004] However, with the increasing complexity of injection molded products and the continuous improvement of dimensional accuracy requirements, traditional elastomer materials and their molding processes have gradually revealed problems such as insufficient fluidity, narrow molding window, and large internal stress in products in practical applications. Summary of the Invention

[0005] The present invention provides a modified elastomer injection molding process to solve related technical problems in the background art.

[0006] The technical solution provided by this invention is as follows: a modified elastomer injection molding process, comprising the following steps: S1. Preparation of modified elastomers: Modified elastomer particles were prepared by melt blending hydrogenated styrene-butadiene-styrene block copolymer SEBS as the matrix elastomer with maleic anhydride-grafted polypropylene PP-g-MAH, ethylene-octene copolymer POE and inorganic micro fillers through a twin-screw extruder. S2, Pretreatment: The modified elastomer particles were subjected to temperature-controlled drying to remove moisture from the particles and release the internal stress generated during the blending process. S3, Injection Molding: The pretreated modified elastomer particles are fed into the injection molding machine barrel, plasticized under stepped barrel temperature conditions, and the melt is injected into the mold cavity under controlled injection speed, injection pressure and holding pressure. S4. Cooling and Demolding: The product is shaped under low-pressure delayed holding conditions, and demolded after cooling by temperature control of the mold to obtain the modified elastomer injection molded product.

[0007] In one embodiment, the mass of SEBS accounts for 60-85 wt% of the total mass of the modified elastomer; the mass of PP-g-MAH accounts for 3-10 wt% of the total mass of the modified elastomer; the mass of POE accounts for 5-20 wt% of the total mass of the modified elastomer; and the mass of inorganic micro-fillers accounts for 1-8 wt% of the total mass of the modified elastomer.

[0008] In one embodiment, the maleic anhydride grafting rate in PP-g-MAH is 0.5-2.0%.

[0009] In one embodiment, the inorganic micro-filler is selected from one or more of talc, silica powder or silicon dioxide, and has an average particle size of 0.5 to 5 μm.

[0010] In one embodiment, in step S1, the melt blending temperature of the twin-screw extruder is 160–220°C, and the screw speed is 150–400 rpm.

[0011] In one embodiment, in step S2, the drying temperature of the temperature-controlled drying process is 60-90°C, and the drying time is 2-6 hours.

[0012] In one embodiment, in step S3, the stepped barrel temperature includes three temperature zones, which are sequentially a feeding zone, a plasticizing zone, and a metering zone along the material conveying direction. The temperature of the feeding zone is 150-170°C, the temperature of the plasticizing zone is 170-200°C, and the temperature of the metering zone is 180-210°C.

[0013] In one embodiment, in step S3, the injection speed is 40-120 mm / s, the injection pressure is 60-120 MPa, and the holding pressure is 40-70% of the injection pressure.

[0014] In one embodiment, step S4 includes a low-pressure delay holding stage and a second holding stage. The holding pressure in the first holding stage is 35-45% of the injection pressure, and the holding pressure in the second holding stage is 20-30% of the injection pressure.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The modified elastomer injection molding process of this invention employs SEBS as the matrix elastomer, introduces maleic anhydride-grafted polypropylene and ethylene-octene copolymer for synergistic modification, and combines a stepped barrel temperature and low-pressure delayed holding injection molding process. By utilizing PP-g-MAH to improve the interfacial compatibility between various components and inorganic micro-fillers, and utilizing the high melt flow rate of POE to regulate melt rheological behavior, and reducing melt shear orientation and molding internal stress during injection molding, the process achieves the goal of improving injection molding stability and product dimensional consistency while ensuring the mechanical and elastic properties of the modified elastomer. This results in injection molded products with good surface quality, fewer molding defects, low shrinkage, and uniform performance distribution, thereby solving the technical problems of insufficient fluidity, internal stress concentration, easy deformation, and poor molding stability of existing elastomer materials during injection molding. Attached Figure Description

[0016] Figure 1 This is a flowchart of the injection molding process for the modified elastomer of this invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0018] like Figure 1 As shown, this invention is a modified elastomer injection molding process. Specifically: First, the modified elastomer was prepared. Hydrogenated styrene-butadiene-styrene block copolymer (SEBS) was selected as the matrix elastomer, accounting for 60–85 wt% of the total mass of the modified elastomer, to ensure good resilience and aging resistance of the product. Simultaneously, maleic anhydride-grafted polypropylene (PP-g-MAH) was added, accounting for 3–10 wt% of the total mass of the modified elastomer. The maleic anhydride grafting rate of the PP-g-MAH was controlled at 0.5–2.0% to improve the polarity matching of the system and enhance the interfacial bonding ability between the components. Further, ethylene-octene copolymer (POE) was added, accounting for 5–20 wt% of the total mass of the modified elastomer, to adjust the rheological properties of the overall melt. In addition, inorganic micro-fillers were introduced, accounting for 1–8 wt% of the total mass of the modified elastomer. These inorganic micro-fillers were selected from one or more of talc, silica powder, or silicon dioxide, with an average particle size of 0.5–5 μm, to reduce the shrinkage differences in different regions of the product during the molding and cooling stage.

[0019] Furthermore, in this embodiment, the melt flow rate of the POE is higher than that of the SEBS. By selecting POE, which has a higher melt flow rate, as the flow conditioning phase, it preferentially flows under injection molding shear conditions, thereby forming low-resistance flow channels in the SEBS matrix melt that are conducive to overall flow. This reduces the apparent viscosity of the modified elastomer system, improves the uniformity of melt filling in the mold cavity, and enhances the stability of the injection molding process without significantly reducing the mechanical properties of the product.

[0020] The above components are added in proportion to a twin-screw extruder for melt blending. The blending temperature is controlled at 160–220°C, and the screw speed is controlled at 150–400 rpm. Through this melt blending process, PP-g-MAH is uniformly dispersed in the SEBS continuous phase, POE forms a regulating phase that facilitates melt flow, and the inorganic microfiller is embedded in the elastomer matrix in a finely dispersed state, thereby obtaining modified elastomer particles with a uniform structure.

[0021] Subsequently, the obtained modified elastomer particles are pretreated. Specifically, the modified elastomer particles are placed in a drying equipment for temperature-controlled drying, with the drying temperature controlled at 60-90℃ and the drying time at 2-6 hours, to effectively remove moisture from the inside and surface of the particles, while releasing the internal stress formed during melt blending, thereby reducing the risk of air marks, silver streaks and surface defects in the subsequent injection molding process.

[0022] During the injection molding stage, the dried modified elastomer granules are fed into the injection molding machine barrel, where plasticization is completed under stepped barrel temperature conditions. The stepped barrel temperature is sequentially set along the material conveying direction as a feeding section, a plasticizing section, and a metering section. The feeding section temperature is 150–170°C to achieve slow heating of the material and prevent premature softening of low-melting-point components. The plasticizing section temperature is 170–200°C to ensure that SEBS and PP-g-MAH are fully melted and uniformly mixed. The metering section temperature is 180–210°C to ensure melt fluidity while preventing thermal degradation of the grafted structure due to excessive temperature.

[0023] After plasticization is completed, the injection speed is controlled at 40-120 mm / s and the injection pressure is controlled at 60-120 MPa during the injection stage, and the melt is injected into the mold cavity under these conditions; the holding pressure is set to 40-70% of the injection pressure to avoid excessive orientation of the elastomer system under high pressure while ensuring complete filling of the mold cavity.

[0024] During the pressure holding, cooling, and demolding stages, a low-pressure delayed pressure holding method is used to shape the product. This includes a first pressure holding stage and a second pressure holding stage. The pressure in the first stage is 35-45% of the injection pressure, and the pressure in the second stage is 20-30% of the injection pressure. By extending the pressure holding time under lower pressure conditions, the modified elastomer within the mold cavity gradually cools and solidifies under low internal stress, which helps release residual stress formed during injection molding and reduces springback deformation after demolding. Subsequently, demolding is completed through temperature-controlled cooling of the mold, resulting in a modified elastomer injection molded product with high dimensional stability and good surface quality.

[0025] Example 1 By mass percentage, SEBS accounts for 85 wt% of the total mass of the modified elastomer, PP-g-MAH accounts for 3 wt%, POE accounts for 5 wt%, and the inorganic fine filler is talc powder, accounting for 2 wt%, with an average particle size of 5 μm.

[0026] The above raw materials were added to a twin-screw extruder and mixed at a melt blending temperature of 170°C with a screw speed of 200 rpm. The mixture was then extruded and granulated to obtain modified elastomer particles.

[0027] The modified elastomer granules are dried at 70℃ for 3 hours and then fed into the injection molding machine barrel. The temperature of the barrel feed section is 150℃, the temperature of the plasticizing section is 175℃, and the temperature of the metering section is 185℃. The injection speed is 50mm / s, the injection pressure is 80MPa, and the holding pressure is 50% of the injection pressure.

[0028] The molding process is carried out under low-pressure delayed holding conditions, where the pressure in the first holding stage is 40% of the injection pressure and the pressure in the second holding stage is 25% of the injection pressure. After cooling in the mold, the product is demolded and formed.

[0029] Example 2 By mass percentage, SEBS accounts for 75 wt% of the total mass of the modified elastomer, PP-g-MAH accounts for 6 wt%, POE accounts for 12 wt%, and the inorganic fine filler is talc powder, accounting for 4 wt%, with an average particle size of 3 μm.

[0030] The above raw materials are added to a twin-screw extruder and mixed at a melt blending temperature of 180°C with a screw speed of 250 rpm. The resulting material is then extruded and granulated to obtain modified elastomer particles.

[0031] The granules are dried at 75℃ for 4 hours and then fed into the injection molding machine barrel. The temperature of the barrel feed section is 155℃, the temperature of the plasticizing section is 185℃, and the temperature of the metering section is 195℃. The injection speed is 70mm / s, the injection pressure is 90MPa, and the holding pressure is 55% of the injection pressure.

[0032] The molding process is carried out under low-pressure delayed holding conditions, with the pressure in the first holding stage being 45% of the injection pressure and the pressure in the second holding stage being 30% of the injection pressure. After cooling in the mold, the product is demolded and formed.

[0033] Example 3 By mass percentage, SEBS accounts for 70 wt% of the total mass of the modified elastomer, PP-g-MAH accounts for 8 wt%, POE accounts for 15 wt%, and the inorganic micro-filler is silica powder, accounting for 5 wt%, with an average particle size of 2 μm.

[0034] The above raw materials were added to a twin-screw extruder and mixed at a melt blending temperature of 190°C with a screw speed of 300 rpm. The mixture was then extruded and granulated to obtain modified elastomer particles.

[0035] The granules are dried at 80℃ for 3 hours and then fed into the injection molding machine barrel. The temperature of the barrel feed section is 160℃, the temperature of the plasticizing section is 190℃, and the temperature of the metering section is 200℃. The injection speed is 90mm / s, the injection pressure is 100MPa, and the holding pressure is 60% of the injection pressure.

[0036] The molding process is carried out under low-pressure delayed holding conditions, where the pressure in the first holding stage is 40% of the injection pressure and the pressure in the second holding stage is 25% of the injection pressure. After cooling in the mold, the product is demolded and formed.

[0037] Example 4 By mass percentage, SEBS accounts for 65 wt% of the total mass of the modified elastomer, PP-g-MAH accounts for 9 wt%, POE accounts for 18 wt%, and the inorganic micro-filler is silica, accounting for 6 wt%, with an average particle size of 1 μm.

[0038] The above raw materials were added to a twin-screw extruder and mixed at a melt blending temperature of 200°C with a screw speed of 350 rpm. The mixture was then extruded and granulated to obtain modified elastomer particles.

[0039] The granules are dried at 85℃ for 4 hours and then fed into the injection molding machine barrel. The temperature of the barrel feed section is 165℃, the temperature of the plasticizing section is 195℃, and the temperature of the metering section is 205℃. The injection speed is 100mm / s, the injection pressure is 110MPa, and the holding pressure is 65% of the injection pressure.

[0040] The molding process is carried out under low-pressure delayed holding conditions, with the pressure in the first holding stage being 45% of the injection pressure and the pressure in the second holding stage being 30% of the injection pressure. After cooling in the mold, the product is demolded and formed.

[0041] Example 5 By mass percentage, SEBS accounts for 80 wt% of the total mass of the modified elastomer, PP-g-MAH accounts for 5 wt%, POE accounts for 10 wt%, and the inorganic fine filler is talc powder, accounting for 3 wt%, with an average particle size of 5 μm.

[0042] The above raw materials were added to a twin-screw extruder and mixed at a melt blending temperature of 160°C with a screw speed of 150 rpm. The mixture was then extruded and granulated to obtain modified elastomer particles.

[0043] The granules are dried at 60℃ for 6 hours and then fed into the injection molding machine barrel. The temperature of the barrel feed section is 150℃, the temperature of the plasticizing section is 170℃, and the temperature of the metering section is 180℃. The injection speed is 40mm / s, the injection pressure is 60MPa, and the holding pressure is 40% of the injection pressure.

[0044] The molding process is carried out under low-pressure delayed holding conditions, with the pressure in the first holding stage being 35% of the injection pressure and the pressure in the second holding stage being 20% ​​of the injection pressure. After cooling in the mold, the product is demolded and formed.

[0045] Example 6 By mass percentage, SEBS accounts for 60 wt% of the total mass of the modified elastomer, PP-g-MAH accounts for 10 wt%, POE accounts for 20 wt%, and the inorganic micro-filler is silica, accounting for 8 wt%, with an average particle size of 0.5 μm.

[0046] The above raw materials were added to a twin-screw extruder and mixed at a melt blending temperature of 220°C with a screw speed of 400 rpm. The mixture was then extruded and granulated to obtain modified elastomer particles.

[0047] The granules are dried at 90℃ for 2 hours and then fed into the injection molding machine barrel. The temperature of the barrel feed section is 170℃, the temperature of the plasticizing section is 200℃, and the temperature of the metering section is 210℃. The injection speed is 120mm / s, the injection pressure is 120MPa, and the holding pressure is 70% of the injection pressure.

[0048] The molding process is carried out under low-pressure delayed holding conditions, with the pressure in the first holding stage being 45% of the injection pressure and the pressure in the second holding stage being 30% of the injection pressure. After cooling in the mold, the product is demolded and formed.

[0049] The performance of the injection molded products prepared in Examples 1–6 was tested, and the test items included: Tensile strength (GB / T 528), elongation at break (GB / T 528), Shore A hardness (GB / T 531.1), notched impact strength (GB / T 1843), melt flow rate (MFR) (GB / T 3682) and molding shrinkage.

[0050] As can be seen from the above embodiments and test results, by adjusting the ratio of SEBS, PP-g-MAH, POE and inorganic micro-fillers, and combining the stepped barrel temperature and low-pressure delayed holding process parameters, the modified elastomer products can achieve synergistic optimization in mechanical properties, toughness, flowability and dimensional stability while ensuring the stability of injection molding. This is suitable for injection molded products with high requirements for molding quality and comprehensive performance.

[0051] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0052] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A modified elastomer injection molding process characterized by, The method comprises the following steps: S1, preparation of modified elastomer: Taking hydrogenated styrene-butadiene-styrene block copolymer SEBS as the base elastomer, maleic anhydride grafted polypropylene PP-g-MAH, ethylene-octene copolymer POE and inorganic micro-filler are added to the base elastomer, and then melt blending is carried out through a double-screw extruder to obtain modified elastomer particles; S2, pretreatment: The modified elastomer particles are subjected to temperature-controlled drying treatment to remove water in the particles and release internal stress generated in the blending process; S3, injection molding: The pretreated modified elastomer particles are fed into the cylinder of an injection molding machine, plasticization is completed under the condition of a stepped cylinder temperature, and the melt is injected into the mold cavity under the control of injection speed, injection pressure and holding pressure; S4, cooling and demolding: The product is shaped under the condition of low pressure delay holding pressure, and demolding is completed after cooling through mold temperature control, thereby obtaining a modified elastomer injection molded product.

2. A modified elastomer injection molding process as set forth in claim 1, characterized in that, The mass of the SEBS accounts for 60-85 wt% of the total mass of the modified elastomer; the mass of the PP-g-MAH accounts for 3-10 wt% of the total mass of the modified elastomer; the mass of the POE accounts for 5-20 wt% of the total mass of the modified elastomer; and the mass of the inorganic micro-filler accounts for 1-8 wt% of the total mass of the modified elastomer.

3. A modified elastomer injection molding process as in claim 1, wherein, The grafting rate of maleic anhydride in the PP-g-MAH is 0.5-2.0%.

4. A modified elastomer injection molding process as in claim 1, wherein, The inorganic micro-filler is selected from one or more of talc, silica powder or silicon dioxide, and has an average particle size of 0.5-5 μm.

5. A modified elastomer injection molding process as in claim 1, wherein, In step S1, the melt blending temperature of the double-screw extruder is 160-220°C, and the screw rotation speed is 150-400 rpm.

6. A modified elastomer injection molding process as in claim 1, wherein, In step S2, the drying temperature of the temperature-controlled drying treatment is 60-90°C, and the drying time is 2-6 hours.

7. A modified elastomer injection molding process as in claim 1, wherein, In step S3, the stepped cylinder temperature includes three temperature zones in the order of feeding section, plasticizing section and metering section along the material conveying direction, the feeding section temperature is 150-170°C, the plasticizing section temperature is 170-200°C, and the metering section temperature is 180-210°C.

8. A modified elastomer injection molding process as in claim 1, wherein, In step S3, the injection speed is 40-120 mm / s, the injection pressure is 60-120 MPa, and the holding pressure is 40-70% of the injection pressure.

9. A modified elastomer injection molding process as in claim 1, wherein, In step S4, the low pressure delay holding pressure includes a first holding pressure stage and a second holding pressure stage, the holding pressure of the first holding pressure stage is 35-45% of the injection pressure, and the holding pressure of the second holding pressure stage is 20-30% of the injection pressure.

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