Secondary injection molding encapsulation molding process of plastic product

Abstract

The invention provides a secondary injection molding encapsulation molding process of a plastic product, and belongs to the technical field of injection molding, the molding process comprises the following steps: (1) placing a primary injection molding material in a primary molding mold, and carrying out primary injection molding and cooling molding to complete injection molding of a body; and (2) taking the injection-molded body as an insert, fixing the insert in a secondary injection mold, and carrying out a secondary injection rubber coating process on the periphery of the insert by using a secondary injection material. According to the invention, the tackifier and the auxiliary agent are added, so that the bonding performance between PC and a TPE base material is greatly improved. By arranging the vacuum converter suction cup positioning structure, a plastic product body can be accurately positioned, the glue feeding amount is accurately and effectively adjusted through reasonable matching of injection molding unit elements and a large-tonnage machine table, and finally a qualified sample piece is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of injection molding, and in particular to a secondary injection molding process for plastic products. Background Art

[0002] TPE, the full name of thermoplastic elastomer, is a material that combines the elasticity of rubber and the processability of plastic. It exhibits rubber elasticity at room temperature and can be thermoformed like plastic under high temperature conditions, making it more flexible and efficient in the manufacturing process. The elasticity of TPE material is comparable to that of natural rubber, with a soft feel, strong resilience, and good wear resistance and tear resistance. TPE material can maintain stable performance over a wide temperature range (-60°C to 135°C), meets international environmental standards, and is recyclable. PC, the full name of polycarbonate, is a high molecular polymer containing carbonate groups in the molecular chain. It is a colorless, transparent, heat-resistant, and impact-resistant thermoplastic resin. It has good electrical insulation, flame retardancy, and dimensional stability over a wide temperature and humidity range. Therefore, it is widely used in the field of electronics and electrical appliances, especially in industries such as electric meter boxes and electronic instruments. Windows made of PC need to be coated with soft glue for protection to improve the product's anti-scratch and anti-fall properties.

[0003] In the prior art, a secondary injection molding method is usually used to inject TPE soft materials onto PC hard plastic parts, and then the secondary injection molding products are obtained after cooling and molding. However, in the actual production process of secondary injection molding products with PC as the hard material and TPE as the soft material, there are usually the following problems: when using TPE to encapsulate PC, the adhesion between the TPE soft material and the PC hard material is poor, resulting in the TPE coating layer being easy to crack or not adhering firmly. An important reason for this situation is that the polarity difference between TPE and PC is large. Modifying the TPE material or adding sticky materials can help improve the adhesion between the two materials of TPE and PC. At present, there are many patents on the secondary injection molding and encapsulation process. For example, the invention patent with application number 201610330408.4 discloses a TPE secondary injection molding and encapsulation process, which includes the following steps: (1) first molding PP, ABS, PC or PA hard materials; (2) then fixing the molded hard plastic parts on the encapsulation mold; (3) then injecting TPE onto the hard plastic parts at a temperature range of 170-250°C. Although this patent improves the cushioning and comfort of the material products, it also has the problem that the coating layer is easy to crack or not sticky.

[0004] In view of this, it is of great significance to provide a secondary injection molding encapsulation material that has good cushioning, comfort and adhesion, increase the yield rate of products, improve production efficiency and promote the diversified development of products. Summary of the invention

[0005] In view of this, the present invention provides a secondary injection molding process for plastic products, comprising the following steps:

[0006] (1) placing a primary injection molding material in a primary molding mold, performing a primary injection molding, cooling and molding, and completing the injection molding of the main body;

[0007] (2) The injection molded body is used as an insert, the insert is fixed in a secondary injection mold, and a secondary injection molding material is used to perform a secondary injection molding process on the outer periphery of the insert.

[0008] Furthermore, the primary injection molding material in step (1) is PC material.

[0009] Furthermore, the secondary injection molding material in step (2) includes a soft material, a tackifier and an auxiliary agent.

[0010] Furthermore, the soft material is TPE material.

[0011] Furthermore, the tackifier is TPU (full name in Chinese: thermoplastic polyurethane elastomer).

[0012] Furthermore, the auxiliary agent is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride.

[0013] Furthermore, the tackifier, the auxiliary agent and the soft material are mixed and kneaded and then secondary injection molding is performed.

[0014] Furthermore, a twin-screw extruder is used for mixing, and the rotation speed is controlled at 200-500 rpm to fully mix the tackifier, the auxiliary agent and the TPE matrix.

[0015] Furthermore, the injection molding cycle in step (1) is 60 to 70 seconds, and the pressure is 120 to 140 MPa.

[0016] Furthermore, the cycle of the secondary injection molding in step (2) is 70 to 80 seconds, and the pressure is 40 to 70 MPa.

[0017] Furthermore, the temperature of the secondary injection molding is lower than the melting temperature of the primary injection molding material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention improves the bonding performance between PC and TPE substrates by adding tackifiers and additives in the injection molding process, and the 180° peel strength between the two is as high as 15.3 kN / m, and the bonding water boiling resistance can reach 9.3 kN / m.

[0020] During the secondary injection molding and overmolding process, the present invention can realize accurate positioning of the plastic product body with high precision by setting a vacuum converter suction cup positioning structure device, and utilizes the reasonable combination of injection molding unit components and large-tonnage machines to accurately and effectively adjust the amount of glue fed, and finally obtain qualified samples. DETAILED DESCRIPTION

[0021] The present invention provides a secondary injection molding process for a plastic product, comprising the following steps:

[0022] (1) placing a primary injection molding material in a primary molding mold, performing a primary injection molding, cooling and molding, and completing the injection molding of the main body;

[0023] (2) The injection molded body is used as an insert, the insert is fixed in a secondary injection mold, and a secondary injection molding material is used to perform a secondary injection molding process on the outer periphery of the insert.

[0024] In some embodiments of the present invention, the primary injection molding material in step (1) is PC material.

[0025] In some embodiments of the present invention, the secondary injection molding material in step (2) includes a soft material, a tackifier and an auxiliary agent.

[0026] In some embodiments of the present invention, the soft material is TPE material.

[0027] In some embodiments of the present invention, the tackifier is TPU (full name in Chinese: thermoplastic polyurethane elastomer).

[0028] In some embodiments of the present invention, the auxiliary agent is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride.

[0029] In some embodiments of the present invention, the tackifier, the auxiliary agent and the soft material are mixed and then subjected to secondary injection molding.

[0030] A twin-screw extruder is used for mixing, and the rotation speed is controlled at 200-500 rpm to fully mix the tackifier, additives and TPE matrix.

[0031] In some embodiments of the present invention, the injection molding cycle in step (1) is 60 to 70 seconds, and the pressure is 120 to 140 MPa.

[0032] In some embodiments of the present invention, the cycle of the secondary injection molding in step (2) is 70 to 80 seconds, and the pressure is 40 to 70 MPa.

[0033] In some embodiments of the present invention, the temperature of the secondary injection molding is lower than the melting temperature of the primary injection molding material.

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0035] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the raw materials and auxiliary agents are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0036] Example 1

[0037] A secondary injection molding process for plastic products, the specific steps are as follows:

[0038] (1) placing the PC material in a primary molding mold for primary injection molding, the injection molding cycle is 65 seconds, the pressure is 130 MPa, the melting temperature of the PC material is 300° C., and then fully cooling the mold to complete the injection molding of the main body;

[0039] (2) The injection molded body is used as an insert and fixedly installed in the secondary injection mold through a vacuum converter suction cup positioning structure device to achieve accurate fixed positioning;

[0040] (3) TPE, TPU and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride were placed in a twin-screw extruder for mixing in a weight ratio of 45:4:1, and the mixing speed was controlled at 400 rpm to ensure that the raw materials were fully mixed to obtain a secondary injection molding material. Then, an injection unit component was used to match a 700T large injection molding machine, and the secondary injection molding material was used for secondary injection molding. The secondary injection molding cycle was 78 seconds, the pressure was 50 MPa, and the melting temperature of the secondary injection molding material was 180°C.

[0041] Example 2

[0042] A secondary injection molding process for plastic products, the specific steps are as follows:

[0043] (1) placing the PC material in a primary molding mold for primary injection molding, the injection molding cycle is 60 seconds, the pressure is 120 MPa, the melting temperature of the PC material is 280° C., and then fully cooling the mold to complete the injection molding of the main body;

[0044] (2) The injection molded body is used as an insert and fixedly installed in the secondary injection mold through a vacuum converter suction cup positioning structure device to achieve accurate fixed positioning;

[0045] (3) TPE, TPU and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride were placed in a twin-screw extruder for mixing in a weight ratio of 45:4:1, and the mixing speed was controlled at 200 rpm to ensure that the raw materials were fully mixed to obtain a secondary injection molding material. Then, an injection unit component was used to match a 700T large-scale injection molding machine, and the secondary injection molding material was used for secondary injection molding. The secondary injection molding cycle was 70 seconds, the pressure was 40 MPa, and the melting temperature of the secondary injection molding material was 160°C.

[0046] Example 3

[0047] A secondary injection molding process for plastic products, the specific steps are as follows:

[0048] (1) placing the PC material in a primary molding mold for primary injection molding, the injection molding cycle is 70 seconds, the pressure is 140 MPa, the melting temperature of the PC material is 320° C., and then fully cooling the mold to complete the injection molding of the main body;

[0049] (2) The injection molded body is used as an insert and fixedly installed in the secondary injection mold through a vacuum converter suction cup positioning structure device to achieve accurate fixed positioning;

[0050] (3) TPE, TPU and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride were placed in a twin-screw extruder for mixing in a weight ratio of 45:4:1, and the mixing speed was controlled at 500 rpm to ensure that the raw materials were fully mixed to obtain a secondary injection molding material. Then, an injection unit component was used to match a 700T large injection molding machine, and the secondary injection molding material was used for secondary injection molding. The secondary injection molding cycle was 80 seconds, the pressure was 70 MPa, and the melting temperature of the secondary injection molding material was 190°C.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that no tackifier and auxiliary agent are added.

[0053] Comparative Example 2

[0054] The difference from Example 1 is that no viscosity enhancer was added.

[0055] Comparative Example 3

[0056] The difference from Example 1 is that no auxiliary agent is added.

[0057] Test Case

[0058] According to GB / T15254-2014 standard, the secondary injection molded products produced in Examples 1-3 and Comparative Examples 1-3 were subjected to 180° peeling test using a WDW-100H electronic universal testing machine. The test method is as follows: fix the PC material at one end of the test machine fixture, fix the modified TPE coating material with another fixture, and after both ends are fixed, start the test, perform the peeling strength test at an angle of 180°, until the coating layer and the PC material are completely peeled off, and record the peeling strength of the sample.

[0059] The 180° peel strength bonding boiling resistance between the coating layer and the PC material of the secondary injection molded products produced in Examples 1-3 and Comparative Examples 1-3 was tested. The boiling temperature during the test was 100 degrees Celsius and the boiling time was 30 minutes.

[0060] The test results of the bonding properties of the secondary injection molded products produced in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0061] Table 1

[0062] Group Adhesive performance (kN / m) Adhesive performance retention rate after boiling (%) Example 1 5.3 79.6 Example 2 4.9 74.1 Example 3 4.7 72.6 Comparative Example 1 1.6 51.2 Comparative Example 2 1.7 63.5 Comparative Example 3 1.9 42.5

[0063] As can be seen from Table 1, TPU and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride were not added to the secondary injection molding product produced in Comparative Example 1, resulting in the worst bonding performance of the product in Comparative Example 1, which was only 1.6 kN / m, and the bonding performance retention rate after boiling was also low, indicating that when preparing the secondary injection molding product of the PC substrate and the TPE coating layer, adding TPU and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride has a positive effect on improving the bonding performance between the PC substrate and the TPE coating layer.

[0064] In the secondary injection molding product produced in Comparative Example 2, only the auxiliary agent dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride was added, and the tackifier TPU was not added. Its bonding performance was also poor, but the bonding performance retention rate of Comparative Example 2 after boiling in water was slightly better than that of Comparative Example 1, indicating that the addition of the auxiliary agent dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride helps to improve the boiling resistance of the secondary injection molding product.

[0065] The bonding performance of the secondary injection molding product produced in Comparative Example 3 is improved compared with that in Comparative Example 1, but its boiling resistance bonding performance is poor, which is obviously inferior to that in Example 1, indicating that the addition of dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride can effectively improve the boiling resistance bonding performance between the PC substrate and the TPE coating layer.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A secondary injection molding process for plastic products, characterized in that: The following steps are involved: (1) placing a primary injection molding material in a primary molding mold, performing a primary injection molding, cooling and molding, and completing the injection molding of the main body; (2) The injection molded body is used as an insert, the insert is fixed in a secondary injection mold, and a secondary injection molding material is used to perform a secondary injection molding process on the outer periphery of the insert.

2. The secondary injection molding process for plastic products according to claim 1, characterized in that: The primary injection molding material in step (1) is PC material.

3. The secondary injection molding process for plastic products according to claim 1, characterized in that: The secondary injection molding material in step (2) includes a soft material, a tackifier and an auxiliary agent.

4. The secondary injection molding process for plastic products according to claim 3, characterized in that: The soft material is TPE material.

5. The secondary injection molding process for plastic products according to claim 3, characterized in that: The tackifier is TPU.

6. The secondary injection molding process for plastic products according to claim 3, characterized in that: The auxiliary agent is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride.

7. The secondary injection molding process for plastic products according to claim 3, characterized in that: The tackifier, additives and soft material are mixed and then subjected to secondary injection molding and encapsulation.

8. The secondary injection molding process for plastic products according to claim 1, characterized in that: The injection molding cycle in step (1) is 60 to 70 seconds, and the pressure is 120 to 140 MPa.

9. The secondary injection molding process for plastic products according to claim 1, characterized in that: The cycle of the secondary injection molding in step (2) is 70 to 80 seconds, and the pressure is 40 to 70 MPa.

10. The secondary injection molding process for plastic products according to claim 1, characterized in that: The temperature of the secondary injection molding is lower than the melting temperature of the primary injection molding material.