DE10114418B4 - Method for injection molding of thermosetting plastic moldings having at least one cavity - Google Patents

Abstract

A method of injection molding molded parts (2) of thermosetting or vulcanizing plastic material having at least one cavity (1), comprising the steps of:
a) injecting plastic material from an injection unit (3) along a Kunststofffließweges (4) in the cavity (5) of an injection mold (6);
b) injecting a fluid into the uncured plastic material so that it is pressed against the walls (7) of the cavity (5);
c) curing the plastic material until it self-supporting forms the molding (2);
d) removing the molding (2) from the cavity (5) of the injection mold (6);
characterized,
in that a fluid having a high heat capacity is used as the fluid which is injected according to step b) into the as yet uncured plastic material,
wherein the liquid is heated prior to injection into the still molten plastic material after step a).

Description

• a) Einspritzen von Kunststoffmaterial von einer Einspritzeinheit entlang eines Kunststofffließweges in die Kavität eines Spritzgießwerkzeugs;
• b) Einspritzen eines Fluids in das noch nicht ausgehärtete Kunststoffmaterial, so dass dieses an die Wandungen der Kavität gepreßt wird;
• c) Aushärten des Kunststoffmaterials, bis dieses selbsttragend das Formteil bildet;
• d) Entformen des Formteils aus der Kavität des Spritzgießwerkzeugs.

The invention relates to a method for injection molding of at least one cavity having moldings of thermosetting or vulcanizing plastic material, comprising the steps:

• a) injecting plastic material from an injection unit along a Kunststofffließweges in the cavity of an injection mold;
• b) injecting a fluid into the uncured plastic material so that it is pressed against the walls of the cavity;
• c) curing the plastic material until it self-supporting forms the molding;
• d) removal of the molding from the cavity of the injection mold.

The generic method is known and widely used as a gas-internal pressure method in the production of molded parts made of thermoplastic material. Such a method is for example from the US 4,101,617 or the EP 0940 241 A2 known. In this case, a fluid is introduced under pressure in the still molten plastic melt. By the pressure thus generated in the interior of the melt, the melt is pressed against the cavity wall of the injection mold; Drop marks due to volume contraction during cooling are thus avoided.

When Fluid injected under pressure into the melt usually becomes Nitrogen gas used. It has the advantage of being inert Gas is not subject to any chemical reaction in the hot melt. there the disadvantage is accepted that the nitrogen is usually right expensive to manufacture. Either the injection molding device must be supplied with nitrogen from bottles or with liquid nitrogen or the gas will be on site - at greater gas demand - for example obtained by molecular filter.

The DE 24 61 580 A1 also discloses a manufacturing method in which a mold cavity is created by introducing pressurized gas into the still molten resin. The article "Gas or Water?", Published in Kunststoffmagazin, 1999, Issue 9, pages 56-62, deals with the benefits of using water rather than gas as the injected medium.

The ever increasing demands on economic efficiency of the process require ever shorter injection molding cycles if possible increasing quality the moldings to be manufactured.

at The previously known method, it is disadvantageous that, firstly after as before expensive nitrogen is needed and secondly despite all measures due to the limited Heat capacity of the gas the heating process is limited remains. Independently this is due to the strong difference in viscosity between the melt and gas on the problem that sometimes flow marks occur on the molding surface, the quality of the molded part to negatively influence.

Of the The invention is therefore based on the object, the injection molding of the generic type develop so that the disadvantages mentioned are avoided. The procedure should therefore be possible make do without the use of expensive nitrogen.

Of another should be possible short curing time be realized, which significantly shortens the injection molding process. Finally, should The procedure also ensure that the flow path is as homogeneous as possible the plastic material takes place in the injection mold, so that Switching marks as possible can be avoided.

These This object is achieved in conjunction with the preamble of claim 1 solved, that as fluid, the according to step b) in the not yet cured Plastic material is injected, a liquid with high heat capacity is used, being the liquid before injection into the still molten plastic material Step a) is tempered.

Here is especially thought of, that the liquid on a given Temperature range heated becomes. In this case, a temperature range is particularly advantageous between 20 ° C and 250 ° C, preferably between 40 ° C and 180 ° C, intended.

When thermosetting or vulcanizing plastic material is for example the Use of elastomers or thermosets provided. But it is Also conceivable silicones, such as liquid silicone to use.

in the Process step a), the cavity volumetrically complete or even partially, for example, be filled to 80%.

advantageously, is during or after step b) and before step c) of the further compressed gas in the through the liquid introduced formed cavity.

The core idea of the invention therefore depends on that as to be injected into the melt Fluid is used a liquid with high heat capacity, thereby achieving that a faster curing process takes place, so that the cycle time of the injection molding cycle can be significantly reduced. The additional input of a compressed gas, here, for example, air or nitrogen (N ₂ ) can be used, supports the molding process. With the gas, a high pressure can be maintained until the molding is self-supporting. Furthermore, it is possible to introduce the liquid so that largely a channel for the gas is created and this then ensures the actual molding. That is, in the first step, liquid is introduced to preform a cavity, then gas is introduced to at least partially remove the liquid, and then the gas is held under pressure to form the molding.

at This approach has surprisingly been that by the features mentioned hardly occur flow marks, the otherwise to fear and observe in the gas internal pressure process. This is due to the small differences in viscosity between the thermosetting or vulcanizing plastic material and the injected liquid high heat capacity returned.

According to one first refinement, it is provided that during the above process step b) a part of the not yet hardened Plastic material is displaced from the cavity in a demolding Nebenkavität. The river of Plastic material from the cavity in the Nebenkavität is preferably controlled by valve means, which according to temporal Default opens or closed. This is a purposeful influence on the overflow of the Plastic material from the main to the Nebenkavität possible. Farther It is conceivable to have several secondary cavities independent of each other to be controlled.

The liquid can along the Kunststofffließweges through the gate area directly or via the machine nozzle, over the the plastic material supplied will, in the cavity be injected or alternatively directly by means of an injection nozzle in the Cavity, with the requirement of forming multiple cavities for each Cavity a separate injection nozzle is provided.

in the second case, it may be advantageous if a part of himself in the cavity located plastic material during the above step b) through the injected liquid towards the injection unit to out of the cavity again driven back out becomes.

A further improvement of the flow behavior of the plastic material or the control of this behavior results when, prior to injecting the plastic material in the cavity, one opposite to the Ambient pressure increased Pressure is built up by introducing a gas. This gas pressure can while the above step a) depending be controlled and / or regulated therefrom, such as the injection pressure the plastic material during their Injection increases. Preferably, the gas pressure after a drove predetermined pressure or time profile.

at The above temperature ranges were initially on thought the use of water. But it is also conceivable, for example, to use oil, around the warming effect especially to reinforce. Because the liquid under increased pressure entered into the plastic material is achieved that too above the boiling point, the fluid can be entered in liquid form.

at comes the concept of the invention the removal of the injected liquid - if possible still in the injection molding - a special Meaning too. There are several possibilities according to the invention here.

• c') Einpressen von Druckgas, vorzugsweise Druckluft, entlang des Weges, über den die Flüssigkeit in das Kunststoffmaterial eingespritzt wurde, und Ausblasen der Flüssigkeit aus dem Hohlraum des Formteils an mindestens einer Ausblasstelle, die sich an einer Stelle befindet, die von der Eingabestelle der Flüssigkeit entfernt ist.

First, it can be provided that after curing and before demolding the following process step is carried out:

• c ') injecting pressurized gas, preferably compressed air, along the path through which the liquid has been injected into the plastics material and blowing out the liquid from the cavity of the molded part to at least one blow-out point located at a location remote from the input port of the mold Liquid is removed.

The Blow-out point is preferably in the region of the flow path end of the plastic material arranged. To a further increased Aushärteffekt to achieve, according to step c ') instead of Compressed gas again liquid be entered and thus a circulation of the liquid be achieved by the molding.

• c'') Einpressen von Druckgas, vorzugsweise Druckluft, an einer Gaseingabestelle, die von der Stelle entfernt ist, an der die Flüssigkeit in das Kunststoffmaterial eingespritzt wurde, und Ausblasen der Flüssigkeit aus dem Hohlraum des Formteils über die Stelle, an der die Flüssigkeit in das Kunststoffmaterial eingespritzt wurde.

Alternatively, it can be provided that the following method step is carried out at the named time:

• c '') injecting pressurized gas, preferably compressed air, at a gas input location remote from the location at which the liquid was injected into the plastic material and blowing out the liquid from the cavity of the molding over the location at which the liquid enters the plastic material was injected.

In this case it can be provided to use means which, via a suitable switching device, the liquid and / or the compressed gas via the Enter the same media path and release again.

• c''') Anlegen eines Vakuums an einer fluidisch mit dem flüssigkeitsgefüllten Hohlraum in Verbindung stehenden Stelle, um die sich im Hohlraum befindliche Flüssigkeit aus dem Hohlraum abzusaugen.

In addition to the blowing out of the liquid from the cavity and a suction of the liquid in question. Then it is provided that the following method step is carried out:

• c ''') applying a vacuum at a fluidly connected to the liquid-filled cavity location to suck the liquid in the cavity from the cavity.

there Advantageously, the vacuum is applied to the injection nozzle for liquid created. To make sure that by the vacuum the molding is not contracted before, or during the application of the vacuum created a ventilation opening become.

Of the Forming process during the Injection of plastic material and liquid and during the curing the material can be favorably influenced by appropriate control or regulation of the media pressures. It is therefore advantageously provided that in the in the not yet cured Plastic material introduced during the above steps b) and / or c) exerted pressure will, according to one predetermined time profile is regulated or controlled. The pressure profile can according to a pulsating on and off regulated or controlled descending course; it is present all a sinusoidal around a predetermined constant pressure value extending pressure curve thought. Alternatively, it can also be provided that the pressure in a first time phase on a first, preferably constant, Level and in a later, second time phase at a second, preferably constant, level is regulated or controlled, the first pressure level lower as the second one is. Here, the pressure on both the entered liquid as well as on the additional input compressed gas, since the compressed gas during the Input of the liquid can be done.

When a further advantageous development, the injection mold be formed so that the cavity or the volume of the molding forming cavity before, while or after step b), ie the input of the fluid into the still not cured Plastic material is reduced, so an injection-compression process is carried out.

When a further advantageous development, the injection mold be formed so that the cavity or the volume of the molding forming cavity before, while or after step b), ie the input of the fluid into the still molten Plastic material is increased. This embodiment of an injection molding tool becomes general referred to as a breathing tool.

After this the liquid has been removed from the cavity, the openings) through the cavity Aftermelting of melt to be sealed.

When liquid comes with high heat capacity preferably water or oil in question.

In the drawing is an embodiment of Invention shown. The figures show:

1 the schematic section through an injection molding apparatus;

2 the schematic section through an injection mold with Nebenkavität;

3 the same cut as in 2 but without secondary cavity;

4 a section through the injection area for plastic material and liquid.

In 1 is an injection molding apparatus, which is an injection unit 3 having, recycled in the usual way plastic material and in an injection mold 6 injects. The tool 6 has a cavity 5 with a cavity wall 7 , The plastic material is doing along a Kunststofffließweges 4 through a machine nozzle from the injection unit 3 in the tool 6 injected.

The molded part to be produced 2 has a cavity 1 which, on the one hand, makes the part lighter and requires less use of material, which, on the other hand, makes it possible, during the cooling of the melt in the cavity 5 this against the cavity wall 7 is pressed. The produced moldings 2 therefore have a particularly good surface quality.

It can be provided that during Einspitzens the plastic material in the cavity 5 and / or during the input of the fluid, a portion of the plastic material in an overflow cavity 8th overflows. The overflow can by valve means 9 be controlled or regulated.

The injection of the fluid takes place predominantly via the injection nozzle 10 , As can be seen, therefore, the fluid spreads along the Kunststofffließweges 4 in the direction of the cavity 5 out.

As fluid comes according to the invention a Flüs high heat capacity, which is preferably heated. This leads to a very short cycle time, since the liquid can additionally introduce heat into the plastic material. This therefore cures in a short time, which is why the Entformungsprozeß - compared to known methods - can start earlier.

The cavity 5 is completely filled before injecting the liquid. Then the liquid, preferably water, is injected.

In 1 can be seen that the input of liquid along the Kunststofffließweges 4 in the area of the sprue 11 he follows. The detail lier embodiment of the region of the injection mold is in the 2 and 3 played.

As in 2 can be seen, plastic material S is in the gate area 11 into the cavity 5 injected. About the injector for liquid 10 For example, water is entered. The displaced plastic material flows, as already mentioned above, at the flow path end from the main cavity 5 in the Nebenkavität 8th , wherein by means of valve means 9 the overflow is regulated. After at least partially curing must be the liquid that the cavity 1 fills, be removed from this again. For this purpose, compressed air is in the injection nozzle for liquid 10 initiated.

Again 2 it can be seen, the cavity extends 1 over the cavity 5 out into the subcavity, which was accomplished by the introduction of liquid into the plastic material. In the area of the overflow cavity 8th namely at the blow-out point 12 for liquid, is a blowing nozzle 13 positioned. Through the compressed air injection through the nozzle 10 can all the liquid from the cavity 1 be blown out again. It gets through the blower nozzle 13 expelled. It can - supportive way - to the exhaust nozzle 13 a vacuum is applied. The blowing nozzle 13 can also be at the end of the main cavity 5 to be ordered.

In 3 another method of the invention is shown. The cavity, which is completely filled with plastic material, is transferred via the liquid injection nozzle 10 , which is arranged at the end of the cavity, applied with liquid. The thus displaced plastic material is contrary to its flow direction on the Kunststofffließweg 4 pushed back so far that the gas input point 15 in the formed cavity 1 can protrude into it. Subsequently, the cavity 1 pressurized gas is applied to the liquid via the liquid ejection point 13 at least partially remove from the cavity.

It is provided, a nozzle as in 4 described use. However, the method can also be used without pushing back the plastic material, it is only necessary to ensure that the gas input 15 is positioned so as to ensure that they are in the cavity as described above 1 can protrude into it, since the pure volume compensation this will be much smaller.

In 4 It can be seen that device technology results in a particularly advantageous embodiment when an injection element 14 is used, through which either liquid (water) W or compressed air (gas) G can be injected. In 4 reaches the injector 10 for liquid and gas, although in the range of Kunststofffließweges 4 from the injection unit 3 into the tool cavity. However, it is just as possible the combined injection element 14 For liquid and gas to be arranged so that it injects liquid or gas directly into the cavity of the tool via the corresponding nozzle.

The The method described above can also be advantageous with other injection molding, z. For example thermoplastic materials, combine. For example, it can also be used well if the molding consists of more than one Plastic component is injected. (2-K) method.

Farther is it possible, for example, the liquid to inject into the tool in two places, so that two media bubbles to generate and to cause them by appropriate pressure control to merge together. This technology is known as such.

The Input of the liquid can also continue in the gate distributor take place, whereby several partial cavities can be supplied with liquid.

Claims (25)

Method for injection molding at least one cavity ( 1 ) having molded parts ( 2 ) of thermosetting or vulcanizing plastic material, comprising the steps of: a) injecting plastic material from an injection unit ( 3 ) along a plastic flow path ( 4 ) into the cavity ( 5 ) of an injection molding tool ( 6 ); b) injecting a fluid into the not yet cured plastic material, so that this on the walls ( 7 ) of the cavity ( 5 ) is pressed; c) curing of the plastic material, until this self-supporting the molded part ( 2 ) forms; d) removal of the molded part ( 2 ) from the cavity ( 5 ) of the injection molding tool ( 6 ); characterized in that as fluid, the step b) in the not yet cured plastic material is injected, a liquid is used with high heat capacity, wherein the liquid is heated prior to injection into the still molten plastic material after step a). Method according to claim 1, characterized in that that the predetermined temperature range between 20 ° C and 250 ° C, preferably between 40 ° C and 180 ° C, lies. Method according to claim 1 or 2, characterized that as a thermosetting or vulcanizing plastic material an elastomer, a thermoset or a silicone, for example a liquid silicone, is used. Method according to one of claims 1 to 3, characterized in that during or after step b) and before step c) further pressurized gas in the cavity formed by liquid ( 1 ) is introduced. Method according to claim 1, characterized in that the filling of the cavity ( 5 ) is carried out with plastic material according to step a) according to claim 1 such that the cavity ( 5 ) is filled completely volumetrically with plastic material. Method according to claim 1, characterized in that the filling of the cavity ( 5 ) is carried out with plastic material according to step a) according to claim 1 such that the cavity ( 5 ) is partially, preferably 80%, filled with plastic material. A method according to claim 5 or 6, characterized in that during the process step b) according to claim 1, a part of the not yet cured plastic material from the cavity ( 5 ) in a demoulding secondary cavity ( 8th ) is displaced. Method according to claim 7, characterized in that the flow of plastic material from the cavity ( 5 ) in the Nebenka vita ( 8th ) by valve means ( 9 ) is controlled, which are opened or closed according to timing. Method according to one of claims 1 to 8, characterized in that the liquid along the Kunststofffließweges ( 4 ) through the sprue area ( 11 ) into the cavity ( 5 ) is injected. Method according to one of claims 1 to 8, characterized in that the liquid directly by means of at least one injection nozzle ( 10 ) into the cavity ( 5 ) is injected. A method according to claim 10, characterized in that a part of the in the cavity ( 5 ) during step b) according to claim 1 by the injected liquid in the direction of the injection unit ( 3 ) to out of the cavity ( 5 ) is driven back out. Method according to one of claims 1 to 11, characterized in that prior to the injection of the plastic material according to step a) according to claim 1 in the cavity ( 5 ) is constructed with respect to the ambient pressure increased pressure by introducing a gas. Method according to claim 12, characterized in that that the gas pressure during of step a) according to claim 1 is controlled and / or regulated according to a pressure-time profile. Method according to claim 13, characterized in that that the reduction of the gas pressure depending on it or controlled is regulated as the injection pressure of the plastic material during the Step a) according to claim 1 increases. Method according to one of claims 1 to 14, characterized in that after step c) and before step d) according to claim 1, the following method step is carried out: c ') pressing compressed gas, preferably compressed air, along the path through which the liquid in the Plastic material was injected, and blowing the liquid from the cavity ( 1 ) of the molded part ( 2 ) at least one blow-out point ( 12 ) located at a location remote from the liquid entry point. Method according to claim 15, characterized in that the blow-out point ( 12 ) is arranged in the region of the flow path end of the plastic material. Method according to one of claims 1 to 14, characterized in that after step c) and before step d) according to claim 1, the following method step is carried out: c '') injection of compressed gas, preferably compressed air, at a gas input point which removes from the site is, at which the liquid was injected into the plastic material, and blowing the liquid out of the cavity ( 1 ) of the molded part ( 2 ) about where the liquid was injected into the plastic material. Method according to one of claims 1 to 14, characterized in that after step c) and before step d) according to claim 1, the following method step is carried out: c ''') applying a vacuum to a fluidically filled with the liquid-filled cavity ( 1 ) in communication with the location in the cavity ( 1 ) located liquid from the cavity ( 1 ) gene. A method according to claim 18, characterized in that the vacuum at the injection nozzle ( 10 ) is applied for liquid. Method according to one of claims 1 to 11, characterized that on the introduced into the plastic material liquid during the Steps b) and / or c) according to claim 1 exerted a pressure will, according to one predetermined time profile is regulated or controlled. Method according to claim 20, characterized in that that the pressure according to a pulsating rising and falling profile is regulated or controlled. Method according to claim 21, characterized that the pressure curve sinusoidal runs around a predetermined constant pressure value. Method according to claim 20, characterized in that that the pressure in a first time phase on a first, preferably constant, level and in a later, second time phase on one second, preferably constant, regulated or controlled level is, wherein the first pressure level is lower than the second. Method according to one of claims 1 to 23, characterized that as a liquid water is used. Method according to one of claims 1 to 23, characterized that used as liquid oil becomes.