DE2320098A1 - INJECTION MOLDING PROCESS - Google Patents

Description

PATENT OFFICE TlEDTKE - BüHLING - KlNNE 2320098

TEL. (0811) 539653-56 TELEX: 524845 tlpat CABLE ADDRESS: Germaniapatent Munich

8000 Munich 2

Bavariaring 4

P.O. Box 202403 April 19, 19 73

Imperial Chemical Industries Limited London (Great Britain)

Injection molding process

The invention "relates to injection molding and in particular a process in which two or more plastic materials are used are sequentially injected into a mold cavity so that the second (and each subsequent) material into the the first material is injected before the latter solidified and the first material as a skin including a core of the second material in the outermost zones of the mold cavity expands. In this way, an article is produced that has a skin of a material that is exposed from the pouring-in area, i.e. the place or places where the plastic materials enter the mold cavity have been injected, completely enclosing a core made of a different material.

One form of this process in which the material forming the core is foamable is described in GB-PS 1 156 217

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When plastic materials are in a liquid state, i.e. as Melt through a sprue into a mold cavity of constant cross-section are injected, they flow out of the sprue until the front of the melt locally to Standing comes by hitting the walls of the mold cavity. Usually the front of the melt touches the walls of the mold cavity in urgent places earlier than in others, i. the lengths of the flow paths from the sprue to the outermost zones of the mold cavity are from one part of the mold to the other different. This also applies, and this is the more general case, when the cavity does not have a constant cross-section.

When a second material, after a predetermined amount of a first material has been injected into that first. material is injected into it, the second material expands the enveloping skin from the first material until the Mold cavity is filled. 'Because of the different lengths. The enveloping skin must flow paths in several directions stretched more than in others, so that it becomes stretched and thinner in some places than in others and so uneven Skin strength is obtained.

In other cases it may be desirable in certain places of the molded article has a more uneven skin thickness than it would otherwise be received.

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While it is often possible to change the distribution of the breeding material modify it relative to the core material by changing the position of the gate and / or the thickness of the desired article, There is a need for an alternative method that, in addition to modifying the position of the gate and / or the .Article strength can be used, to the To give founders another opportunity.

GB-PS 1 303 517 describes a process for the production of articles with a foam core, according to which, among other things, a foamable mass is injected into the SOrmhohlraum and then an insert is withdrawn in one or more of the mold walls, so that the foamable Bulk can foam into selected areas or a further amount of foamable material can be introduced. In a preferred method, 6-bs foamable material is injected into non-foamable material that has previously been injected into the body cavity.

The invention is a modification of this process, the use of which is prior to the injection of this core material or during the injection of the core material but before the mold cavity, as determined by the molded parts with the insert in its non-retracted position, is filled is being withdrawn. The invention is also applicable to the production of non-foamed core structures, i.e., it is not essential that the xerii material, as below described containing a propellant, although this

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is advantageous.

In GB-PS 1 255 970 a method is described according to which the mold cavity is filled with the skin material and then the core material is injected, the shape being enlarged to accommodate the core material. In contrast for this purpose, according to the invention, the insert is withdrawn before the mold cavity is filled.

Accordingly, the invention relates to a method for. Manufacture of injection molded articles made with a skin a plastic material that has a core. completely encloses another plastic material except for the sprue surface, by what method a batch of the plastic material forming the skin through a sprue in liquid State is injected into a mold cavity, which has opposing mold surfaces, which by at least two mold parts are formed, at least one of which has at least one slidably mounted retractable mold insert which is used to form a. Constriction between the part of the mold cavity adjacent to the runner and the part of the mold cavity lying beyond the retractable mold insert, preferably in the mold / cavity protrudes, wherein the material forming the skin is injected through the sprue into the mold cavity, while the mold insert is in its non-retracted position holds, a batch of the material forming the core -

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before the inside of the batch of the skin "forming material" solidified - injected in a liquid state into the interior of the batch of skin-forming material, the retractable mold insert is withdrawn and the skin forming material enveloping the core forming material, is stretched by the material forming the core into the outermost zones of the mold cavity. and then the plastic materials can harden.

According to the invention, the retractable mold insert is before or withdrawn during the injection of the material forming the core, but before the mold cavity is filled.

Preferably, the retractable mold insert protrudes or the retractable mold inserts protrude in their non-retracted Position in the mold cavity so as to be an obstacle to the passage of the skin forming material. In however, in some cases it may be desirable to make the original arrangement so that the retractable Mold inserts in their non-retracted position are flush with the rest of the surface of the mold so that the flow path is expanded when the mold inserts are in their retracted position, and for the flow of the melt represents even less resistance.

Where there is a retractable mold insert in its non-retracted Position protrudes into the mold cavity, he can

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until the opposite // and the mold cavity touch or another retractable mold insert projecting from this wall, so that the skin constituent material is prevented from flowing past the retractable mold insert.

Therefore, if there are areas where with the aid of the invention If a decrease in the strength of the skin is to be achieved, one or more retractable procedures are required Mold inserts are arranged between these areas and the sprue. On the other hand, when using the method according to the invention, an increase in skin thickness in one certain area is to be achieved, one or more retractable mold inserts between the sprue and others Areas of the mold cavity are arranged so that the flow path to those other areas is restricted thereby and the skin thickness in these other areas decreases relative to that in the particular area. .

A protruding retractable mold insert can be retracted, be drawn so that it is flush with the surface of the mold in which it is mounted, or it can be more or less than be withdrawn necessary for a flush finish, where.-by protrusions or depressions in the finished Resulting molding. By carefully designing the shape ·. In this way, desired projections or depressions can be achieved in the finished molding.

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To ensure that the core-forming material is injected into the interior of the skin "forming material, both materials should advantageously be injected through the same sprue channel, although separate ones if necessary Sprues can be used, as described in German patent applications 2 159 3 ^ 4, 2 159 3 ^ 5 and 2 159 is described. . ·

To carry out the invention. Process usable Plastic materials are the ones that are in the state of a viscous liquid can be injected into a mold cavity and then caused to expand in the mold cavity solidify. Thermoplastic resin-like materials that solidify on cooling can therefore be used, which can be injected in the form of viscous melts and solidify by cooling in the mold cavity. on the other hand thermosetting resinous materials can be used which can be injected into the mold cavity in the state of a viscous liquid and then passed through an in the cross-linking caused by the cavity can be brought to solidify. The thermosetting resinous materials are generally crosslinked by heating. On the other hand, a mixture of reaction components can be injected which react in the mold cavity and form a thermosetting resin.

Examples of suitable injection moldable thermoplastic resins,

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which can be used are polymers and copolymers of <Ä, -O: lefi £ th, such as high- and low-density polyethylene, polypropylene, polybutene, .Poly-4-methylpentene-i, propylene / ethylene copolymers, copolymers of 4- Methylpentene-1 with linear <X, -olefins with U- to 18 carbon atoms and ethylene / vinyl acetate copolymers; Polymers and copolymers of vinyl chloride, vinyl acetate, vinyl butyral, styrene, substituted styrenes, such as Q <- -Methylstyrene, acrylonitrile, butadiene, Me-. ethyl methacrylate, vinylidene chloride. Specific examples of such polymers are VinylchloiicUiomopolymere and-cop olymers of vinyl chloride with vinyl acetate, propylene, lthylen, vinylidene chloride, alkyl acrylate, _a, such as 2-ethylhexyl acrylate, alky fumarate, alkyl vinyl ether, such as Cetylvinyläther and N-aryl maleimides such as NO-Ghlorphenyl-maleimide!; Polyvinyl acetate, polyvinyl butyral; Polystyrene, styrene / acrylonitrile copolymers; Copolymers of butadiene with methyl methacrylate and / or styrene and optionally acrylonitrile; Polymethyl methacrylate; Copolymers of methyl methacrylate with minor amounts of alkyl acrylate such as methyl acrylate, ethyl acrylate and butyl acrylate; Copolymers of methyl methacrylate, Ν-acrylic maleimides and, if appropriate, styrene, as well as vinylidene chloride / acrylonitrile copolymers; Melt-processable oils of cetrafluoroethylene and hexafluoropropylene. . . ·

Halogenated polymers or copolymers can be used, e.g. halogenated olefin polymers such as chlorinated polyethylene, or halogenated vinyl chloride polymers such as

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chlorinated polyvinyl chloride.

Other injection moldable thermoplastic polymers that can be used are condensation polymers, such as the injection moldable Grades of linear polyesters such as polyethylene terephthalate; Polyamides such as polycaprolactam, polyhexamethylene adipamide and copolyamides such as copolymers of hexamethylene diamine adipate and hexamethylene diamine isophthalate, especially those with 5 "to 15% by weight of hexamethylene diamine isophthalate; polysulphones and copolysulphones; Polyphenylene oxides; Polycarbonates, thermoplastic oxymethylene polymers; thermoplastic linear polyurethanes; and the thermoplastic derivatives of cellulose, such as cellulose acetate, cellulose nitrate and cellulose butyrate, and mixed cellulose esters, e.g., cellulose acetate butyrate.

When a copolymer is used, the amounts of comonomers used in the copolymers vary among other things, on the desired properties of the moldings.

Thermosetting resins include plastic materials that either by itself or as a counterpart to a hardener or catalyst are exposed to cross-linking when heated to a sufficiently high temperature. The term closes hence a material falling within the scope of the term "thermosetting" as it is commonly understood, and also a plastic material that is usually thermoplastic,

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however, a crosslinking agent such as peroxide contains one Cross-linking is justified when the plastic is on a sufficient level high temperature is heated.

Examples of suitable thermosetting resins that can be used are phenol-aldehyde resins, amine-formaldehyde resins, Epoxy resins, polyester resins, thermosetting polyurethanes and vulcanizable rubbers.

The resins can, where necessary, hardeners or catalysts included to make the resins curable.

Injection-moldable cross-linkable thermoplastics are copolymers of methyl methacrylate and glycol dimethacrylate and ethylene / Vinyl acetate copolymers containing a crosslinking agent.

Mixtures of plastic materials can also be used.

The material forming the core can be the same as that of the ■ Skin-forming material, with the exception of additives used in one or the other of the materials or in both, but in different proportions. on the other hand the plastics can be very different and also contain different additives.

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As mentioned above, the material forming the core is preferably foamable * It advantageously contains a polymer Material and a blowing agent that when heated to a temperature Above a certain temperature, which is called the activation temperature here, a gas develops, namely by evaporation or decomposition, and is at a temperature above the activation temperature, of the propellant injected, '

When the material forming the core is injected in the usual amount and under a usual pressure in injection molding essentially no foaming will occur until the desired amount of the core-forming material is injected has been. When a foamable material is used to form a hemophosphate, it can be done in two different ways be proceeded. For the first, the amount of skin-forming material and foamable material injected is enough, however not yet made of non-foamed material forming the core. to fill the mold cavity, and the material forming the kera can foam and at the same time envelop the skin stretch forming material so that it gets into the outermost zones of the mold cavity. On the second and preferably intended type is the injected amount of the- ' Skin-forming material and the foamable, but as yet unfoamed, core-forming material so large that the cavity {with the retractable mold insert or Mold inserts) is filled before noticeable foaming

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takes place and the mold cavity is then enlarged so that foaming can take place. Instead of enlarging the mold cavity to allow foaming, the pressure on the material forming the core, for example by pulling back of the plunger can be reduced so that the pressure generated by the propellant some of the foamable material presses back into the injection cylinder.

According to the invention it is necessary that the retractable Mold insert or the retractable mold inserts are withdrawn = before the material forming the core is injected or during the injection of the material forming the core but before the mold cavity is filled. In In this case, the mold cavity means that space that through the molded parts with the retractable mold insert in whose non-retracted position is formed.

According to a further advantageous embodiment of the invention, after the injection of the material forming the core a third batch of material of the same constitution as the material making up the skin by that for the injection of the sprue used to form the core. When the sprue is removed from the molding, points the exposed surface in this way only a narrow ring of exposed material forming the core, since the the central part of the runner is filled with the further batch of the skin-forming material.

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The invention is explained in more detail below on the basis of the description of exemplary embodiments with reference to the drawing explained:

Fig. 1 shows a plan view of a molded part,

FIG. 2 is a section along the line II-II of FIG. 1. and shows the molded part of FIG. 1 in combination with a further molded part for forming a hollow, space as well as injected, skin-forming material,

Fig. 3 is a view similar to Fig. 2 showing the core material partially injected;

Fig. 4- is a view similar to Figs. 2 and 3 and shows all injected core material,

Fig. 5 shows a section through another mold after the injection of the skin material,

FIG. 6 is a sectional view similar to FIG. 5 after Injecting the foamable core material and another batch of skin material,

Fig. 7 is a sectional view similar to Fig. 6 and shows the Mold cavity enlarged to allow foaming,

Fig. 8 is a top plan view of a female die part in a further embodiment of the invention and

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Fig. 9 shows a section along the line HI-III of Fig. 8, in which the position of the opposite Male part is shown in dashed lines.

In Fig. 1, a molded part 1 is shown, which forms half the mold cavity for the production of a three-blade article, such as a simple fan. The molded part Λ has a central sprue 2 in the center of a part 3 of the cavity, which forms a hub. From Figs. 1 and 2 it can be seen that the flow path from the sprue 2 to the. outermost ends 4 of the wings of the molding is much larger than the flow path from the sprue 2 to the periphery of the hub cavity part 3, so that when a skin material is injected and then a core material is injected, the enveloping skin is stretched and pressed into the outermost zones of the mold cavity , the skin thickness at the hub periphery would be much greater than that at the extreme ends 4 of the wings. .

To reduce this inequality in skin thickness are mounted between the sprue 2 and the periphery of the hub cavity part 3 retractable mold inserts 5, which the flow path from the sprue 2 to. Narrow the periphery of the hub.

These retractable mold inserts 5 cannot with the help the devices shown hydraulically or mechanically

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be withdrawn in order to be flush with the surface 6 of the molded part 1.

In injecting the skin-forming material 7 '- (see Fig. 2) limited the mold insert 5 the flow of the skin material 7 ^o f the part of the mold cavity 8 beyond the .Formeinsatzes 5 so that the skin material 7 further towards the extreme end 4- of the sash advances than when the mold insert is withdrawn 5

During the injection of the material 9 forming the core, the mold insert 5 is withdrawn, for example by reducing the hydraulic pressure which holds the mold insert 5 in its position protruding into the mold cavity. If it is desired, the return of the mold insert 5 need not be started until the injection of the material 9 forming the core has progressed well. The mold insert 5 can therefore be held in its position, if necessary, until the material 9 forming the core has expanded the enveloping skin 7 to the outermost end 4- of the mold cavity. However, it should be withdrawn before the mold cavity is filled with the mold insert 5 in its non-retracted position. . '

When the mold insert 5 is withdrawn, this is applied to the mold insert adjacent skin tissue located in the cavity 8

material 7 expanded from the core material 9 so that it is the

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Best of the mold surface 6, as shown in Fig. 4, touches,

In Fig. 5 a mold for forming a shoe sole is shown. The mold is made of two relatively movable Moldings 10 and 11 and retractable mold inserts 12 and 13 are formed in the moldings 10 and 11 in the vicinity of the Heel portion 14 of the mold cavity are mounted.

In this embodiment, a first batch of non-foamable Plastic material 15 that forms the skin over a sprue 16 is injected into the mold cavity in a liquid state. Touch the protruding mold inserts 12 and 13 each other so that the skin-forming material 15 is prevented from flowing into the heel part 14 of the mold cavity will. This means that the skin-forming material 15 is pressed further into the toe part I7 of the mold cavity, than would be the case if it could also flow into the heel part 14. ,

When injecting a batch of foamable, core-forming Plastic material 18 at a temperature of the foaming agent in the temperature above the activation temperature Mixing through a sprue 16 becomes the retractable Mold inserts, as shown in Fig. 6, withdrawn and the enveloping, skin-forming material 15 by means of inject the core forming material 18 stretched and up

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into the extreme ends of the toe section 17 of the hollow mold. space and down to the outermost zones of the heel space 14- des Mold cavity pressed. In this way the thickness of the skin in the toe part is greater than in the heel part. After this Injecting the core-forming material 18 through another small batch 19 of the skin-forming material injected the sprue 16 so that after the removal of the sprue 20 formed in the sprue 16 from the cast ■ Shoe sole the central part of the exposed sprue surface of the moldings is covered with skin material 19, with only one narrow ring of the material forming the core 18 remains exposed.

After injecting the next batch of skin-forming Material 19 becomes the mold parts 10 and 11 together with their associated retractable mold inserts 12 and 13 from one another moved away to enlarge the mold cavity, as shown in Fig. 7, and the foaming of the foamable, the To enable core-forming material 18.

The plastic materials are then for example by cooling, if they are thermoplastic, or solidified by heating if they are thermosetting.

Another guide is shown in FIGS. Here the mold cavity is usually rectangular in shape 23 cm long, 7 »5 cm wide and 0.65 cm thick. The matrix part 21 is provided with a central sprue 22 and a pair of back-

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Drawable strips 23 are provided, which are symmetrical to the sprue 22 and are arranged parallel to the longer sides of the cavity. The strips have a length of 15 cm and a counter- ' lateral distance of 3? 8 cm.

As shown in Figure 9, the ledges contact the surface of the opposing male part 24 when in their non-retracted position. The skin material will therefore held between the ledges when injected. The location of the skin material at the end of the injection and before the retraction of the strips is shown in Fig. 8 in dashed lines. After injecting the skin material the strips are withdrawn so that they are flush with the surface of the standard part 21.

In this way, the batch of skin material is in a mold which is similar to that of the final mold cavity, resulting in an even distribution of the skin material contributes to the finished molding.

The invention relates to an injection molding process the different materials are injected one after the other into a mold cavity, which is formed by at least two mold parts is formed, at least one of which has a slidably mounted retractable mold insert which originally in its non-retracted position and preferably beyond the surface of the molded part in

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the cavity protrudes and in front of the vein during the injection of the second material, but before the lorm cavity is filled, is withdrawn. This enables the distribution of the first and second materials to be modified within the mold cavity.

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Claims (4)

2320096 Claims Λ.) Process for the production of injection-molded articles with a skin made of a plastic material which completely encloses a core made of another plastic material apart from the sprue area, in which a charge of the material forming the skin is in the liquid state through a sprue channel into a mold cavity with opposite sides Mold surfaces is injected formed by at least two mold parts, at least one of which has at least one slidably mounted, retractable mold insert, the mold insert being in its non-retracted position when the skin forming material is injected through the sprue into the cavity, a batch of the core-forming material is injected in a liquid state into the interior of the batch of skin-forming material before the batch of skin-forming material has solidified, the retractable mold insert withdrawn and the skin-forming and d The material that forms the core, enveloping material is stretched by the material forming the core into the outermost zones of the mold cavity and then the plastic materials become 309845/0899 can consolidate, characterized in that the retractable Formeinsatζ before or during the Injecting the material forming the core "but withdrawing it before the mold cavity is filled. 2. The method according to claim 1, characterized in that the one or more retractable mold inserts in their non-retracted Position protruding into the mold cavity and an obstacle to the passage of the skin-forming material represent. 5. The method according to claim 1 or 2, characterized in that that the retractable mold insert in its non-retracted position protrudes into the mold cavity in such a way that that he has the opposite V / and of the mold cavity or another retractable, protruding from this wall Mold insert contacts so that the skin-forming material is prevented from going over the retractable or retractable Flow out mold inserts. 4. The method according to any one of the preceding claims, characterized characterized in that the retractable mold insert, in its retracted position, is flush with the surface of the mold part in which it is mounted. 309848/0899 L e r se Ί t e