ITMO20080270A1 - MANUFACTURING METHOD - Google Patents

Description

MANUFACTURING METHOD

Background of the invention

The invention concerns a method for manufacturing plastic products.

Specifically, but not exclusively, the method can be used to make caps for containers equipped with a guarantee band having a flap portion folded inwards, this flap portion being in particular configured to form an abutment element which cooperates with the neck of the container in order to detach the guarantee band at the first opening of the container.

A method is known for bending an annular flange of a guarantee band of a plastic cap according to which the cap, just extracted from the mold, has the flange oriented according to an inclination different from that of use; the cap is then cooled to room temperature, after which the flange is folded mechanically into the configuration of use.

A method is known from EP 1165391 for making a plastic cap provided with a flexible band which is molded in the configuration of use (folded towards the inside of the cap), and in which the elastic return of the band towards its original forming position it is mechanically forced immediately after the molding of the cap, by means of an element of the forming mold or by means of another element which acts after the extraction of the cap from the mold, before cooling the band itself.

From United States Patent No. US 5,846,471 is known a method for printing a closure with a safety band provided with flaps extending radially inward and upward, in which the flaps are first molded at the desired inclination, then the the mold is opened by temporarily altering the angle of inclination of the fins, finally the fins return to the original inclination due to contact with a part of the mold itself.

The methods of the known art can be improved in various respects. In the first place, it would be desirable to be able to reduce the elastic return effect of the material after the plastic element has been folded, so as to easily and reliably reach a final configuration that is as close as possible to the desired one. drawback being encountered in particular when the bending is carried out while hot. Secondly, it would be desirable to minimize the yielding effect of the material in the vicinity of the bending area, so that the connection between the folded element and the rest of the piece is not weakened, this drawback being encountered in particular when the bending it is carried out cold.

Summary of the invention

An aim of the invention is to improve the known technique in one or more of the aforementioned aspects.

Another object is to provide a method for manufacturing plastic bodies, in particular caps, which is simple, practical and economical to implement.

A further object is to provide a method of manufacturing plastic products having a folded part after molding, in which it is easier to achieve the desired configuration of this folded part in a precise and reliable manner.

Yet another object is to make a plastic product available, and a method for manufacturing it, in which a folded element is connected in a stable and tenacious manner to the rest of the body of the product.

An advantage of the invention is to give rise to a method of manufacturing a plastic product that is feasible with known manufacturing systems or with a few simple modifications of such systems.

Another advantage is to provide a suitable method of manufacturing plastic plugs each comprising a security band having an annular sidewall and an annular flange, in which that flange is folded inward and is configured to expand radially during the application of the cap on the mouth of a container, thus facilitating the passage of the guarantee band, to then return elastically to the original position at the end of the application, forming an abutment element capable of collaborating, upon first opening of the container, with a corresponding abutment element associated with the container itself to determine the detachment of the guarantee band.

These aims and advantages and others besides are all achieved by the method according to one or more of the claims reported below.

The element that is folded after molding can include, as mentioned, the flexible flange which is normally equipped with a guarantee band of a plastic cap. This folding flange can have any of the geometries of the known types of folding flanges: this flange can comprise, for example, a single smooth and continuous annular strip, or a single annular strip equipped with one or more continuity solutions such as through holes and / or non-through openings, or an annularly extended and corrugated element in whole or in part, or a series of elements (fins) connected to the side wall of the guarantee band and spaced apart, or a series of elements arranged annularly and interconnected between them, or any other known type of collapsible flange of a guarantee band.

The element that is folded after molding may have been printed in the same configuration (for example with the same inclination) that this element should assume after the next folding, or it may have been printed in a different configuration (inclination), such as for example a suitable configuration to facilitate its extraction from the molding cavity. In the specific case of the production of caps with a guarantee band, it is possible to provide that the folding flange of the guarantee band has been printed in the configuration of use, i.e. facing the upper wall of the cap (where upper is intended with reference to the configuration in which the cap closes the upper mouth of a container arranged upright), or in a different configuration in which it is, for example, facing away from the top wall of the cap. It is known that a bending operation after molding is generally necessary, because in order to allow the extraction of the cap from the molding cavity, the flange will generally have to be folded on the opposite side to the top wall of the cap.

The bending operation can be performed with mechanical guiding means, in particular with known mechanical guiding means. Said guiding means can be configured to operate in the mold or even in a position external to the mold itself.

The molding operation can be performed by injection or compression or by any other plastic material forming process. The molding device can be configured to operate continuously or intermittently.

The cooling operation can be performed using active cooling means, such as a cooling tunnel, a conveyor of a cooling fluid, a conveyor belt equipped with cooling means, etc.

The cooling operation can be performed using passive cooling means, such as for example a path arranged between the molding zone and the folding zone and configured so that each molded piece is conducted along the path and therefore reaches the folding zone. having the desired temperature. This path can also include a stationing or storage phase (at controlled temperature and / or stationary time) of the printed product. This path can have a predetermined and known temperature (for example the ambient temperature). This path can be configured so that a specific printed product travels from the molding area to the bending area in a predetermined time or a preset time depending on the type of product and / or the desired bending temperature and / or temperature. of the route.

It is possible to provide for the use of the manufacturing method described here not only for plastic caps, but also for other types of product (in particular for plastic molded products having a part that is folded after removal from the molding cavity), or also for elements that are generally bent in a forced and / or guided way after molding and that do not have an annular shape and / or are not connected to the rest of the body of the molded piece along an annular-shaped connection or bending area .

Brief description of the drawings

The invention can be better understood and implemented with reference to the attached drawings that illustrate some exemplary and non-limiting forms of implementation.

Figures 1A to 1E show in succession five phases of the folding operation of a flexible annular flange associated with an annular safety band of a plastic cap.

Figure 2 is a diagram that qualitatively indicates the variations of the storage modulus E of the materials, in particular of the polymeric materials, as the temperature varies in order to highlight the transition temperatures in the materials themselves.

Figure 3A is the diagram of the variations of the dissipation modulus as a function of temperature for three different plastic materials (HDPE, LDPE, EVA).

Figure 3B is the diagram of the variations of Tan_delta (ratio E '/ E' '), that is a parameter that is indicative of the energy dissipation of a material and which is often called damping, for five different materials obtained with mixtures in different percentages of PP (polypropylene) and EOC (ethylene-octene copolymer).

Figure 4 is a diagram of the accumulation module E ', the dissipation module E' and the damping parameter Tan_delta, as the temperature varies for a sample taken from a polypropylene cap.

Figure 5 is a section of a first embodiment of a plastic cap obtained after the step of bending the flange.

Figure 6 is an enlarged detail of Figure 5.

Figure 7 is a side view of a second example of a plastic cap obtained after molding and before the step of bending the flange.

Figure 8 is a section of the cap of Figure 7 along the line VIII-VIII of Figure 9.

Figure 9 is a section of the cap of Figure 7 along the line IX-IX of Figure 8.

Figure 10 is an enlarged detail of Figure 9.

Figure 11 is a section along line XI-XI of Figure 12 of a third example of a plastic cap obtained after the flange bending step.

Figure 12 is a section along the line XII-XII of Figure 11.

Figure 13 is an enlarged detail of Figure 12.

Figure 14 is a section of a fourth example of a plastic cap obtained after the flange bending step. Figure 15 shows a section of a plastic cap equipped with a detachable guarantee band along a facilitated breaking zone and also equipped with rigid contrast means.

Figure 16 shows a section of a plastic cap in which the facilitated detachment area includes a continuous cutting line which extends along an area provided with protrusions which form connecting bridges between the guarantee band and the rest of the cap.

Figure 17 is an enlarged detail of Figure 16.

Figure 18 shows a detail of a plastic cap equipped with a guarantee band delimited by a continuous cutting line.

Figures 19A and 19B are two parts of a top plan view of a first example of a plant for the manufacture of plastic caps having a safety band equipped with a flexible flange to be folded inwards.

Figures 20A and 20B are two parts of a top plan view of a second example of a plant for the manufacture of plastic caps having a safety band equipped with a flexible flange to be folded inwards.

Figure 21 shows a diagram of a folding device usable in the subject method for folding the wing portion of the guarantee bands of plastic caps.

Figure 22 shows a diagram of a cutting device which can be used in the method in question to form the area for facilitated detachment of the guarantee bands of plastic caps.

Figure 23 shows in section a cutting tool which can be used in the method in question to form the area for facilitated detachment of the guarantee bands.

Detailed description

A method for the manufacture of plastic products, in particular for the manufacture of container caps, such as for example for the manufacture of any of the caps illustrated in Figures 5 to 18, is now described. The method comprises the step of molding a piece made of a plastic material, for example a semi-crystalline plastic material, in which the molded piece can have at least a jacket portion and an edge portion (for example of an annular shape) connected to the jacket portion along a connection area that can be , for example, of an annular shape (closed or open) or arranged along a region of circumferential extension, and which can be continuous or discontinuous (for example in segments). As is known, a plastic cap is usually equipped with this shirt-like portion which generally (when the cap is coupled to a neck of a container to close the upper mouth) surrounds at least part of the neck. This liner portion can be equipped with a thread for screw coupling with the neck of the container. It is possible to provide for the manufacture of other types of caps provided with other means (of known type) for coupling with the container (alternatively or in addition to the screw coupling means). This molding step can comprise an operation performed with molding means and with substantially known operating methods. This molding can comprise one or more injection molding operations (performed with known means and methods), or one or more compression molding operations (also performed with known means and methods) or other operations (performed with known methods and methods) for the hot forming of a plastic material product.

In this molding step, a part of the product is also printed (generally a part that protrudes or emerges from a main body) which is subsequently destined for folding. This part intended for folding can be, as in the specific case, the aforementioned edge portion connected to the jacket portion. This part intended for bending can be a part which in the final product will form an undercut and which therefore generally cannot be extracted from the molding cavity remaining in the desired final configuration (i.e. in the undercut configuration). In these cases, a subsequent bending operation is then carried out after molding. It is possible that the manufacturing method in question provides that the piece is molded in such a way that this undercut part (fin) already assumes the final configuration of use in the molding cavity (i.e. the undercut configuration): in this case, therefore, this part in the undercut, during the extraction phase of the molded piece from the forming cavity, a deformation in the direction of extraction which causes the overturning towards the outside of the molded part in the undercut (fin). In order to facilitate and / or guide this undercut part to return to the configuration of use (corresponding, exactly or approximately, to the molding configuration in the forming cavity), a bending is performed.

It is also possible that the manufacturing method in question provides for the piece to be molded so that the part intended to be undercut is formed in a configuration other than that of use, in particular it is possible that this part is molded in a configuration that is already able to allow / facilitate extraction from the molding cavity. In the specific case of the production of plastic caps, it is therefore possible that the portion to be folded (which in practice is the wing part of the guarantee band of the cap intended to form, in use, the abutment element that must be beaten on the collar of the bottle neck) is already formed during the molding phase in the configuration of use - i.e. folded inwards and upwards (with reference to the usual configuration in which the cap is applied to the neck of a container placed upright) or towards the closure portion or top portion of the cap generally in the shape of a disc - or in a configuration other than that of use, for example an axial configuration (not inclined with respect to the axis of the cap) or with a slight inward inclination but oriented on the opposite side with respect to the closure portion of the cap (in practice an orientation of the type of that of the flap 2 illustrated in Figure 1A).

The manufacturing method provides, after molding the product and opening the forming cavity, to mechanically bend the aforementioned annular portion around the connection area (or bending area) at a predetermined bending temperature (as will be better explained below) above ambient temperature.

This folding can take place before completely cooling the hot product that has just undergone the hot forging operation, or after the complete cooling of the molded product and its subsequent second heating to a predetermined temperature higher than the ambient temperature, this second heating being able be performed immediately after cooling or at a great distance in time and / or place from it.

With reference to Figures 1A to 1E, 1 indicates the molded piece, 2 indicates the annular portion to be bent, 3 indicates a support (of a known type) for the molded piece, 4 indicates a bending tool (of known type). The bending operation can comprise, as in this case, a reciprocal (axial) movement of the lower support 3 and of the bending tool 4 (Figures 1A to 1C) to bring the molded piece closer to the cutting tool 4, and hence the movement of a movable portion 5 of the tool which mechanically acts in contact with the portion 2 to be bent (Figures 1D and 1E).

The manufacturing method comprises the step of choosing the aforementioned predetermined folding temperature (i.e. the temperature of the material of the molded product or, more specifically, of the portion to be folded of this product, during the folding operation) as a function of the temperature of physical transition of alpha Tα type of the plastic material with which the product was obtained by molding.

For example, the bending temperature can be chosen to be lower than the aforementioned physical transition temperature of the alpha type Tα. The aforementioned bending temperature can also be higher than the beta-type physical transition temperature Tȕ of the plastic material. The aforementioned transition temperatures Tα and Tȕ, which can vary depending on the material and other parameters, are known temperatures in plastics technology. However, a brief explanation of the significance of these transition temperatures Tα and Tȕ of the materials is provided below.

It should be noted that it is known that semi-crystalline polymeric plastic materials (for example PE, PP, PA, POM, PET, etc.) are characterized by having some parts in the amorphous phase (in which the polymer chains are disordered giving rise to zones more flexible) and other parts in the crystalline phase (in which the polymer chains are ordered giving rise to more rigid zones). It is also known that semi-crystalline polymers have, in addition to a melting temperature Tm in which the transition between the solid phase and the liquid phase takes place, also a glass transition temperature Tg in which the amorphous portion passes from a rigid solid phase to a plastic solid phase (rubbery), while for amorphous polymers the glass transition temperature Tg marks the transition between a rigid solid phase (glassy and brittle) and a rubbery solid phase which, as the temperature increases, then transforms into a phase viscous liquid.

Above the glass transition temperature Tg, reciprocal movements between polymer chain segments become possible. At temperatures below the glass transition temperature Tg, movements in the polymer mass can still occur, generally limited to small groups of atoms. These movements are characterized by transition temperatures (so-called secondary transition temperatures) generally indicated with Tȕ, TȖ, Tδ. In some cases it happens that below the temperature Tg, while the movements of relatively long polymer chain segments (i.e. containing a certain number of monomer units) are blocked, certain secondary movements are still possible, for example the movements of chain segments shorter or smaller groups of atoms contained in the single monomer units; the movements of other groups of atoms can then be blocked only below the temperature Tȕ, while other movements of the same groups of atoms and / or certain movements of other groups of atoms can be blocked only below the temperature TȖ or Tδ. Figure 2 shows how these secondary transitions are detectable by a diagram of the elastic dynamic modulus or accumulation modulus E '(Storage Modulus) as a function of the temperature obtained by mechanicodynamic analysis (DMA) techniques.

In particular, it was found, again by mechanical-dynamic analysis techniques, that isotactic polypropylene (i-PP) shows three transition phases Ȗ-, ȕ- and α in the temperature range from -150 to 150 ° C, and that polyethylene (PE) below the melting point Tm shows three transition points in which the transition Ȗ occurs in a range between -150 and -100 ° C while the transition α generally occurs between 30 and 100 ° C, depending on the type of PE. It is generally believed that for semi-crystalline polymers the α transition is representative of the crystalline phase and has its origin in fact from some movement within the crystals.

Figure 3A shows the graph of the trend of the viscous dynamic modulus or dissipative modulus (Loss Modulus) as a function of the temperature for the three plastic materials HDPE, LDPE and EVA, as reported in the technical literature. Figure 3B shows the graph of the trend, as a function of temperature, of the damping parameter Tan_delta (i.e. the tangent of the phase delay δ between voltage and deformation in the material, i.e. the ratio between the dissipation modulus and the accumulation modulus , also called damping) for various mixtures of PP and EOC, as reported in the technical literature. Figure 4 shows the graph of the trend as a function of the temperature of the viscous dynamic modulus or dissipative modulus E '' (Loss Modulus), of the elastic dynamic modulus or accumulation modulus E '(Storage Modulus), and of the damping parameter tg_delta of a sample of material taken from a PP polypropylene cap.

The applicant found that the bending (and / or cutting) of a part of a piece obtained by molding of plastic material (for example the bending of a wing portion of a safety band of a plastic cap), if performed at a temperature approximately equal to or lower than the material transition temperature Tα (temperature below which presumably no more movement within the crystallites can occur) and above the transition temperature Tȕ (glass transition temperature), or even higher than the ambient temperature Tamb if Tamb> Tȕ, it is better than a bending (and / or cutting) of the same part (wing portion) performed at a temperature higher than the transition temperature Tα (for example by bending immediately after the hot molding of the cap with band, using a tool inside the same mold or as soon as the cap is extracted from the mold), or respecting or to a bending (and / or cutting) of the same part (wing portion) performed after cooling the molded piece (cap with guarantee band provided with a wing portion) at room temperature.

In particular, it has been found that if the bending of the flap portion of the safety band is carried out at a temperature approximately equal to or lower than the transition temperature Tα, the springback of the flap portion itself is reduced after the bending operation. . This reduction in springback could be due to the fact that at the transition temperature Tα or at temperatures slightly below Tα, some parts or areas or components of the semi-crystalline plastic material that form the cap (for example the crystallites contained in the mass of material ) have lost at least part of their mobility. It has also been found by the applicant that bending at the aforementioned temperature (higher than the ambient temperature and approximately equal to or slightly lower than the temperature Tα) does not produce on the folded part, in particular along the bending area, significant phenomena of yielding or other types of weakening.

In greater detail, it has been found that in a plastic cap, for example as one of those described with reference to Figures 5 to 18, in which the flap can be folded with known systems, for example with the described folding system with reference to figures 1A to 1E, this folding (and / or cutting of the easy release zone) is carried out with particular effectiveness at the following temperatures: for a cap in high-density polyethylene HDPE in a temperature range between 15 and 60 ° C, for a PP polypropylene cap in a temperature range between 25 and 70 ° C.

The caps illustrated in Figures 5 to 18 are molded products in plastic material each equipped with a part (in particular the wing or flange portion of the safety band) which can be folded according to the method of the present invention and / or with a part that can be cut to form the easy detachment area of the guarantee band. The products illustrated here represent only some examples of products, in particular caps for containers, for which it is possible and convenient to use the present manufacturing method. It is in fact possible to foresee that other products are manufactured with the present manufacturing method. In general, the manufacturing method described here can be applied to any type of product made of a material which has a transition temperature of the alpha type Tα higher than the ambient temperature. In particular, the manufacturing method can be usefully applied for semi-crystalline polymers.

In the examples illustrated here, the molded products (in particular they are caps with an annular safety band to witness the first opening of a container closed by the cap itself) each have an annular part (or portion with wings) which is folded afterwards. forming and which is connected to the rest of the body of the product along a connection zone or bending zone of annular shape. However, it is possible to provide for the use of the manufacturing method described here also for folded elements not having an annular shape and / or not connected to the rest of the body of the molded piece along an annular-shaped connection or folding area.

It is possible to provide, in particular to reduce both the yielding in the bending area and the elastic return after bending, that the aforementioned bending temperature is higher than a limit temperature Tinf equal to

where Tα is the alpha-type physical transition temperature of the plastic material, and Tamb is the ambient temperature (which can be considerably variable depending on the manufacturing site).

Particularly in order to reduce both the yielding in the bending area and the elastic recovery after bending, the aforementioned bending temperature can be lower than a limit temperature Tsup equal to Tsup = Tα 10 ° C, where Tα is the transition temperature alpha-type physics of the plastic material.

The aforementioned bending temperature could be included, for example for the particular purpose of reducing both the yielding in the bending area and the springback after bending, in a range of values with an upper limit value Tsup = Tα Δsup and a lower limit value Tinf = Tα - Δinf, where Δsup is between 0 ° C and 20 ° C and Δinf is between 0 ° C and 40 ° C. The bending temperature could be included, for example, between Tα - 40 ° C and Tα, or between Tα - 40 ° C and Tα 10 ° C, or between Tα - 20 ° C and Tα.

The aforementioned plastic material used in forming the product can comprise, as mentioned, a semi-crystalline plastic material, in particular one of the following materials or a mixture of materials containing at least one or more of the following materials: polyethylene, polypropylene, polyethylene terephthalate.

It is possible to provide, after the molding phase and before the bending phase, a controlled cooling phase of at least a part of the molded piece to be bent. This cooling phase may include the operation of directing a flow of a cooling fluid (for example air) towards the part of the molded piece to be cooled. The cooling fluid can have a predetermined temperature and can be controlled by thermal conditioning means (of known type) which can be equipped with a control unit which receives a desired temperature value of the cooling fluid and / or of the product to be cooled.

It is possible, for example, that during the aforesaid cooling the molded piece is moved along a predetermined cooling path comprised between a molding area and a bending area. Such a cooling path may include, for example, a transfer channel (closed or at least partially open), and / or a rotating tunnel, and / or a cooling silo, and / or a conveyor belt, or any other cooling system. , particularly suitable for operating continuously or discreetly on a series or a considerable number of products. It is possible to provide that along the aforementioned path measuring means are provided to detect the temperature of the products (in particular of the area intended for folding) and / or the temperature of an area of the path itself, and that these measuring means are configured to emit a signal that is received by a control unit which can, for example, control cooling means placed along the path and / or can control the travel time of the molded pieces along the path itself in order to vary the temperature, for example example with a feedback control according to a desired temperature.

With reference to Figures 5 and 6, a plastic cap made with the method in question is illustrated. The cap can be made of a semi-crystalline plastic material. The cap has a closure portion 6 (upper portion, where by upper we mean the position that this portion assumes in the usual closure configuration in which it closes the upper mouth of a container normally arranged in vertical elevation) of a substantially flat shape or discoid. The closing portion 6 can be substantially circular.

The cap also has a jacket portion or tubular portion 7 that emerges from the peripheral end of the upper portion 6. The jacket portion 7 can carry internally (as in this case) a thread for coupling with a corresponding thread carried by the neck of the container. It is possible to provide other types of caps equipped with a coupling system (of a known type) with the container other than the screw coupling.

At the end of the jacket portion 7 opposite the closing portion 6 an annular safety band 8 is connected, configured to detach from the jacket portion 7 at the first opening of the container to clearly signal the first opening. The annular safety band 8 is connected to the jacket portion 7 by means of an annular area of facilitated breaking. This facilitated breaking area can be obtained after molding by means of the material removal action obtained with a known type of cutting tool. In the cap, the breaking zone was obtained by cutting and indicated with a dashed line 9.

The annular safety band 8 is equipped with an annular part with a flap 10 folded inwards and upwards (with reference to the configuration of use of the cap coupled to the neck of the standing container). This annular wing part 10 is intended, upon the first opening of the container, to act in axial abutment relationship with a abutment element (for example a collar) protruding radially from the neck of the container to limit or prevent the axial movement of the safety band. in solidarity with the rest of the cap when it is lifted to allow the container to be opened.

In the specific case, the annular wing part 10 is formed by a body extending in a circumferential direction around the edge of the safety band 8. This annular wing part 10 has a series of radial projections or corrugated elements. In the specific case, this annular wing part 10 comprises a plurality of triangular elements connected in series one after the other along a respective side. This annular part with a folded flap 10 can comprise an upper edge, which is oriented upwards (with reference to the configuration of use of the cap that closes the upper neck of the container placed upright), that is, which faces the upper part of the closure 6 of the main body of the cap, in which this upper edge has a wavy or zigzag shape, forming as a whole a plurality of radial protrusions inward and arranged side by side to each other in a circumferential direction.

In the specific case, the cap has a sealing seal 11, for example shaped like a disc, arranged below the upper closing portion 6 and intended in use to seal fluid, in a known way, on the upper end of the container neck. .

The annular wing part 10 undergoes a folding operation in the configuration of use, such as that illustrated in Figures 1A to 1E, after the cap has been molded (the molding taking place by injection, compression, or with other known systems of hot forming of plastic material).

The bending operation may consist, as mentioned, in modifying the orientation of the wing part 10 in a mechanically guided way. Typically this orientation is modified so that the wing part 10 is displaced from a configuration in which it is facing downwards (again with reference to the configuration of use of the cap), i.e. facing away from the upper closing portion 6 of the cap, to a configuration in which it faces upwards, i.e. towards the aforementioned upper closing portion 6. The folding operation takes place using a substantially known folding tool, i.e. any one of the known type folding tools for folding in the use position of an annular wing part of a safety band of a molded plastic cap. As mentioned, the bending operation takes place when the temperature of the molded piece, in particular the temperature of the wing part to be folded, is lower not only than the forming temperature or the outlet temperature of the molded piece from the molding cavity, but more particularly at an even lower temperature, ie lower than the alpha transition temperature of the plastic material with which the cork is made.

In particular, if the temperature Tα of the material is around 80 ° C, the bending temperature is around 40-80 ° C, or around 70-80 ° C; if the temperature Tα is around 70 ° C, the bending temperature is around 40-70 ° C, or around 60-70 ° C; if the temperature Tα is around 100 ° C, the bending temperature will be around 60-100 ° C, or around 90-100 ° C. In practice, it is possible and advantageous to use a temperature range that goes from Tinf = Tα - 30/40 ° C to Tsup = Tα 0/10 ° C.

The operation of forming the area of facilitated detachment of the safety band occurs subsequently, in practice immediately after, (or previously, in practice immediately before) so that the temperature at which this subsequent operation is performed is substantially the same, or slightly lower, or slightly higher, (for example with a difference of no more than 5-15 ° C less or more), to the bending execution temperature. As said, the formation of the facilitated detachment zone can comprise a removal of material carried out, in particular, by means of a cutting tool. Therefore also the cutting operation (which generally includes a continuous cut or a series of cuts performed along an external or internal circumferential area of the cap) can take place with advantage at a temperature approximately equal to or lower than the alpha transition temperature of the cap material.

The cutting devices used for forming the easy detachment areas are of a known type and therefore do not require particular explanations.

With reference to Figures 7 to 10, a second type of cap is illustrated. The elements similar to those of figures 5 and 6 have been indicated for greater clarity with the same numbering. As in the previous case, the cap is manufactured with a bending of the annular wing part 10 at a temperature chosen according to the type of material and, in particular, to the alpha transition temperature of the material itself. Also in this case, the bending operation can take place at a temperature approximately equal to the alpha transition temperature or at the same temperatures described above. In the specific case, the annular wing part 10 comprises a strip of material with a substantially continuous height and equipped with a plurality of notches or through holes 12 arranged spaced apart from one another in a circumferential direction along the bending area.

Figures 11 to 13 illustrate another example of a cap provided with an annular part with a fin with characteristics that are still different from the previous examples. The elements similar to those in figures 5 to 10 have been indicated with the same numbering. In particular, this annular fin part 10 (which is shown here in the configuration of use, therefore after bending at the predetermined temperature) comprises a series of steps which are defined by parts of fins at different heights which alternate with each other in a circumferential direction. In the specific case, moreover, some winged parts comprise a series of end portions 13 folded inwards to give rise to a series of abutment elements which as a whole define an abutment element (substantially extended along a ring) intended for the abutment axial with the container neck collar. Each of such end portions emerges from an end edge of the fin parts of greater height. The annular detachment area will be performed, in a known way (for example by material removal), at the predetermined temperature lower than the temperature Tα, for example immediately after or immediately before the bending operation. The temperatures of bending and removal of material are however chosen, also for this cap, with the same criteria described above.

Figure 14 illustrates a further example of a cap that can be made with one of the manufacturing methods described above. In this example the fin part 10 comprises a plurality of fin portions (for example rectangular or trapezoidal) arranged side by side along an end edge of the safety band 8. These fin portions are spaced apart from each other. one from the other in the circumferential direction. These flap portions form a plurality of flap-like (folded) and mutually independent abutment elements. The bending and material removal temperatures are selected as described above.

It is therefore envisaged that a cap is manufactured with a bending of the annular wing part 10 at a temperature chosen according to the type of material and, in particular, to the alpha transition temperature of the material itself, and in which the operation of formation of the facilitated detachment zone (an operation which may include a material removal by means of a cutting tool) is carried out before (or after) the bending operation of the annular wing part. The two operations (material removal and bending) can take place in rapid succession (by means of known devices), so that in practice the execution temperature is, for both operations, lower or almost equal to the transition temperature. alpha of the material and higher than ambient temperature.

It is also possible that no bending operation is envisaged in a cap but that an operation of formation of the facilitated detachment area is provided (an operation which may include, as mentioned, a removal of material by means of a cutting tool) and that this operation is carried out to a temperature chosen as described above, i.e. based on the type of material and, in particular, on the alpha transition temperature of the material itself, so that in practice the execution temperature can be approximately equal to or lower than the alpha transition temperature of the material.

Figure 15 shows a plastic cap equipped with a detachable guarantee band 8 when the container is first opened in which the facilitated detachment area has been obtained by means of a material removal operation, in particular by cutting, performed at a temperature chosen as described above. In this specific case, the contrast element 14, which cooperates in a known way with a corresponding contrast agent on the neck of the container, does not have, as in the previous examples, wing parts that must be folded after extraction from the molding cavity.

In the cap of Figures 16 and 17 the wing portion 10 has been folded simultaneously, or immediately before, or immediately after, with respect to the shaping by cutting of the facilitated detachment area. In this case, this detachment area comprises a continuous cutting line which sinks into the material of the jacket portion of the cap without sinking completely into several protrusions 15 (which emerge towards the inside of the cap) angularly spaced from each other so as to to form connection areas (bridges intended for fracture) between the guarantee band 8 and the rest of the cap.

Figure 18 shows the continuous cutting line, which forms the easy detachment zone 9, in the presence of the series of radial projections 15 (facing towards the inside of the cap) arranged spaced apart in a circumferential direction, whose thickness is not fully affected by the cut.

With reference to figures 19A and 19B, which illustrate a first example of a layout of a plant for implementing a method for the manufacture of molded products in which both the folding and the removal of material are performed, 101 indicates a cooler, with 102 and 103 two feeders of plastic material in sliding solid form to be processed, with 104 a material mixer, with 105 a compression molding apparatus for forming caps in particular, with 106 an optical control system of the caps with 107 a heat exchanger, with 108 a cooling device for the molded caps, with 109 an elevator (for example of the cup type) for the caps, with 110 a device for orienting the caps, with 111 a conveyor for the '' advancement of the caps (for example of the air jet type), with 112 a cutting and folding device (to form the facilitated breaking area and to bend the flange of the band of guarantees to caps), with 113 another optical cap control system, with 114 a device for introducing the caps into packaging containers. It should be noted that in the system of figure 15 the cooling of the caps before the bending and cutting area is carried out by means of specific cooling actuators which are configured to bring the caps to the bending and cutting area at the predetermined temperature approximately equal to or lower. at the transition temperature Tα. The known type of cutting and folding device 112 comprises two continuous-operation vertical axis carousels, each equipped with a plurality of identical working apparatuses which operate in a cyclical manner, completing a work cycle at each revolution of the carousel, in which the two carousels are part of a work path along which a series of pieces to be worked continuously proceeds arranged in a row one after the other.

With reference to figures 20A and 20B, which illustrate a second example of layout of a plant for implementing a method for manufacturing molded products, with 201 a cooler has been indicated, with 202 and 203 two plastic material feeders in the form sliding solid to be processed, with 204 a material mixer, with 205 a compression molding apparatus for forming caps in particular, with 206 an optical control system of the molded caps, with 207 a conveyor for feeding the caps ( for example of the air jet type), with 208 a cutting and folding device (to form the facilitated breaking zone and to bend the flange of the guarantee band of the caps), with 209 another system for optical control of the caps, with 210 a device for introducing the caps into packaging containers. It should be noted that in the system of figure 16 the cooling of the caps before the bending and cutting area is carried out by means of the appropriate adjustment of the residence time of the caps between the molding area and the cutting-bending area so that the temperature of shear-bend is the desired one, i.e. approximately equal to or lower than the transition temperature Tα. The cooling of the caps could take place by adjusting the temperature of the air (or other transport fluid) used to advance the caps (with a known type of fluid transport system); if the advancement of the caps takes place in another way (for example by means of a conveyor belt), the temperature control can be performed using air or other fluid introduced into the transport channels.

The cutting and folding device 208 is of the type described above. All the known devices used for this purpose are included among the cutting devices that can be used for forming the easy release area, such as the devices described in the following patent publications EP 0619168, WO 99/17911, WO 00/44538, WO 2004 / 004993, which are hereby incorporated by reference.

Figure 21 schematically illustrates the lay-out of a continuous cycle folding device which can be used for folding, according to the various methods described above, the wing portion of a guarantee band for caps. Figure 21 shows the path (in continuous advancement in the direction indicated by the arrows) of the caps 16 which includes an inlet system which introduces the caps one after the other in a rotating carousel 17 with a vertical axis equipped with a series of bending tools (not shown) that operate continuously (in a known way) along the circular path of the caps so that each cap is associated with at least one bending tool, and an output system that picks up the caps after bending and starts them, always one after the other, to the following operational areas.

Figure 22 schematically illustrates the lay-out of a cutting device that can be used for forming the easy release zone, according to the various methods described above, of a guarantee band for caps. The cutting device (of known type) comprises an inlet path for the continuous advancement of the caps 16 one after the other, a cutting carousel 18 which picks up the caps one by one and moves them towards a cutting tool 19 (in this case arranged inside the circular path of the caps 16) with a motion that allows (in a known way) the formation of the easy release zone.

Figure 23 shows in section a detail of a cutting device (of known type) comprising a carousel 20 for moving the caps which leads the caps 16 towards the cutting tool 21 (which in the particular case operates outside the circular path caps). The cutting device illustrated here is configured in particular for the formation of a continuous cut along an entire circumference of the cap (which is made to rotate on itself) and may be particularly suitable for caps with projections arranged along the detachment area. , such as the projections 15 in figures 16 and 18. The structure and operation of the cutting device of figure 23 are substantially known.

Claims (15)

CLAIMS 1. Method comprising the steps of: - molding a piece in a plastic material, said molded piece having at least a first portion and a second portion connected to said first portion along a connection zone; - mechanically bending said second portion in a guided manner around said connection zone at a bending temperature higher than room temperature; characterized in that it comprises the step of selecting said bending temperature as a function of at least one intermediate physical transition temperature of said plastic material. Method according to claim 1, wherein said at least one intermediate physical transition temperature comprises the alpha-type physical transition temperature of said plastic material. Method according to claim 1 or 2, wherein said bending temperature is lower than the alpha-type physical transition temperature of said plastic material. Method according to any one of the preceding claims, wherein said plastic material comprises at least one semicrystalline plastic material. Method according to claim 4, wherein said semicrystalline plastic material comprises at least one material selected from the following group of materials: polyethylene, high density polyethylene, polypropylene, polyethylene terephthalate. Method according to any one of the preceding claims, wherein said first portion comprises a liner portion and said second portion comprises an edge portion. Method according to any one of the preceding claims, wherein said bending temperature is higher than the beta-type physical transition temperature of said plastic material. Method according to any one of the preceding claims, comprising a step of cooling at least a part of said molded piece, said at least a part of said molded piece comprising said first part and / or said second part and / or said connection area, said cooling step being performed before said folding step and also being performed in a controlled manner in order to make said at least one part of said molded piece reach the desired folding temperature. The method of claim 8, wherein said cooling step comprises directing a flow of a cooling fluid towards said at least one part of the molded part to be cooled. Method according to claim 8 or 9, wherein said cooling step comprises moving said molded piece along a predetermined cooling path comprised between a molding area and a folding area. Method according to any one of the preceding claims, wherein said connection area is annular in shape. Method according to any one of the preceding claims, wherein said bending temperature is higher than a limit temperature Tinf equal to Tα being the alpha-type physical transition temperature of said plastic material, and Tamb being the ambient temperature. Method according to any one of the preceding claims, wherein said bending temperature is lower than a limit temperature Tsup equal to Tsup = Tα 10 ° C Tα being the physical transition temperature of the alpha type of said plastic material. Method according to any one of the preceding claims, wherein said bending temperature is higher than a limit temperature Tinf equal to Tα being the physical transition temperature of the alpha type of said plastic material. Method according to any one of the preceding claims, comprising a step of removing material from said molded piece at a material removal temperature selected as a function of said at least one intermediate physical transition temperature of said plastic material, said removal temperature of material being included in an interval equal to said bending temperature plus / minus 15 ° C.