WO2011061638A1

WO2011061638A1 - Injection molding process of an element and apparatus for implementing said process

Info

Publication number: WO2011061638A1
Application number: PCT/IB2010/054345
Authority: WO
Inventors: Claudio Bariselli
Original assignee: Borromini S.R.L.
Priority date: 2009-11-23
Filing date: 2010-09-27
Publication date: 2011-05-26
Also published as: EP2504142A1; IT1397037B1; ITVR20090199A1

Abstract

It refers to an injection molding process and to the related apparatus, comprising the following phases: - injection molding of a first layer of melted plastic material in the cavity of a matrix by utilizing a first injecting mold comprising a first sector pressing said first layer; - injection molding of a further layer of fused plastic material on the previously molded layer by utilizing a further injecting mold comprising a further sector pressing said further layer so that said further layer melts with the previously molted layer so as to obtain an only layer; - cooling of said only layer so as to obtain a finished manufacture; - extraction of the so-obtained manufacture from the cavity of the matrix.

Description

INJECTION MOLDING PROCESS OF AN ELEMENT AND APPARATUS FOR IMPLEMENTING SAID PROCESS

SPECIFICATION

The present invention refers in general to an injection molding process and to an apparatus for implementing said process.

More particularly, it refers to a particular injection molding process which reduces the time of production of the element and to an apparatus for implementing said process.

As is known, for the production of plastic articles it is possible to utilize the injection molding process in which a thermoplastic material is melted and then, it is injected under pressure in a mold formed by two matrices, one of the matrices being movable to allow the removal of the finished piece.

One of the critical factors in the injection molding is the possible shrink of the piece material in the mold during the phase of solidification and cooling; for the control of the shrink, the injection molding process according to the prior art provides that the melted material is injected continuously and put under pressure even during the phase of cooling and solidification of the piece.

Consequently, said delicate phase of cooling and solidification must take place slowly and under control, which involves a longer time of production and higher costs to obtain the final product.

Said problems become heavier in case the article to be produced has big dimensions and in particular, if it is very thick. Indeed, in case of considerable thicknesses, the cooling time is longer and the costs of production raise.

For instance, in case a lens is produced in a plastic material, this process allows to improve the qualitative standard, to reduce the weight of the finished product and to reduce the costs of production in comparison with a lens of glass. In fact, the production of lenses through the injection molding allows a repetition of the productive process and to give the product a measurable qualitative standard that can be controlled and reproduced easily in order to eliminate the variable factor of the ability of the operator who manufactures the lens of glass.

As explained above, the production of a lens of plastic needs a long time of production and the thicker the lens is, the longer the time of production is. For instance, in case of a lens having a spherical bowl of a diameter of about 6 cm, the molding cycle according to the known art may last 10 to 20 min to obtain a finished article.

In fact, by injecting, in an only phase, the whole melted material in a mold, it is necessary to go on feeding the material in said mold in order to compensate the shrink of the hot material in the core of the lens.

An aim of the invention is to remove the aforesaid drawbacks and further ones by carrying out an injection molding process, adapted to reduce the time of production of the article in comparison with the known technology.

Another aim of the invention is to carry out a simple repeated injection molding process giving a measurable qualitative standard to the finished product, which standard is controlled and reproduced easily.

A further aim of the invention is to carry out an apparatus for producing an article through injection molding, said apparatus being rapid and simple to be used.

A further aim of the invention is to reduce the time of the injection molding of a lens manufactured in a plastic material.

All said aims and advantages are achieved according to the invention through an injection molding process, characterized in that it comprises the following phases:

- injection molding of a first layer of melted plastic material in the cavity of a matrix by utilizing a first injecting mold comprising a first sector pressing said first layer;

- injection molding of a further layer of melted plastic material on the previously molded layer by utilizing a further injecting mold comprising a further sector pressing said further layer so that said further layer melts with the previously molted layer so as to obtain an only layer; - cooling of said only layer so as to obtain a finished manufacture;

- extraction of the so-obtained manufacture from the cavity of the matrix. The process according to the invention provides, therefore, the injection molding of at least two layers of thermoplastic material, one upon the other, at temperatures of molding and in times of molding that make the various layers melt in an only body, but at the same time make the cooling temperatures of the single layers reduce in order to reduce the time of production of the finished product.

Advantageously, as the number of layers increases and their thickness diminishes, the time of production of the finished manufacture may be reduced further on.

Besides, the process provides that after each phase of injection molding, the movable matrix shifts and the cavity translates to reach the further injecting mold. In this way, a continuous process if obtained.

In case a manufacture has to be obtained through injection, molding and subsequent melting of a determinate number of layers, the number of the injecting molds must be the same as the number of the layers. In case more cavities are obtained in the matrix, in at least the same number of said layers, it is possible to obtain a continuous process through which a finished manufacture is produced whenever a single layer is molded.

In fact, the injection molding of all the necessary layers, each of them in the relative cavity of the matrix, corresponding to the relative injecting mold may occur simultaneously.

In order to speed up the production of the finished manufacture and therefore, to facilitate the solidification of same, the temperature of each further layer is, in the injection phase, lower than the temperature of the layer, in the injection phase, molded before said further layer, the temperature of the injecting molds being regulated through a cooling circuit operating autonomously for each injecting mold.

In addition, the aims and advantages of the invention are achieved by an injection molding apparatus comprising a first die and a second die, said first die being provided with a plate which is movable and rotating in relation to said second die.

Thus, the apparatus is obtained to mold a manufacture through the injection and molding of subsequent layers continuously.

The injection molding apparatus may provide that the second die comprises a cooling circuit, adapted to independently cool each male impression.

Besides, the second die may comprise a cooling sector, positioned between the male impression, provided with the more protruding spherical bowl, and the male impression, provided with the less protruding spherical bowl so that once the manufacture is finished, it is cooled further on before being extracted since the manufacture goes in contact with said cooling sector.

In order to obtain a continuous process, the number of the female impressions may be the same as the number of the male impressions plus one, and the female impressions may be arranged so as to correspond to the male impressions and to the cooling sector.

Each female impression comprises perimetrically a movable ring nut, fixed on at least an actuator so that once the injection molding of all the layers has been ended and a finished manufacture has been obtained, the ring nut is made translate outwards through the actuator and the finished manufacture is extracted from the female impression.

Advantageously, the movable plate may comprise a cylindrical element, arranged in the middle of the face that is provided with the female impressions and on the side surface of which a guide is obtained and in which in the face of the second die having the male impressions, a cylindrical seat is obtained in the inner surface of which there is provided at least a pin which inserts in the guide which is shaped in such a way as to guide the movement of translation and rotation of the plate in a determinate way in respect to the second die.

Further features and details of the invention will be better understood from the following specification which is given as a non-limiting example as well as from the accompanying drawings wherein:

Fig. 1 is an axonometric view of an apparatus according to the invention;

Fig. 2, 3 are views of a first die and a second die, respectively;

Fig. 4 is an axonometric view of a first sector of the first die, namely, a plate that supports matrices;

Fig. 5 is an axonometric view of a second sector of the first die, namely, a plate that supports nozzles;

Figg. 6, 7 are front views of the second die and first die, respectively; Fig. 8 is a side view along cross section A-A in Fig. 6;

Fig. 9 is a side view along cross section B-B in Fig. 6;

Fig. 10 is a side view along cross section C-C in Fig. 6;

Fig. 11 is a side view along cross section D-D in Fig. 6;

Fig. 12 is a side view along cross section E-E in Fig. 6;

Fig. 13 is a side view along cross section F-F in Fig. 6;

Fig. 14 is a side view along cross section G-G in Fig. 6.

With reference to the accompanying drawings, in particular Fig. 1 , reference number 10 denotes an apparatus to produce lenses in a plastic material through an injection molding process.

Apparatus 10 comprises a first die 11 and a second die 13. Said dies are arranged one before the other and comprise female matrices and male matrices. Said female matrices and male matrices beat the ones against the others and form a lens-shaped cavity.

The first die 11 , represented in Fig. 2, comprises a first fixed plate 12, adapted to be fixed on the press of a molding plant according to the prior art.

A first matrices-holding plate 14 is connected with said fixed plate so as to rotate. Besides, the first die 11 comprises a first ring 15 which is fixed on the first fixed plate 12 and is adapted to facilitate a possible shifting of the first die 11 itself. Likewise, the second die 13, represented in Fig. 3, comprises a second fixed plate 18, adapted to be fixed on the press of a molding plant according to the prior art. A second matrices-holding plate 16 is fixed on said plate 18. Like the first die 1 1 , the second die 13 comprises a ring 17 which is fixed on the second matrices-holding plate 16 and is useful in the operations of displacement and removal of said die 13 from the plant. The first fixed plate 12, the first matrices-holding plate 14, the second matrices-holding plate 16 and the second fixed plate 18 have a prismatic shape with octagonal base.

The first matrices-holding plate 14 comprises eight female matrices showing the same shape and size, only one of them being represented with reference number 20 in Figures 2, 6. The eight female matrices 20 are arranged in a circle and are equidistant from one another so that the centers of female matrices 20 are spaced from one another at an angle of 45°.

A cylindrical element 19 is fixed centrally on the same face of the matrices- holding plate 14 comprising the eight female matrices 20. A guide 23 is obtained on the side surface of the cylindrical element 19. Eight conical female centering element 21 are obtained on the same face and are arranged along the perimeter at the same angular distance, namely, 45° from one another.

In addition, a conditioning system 5 according to the prior art is obtained in the first matrices-holding plate 14 to control the temperature of the female matrices 20.

The second matrices-holding plate 16 comprises seven male matrices 31 , 32, 33, 34, 35, 36, 37 on the face beating the first matrices-holding plate, said male matrices being different from one another, as well as an eighth cooling sector 38. On the same face, a cylindrical hole 4 is obtained in the middle and is delimited perimetrically by a cylindrical crown 24 in the inside of which eight pegs 25 protrude and are arranged at the same distance from one another.

In the approaching and moving away of the two matrices-holding plates 14, 16, the pegs 25 may move in the inside of the guide 23 obtained in the cylindrical element 19 so as to guide the rotation and the translation between the two dies 1 1 , 13.

Besides, the face of the second matrices-holding plate 16 with the seven male matrices comprises four male conical elements 60 arranged along the perimeter at the same angular distance, namely, 90° from one another.

An exact centering between the two dies 1 1 , 13 is obtained thanks to the insertion of the four male conical elements 60 in the eight female conical elements 21 of the first matrices-holding plate 14 and thanks to the shape of the guide 23 that provokes a determined displacement between the two matrices-holding plates 14, 16. In this way, when the two dies 1 1 , 13 beat against each other, the eight female matrices 20 correspond to the seven male matrices 31 , 32, 33, 34, 35, 36, 37 and to the eighth sector 38.

A cooling system is obtained in the second matrices-holding plate 16, as well. In the accompanying figures, the cooling system is indicated with the only reference number 22 but it comprises independent channels for each male matrix in order to autonomously control the temperatures of the male matrices.

Each male matrix comprises and injection point in the middle of the impression. The injection point is connected with a respective nozzle 29.

As it appears from Figure 5, the second fixed plate 8 comprises seven injectors 29, connected with each other, and a stellar distributor 39 which in turn is connected with a hot chamber.

Seven holes 26 are obtained in the second matrices-holding plate 16 so as to allow the tips of the nozzles 29 to beat against the injection point of each male matrix.

As shown in Figures 6, 8 and following ones, the first matrices-holding plate comprises eight equal female matrices 20. Each female matrix 20 comprises a female impression 30 which is fixed on the plate 14 and in which a cavity 59, shaped like a spherical bowl, is obtained. A ring nut 40 is arranged along the female impression 30 and translates in respect to the impression 30 by means of three actuators 49. In Figure 6, the aforesaid reference numbers denote only the elements of a female matrix but it is to be intended that the same reference numbers denote the same elements of the other seven female matrices, as well.

As shown in Figure 7 and following ones, the second matrices-holding plate 16 comprises the seven male matrices and the cooling sector 38.

The first male matrix 31 comprises a male impression 51 from which a spherical bowl 41 protrudes, the diameter of this bowl being slightly shorter than the cavity 59.

The second male matrix 32 comprises a male impression 52 from which a spherical bowl 42 protrudes, the diameter of this bowl being slightly shorter than the spherical bowl 41.

The third male matrix 33 comprises a male impression 53 from which a spherical bowl 43 protrudes, the diameter of this bowl being slightly shorter than the spherical bowl 42.

The fourth male matrix 34 comprises a male impression 54 from which a spherical bowl 44 protrudes, the diameter of this bowl being slightly shorter than the spherical bowl 43.

The fifth male matrix 35 comprises a male impression 55 from which a spherical bowl 45 protrudes, the diameter of this bowl being slightly shorter than the spherical bowl 44.

The sixth male matrix 36 comprises a male impression 56 from which a spherical bowl 46 protrudes, the diameter of this bowl being slightly shorter than the spherical bowl 45.

The seventh male matrix 37 comprises a male impression 57 which, unlike the other impressions, does not have any protruding element.

The sector 38 comprises a simple circular element which is subject to the action of suitable channels that are connected with the cooling circuit.

The apparatus 10 according to the invention allows to mold, through injection, seven layers of lens in succession with a rotation of the first matrices- holding plate 14 in respect to the second matrices-holding plate 16. The temperatures and times of each of the seven injection phases allow a fusion of the layers that form an only homogeneous body. This is obtained at higher cooling speeds than that of the solidification of a lens obtained through molding in an only phase of injection molding.

In the first phase of injection and molding as represented in Fig. 8, once the two dies 11 , 13 have been approached and put under pressure one upon the other , a female impression 30, the cavity of which is completely empty, is arranged in front of the first male impression 51 from which the spherical bowl 41 protrudes. A melted thermoplastic material goes out of the nozzle 29, namely, from the central injection point of the spherical bowl 41 so as to completely fill the empty space between the male impression 51 and the female impression 30 and to form a first layer 61 of lens.

Said first layer 61 is slightly cooled by the conditioning and cooling circuit so as to reach a satisfying status of solidification.

In the second phase of the process, the first movable matrices-holding plate 14 is translated so as to move away from the second fixed matrices-holding plate 16; then, the same plate 14 is rotated 45° and approached to the plate 16 so that the female impression 30, on which the first layer 61 is placed, is in front of and beats against the second male impression 52, as it appears from Figure 9.

A melted thermoplastic material goes out of the nozzle 29, namely, from the central injection point of the spherical bowl 42 so as to completely fill the empty space between the first layer 61 and the male impression 52 and to form a second layer 62 of lens.

The temperatures of the first layer 61 and second layer 62 are such to fuse the same layers into an only homogeneous layer 71.

The molding process goes on with further phases as the above one.

In the third phase of the injection molding process, the first movable matrices-holding plate 14 is translated again so as to move away from the second fixed matrices-holding plate 16; then, the same plate 14 is rotated 45° and approached to the plate 16 so that the female impression 30, on which the homogeneous layer 71 is placed, is in front of and beats against the third male impression 53, as it appears from Figure 10.

A melted thermoplastic material goes out of the nozzle 29, namely, from the central injection point of the spherical bowl 43 so as to completely fill the empty space between the homogeneous layer 71 of lens and the male impression 53 and to form a third layer 71 of lens.

The temperatures of the homogeneous layer 71 and third layer 63 are such to fuse the same layers in an only homogeneous layer 72. Besides, the temperatures of the male impression 53 are regulated in such a way as to lower the temperature of the homogeneous layer 72 and to accelerate its solidification.

In the fourth phase of the injection molding process, the first movable matrices-holding plate 14 is translated again so as to move away from the second fixed matrices-holding plate 16; then, the same plate is rotated 45° and approached to the plate 16 so that the female impression 30, on which the homogeneous layer 72 is placed, is in front of and beats against the fourth male impression 54, as it appears from Figure 1 1.

A melted thermoplastic material goes out of the nozzle 29, namely, from the central injection point of the spherical bowl 44 so as to completely fill the empty space between the homogeneous layer 72 of lens and the male impression 54 and to form a fourth layer 64 of lens.

The temperatures of the homogeneous layer 72 and fourth layer 64 are such to fuse the same layers in an only homogeneous layer 73. Besides, the temperatures of the male impression 54 are regulated in such a way as to further lower the temperature of the homogeneous layer 73 and to accelerate its solidification.

In the fifth phase of the injection molding process, the first movable matrices-holding plate 14 is translated again so as to move away from the second fixed matrices-holding plate 16; then, the same plate 14 is rotated 45° and approached to the plate 16 so that the female impression 30, on which the homogeneous layer 73 is placed, is in front of and beats against the fifth male impression 55, as it appears from Figure 12.

A melted thermoplastic material goes out of the nozzle 29, namely, from the central injection point of the spherical bowl 45, so as to completely fill the empty space between the homogeneous layer 73 of lens and the male impression 55 and to form a fifth layer 65 of lens.

The temperatures of the homogeneous layer 73 and fifth layer 65 are such to fuse the same layers in an only homogeneous layer 74. Besides, the temperatures of the male impression 55 are regulated in such a way as to further lower the temperature of the homogeneous layer 74 and to accelerate its solidification.

In the sixth phase of the injection molding process, the first movable matrices-holding plate 14 is translated again so as to move away from the second fixed matrices-holding plate 16; then, the same plate 14 is rotated 45° and approached to the plate 16 so that the female impression 30, on which the homologous layer 74 is placed, is in front of and beats against the sixth male impression 56, as it appears from Figure 13.

A melted thermoplastic material goes out of the nozzle 29, namely, from the central injection point of the spherical bowl 46, so as to completely fill the empty space between the homogeneous layer 74 of lens and the male impression 56 and to form a sixth layer 66 of lens.

The temperatures of the homogeneous layer 74 and sixth layer 66 are such to fuse the same layers in an only homogeneous layer 75. Besides, the temperatures of the male impression 56 are regulated in such a way as to further lower the temperature of the homogeneous layer 75 and to accelerate its solidification.

In the seventh and last phase of the injection molding process, the first movable matrices-holding plate 14 is translated again so as to move away from the second fixed matrices-holding plate 16; then, the same plate 14 is rotated 45° and approached to the plate 16 so that the female impression 30, on which the homologous layer 75 is placed, is in front of and beats against the seventh male impression 57, as it appears from Figure 14.

A melted thermoplastic material goes out of the nozzle, namely, from the central injection point of the spherical bowl 47, so as to completely fill the space between the homogeneous layer 75 of lens and the male impression 57 and to form a seventh layer 67 of lens.

The temperatures of the homogeneous layer 75 and seventh layer 67 are such to fuse the same layers in an only homogeneous body, namely, the lens. Besides, the temperatures of the male impression 57 are regulated in such a way as to further lower the temperature of the so-obtained lens and to accelerate its solidification.

The cooling and solidification are further facilitated by the last translation and rotation of 45° of the movable plate 14 in respect to the fixed plate 16. In this way, the lens is positioned so as to beat with the cooling sector 38.

Then, the lens is extracted from the female impression 30 by actuating the three actuators 49 which push the ring nut 40 towards the outside. The finished lens is collected and is ready for the use.

Of course, the process is continuous and once the first male impression 51 has injected and molded the first layer and the female impression 30 has moved away with the first layer 61 , the same first male impression 51 is operating again and injects and molds a new first layer 61 in the female impression 30 which is now free from the finished lens.

In this way, all the seven male impressions are always operating.

In addition, the injection system is fixed so that the contribution of each male impression 51 , 52, 53, 54, 55, 56, 57, which injects the melted thermoplastic material, remains constant as the movable part of the mold rotates, namely, the movable part of the first matrices-holding plate 14.

As a matter of fact, in the succession of the seven phases of the injection molding, in front of each male impression, the first plate 14 always puts the same volume of the material to be injected.

The invention has been described according to a form in which the manufacture, namely, a lens, is obtained in an injection molding process in which seven layers are molded through injection, said layers being overlapped and homogeneous.

It is to be intended that the scope of protection of the invention comprises those processes and apparatuses that according to the invention relate to the injection molding of two or more layers in order to obtain an only homogeneous body, a lens or another article on saving time.

Claims

1) Injection molding process, characterized in that it comprises the following phases:

- injection molding of a further layer of fused plastic material on the previously molded layer by utilizing a further injecting mold comprising a further sector pressing said further layer so that said further layer melts with the previously molted layer so as to obtain an only layer;

- cooling of said only layer so as to obtain a finished manufacture;

- extraction of the so-obtained manufacture from the cavity of the matrix.

2) Injection molding process according to the preceding claim, wherein the injection molding phase for the further layer of melted material is repeated at least once.

3) Injection molding process according to any of the preceding claims, wherein said matrix, which is moveable, shifts after each injection molding phase and the cavity translates and reach the further injecting mold.

4) Injection molding process according to any of the preceding claims, wherein the temperature of each further layer is, in the injection phase, less than the temperature of the layer, in the injection phase, molded prior to said further layer.

5) Injection molding apparatus (10) comprising a first die (11) and a second die (13), said first die (11) being provided with a plate (14) which is moveable and rotating in relation to said second die (13), characterized in that two female impressions (30) are obtained in said moveable plate (14) and that said second die (13) comprises male impressions (51 , 52, 53, 54, 55, 56, 57), each of them being provided with an injector (29) which injects melted thermoplastic material, the number of said female impressions (30) being at least the same as the number of the male impressions, said male impressions (51 , 52, 53, 54, 55, 56, 57) being arranged so as to correspond with the female impressions; cavities (59) having the same shape and dimension being obtained in said female impressions (30); said male impressions (51 , 52, 53, 54, 55, 56, 57) being provided with spherical bowls (41 , 42, 43, 44, 45, 46) of different dimension, arranged homogeneously on a face of the second die so that the spherical bowls are arranged from the biggest to the smallest one and once a nozzle of a mal impression has filled the female impression so as to create a layer of thermoplastic material between the cavity (59) and the spherical bowl of said male impression and once the moveable plate (14) has been rotated, the subsequent male impression can inject thermoplastic material on the previously injection molded layer.

6) Injection molding apparatus according to claim 5, wherein the second die comprises a cooling circuit (22) to independently cool each male impression (51 , 52, 53, 54, 55, 56, 57).

7) Injection molding apparatus according to any of claims 5, 6, wherein the second die comprises a cooling sector (38) positioned between the male impression (51 ), provided with the more protruding spherical bowl (41 ), and the male impression (57), provided with the less protruding spherical bowl.

8) Injection molding apparatus according to claim 7, wherein the number of female impressions (30) is the same as the number of male impressions (51 , 52, 53, 54, 55, 56, 57) plus one, and wherein said female impressions (40) are arranged so as to correspond with the male impressions (51 , 52, 53, 54, 55, 56, 57) and with the cooling sector (38).

9) Injection molding apparatus according to any of claims 5 to 8, wherein the perimeter of each female impression (30) comprises a moveable ring nut (40) which is fixed on at least an actuator (49) and once the injection molding of all the layers has been finished and a finished manufacture has been obtained, the ring nut (40) is translated outward through the actuator (49) and the finished manufacture is extracted from the female impression (30).

10) Injection molding apparatus according to any of claims 5 to 9, wherein the moveable plate (14) comprises a cylindrical element (19) arranged in the middle of the face provided with the female impressions (30) and a guide (23) is obtained on the side surface of said cylindrical element and wherein a cylindrical seat (4) is obtained in the face of the second die (13) in which there are the male impressions (51 , 52, 53, 54, 55, 56, 57), at least a pin (25) being provided in the inner surface of the cylindrical seat and being inserted in the guide (23) shaped so as to guide the translating and rotating movement of the plate (14) in a given way in comparison with the second die (13).