DE2264659A1 - Injection moulding core and surrounding skin - in one machine with two ducts feeding sprue while maintaining boundary surface between two materials - Google Patents

Abstract

The patent DT 2103885 describes a method of making injection moulded objects having a closed external skin and a core of a different material, where the skin material is injected in first and third stages and the core material in the second stage, the boundary surface between the two materials during the first and third stages being displaced backwards from the sprue duct in the feed duct for the second or core material by a controlled amt. In the patent of addn. the two feed ducts for the different materials are cut off from each other and from the sprue duct after the third stage. This arrangement enables the posn. of the boundary surface in the feed duct for the second material to be maintained, without flowback of material, after the completion of each injection cycle and before starting the next one.

Description

Method and device for the production of injection molded articles Addition to patent ... <patent application P 21 03 885.7) The invention relates to a method of making injection molded articles from two different ones Plastic materials, of which a first plastic material is a closed one forms outer skin around a serving as a second plastic material and in which when injecting the plastic materials feed channels with a common Sprue are connected and in a first step of the injection cycle that The first plastic material is injected into a mold cavity, the first being ICoplastic material is located in the feed channel for the second plastic material and in a second step the second plastic material into the mold cavity is injected, whereby a penetration of the second äunst @ @effmaserials in the Feed channel for the first plastic material is prevented, and in one In the third step, the first plastic material is injected again. - The invention also relates to an injection molding apparatus for performing this method with two injection units each controllable via a hydraulic cylinder for the first and the second plastic material (according to Ilauptpatcnt ... (patent application P 21 03 885.

The 1! Creation of injection molded objects from one of an Ilaut enclosed core is carried out in such a way that the first step is the first injecting plastic material and then using this in the second step of the second plastic material, so to speak, inflates like a balloon and thereby increases presses the mold walls. The second plastic material forming the core is in usually have different properties than the first plastic material, so that for Achieve an undisturbed uniformity of any contamination of the first Plastic material must be prevented. To achieve this, in the case of the In the third step, ilauptpatents injected the first plastic material again and in the third step and in the first step the interface between the two Plastic materials in the feed channel for the second plastic material in the direction moved away from the runner controlled. By injecting the first one again Plastic material in the third step will be in the starting position for the plant the injection cycle is returned and at the same time the runner from the second Plastic material besüubeirt and the skin surrounding the core of the injection molded article at the point of the sprue cone practically closed.

It has also been shown that the controlled moving of the Interface between the two plastic materials, the contamination of the first Plastic material can be effectively prevented by the second plastic material can.

After the two plastic materials have been injected, the Injection units again with plastic materials in preparation for the next Injection cycle.

Because the two feed channels when injecting with the sprue are connected and at the end of the injection cycle, the first plastic material is already in the feed channel for the second plastic material in readiness for the next one Cycle, it is difficult to reload the two injection units to the effect of the interface between the two plastic materials during loading hold in the desired place. This means that the pressures on the plastic materials must be carefully monitored during the loading process; however, this is a limitation unnecessarily enter the working conditions for reloading. - Furthermore the injection-molded article must solidify after the injection of the two materials and it must be removed from the mold cavity. For this to be possible, it is necessary, the flow of further material from the supply channels into the mold cavity to prevent when removing the injection molded article. Although these problems could be solved cope by solidifying the material in the feed channels leaves, but it introduces unnecessary delays in the injection cycle.

The object of the invention is to take measures for the transition from one injection cycle to the next compliance with the interface between the Ensure plastic materials in the feed channel for the second plastic material and the reflow of plastic material after removal of the injection molded article impede.

With regard to the method, this object is achieved in that one blocks the feed channels from each other and from the runner. This can be done through this achieve that one uses shut-off valves located in the supply channels; however, a single valve is preferred, which is located at the meeting point of the supply channels and the runner is located and has two positions, one in which the two feed channels are connected to the runner and a second one Position in which the feed channels are separated from the runner and from each other are.

The use of such valves allows the injection units separate from each other so that they can again be independently of each other without disturbing the Location of the interface between the plastic materials can be charged.

This also ensures that the injection molded article from the Form in a short time regardless of the operating conditions in the injection units can be taken.

The use of such a valve or such valves brings furthermore the advantage that the injection units are under pressure before the injection cycle can be set so that when opening the valves to establish a connection between the supply channels and the runner, the injection with full available Printing can be started.

The invention is described below with reference to schematic drawings explained in more detail using an exemplary embodiment.

Fig. 1 is a schematic representation of the plant with the associated Hydraulic system, the arrangement for the moment of the start of the injection cycle is shown; FIG. 2 is a diagram corresponding to FIG. 1 showing the system shows when the skin material is injected; FIG. 3 is a corresponding to FIGS. 1 and 2 Diagram showing the system at the start of injection of the raw material; Fig. Figure 4 is a view corresponding to Figures 1 through 3 showing the system being injected of the core material after stopping the llaut material injection; Fi <j. 5 is a diagram corresponding to FIGS. 1 through 4 showing the system on Wound of the injection of the hernial material and in a state to be cut one shows further amount of ilaut material; Figure a is a figure corresponding to Figures 1 to 5 Representation that the system is injecting the further amount of llaut material shows; Fig. 7 is a diagram corresponding to Figs. 1 through 6 showing the system after injecting the further amount of IIautmatcrial and during the cooling cycle shows in which the E. injection cylinders are refilled.

In this embodiment, the core material injection plunger While injecting the IIautmatcrial, move backwards while the skin material injection plunger is prevented from moving backward when injecting the core material.

The machine has two injection cylinders 10, 20, from which skin material 11 or core material 21 with the aid of screws 12, 22 which can be moved back and forth associated supply channels. le 13, 23 into a valve 1 and from there can be conveyed into a mold cavity 2 via a sprue channel 3. The injection cylinder 10 and 20 with the associated screws have different inner diameters, wherein the injection cylinder 20 is larger in diameter than the injection cylinder 10. Skin or core material is fed to the screws 12 and 22 via conveyor funnels 14 and 24 supplied. The worms can be rotated and rotated with the aid of motors (not shown) be moved forward with the aid of injection pistons 15, 25. The injection pistons 15, 25 are driven hydraulically with the aid of pistons 16 or 2G, which are in cylinders 17, 27 act. The pistons 1G, 26 divide the cylinders into two compartments 18, 28 or 19, 29.

With the aid of a pump 4, hydraulic fluid can be extracted from a memory 5 a compartment 18, 28 of the cylinders 17, 27 via valves 110, 210. (llydraulil; fluid can also in an emergency the other compartments 19, 29 of the cylinder 17, 27 are supplied via valves 111, 211). The pump 4 works normally continually; it delivers fluid at a pressure above a certain limit value, this returns to the memory 5 via a relief valve 6. The hydraulic fluid in the compartments 18, 28 of the cylinders 17, 27 can be to the memory 6 via valves 112, 212 and pressure-dependent valves 113, 213 are fed back.

As will be explained later, a second pump 214 and a Associated relief valve 215 can be provided to divert hydraulic fluid to the compartment 28 of the cylinder 27 via a valve 216. According to the following description can this pump and the associated relief valve in addition to the pump 4 or the supply from the pump 4 to the compartment 28 of the cylinder 27 can be omitted via valve 210. In the embodiment now described the pump 214 and valves 215 and 216 are omitted.

In the hydraulic circuit for the skin material injection unit is an accumulator 114 turned on, which has a piston 115, the accumulator divided into two compartments 116, 117. Compartment 116 contains hydraulic fluid and is connected to the compartment 18 of the cylinder 17 via a valve 118. The other Compartment 117 contains gas and is sealed.

At <Ieri injection plunger 15 a collar 119 is provided which against can slag an axially adjustable limit stop 120 that auner contact with your collar 119 can be moved. If the collar 119 hits the limit stop 120, the injection plunger cannot be moved forward.

At the start of the cycle, oil is poured into the compartment at a constant volume rate 18 of the cylinder 17 is pumped in via the valve 120 until the pressure is so high that the relief valve 6 returns excess oil to the memory 5.

The compartment 28 of the cylinder 27 is initially set on a predetermined basis Pressure maintained (it is advisable to bring it to the same pressure as compartment 18 of cylinder 17 by keeping valve 210 open and valve 212 closed, valve 210 is then closed and valve 212 is opened so that the Nuclear material hydraulic system closed except for relief valve 213 which is set so that it is open when the pressure difference between the compartment 13 of the cylinder 17 and the compartment 2 of the cylinder 27 a predetermined This system is shown in FIG.

The check valve 1 is opened, so that the pressure in the melt ain the sprue channel end of the flow material feed channel 13 drops (to atmospheric pressure, when the mold 2 is at atmospheric pressure). With regard to the pressure difference between the sprue channel end of the feed channel 13 and the injection cylinder 10 is Nautmaterial 11 injected.

The injection piston n 15 thus moves and there is more oil in the Compartment 18 pumped in so that the pressure necessary is maintained so that the nautical material 11 flows.

while a pressure drop also occurs in the supply channel 23, it occurs only a little kenu material, since no oil is pumped into the compartment 28 of the cylinder 27, so that the injection plunger 25 is not moved forward. The pressure of the core material 21 in the injection cylinder dei 'Po it falls down on the pressure at the connection of the supply channels 13 and 23. The injection plunger 15 moves at a constant feed rate with the pumping in of the oil at a constant rate. The build-up of pressure in the mold also increases the pressure at the connection of the supply channels 13 and 23. I) r pressure at the connection point thus exceeds the pressure in the core material injection cylinder 20, so that a small Amount 121 of nautical material 11 in the core material feed channel 23 in the direction of the core material injection cylinder 20 flows. This material flow is controlled by allowing return movement of the plunger 25 by drawing oil from the compartment 28 of the cylinder 27 can drain through the valves 212 and 213. The material flow also occurs because the core material melt 221 compresses. The system then has the state according to FIG. 2.

If a predetermined amount of llaut material 11 has been injected, the valve 212 is closed and then the valve 210 is opened, so that now oil is pumped to the two compartments 18 and 28 of cylinders 17 and 27, respectively. The skin material Injection piston 15 is thus delayed while the core material injection piston 25th accelerated. The system is now in the state of FIG. 3. Injection of the core material 21 thus begins while the Ilaut material 11 is still being injected will. The collar 119 of the skin material injection piston 15 then meets the limit stop 120 so that the lens spraying of the skin material 11 is stopped. The valve 110 is then closed and the accumulator valve 118 is opened, so that the skin material hydraulic circuit forms a closed system. The hydraulic fluid in compartment 116 is previously essentially been compressed to the full pressure allowed by the relief valve 6 so that the piston 115 compresses the gas in the compartment 114. I want this gas expand so that full pressure from accumulator 114 on compartment 18 ilcs Cylinder 17 is transmitted. This prevents backward movement of the skin material injection plunger 15, since the pressure in compartment 28 of cylinder 27 does not reach the maximum pressure, which the relief valve 6 allows and because the pressure of the nautical material in the injection cylinder 10 cannot be larger than tier of the core material 21 and because the core material injection cylinder 20 larger diameter than the nautical material injection cylinder r 10, so that the Pressure in compartment 18 of cylinder 17 is always greater than that in compartment 28 of the Cylinder 27 must be. Thus, the core material can only be compressed by the Melt of fluid material in the Nautmsterialzuführkanal 13 flow upwards. That The system is now in the state of FIG. 4.

Unless there is an overlapping injection of skin and core material 11 and 21 is desired, the compartment 18 of the cylinder 17 is inflated to full pressure, as soon as the protrude 119 hits against the limit stop 120, the excess on BydraulikfluiE is pumped via the relief valve 6 to the reservoir 5, (soferii no injection overlap is desired, there is no need for the accumulator valve 118 and for the accumulator 114, since the oil in the compartment 18 of the cylinder 17 acts as its own Ak accumulator) the valves 110 and 212 is closed and then valve 210 is opened to allow injection of the core material is initiated.

(Because the injection cylinder 20 has a larger diameter than the injection cylinder 10 has and there the back pressure in the injection piston 18 for the llautlnaterial 11 for its The return movement cannot exceed the pressure exerted by the injection piston 25 is dispensed onto the core material 21, the valve 110 can alternatively be used in the Core material injection are kept open because the back pressure or back pressure, how it is applied to the fluid in the compartment 18 of the cylinder 17, not the pressure can exceed that prevails in compartment 28 of cylinder 27. On this second is the use of the accumulator 114 and valve 118 during core material injection not required, so that the accumulator can be used instead if necessary can be to the initial pulse in skin material injection to deliver. When the injection of the core material 21 is finished, the valve 110 becomes <each opened and the limit stop 120 withdrawn while the valve 210 is closed and valve 212 is opened. The system is then in the state according to Fig. 5. The compressed gas in compartment 117 of accumulator 114 expands and pushes the piston 115 forward so that oil is supplied to the compartment 18 of the cylinder 17 will. In this way the injection receives a further amount of skin material an initial additional impulse. The skin material injection plunger 15 moves thus forward and inject more nautical material 11 and cause some llaut material 121 flows up the core material supply channel 23 when the injection plunger 25 something by draining oil from compartment 28 of cylinder 27 through valves 212 and 213 is withdrawn.

This state of the system is illustrated in FIG. The full one Injection pressure is generally required in the compartment 18 of the cylinder 17 to the remaining Dlenrje to inject nautical material 11, so that the compartment 116 of the accumulator 114 is loaded to full pressure at the same time. The shut-off valve 1 and the accumulator valve 118 are then closed and the molding is cooled and out of the mold cavity 2 taken.

During cooling, the valve 110 is closed and the valve 112 is opened Un <t the injection pistons 15 and 25 by screwing back the screws 12 and 22 withdrawn to the injecting cylinder 10 and 20 with Ilaut and refilling core materials from feed hoppers 12 and 24, respectively. The system is then in the state according to FIG. 7 while the screws are being screwed back. If the injection cylinders 10 and 20 are filled, i.e. the pistons 16 and 26 are withdrawn, the valves 112 and 212 are closed, the valves 110 and 210 are opened to pressurize the system for the next injection cycle.

(Valves 111 and 211 are normally open to accumulator 5 and only need to be operated in an emergency to the injection plunger 15 and 25, if this would become necessary.) If it is desired, to move the injection plunger 25 at the front host during the core material injection As previously described, a second pump 214 is used to continuously run the compartment 28 of the cylinder 27 to be applied during the injection of the Hauüaaterials. Provided this pump 214 is also used for injecting the core material Feeding of the cylinder 27 from the pump 4 via the valve 210 can be omitted.

Plastic materials that can be used in the invention, are those that can be injected into a mold cavity while it is moving in the state of a viscous Liquid and then can harden in the mold cavity. Thus, thermoplastic resin materials be used, which are injected into the mold in the form of a viscous melt and which can solidify by cooling in the mold cavity. Alternatively you can thermosetting resin materials are used, which in the mold cavity in the form of a viscous melt can be injected and then cross-linked within solidify the mold cavity. In general, thermosetting resin materials are used cross-linked by heating.

Examples of suitable thermoplastics that can be processed by injection molding liarzc are: Polymers and copolymers of @ -olefins such as high and low density Polyethylene, polypropylene, polybutene, poly-4-methylpentene-1, propylene / ethylene copolymers, Copolymers of 4-methylpentene-1 with lingary α-olefins, the 4 to 18 Containing carbon atoms and ethylon / vinyl acetate copolymers; Polymers and Mi copolymers of vinyl chloride, vinyl acetate, vinyl butyral, styrene, substituted Styrenes, such as α-methylstyrene, acrylonitrile, butadiene, methyl methacrylate, vinylidene chloride. Specific examples of such polymers are vinyl chloride homopolymers and interpolymers of vinyl chloride with vinyl acetate, propylene, ethylene, vinylidene chloride, alkyl acrylates such as 2-ethylhexyl acrylate, alkyl fumarates, alkyl vinyl ethers, such as cetyl vinyl ether and N-aryl maleimides such as N-o-chlorophenyl maleimide; Polyvinyl acetate, Polyvinylburyral; Polystyrene, styrene / acrylonitrile copolymers; Polyacrylonitrile; Minch polymers from Butadiene with methyl methacrylate and / or styrene and preferably acrylonitrile; Polymethyl methacrylate; Mixed polymers of methyl methacrylate with small amounts of alkyl acrylate such as methyl acrylate, Ethyl acrylate and butyl acrylate; Mixed polymers of methyl methacrylate, N-aryl maleimides and preferably; tyrene; and vinylidene chloride / acrylonitrile copolymers, melt processable Mixed polymers of tetrafluoroethylene and nexafluoropropylene.

Halogenated Polyncrc or Slischpolymer, e.g. halogenated O (-Oiefinpolymers, such as chlorinated polyethylene or halogenated vinyl chloride polymers such as chlorinated Polyvinyl chloride can be used. Other injection moldable thermoplastics Polymers that can be used include condensation polymers such as those injection processable Fit linear polyesters such as polyethylene terephthalate, polyamides such as polycaprolactam, Polyhexamethylene adipanides and copolyamides such as copolymers of nexamethylene diamine adipate and jiexamethylene diamine isophthalate, especially those compounds which 5 to Contains 15% by weight of nexamethylene diamine isophthalate, polysulfones and copolysulfones, Poly phenylene oxides, polycarbonates, thermoplastic polymers and mixed polymers from formaldchyd, thermoplastic linear polyurethanes and the thermoplastic derivatives of cellulose such as cellulose acetate, cellulose nitrate and Cellulose butyrate and mixed cellulose esters, e.g. 13. Cellulose acetate butyrate.

Where a mixed polymer is used, it depends in a mixed polymer amounts of comonomers used, inter alia, on the desired properties of the molding.

Thermosetting resins include plastic materials that either are subject to cross-linking by themselves or in the presence of an II: irters or a catalyst if heated to a sufficiently high temperature .. Thus, the term includes a material that is normally under the term "thermosetting" falls, as well as plastic material that is normally thermoplastic but is a crosslinking agent, e.g. contains a peroxide that causes crosslinking, when the plastic material is heated to a sufficiently high temperature.

Examples of such heat-treatable Ilarze are phenol aldehyde resins, Amine-formaldehyde resins, npoxv resins, polyester resins, thermosetting polyurethanes and vulcanizable rubber compounds.

The llarzc can be a nutrient or a catalyst contain, where it is necessary for the resin to solidify.

Cross-linkable thermoplastics that can be molded by injection molding Materials include copolymers of methyl methacrylate and glycol dimethacrylate and ethylene / vinyl acetate copolymers containing a crosslinking agent.

Mixtures of plastic materials can be used.

The choice of materials from which the item is to be made, depends on the use to which these articles are put. The inventive Process provides a particularly useful way of producing objects which have a core made of relatively cheap material with a good outer skin. For example, the core can consist of a thermoplastic material that a filler material entlijit, while the outer ile is made of a material, that provides any desired surface finish unit. Unless the procedure used to make parts of automobile bodies becomes a rigid exterior It may be necessary, with filled polypropylene being a particularly good Ilarz is from which the outer Ilaut can be made. But if a flexible molding is desirable e.g. for the interior lining of a motor vehicle, then plasticized vinyl chloride polymer would be extremely useful as the exterior Layer of the Eormling.

The proportions of Ilaut and core materials ik: ifln used by one Variety of issues and it is preferred that for any given material, Form designs and process conditions such as temperatures, pressures a minimum amount of nautical material can be injected prior to the start of the injection of the core material must in order to avoid that the core material breaks through the skin.

This minimum can be determined in a simple manner by means of test moldings will.

The core material can be the same material as the nautical material with the exception of additives in one or the other of the materials are provided or in both in different proportions. Alternatively you can the plastics can be very different and also contain different additives.

In a preferred embodiment, the skin material is unsciiuchable and the core material is foamable. The core material preferably contains a blowing agent, this is done when welding above a certain temperature - hereinafter referred to as the activation temperature designated - gas evolved, i.e. by Volatilization (if the Pressure on the mass is reduced, or by decomposition, whereby the Injection at a temperature above the activation temperature of the blowing agent he follows. It is preferred that the plastic material is adjusted to the foaming temperature, i.e. heated above the activation temperature with the injection into the runner is done by focusing on the dynamic heating as the material passes through leaves the injection nozzle of the injection molding machine.

Will <read core material at normal injection speeds and pressing in injection molding, there is substantially no foaming until the desired amount of core material has been injected. Unless a Foamable core material is used, two alternative modes of operation can be used be applied. For the first, the injected amount of llaut material is sufficient and foamable, but not yet foamed core material around the mold cavity to fill, whereby inan lets the core material foam and at the same time the Enveloping Nautmaterial can be dellnen to the ends of the mold cavity. In the The second mode of operation is the injection amount of Iiautmaterial and foamable, however still unfoamed core material so that the mold cavity is filled before essential Foaming takes place, in which case the mold cavity is enlarged, un foaming to allow.

It is preferable to use the second of these modes of operation because thereby maintaining a more uniform cell structure in the core of the molded object and, moreover, the object receives a better surface finish.

In this preferred embodiment for the preparation of foamed Moldings as described above, the enlargement of the mold cavity in a be effected in two ways. There can be one or more of the mold cavity limiting moldings are withdrawn by any external force that is instantaneously expand the mold cavity to the desired extent or gradually expand the mold cavity enlarged.

Alternatively, if a vertical squeeze shape is used, the the mold halves zuannenllaltende clamping pressure are reduced, so that the pressure the gases produced by the decomposition or volatilization of the blowing agent, the Mold cavity enlarged; the clamping pressure for gradual expansion can also be used here of the mold cavity can be gradually reduced or for sudden expansion instantly.

The shape of the mold should be such that there is minimal loss material from the mold occur during the molding cycle, especially if the materials under high Standing under pressure. L "s was found that forms of those i3Lii kind, commonly called vertical squash forms is known, are particularly suitable when it is desired to close the mold cavity enlarge. Where there is a possibility that between the advancing skin material fronts If air is trapped in the mold cavity, vents may be provided in the mold so that the trapped air is pushed out.

The size and shape of the mold cavity depends on the item to be created starting, with forms with a maximum cavity thickness of less than 25 mm and preferably between 2 and 10mm are particularly useful.

The method according to the invention can be used for the production of a large number of applied by objects. According to the description above, the method is in particular useful for the production of moldings, which consist of a 'thin section and consist of a thick section, e.g. I3. like shoe soles. The items with a rigid or flexible skin can be produced by the method according to the invention will. Examples of objects with a rigid llaut are parts of furniture or Cladding, e.g. buildings or facade panels, paneling or panels for formation of motor vehicle bodies or railroad cars. In addition to shoe soles as examples of Objects with a flexible skin that can be made include parts of the interior lining of motor vehicles, of railroad cars, of Caravans, airplanes, and a host of other uses. At a Embodiment of the invention can include at least part of one or more walls of the mold cavity prior to injecting the materials into the mold cavity with a removable liner made of a material that maintains its shape the temperature at which the plastic materials are injected into the mold cavity will. The plastic materials then stick to the lining when they are in injected into the mold cavity, with the sandwich item firmly adhered to it Liner after attaching the plastic materials from the mold cavity can be taken. This working method can be used in a rigid manner Support e.g. to be in front of a cell-shaped object with unfoamed skin. This is particularly useful in the production of flexible moldings for The interior lining of motor vehicles, where it is desired: is, a resiliently flexible one To obtain a lining with an attractive surface, this lining is rigid to be attached to a motor vehicle. In this case, one of the walls can The mold can be lined to provide a support layer for attaching the liner while the other sides are not lined so that one can get the the desired pleasing surface. Examples of such lining materials Are wooden Sheets such as plywood or fiberboard, sheet metal or sheets of thermoplastic material that retains its shape, i. e. is dimensionally stable at the mold temperatures. Alternatively, the lining can be used if necessary be made of a flexible material, e.g. as the upper material of a shoe or boot, to which the sole is molded using the method according to the invention.

The invention thus provides a sandwich injection molding process the building and core materials successively from separate injection cylinders is injected into a mold cavity via a common runner, so that when injecting skin material into the mold cavity, skin material in the core material supply channel flows upward toward the core material injection cylinder.

Claims (3)

Claims Method for producing injection molded articles consisting of two different plastic materials, a first of which is plastic material a closed outer skin around a core of a second plastic material forms and in the case of the injection of the plastic materials with feed channels a common runner are in communication and in a first step of the Injection cycle the first plastic material is injected into a mold cavity, wherein the first plastic material is in the feed channel for the second plastic material is located, in which in a second step the second plastic material in the Mold cavity is injected, wherein a penetration of the second plastic material is prevented in the feed channel for the first plastic material and at In a third step, the first plastic material is injected again and in this step and the first step, the interface between the two plastic materials in the feed channel for the second plastic material in the direction of the sprue channel is shifted away controllably, according to patent ... (patent application P 21 03 885.7), characterized in that after the third step the feed channels are separated from each other and separated from the runner. 2. Injection molding device for performing the method according to claim 1 with two injection units each controllable via an Elydraulic cylinder for the first and the second plastic material where the hydraulic cylinder for the injection unit of the second plastic material with a control valve is connected, which can be controlled by the hydraulic pressure of the other hydraulic cylinder is to get hydraulic fluid from the hydraulic cylinder for the second plastic material to vent when the pressure in this cylinder exceeds a level that by the pressure in the hydraulic cylinder for the first plastic material is determined, characterized in that a device (1) is provided around the feed channels (13, 23) to isolate from each other and from the runner (3) after the first plastic material has been injected for the second time. 3. Injection molding device according to claim 2, characterized in that that this device is formed by a single valve (1) which is located on the Connection point of the feed channels (13, 23) with the sprue channel (3) is located and can assume a first position in which the two feed channels (13, 23) are connected to the sprue (3), as well as a second position in which the Feed channels (13, 23) are separated from each other and from the sprue channel (3). L e r s e i t e