FR2764230A1 - Plastic tube injection-blow moulding process - Google Patents

Abstract

A process for injection-blow moulding of a flexible plastic tube, having one open end forming a neck and an opposite open end which is to be sealed after tube filling, comprises moulding a preform (39) in an injection mould (36), placing the preform (39) in a blowing mould and then using a compressed gas to blow mould the preform in the zone located between its opposite end zones (40, 42). Also claimed is a plastic tube as described above, the opposite end zones of the tube having longitudinal lines defining a joint plane and the intermediate body portion of the tube having longitudinal lines defining a double joint plane.

Description

 The present invention relates to a method of manufacturing by injection-blowing a flexible plastic tube provided with two zones of opposite open ends, one of which forms a neck. It also relates to a tube obtained using such a process. It applies in particular to the production of packaging and distribution tubes of viscous product, in particular in the field of cosmetics.

 The filling of such a tube is carried out by the end opposite the neck, this end being subsequently closed by pinching and welding.

 To carry out this welding, it is necessary to have a very regular thickness of the tube at this end. In addition, this thickness must be relatively small, typically less than 1 mm.

 To date, flexible tubes are generally produced by extrusion blow molding.

 According to this technique, a bottle provided with an open end forming a neck is produced by extrusion-blowing, then the bottom of the bottle is cut off so as to form a tube.

 For the production of flexible tubes, this technique has many drawbacks, in particular due to the fact that the cutting of the bottom generates electrically charged shavings which adhere to the wall of the tube, which greatly complicates the subsequent decoration operations.

 In addition, according to this technique, the tubes obtained have an insufficient regularity of thickness which can cause leaks during their closing.

 The object of the invention is to overcome these drawbacks and to allow the reliable and repetitive production, by injection-blowing, of a flexible plastic tube open at its two opposite ends, one of which forms a neck.

To this end, the injection-blowing manufacturing method according to the invention is characterized in that it comprises the steps consisting in:
- Forming by molding a blank comprising two opposite end zones respectively forming the end zones of the tube, by injection of a plastic material into an injection mold;
- place the blank in a blow mold; and
- blow, using a pressurized gas, the blank area located between the opposite end areas.

The process according to the invention can also include one or more of the following characteristics:
the step of forming the blank consists of molding a blank whose end zone opposite the end zone forming a neck has a thickness of between 0.3 mm and 1 mm, preferably 0.5 mm
the step of forming the blank consists of molding a blank whose area between the end areas has a thickness suitable for obtaining, after blowing, a corresponding area of thickness less than approximately twice , preferably 1.05 times, the thickness of the end region opposite the neck end region;
- Prior to the step consisting in placing the blank in the blowing mold, a label for decorating the tube is applied to the bottom thereof.

The invention also relates to a plastic tube obtained using the process defined above, characterized in that the opposite end zones have longitudinal lines delimiting a joint plane and in that the middle part of the body extending between said end zones is provided with longitudinal lines delimiting a double joint plane;
Preferably, the end neck is connected to the body by a flexible shoulder of generally frustoconical shape.

Other characteristics and advantages of the invention will emerge from the following description, given solely by way of example and made with reference to the appended drawings in which
- Figure 1 shows a longitudinal sectional view of an injection-blowing machine used for the manufacture of a tube according to the method of the invention, at a station for injecting the blank
- Figure 2 is a longitudinal sectional view of the machine of Figure 1 at a blowing station of the blank
- Figure 3 is a view of a tube obtained after blowing the blank; and
- Figure 4 is a longitudinal sectional view of a tube obtained after filling and closing of the lower end of the tube.

 In Figure 1 there is shown an injection-blowing machine for the implementation of a method according to the invention.

 It is intended for the manufacture of a flexible plastic tube provided with a first open end forming a neck and with an open opposite end intended to be closed by pinching and welding after filling the tube, using a suitable machine of conventional type.

 In this figure 1, the machine, designated by the general reference 10, is shown at a station for injecting a blank. It comprises a punch 12 with a horizontal axis XX ′ fixed in leaktight manner to a carousel 14 of the machine. The carousel 12, of vertical axis Y-Y ', is rotated by motor means not shown to successively bring the punch 12 to an injection station, as illustrated in Figure 1, and a blowing station , shown in Figure 2.

 Referring to Figure 1, the punch 12 comprises a punch body 16 made in one piece and of substantially tubular shape. It is provided with an open proximal end 18 fixed on the carousel 14 by means of a flange 20 and with a closed opposite distal end 22 disposed opposite an injection station 24 of a plastic material, of the classic type.

 The punch body 16 comprises a proximal section 26 of generally cylindrical shape and of diameter equal to the internal diameter of one of the open ends of the tube to be produced.

 The proximal section 26 is extended, in the direction of the distal end 22, by an intermediate section 28 of linearly decreasing section in the direction of the distal end and by a distal section 30, also of cylindrical shape and of diameter equal to the internal diameter. of the neck of the tube to be produced.

 Furthermore, and as can be seen in FIG. 2, the body 16 is provided, at the intermediate section 28 with lights, such as 32, regularly formed in the wall of the body of the punch, these lights being associated with a valve ( not shown) controlled by a control rod 34 connected to suitable motor means, not shown, so as to cause the shutters of the lights 32 to be closed when the machine is in the position shown in FIG. 1 in which it is located at the station injection 24 and the opening thereof when the machine 10 is in the position shown in Figure 2, in which it is located at the blowing station.

 As will be described in detail below, the lights 32 are connected, in operation, to a source of supply of pressurized gas.

 The machine which has just been described allows the production of flexible tubes having two opposite open ends, one of which forms a neck, of the type shown in FIG. 3.

 For the production of such tubes, the punch 12 is brought to an injection station, as shown in FIG. 1. At this station, an injection mold 36 is placed around the punch and defines therewith a injection cavity 38, the shape of which corresponds to the blank to be produced.

 This cavity 38 has a substantially constant thickness at the level of the intermediate 28 and distal 30 sections of the punch and decreases regularly in the direction of the proximal section 26 to the right of which it is clearly reduced to a value of between 0.3 mm and 1 mm, preferably 0.5 mm.

 The injection head of the station 24 is then introduced into the distal end of the injection mold 36 and the plastic material of the tube is injected under very high pressure, typically of the order of 200 bars.

 This operation produces the blank 39 visible in FIG. 1 which includes a proximal end region 40 and a distal end region 42, these two ends 40 and 42 being open and intended respectively to be closed after filling the tube and to constitute the neck of it.

 It will be noted that these two end zones each have a diameter which corresponds to the diameter of the finished tube.

 During the next step, the injection station 24 is moved back and the mold 36 is opened. The carousel 14 pivots to bring the blank thus produced to the blowing station shown in FIG. 2.

 At this station, a blow mold 44 having the configuration of a finished tube below is closed on the punch 16. This mold 44 exactly matches the end zones 40 and 42 of the blank.

 The rod 34 is then actuated so as to open the openings 32.

 Consequently, the compressed air delivered by the compressed air supply source passes through the latter, which causes the separation of the area of the blank situated in line with the intermediate section 28 of the punch, the swelling of this part of the blank, which is thus placed against the internal wall of the blow mold 44.

 Referring again to FIG. 1, it should be noted that the injection mold 36 has an internal configuration adapted to delimit with the intermediate section 28 of the punch 12 a molding cavity 38 of thickness suitable for obtaining, after blowing, a corresponding area of the tube having a thickness less than approximately twice, preferably 1.05 times, the thickness of the proximal end 40 of the blank.

 It should also be noted that the bottom of the blowing mold 44 can advantageously include inverted and self-adhesive labels, which allows labeling of the tubes during the blowing operation.

 After the blowing operation, the blowing mold 44 is finally opened and, after cooling, a tube obtained, shown in FIG. 3, is ejected. This tube, designated by the general reference numeral 46, comprises a flexible body 48 provided with an upper and distal end 50 extended, by means of a shoulder 51 of generally frustoconical shape, by a neck 52 and an end proximal and lower 54, these two ends being open.

 As will be appreciated, the neck 52 and the lower end 54 are produced by injection, while the rest of the tube is produced by blow molding.

 The tube thus obtained therefore comprises, at the level of the injected parts, longitudinal lines, such as 56, delimiting a joint plane resulting from the injection, while, as can be seen in FIG. 3 in which certain details have been exaggerated to improve clarity, the part obtained by injection-blowing comprises a double joint plane delimited by two sets of longitudinal lines, respectively 58 and 60, substantially merged.

 As can also be seen in FIG. 3, the neck 52 of the tube can advantageously be provided with a thread, by providing an additional thread in the corresponding distal part of the injection mold 36.

 Advantageously, the tube 46 is provided with a shoulder 51, connecting the neck 52 to the body 48, having a flexible structure, using a blank having in this zone an appropriate thickness, in order to increase, when the tube is used. , the restitution by manual crushing of the shoulder 51.

 The tube thus produced is then provided with a cap (not shown) covering the neck 52 and is then filled, by its proximal end 54, this latter end then being closed by pinching and welding.

 The filled tube shown in FIG. 4 is thus obtained.

 It is understood that the method according to the invention which has just been described allows the production of a tube, the two end zones of which are produced by injection, while the middle part of the body is produced by injection-blowing.

 This technique makes it possible to obtain a relatively precise tube thickness, at the end zones, and in particular at the end intended to be welded, which thus makes it possible to obtain a very reliable weld.

 Furthermore, the middle part of the body being produced by injection-blowing, the corresponding zone of the blank has a relatively large thickness compared to that of the end zones, which makes it possible to limit the injection pressure of the material. plastic.

Claims (6)

 1. A method of manufacturing by injection-blowing a flexible plastic tube (46) having two open opposite end zones (50,54), one of which forms a neck (52) and the other of which is intended to be closed after filling the tube, characterized in that it comprises the steps consisting in  - Forming by molding a blank (39) having two opposite end zones (40,42) respectively forming the end zones of the tube, by injecting a plastic material into an injection mold (36);  - Place the blank (39) in a blow mold (44); and  - blow, using a pressurized gas, the area of the blank located between the opposite end areas (40,42).  2. Method according to claim 1, characterized in that the step of forming the blank (39) consists in molding a blank whose end zone opposite to the end zone (42) forming a neck has a thickness between 0.3 mm and 1 mm, preferably 0.5 mm.  3. Method according to one of claims 1 and 2, characterized in that the step of forming the blank (39) consists in molding a blank whose zone located between the end zones (40,42) has a thickness suitable for obtaining, after blowing, a corresponding zone of thickness less than approximately twice, preferably 1.05 times, the thickness of the end zone opposite the end zone (42 ) forming a collar.  4. Method according to any one of claims 1 to 3, characterized in that prior to the step of placing the blank (39) in the blow mold (44), it is applied to the bottom thereof a tube decoration label.  5. Plastic tube comprising a flexible body (48) provided with two open ends (50,54) extended one (50) by a neck (52) and intended for the other (51) to be closed after filling of the tube, characterized in that the opposite end zones (50,54) have longitudinal lines (56) delimiting a joint plane and in that the middle part of the body extending between said end zones is provided with lines longitudinal (58.60) delimiting a double joint plane.  6. Tube according to claim 5, characterized in that the neck (52) end is connected to the body (48) by a flexible shoulder (51) of generally frustoconical shape.