JPS6241093B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in multilayer injection molding methods that include resin layers with poor compatibility. 2. Description of the Related Art Methods for producing laminated articles by injecting two or more materials into one mold are well known, and various methods have been proposed. By the way, many of them inject two or more resins sequentially or simultaneously into a cavity that is clamped with a force greater than the injection pressure.
The material is laminated, and is then injected into a fixed cavity that hardly changes except for opening the mold to foam. When the viscosity and flow between resins are not significantly different, or when the shape and thickness of the cavity are complex, the surface does not necessarily reproduce the mold surface and the flow of each resin layer is disturbed. In addition, unevenness appears on the surface as unevenness, and other hesitation marks and streaks due to resin mixing are likely to occur on the surface, resulting in a marked decrease in the commercial value of these molded products. I have a problem with getting used to it. Here, the unevenness of the surface is due to the difference in the shrinkage rate of each resin, and it is thought that in areas where the ratio of resins with large shrinkage is large, it will shrink greatly and become concave, and vice versa. . In addition, in such a molding method, unless the inner core material is injected in an amount close to or greater than the same amount as the skin resin, it is not possible to form a uniform layer over the entire cavity. Therefore, when it is desired to inject the inner core material thinly and uniformly, for example, when molding a gas-barrier container etc. using an expensive resin such as nylon resin as the inner core material and using modified polyolefin as the skin resin,
Although it is cost-effective to inject the inner core material thinly and uniformly, it is difficult to obtain such a molded product using the above method. In contrast to the above method, the vertical flash type (i.e., the mold cavity is surrounded by mold members that slide relative to each other;
By using a mold with a volume variation method and displacing part or all of the mold, it is possible to increase the number of secondary and subsequent molding cavities that are connected to the molding cavity during the primary injection. A method has been proposed for obtaining two or more types of integrated products using a molding die and secondary and subsequent injection devices. However, with this method, if each layer is thin, adhesiveness may deteriorate due to a drop in resin temperature away from the gate unless molding is performed using sufficiently compatible resins such as the same type or its homopolymer or copolymer. big,
There is no strong adhesive force. In addition, it is very difficult to inject each layer to a thickness of 1 mm or less unless the melt viscosity is low and it is difficult to cool down. To injection mold a certain container, this method requires a wall thickness of nearly 3 mm or more. Moreover, in the case of a combination such as the above-mentioned nylon resin and modified polyolefin, which are not sufficiently compatible, the adhesive force will be strong unless the value of L/t (L: length from the gate to the peripheral edge, t: cavity thickness) is made sufficiently small. I can't get it. In addition, it is not suitable for molding other than flat plates because the layer ratio differs depending on the location, and molded products using molds as shown in Figure 10 can only produce stressed molded products, which may deform after molding. . The present invention eliminates these drawbacks and provides a method for obtaining a multilayer injection molded product that is faithful to the mold cavity and in which each resin layer is firmly adhered. In the method of manufacturing the multilayer injection molded article of the present invention, a vertical flash type mold is preferably used as shown in FIG. That is, the thickness of the mold cavity 1 changes due to the relative sliding of the mold members, that is, the injection machine side mold 2, which is a fixed mold and has a female shape, and the mold 3, which is a movable mold and has a male shape, on the open/close cylinder side. It uses a mold that In the present invention, the first molding cavity is made to the capacity of the final molded product and the mold is clamped, and the first resin 4 is injected in an amount insufficient to fill the first primary molding cavity (Fig. 1). , this first resin 4
While the center of the liquid remains in a fluid state without solidifying,
A second resin 5 having poor compatibility with the first resin is injected into the first resin 4 (FIG. 2). Here, the first resin 4 and the second resin 5 may be simultaneously injected using a concentric circle multiple nozzle, and the second resin 5 may be injected so as to be wrapped with the first resin. As described above, multilayer (two layers in the drawings) injection molding was performed in the primary molding cavity to form a multilayer (two-layer) molded product filled with the primary molding cavity resin. After that, the mold cavity 1 is opened until it reaches the final thickness of the molded product, and then a resin of the same type as the first resin 4 or having at least a part of the same main chain as the first resin, or a resin thereof A resin such as a blend having sufficient compatibility with the first resin 1, that is, a third resin 6, is injected (FIG. 3). In the multilayer injection molded product thus obtained, for example, the thickness of the second resin is not uniform during the injection of the first molding cavity, and depending on the location, the thickness is about 10% compared to the shape of the mold cavity. Even if unevenness occurs, the subsequent injection of the third resin results in a multi-layer molded product that is faithful to the mold cavity, almost like a single-layer product. The synthetic resin material that can be used in the present invention is one that can be injected into a mold cavity while in a viscous liquid state, and can be injected into the mold cavity afterwards, and can then solidify within the mold. It is something that can be caused by Further, it is preferable that the first resin and the second resin are adhesive resins, but if they are not adhesive, a resin that can adhere to both the first resin and the second resin is used.
The third resin that is injected after opening the mold to the final molded product may be the same as the first resin, but it may also be a different color resin, a homopolymer or copolymer of the first resin, or a blend thereof, or other materials that are easy to use. Use resin filled with a scorching inorganic material. Furthermore, by injecting foamed resin as the third resin, it is possible to reduce the cost and weight. Typical examples include polypropylene grafted with maleic anhydride as the first resin, 6-nylon resin as the second resin, and unmodified polypropylene as the third resin. Further, the first resin is polyethylene, the intermediate between the first resin and the second resin is an ethylene-vinyl acetate copolymer resin, the second resin is a vinylidene chloride resin, and the third resin is a polyethylene resin containing a high filler. It is possible to manufacture molded containers that have the gas barrier properties of vinylidene chloride and the easy burning properties and good feel of high filler. Next, practical example 1 using the manufacturing method of the present invention using a center-date square plate (200 mm x 200 mm) shaped vertical flat molding mold as shown in FIGS. 1 to 9, and a conventional manufacturing method. Certain comparative examples 1 and 2
shows. The common conditions of Example 1 and Comparative Examples 1 and 2 below are as follows: (a) Resin used: Modified polypropylene (modified PP) resin... (Maleic anhydride grafted modified polypropylene, 10 ^-3 gram equivalent in 1 g of polypropylene) Maleic group, MI=7, specific gravity=0.91) 6-Nylon resin... (melting point 224℃, specific gravity=1.4) Polypropylene (PP) resin... (MI=7, specific gravity=0.91) (b) Melting temperature PP resin, modified PP Resin... 240℃ 6-Nylon resin... 260℃ (C) Mold temperature... 40℃ Example 1 Conditions: Thickness of primary molding cavity...1.0mm Amount of first injection resin (modified PP)...20 c.c. Second injection resin (6- Nylon resin) amount...20c.c. Third injection resin (PP) amount...40c.c. Method; By the method of the present invention, the mold is made to have the thickness of the first molding cavity and modified polypropylene, which is the first injection resin, is injected into the mold. 0.5 seconds after injection, the second injection resin, 6-nylon resin, is injected. Next, while keeping the pressure, the mold was cooled for 7 seconds, and then the cavity was opened to 2 mm, and polypropylene was injected. The cooling time was 12 seconds, and after cooling, the mold was opened and the three-layer injection molded product was taken out. (1st to 4th
Figure) Comparative example 1 Conditions; First molding cavity thickness...0.5mm First injection resin (modified PP) measurement value...20c.c. First mold opening amount...0.5mm Second injection resin (6-nylon resin) Weighing value…
20c.c. 2nd mold opening amount... 1.0mm Measured value of 3rd injection resin (PP)... 40c.c. Method: Inject modified polypropylene, which is the first injection resin, with a molding cavity thickness of 0.5mm, and cooling time. 2 seconds, then open the 0.5mm mold, make the molding cavity 1mm, inject the second injection resin, 6-nylon resin, set the cooling time to 4 seconds, then open the 1.0mm mold, and make the molding cavity thickness 2.0mm. Then, the third injection resin, modified PP, was injected, the cooling time was set to 12 seconds, and after cooling, the mold was opened and the three-layer injection molded product was taken out. (5th ~
Figure 7) Comparative Example 2 Conditions: Molding cavity thickness: 2.0 mm Skin resin (modified PP) amount: 60 c.c. Inner core material (6-nylon resin) amount: 20 c.c. Method; Molding cavity thickness: 2.0 mm, skin The resin, modified polypropylene, was injected, and 1 second later, the inner core material, 6-nylon resin, was injected, the cooling time was set to 17 seconds, and after cooling, the mold was opened and the molded product was taken out. (FIGS. 8 and 9) Next, Table 1 shows the results of the layer shapes and interlayer adhesion strengths of Example 1 and Comparative Examples 1 and 2.

[Table] As described above, in the method of Comparative Example 2, it is difficult to mold the inner core material (6-nylon resin) thinly, and in order to uniformly inject the inner core material with this method, it is difficult to mold the inner core material (6-nylon resin) thinly.
Requires more expensive 6-nylon resin. In addition, even with the method of Comparative Example 1, the mold cavity L/t corresponding to the first and second injection resins becomes large, causing the problem that the resin flows only around the gate, and the resin temperature at the edges increases. Because of this decrease, the adhesive strength between each layer at the edge was significantly reduced, and the T-peel was as small as 0 to 50 g/15 mm. Furthermore, in the method of Comparative Example 1, unmodified PP
In order to use it, it is impossible to use it without making the wall thicker and increasing the number of steps, and the number of stepwise operations (processes) of opening and closing the mold increases, which increases the problem of material cost and machine equipment cost. For example, in a container-shaped mold as shown in FIG. 10, it is practically difficult to change the cavity capacity in two or more stages. Therefore, in the method of the present invention as in Example 1, the first injection resin and the second injection resin are uniformly injected to every corner, making it easy to form multiple layers. 2 The adhesive strength with the injection resin is T
The adhesive strength between the first injection resin and the third injection resin is 3000g/15mm.
With this, it did not peel off easily. Therefore, according to the method according to the present invention, injection molding of the shape shown in FIG. 11 was carried out using the mold shown in FIG. No visible defects were observed, and a stable molded product was obtained. In addition, the present invention has advantages in terms of cost, as it is possible to use inexpensive general-purpose resins or foamed resins as the third injection resin, and it also has advantages in terms of cost, and it does not require the use of easily flammable inorganic materials. It is also possible to use vine high filler resin, etc., and multi-layer injection molding is possible in a wide range from thin to thick walls, and the second injection resin is a resin with gas barrier properties, such as nylon resin, vinylidene chloride resin, etc. ethylene-
By using saponified vinyl acetate copolymer, gas-barrier containers can also be formed. Furthermore, good multilayer injection molding is now possible even for injection molded products whose shapes cannot be stably and well molded due to the uneven layer thickness in the conventional method as shown in Figure 10.
The multilayer injection molded product obtained by the manufacturing method of the present invention can be molded to uniformly guide the inner core material, has strong adhesive strength between each resin layer, is inexpensive, lightweight, and can be easily burnt. This is a method for manufacturing a transfer molded product.

[Brief explanation of the drawing]

Figures 1 to 4 are simplified process diagrams showing an embodiment of the molding method of the present invention, and Figures 5 to 7 and 8 to
FIG. 9 is a simplified process diagram showing a conventional molding method, and FIGS. 10 and 11 show examples of other molds and a multilayer injection molded product. 1...Mold cavity, 2...Injection machine side mold, 3...
Opening/closing cylinder side mold, 4...first resin, 5...second
Resin, 6...Third resin.

Claims (1)

[Claims] 1 Regarding the multilayer molding method that includes a resin with poor compatibility in the molding cavity, first, the capacity of the primary molding cavity is set to 5 to 90% of the final cavity capacity,
A first resin and a second resin that is poorly compatible with the first resin are injected sequentially or simultaneously, and after molding a multilayer molded product in which the first resin wraps the second resin, it is placed in a mold with the capacity of the final cavity. A multilayer injection molding method in which a third resin having good adhesiveness and compatibility with the first resin is injected.