CN118269305A

CN118269305A - IML injection mold

Info

Publication number: CN118269305A
Application number: CN202410580768.4A
Authority: CN
Inventors: 张亚伟; 高浪; 熊书强; 周善意; 贾宇翔
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2024-05-10
Filing date: 2024-05-10
Publication date: 2024-07-02

Abstract

The technical scheme of the invention is to provide an IML injection mold, which adopts a cold runner with a parabolic cross section, and has the advantages that the mold is closest to a circular cross section, and only half of the mold is required to be simply processed. The provision of the film gate near the cold runner provides a uniform flow front and the cold runner can reduce the heat at the time of film gate pouring, thereby obtaining a flat molded article with small molding stress and small tendency to warp. The IML injection mold provided by the invention is embedded with two pressure and temperature combination sensors, so that the real-time measurement of the melt pressure and the melt temperature is ensured, instead of only measuring the mold temperature, and the melt pressure and the temperature change in the injection molding process can be better detected.

Description

IML injection mold

Technical Field

The invention relates to the technical field of injection molding, in particular to an IML injection mold.

Background

The In-mold labeling (IML) process has the remarkable characteristics that the surface of a product produced by the IML process is a hardened transparent film, the middle is a printed pattern layer, and the back is a plastic layer. Because the transparent film covers the printed pattern layer, in the use, the transparent film is contacted at first, the transparent film can protect the product, increase the wear resistance of the product surface, prevent the surface of the positive product from being scratched, simultaneously, because the printing ink on the printed pattern layer is clamped in the middle, the printing ink can be prevented from being scratched, the vivid color of the printing ink can be kept for a long time, and the color is not easy to fade.

The technology is different from the traditional brand new label packaging form of direct silk screen printing, heat shrinkage labels and self-adhesive labels, and is mainly used for injection molding products. The printed in-mold label is put into an injection mold cavity before injection molding, when the mold is closed for injection molding, the in-mold label and the surface of an injection molding piece are melted into a whole under the action of high temperature and high pressure in the mold, and after the mold is opened, the product packaged by the in-mold label is printed in an exquisite manner at one time.

Compared with the traditional molding printing process, the process has the following advantages: 1. one step in place (downstream process directly combined with injection molding process); 2. more reliable print quality (abrasion and chemical resistance); 3. production does not need to be stopped when a new printed pattern is replaced; 4. the environmental pollution of secondary printing and labeling is avoided; 5. the label is integrated with the container; 6. the wall thickness is reduced, and less material is used, so that the material cost is reduced; 7. is easy to recycle.

The use of in-mold labeling in injection molding techniques can provide significant advantages to the product manufacturer or distributor, as well as to the end user, which eliminates secondary steps in the manufacturing process, with the end result being permanent. The in-mold injection labeling is an injection molding process, namely, the back surface is injected to form a flat and uniform film surface. In the packaging industry, in-mold labeling is often an alternative to printing when design requirements are high flexibility or the ability to directly mold a stamp onto a part is not available. In-mold labeling products are widely used in packaging containers for medicines, health products, foods, beverages, and the like.

Disclosure of Invention

The purpose of the invention is that: a flat molded article with little molding stress, little tendency to warp and no flash is obtained.

The technical scheme of the invention is to provide an IML injection mold, which is used for obtaining an IML part by pouring polymer melt, and comprises a cavity component for opening and closing the IML injection mold and a fixing component for pouring the polymer melt into the IML injection mold, wherein the direction of the cavity component moving towards the fixing component is defined as a first direction when the polymer melt is poured;

The cavity assembly includes:

A cavity plate provided with an IML part groove, a first cooling channel group and a vacuum channel;

The IML part groove is provided with N vacuum suction nozzle groups, a cold runner and a pressure-temperature combination sensor, the vacuum suction nozzle groups are connected with the vacuum channels and used for adsorbing labels in the film, the periphery of each vacuum suction nozzle group is provided with a first thimble, the cross section of the cold runner is parabolic and is arranged on the movable side of the IML part groove, one side of the cold runner, which is close to the IML part, is provided with a film gate, and the pressure-temperature combination sensor is embedded in the wall of the IML part groove and used for directly measuring the pressure and the temperature of a polymer melt;

The first cooling channel group comprises a first cooling channel and a second cooling channel, the first cooling channel and the second cooling channel are symmetrically arranged on the surface of the cavity plate, and one side of the first cooling channel group is provided with a water inlet and a water outlet for cooling the poured polymer melt through flowing cooling liquid;

the supporting plate is connected with the cavity plate by adopting the guide sleeve and is used for providing supporting force for the cavity plate;

the ejection mechanism is connected with the supporting plate by adopting a supporting column and comprises an ejector rod and an ejector plate provided with an ejector pin and a return pin, wherein the ejector pin is internally provided with a second ejector pin, and the return pin is internally provided with a spiral spring;

When the polymer melt is poured, the ejector rod moves in a first direction, the ejector plate is driven to transmit pressure in the first direction to the cavity plate connected with the supporting plate by the second ejector pin, and then the first ejector pin is driven to eject the IML part positioned in the IML part groove, and the spiral spring is in a compressed state; when the polymer melt is poured, the spiral spring returns to a normal state and drives the ejector plate to move along the reverse direction of the first direction, so that the cavity assembly reciprocates according to the pouring state of the polymer melt;

The fixing assembly includes:

a mold plate with a second cooling channel group, which is used for forming a space for pouring polymer melt with the cavity plate and is matched with the first cooling channel group for cooling when the polymer melt is poured;

the mold base plate is connected with the mold plate by adopting a guide pillar, the positioning ring is adopted for positioning, the sprue bush is fixed to the mold base plate, and the sprue bush is nested with the sprue bush so as to extend to the mold plate and be used for pouring polymer melt.

Preferably, the diameter of the second cooling channel group is larger than the diameter of the first cooling channel group.

Preferably, the sprue bushing is provided with a tapered sprue at one end of the mold plate for pouring the polymer melt.

Preferably, the water inlet is arranged at a position close to the cold runner.

Drawings

FIG. 1 is an exploded view of an IML mold;

FIG. 2 is a schematic diagram of the geometry of an IML component;

FIG. 3 is a schematic diagram of a cold runner cross section and gate;

FIG. 4 is a cavity plate with a cooling channel arrangement;

FIG. 5 is a mold plate with a cooling channel layout;

fig. 6 is an IML mold cavity plate with a vacuum nozzle and an ejector mechanism.

Description of the reference numerals:

1-positioning rings; 2-sprue bushing; 3-a die plate; 4-a die plate; 5-a cavity plate; 6-supporting plates; 7-supporting columns; 8-a guide post; 9-guiding sleeve; 10-thimble; 11-ejector plate.

Detailed Description

The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present application, and such equivalents are intended to fall within the scope of the application as defined in the appended claims.

As shown in fig. 1, an embodiment of the present invention provides an IML injection mold, which is a dual-plate mold including a half cavity mold, a half fixed mold, a sprue bushing, a cold runner, and an ejection mechanism driven by a coil spring. The cavity mold half of the double-cavity mold consists of a cavity plate, a supporting column, an ejection mechanism (comprising an ejection pin and a return pin) and a mold base plate, and the fixed mold half mainly consists of a mold plate, a mold base plate and a sprue bushing.

In this case, the mold halves need not be precisely aligned, as the part to be molded is located only in the cavity plate, and the mold plate is only a flat surface. The mold is opened on a parting line between the cavity plate and the mold plate, wherein the parting line is a small gap at the joint position between the cavity plate and the mold plate. When the mold is opened, the molded part (IML part) is secured to the cavity by a low temperature bullet well at the end of the gate. When the ejector rod pushes forwards, the ejector plate is driven, the ejector pin moves forwards, and the molded part is stripped from the cavity. Then, the spiral spring triggers the ejector plate to move backwards, the mold can be closed, and a new injection molding cycle is entered.

The IML part is a polypropylene planar IML part, as shown in fig. 2. On the upper side, two polypropylene in-mold labels are attached to the substrate inseparably during the molding process. The in-mold label used was two perforated labels with thickness of 75um and 50um respectively, offered by Inotec bar code security limited, germany. The thick label is a porous label composed of a polyolefin polymer and silica, while the thin label is composed of only a polyolefin polymer. To ensure the uv resistance of the printed layer, both labels are coated with an unknown special substance. Tensile testing indicated that the elastic modulus of the IML part was higher than the unlabeled molded part. This is because the label reinforces the IML molded part to some extent, depending on the type of label used and molding conditions.

The IML die uses a cold runner of parabolic cross-section (fig. 2), as shown in fig. 6, which is a length of groove above and in the middle, which has the advantage of closest circular cross-section and requires simple machining only in half of the die (usually the active side for ejection).

The polymer melt enters the film gate at the top of the two cavities through a conical gate in the gate sleeve and a cold runner on the parting plane (fig. 3). In order to obtain a flat molded article with small molding stress and small tendency to warp, a film gate (fig. 2 and 6) having a height of 0.7mm is provided near the cold runner, which contributes to providing a uniform flow front. By modifying the cross-section of the gate, the tendency of the melt to accelerate near the gate or the interior corner can be counteracted. According to fig. 2, 3, the gate is located on only one side (top) of the component. This eccentric position of the gate causes the mold to open on one side, thereby forming flash. However, since the mold clamping force overcomes the cavity pressure, burrs generated on the molded part by the mold opening are not detected. The film gate must be trimmed from the part after removal, but this does not affect the automated operation.

In order to cool the cavity, cooling channels must be installed in the cavity plate and the mold plate. On the cavity plate (fig. 4), there are two symmetrical cooling channels under the cavity surface. The water flow enters the cooling channel at the position of the top of the part close to the cold runner, the heat in the cold runner is the most, and then the water flow is discharged out of the die through a water outlet at the tail end of the die cavity. In this way, heat can be removed from the melt at regular intervals most effectively.

The cooling channel layout of the mold plate is similar to the cavity plate (fig. 5), except that the cooling channel diameter of the cavity plate is larger, so the distance between the cooling channels and the cavity wall must be larger in order to maintain regular cooling throughout the part. The cooling efficiency of the cavity plate is high because the cooling channels machined transversely are smaller in diameter and the distance between the channels is also smaller. This technique is suitable for label backside injection molding because the label can act as an insulating function. Without reasonable cooling compensation, IML parts are prone to warpage after demolding.

Fig. 6 shows a cavity plate of an IML mold. To secure the labels in the mold cavities, each mold cavity is provided with three vacuum suction nozzles, each of which is occupied by sintered metal, the labels can be secured in the correct position in the mold cavity without falling off. In addition, four pins are required in the cavity and six pins are required in the grooves of the cold runner to peel the molded part from the mold. The IML part is ejected through an ejection mechanism. In the die assembly process, the return pin presses the ejector plate back, so that the die cavity is completely emptied, and the ejector pin cannot be damaged by melt flow. If the return pin is not provided, trace can be left on the surface of the part when the ejection pin is not completely retracted.

Such IML molds do not require any vent gaps, vent channels or special vent designs because air is vented along the ejector pins and parting lines, so-called passive venting. When passive exhaust is adopted, air is mainly exhausted through a parting line in the mold filling process. This method has proven to be viable, especially at the ends of the components, where combustion residues due to the diesel effect can be observed.

For measuring the pressure and temperature variations during injection molding, two pressure and temperature combination sensors are mounted on a fixed mold half, the sensors being embedded in the injection mold with their front ends fully abutting the mold cavity walls, which ensures a direct measurement of the melt pressure, temperature, rather than only measuring the mold temperature, as shown in fig. 6, in comparison with conventional contact temperature sensors (e.g. thermocouples). Furthermore, infrared temperature sensors have advantages over thermocouple in terms of measurement accuracy, since shear heating of the melt can be neglected. And, when using a thermometer operating over a narrow band, the emissivity of the material does not vary greatly with temperature.

First, a robot end-of-arm tool equipped with a small vacuum chuck removes the label from the label stock. The robot then transfers the label into the mold cavity and places it in the desired location on the mold cavity wall. When the vacuum on the mechanical arm is released, the vacuum in the mold cavity is also raised at the same time, so that the label is fixed at a required position. At this time, the prepared mold can be injection molded. Care must be taken in injection molding to avoid damaging the robot. As long as the robot is still between the mold halves, the mold cannot be closed. In this case, a digital pressure switch can be integrated into the injection molding automation system, and the signal from the digital pressure switch directly controls the mold closing. If the label is leaked from the mold cavity, insufficient vacuum is generated, and the digital pressure switch informs the injection molding machine that the mold cannot be started.

Compared with the prior art, the invention has the following beneficial effects:

the IML mould in the injection mould adopts a cold runner with a parabolic cross section, has the advantage of being closest to a circular cross section, and only needs to be simply processed in half of the mould. Providing a film gate over the entire width of the molded article provides a uniform flow front, thereby obtaining a flat molded article with less molding stress and less tendency to warp.

Two pressure and temperature combined sensors are embedded in the injection mold, so that the real-time measurement of the melt pressure and the melt temperature is ensured, and the mold temperature is not measured only. Compared with the traditional thermocouple sensor, the thermocouple sensor can better detect the melt pressure and temperature change in the injection molding process.

Claims

1. The IML injection mold is characterized in that the IML injection mold is used for obtaining an IML part by pouring polymer melt, and comprises a cavity component for opening and closing the IML injection mold and a fixing component for pouring the polymer melt into the IML injection mold, wherein the direction of the cavity component moving towards the fixing component is defined as a first direction when the polymer melt is poured;

The cavity assembly includes:

The fixing assembly includes:

2. The IML injection mold of claim 1, wherein said second set of cooling channels has a diameter greater than a diameter of said first set of cooling channels.

3. An IML injection mold according to claim 1, wherein said sprue bushing is provided with a tapered sprue at one end of said mold plate for injecting a polymer melt.

4. An IML injection mold according to claim 1, wherein said inlet is located adjacent said cold runner.