Double-color injection molding process

Abstract

The invention relates to the technical field of injection molding, discloses a double-color injection molding process, and relates to the technical field of injection molding. The method comprises the following steps: pretreating raw materials, removing impurities, and drying until the water content is less than or equal to 0.05%; double-color injection molding is conducted, ABS plastic is injected into a mold to form a first-color product, and then a TPR material with the melting temperature lower than 50-100 DEG C is injected and combined; cooling and demolding, controlling the cooling rate to be 5-15 DEG C / s, and adopting mechanical or gas-assisted demolding; post-treatment comprises deburring, polishing and the like. According to the process, by optimizing the material temperature difference, junction surface design and cooling parameters, the product bonding strength is improved by 60% or above, the percent of pass reaches 96% or above, the production period is shortened by 30%, and the process can be compatible with various material combinations and is suitable for the fields of consumer electronics, automotive interiors and the like.

Description

Technical Field

[0001] The invention relates to the field of injection molding, in particular to a two-color injection molding process. Background Art

[0002] As a key process for achieving functional integration and diversified appearance of plastic products, two-shot injection molding technology has been widely used in consumer electronics, automotive interiors, medical devices and other fields. However, the existing technology still has the following prominent problems in actual production:

[0003] 1. Inadequate material bonding strength: In traditional processes, the melting interface between two materials often suffers from temperature mismatch (e.g., improper temperature control between TPR and ABS), leading to weak intermolecular forces. This can easily lead to delamination and cracking after impact or prolonged use. For example, in a drop test, the peel strength of a mobile phone case at the two-color bond was only 2.0 MPa, far below the industry standard requirement of 3.5 MPa.

[0004] 2. Poor production stability: Due to the lack of precise control in the raw material pretreatment process, undried ABS plastic (moisture content > 0.05%) will produce bubbles due to the high temperature during injection molding, resulting in pinholes on the surface of the first-color product. The irrational design of the cooling system (such as uneven distribution of cooling water channels) causes the cooling rate of the product to vary by more than 8°C / s, causing warping (deformation > 0.3mm / m). Therefore, the present invention proposes a two-color injection molding process to address the above problems. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a two-color injection molding process.

[0006] The present invention provides a two-color injection molding process that adopts the following technical solutions:

[0007] A two-color injection molding process, characterized by comprising the following steps:

[0008] S1. Raw material pretreatment:

[0009] 1) ABS plastic and TPR materials were selected and passed through a vibration screening machine to remove impurities with a particle size of ≥0.5mm, and then passed through an electromagnetic iron remover to remove metal particles;

[0010] 2) Dry the pre-treated ABS plastic and TPR material separately to control the moisture content to ≤0.05%;

[0011] S2, two-color injection molding:

[0012] 1) Melt the dried ABS plastic and inject it into the first cavity of the mold. Maintain the pressure for 15-60 seconds at an injection pressure of 70-120 MPa to form the first color product.

[0013] 2) After the mold is opened, the movable mold plate is rotated 180 degrees. After the mold is closed, the dried TPR material is melted and injected into the second mold cavity. The melting temperature of the TPR material is 50-100 ° C lower than that of ABS plastic. It is combined with the first color product under an injection pressure of 60-100 MPa.

[0014] S3, cooling and demoulding:

[0015] 1) The mold cooling system controls the cooling rate to 5-15°C / s and the cooling time to 15-50s, so that the center temperature of the product drops to 40-60°C;

[0016] 2) Use mechanical ejection or gas-assisted demoulding to remove the product from the mold;

[0017] S4, post-processing:

[0018] 1) Deburring and surface polishing of products;

[0019] 2) Perform plasma surface activation or UV curing coating treatment.

[0020] Preferably, the melt index of the ABS plastic is 15-30 g / 10 min (220° C., 10 kg), and the Shore hardness of the TPR material is 70-90A.

[0021] Preferably, a wavy joint surface is provided between the first cavity and the second cavity of the mold, and the wave height of the joint surface is 0.3-1.0 mm and the wavelength is 1.0-3.0 mm.

[0022] Preferably, the process parameters of the drying process are:

[0023] ABS plastic: drying temperature 80-95°C, drying time 2-4 hours;

[0024] TPR material: drying temperature 60-80℃, drying time 3-5 hours.

[0025] Preferably, the cooling system comprises a spiral cooling water channel distributed along the contour of the mold cavity, the diameter of the cooling water channel is 6-12 mm, and the temperature of the coolant is 10-25°C.

[0026] Preferably, in the injection molding step:

[0027] The barrel temperature of ABS plastic is 210-250℃, and the nozzle temperature is 230-260℃;

[0028] The barrel temperature of TPR material is 160-200℃, and the nozzle temperature is 180-210℃.

[0029] Preferably, the ejection device comprises at least 4 ejector pins distributed on the non-exterior surface of the product, the diameter of the ejector pins is 2-6 mm, and the ejection speed is 10-30 mm / s.

[0030] Preferably, the plasma surface activation treatment parameters in the post-treatment step are: power 100-500W, treatment time 10-60s, and gas pressure 10-50Pa.

[0031] In summary, the present invention includes at least one of the following beneficial technical effects:

[0032] By precisely controlling the melting temperature difference between TPR and ABS (50-100°C), the diffusion and fusion of interface molecules are promoted, and the peel strength of the bonding part is increased to 4.2-5.0MPa, which is more than 60% higher than the traditional process; the wavy bonding surface design (wave height 0.3-1.0mm) enhances the mechanical interlocking force by 30%, and there is no delamination after 500 high and low temperature cycles (-40°C to 85°C).

[0033] The moisture content of the raw materials is controlled below 0.03%, and the spiral cooling water channel (diameter 6-12mm) is used to achieve uniform cooling (rate difference ≤ 3℃ / s), which increases the product qualification rate from 80% to over 96%. The integration of automated deburring and plasma treatment increases post-processing efficiency by 40%, shortening the single-mold production cycle to 75-90s. DETAILED DESCRIPTION

[0034] The present invention is described in further detail below.

[0035] Example 1: Molding process of two-color plastic mobile phone housing

[0036] Specific steps:

[0037] S1. Raw material selection

[0038] 1) Main material: Chimei PA-757 black ABS plastic from Taiwan, China (melt index 20g / 10min, heat deformation temperature 95℃).

[0039] 2) Auxiliary materials: China Dongguan Subo SB-7100 transparent TPR material (hardness 80A, melt index 15g / 10min) is selected.

[0040] 3) Pretreatment: The two raw materials were passed through a vibrating screener (model: XZS-1000) to remove impurities with a particle size greater than 0.5 mm, and then passed through a permanent magnet drum magnetic separator (model: CTB-6012) to remove metal particles.

[0041] S2. Raw material drying

[0042] 1) ABS plastic: Use hot air circulation dryer (model: SHG-100), temperature 85℃, drying time 2.5 hours, stirring speed 30r / min.

[0043] 2) TPR material: Use a dehumidifying dryer (model: D-500), temperature 65°C, drying time 3 hours, stirring speed 25 r / min.

[0044] 3) After drying, the moisture content of the raw materials is controlled below 0.03%.

[0045] S3, injection molding

[0046] 1) Equipment: A Risin ASB-100DP two-color injection molding machine equipped with a rotary mold (one mold, two cavities) was selected.

[0047] 2) First color (ABS) injection molding:

[0048] Barrel temperature: rear section 210℃, middle section 230℃, front section 240℃, nozzle 245℃.

[0049] Injection pressure: 90 MPa, injection speed 60 mm / s, injection volume 85 g.

[0050] Holding pressure: 60MPa, holding time: 30s.

[0051] Mold temperature: movable mold 50℃, fixed mold 60℃.

[0052] After cooling for 30 seconds, the mold is opened and the male mold part rotates 180° along with the turntable.

[0053] 3) Second color (TPR) injection molding:

[0054] Barrel temperature: rear section 160℃, middle section 175℃, front section 185℃, nozzle 190℃.

[0055] Injection pressure: 75MPa, injection speed 50mm / s, injection volume 15g.

[0056] Holding pressure: 50 MPa, holding time: 20 s.

[0057] Mold temperature: movable mold 45℃, fixed mold 50℃.

[0058] S4, cooling and demoulding

[0059] 1) Cooling system: The mold has a built-in spiral cooling water channel, which is fed with 15°C circulating cooling water and a cooling time of 40s.

[0060] 2) Demolding: Using air pressure ejection device, the ejection speed is 20mm / s, and the ejection force is 5kN to ensure the complete demoulding of the product.

[0061] S5. Post-processing

[0062] 1) Deburring: Use an ultrasonic cleaner (model: CX-1000) at 40kHz for 5 minutes.

[0063] 2) Surface treatment: Use a plasma surface activation machine (model: PT-2000) for 30 seconds to enhance coating adhesion.

[0064] 3) Quality Inspection: A three-dimensional coordinate measuring machine (model: ZEISSPRISMO) is used to inspect dimensional accuracy, and a colorimeter (model: NR110) is used to inspect color consistency.

[0065] Product performance:

[0066] Bonding strength of two materials: tensile test ≥3.5MPa (ASTMD413 standard).

[0067] Drop resistance: 1.5-meter free fall test (3 times on each of the six sides) without cracking.

[0068] Production cycle: Single-mode cycle is about 90 seconds, and the yield rate is 96.8%.

[0069] Example 2: Molding process of dual-color buttons for automobile interiors

[0070] Product requirements: Produce a dual-color button for the central control of a car (white PC + black TPU), which should be soft to the touch, wear-resistant, and have excellent high and low temperature resistance.

[0071] Specific steps:

[0072] S1. Raw material selection

[0073] 1) Main material: Bayer Makrolon 2808 white PC plastic (light transmittance 89%, heat deformation temperature 130℃).

[0074] 2) Auxiliary materials: BASF Elastollan 1185A10 black TPU (hardness 85A, tear strength 45kN / m) is selected.

[0075] 3) Pretreatment: The two raw materials are respectively passed through an airflow screening machine (model: QS-800) and an electromagnetic iron remover (model: RCDD-6) to remove impurities.

[0076] S2. Raw material drying

[0077] 1) PC plastic: Use a vacuum dryer (model: ZKG-50), temperature 120°C, drying time 4 hours, vacuum degree -0.09MPa.

[0078] 2) TPU material: Use hot air dryer (model: HG-200), temperature 80℃, drying time 3 hours.

[0079] S3, injection molding

[0080] 1) Equipment: A Haitian HTF160W2 two-color injection molding machine equipped with a turntable mold (one mold with four cavities) was selected.

[0081] 2) First color (PC) injection molding:

[0082] Barrel temperature: rear section 270℃, middle section 285℃, front section 295℃, nozzle 300℃.

[0083] Injection pressure: 100 MPa, injection speed 40 mm / s, injection volume 25 g.

[0084] Holding pressure: 70 MPa, holding time: 25 s.

[0085] Mold temperature: movable mold 80℃, fixed mold 90℃.

[0086] 3) Second color (TPU) injection molding:

[0087] Barrel temperature: rear section 180℃, middle section 195℃, front section 205℃, nozzle 210℃.

[0088] Injection pressure: 85MPa, injection speed 35mm / s, injection volume 5g.

[0089] Holding pressure: 60MPa, holding time: 15s.

[0090] Mold temperature: movable mold 70℃, fixed mold 80℃.

[0091] S4, cooling and demoulding

[0092] 1) Cooling system: The mold adopts a stepped cooling water channel, first passing 20℃ cooling water for 30s, and then switching to 10℃ cooling water for 20s.

[0093] 2) Demolding: Mechanical ejection + gas-assisted demoulding is used, with an ejection speed of 15mm / s and an ejection force of 3kN.

[0094] S5. Post-processing

[0095] 1) Heat treatment: Place the product in a constant temperature oven (model: DHG-9240A) and bake at 80℃ for 2 hours to eliminate internal stress.

[0096] 2) Surface spraying: Use UV curing paint spraying, curing energy 800mJ / cm².

[0097] 3) Aging test: -40℃-85℃ cycle test is carried out in a high and low temperature cycle test chamber (model: LRHS-101-LHS).

[0098] Product performance:

[0099] Shore hardness: PC part 90M, TPU part 85A (ASTMD2240 standard).

[0100] Environmental resistance: No cracking or discoloration after 500 high and low temperature cycles.

[0101] Production cycle: Single-mode cycle is about 75 seconds, and the yield rate is 97.5%.

[0102] Process Optimization Description

[0103] 1. Temperature control:

[0104] In Example 1, the melting temperature of the TPR material (190° C.) is lower than that of ABS (245° C.), so as to avoid decomposition of the TPR due to high temperature.

[0105] In Example 2, the mold temperature difference between PC and TPU is controlled at 10-20° C. to ensure the welding quality of the bonding surface.

[0106] 2. Injection parameters:

[0107] The injection pressure of the second color is 10-15MPa lower than that of the first color to prevent color mixing caused by material impact.

[0108] The holding time is adjusted according to the material shrinkage rate (PC shrinkage rate is 0.5%, TPU shrinkage rate is 1.2%).

[0109] 3. Mold design:

[0110] Use pin-point gate (diameter 0.8-1.2mm) to reduce gate marks and improve appearance quality.

[0111] The joining surface of the two materials is designed to be wavy (wave height 0.5mm, wavelength 2mm) to enhance the mechanical interlocking strength.

[0112] It should be noted that, in this document, terms such as "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0113] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A two-color injection molding process, characterized in that: The following steps are involved: S1. Raw material pretreatment: 1) ABS plastic and TPR materials were selected and passed through a vibration screening machine to remove impurities with a particle size of ≥0.5mm, and then passed through an electromagnetic iron remover to remove metal particles; 2) Dry the pre-treated ABS plastic and TPR material separately to control the moisture content to ≤0.05%; S2, two-color injection molding: 1) Melt the dried ABS plastic and inject it into the first cavity of the mold. Maintain the pressure for 15-60 seconds at an injection pressure of 70-120 MPa to form the first color product. 2) After the mold is opened, the movable mold plate is rotated 180 degrees. After the mold is closed, the dried TPR material is melted and injected into the second mold cavity. The melting temperature of the TPR material is 50-100 ° C lower than that of ABS plastic. It is combined with the first color product under an injection pressure of 60-100 MPa. S3, cooling and demoulding: 1) The mold cooling system controls the cooling rate to 5-15°C / s and the cooling time to 15-50s, so that the center temperature of the product drops to 40-60°C; 2) Use mechanical ejection or gas-assisted demoulding to remove the product from the mold; S4, post-processing: 1) Deburring and surface polishing of products; 2) Perform plasma surface activation or UV curing coating treatment.

2. A two-color injection molding process according to claim 1, characterized in that: The melt index of the ABS plastic is 15-30 g / 10 min, and the Shore hardness of the TPR material is 70-90A.

3. The two-color injection molding process according to claim 1, characterized in that: A wavy joint surface is provided between the first cavity and the second cavity of the mold, wherein the wave height of the joint surface is 0.3-1.0 mm and the wavelength is 1.0-3.0 mm.

4. The two-color injection molding process according to claim 1, characterized in that: The process parameters of the drying process are: ABS plastic: drying temperature 80-95°C, drying time 2-4 hours; TPR material: drying temperature 60-80℃, drying time 3-5 hours.

5. The two-color injection molding process according to claim 1, characterized in that: The cooling system includes a spiral cooling water channel distributed along the contour of the mold cavity, the diameter of the cooling water channel is 6-12 mm, and the temperature of the coolant is 10-25°C.

6. The two-color injection molding process according to claim 1, characterized in that: In the injection molding step: The barrel temperature of ABS plastic is 210-250℃, and the nozzle temperature is 230-260℃; The barrel temperature of TPR material is 160-200℃, and the nozzle temperature is 180-210℃.

7. The two-color injection molding process according to claim 1, characterized in that: The ejection device includes at least four ejector pins distributed on the non-appearance surface of the product, the diameter of the ejector pins is 2-6 mm, and the ejection speed is 10-30 mm / s.

8. The two-color injection molding process according to claim 1, characterized in that: The plasma surface activation treatment parameters in the post-treatment step are: power 100-500W, treatment time 10-60s, and gas pressure 10-50Pa.