Equipment for thermoforming polypropylene bands

Abstract: The equipment comprises band heating plates, a pressing station where transverse rows of blisters are made on a band by a die, a device for advancing the band in step, a striker device located at the outlet of the pressing station and operated in a suitable phase relationship with the advancement in step of the band, after every pressing stage. The striker device comprises a plurality of pins which are borne by a movable bar on a plane transverse to the band and which are suited to intercept, when the die is closed, a transverse row of blisters of the band, so as to prevent any sliding of the portion still to be formed.

Description: This invention relates to the technical field concerning the thermoforming of polypropylene bands. Various types of automatic equipment are known, for making parallel rows of blisters on a band of thermoformable material. The blisters are suited to contain various items, particularly medicinal preparations, like capsules, pills, tablets, and the like. The blister band shall later be closed with a film of heat-sealing material, and subdivided into a plurality of equal portions, commonly called blister packs. PVC bands and the like have been used to make blister packs for quite a long time. At the present time, however, the use of polypropylene bands is in great demand, owing to the better biodegradability of that material. These types of equipment usually provide for band preheating means; a pressing station where the formation of blisters on the band is carried out; and pulling means suited to actuate the advancement in step of the band. The pressing station usually features a movable plate and a stationary plate cooperating together to form the blisters; such plates feature respectively a series of hollows having a shape complementary with the blisters to be formed and a corresponding series of holes, coaxial to said hollows, through which compressed air is blown in. The thermoforming of the band is carried out by clamping the band between the die plates, and subsequently blowing compressed air into said hollows through the holes of the stationary plate. In the equipment mentioned above, the need arises to keep constant the step of advancement of the band after every pressing stage, in such a way as to ensure that the transverse rows of blisters are equally spaced from each other. This turns out to be particularly difficult with the polypropylene bands, since this material shows a remarkable shrinkage in the cooling phase. In fact, at the outlet of the pressing station the cooling of the band causes a traction on the portion of the same band which is about to undergo the action of the die plates, and consequently the distance between the two series of blisters is changed. Such a drawback is made even more serious by the features of low isotropy of the material, which may involve, among other things, substantial differences in behaviour among different coils of band. The problem concerning the regularity of distance among the rows of blisters also arises when the operation of the equipment is started again after a stop of any nature. In fact, this may often cause a displacement of the band, if it is not held properly. However, the safety regulations in force do not allow to keep the die plates clamped, in order to keep the band in position, owing to the very high clamping pressure. The DE-A-23 29 393, which forms the preamble of claim 1, discloses a film deep-drawing system wherein the lower die is fitted with an extension with recesses to fit the vessels already deep-drawn in the film, to locate the lower die for the moulding of the next group of vessels. This device ensures a constant interval between moulded vessels, to compensate for film distortion, to prevent displacement at the vessel filling station. In one of the embodiments disclosed therein, the extension with recesses is replaced with a lever arm that is made to move vertically along with the lower mould. The aim of the lever arm is to set the position of the lastly formed vessel wall thus preventing the newly formed vessel to be displaced with respect to the correct position. Moreover the action of the device is possible only with mould being closed. In other words, when the lower mould-half is set away from the upper one, the band is completely free to move with respect to the mould. The object of the invention is to propose an equipment which makes it possible to keep perfectly constant the distance among the blister rows in the thermoforming of polypropylene bands by avoiding shrinkage of the same band both during the normal operation and at the moment of starting again after a stop. A further object of this invention is to propose an equipment for the thermoforming of polypropylene bands which can be realised through a technical solution which turns out to be simple, functional, and reliable, as well as versatile. The objects mentioned above are accomplished through an equipment as described in the following claims and comprising: means for pre-heating the band; a pressing station provided with a die; pulling means suited to cause the advancement in step of the band. The equipment comprises a striker device located at the outlet of the pressing station and operated in a suitable phase relationship with the advancement in step of the band after every pressing stage, with this striker device comprising a plurality of pins which are borne by a bar movable on a plane transverse to the band and which are suited to intercept, when the die is closed, a transverse row of blisters of the band, so as to prevent any sliding of the portion of band still to be formed. With the die closed any slidings of the band are prevented, therefore, when the operation is started again, it is ensured that the distance among blister rows is kept constant. The equipment being the subject of this invention allows to keep perfectly constant the distance among the rows of blisters in the thermoforming of polypropylene bands, both during the normal operation and when the equipment is started after a stopping phase. The features of this invention, not emerging from what has been said above, are pointed out here below, with a particular reference to the drawings enclosed herewith, where: Figure 1 shows a side view of the equipment for the thermoforming of polypropylene bands which is the subject of this invention; Figure 2 shows a side view of the pressing station being a part of the equipment; Figure 3 shows a detailed view of said striker device; Figure 4 shows a sectional view according to the line IV-IV of fig.3; Figure 5 shows a side view of said die with the equipment stopped; Figure 6 shows a cross-section view according to the line VI-VI of fig. 5; Figures 7, 8 and 9 show, in a cross-section view, a different form of construction of said die, respectively illustrated in a pressing phase, with the die open and with the equipment stopped. With reference to the above-mentioned figures, the equipment for the thermoforming of polypropylene bands comprises means for pre-heating the band 1, generically indicated by 2. Such pre-heating means 2 feature a pair of heating plates 3 suited to be closed onto the band 1 by the action of respective jacks 4. Downstream of the pre-heating means 2, in the direction of advancement A, a pressing station 5 is located, designed to form rows of blisters 1a on the band 1. At the outlet of the pressing station 5 the blister band, guided by a stationary striker 6, winds round a pulling means 7 suited to control the advancement in step of the same band. The pulling means 7 is suited to revolve in a suitable phase relationship with the previous phases of pre-heating and pressing of the band 1. The pressing station 5 is provided with a die 8 made up of a movable plate 9, featuring a series of hollows 10 having a shape complementary with the blisters 1a to be formed on the band 1, and a stationary plate 11, from which a corresponding series of strikers 13 are suited to protrude, through respective holes 12. The hollows 10 and the corresponding holes 12 are disposed so to form, according to well-known techniques, a plurality of blister rows 1a transverse to the band 1. The strikers 13 are borne by a plate 14 movable inside a chamber 15 formed by the stationary plate 11 of the die; the movable plate 14 is operated by a jack 16 in a direction transverse to the plates themselves. In the chamber 15 also a duct 17 has its outlet, conveying a jet of compressed air having the purpose to carry out, in a way known in itself, the complete forming of the blisters 1a. At the outlet of the pressing station 5 there is located a striker device 18 suited to keep constant the distance among the transverse rows of blisters 1a when the band 1 is advanced in step after every pressing phase. In substance, the device 18 provides a plurality of pins 19 borne by a bar 20 which is movable on a plane transverse to the band 1. The pins 19 correspond, in practice, to a transverse row of blisters 1a. The bar 20 is guided through a pair of stems 21 inside a cavity 22 comprised in a support 23 integral with the stationary plate 11 of the die and it is subject to the action of two helical springs 24 housed in the same support 23. The pins 19 are suited to protrude through relative holes 25 from the support 23, so to intercept the last row of blisters made on the band 1, at the moment of closing the die 8 for forming a subsequent series of such blisters. On the bar 20 is able to act an end of a rocking lever 26 which has centrally its fulcrum 27 on the stationary plate 11 of the die and bears, protruding at the other end, a pivot 28 which engages a guide cavity 29 made longitudinally on an arm 30 fastened to the movable plate 9. The arm 30 features a slot 31 which allows to regulate the position of the screw 32 for fastening to the movable plate 9. Therefore, at the end of every pressing stage, the opening of the movable plate 9 of the die 8 is actuated, as indicated by the arrow B in fig. 2. The moving of the movable plate 9 causes the revolving of the lever 26 pulled by the arm 30; the lever 26, in its turn, causes the movement of the bar 20 (arrow C), in contrast to the springs 24, so to cause the retraction of the pins 19 into the support 23. The band 1 is then caused to advance by a step by the pulling means 7. Once the advancement of the band 1 is completed, the movable plate 9 of the die is caused to close, in the direction indicated by the arrow D in fig.3. The movement of the plate 9 progressively releases the lever 26, allowing the return of the bar 20 under the thrust of the springs 24 (arrow E). Therefore the pins 19 come out of the support 23 and intercept the last row of blisters previously formed. It is to be noticed that the pins 19 engage the side of the blisters 1a facing the die 8, so that they act as strikers and prevent any shrinkings of the band in the portion already provided with the blisters from affecting the portion of the band still to be formed, by varying the distance among blister rows. In the case that the equipment operation is stopped, the strikers 13 are pushed into the blisters 1a just formed, and are left there while the die 8 is opened, as shown in figures 5 and 6. Therefore, when the die is open, the band 1 cannot slide, in this way the distance among the blister rows is ensured to be kept constant when the operation is started again. According to a variation of construction of the equipment described above, illustrated in fig. 7, 8 and 9, the movable plate 9 is guided through a pair of stems 33 on a stationary frame 34 and it is controlled under pressure by a jack 35, integral with the same frame 34; the stem 35a of the jack 35 is able to strike against the movable plate 9. The movable plate 9 is supported by a pair of auxiliary jacks 36, integral with the stationary frame 34. During the normal operation of the equipment, the jack 35 supplies the pressure necessary for carrying out the pressing phase of the band 1; the stem 35a acts on the movable plate 9, as indicated by the arrow F in fig.9, while the auxiliary jacks 36 act in the opposite direction, so to keep the stem 35a elastically striking against the plate 9. Furthermore, the auxiliary jacks 36 actuate the opening of the movable plate 9, after the thermoforming of the blisters 1a, as indicated by the arrow G in fig. 8. On the other hand, when the operation of the equipment is stopped, the auxiliary jacks 36 actuate the closure of the movable plate 9, as indicated by the arrow H in fig. 9. In that case the die may be kept closed, with the equipment stopped, since the auxiliary jacks 36 operate at a low pressure, differently from the jack 35. With the die closed any slidings of the band 1 are prevented, therefore, when the operation is started again, it is ensured that the distance among blister rows is kept constant.

Claims: An equipment for the thermoforming of polypropylene bands, comprising: means (2) for pre-heating the band (1); a pressing station (5) provided with a die (8) made up of a movable plate (9), featuring a series of hollows (10) having a shape complementary with the blisters (1a) to be formed on said band (1), and a stationary plate (11) featuring a series of holes (12), respectively coaxial with said hollows (10), through which compressed air is blown in to form, in cooperation with said hollows (10), transverse rows of said blisters; pulling means (7) suited to cause the band (1) to advance in step; a striker device (18) located at the outlet of said pressing station (5) and operated in a suitable phase relationship with the advancement in step of said band (1) after every pressing stage, with said striker device (18) comprising a plurality of pins (19) which are borne by a bar (20) movable on a plane transverse to the band (1) and which are suited to intercept, when said die (8) is closed, a transverse row of blisters (1a) in a portion of the band (1) already provided with blisters, so to prevent any slidings of a portion of band still to be formed; the equipment being characterised in that said bar (20) is linked to said movable plate (9) of the die (8) by means of a rocking lever (26) pivoting on said stationary plate (11) and acting with an end on said bar, so that when said movable plate (9) is pressed against said stationary plate (11) said pins (19) are pushed out to intercept said transverse row of blisters (1a), while when said movable plate (9) is moved away from said stationary plate (11) said pins are drawn back to release said blisters (1a); and in that it further includes a plurality of strikers (13) borne by a plate (14) movable inside a chamber (15) formed in said stationary plate (11) of the die (8), said plate (14) being moved by a jack (16) towards said band (1), in case that the equipment operation is stopped, in such a way that said strikers (13) are pushed into said blisters (1a) just formed on the band (1) and kept there while the die (8) is opened, so as to prevent any slidings of said band (1). An equipment according to the claim 1, characterised in that said rocking lever (26) is guided at another end in a guide cavity (29) made longitudinally on an arm (30) fastened to said movable plate (9), with spring means (24) linked to said rocking lever (26). An equipment according to the claim 1, characterized in that said bar (20) is guided inside a cavity (22) made in a support (23) integral with said stationary plate (11) of the die (8), with spring means (24) pushing said bar (20) so as to make said pins (19) to come out of said support (23) through holes (25), in such a way as to intercept said blisters (1a) formed on said band (1). An equipment according to claim 1, characterized in that said movable plate (9) is actuated under pressure by a jack (35), whose stem (35a) is suited to strike against said movable plate (9), and it is borne by a pair of auxiliary jacks (36) suited to act in a direction opposite to the action of said jack (35) so to keep said stem (35a) elastically striking against the plate (9) in the pressing stage, said auxiliary jacks being also suited to actuate the moving of the movable plate (9) away from said stationary plate (11) after the thermoforming of the blisters (1a). An equipment according to the claim 4, characterized in that said auxiliary jacks (36) are suited to operate, in case of stopping of the equipment operation, the closure at a low pressure of said movable plate (9), so to prevent any slidings of the band (1).

Inventors: MARCHESINI MASSIMO, MARCHESINI, MASSIMO
Applicants: MARCHESINI MASSIMO, MARCHESINI, MASSIMO
Application year: 1990
Main classification: B29C51
IPC codes: B29C51