WO2004078444A2

WO2004078444A2 - Process and mold for plastic pack molding

Info

Publication number: WO2004078444A2
Application number: PCT/BR2004/000007
Authority: WO
Inventors: Paulo R. Villas; Eugenio F. N. Barroso
Original assignee: Logoplaste Do Brasil Ltda.
Priority date: 2003-03-07
Filing date: 2004-02-06
Publication date: 2004-09-16
Also published as: BR0300672A; WO2004078444A3

Abstract

The present invention refers to a process and mold (1) for plastic pack molding by using the blow molding technique by extrusion with cavities joined by the neck by a lost-head (20). The process of the present invention basically comprises: (i) formation of parisons (13); (ii) closure of the mold (1) so that the higher (2) and lower (3) cavities are closed over said parisons (13) by pressing and welding the ends of said parisons on the regions of higher (7) and lower (8) insert; (iii) clipping the lost-head region (4) with tweezers; (iv) advance of a set of needles (11), so that all blowing needles penetrate simultaneously through all parisons included in the mold; (v) feeding of pressed air until the walls of the parisons touch the internal surface of higher (2) and lower (3) cavities; (vi) air exhaustion and opening of the mold (1) to extract the packs which are suspended by the lost-head (20); (vii) stamping of newly molded packs to take out the scraps (17) from the bottoms; and (viii) transport of the packs to a cutter, in which packs are separated from the lost-heads (20). The invention also deals with an appropriate mold (1) to be used in the process disclosed.

Description

"PROCESS AND MOLD FOR PLASTIC PACK MOLDING"

FIELD OF THE INVENTION

The present invention refers to an extrusion blow molding process for packs production and to a mold to manufacture packs. More specifically, the present invention refers to a process to significantly increase plastic molding productivity, such as flasks, bottles, gallons and hollow recipients in general.

More particularly, the present invention refers to a mold for plastic pack molding that allows the maximization of the number of cavities and consequently improves the productivity of blowers.

In additional, the present invention refers to a plastic packs manufacture process by means of extrusion blow molding for the production of plastic packs formed from molds that allows the maximization of cavities, thus obtaining considerable production gain, optimizing the use of the blower and the productivity of this operation.

The process and mold of the present invention can be embodied and used respectively for the continuous or reciprocating extrusion blow molding process wherein:

- in continuous extrusion, the mold is moved to an adjacent station where parisons are being formed, the mold captures the parisons and then returns to the molding station;

- in reciprocating extrusion, the parison forming station is positioned on the molding station, so that the mold does not move from one station to another. In this case, the plastic resin is accumulated over the mold while the mold is closed. The plastic resin is released at a single time after withdrawing the newly molded packs for the following cycle.

BACKGROUND OF THE INVENTION The blowing process has been known for many decades and has been continually studied by those skilled in the art with the purpose to develop alternative process and machineries, in order to increase the productivity and simultaneously reduce costs of the production of plastic packs and objects, such as flasks, bottles, gallons, parts and recipients.

The analysis of the extrusion blowing process shows that that the basic steps consist of forming "parisons", which are semi-manufactured hollow tubes of specific plastic for blow molding, being said parisons located inside a mold and attached by their higher end and welded in the bottom. At the higher end, a blowing pin is introduced through a housing. Said blowing pin injects air into said parisons that expand to touch the internal walls of the mold and conform to the geometry of the cavities. Subsequently, molds are opened and packs are taken off for the steps of finishing and later packing and labeling, if it is desired.

Conventional molds of the prior art, use parisons which are located inside the mold with their open' end turned above, thus allowing to form just one pack per cavity since compressed air injection is made through said open end.

Although expensive, the use by many companies manufacturing bottles, flasks, gallons and machinery recipients in which the parison comprises two flasks joined by their bases, i. e. by the closed ends of the tubes is already known. In this configuration, one single mold allows to manufacture at least two objects at the same time. However, the blowing machine needs two sets of blowing pins, a higher one and a lower one, to feed air through the respective parison holes. This configuration has technical and economical application restricted to a few models of blowers, which are currently considered as outdated.

Another process variant using molds with cavities joined by the neck is also known, but this process is restricted to a single parison, and is usually applied to blowers which molds are located in a wheel-type table. This process is limited by the fact that the blowing needle penetrates into said parison diagonally at 45°, thus needing a relatively large distance between the centers of the cavities to accommodate and penetrate the blowing needles, consequently reducing the number of cavities to form the packs. Complex machinery is another inconvenience of this process, because the full disassembly of the molds is required to reach the access to the blowing needles and the respective internal devices of the mold, i.e. disassembly of all components comprising the mold, causing undesired stops of the blower and consequent economical losses to pack manufacturers.

BRIEF DESCRIPTION OF THE INVENTION

It is therefore an object of the present invention to overcome the inconveniences of the processes and molds for blow molding plastic pack production known in the state of the art.

Another object of the present invention is to provide an efficient process and mold to obtain a safe and highly productive process, maintaining the quality of the pack in comparison to conventional systems.

Another object of the present invention is to provide a process and mold for the production of plastic recipients, particularly flasks, bottles and gallons by extrusion blow molding, in which each mold has a single set of blowing needles that allows the simultaneous production of at least two pairs of packs for each parison in single mold machines. It must be understood that the present invention is not limited to these types of machines, and may be used in other types of machines, such as double mold stations.

It is also a further object of the present invention to provide a process and mold for the manufacture of plastic packs with high productivity and no risks of damage or leakage for the packed products.

The present invention has also the object to reduce distances between the centers of cavities, in order to increase the number of cavities of a mold without increasing its dimensions because, according to the present invention, the blowing needles penetrate into the parisons horizontally and perpendicularly in response to the plane of the mold closure. According to this configuration, the access to the blowing needles becomes easier, since it is only necessary to disassembly the component in which the blowing needles are located. The disassembly is made with the mold assembled on the blower and consequently reduces the idle time for maintenance and increases the machine productivity.

A further object of the present invention is to provide a process and mold for the blow molding production of plastic recipients, which reduces the manufacturing costs by increasing the productivity of the process in comparison with processes and molds of the state of the art.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, enhancements and effects of the process and mold for plastic pack molding, object of the present invention, will be evident for those skilled in the art from the attached schematic figures, in which:

- Figure 1 is a front view of a mold containing various cavities for plastic bottle manufacturing of the present invention;

- Figure 2 is a front view of a closed mold with parisons located inside the cavities;

- Figure 3 shows the mold of Figure 1 in an upper view of the crosswise section showing the detail of the blowing needles introduced into the parisons and their respective mechanism;

- Figure 4 shows the mold object of the present invention being closed to press the parisons;

- Figure 5 is a detailed cross-sectional view of the mold for plastic bottle molding, object of the present invention; 6

- Figure 6 is a view of newly molded bottles according to the invention;

- Figure 7 shows a view of the medium section of the lost-head region with the blowing needle introduced into the parison; and

- Figure 8 shows the bottles of Figure 6 being separated one from another in a peripheral device (cutter), which cuts and finishes the necks.

DETAILED DESCRIPTION OF THE INVENTION The plastic bottle manufacturing process using molds of the present invention comprises the following basic steps:

- Forming parisons;

- Closing the mold to close the higher and lower cavities over their respective parisons,

• pressing and welding the ends of said parisons on the regions of higher and lower insert;

• clipping them in the region of the lost-heads (oval section) where the needle penetrates;

- advancing a set of needles to penetrate all blowing needles horizontally and perpendicularly to the plane of the mold closure and substantially simultaneously through all parisons included in the mold;

- Feeding compressed air through the needles, causing the expansion of parisons until they touch the internal surface of the higher and lower cavities, quickly cooling and assuming their geometrical shape;

- exhausting the air followed by opening the mold to extract the packs which are suspended by pins located at the higher region of cavities through scraps of the bottoms formed by the higher cavities;

- Stamping newly molded packs to take off the scraps from the bottoms; and

- Transporting the packs to a cutter, in which packs are separated from the lost-heads.

The parison formation step is conventional, made in an extruder coupled to a head to form parisons. The process starts by feeding a plastic resin at ambient temperature that is plastified by means of mechanical and thermal work. At the outlet of the extruder, the mass of resin goes through the head in which parison(s) are formed.

Said parisons are pressed when molds are closed and their ends are welded to the cavities. Simultaneously, the insert of the lost-heads partially arrest the parisons on the lost-head region to guarantee additional strength to the parisons in order to avoid their collapsing when the blowing needles are introduced to feed pressed air.

The set of needles advances towards the mold and penetrates simultaneously through all existing parisons, with all said needles positioned horizontally and perpendicularly to the mold. Said needles are introduced in a non-centered manner in the lost-head region, which section presents oval contour. All these requirements are necessary to avoid the collapse of the parison during penetration of the needles and to guarantee the efficiency of the flask production.

When the set of needles is fully advanced and needle edges are appropriately positioned in the parisons, the feed of pressed air starts, thus expanding the parisons until their walls touch the internal surfaces of the mold higher and lower cavities and shaping the packs that are linked by their respective lost-heads.

At the end of the parison blowing step, air is exhausted and the mold is opened. Simultaneously, an extraction device advances by means of springs towards the lost-heads. After the opening of the mold, the newly molded packs are suspended by the scraps formed on the bottom of the upper packs, which on the other hand are attached by conveyor pins. In the following cycle, said extraction device is recessed at the same time when the mold is closed jointly with the parisons to form new packs in the subsequent cycle process.

Subsequently, newly molded packs, still joined by the lost-heads, are sent to the stamping step, in which scraps will be taken off from the higher and lower cavities. Subsequently, said packs are transported by a set of belts or mats to a cutter to separate said packs from the lost-heads in order to pack, label and sell the molded packs.

The process disclosed above is appropriately executed with the use of the mold shown in Figures 1 to 8, mentioned above, which is described below. Bearing in mind the high number of constituents of the mold for plastic pack molding of the present invention, and to facilitate the understanding of the present invention, some numerical references are not reproduced in all figures, since it would be difficult to understand some important details.

According to the figures mentioned above, a mold (1) is provided with various higher (2) and lower (3) cavities, in which higher cavities (2) are interconnected to the lower cavities (3) by means of the lost-head region (4). The mold (1) is basically formed by the lateral insert (5) that form the side walls of said cavities (2) and (3) fitted on the insert of the lost-heads (6). The mold is closed by the insert on the higher (7) and lower (8) bottom, which are provided with a region (9) to form pack bottoms and cool scraps. It should be observed that the insert of the lost-heads (6) corresponding to the shape of the lost-head regions (4) present simplified configuration, which facilitates their quick disassembly, thus allowing access to the blow needles and respective internal devices of the mold. To disassemble this constituent, just a few screws need to be taken off and this operation may be realized within a few minutes, not requiring to take off the mold from the blower.

In the lost-head additional (6), and more specifically in the lost- head region (4) of each set of higher and lower cavities (2) (3), a channel (10) is provided to introduce the blowing needle (11). Said channel (10) is located between the extractors (12) of the device to extract the plastic packs from respective cavities for the start of the mold opening (1). It should be stressed that for each set of cavities (2) and (3) there is just a single channel (10). The channel (10) is not in a centered position towards the vertical center line of the higher (2) and lower (3) cavities to penetrate the needle edges (11) in the parisons (13) in the most favorable position, avoiding the closure of them (by collapse), which would cause molding failure and loss of packs.

Just as an example, the attached figures show a particular mold to manufacture plastic bottles, which should not be considered as a limitative example of one embodiment of the present invention, but rather just an explanatory. Figures 2 and 3 show a mold (1) containing five sets of higher (2) and lower (3) cavities for the manufacture of plastic bottles (18), (19) (shown by Figure 6), in which each set of cavities is able to manufacture two bottles, which are fixed by the lost-heads (20). For each set of cavities (2) and (3), a parison (13) is used. The shape of the parison may vary according to the surface of the object to be molded. Still in that example, the parison (13) has a cylindrical shape, although their higher (14) and lower (15) ends have other shape when smashed during the accommodation in the regions (9) of the respective higher (7) and lower (8) insert.

Specifically on Figure 3, said mold (1) crosswisely receives a set (21) formed by various blowing needles (11) which are decentralized introduced through the channels (10) of the mold (1). The number of needles (11) located in the set (21) varies according to the number of parisons that in turn vary according to the capacity of the blower and manufacturer's requirements. In the attached figures, a set of needles is shown as an example to meet five sets of higher (2) and lower (3) cavities and manufacture ten bottles (18) and (19) per mold in a single cycle. Said set (21) may comprise at least two needles, but a 10

higher number is possible as long as all required technical aspects are met.

Said parisons (13) are pressed inside the higher (2) and lower (3) cavities when the mold (1) is closed and their ends (14), (15) are welded to the regions (9) of the insert (7) and (8). Figure 4 shows said parison (13) shortly before the closure of the mold (1).

Figure 5 shows further details of the mold (1) according to the example above. The mold is used for the manufacture of plastic bottles. Figure shows that the lost-head interconnects higher (2) and lower (3) cavities, which have the shape of bottles. It is also shown the channel (10) to introduce the blowing needle (11) located between the extraction device provided with extractors (11).

Still with reference to Figure 5, the higher bottom additional (7) is provided with a channel (16) where transport pins (22) attach the scraps (17) formed on the bottom of newly molded packs in order to carry them to the subsequent stamping and finishing stations.

Figure 6 shows newly molded bottles (18) and (19) provided with lost-heads (20) and joined by them. Shortly after opening the mold (1), said bottles are suspended by the transport pins (22), which attach the scraps (17) of the bottom of the upper bottles (18). This detail is required to forward the bottles to the later finishing step, which includes the removal of scraps from their bottom. In Figure 6, it is observed the detail (A) of taking the parison (13) with tweezers to avoid its collapsing.

Figure 7 shows the section of the lost-head region (4) when the blowing needle (11) is inside the parison (13). The figure shows that the section has an oval contour (23) with the edges being pressed by the lost-head additional (6), guaranteeing the required strength to the parison (13) when the needles (11) are introduced. It is also shown the blowing needle (11) located slightly out of center and positioned at a right angle over the mold (1), i.e. 11

perpendicularly to its closing plane. These features guarantee that the needle (11) penetrates without collapsing the parison (13), which would cause bad formation of molded objects, loss of raw material, interruption of the automatic production cycle and consequent production costs increase.

Figure 8 shows the bottles (18), (19) joined by the lost-head (20) within the cutting station (cutter), shortly after being taken off from the stamping station, where bottom scraps (17) were taken off. Shortly after taking off the bottom scraps, collecting tweezers (not shown) carry the bottles (18) and (19) still joined by the lost-heads (20) to the cutting station (cutter). Inside that station, packs are turned by pulleys (24) and belts (25), and blade devices (26) are provided in their route to cut, consequently separating bottles (18) and (19) from the lost-heads (20). From that point, the bottles (18) and (19) are ready to receive stickers, labels and to be filled.

It must be understood that for those skilled in the art, various accessories, constituents and peripherals may be adapted to the invention to automatically mold packs to increase the productivity of manufacturers, not however deviating from the scope of the invention as defined in the attached claims.

Claims

12CLAIMS

1. A PROCESS FOR PLASTIC PACK MOLDING, by using blow by extrusion, characterized by steps of:

(i) forming multiple parisons;

(ii) closing the mold to close the higher and lower cavities over said parisons by pressing and welding the ends of said parisons on the regions of higher and lower bottom insert;

(iii) clipping the lost-head region with tweezers;

(iv) advancing a set of needles to penetrate all blowing needles, horizontally and perpendicularly to the plane of mold closure and substantially simultaneously through all parisons included in the mold;

(v) feeding com pressed air through the needles, causing the expansion of parisons until they touch the internal surface of the higher and lower cavities, quickly cooling and assuming their geometrical shape;

(vi) exhausting the air followed by opening the mold to extract the packs which are suspended by conveying pins located at the higher region of the insert higher bottom through the bottom scraps;

(vii) stamping of newly molded packs to take off the scraps from the bottoms; and

(viii) transporting the packs to a cutter, in which packs are separated from the lost-heads.

2. PROCESS FOR PLASTIC PACK MOLDING of claim 1 , characterized in that during the closing step of said mold, the insert of the lost- heads fix the region of each lost-head, thus guaranteeing additional strength to said parisons at the time when blowing needles are introduced.

3. PROCESS FOR PLASTIC PACK MOLDING of claim 1 , characterized in that at the same time when the mold is being opened, the extractors of the extraction device advance towards the lost-heads to extract the 13

molded set from inside the cavities.

4. PROCESS FOR PLASTIC PACK MOLDING of claim 1 , characterized in that the introduction of blowing needles within said parisons is decentralized in response to the center line of the lost-head region.

5. MOLD FOR PLASTIC PACK MOLDING characterized by the fact it comprises:

- side insert (5) forming the walls of the higher (2) and lower (3) cavities;

- said insert (5) are fit into insert of the lost-heads (6) and closed by the insert of higher (7) and lower (8) bottom;

- each higher cavity (2) is interconnected to the lower cavity (3) through the lost-head region (4);

- said additional of the lost-heads (6) is provided with appropriate channels (10) for the introduction of blowing needles (11) and provided with extractors (12) from an extraction device to take off newly molded packs (18), (19);

- said newly molded packs (18), (19) are attached opposed to the lost-heads (20);

- said channels (10) are decentralized and perpendicular to the mold (1) and the blowing needles (11) penetrate the parisons (13) and not collapse them.

6. MOLD FOR PLASTIC PACK MOLDING of claim 5, characterized in that said higher (7) and lower (8) bottom insert are provided with a region (9) to accommodate and weld the ends (14) and (15) of the parisons (13).

7. MOLD FOR PLASTIC PACK MOLDING of claim 5, characterized in that the insert of the lost-heads (6) fix the parisons (13) and form an oval contour (23) for the introduction of blowing needles (11). 14

8. MOLD FOR PLASTIC PACK MOLDING of claim 5, characterized in that said mold (1) can comprise various sets of higher (2) and lower (3) cavities.