DE102013202626A1 - Method for manufacturing injection molded part for e.g. bumper, of vehicle, has adding plastic melt before injection of physical foaming agent, and forming closed pores with gas intercalations when pressure in plastic melt is reduced - Google Patents

Abstract

The method involves injecting (S2) a first plastic melt into region of injection mold and injecting (S3) a second pressurized plastic melt into another region of injection mold. A base body is formed from the first plastic melt and the seal elements are formed (S4) from the second plastic melt. The second plastic melt is added before the injection of a physical foaming agent e.g. gas or a granule. Closed pores with gas intercalations are formed when pressure in the second plastic melt is reduced. An inert gas is supplied to the second plastic melt in an external container. An independent claim is also included for an injection molded part.

Description

The present invention relates to a method for producing an injection molded part having at least one main body and a sealing body formed integrally with the main body and an injection molded part with at least one base body and a sealing body formed integrally with the main body, which has an at least partially foamed core. In particular, the present invention relates to a method having the features of the preamble of claim 1 and an injection molded part according to the preamble of claim 11.

STATE OF THE ART

The production of injection molded parts by means of injection molding has been widely used for various technical applications. In order to produce injection molded parts with elastic properties, it has also become known to foam the injection molded parts produced in the injection molding process. For this purpose, a plastic, such as a thermoplastic, is melted and enriched with a blowing agent, and the plastic melt formed is injected into a cavity of a suitably trained tool, whereupon it comes as a result of a pressure drop to the expansion of the melt. After a corresponding cooling of the foamed plastic body, the tool is opened, and the finished injection-molded part can be removed from the cavity. The injection-molded parts produced in this way have elastic properties due to their foamed structure and can be used, for example, as a sealing body.

From the publication EP 1 992 761 A1 For example, a process for producing a plastic gasket by means of a thermoplastic foam casting process (TSG process) from thermoplastics or thermoplastic elastomers is known. Such plastic seals are typically used to seal penetrations in sealing elements, especially in plastic films, eg. B. at sub-roofs.

From the publication EP 1 161 333 B1 a further method for producing an injection-molded part using a physical foaming method is known in which in a first step a propellant-free first fraction of melt is injected into a cavity of a tool and in a second step a second blowing fraction enriched with a physical blowing agent is injected into the cavity, followed by the formation of an injection molded part with a foamed and a non-foamed section. At least in part, according to the EP 1 161 333 B1 Finally, the injection-molded part produced by known methods is known from the German Patent Application, which is based on the Applicant DE 10 2010 040 501 known.

For some applications, in particular for the arrangement in a land, air or water vehicle, it is particularly advantageous if injection-molded parts comprises at least two different sections, which are constructed of different materials. The one section can then be elastic and possibly also volumenkompressibel, the other hard trained. The elastic portion is particularly suitable to represent a seal, for example in a cable feedthrough, with grommets and covers for containers, when recording electrical and / or electronics, eg. As in electronic boxes, fuse boxes or vehicle doors, speakers and windows mechanisms. From the prior art, it is known to manufacture elastic or volume-compressible foams one-piece and to connect them with also manufactured in one piece thermoplastics. However, the one-piece production has the disadvantage of higher manufacturing costs, and the connection area between a thermoplastic and a foam is insufficiently suitable for the development of a sealing effect. The known injection molding methods are also not suitable for producing a one-piece injection-molded part with two sections constructed from two different materials, one of which should be designed to be elastic or volume-compressible.

PRESENTATION OF THE INVENTION

In view of the above-described prior art, it is an object of the present invention to provide a simple and inexpensive method of making an injection molded article having at least two sections formed of different plastics, one of which is volume-compressible. Volumetric compressibility is a property of the plastic body that goes beyond the elasticity of the plastic. An elastic plastic body is deformable. When a force acts on the elastic plastic body, it tends to yield to the force and to move in a direction determined by the force, but the volume of the plastic body is substantially retained and only its shape changes. In contrast, a volumenkompressibler plastic body not only dodge, ie deform, but reduced or increased its volume in response to an externally acting on him force. A volumenkompressibler plastic body can thus both deform as well as change its volume. From this it can be deduced that an elastic plastic body is not always volumenkompressibel. Preferably, a volume-compressible plastic body is also elastic at the same time, namely if the volume compressibility is based on an elastically compressible material, for example a gas introduced into a closed space.

This object is achieved by a method with features of claim 1 and an injection molded part according to claim 11. Advantageous developments are described in the subclaims.

The invention provides a method for producing an injection-molded part having at least one main body and a sealing body integrally formed with the main body, which has an at least partially foamed core and preferably an unfoamed outer skin, wherein a first plastic melt in a first region and a second, pressurized Plastic melt are injected into a second region of a cavity of an injection mold. For injection, an injection molding machine, for example a screw piston injection molding machine, can be used. The main body of the injection-molded part is formed from the first plastic melt and the sealing body from the second plastic melt, the second plastic melt is added prior to injection, a physical blowing agent or granules and with a drop in pressure in the second plastic melt closed pores are formed with gas deposits. The area of the second plastic melt with the closed pores with gas deposits forms the core of the sealing body. The foamed in the manner described core has closed-cell cells with gas deposits, so that the sealing body is given a volume-compressible structure.

After foaming described a tool in which the cavity is provided, cool, then open, and the finished injection molded part can be removed from the cavity. Plastic melts for use in combination with the method according to the invention can be provided on the basis of different plastics, for example based on thermoplastics and / or elastomers. A sealing body of an injection-molded part produced by the process according to the invention may thus comprise, for example, an elastomer with air inclusions. The sealing body is not only elastic, but also at least partially volumetrically compressible because of the gas pockets whose contents are compressible.

The inventive method can injection molded parts for a large number of applications, especially for vehicles, such as electronic boxes or bumpers, air ducts, trim elements, fuse boxes, bulkhead seals, such as subframe for doors and cable glands, especially spouts, or for other applications, for the at least partially volumenkompressibles injection molded part is required or advantageous, manufacture.

The second plastic melt is preferably first fed to an inert gas in a container located externally relative to the cavity, whereupon the melt-gas mixture is mixed to form a single-phase solution and then injected into the cavity. In this case, for example, nitrogen or carbon dioxide can be used as the inert gas. The second plastic melt is then seeded by supplying the gas with gas bubbles. The single-phase solution with the dissolved gas in the plastic melt then collects initially under pressure. After injecting the mixture into the cavity, the latter undergoes a pressure drop, whereupon the gas is distributed in the second region of the cavity, cell formation, ie nucleation, and generally cell growth occurs.

The cells formed in the manner described above increasingly fill the second region or at least part of the second region of the cavity so that a foam with intercalated gas is formed in the second region of the cavity. The region formed by these cells finally forms the volume-compressible core of the sealing body. The advantage of this preferred embodiment lies in a further reduction in density in the sealing body and consequently in a reduction in weight in the entire injection molded part. It can also create a particularly homogeneous and uniform cell structure in the foamed core and the manufacturing process is shortened, as higher injection rates when injecting the melt-gas mixture are possible because a single-phase solution is injected. As a result of the injection of the second plastic melt with gas bubbles, the viscosity of the plastic melt is also reduced and their flow properties are improved. It can also form sealing body with compact edge layers, even if a very small surface layer, in particular thinner than 1 mm, to be created. In the tool with the cavity also takes place in the context of the manufacturing process, a uniform pressure distribution, and it suffice low machine closing forces for fixing the tool with the cavity during the manufacturing process.

The inert gas is preferably injected via a screw antechamber provided for this purpose, and the single-phase solution collects preferably in the antechamber. For injection molding, an injection molding machine with an injection unit, which has a special screw geometry with the screw antechamber, is used for this purpose. A preferred method, which can be used in particular in the production of the sealing body, is also known under the name MuCell ^® method.

According to a further, preferred embodiment of the method, a pressurized physical blowing agent is pumped into the second plastic melt in a container located externally relative to the cavity, and the melt-blowing agent mixture is then injected into the cavity. The propellant is pumped in the liquid, supercritical or gaseous state. The injection pressures required for this purpose are particularly low, and physical blowing agents allow an optimal adjustment of the melting temperature to each selected plastics, whereby this embodiment of the method is particularly energy efficient and the risk is reduced that it comes as a result of excessive temperatures to an impairment of plastic materials used. As a physical blowing agent can also be used inexpensive gases such as carbon dioxide or nitrogen. In this embodiment of the method, in particular a known thermoplastic foam casting method (TSG method) can be used.

According to a further preferred embodiment, the granules, a chemical blowing agent is added. The foaming of the second plastic melt is then carried out by a chemical reaction. The propellant is enclosed, for example, in individual granules and is released at a critical temperature. In this way, a TSG process with chemical blowing agents for foaming the core of the sealing body can be used.

According to an advantageous embodiment of the invention, a first portion of the second plastic melt is first injected propellant into the cavity, a second portion of the second plastic melt added a pressurized physical blowing agent and then injected the second portion of the second plastic melt into the cavity, wherein the dosage of Propellant pressure-controlled or pressure-controlled. In this case, the blowing agent is added to the second plastic melt as part of the pressure-controlled or pressure-controlled propellant, in particular when a predetermined pressure threshold is exceeded. With this embodiment of the method, a core of the sealing body with closed pores and an outer skin without pores, which is produced without propellant, create. In this case, for example, a thermoplastic which is suitable for injection molding and can be foamed can be used as the plastic that enters the second plastic melt. Thus, for example, a ceramic or metallic melt with aluminum, magnesium, zinc, tin or with noble metal serves as a second plastic melt. This embodiment of the method makes use, inter alia, of a method which is also known as Stieler method and in the document EP 1 161 333 B1 is described in more detail whose content is incorporated herein by reference.

It is particularly preferred if, after the injection of the second portion of the second plastic melt, a third propellant-free portion of the second plastic melt is injected into the cavity. In this way, can also form an outer skin of the sealing body, which is unfoamed and has no pores. It is therefore preferably first a propellant-free portion, then injected with a blowing agent enriched portion and finally again a blowing agent-free portion of the second plastic melt in the cavity.

Preferably, the physical blowing agent is a compressible fluid. This may include, for example, carbon dioxide or nitrogen. A compressible fluid may also be combined in combination with any of the aforementioned embodiments of the method.

Furthermore, it is preferred if at least one further plastic melt enriched with a physical blowing agent or a granulate is injected into a further region of the cavity and a further sealing body is formed from the further plastic melt. In this way, a one-piece injection-molded part can be provided with a plurality of regions formed of different plastics, wherein a plurality of regions are volume-compressible and can differ from each other selectively with regard to their volume compressibility. For example, it is possible to produce a non-compressible main body with a first, strongly volume-compressible sealing body and a second, slightly volume-compressible sealing body. The core of the first sealing body is this foamed more than the core of the second sealing body. In this case, the base body can be formed, for example, from a thermoplastic and the two sealing bodies made of different elastomers.

Preferably, the first and / or the second plastic melt is formed by melting at least one thermoplastic or an elastomer.

Finally, the invention also encompasses an injection-molded part with at least one main body and a sealing body formed integrally with the main body, which has an at least partially foamed core, wherein the sealing body is configured at least partially volume-compressible.

Further advantages and features of the present invention, which may be implemented alone or in conjunction with one or more of the above features, insofar as the features do not conflict, will be apparent from the following description of preferred embodiments.

This is done with reference to the accompanying drawing, in which:

1 a block diagram of a preferred method for producing an injection molded part shows.

1 shows a block diagram of a method for producing an injection molded part with a base body and a sealing body integrally formed with the base body, which has at least partially a foamed core and a non-foamed outer skin.

To carry out the illustrated embodiment of the method, at least one worm-piston injection molding machine, a tool having a cavity, which has two regions which are formed in a complementary manner to the base body and the sealing body of the injection-molded part to be produced, and two melt cylinders are provided.

In a first method step S1, in a first melt cylinder, a first plastic, in the illustrated case a thermoplastic, is melted down into a first plastic melt and in a second melt cylinder a second plastic, in the illustrated case an elastomer, is melted down into a second plastic melt.

In a second method step S2, the first plastic melt is injected into the first region of the cavity of the provided tool, which is designed to be complementary to the base body, with the injection molding machine, and a first portion of the second plastic melt is also started in the second Inject area of the cavity, which is complementary to the sealing body.

The injection of the first plastic melt into the first region of the cavity is continued in a third method step S3 as needed, while the second plastic melt is a pressurized physical blowing agent, in the illustrated embodiment, an inert gas, in the present case carbon dioxide, added and the melt Gas mixture is injected into the second region of the cavity.

The pumping of physical blowing agent to the second plastic melt takes place under pressure or pressure controlled. In particular, a pressure threshold value is predetermined, at which carbon dioxide is pumped in when it is exceeded by the pressure of the second plastic melt, that is to say the melt of the elastomer. The introduction of the third method step S3 is thus pressure-controlled.

After, in the second method step S2, as described above, a first blowing agent-free portion of the second plastic melt was injected, in the third method step S3, a blowing agent-enriched, second portion of the second plastic melt is injected. In the course of process step S3, a single-phase solution is formed from the gas and the second plastic melt before it reaches the second region of the cavity.

After injecting the second portion of the second plastic melt in the second region of the cavity, there is a pressure drop, as a result, dissolved in the second plastic melt gas, in this case carbon dioxide, to begin to distribute and expand.

In this way, nucleation begins and growing cells are formed with gas deposits. However, since in the preceding method step S2 first a propellant-free, first portion of the second plastic melt was injected, the said nucleation of cells with subsequent cell growth does not take place at the edge of the second region of the cavity, but only in its core, It is thus a frothed, formed elastic core of the sealing body, which is surrounded by a non-foamed outer skin. In the first region of the cavity, no foaming was carried out in the illustrated embodiment of the method, so that an unfoamed basic body is formed. In other embodiments, however, the main body could also be foamed completely or in sections.

In a fourth method step S4, the tool is cooled with the cavity so that in the first region of the cavity the base body and in the second region of the cavity the sealing body with unfoamed outer skin and with a foamed core are strengthened. With the described method, a one-piece injection-molded part is thus produced, which comprises a main body and a sealing body having foamed core. The sealing body is formed volume-compressible due to the closed-cell cells with gas deposits.

In a fifth method step S5, the tool with the cavity is opened and the finished injection-molded part is removed from the cavity.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1992761 A1 [0003]
• EP 1161333 B1 [0004, 0004, 0016]
• DE 102010040501 [0004]

Claims (11)

A method for producing an injection-molded part having at least one base body and a sealing body integrally formed with the base body having an at least partially foamed core and preferably an unfoamed outer skin, characterized in that a first plastic melt in a first region and a second, pressurized plastic melt are injected into a second region of a cavity of an injection mold (S2, S3) and the base body of the first plastic melt and the sealing body of the second plastic melt are formed (S4), wherein the second plastic melt is added before injection, a physical blowing agent or granules (S2) and with a drop in pressure in the second plastic melt closed pores are formed with gas deposits (S3). A method according to claim 1, characterized in that the second plastic melt in an external container, an inert gas is supplied (S3) and the melt-gas mixture to a single-phase solution mixed (S3) and then injected into the cavity (S3). A method according to claim 2, characterized in that the single-phase solution collects in the screw antechamber and the gas is injected via a space provided for this purpose Schneckenvorraum (S3). Method according to one of the preceding claims, characterized in that the second plastic melt in an external container initially a pressurized, physical blowing agent is pumped (S3) and the melt-blowing agent mixture is then injected into the cavity (S3). Method according to one of the preceding claims, characterized in that the granules, a chemical blowing agent is added. Method according to one of the preceding claims, characterized in that first a first portion of the second plastic melt is propellant-free injected into the cavity (S2), a second portion of the melt added a pressurized physical blowing agent (S3) and then the second portion of the second Plastic melt is injected into the cavity (S3), wherein the metering of the blowing agent is pressure-controlled or pressure-controlled. A method according to claim 6, characterized in that after the injection of the second portion of the second plastic melt, a third, propellant-free portion of the second plastic melt is injected into the cavity. A method according to claim 6 or 7, characterized in that the physical blowing agent is a compressible fluid, preferably a gas. Method according to one of the preceding claims, characterized in that at least one further plastic melt enriched with a physical blowing agent or a granulate is injected into a further region in the cavity and a further sealing body is formed from the further plastic melt. Method according to one of the preceding claims, characterized in that the first and / or second plastic melt is formed by melting at least one thermoplastic or an elastomer. Injection molded part having at least one base body and a sealing body integrally formed with the base body, which has an at least partially foamed core, characterized in that the sealing body is configured at least partially volume-compressible.

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