NL1019235C2 - Formation of thin-walled products from plastic mold comprises introducing heated plastic in mold cavity while mold is partly open, and pressing away plastic in mold cavity by wall parts of mold cavity - Google Patents

Abstract

A method for forming thin walled products comprises introducing heated plastic (30) in mold cavity (10) while mold is partly open, and pressing away plastic in mold cavity (16) by wall parts of mold cavity after mold is closed so the plastic completely fills the mold. An Independent claim is also included for an apparatus for forming products comprising mold having mold cavity, mechanism for introducing plastic, and mechanism for closing the mold after plastic is introduced.

Description

Title: Method and device for forming thin-walled products and a product manufactured with them.

The invention relates to a method for forming thin-walled products from low-melt plastic in a mold.

Thin-walled products are usually made from plastic by injection molding in a mold. Materials 5 with a relatively high Melt Flow Index (MFI), or at least a high melt, are used for this. Such a high MFI means that the plastic in liquid form has a low viscosity and can therefore travel relatively long flow paths with small dimensions in a mold cavity. The ratio between the length of a flow path and the minimum passage height of the flow path in question is usually referred to as the Melt Flow Rate (MFR). A high MFR therefore means a relatively long, narrow flow path. Injection molding is in principle possible with plastics with a high MFI, where there is a direct relationship between the MFI and the MFR. A higher MFR requires a higher MFI. It will be clear, therefore, that plastics with a low melt, or at least a low MFI, cannot be injection molded, at least not in thin-walled plastic products. After all, thin-walled plastic products have an MFR that is too high for that. Dn means that from low-melt plastics only products are injection molded with relatively thick walls and relatively short flow paths.

The object of the invention is to provide a method for forming thin-walled plastic products from low-melt solidified plastic in a mold, to which end a method according to the invention is characterized by the features of claim 1.

In a method according to the invention, low-melt plastic is introduced into a mold shell, wherein the mold is at least partially opened. Without wishing to be bound by any theory, this appears to result in flow paths being obtained over a first part of the filling path of the mold 2 with dimensions such that an MFR is obtained that matches the MF of the plastic in question. During or after insertion of the plastic into the mold cavity, such that it is partially filled with the plastic, the mold is closed, at least the mold cavity is brought into the shape corresponding to the desired.

end product, whereby the plastic is pressed further into the mold cavity. Because the mold cavity is initially only partially filled, due to the fact that the total volume of the mold cavity with the mold open is larger than the mold volume with the mold closed, a filling front is created. In this context, filling front is to be understood to mean the edge of plastic in the mold cavity in front of flow direction. The closure of the mold can in this case be regulated such that a flow path always remains from said filling front, the Melt-Flow Rate of which approximately matches, is at least equal to or smaller than the MFI of the plastic in question. This means that it is always ensured that the plastic is displaced over the desired distance and therefore in a simple manner leads to complete filling of the mold cavity.

In a method according to the invention, a mold cavity is preferably used. in a completely closed state, from the or each injection point for the plastic has a Melt Flow Rate that is higher, in particular much higher than the MFI of the plastic to be used, at least higher than suitable for injection molding the plastic in question . However, at the start of the injection of the plastic, the shape of the mold cavity is adjusted such that a suitable MFR is obtained for the MFI of the plastic in question. The mold cavity is preferably brought increasingly further in the direction of the desired desired shape as the degree of filling increases, so that the plastic is constantly kept moving and a suitable MFR is always maintained for the relevant or remaining part of the flow paths.

3

In a method according to the invention, it is preferred that the plastic is constantly kept moving during filling of the mold cavity by movement of mold parts and / or mold cavity parts. This prevents unwanted solidification 5 from occurring, whereby undesirable haze formation can be prevented, in particular when transparent plastics are used. In particular with plastics such as PET (polyethylene terephthalate) with particularly good transparency and high impact strength, a method according to the invention is particularly advantageous because it allows the brightness to be retained, also with mold forming of thin-walled products, without using conventional blow molding techniques.

In further elaboration, a method according to the invention is preferably characterized by the features according to claim 4.

As a result of the thermal insulation of mold cavity-forming parts of the further mold, at least of cooling means thereof, the advantage is achieved that cooling of the plastic or that is introduced into the mold cavity can be postponed, in particular until the mold is partially or completely closed , at least the mold cavity is completely filled in the final shape. The heat capacity of the hermically insulated molded parts is preferably such that they can be heated up particularly quickly by the heated imported plastic, while these can be cooled relatively quickly by the cooling means of the mold. With such a method the flow of the plastic is promoted even better, while moreover with clear plastics this brightness is retained even better.

It is furthermore preferred that in a method according to the invention the plastic is dried prior to being fed into the mold cavity, at least that any moisture present therefrom is at least largely removed, so that undesired disturbing influence of the moisture in the mold cavity is avoided. This is particularly advantageous again, especially with clear 4 plastics, because haze formation is thereby prevented even better.

Surprisingly, it has been found that with a method according to the present invention, products can be manufactured in a simple manner that are thin-walled, in addition to which hinges can be formed. Such integrated hinges, commonly referred to as living hinges, offer the advantage that movable parts can be obtained without the necessity of mounting steps. With a method according to the present invention, such hinges can even be formed into substantially completely transparent products, that is to say products with a haze of less than 5%, more in particular less than 3%. whereby, for example, (blister) packages, containers and the like can be formed with a particularly pleasant appearance.

The invention further relates to a mold-shaped, substantially thin-walled plastic product, characterized by the features of claim 13.

Such a product offers the advantage that all kinds of special product properties can be obtained that were possible with products according to the prior art. For example, 20 products can be formed from plastic with a melt that is particularly low, for example an MFI smaller than 18, with wall thicknesses that are particularly small in relation to the other dimensions of the relevant wall parts.

For example, curved or flat wall parts can be obtained with a thickness of a few tenths of millimeters with outer dimensions of the relevant wall part of a few centimeters or more. Products that until now could only be manufactured from plastics with a high MFI. for example polyethylene or polystyrene.

A product according to the invention can be manufactured relatively inexpensively and simply from relatively inexpensive plastic, for example impact-resistant. flexible, with integrated hinges, crystal clear or opaque, in addition to which materials can be used that are less environmentally harmful than, for example, PVC.

A product according to the invention can for instance be manufactured from PET (polvetene terephthalate) with at least one integrated hinge and is in particular suitable as a storage device for for instance disc-shaped information carriers such as CDs, CDi, CD-ROM, Chipcard, Simcard or the like, but also for other products, for example writings, food and the like.

The invention furthermore relates to a device for forming products according to the invention or application of a method according to the invention, characterized by the features according to claim 20.

With such a device, products can be manufactured in a particularly simple manner that are relatively thin-walled, with relatively long flow paths, i.e. with a high MFR, from plastic with a low melt, or at least low MF1. With this, products can be manufactured with particularly advantageous product properties, such as, for example, high brightness, high impact resistance. high flexibility, low costs. FDA approval, recyclability, mono-packaging, suitability for rain, low and / or high temperatures and the like, depending on the plastic chosen.

In a method and device according to the invention, it is furthermore achieved that the closing force for closing and keeping the mold closed is relatively low relative to that required for the manufacture of comparable products in a conventional manner, i.e. by injection molding. Du means that relatively small, light machines can be used.

Further advantageous embodiments of a method, product and device according to the invention are described in the further subclaims. To clarify the invention, 6 exemplary embodiments of a method, product and device according to the invention will be further elucidated with reference to the drawing. It shows:

Figure 1 shows diagrammatically in cross-sectional side view a device 5 according to the invention; figures 2 and 3 use a device according to figure 1 in two steps; Figures 4A-C show the filling of a mold cavity in a method and device according to the invention in three steps; Figure 5 shows, in cross-sectional side view, an alternative embodiment of a device according to the invention; 6-8 show, in side, top and partially sectioned front view, a storage device according to the invention; and figure 9 shows diagrammatically in side view a holder manufactured with a method and device according to the invention.

In this description, the same or corresponding parts have the same or corresponding reference numerals. In this description use is made of the indications Melt-Flow-Rate (MFR) which is a usual indication of the ratio between the minimum passage height in a flow path. at least the minimum passage and the length of the flow path. Moreover, the term Melt-Flow Index (MF1) is used, which is a material-related index for the viscosity in "liquid" form, that is at a temperature at which the plastic can flow somewhat. The MFR and MF1 are, among others, standardized 25 m ISO standard 1133. However, it will be clear that the application is not limited thereto. The only important thing is that the flow path ratios are always adjusted to the viscosity of the plastic.

Figure 1 shows diagrammatically in cross-sectional side view, a part of a device 1 according to the invention, which comprises a mold 2 provided with a first mold part 4 and a second mold part 6. In 7 the second mold part 6 is a female part 8 of a mold cavity 10, a male mold part 12 of said mold cavity 10 is included in the first mold part 4. The male mold part 12 is defined by a molding 14 which is movably received in a cavity 16 in the first mold part 4. The molding 14 is hollow thin walls 18. indicated by the broken line, so that the heat capacity of this molded part 14 is relatively small. A thermally insulating seal 20 is provided around the mold part 14 over a part of the height of the chamber 16, while the first and second mold parts 4, 6 are provided with cooling means 22, schematically indicated by a pipe with a pump 24. These cooling means For example, 22 are designed in the usual manner as cooling channels (not shown) extending around the mold cavity 10 through which cooling liquid can be pumped at relatively low temperatures, for example a few degrees Celsius.

In figure 1 the mold 2 is shown in the open position, such that a distance X exists between the closing surfaces 26. In the chamber 16 pressure means are included for biasing the molded part 14 in an extended position shown in figure 1, such that male part 12 is located at a relatively small distance Hj from the female part 8, at least the bottom 20 thereof. The pressure means in the chamber 16 can be formed, for example, by a slightly compressible liquid, elastic material or the like or. as will be described in more detail with reference to figure 5, comprise adjustable pressure means. The pressure means 28 in the chamber 16 are designed such that upon introduction of artificial si or 30 the male part 12 can be pushed away in the mold cavity 10 in the chamber 16, so that the distance between the male part 12 and the female part 8 increases , for example up to a distance H2. Plastic 30, for example polyethylene terephthalate (PET) or another plastic with a low Melt-Flow Index for example less than 18, more in particular 30 less than 12 and preferably for example about 6 or less becomes via an 8 injection channel 32 using of a pump 34 or other injector known from the injection molding technique introduced into a mold cavity 10, displacing the molded part 14. which molded part is rapidly heated to a comparable PET as a result of the temperature of the plastic, for example approximately 270 ° C for PET temperature, thermally insulated by the seal 20. This prevents premature change in the material properties, in particular coagulation and turbidity of the plastic 30, in particular referred to as PET. Prior to introduction of the plastic 30 into the cavity 10, the plastic 30 is dried in a device 36, for example by suitable preheating, wherein moisture 38 is discharged.

After the plastic 30 has been introduced into the mold cavity 10 as a relatively thick, high-viscosity liquid, the space in the mold cavity 10 being relatively large as a result of the distance, the mold is closed, as shown in Fig. 3. In this condition it is piece 14 is received almost completely in the chamber 16 and the closing surfaces 26 lie against each other. The mold cavity 10 is completely filled with plastic 30, the desired shape of the product 40 being obtained. A relatively large amount of contact exists here between the mold part 4 and thus the cooling means 22 and the mold part 14, whereby the desired cooling of the product 40 is obtained, such that upon complete opening, that is to say further than said distance X in Fig. 1, the product 40 can be taken out and the mold can be made suitable for a new production run. During the filling of the mold cavity and closing of the mold, care is taken that the plastic 30 continues to flow in the direction of the ends of the mold cavity 10, thereby preventing premature changes in material properties from occurring.

It has been found that, in particular when PET is used, for example, it is particularly advantageous if the plastic continues to flow continuously during insertion and filling of the mold, while this plastic is almost completely dried before introduction and the walls of the mold cavity 10 are relatively warm during filling of the mold, because this maximally preserves the brightness of the plastic. This offers the possibility of manufacturing thin-walled products as shown in, for example, Figures 6-9 as a replacement for, for example, polystyrene, polycarbonate, polypropylene and the like.

Figure 5 schematically shows an alternative embodiment of a device according to the invention in cross-sectional side view.

Herein, not only is the male part 12 included as part of a molded part 14 movably in a chamber 16, but also the female part 8 on a second molded part 14A in a second chamber 18A in the second mold part 6. In this embodiment the means are 28 for biasing the molded parts 14, 14A designed as at least one supply line 42 with a pump 44 for introducing into the chamber 16, 16A. or discharging therefrom a pressure fluid as hydraulic oil, with which the back pressure of the two mold parts 14, 14A and thus the distance H can always be accurately controlled. Again, the molded parts 14, 14A of the mold parts 4, 6 are thermally separated by the sealing means 20, 20A, at least in the position shown in Figure 5. Only when the mold 2 is closed does thermal contact arise between the mold parts 4. 6 and the mold parts 14, 14A for cooling thereof and thus of the product. It will be clear that combinations of the different parts as shown in Figures 1-3 and 5 are possible.

Figures 4A-C schematically show the flow of the plastic 30 into the mold cavity 10. The plastic 30 is shown here by hatching, the mold cavity schematically as a rectangle.

In Figure 4A the distance between the mold parts is relatively large, as a result of which the plastic 30 is displaced from the flow line 32 over a relatively short distance D 1 in the mold cavity 10, to either side, at least to all sides. The flow front 50 is therefore close to the inlet opening 32.

After the desired amount of plastic 30 has been introduced into the mold cavity 10, the supply line 32 is closed, schematically represented by a cross 52 and the distance between the mold parts is reduced to Ηχ, thereby the flow front is displaced 50 m in the direction remote from the supply line 32. so that the total flow path of the plastic 30 increases to D2. This means that the plastic is displaced over a distance D2 - D] between figures 4A and 4B, with decreasing passage height H. When parts of the mold are further moved towards each other, forming the mold cavity 10, the flow front 50 becomes even further pressed away until, as shown in Figure 4C, the mold cavity 10 is completely filled and the desired product thickness H] is reached. It will be clear that just before the condition as shown in Fig. 4C is reached, the plastic 15 must be pressed through a minimum passage height Hi. Since this only has to be done over a particularly short distance, a suitable Melt-Flow Rate, which matches the plastic, is always obtained.

In Figs. 6-8 a storage device 70 is shown, known per se from international patent application PCT / NL96 / 00459, which is deemed to be incorporated herein by reference as an example 20. It is explicitly noted that this example should not be construed as being limitative in any way.

A device 70 according to the invention is particularly suitable for storing and sending information carriers such as CDs 72. Information carriers should be understood in the broadest sense of the word and may also comprise other information-bearing products, such as paper, cardboard, plastic, provided with printing, figures, text or the like.

A storage device 70 according to the invention comprises a first cover part 74, a second cover part 76 and an intermediate part 78 connecting the two cover parts 74, 76. The cover parts 74, 76 are provided with edges 80. 82 such that a closed package becomes a closed position 11, as shown schematically by the broken line 84. Closing means 81, 83 are shown schematically, which can keep the storage device 70 in the closed position. The intermediate part 78 is connected on either side via an integrated hinge (living hinge) to an adjacent cover part 74. 76. Securing means 86 are provided on the intermediate part 78, for example in the form of pairs of clamping fingers 88 between which an edge of the information carrier 72 can can be clamped, as shown in figure 8. Optionally, the fingers 88 can be mutually connected by ridges 90 for increasing the clamping force. It will be clear that the information carrier can be secured in many different ways, at least locked within the storage device 70, for example also in a manner as known from the Jewel box on one or both cover parts 74, 76. Such and other fastening means are of sufficiently known in practice.

In a particularly advantageous embodiment, an information carrier 70 according to the invention, for example as shown in the drawing, is made from a clear transparent plastic such as PET and manufactured in a previously described manner, so that the transparency is completely retained. The haze can thereby for instance be smaller than 5%, even smaller than 3%. With suitable process parameters, which can be easily determined by the person skilled in the art within the limits outlined, even a substantially complete plastic can be obtained.

Fig. 9 shows an alternative holder 92, in the form of a cup-shaped container 94 with a lid 98 connected thereto via a hinge 96. The hinge 96 is formed along with it, that is to say integrated with the container 94 and the lid 98. a bhster package can be manufactured in the same way, for example by making the container 94 slightly less high, wherein closing means can be provided in the usual manner, which can be integrally formed 12, for enclosing a product or products to be packaged in the blister .

In a method according to the invention, for example applied to a holder 92 according to figure 9, different parts can get different transparency, for instance by previously cooling the cover part 98 of the mold, whereby this part is made somewhat milky white and less transparent opaque. It is even possible to give different cooling speeds by providing different surface parts of the mold cavity, so that, for example, an opaque logo can be formed as an integral part on a relatively clear cover part. without, for example, other roughness being necessary, although possible.

With a method and device according to the invention, the additional advantage is achieved that relatively low spray pressures can be applied.

The invention is by no means limited to the exemplary embodiments shown in the description and the drawing. Many variations thereof are possible within the scope of the invention as set forth in the claims.

For example, different parts of different exemplary embodiments described can be combined and varied, for example different mold shapes and different means of creating back pressure for the movable mold parts. A plurality of mold cavities can also be included in one mold and products can also be formed without a hinge or with a plurality of hinges. Other plastics can be used with a relatively low Melt-Flow-25 Index, such as PC. PON. PEN and the like. Other types of products can also be manufactured with a method and device according to the invention, for example trays, household products, fence elements, while moreover other means can be used for closing containers, such as screw thread, bayonet means and the like, which can be integrally formed with it. A variety of other means can also be used for biasing the movable molded parts. These movable molded parts can also be designed such that the mold parts are first brought against each other and then the or each molded part is moved such, for example by means as shown in figure 5. that the mold cavity is brought into the desired shape. Incidentally, it is noted that an advantage of the previously described method is that venting of the mold cavity is possible in a particularly simple manner. If desired or necessary, the or each movable molded part can be preheated. It is also possible to use two component technology in a mold 10 according to the invention and several injection points can be used.

These and many comparable variations are understood to fall within the scope of the invention as set forth in the claims.

Claims (20)

Method for forming thin-walled products from low-melt plastic in a mold, wherein an amount of said plastic is introduced into a mold cavity, with at least partially opened mold, after which the mold is closed, such that the Γ) plastic in the mold mold cavity is pressed away by the wall parts of the mold cavity, whereby a complete filling of the mold cavity is obtained. 2. Method as claimed in claim 1. wherein a mold is used of which at least one wall part is arranged movably, wherein during at least one wall part said at least one wall part is pressed away by the plastic, such that between said at least one wall part and an opposite a flow passage for the plastic is formed with a thickness measured between said wall portions that is greater than the thickness of the product part to be formed therefrom, wherein when the mold is closed said flow passage is slightly compressed to the desired thickness for forms product part. 3. Method as claimed in claim 1 or 2, wherein during the introduction of the plastic and the closing of the mold the plastic is kept in constant motion until the entire mold cavity is closed. 4. Method as claimed in any of the foregoing claims, wherein a mold is used of which at least movable wall parts determining the mold cavity and preferably all mold-forming wall parts when the mold is opened are thermally insulated from the further mold, said thermally insulated wall parts of the mold being such can be fed so that they have such a low heat capacity that the temperature of these wall parts is raised when the plastic is introduced, close to the temperature of the plastic while the other mold parts are kept relatively cool, while said wall parts of the mold cavity are cooled by thermal conduction between said wall parts and the further relatively cold mold parts. 5. Method as claimed in any of the foregoing claims, wherein a mold is used wherein the or each mold cavity comprises a male and a female part, wherein at least the male part is movably confined in a mold part, the confinement being embodied such that an outward facing face of the male part when the mold is opened is kept relatively close to an opposite face of the female part, the plastic being inserted between said surfaces under such a pressure that the male part is slightly pressed away to provide a desired flow passage, wherein the pressure with which the male part is forced outward is smaller than the pressure of the plastic when introduced. 6. Method as claimed in any of the foregoing claims, wherein the plastic is dried prior to being fed into the mold cavity, such that at least largely the moisture is removed therefrom. The method of claim 6, wherein drying of the plastic is obtained by pre-heating mg. 8. Method as claimed in any of the foregoing claims, wherein a maize hohe is used with a Melt-Flow Rate (MFR) which in closed condition is too high for the Melt-Flow Index (MFI) of the plastic to be used. , wherein the mold upon introduction of the plastic is adjusted such that at least a first part of the flow path has dimensions such that at the minimum Melt-Flow index (MFI) and Melt-Flow-Rate (MFR) for the relevant plastic and product dimensions are met, wherein the mold is closed during and / or after the desired quantity of plastic has been introduced into the mold cavity, such that a flow front of the plastic is always created that is chosen such that the remaining part still to be filled of the mold cavity has a Melt Flow Rate (MFR) dm matches the Melt Flow Index (MFI) of the plastic. 9. Method as claimed in any of the foregoing claims, wherein at least one hinge is formed in the mold cavity in the product. A method according to any one of the preceding claims, wherein a clear, transparent plastic is used. 11. Method as claimed in any of the foregoing claims, wherein a plastic is used with an MFI that is smaller than 18, in particular smaller than 15, more in particular smaller than 10 and preferably at most 6. A method according to any one of the preceding claims, wherein PET is used, at least a plastic with comparable MFI. 13. Mold formed, substantially thin-walled plastic product, made from a plastic with a relatively small MFI, for example smaller than 18. wherein for parts of the product it holds that the MFR, calculated from a delivery position of the plastic in the mold cavity in which the product has been formed is larger than the MFI of the plastic. A product according to claim 13. wherein the product is formed from a plastic with an MFI of less than 15, in particular less than 10 and preferably at most 6.10. Product according to claim 13 or 14. wherein the product is transparent. in particular clear transparent with a haze of less than 5%, more in particular less than 3%. The product of any one of claims 13 to 15, wherein the product is made from PET. 17. Product as claimed in any of the claims 13-15, wherein the product is provided with at least one integrated hinge. A product according to any one of claims 13-16, wherein the product is a storage device for a multi-media carrier, in particular a storage device for a disc-shaped information carrier. 19. Product according to claim 18, wherein clamping means for the information carrier and closing means for the storage device are also formed. 20. Device for forming products as claimed in any of the claims 13-19 or for applying a method as claimed in any of the claims 1-12, comprising a mold with at least one mold cavity, wherein at least a part of the mold cavity wall is movable arranged and prestressed in an extended position, wherein means are provided for introducing plastic into the mold cavity, at least against said movable mold cavity wall part under such pressure that said mold cavity wall part can be pressed away thereby, means being provided for closing the mold after plastic has been introduced into the mold cavity, which means are arranged such that, with the mold closed and the plastic cavity filled with mold cavity, the or each said movable mold cavity wall part has been moved from the extended position to a collapsed position for determining the outer shape of the product to be formed . Device as claimed in claim 20, wherein the mold cavity is at least partially and preferably wholly determined by one or more mold parts. when the mold is open, thermally insulated from cooling means of the further mold, wherein when the mold is closed a thermal coupling is obtained between the or each molded part and the said cooling means. wherein the heat capacity of the or each molded part is relatively low relative to the heat capacity of the further mold, at least of the cooling means, such that it. or each molded part can be heated relatively quickly by the heat from the plastic to be introduced into the mold cavity, while these can be cooled relatively quickly by the cooling means. Device as claimed in claim 20 or 21. wherein furthermore means are provided for drying the plastic prior to introduction thereof into the mold cavity.