[0001] The invention relates to a heating and welding mould, in particular a mould to heat and weld together zones of a first film of thermoformable plastic material and of a second film of thermoformable plastic material, used to form containers, in particular containers for food, pharmaceutical or cosmetic products consisting of a pair of half moulds welded together.

[0002] In order to make containers, each of which consists of a pair of half moulds welded together along a welding perimeter, the first and the second film of thermoformable plastic material are placed in contact with one another and are welded along zones corresponding to the welding perimeters of the containers, by two welding half moulds, between which the two films of thermoformable plastic material are led.

[0003] In order to perform welding, each film of thermoformable plastic material is normally heated over its entire surface, in a zone comprised between the two welding half moulds. This can be a problem if the plastic material has a welding temperature near the melting temperature.

[0004] In this case, in fact, heating to the welding temperature causes the material to soften to the point of making it collapse and stick also in areas that then have to be subjected to forming, with the result that after forming the container will have clear surface defects that are such as to ruin the aestethics thereof and make the container unsaleable. [0005] The object of the present invention is to provide a heating and welding mould for heating and welding zones of a first sheet of thermoformable plastic material with corresponding zones of a second sheet of thermoformable plastic material, without damaging the zones of the sheets of thermoformable plastic material not affected by the welding operation, said mould having to be easy and cheap to make.

[0006] The object of the invention is achieved by a heating and welding mould according to claim 1.

[0007] Owing to the invention, it is possible to weld together corresponding zones of a first sheet of thermoformable plastic material and of a second sheet of thermoformable plastic material arranged in contact with one another, without damaging the zones of both sheets not affected by the welding operation, in particular when the welding temperature of the thermoformable plastic material is near the melting temperature of the material.

[0008] Further features and advantages of the invention will become clear from the following description of embodiments of the invention provided merely by way of non limiting example, with reference to the attached drawings in which:

Figure 1 is a very schematic view of a mould according to the invention,

Figure 2 is a plan view of a half mould of the mould according to the invention;

Figure 3 is a partial perspective view of the half mould of Figure 2;

Figure 4 is a plan view of a block that is insertable into cavities of the half mould of Figures 2 and 3;

Figure 5 is a section of the block of Figure 4, along the line B-B in Figure 4;

Figure 6 is a perspective view of the block of Figure 4;

Figure 7 is another perspective view of the block of Figure 4;

Figure 8 is a plan view of a variation of the block of Figure 4;

Figure 9 is a section of the block of Figure 8, along the line C-C in Figure 8;

Figure 10 is a perspective view of the block of Figure 8;

Figure 11 is another perspective view of the block of Figure 8;

Figure 12 is a view of the half mould of Figure 2 from which the blocks illustrated in Figures 4 to 7 or 8 to 11 have been removed;

Figure 13 is a section of the half mould of Figure 1, along the line A- A in Figure 1.

[0009] With reference to Figure 1, a mould 1 according to the invention, for heating and welding zones of a first film 4 of thermoformable plastic material with corresponding zones of a second film 5 of thermoformable plastic material (below more shortly as first film 4 and second film 5), consists of a first half mould 2 and of a second half mould 3 that are substantially the same as one another, between which the first film 4 and the second film 5 are led, aligned and superimposed on one another.

[0010] In Figure 2, in a plan view, any one of the two half moulds 2, 3 is illustrated. In the half mould 2, 3, there is a ridge 6 having the shape of three sides of the contour of a plurality of adjacent containers. The ridge 6 defines a series of cavities 7, that can have the same shape and dimensions. When the first half mould 2 and the second half mould 3 are brought near one another, after being heated to the welding temperature of the thermoplastics of the first film 4 and of the second film 5, parts of the first film 4 and of the second film 5, are clamped between the ridges 6 of the first half mould and of the second half mould and welded together to define three sides of the contour of a plurality of containers alongside one another. The parts of the first film 4 and of the second film 5 welded together surround the non- welded areas of the first film 4 and of the second film 5 at which hot air can be blown in to thermoform the bodies of the containers. The non- welded areas of the first film 4 and of the second film 5 are at the cavities 7 of the first half mould 2 and of the second half mould 3.

[0011] Into each of the cavities 7, a block 8, 8a is inserted that has a similar shape to that of the cavity 7, so as to be able to be inserted with clearance into the cavity 7.

[0012] In Figures 4 to 7, a first embodiment is illustrated of a block marked by the reference number 8, whereas in Figures 8 to 11 a second embodiment is illustrated of a block marked by the reference number 8a.

[0013] With reference to Figures 4 to 7, each block 8 is fixed to the half mould 2, 3, inside a respective cavity 7, by mechanical fixing means, for example screws 9, that are inserted into threaded holes 10 made on a first face 11 of the block 8 facing a bottom 13 of the cavity 7, when the block 8 is fixed in a respective cavity 7 of the half mould 2, 3. A second face 12 of the block 8, opposite the first face 11 faces the outside of the cavity 7. When the mould 1 is closed, the second faces 12 of the blocks 8 are intended to come into contact with zones of the first film 4 or of the second sheet 5 in which the bodies of the containers will be thermoformed.

[0014] On the bottom 13 of each cavity 7, holes 17 are made through which the screws 9 are inserted that are intended to fix the blocks 8.

[0015] Each block 8 can be made of a second material that has a heat transmission coefficient that is less than the heat transmission coefficient of a first material with which the half mould 2, 3 is made. Through the effect of the lower heat transmission coefficient, when the half mould 2, 3 is heated, the block 8, the first face 11 of which is in contact with the half mould 2, 3, at the bottom 13 of the cavity 7 into which the block 8 is inserted (Figure 12), is colder than the half mould 2, 3. Accordingly, when the half mould 2, 3 is heated to the welding temperature of the thermoplastic material of the first film 4 and of the second film 5, the blocks 8 will have a lower temperature than that of the rest of the half mould 2, 3, in particular the second faces 12 of the blocks will have a lower temperature than the temperature of the ridge 6.

[0016] Owing to the temperature of the second faces 12 of the blocks 8, which is lower than that of the ridge 6, the parts of the first film 4 and of the second film 5 which are at the blocks 8 heat up less than the parts that are located at the ridge 6, and do not adhere to one another, so as to ensure that at the moment of forming the bodies of the containers they can be obtained without defects that may compromise the aestethics and thus the saleability thereof.

[0017] The transmission of heat between the half mould 2, 3 and the blocks can be adjusted also by varying the contact surface between the blocks and the half mould 2, 3, reducing the contact surface between the first face 11 of each block and the bottom 13 of the corresponding cavity 7 more precisely. In this case, the blocks can be made of the same material with which the half-moulds 2, 3 are made.

[0018] In Figures 8 to 11 a second embodiment 8a of a block is illustrated that has a contact surface with the half mould 2, 3, lower than the contact surface between a block 8 and the half mould 2, 3.

[0019] A block 8a has in a first face 1 la a recess 14 of substantially rectangular shape, on the bottom 15 of which threaded holes 10a are made into which fixing screws 9 are inserted by means of which the block 8a is fixed to the bottom 13 of a respective cavity 7 of the half mould 2, 3. Through the effect of the recess 14, the contact surface between the block 8a and the bottom 13 of the cavity 7 is lower than the surface of the first face 11a and is limited substantially to the edge 16 of the recess 14, whereas, in the case of the block 8 illustrated in Figures 4 to 7, the contact surface between the block 8 and the bottom 13 of the respective cavity 7 is equal to the surface of the first face 11.

[0020] Owing to this solution and/or by choosing suitably the material of the blocks 8a, so that it has a heat transmission coefficient significantly less than the heat transmission coefficient of the material of the half mould 2, 3, it is possible to reduce the quantity of heat that reaches the block 8a when the mould 1 is heated, such that a second face 12a thereof, opposite the first face 11 and facing the outside of the respective cavity 7, has a temperature that is even 10-15° C lower than the temperature of the ridge 6.

[0021] This further ensures that the zones of the first film 4 and of the second film 5 that come into contact with the blocks 8a when the mould 1 is closed cannot soften and stick together so that the bodies of the containers that will be subsequently made by thermoforming do not have defects.

[0022] In Figure 13, a variant is illustrated of a mould according to the invention.

In this version, between the first face 11 of each block 8 and the bottom 13 of the respective cavity 7 of the half mould 2, 3, into which the block 8 is inserted, spacer elements 18 are arranged.

[0023] The spacer elements 18 are preferably made with a thermally insulating material or anyway, with a material having a heat transmission coefficient that is lower than the heat transmission coefficient of the material with which the half mould 2, 3 is made.

[0024] The spacer elements 18 prevent a direct contact between the first face 11 of a block 8 and the bottom 13 of a respective cavity 7, into which the block 8 is inserted. [0025] Each spacer element 18 can have the shape of a ring provided with a central hole 19 that enables the spacer element 18 to be fitted to the stem of a respective screw 9, when the respective block 8 is fixed in the cavity 7.

[0026] Owing to the presence of the spacer elements, there is only one indirect contact between a block 8 and the bottom of the respective cavity 13, what’s more on a surface that is much less than the surface of the first face 11 of the block, corresponding to the total surface of the spacer elements 18.

[0027] This makes it possible to reduce the quantity of heat that reaches the block 8 when the mould 1 is heated, such that a second face 12 thereof, opposite the first face 11 facing the outside of the respective cavity 7, has a temperature that is even 10-15° C lower than the temperature of the ridge 6, so as to ensure that the zones of the first film 4 and of the second film 5 that come into contact with the blocks 8 when the mould 1 is closed cannot soften and stick together such that the bodies of the containers that will be subsequently made by thermoforming do not have defects.