JPS6139174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection molding method and apparatus for a multilayer molded article made of synthetic resin, and more particularly to a method and apparatus for injection molding a multilayer molded article having an extremely thin and uniform layer inside the multilayer molded article. be.

The multilayer molded product produced by the method of the present invention consists of a surface layer and an inner core layer obtained by simultaneous injection molding of two types of synthetic resins, and has a uniform inner core layer that is less than 1/2 the thickness of the molded product. It is characterized by

The product was obtained by injection molding two types of synthetic resins at the same time, which is a so-called multi-stage molding method in which only the inner core layer is first injection molded, then transferred to another slightly larger mold and further injection molded to form the surface area. However, as will be explained in detail later, it means that it is obtained by one injection molding, which is the most common method, and of course it does not apply when two types of synthetic resin are injected at the same time. This also includes the case where only one resin is injected at first, and then other resins are injected before this resin cools and prevents the inflow of resin.

Furthermore, in the multilayer molded product produced by the method of the present invention, the thickness of the solidified layer (hereinafter sometimes simply referred to as the solidified layer) formed at the portion in contact with the mold wall surface forming the mold cavity is reduced from the thickness of the molded product. The multilayer molded article is characterized by having a uniform inner core layer that is thinner than 1/2 of the thickness of the molded article.

Multilayer molded products with two or more different synthetic resin layers have requirements such as rigidity and toughness, or strength and chemical resistance that are difficult to meet with a single synthetic resin, or are extremely expensive even if they can be achieved. Even when multiple properties are required, such as requiring a synthetic resin, the required properties can be met by using a combination of two or more inexpensive resins that can satisfy at least one property. For this reason, it is widely used in general containers, but it is most commonly used in food containers and other containers that require durability.

In general, many of the flexible resins lose their flexibility due to moisture absorption, so it is recommended to create a structure in which the inner core layer made of the flexible resin is covered with a surface layer made of another resin. is preferred.

Also, since hardening resins are generally expensive, the thinner the better as long as the hardness is not compromised. It is economically advantageous if the reduced thickness is less than 1/2.

There are many known methods for obtaining such multilayer molded products, such as injection molding, extrusion molding, or a combination of these with blow molding, thermoforming, etc.; The combination has good mold reproducibility, yields highly accurate molded products, there are no areas where the layers are discontinuous or the strength is weakened, such as pinched areas, and there is no wasted area. This method has many advantages, such as the fact that it does not cause

In order to obtain a multilayer molded product by injection molding, two or more types of synthetic resins are injected into a mold cavity from an injection molding machine that has a mechanism for injecting them in a laminar flow. One method is to maintain the flow while filling the mold cavity, and the other is to first inject an appropriate amount of the synthetic resin that will form the surface layer, and then further inject the synthetic resin that will form the inner core layer to fill the mold cavity. There is.

The former method is used when it is preferable that the outer surface layer and the inner surface layer are formed of different resins,
This is a preferred method when the thicknesses of both layers are approximately equal and the viscosities of the resins forming both layers are approximately equal;
Otherwise, when flowing inside the mold cavity, the leading edge of the flow tends to become unstable, and the resin that will become the inner surface layer may appear on a part of the outer surface layer, or vice versa. The resin that will become the outer surface layer may appear on a part of the inner surface layer, making it impossible to obtain a good molded product. Furthermore, in this method, if the inner surface layer and outer surface layer are molded using the same synthetic resin and the inner core layer is molded from another synthetic resin, a nozzle with two or more manifolds, etc. is required, which significantly increases the equipment. It has the disadvantage of being complicated and expensive.

In the latter method, the injection cylinder that supplies the synthetic resin that forms the surface layer and the injection cylinder that supplies the synthetic resin that forms the inner core layer are connected to a nozzle that is structured so that they can be connected alternately by a switching valve. The general method is to use a device that is
First, the injection cylinder and nozzle that supply the synthetic resin that forms the surface layer are connected to inject into the mold cavity.Then, the injection cylinder and nozzle that supply the synthetic resin that forms the inner core layer are connected and the nozzle is connected and the nozzle is injected into the mold cavity. This is a method of injecting into

This method has the advantage that the equipment is relatively simple and can be used even if the viscosity of the synthetic resin differs, but it can only produce molded products with a thick inner core layer that can hardly be changed. figure,
It is unavoidable that both resins mix to some extent in the area after the switching valve, and if the mold cavity has a complicated shape, the synthetic resin that forms the inner core layer may easily break through the surface layer and appear on the surface. It has the following disadvantages.

As a method to solve these drawbacks, the present inventors first injected only an appropriate amount of the first synthetic resin that would become the surface layer, and then injected the first synthetic resin and the second synthetic resin that would become the inner core layer. We have devised a method in which the two synthetic resins are simultaneously injected to form a concentric laminar flow.

According to this method, the synthetic resin forming the surface layer and the synthetic resin forming the inner core layer do not flow alternately through one flow path, but they flow simultaneously in a layered manner, which is undesirable. There is no mixing, and the synthetic resin forming the inner core layer flows while being surrounded by the synthetic resin forming the surface layer, so even if the flow of both layers becomes somewhat unstable, the inner core layer No synthetic resin will appear on the surface.

However, these methods can only be applied to cases where the thickness of the inner core layer occupies about half of the thickness of the molded product. This had the disadvantage that the resin layer was not formed up to the vicinity of the tip of the molded product.

These drawbacks are that when molding containers with shrinkage properties using a resin with shrinkage properties as the second resin, the containers become extremely expensive and the shrinkage properties This was an extremely difficult problem in practical use, as only incomplete containers could be obtained.

The present inventors have arrived at the present invention as a result of repeated studies to overcome these drawbacks.

A first embodiment of the method according to the invention is to produce an injection molded article of synthetic resin having a multilayer structure by first applying a first synthetic resin, then simultaneously applying the first synthetic resin and the second synthetic resin, and In a method of molding by injecting layered and concentrically into a mold cavity, the amount of first synthetic resin injected at the beginning is assumed to be filled with a sufficient amount of resin to fill the mold cavity. Immediately thereafter, the amount of the solidified layer is substantially equal to that formed at the portion in contact with the mold wall surface forming the mold cavity, and then the first synthetic resin and the second synthetic resin are simultaneously injected. At this time, the melt viscosity of the second resin is made smaller than that of the first resin, and the melt viscosity and injection amount of both resins are adjusted so that both resins flow in a layered manner and are filled into the mold cavity. By adjusting the flow edges of both resin layers to maintain a state of translational flow without being covered by each other, a multilayer molded product with a thin and uniform inner core layer is produced by injection molding. We are trying to provide a way to obtain it. In the above, simultaneous injection means
This means that one resin is injected in a concentric circle, with one resin in the center and the other resin surrounding it.

In injection molding, the flow of resin injected into a mold depends on the shape of the mold cavity and is generally complicated, but when viewed in a cross section parallel to the main flow direction, the injected resin is layered. The flow reaches the tip of the flow, after which it spreads out in a fan shape, touches the inner surfaces of the mold on both sides, which are the boundaries, cools and solidifies, forming a solidified layer.The process repeats as the flow continues. It is known that the tip advances until the end of the mold is filled.

The thickness of the solidified layer that cools and solidifies upon contact with the inner surface of the mold varies in a complicated manner depending on the resin temperature, mold temperature, flow rate, etc., but once these conditions are determined, it becomes a substantially constant value.

Therefore, in a molding method in which the first resin is first injected and then the second resin is injected, if the amount of the first resin is exactly equal to the amount that forms the solidified layer, the first resin is injected into the surface layer, A multilayer molded product having the second resin as the inner core layer is obtained.

However, in this case, forming a thick inner core layer of the second resin is our objective. It is not possible to form a thin and uniform second resin layer.

In a first embodiment of the method according to the invention, instead of injecting only the second resin as described above, the first resin and the second resin are simultaneously injected,
At this time, by maintaining the melt viscosity and injection amount of both resins so that the leading ends of the flow of both resins flow in translation without being covered by the other resin, the second resin is placed at the end of the mold. By making the melt viscosity of the second resin smaller than that of the first resin, the thickness of the second resin layer can be reduced. It can be made thin.

A more detailed explanation will be given below with reference to the drawings.

FIG. 1 shows a prior art technique in which a first resin 1 is first injected in an amount equal to forming a solidified layer 2, and then only the second resin 3 is injected, and when the resin is flowing, FIG. As shown in a, the first resin 1 injected first is in front of the second resin 3 injected next. As the injection progresses, the second resin 3
The first resin is pushed forward and cooled on the inner surface of the mold to form a solidified layer 2, and when the mold cavity is completely filled with resin, the first resin is pushed onto the inner surface of the mold, as shown in Figure 1b. The second resin forms a thick inner core layer 6 that reaches near the tip.

FIG. 2 shows that the first resin 1 is first injected in an amount equal to forming the solidified layer 2, and then the first resin 4 and the second resin 3 are simultaneously injected and the flow of the first resin layer is injected. This shows a case outside the scope of the present invention in which the tip of the resin is injected so that it precedes the tip of the flow of the second resin layer, and when the resin is flowing, the first resin 4 is injected into the first resin layer as shown in FIG. The resin flows while covering the tip of the second resin 3, and the amount increases as the flow progresses, so when the mold cavity is completely filled with resin, the tip part will be covered with the tip of the second resin 3, as shown in Figure 2b. It is occupied only by one resin 5 and 7, and the second resin layer 6 is not present.

FIG. 3 shows a case corresponding to a first embodiment of the method according to the invention, in which first the first resin 1 is injected in an amount equal to forming the solidified layer 2, and then the first resin 4 and At the same time, the first resin 4 and the second resin 3 are layered between the solidified layer 2 formed by the first resin 1 while flowing translationally without covering each other. Fig. 3a shows a state in which the resin is flowing, and Fig. 3b shows a state in which the resin is completely filled into the mold. In this case, the second resin layer is completely formed up to the vicinity of the tip.

The thickness of the inner core layer formed varies depending on the melt viscosity and flow rate of both resins, but as mentioned above, both are constrained by the conditions for the inner core layer to reach near the tip of the molded product. , cannot take any arbitrary value, and in order to obtain a molded product having a uniform inner core layer thinner than half the thickness of the molded product, which is the objective of the present invention, it is necessary to melt the second resin that forms the inner core layer. The viscosity must be less than the melt viscosity of the first resin forming the surface layer.

In other words, if the melt viscosity of the second resin is equal to or greater than that of the first resin, if both resins are flowed simultaneously in layers at the same flow rate, the resin layer with the higher viscosity will push the resin layer with the lower viscosity. Since the pressure acts on the second resin layer, the thickness of the second resin layer becomes equal to or greater than the thickness of the first resin layer, making it impossible to obtain a molded product with the desired thickness.

In order to avoid this, if the flow rate of the second resin is relatively reduced, the first resin will cover the second resin, and the desired molded product will not be obtained.

On the other hand, if the melt viscosity of the second resin is lower than that of the first resin, the pressure acting from the first resin layer toward the second resin layer causes the second resin layer to melt. As the thickness of the resin layer decreases, the linear velocity of the flow at the tip of the second resin layer becomes faster and that of the first resin becomes slower. Since it can be made to flow without being covered with water, the desired molded product can be obtained.

A second embodiment of the method according to the invention provides an injection molded article of synthetic resin having a multilayer structure, in which first the first synthetic resin is simultaneously injected, and then the first synthetic resin and the second synthetic resin are simultaneously injected. In a molding method, the amount of the first synthetic resin that is first injected is changed to the mold wall surface that forms the mold cavity immediately after the first synthetic resin is injected in an amount sufficient to fill the mold cavity. When the first synthetic resin and the second synthetic resin are simultaneously injected, the melt viscosity and injection amount of both resins should be made smaller than the amount of the solidified layer formed in the area in contact with the resin. When the resin flows in a layered manner and is filled into the mold cavity, the leading edge of the second resin layer is covered by the first resin while being held in a thin and uniform state. The present invention aims to provide a method for obtaining a multilayer molded article having an inner core layer by injection molding.

As mentioned earlier, the solidification that forms at the part of the mold in contact with the internal surface immediately after the first injected amount of first resin is filled with enough resin to fill the mold cavity. If the amount of the layer is substantially equal, the next injected resin will form the inner core layer.

If a large amount of the first resin is injected at the beginning, when the mold cavity is completely filled, some of this first resin will occupy the tip, so the amount of the first resin injected later will The second resin layer cannot reach near the tip.

On the other hand, if the amount of first resin injected is small, all of this resin will become a solidified layer before the mold cavity is completely filled, and from then on, the amount of resin injected later will be reduced. Since a portion of the resin will form a solidified layer, there is a risk that the second resin will be exposed on the inner surface. However, at this time, the melt viscosity and injection amount of the first resin and the second resin, which will be injected simultaneously later, are adjusted such that the tip of the flow of the second resin layer is covered by the first resin. If you hold it like this, the first resin injected later will form a solidified layer even after all the first resin injected at the beginning turns into a solidified layer, so inject an appropriate amount of the first resin at the beginning. As in the case, a situation is obtained in which the second resin forms part of the inner core layer.

At this time, the amount of first resin to be injected first,
Before the mold cavity is completely filled due to the difference in melt viscosity and injection amount between the first resin and the second resin, which are injected later, the second resin layer flows before the tip of the flow. The inside of the mold cavity is completely filled if the sum of the amount of the first resin accumulated in the covered state is substantially equal to the amount necessary to form a solidified layer. In some cases, the second resin layer can be made to reach near the tip.

This will be explained in more detail below with reference to the drawings.

FIG. 4 shows a case outside the scope of the present invention in which the amount of the first resin 1 initially injected is greater than the amount that forms the solidified layer 2. FIG. 4a shows the flowing state, and FIG. 4b indicates that the mold is completely filled. As shown in FIG. 4b, since the first resin injected first occupies the tip, the second resin layer cannot reach the vicinity of the tip.

Fig. 5 shows a case where the amount of the first resin injected at the beginning is outside the scope of the present invention and is smaller than the amount to form a solidified layer. Fig. 5 a shows the state in flow, and Fig. 5 b shows the mold. Shows that the inside is completely filled. As shown in Figure 5b, after all of the first resin injected at the beginning becomes a solidified layer, both the first and second resins injected later form the outer and inner solidified layers, respectively. The second resin, which should become the inner core layer,
exposed on the surface.

FIG. 6 corresponds to a second embodiment of the method according to the present invention, in which even after all the first resin injected first becomes a solidified layer, the first resin injected later is transferred to the second embodiment. This forms a solidified layer, and if the amount satisfies the conditions mentioned above, a second resin layer will be formed up to the vicinity of the tip, as shown in Figure 6b. .

The thickness of the inner core layer that is formed varies depending on the melt viscosity and flow rate of both resins, but as mentioned above, the inner core layer reaches near the tip of the molded product and is exposed to the surface. Since it is constrained by the condition that there is no value, it is not possible to obtain an arbitrary value.

In a second embodiment of the method according to the invention, the first resin must flow over the tip of the second resin, and the thickness of the second resin layer is equal to that of the first resin layer. The flow rate of the first resin is greater than the second resin since it must be less than the thickness. Therefore, unlike the first embodiment of the method according to the invention, the desired molded article can be obtained in the following special cases even if the melt viscosity is not lower than that of the second resin.

First, when the melt viscosity of the second resin and the melt viscosity of the first resin are equal, the amount of the first resin retained at the tip of the flow is determined by the difference in flow rate between the first resin and the second resin. If the amount is equal to that required to form a solidified layer, the desired molded product can be obtained.

Next, when the melt viscosity of the second resin is higher than that of the first resin, the pressure acting in a direction such that the second resin layer pushes the first resin layer when the flow rates of both resins are equal is applied to the first resin layer. This can be canceled by the opposite force generated by increasing the flow rate of the resin, and the first resin stays at the tip of the flow due to the difference in flow rate between the first resin and the second resin. If the amount is made equal to the amount required to form a solidified layer, the desired molded product can be obtained.

In these cases, the thickness of the inner core layer of the resulting molded product is approximately half the thickness of the molded product.

On the other hand, if the melt viscosity of the second resin is lower than that of the first resin, even if the flow rate of the second resin is considerably lower than that of the first resin, the difference in viscosity and flow rate will cause , the thickness of the second resin layer decreases due to the pressure that pushes the second resin layer from the first resin layer, so the linear velocity of the flow at the tip of the second resin layer increases, and the On the contrary, since the linear velocity of the flow at the tip of the first resin layer becomes slow, the tip of the second resin layer is not covered excessively by the first resin layer.
As a result, the second resin layer reaches the vicinity of the tip of the molded product thinly and uniformly, so that the desired molded product can be obtained.

As described above, in the second embodiment of the method according to the present invention, even if the melt viscosity of the second resin is not smaller than that of the first resin as in the first embodiment of the method according to the present invention, the objective Particularly favorable results are obtained when molded articles are obtained, but are small.

As a special case of the relationship between the amount required to form a solidified layer and the amount of the first resin accumulated before and over the tip of the second resin layer, If the amount of resin is less than the amount that forms the solidified layer on both surfaces but more than the amount that forms the solidified layer on one side, as shown in Figure 7, solidification during filling on the second resin layer side will occur. It may happen that a part of the layer is formed of the second resin, but this case is of course included in the present invention.

In the present invention, the amount of the first resin that is initially injected is not so small that the second resin appears on the surface at the initial stage of injection, and when the inside of the mold cavity is completely filled, the amount of the second resin increases. It can be arbitrarily selected within a range that is not so large as to prevent reaching near the tip.

In the present invention, the thickness of the inner core layer can be changed to some extent by changing the injection ratio of the first resin and the second resin that are simultaneously injected within the scope of the present invention, but even in one molded product, By changing the injection ratio of the two types of resin over time, the thickness of the inner core layer can be changed. This means that if you want to add special toughness to a part of the container,
Alternatively, it can be effectively used in injection blow molding in which the preliminary hollow body molded by the method of the present invention is further blow molded, and when it is desired to maintain the flexibility of the portion of the molded product where the blow ratio is high.

As the first resin and second resin used in the present invention, any thermoplastic resin that is normally commercially available can be used, but as the second resin, vinyl chloride-vinylidene chloride copolymer can be used. ,
It is particularly preferable to use resins with excellent tenacity, such as saponified ethylene-vinyl acetate copolymers, nylon, and acrylonitrile-styrene copolymers with a high acrylonitrile content.

As is clear from what has been detailed above, only by means of the first and second embodiments of the method according to the invention, first a first synthetic resin and then a first synthetic resin and a second synthetic resin can be mixed together. In the method of injection molding by simultaneously injecting the resin and the resin, it is possible to obtain a multilayer molded product having a thin and uniform inner core layer, which is the objective of the present inventors. The present invention
This differs from similar known methods for molding multilayer molded articles having a thick inner core layer that occupies more than half of the thickness of the molded article or a thick inner core layer with a smooth surface and a foamed surface.

The present invention is based on the principle of molding so that the inner core layer reaches near the tip of the molded product. Of course, it is also possible to mold a container or the like having an inner core layer only in the thin body of the container by the method of the present invention.

Furthermore, the present invention first obtains a molded body in the form of a sheet or disk to serve as a base material, and then presses it against a mold by applying an external force such as heating it, pressurizing it with air pressure, vacuum suction, etc. to form a container-shaped molded body. It can also be used as a base material for thermoforming.

The device of the present invention is an injection cylinder having a movable mandrel with an extension tube attached to the tip between the extension nozzle installed at the tip of the injection cylinder and the injection unevenness, and a flow path provided in the center. In an injection molding device with a movable mandrel, the extension nozzle is provided with a separate flow path that allows the flow rate to be adjusted so that the desired amount of synthetic resin accumulated between the extension nozzle and the movable mandrel can be diverted. The present invention relates to an apparatus for carrying out the methods of the first and second embodiments of the present invention, characterized in that:

As an apparatus capable of carrying out the method of the present invention, the first
As shown in Figure 0, two injection cylinders are connected to a nozzle that can separate the surface layer and the inner core layer and inject them simultaneously, and the injection order and amount are controlled by the injection cylinder drive hydraulic pressure having an automatic control mechanism. An injection molding device that can be adjusted by a device or the like, or an extension nozzle attached to the tip of one injection cylinder as shown in FIG. 11, between this and the injection ram,
There is an injection molding device having an injection cylinder having a movable mandrel with an extension tube attached to the tip and a flow path provided in the center. In either case, the melt viscosity of the resin is adjusted by varying the temperature of the injection cylinder, plasticizing cylinder, nozzle, etc.

However, in the former case, the equipment is extremely complicated and expensive, and in the latter case, although the equipment is relatively simple and inexpensive, the relationship between the injection amount depends on the length of the extension tube and the gap between the extension tube and the extension nozzle. Since the injection amount depends on the size, it is not easy to change the injection amount once determined according to the required thickness of the inner core layer to obtain a different thickness.

In the latter device, the present invention provides a separate channel in the extension nozzle that can adjust the flow rate so that a desired amount of synthetic resin accumulated between the extension nozzle and the movable mandrel can be diverted. This made it possible to carry out the method of the present invention.

Hereinafter, the apparatus of the present invention will be explained with reference to the drawings.

FIG. 12 shows a cross-sectional view of the apparatus of the present invention. First, the second resin 11 forming the inner core layer is accumulated in front of the injection ram 10 which also serves as a plasticizing screw, and Plasticizing cylinder 1
2 accumulates a first resin 14 forming a surface layer in front of the movable mandrel 13. At this time, the "first injection amount of the first resin" in the method of the present invention is between the front end of the extension tube 15 and the extension nozzle 1.
It is determined by the distance from the rear end of the corresponding part of 6. In other words, when the extension tube 15 is separated from the corresponding part of the extension nozzle 16, the flow resistance in this part is small, so even if the injection ram 10 moves forward, only the accumulated first resin 14 is injected. It will be done. Next, when the movable mandrel 13 moves forward and the front end of the extension tube 15 reaches the rear end of the corresponding part of the extension nozzle 16, the flow resistance in this part becomes extremely large because the gap between them is small.
The resin flows out through a flow path 18 having a flow control valve 17. At this time, the flow rate control valve 17
Therefore, if the flow resistance of the flow path is made comparable to that of the center flow path of the movable mandrel, the resin 11 accumulated in front of the injection ram will be simultaneously injected through the center flow path of the movable mandrel 13. Become so.

This state corresponds to "then injecting the first resin and the second resin simultaneously" in the method of the present invention, and by adjusting the flow rate control valve together with the melt viscosity of the resin, that is, the temperature, the desired thickness can be achieved. It is possible to obtain a molded article having an inner core layer of .

Example 1 Using the apparatus shown in Figure 12, 30% by weight of acrylonitrile and 70% by weight of styrene were used as the first resin.
A copolymer resin consisting of 75% by weight of acrylonitrile and 25% by weight of styrene as a second resin.
Using a copolymer resin with excellent stiffness consisting of
A cylindrical molded product with a length of 20 cm, a length of 4 mm, and a thickness of 4 mm was molded.

At this time, the first resin is colored red and the second resin is colored white in advance, and first the red resin surrounds the white resin in concentric circles. The flow control valve of the device was adjusted so that both resins were injected simultaneously to the end.

Both the inner and outer surfaces of the obtained molded product were covered with red resin 8, and when the cross section was viewed by cutting in the axial direction of the cylinder, as shown in Figure 8, white resin 9 reached near the tip. Inner core layer (white resin layer)
A uniform layer of approximately 0.6 mm and a solidified layer (red resin between the inner surface and the inner core layer) of approximately 0.8 mm was formed.

At this time, the melt viscosity of the first resin is approximately 3×
10 ³ poise, and the second resin was about 3×10 ² poise.

Example 2 The flow control valve of the device was adjusted so that initially about 39 c.c. of the first resin was injected, and then both resins were injected simultaneously to the end with the first resin concentrically surrounding the second resin. A molded article of the same shape was molded using the same equipment, resin, and molding conditions as in Example 1, except that the following adjustments were made.

As in Example 1, the obtained molded product was covered with the first resin on both the inside and outside, and had a uniform thin inner core layer that reached near the tip.

Comparative Example 1 A molded article of the same shape was molded using the same equipment, resin, and molding conditions as in Example 1, except that the resin temperatures of the first resin and the second resin were 260° C. and 180° C., respectively.

Both the inner and outer surfaces of the obtained molded product were covered with the first resin, but when looking at the cross section, as shown in Figure 9, the second resin layer 9 ended halfway and was thick and uneven. It was the inner core layer.

Comparative Example 2 A molded article of the same shape was molded using the same equipment, resin, and molding conditions as in Example 2, except that the resin temperatures of the first resin and the second resin were 240° C. and 210° C., respectively.

As in Comparative Example 2, the resulting molded product had an inner core layer that ended halfway and was thick and non-uniform.

At this time, the melt viscosity of the first resin is approximately 5×
10 ² poise, and the second resin was about 3×10 ³ poise.

[Brief explanation of the drawing]

1, 2, 4, and 5 are explanatory diagrams showing injection states of resins outside the scope of the present invention, and Figures 3 and 6 are explanatory diagrams showing injection states of resins within the scope of the present invention.
In each figure, a shows a flowing state, and b shows a state in which the mold cavity is completely filled. FIG. 7 is an explanatory view showing another example of the resin injection state within the scope of the present invention, FIG. 8 is a cross-sectional view of the molded product obtained in Example 1, and FIG. 9 is a cross-sectional view of the molded product obtained in Comparative Example 1. FIG. 10 and 11 are cross-sectional views showing examples of conventional injection molding apparatuses, and FIG. 12 is a cross-sectional view of the main parts of the injection molding apparatus of the present invention. In the figure, 1 is the first resin that was first injected, 2 is the first resin that has become a solidified layer, 3 is the second resin that was then simultaneously injected, and 4 is the first resin that was then simultaneously injected. , 5 is a surface layer (solidified layer) formed by the first resin injected first, 6 and 9
7 is an inner core layer formed by the second resin, 7 is an inner core layer formed by the first resin that was injected at the same time, 8 is a surface layer formed by the first resin, and 10 is an inner core layer formed by the first resin. Injection ram, 11 is a resin that becomes the accumulated inner core layer, 12 is a plasticizing cylinder, 13 is a movable mandrel, 14 is a resin that is an accumulated surface layer, 15 is an extension tube, 16 is an extension nozzle, 17 is a flow rate adjustment Valve 18 is a branch flow path.

Claims (1)

[Claims] 1. First, the melt of the first synthetic resin is poured into the mold cavity, and then the melt of the first synthetic resin and the melt of the second synthetic resin are simultaneously layered and concentrically formed into the mold cavity. In a method of molding a synthetic resin injection molded article having a multilayer structure by injection, the following steps are taken: (a) the amount of the first synthetic resin to be initially injected and the amount of resin sufficient to fill the mold cavity; Immediately after the first synthetic resin is filled, the amount of the solidified layer formed at the portion in contact with the mold wall surface forming the mold cavity is made substantially equal; (b) Next, the first synthetic resin and the second synthetic resin are When simultaneously injecting a synthetic resin, the melt viscosity of the second synthetic resin is made smaller than that of the first resin, and the melt viscosity and injection amount of both resins are controlled so that both resins flow in layers and mold. A method for injection molding a multilayer molded product, characterized by: holding the leading ends of both resin layers so that they flow in translation without being covered by each other as they are filled into a cavity. 2 A synthetic resin injection molded product with a multilayer structure,
By first injecting a first synthetic resin melt, then a first synthetic resin melt and a second synthetic resin melt simultaneously, layered, and circularly into the mold cavity. (a) Immediately after the first synthetic resin is injected in a sufficient amount to fill the mold cavity, the mold wall surface forming the mold cavity is (b) Then, when simultaneously injecting the first synthetic resin and the second synthetic resin, the melt viscosity and injection amount of both resins are When both resins flow in a layered manner and are filled into the mold cavity, the leading end of the flow of the second resin layer is held so as to be covered by the first resin while flowing. Injection molding method for multilayer molded products. 3. An injection molding device having an injection cylinder having a movable mandrel with an extension tube attached to the tip and a flow path provided in the center between the extension nozzle attached to the tip of the injection cylinder and the injection ram. is characterized in that the extension nozzle is provided with a separate flow path whose flow rate can be adjusted so that a desired amount of the synthetic resin accumulated between the extension nozzle and the movable mandrel can be diverted. Equipment for forming multilayer molded products.