Injection molding process and system for preparing lightweight plastic

Abstract

The invention belongs to the technical field of plastic forming processing, and particularly relates to an injection molding process and system for preparing light-weight plastic. Controllability of air pressure in the mold cavity is realized through process control, so that the volume of the polymer melt can be effectively controlled, and 10-15% of plastic weight reduction is realized under the condition that the mold is not changed.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic forming and processing, and in particular relates to an injection molding process and system for preparing lightweight plastics. Background Art

[0002] With the development of industry and the improvement of people's quality of life, traditional plastics can no longer meet the technical requirements of cutting-edge materials. For plastic products used in automotive parts, engineering machinery components, aerospace products, etc., there is an increasing need to achieve lightweight. The commonly used method currently includes adding chemical foaming agents or active foaming agents during the plastic preparation process, and foaming by injection molding into the mold and controlling the change in mold size to obtain foamed lightweight plastic. However, this requires finely controlling the size of the mold under different pressures during the injection molding process, resulting in cumbersome processes, high costs, and difficult-to-control foaming effects. Summary of the invention

[0003] In order to solve the above problems, the present invention makes a revolutionary change to the injection molding process, so that the weight of the plastic can be reduced by 10-15% without changing the mold.

[0004] Specifically, the present invention provides an injection molding process for preparing lightweight plastics, which comprises the following steps:

[0005] (1) preparing a polymer melt containing a chemical blowing agent;

[0006] (2) Before injection molding, the mold cavity pressure is controlled at 1MPa-2MPa;

[0007] (3) injecting the polymer melt prepared in step (1) into the mold of step (2), during which the cavity pressure is controlled to be always stable at 1 MPa-2 MPa, so that the material is compressed to 85%-90% of the cavity thickness after the injection molding is completed;

[0008] (4) After the injection molding is completed, the gas in the mold cavity is evacuated, and the chemical foaming agent begins to foam, causing the polymer melt to expand to the normal thickness of the mold cavity;

[0009] (5) After the mold is cooled to room temperature, the mold is opened and the product is taken out to obtain the lightweight plastic.

[0010] Furthermore, the pressure control in step (2) is achieved by air intake through a back pressure system.

[0011] Furthermore, the volume of the polymer melt prepared in step (1) and injected into the mold of step (2) is the volume of the mold cavity.

[0012] Furthermore, in step (3), controlling the cavity pressure to always be stable at 1MPa-2MPa is achieved by a one-way pressure control valve.

[0013] Furthermore, in step (4), the gas in the mold cavity is extracted by a vacuum system.

[0014] Further, after the injection molding is completed, the temperature of the mold cavity is heated to 60-250°C.

[0015] Further, the heating is achieved by a heating system. Further, the heating system can be an electric heating system or a steam heating system.

[0016] Furthermore, the mold is a mold of fixed size.

[0017] The present invention also provides an injection molding system for preparing lightweight plastics, comprising:

[0018] Mould;

[0019] A back pressure system connected to the mold through an air path;

[0020] A vacuum system connected to the mold through an air path;

[0021] An exhaust gas path controlled by a one-way pressure control valve; and

[0022] An injection molding machine used to inject polymer melt into a mold.

[0023] Furthermore, the injection molding system further comprises a heating system for heating the mold. Furthermore, the heating system may be an electric heating system or a steam heating system.

[0024] Furthermore, the mold is a mold of fixed size.

[0025] Beneficial Effects of the Invention

[0026] The present invention realizes controllable air pressure in the mold cavity through process control, so that the volume of the polymer melt can be effectively controlled, thereby achieving 10-15% plastic weight reduction without changing the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of an injection molding system for preparing lightweight plastics according to the present invention is shown. DETAILED DESCRIPTION

[0028] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0029] Example 1

[0030] An injection molding process for preparing lightweight plastics comprises the following steps:

[0031] (1) preparing a polymer melt containing a chemical blowing agent;

[0032] (2) Before injection molding, the mold cavity pressure is controlled at 1 MPa through the back pressure system;

[0033] (3) injecting the polymer melt of step (1) having a volume equal to the volume of the mold cavity into the mold of step (2), during which the cavity pressure is controlled to be always stable at 1 MPa by a one-way pressure control valve, so that after the injection molding is completed, the material is compressed to a range of 85% to 90% of the thickness of the mold cavity;

[0034] (4) After the injection molding is completed, the gas in the mold cavity is evacuated by a vacuum system, and the temperature of the mold cavity is heated to 120°C by an electric heating system. At this time, the chemical foaming agent begins to foam, causing the polymer melt to expand to the normal thickness of the mold cavity;

[0035] (5) After the mold is cooled to room temperature, the mold is opened and the product is taken out to obtain the lightweight plastic.

[0036] Example 2

[0037] An injection molding process for preparing lightweight plastics comprises the following steps:

[0038] (1) preparing a polymer melt containing a chemical blowing agent;

[0039] (2) Before injection molding, the mold cavity pressure is controlled at 1.5 MPa through the back pressure system;

[0040] (3) injecting the polymer melt of step (1) whose volume is equal to the volume of the mold cavity into the mold of step (2), during which the cavity pressure is controlled to be always stable at 1.5 MPa by a one-way pressure control valve, so that after the injection molding is completed, the material is compressed to a range of 85%-90% of the thickness of the mold cavity;

[0041] (4) After the injection molding is completed, the gas in the mold cavity is evacuated by a vacuum system, and the temperature of the mold cavity is heated to 120°C by an electric heating system. At this time, the chemical foaming agent begins to foam, causing the polymer melt to expand to the normal thickness of the mold cavity;

[0042] (5) After the mold is cooled to room temperature, the mold is opened and the product is taken out to obtain the lightweight plastic.

[0043] Example 3

[0044] An injection molding process for preparing lightweight plastics comprises the following steps:

[0045] (1) preparing a polymer melt containing a chemical blowing agent;

[0046] (2) Before injection molding, the mold cavity pressure is controlled at 2 MPa through the back pressure system;

[0047] (3) injecting the polymer melt of step (1) whose volume is equal to the volume of the mold cavity into the mold of step (2), during which the cavity pressure is controlled to be always stable at 2 MPa by a one-way pressure control valve, so that after the injection molding is completed, the material is compressed to a range of 85%-90% of the thickness of the mold cavity;

[0048] (4) After the injection molding is completed, the gas in the mold cavity is evacuated by a vacuum system, and the temperature of the mold cavity is heated to 120°C by an electric heating system. At this time, the chemical foaming agent begins to foam, causing the polymer melt to expand to the normal thickness of the mold cavity;

[0049] (5) After the mold is cooled to room temperature, the mold is opened and the product is taken out to obtain the lightweight plastic.

[0050] Comparative Example

[0051] The same raw materials as in Examples 1-3 and a mold with the same initial size but adjustable size are used to prepare a foamed plastic by a normal foaming process with controllable mold size, wherein the volume of the polymer melt containing a chemical foaming agent injected into the mold is the same as in Examples 1-3.

[0052] The weights of the plastics prepared in Examples 1-3 and the comparative example were tested and the weight loss ratio was calculated. The results are shown in Table 1.

[0053] Table 1

[0054] Cavity pressure Weight(g) Weight loss ratio (%) Normal process 130 0 1MPa 117 10 1.5MPa 114 12.3 2MPa 110 15.4

[0055] It can be seen from the results in Table 1 that, compared with the comparative example, Examples 1-3 of the present invention achieve significant weight reduction of the plastic without changing the mold.

[0056] It should be noted that the preferred embodiments of the present invention are given in the specification and drawings of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not used as additional limitations on the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. In addition, the above-mentioned technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope of the present invention; further, for ordinary technicians in this field, they can be improved or transformed according to the above description, and all these improvements and transformations should belong to the protection scope of the claims attached to the present invention.

Claims

1. An injection molding process for preparing lightweight plastics, characterized in that: The following steps are involved: (1) preparing a polymer melt containing a chemical blowing agent; (2) Before injection molding, the mold cavity pressure is controlled at 1MPa-2MPa; (3) injecting the polymer melt prepared in step (1) into the mold of step (2), during which the cavity pressure is controlled to be always stable at 1 MPa-2 MPa, so that the material is compressed to 85%-90% of the cavity thickness after the injection molding is completed; (4) After the injection molding is completed, the gas in the mold cavity is evacuated, and the chemical foaming agent begins to foam, causing the polymer melt to expand to the normal thickness of the mold cavity; (5) After the mold is cooled to room temperature, the mold is opened and the product is taken out to obtain the lightweight plastic.

2. The injection molding process according to claim 1, characterized in that: The pressure control in step (2) is achieved by air intake through the back pressure system.

3. The injection molding process according to claim 1, characterized in that: The volume of the polymer melt prepared in step (1) and injected into the mold in step (2) is the volume of the mold cavity.

4. The injection molding process according to claim 1, characterized in that: In step (3), controlling the cavity pressure to always be stable at 1MPa-2MPa is achieved by a one-way pressure control valve.

5. The injection molding process according to claim 1, characterized in that: In step (4), the gas in the mold cavity is extracted by a vacuum system.

6. The injection molding process according to claim 1, characterized in that: After the injection molding is completed, the temperature of the mold cavity is heated to 60-250°C.

7. The injection molding process according to claim 6, characterized in that: The heating is achieved by a heating system.

8. An injection molding system for preparing lightweight plastics, characterized in that: include: Mould; A back pressure system connected to the mold through an air path; A vacuum system connected to the mold through an air path; Exhaust gas circuit controlled by a one-way pressure control valve; as well as An injection molding machine used to inject polymer melt into a mold.

9. The injection molding system according to claim 8, characterized in that: Also included is a heating system for heating the mold.

10. The injection molding system according to claim 8, characterized in that: The mold is a mold of fixed size.

Images