JP2024047574A - Injection molding method for cosmetic containers - Google Patents

Abstract

[Problem] To provide a method for injection molding a cosmetic container that can seal the container with a container lid without causing warping in the container lid. [Solution] The flow rate of molten resin filled from gates 25A, 25B, and 25C can be adjusted for each gate. [Selected Figure] Figure 1

Description

This invention relates to a method for injection molding cosmetic containers.

Modern society is continually developing while also becoming more diverse and multifaceted, and with these social changes, people of all ages and genders are using cosmetics that are appropriate for their personalities, tastes, and purposes.

In particular, such cosmetics not only help to keep the skin healthy and clean, but also greatly contribute to the beauty of the individual user by allowing them to more appropriately express their individuality by adding color to the cosmetics, which is why cosmetics in a variety of colors are widely used.

The above-mentioned color cosmetics are used to make the face more beautiful after basic makeup has been applied, and there are many different types to allow makeup suitable for different parts of the face. Colors that suit the user's skin color, the design and color of the clothes they are wearing, and the place they are going out are selected and used.

Various types of cosmetics, including color cosmetics, are generally stored in compact containers, which store the cosmetic contents in an impregnated or gel form. When in use, the outer lid is opened from the container body, and the cosmetic contents are applied to the face using makeup tools such as puffs and brushes.

On the other hand, in recent years, cosmetics called balms have come into use. Balms are thick creams or pastes that are very viscous and have a consistency that does not drip even when the container is turned upside down. However, since there is no clear definition, the viscosity of the contents varies depending on the cosmetics company and brand.

Tiger Balm, a well-known topical anti-inflammatory and analgesic, is also a type of balm, and because the word balm can give the impression of having medicinal properties, it is sometimes intentionally named after the product, and sometimes it is used to differentiate it from creams.

In short, cosmetics known as balms are hard formulations, but from the moment they are applied to the skin, they gradually loosen due to the skin temperature, allowing the oil components to spread smoothly. As such, cosmetics known as balms contain volatile solvents and moisture, and if the sealing strength of the container that holds the balm weakens, the volatile solvents and moisture will evaporate into the atmosphere, causing the balm to harden and lose its original functions, so a method is needed to prevent the evaporation of the balm's volatile solvents and moisture.

For example, as shown in FIG. 12, a cosmetic container is known that is made up of a container-side lid 50 that contains the contents and a hinge-side lid 51 that seals the container-side lid 50, and a sealing protrusion 52 formed on the hinge-side lid 51 engages with an inner wall surface 53 of the container-side lid 50 to seal the container-side lid 50 (Patent Document 1). 54 is a hinge, 55 is a lid handle for opening and closing the hinge-side lid 51, and 56 is the contents. This cosmetic container is manufactured by injection molding a synthetic resin, and 57 is a filling hole (gate) for filling the cavity of the injection molding machine with molten resin. That is, the cosmetic container shown in FIG. 12 is manufactured by injection molding using a one-point gate type mold.

However, when injection molding is performed using a one-gate mold, the molten resin has some parts where the flow distance is long and some parts where it is short, and a large pressure difference occurs in the molten resin filling the mold between the area near the gate and the end of the flow, which makes it easy for the hinge-side lid 51 to warp, making it difficult to seal the container-side lid 50 with the hinge-side lid 51, which is an injection molded product.

JP 2020-521614 A

In view of the problems inherent in the prior art, the present invention aims to provide an injection molding method for cosmetic containers that can seal the container with a container lid without causing warping of the container lid.

The present invention is a method for injection molding cosmetic containers, which uses a mold having filling holes for filling the cavity with molten resin, and is characterized by the fact that the flow rate of the molten resin filling through the multiple filling holes can be adjusted for each filling hole.

According to the injection molding method of the present invention, the flow rate of the molten resin filled from the multiple filling holes can be adjusted for each filling hole, so there is little difference in the flow distance of the molten resin filled from each filling hole. As a result, there is little pressure difference between the molten resin filled in the mold, so the injection-molded container lid does not warp and the container can be sealed with the container lid.

FIG. 1 is a cross-sectional view showing an embodiment of an injection molding machine capable of carrying out the injection molding method of the present invention. FIG. 2(a) is a plan view showing a cosmetic container obtained by injection molding using the injection molding method of the present invention with its container lid open, and FIG. 2(b) is a cross-sectional view taken along the line B-B of FIG. 2(a). FIG. 3 is a diagram showing the results of flow analysis of the deformation amount of a cosmetic container obtained by injection molding using the injection molding method of the present invention. FIG. 4 is a diagram showing the results of flow analysis of the deformation amount of a cosmetic container obtained by injection molding using the injection molding method of the comparative example. FIG. 5 is a schematic diagram for explaining the injection molding method of the present invention. 6(a), (b), and (c) are perspective views showing injection molding methods using different runners. 7(a), (b), and (c) are plan views of the injection molding methods of FIGS. 6(a), (b), and (c) seen from above, respectively. FIG. 8(a) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in FIG. 6(a) at an injection time of 4 seconds, and FIG. 8(b) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in FIG. 6(a) at an injection time of 2 seconds. FIG. 9(a) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in FIG. 6(b) at an injection time of 4 seconds, and FIG. 9(b) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in FIG. 6(b) at an injection time of 2 seconds. FIG. 10(a) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in FIG. 6(c) at an injection time of 4 seconds, and FIG. 10(b) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in FIG. 6(c) at an injection time of 2 seconds. 11(a) and (b) are schematic diagrams illustrating a method for cooling the cosmetic container shown in FIG. 2(a) and (b). FIG. 12 is a perspective view of a cosmetic container described in Patent Document 1.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that the embodiment described below is merely an example, and the present invention is not limited to the embodiment described below. Various changes and modifications are possible without departing from the technical scope of the present invention.

Figure 1 shows an injection molding machine 1, which is an embodiment of an injection molding machine capable of carrying out the injection molding method of the present invention. The injection molding machine 1 includes an injection device 10 that injects synthetic resin, and a mold 20, which is a mold for molding. The injection device 10 kneads the molten resin R inside a cylindrical barrel 11 with a screw 12 inside the barrel 11. A nozzle 13 is provided at the tip of the barrel 11, and injection molding is performed by connecting this nozzle 13 to a bushing 21 on the mold 20 side and filling the inside of the mold 20 with the molten resin R.

The mold 20 is divided into a fixed mold part 20A on the right side in the figure and a movable mold part 20B on the left side, and a cavity 22 filled with molten resin R is provided between the fixed mold part 20A and the movable mold part 20B. A recess that becomes the cavity 22 is formed in the movable mold part 20B. The fixed mold part 20A is attached to the fixed side die plate 2A on the right side in the figure, and the movable mold part 20B is attached to the moving side die plate 2B on the left side. These die plates 2A, 2B are clamped from both sides by a clamping device (not shown). By filling the mold 20 with molten resin R in this state, the molten resin R in the cavity 22 can be maintained at high pressure.

Inside the fixed mold section 20A, there are a sprue 23, a runner 24, and multiple gates 25A, 25B, and 25C, which are passages for the molten resin R supplied from the injection device 10. The sprue 23 is opened at the center of the bush 21, and guides the molten resin R injected from the nozzle 13 of the injection device 10 connected to the bush 21 to the runner 24. The runner 24 is connected to multiple gates 25A to 25C, and guides the molten resin R from the sprue 23 to the gates 25A to 25C. Each of the gates 25A to 25C is a filling hole for filling the cavity 22 with the molten resin R, and the tip opens to the inner surface of the cavity 22. The inner diameter of each of the gates 25A to 25C is gradually narrowed toward the cavity 22. Inside each of the gates 25A to 25C, a rod-shaped valve rod 26A to 26C is provided so as to be able to advance and retreat toward the opening of each of the gates 25A to 25C.

The outer diameter of the tip end (the end on the left side in the figure) of each valve rod 26A-26C is made larger than the inner diameter of the opening of the gate 25A-25C, and the base end (the end on the right side in the figure) is connected to the piston of the hydraulic cylinder device 27A-27C. When each hydraulic cylinder device 27A-27C is driven to advance each valve rod 26A-26C, each gate 25A-25C is closed, and when each valve rod 26A-26C is retreated, each gate 25A-25C is opened. This allows the filling of molten resin R to start separately for each gate 25A-25C. Here, the valve rods 26A-26C and the hydraulic cylinder devices 27A-27C constitute a valve mechanism that can block and open the flow of molten resin R. In addition to the opening and closing function of blocking and opening the molten resin, the valve mechanism also has a flow rate adjustment function for adjusting the flow rate of the molten resin.

Next, the procedure for injection molding in this embodiment will be described. First, the mold 20 is set in the injection molding machine 1, and then the valve rod 26A of gate 25A, the valve rod 26B of gate 25B, and the valve rod 26C of gate 25C are retracted to open gates 25A, 25B, and 25C. In this state, filling of the molten resin R begins from gates 25A, 25B, and 25C.

Once the cavity 22 has been filled with the molten resin R, a pressure-holding process is started to cool and solidify the molten resin R. Once the resin has sufficiently cooled and solidified, the mold 20 is opened and the molded product is removed, completing the injection molding process.

In this way, since the molten resin R is filled from the multiple gates 25A, 25B, and 25C, differences in the flow distance of the molten resin filled from each gate are unlikely to occur, and pressure differences are unlikely to occur between the molten resin filled in the mold, so that warping is unlikely to occur in the components of the container obtained by injection molding. In addition, the flow rate of the molten resin filled from each gate 25A, 25B, and 25C can be adjusted as necessary using the above-mentioned flow rate adjustment function. For example, if the flow rate of the molten resin filled from the central gate 25A is Q liters/min, the flow rate of the molten resin filled from the gates 25B and 25C on both sides can be set to 1.05Q liters/min to slightly increase the amount of molten resin filled from the gates on both sides compared to the central gate, or conversely, the flow rate of the molten resin filled from the gates 25B and 25C on both sides can be set to 0.95Q liters/min to slightly decrease the amount of molten resin filled from the gates on both sides compared to the central gate. Furthermore, the flow rates of the molten resin filled from the gates 25B and 25C on both sides do not necessarily need to be the same, and in order to obtain the effects of the present invention, the flow rates of the molten resin filled from the gates 25B and 25C on both sides can be made different depending on the case. In this way, by appropriately adjusting the flow rates of the molten resin filled from each gate 25A, 25B, and 25C, it is possible to make it difficult for a pressure difference to occur between the molten resin filled in the mold, and to make it difficult for warping to occur in the components of the container obtained by injection molding. The number of gates is not limited to three, and may be two or four or more depending on the situation.

Next, the effects of the present invention will be described based on specific experimental examples.
[Example of the present invention] In the example of the present invention, injection molding was performed under the condition that the flow rate of the molten resin filled from the gate 25B and 25C on both sides was 0.95Q liters/min, while the flow rate of the molten resin filled from the gate 25A in the center was Q liters/min. As a result, a cosmetic container as shown in Figures 2(a) and 2(b) was obtained. In Figures 2(a) and 2(b), L is the container lid, C is the container, and it has an appearance similar to the cosmetic container shown in Figure 5. The parts marked 25A, 25B, and 25C indicate the positions corresponding to each gate. As shown in Figure 2(b), a screw groove th is formed on the inner side of the container C, and a container obtained by separate injection molding, which has a screw groove that can be screwed into the screw groove th, is screwed to the container C.
[Comparative Example] In this comparative example, the same mold 20 as in the above experimental example was used, and the molten resin R was filled only through the gate 25A, while the gates 25B and 25C were closed.

[Injection Conditions] In these experimental examples and comparative examples, injection molding was carried out under the same injection conditions as follows.
Injection conditions: Material used: Polypropylene (Melt flow index = 15 g/10 min, 230°C, 2.16 kg)
Molding temperature: 200°C
Mold temperature: 30°C

[Experimental Results] Figure 3 shows the flow analysis results of the deformation amount of a cosmetic container obtained by injection molding using the injection molding method of the present invention, and Figure 4 shows the flow analysis results of the deformation amount of a cosmetic container obtained by injection molding using the injection molding method of the comparative example. In Figures 3 and 4, the darker the black, the greater the deformation amount. As is clear from comparing Figures 3 and 4, the deformation amount of the cosmetic container obtained by injection molding using the injection molding method of the present invention is less than the deformation amount of the cosmetic container obtained by injection molding using the injection molding method of the comparative example. The above flow analysis results were obtained by performing flow analysis using the flow analysis software "3D TIMON (registered trademark)" made by Toray Engineering D Solutions Co., Ltd. under the following conditions: resin (polypropylene) temperature 200°C, mold temperature 30°C, injection speed 50 mm/sec, holding pressure 80 mPa, and cooling time 10 seconds.

Figure 5 is a schematic diagram for explaining the injection molding method of the present invention, and the injection molding method of the present invention will be explained based on Figure 5. In Figure 5, 31 is a container lid, 32 is a container filled with the cosmetic content, 33 is a hinge, and 34, 35, and 36 are filling holes (gates) for filling the cavity with molten resin. If the cavity is filled with molten resin only from gate 34, the pressure of the molten resin filling the container lid 31 side is high, and the pressure of the molten resin filling the container 32 side through hinge 33 is relatively low, so that the molded product is likely to warp. Therefore, after injection molding, a shape correction process may be required in which the container 32 is closed with the container lid 31 and a weight is placed on the container lid 31 to correct the warping of the molded product. Since the shape correction process is an unnecessary process, it leads to an increase in manufacturing costs and is not preferable.

Therefore, by filling the cavity with molten resin from multiple gates 34, 35, and 36, differences in the flow distance of the molten resin filled from each gate are unlikely to occur, and pressure differences are unlikely to occur between the molten resin filled into the cavity, so that the molded product obtained by injection molding is unlikely to warp. In addition, by using the above-mentioned flow rate adjustment function to adjust the flow rate of the molten resin filled into the cavity from each gate 34, 35, and 36 as necessary, the shape of the injection molded product becomes better and the above-mentioned shape correction process becomes unnecessary. Furthermore, by combining the injection molding method of the present invention with the above-mentioned flow analysis software, the shape of the injection molded product becomes even better, which is preferable. In other words, by linking the flow analysis software with the injection molding method of the present invention, an injection molded product with a nearly perfect shape with the center of point symmetry at the center of the container 32 can be obtained.

As mentioned above, the molten resin is not filled directly into the cavity of the mold from the injection device. Instead, the molten resin is injected from the nozzle of the injection device towards the mold, through an initial passage called a sprue, through a passage called a runner, which has a design (diameter, length, shape) suited to the injection molded product, and is guided to the gate, which is a filling hole for filling the cavity with the molten resin. Runner design is extremely important in order to obtain injection molded products with a good shape. Therefore, the suitability of runner design will be explained based on specific examples.

In other words, using polypropylene resin with a melt flow rate of 25 g/10 min, the resin temperature was set to 230°C, the mold temperature to 30°C, the injection time (passing time of the runner) to 2 or 4 seconds, the runner diameter to 4 mm, the gate diameter to 0.7 mm, and three types of runners were used as shown in Figures 6(a), (b), and (c) to obtain three injection molded products A, B, and C through one gate. Flow analysis was performed using the flow analysis software "3D TIMON (registered trademark)". In Figures 6(a), (b), and (c), the arrow pointing downward from the top to the top on the right indicates the inlet of the molten resin. Figures 7(a), (b), and (c) are plan views of the injection molding methods of Figures 6(a), (b), and (c) seen from above, respectively.

Figures 8(a)(b), 9(a)(b), and 10(a)(b) show the injection pressure (MPa) over time (seconds) for each injection molding method. Injection pressure refers to the pressure applied to the gate. Figure 8(a) shows the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in Figure 6(a) at an injection time of 4 seconds, and Figure 8(b) shows the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded products A, B, and C in Figure 6(a) at an injection time of 2 seconds. In Figure 8(a), a difference of 7 MPa in injection pressure was observed between molded products B and A immediately after the injection time of 4 seconds. Also, in Figure 8(b), a difference of 3 MPa in injection pressure was observed between molded products B and A immediately after the injection time of 2 seconds.

Figure 9(a) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded parts A, B, and C in Figure 6(b) at an injection time of 4 seconds, and Figure 9(b) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded parts A, B, and C in Figure 6(b) at an injection time of 2 seconds. In Figure 9(a), immediately after the injection time of 4 seconds, a difference in injection pressure of 4 MPa was observed between molded parts B and A and C. Also, in Figure 9(b), immediately after the injection time of 2 seconds, a difference in injection pressure of 3 MPa was observed between molded parts B and A and C.

Figure 10(a) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded parts A, B, and C in Figure 6(c) at an injection time of 4 seconds, and Figure 10(b) is a diagram showing the relationship between injection pressure (vertical axis: MPa) and time (horizontal axis: seconds (sec)) for molded parts A, B, and C in Figure 6(c) at an injection time of 2 seconds. In Figure 10(a), immediately after the injection time of 4 seconds, a difference in injection pressure of 2 MPa was observed between molded parts C and A and B. Also, in Figure 10(b), immediately after the injection time of 2 seconds, a difference in injection pressure of 7 MPa was observed between molded parts C and B.

From the above results, it can be said that the runner in Figure 6(b) has a small pressure difference due to injection time (injection speed) and a good filling balance. In other words, by using a runner designed to have a small pressure difference due to injection time (injection speed), it is possible to obtain an injection molded product with a good shape.

The present invention aims to provide a method for injection molding a cosmetic container that can seal the container with a container lid without warping the container lid. The causes of warping of the container lid include the pressure distribution of the molten resin filled in the mold, the difference in the amount of shrinkage of the molten resin filled in the mold, and the difference in the amount of cooling of the molten resin filled in the mold. The difference between the pressure distribution of the molten resin and the amount of shrinkage of the molten resin can be solved by performing the flow analysis and appropriate runner design. The difference in the amount of cooling of the molten resin can be solved by appropriately cooling the mold. A typical cooling method is to use a two-layer mold and circulate an appropriate cooling medium (e.g., water) on the outer layer side of the mold, but this makes it impossible to avoid uneven cooling. Therefore, as shown in Figures 11(a) and (b), by circulating the cooling medium along the inside of the injection molded product, it becomes possible to cool the injection molded product uniformly. As a result, warping does not occur in the container lid and the container.

That is, as shown by arrows 37 and 38 in FIG. 11(b), the cooling medium (water) supplied to the container is circulated around the inside of the injection molded product as shown by arrows 39, 40a, and 40b, and then discharged outside the mold as shown by arrows 41, 42, and 43. This allows the injection molded product to be cooled uniformly, and no warping occurs in the container lid or container.

As explained above, the present invention is suitable as an injection molding method for cosmetic containers.

REFERENCE SIGNS LIST 1 injection molding machine 10 injection unit 20 mold 11 barrel 12 screw 13 nozzle 21 bush 20A fixed mold part 20B movable mold part 22 cavity 23 sprue 24 runner 25A, 25B, 25C gate 26A, 26B, 26C valve rod 27A, 27B, 27C hydraulic cylinder device 31 container lid 32 container 33 hinge 34 gate 35 gate 36 gate

Claims (1)

This is an injection molding method for cosmetic containers, which uses a mold with filling holes to fill the cavity with molten resin, and is characterized in that the flow rate of the molten resin filling through multiple filling holes can be adjusted for each filling hole.

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