JPH03106623A - Multi-layer forming process for thermoplastic resin - Google Patents

Abstract

PURPOSE:To prevent unevenness or the like from generating on a boundary of surface between both resins by setting the melt viscosity of thermoplastic resin injected in the following stage in a mold 1/2 or less of the melt viscosity of thermoplastic resin injected in the foregoing stage. CONSTITUTION:When different kinds of thermplastic resins are injected into a mold successively to manufacture a multi-layer molded product, the melt viscosity of thermoplastic resin 4 injected in the following stage is made 1/2 or less of the viscosity of thermoplastic resin 3 injected in the foregoing stage, and the resin temperature and injection pressure at the time of injecting the resin in the following stage can be lower and smaller compared with those in the foregoing stage. The resin already injected, therefore, is not melted by the injection temperature of the following stage nor follows the flow of resin in the following stage. As a result, unevenness or the like is not generated on a boundary face between both resins. When the crystallization degree of resin injected in the foregoing stage is made larger than that of resin injected in the following stage, and the resin in the foregoing stage is cooled down to a substantial extent at the time of injecting the thermoplastic resin in the following stage, and the resin in the foregoing stage forms the state of considerably advanced crystallization. The thermoplastic resin in the foregoing stage, therefore, will not melt to reduce the generation of unevenness or the like on the boundary face between both resins.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention has an object to prevent unevenness from occurring at the interface between the resins when stacking different types of thermoplastic resins in multiple layers using an injection molding method. This invention relates to a multilayer molding method of thermoplastic resin that enables beautiful laminated state.

(Prior Art) Automotive conditioner lamps are manufactured by a two-color injection molding method using acrylic resin.

In this method, transparent acrylic resin at a predetermined temperature is first injected into a mold that is maintained at a predetermined temperature at a predetermined injection pressure, and the injected acrylic resin molded product is molded before it has completely cooled. A part of the mold is replaced and acrylic resin colored, for example, red is injected into it. In this way, a two-color molded product is obtained, in which one part is transparent and the other part is red.

(Problem to be Solved by the Invention) However, in the case of the two-color molding described above, the thermoplastic resin that is first cast into the mold is heated to the next high pressure and high temperature before it is completely cooled and solidified. When another thermoplastic resin is injected into the mold, a portion of it melts when it comes into contact with it, and it flows through the mold following the flow of the thermoplastic resin that was cast later. .

Therefore, unevenness in color and the like occurs at the interface between the first-stage thermoplastic resin and the second-stage thermoplastic resin, resulting in poor appearance.

For this reason, in the past, as shown in Fig. 4, for example, it was only possible to manufacture a molded product in which parts 1 and 2 of each independent hue were slightly laminated at each other's ends. could not.

The present invention solves the above-mentioned problems. For example, even if thermoplastic resins have different hues, they can be sufficiently overlapped without causing unevenness at the interface, and as a result, an excellent design can be obtained. The purpose of this invention is to provide an effective multilayer molding method for thermoplastic resin.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a method for manufacturing a multilayer molded article by sequentially injecting different types of thermoplastic resins into a mold. A multilayer molding method for thermoplastic resin is provided, characterized in that the melt viscosity of the thermoplastic resin to be injected is 1/2 or less of the melt viscosity of the thermoplastic resin injected in the previous step, A method for manufacturing a multilayer molded body by sequentially injecting plastic resin into a mold, characterized in that the crystallinity of the thermoplastic resin injected in the first stage is greater than the crystallinity of the thermoplastic resin injected in the second stage. A method for forming a multilayer thermoplastic resin is provided.

(Function) First, in the first method, the thermoplastic resin that is cast in the latter stage has a melt viscosity that is 1/2 or less than that of the thermoplastic resin that has already been cast in the former stage. Therefore, the resin temperature and injection pressure during the subsequent casting of the thermoplastic resin need only be lower and lower pressure than in the conventional case.

Therefore, there is no possibility that the thermoplastic resin that has already been cast will melt due to the temperature in the subsequent casting process, or that it will not follow the flow of the subsequent thermoplastic resin. As a result, no unevenness occurs on the interface between the two resins, and the surface of the thermoplastic resin cast in the previous stage is not damaged.

If the melt viscosity of the thermoplastic resin to be cast later does not satisfy the above-mentioned conditions, the above-mentioned effects will not be obtained and unevenness will occur at the boundary surface, which is disadvantageous.

The thermoplastic resin used in the latter casting may be the same type of resin as the resin used in the previous stage, but with a lower molecular weight, or a different type of thermoplastic resin with a lower melt viscosity.

In addition, in other methods, the crystallinity of the thermoplastic resin that has already been cast is higher than that of the thermoplastic resin used in the subsequent casting process, so when casting the thermoplastic resin in the subsequent process, Due to considerable cooling, crystallization is advanced. Therefore, in such a state, even if the later thermoplastic resin is cast, the earlier thermoplastic resin, which has already been crystallized, is unlikely to melt, and the interface between the two resins will not melt. The occurrence of unevenness, etc. will be reduced.

Therefore, in either method, it is possible to produce a multilayer molded product that has a beautiful laminated state with no unevenness on the boundary surface.

(Example) The present invention will be described below with reference to the accompanying drawings. First, the lth
As shown in the figure, a transparent acrylic resin is cast into a predetermined mold (not shown) to form a transparent acrylic plate 3 with a missing peripheral edge on one side. Next, the mold was changed, and an acrylic resin 4 colored red, which had a molecular weight smaller than that of the acrylic resin described above and a melt viscosity of about 2/5, was cast into the mold. Transparent acrylic plate 3
integrated into the periphery of the

In the obtained multilayer molded product, no color unevenness was observed at the interface between the transparent acrylic plate 3 and the subsequent acrylic resin 4,
It was confirmed that the two were beautifully layered. Moreover,
When the transparent acrylic plate 3 was observed from the outside, the red color of the acrylic resin had a very deep feeling, and the overall design effect was good.

In FIG. 2, a transparent acrylic resin having a melt viscosity of 2/5 of the melt viscosity of the acrylic resin 4 is further cast and integrated on the back surface of the multilayer molded product shown in FIG. In this case as well, no color unevenness was observed at each boundary surface, and a deep red color was visible.

Figure 3 shows three samples manufactured using each of the acrylic resins described above.
FIG. 2 is a cross-sectional view of a laminate of layers. In this case as well, no color unevenness was observed between the layers.

(Effects of the Invention) As is clear from the above explanation, the thermoplastic resin multilayer molding method of the present invention is a method for manufacturing a multilayer molded body by sequentially injecting different types of thermoplastic resins into a mold. , a thermoplastic resin multilayer molding method characterized in that the melt viscosity of the thermoplastic resin injected in the latter stage is 1/2 or less of the melt viscosity of the thermoplastic resin injected in the former stage, and In a method of manufacturing a multilayer molded body by sequentially injecting different types of thermoplastic resins into a mold, the crystallinity of the thermoplastic resin injected in the first stage is higher than the crystallinity of the thermoplastic resin injected in the latter stage. In either case, when casting the thermoplastic resin in the later stage, the thermoplastic resin in the earlier stage that has already been cast will not melt and fluidize, and the gap between the two resins will be reduced. There is no color unevenness at the interface, and a beautiful layered state is achieved.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing one example of a multilayer molded product produced by the method of the present invention, Fig. 2 is a sectional view of another example, Fig. 3 is a sectional view of still another example, and Fig. 4 is a sectional view of a multilayer molded product formed by the conventional method. It is a sectional view showing one example of the product. 3...Transparent acrylic resin plate (previous thermoplastic resin),
4...Colored acrylic resin (second stage thermoplastic resin), 5
...Transparent acrylic resin.

Claims (2)

[Claims] (1) In a method of manufacturing a multilayer molded body by sequentially injecting different types of thermoplastic resins into a mold, the melt viscosity of the thermoplastic resin injected in the later stage is equal to the melt viscosity of the thermoplastic resin injected in the earlier stage. A multilayer molding method for thermoplastic resin, characterized in that the molding temperature is 1/2 or less. (2) In a method of manufacturing a multilayer molded body by sequentially injecting different types of thermoplastic resins into a mold, the crystallinity of the thermoplastic resin injected in the first stage is the same as the crystallization of the thermoplastic resin injected in the latter stage. A multilayer molding method for thermoplastic resin that is characterized by being larger than 100%.