CH710919B1 - Two-part insert with texturing patterns for molding parts made of polymeric material. - Google Patents

Abstract

The present invention relates to an insert (6) for an injection mold intended for the production of parts made of polymeric material, such as thermoplastic and thermosetting polymers, which have a structured surface, preferably nano-structured, characterized in that it comprises: a first part (9) made of a thermosetting resin, said first part comprising a molding surface (20) which comprises at least one texturing pattern; a second part (2) made of a metallic material, said second part (2) of the insert (6) comprising at least one surface which is in contact with the first part (9) of the insert (6). The present invention also relates to a mold comprising said insert (6), as well as to its method of manufacture by casting resin on a master mold.

Description

Description: The present invention relates to mold inserts and molds intended for injection molding processes for parts made of polymeric material, such as thermoplastic and thermosetting polymers, which have a structured surface, preferably nano-structured, as well as their manufacturing process.

These mold inserts and these molds have a structured surface (or in other words a texturing pattern), preferably nano-structured, which is the negative of the structured surface of the part obtained by injection.

In the context of the present invention, the term "nano-structured surface", also known by the Anglo-Saxon name "nano-patterned surface", a surface having at least one pattern defined by areas in relief and hollow areas and the dimensions of these areas (width, height, pitch) are of nanometric order, for example up to a few hundred nanometers.

Similarly, a micro-structured surface means that the surface has at least one pattern defined by raised areas and recessed areas and the dimensions of these areas (width, height, pitch) are of order micrometric, for example up to a few hundred micrometers.

Polymeric materials are widely used to manufacture consumer goods in a wide variety of fields such as packaging, the automotive industry and even medical devices.

In fact, the use of polymeric materials in the manufacture of these consumer goods has the advantages of being able to produce them in very large quantities and at low cost according to conventional processes in the plastics industry. One of these processes consists of injection molding in which the polymeric material is melted in a mold.

In recent years, we have also sought to incorporate texturing patterns on a micrometric or even nanometric scale on the surface of these objects which are made of polymeric material. The advantage of this texturing is to functionalize the surface of objects, in particular to obtain optical effects such as scattering, anti-reflection, diffraction or tribological effects such as the anti-fingerprint effect, the anti-adhesion or modification of the surface tension.

There are technologies which make it possible to enrich the surfaces of parts made of polymer material with texturing patterns, and this without significantly increasing the cost of manufacturing these parts. For example, an engraving of the molding tool can be carried out. This certainly generates an additional cost of the molding tools, but this is amortized over large production runs of these parts.

More specifically, when the mold is a metallic mold, in particular made of steel, several technologies are known which make it possible to obtain different degrees of fineness of the texturing patterns, among which there may be mentioned:

1) Chemical etching; the desired texturing pattern is applied to the molding surface of the mold. The part of the molding surface which must not have a texturing pattern is protected. The mold is then immersed in an acid bath compatible with the metal of which it is made; which allows the selective etching of the texturing pattern on the molding surface. Chemical etching requires a great deal of know-how with specific installations due to the use of acid, the placement of the texturing pattern by an operator on the molding surface, the creation of complicated connections for the molding surfaces. in three dimensions, as well as the fittings.

2) Die sinking EDM is a technique that allows texturing patterns to be reproduced. To do this, an electrode of complementary shape to the shape to be engraved on the mold molding surface is pressed into the mold to reproduce it in hollow. This technology is limited in the fineness of the texturing pattern and may require several electrodes if the mold has multiple cavities.

3) Laser texturing is a technology which consists in machining the molding surface of the mold by a focused laser beam which ablates said surface at the location of the impact, thus giving it a texturing pattern. The depth and size of the texturing pattern depends on the settings of the laser (for example its power, frequency).

However, these different technologies have the drawbacks of structuring the molding surfaces of a metal mold (such as steel) with a limited fineness of the micrometric order (namely with an accuracy of between approximately 1 and 10 μm) and therefore without being able to reach the nanometric scale of the texturing patterns. In other words, the technologies described above have the drawback of not being suitable for producing finer texturing patterns, that is to say which are less than a micrometer, or even a few tens of nanometers . In addition, these technologies are limited for the production of a three-dimensional geometry of the patterns.

In addition, with regard to laser texturing, the steel around the impact of the laser is often thermally degraded and projections can be deposited at the edges of the texturing pattern.

Furthermore, these different technologies require etching directly into the metal of each mold molding surface according to methods that are difficult to reverse.

In addition, the texturing patterns obtained on steel mold molding surfaces often prove to be fragile and very difficult to repair in the event of alteration by a tool or by the residues of the gases emitted during the injection of the polymer material in fusion or by corrosion of tool steels.

Furthermore, a steel mold has the disadvantage of reacting to the rise in temperature in the second when the polymeric molten material was injected. Indeed, the steel mold immediately stores the heat of the molten polymeric material which is injected so that a small surface layer of this polymeric material freezes even before said polymeric material has filled the cavities. scale, for example nanometric, of the steel mold. This phenomenon of freezing of the polymeric material during its injection is known under the name of "skin effect" (or according to the English name: "skin effect").

Application US 2011/0 123 711 A1 has attempted to overcome this “skin effect” disadvantage which inevitably occurs with a steel mold by proposing a method for manufacturing a hybrid mold which comprises a layer of thermoplastic or thermosetting polymer having a texturing pattern whose dimensions are between 0.01 μm and 100 μm and the height is between 0.01 μm and 800 μm, said layer of polymer is covered with a metallic deposit, the thickness is between 0.5 μm and 500 μm.

However, the manufacturing process described in application US 2011/0 123 711 A1 has the following drawbacks:

- It is limited to the manufacture of two-dimensional molding surfaces, namely of the plate type. It therefore does not allow the production of molding surfaces with 2.5 dimensions (namely rounded surfaces) and 3 dimensions (namely spheres).

- It is complicated to implement, since it requires in particular a stamping step and a step of depositing a metal layer.

- When the polymer used for the manufacture of this hybrid mold is a thermoplastic polymer, that is to say an insulating material with a high heat capacity, this does not allow the molding under industrial conditions of parts of polymeric material with a surface with fine texturing patterns. In fact, the accumulation of heat during the injection of the molten polymeric material can generate a significant "bimetallic strip" effect if the part of the mold opposite (namely the counter mold) to that which comprises the nano-structured patterns. is made of steel; which is generally the case in injection molding devices. Indeed, the advantages that the second part of the mold (in other words "the counter-mold") is made of steel is to guarantee a better joint plane to avoid burr phenomena and to lengthen its duration of use. The bimetallic effect has the harmful consequence of deforming the molded part of polymeric material.

- It has a limited lifespan, around 1000 injection cycles for obtaining parts made of polymeric material.

Furthermore, application EP 2 181 824 A1 is known which describes a process for manufacturing a mold for parts made of polymeric material which comprises a metal support on which a thin layer of quasi-diamond carbon has been affixed. The nano-texturing pattern is applied directly to the quasi-diamond carbon layer by selective chemical etching in the dry phase.

In addition, application FR 2 991 312 A1 describes a method of manufacturing a mold insert consisting of an electro-formed metal support which implements the technology known as "LIGA" (namely the German acronym). of "Lithography, Galvanoformung, Abformung" resulting in "lithography, electroforming and molding") and an electroforming operation to obtain a mold insert. This metal support can be made, for example, of gold, copper, nickel or a nickel alloy.

The mold or mold insert manufacturing methods described in these applications EP 2 181 824 A1 and FR 2 991 312 A1 have the drawbacks of being complicated to implement because they comprise numerous steps meticulous to carry out such as stages of deposition of thin layer and engravings.

In addition, it is known that the durability, maintenance, upkeep and aging of the molds used and more particularly of their molding surfaces are key factors in ensuring the lasting quality of the objects produced. However, all of these constraints are even more limiting when the molds have a molding surface having structured patterns, and in particular nano-structured.

Finally, the release phase of parts made of polymeric material obtained by injection is also one of the crucial steps in their manufacturing process, because this phase plays an important role in the productivity of these parts. Indeed, this phase can generate a large number of rejects if there is a poor reproducibility of the mold surface or scratches on the surface of said mold. It can also disturb the manufacturing process, for example in the event of fouling due to possible sticking of the polymeric material in the mold. This is why it is essential that the molding surface having texturing patterns be of excellent quality, and that it preserve it throughout its duration of use which preferably must be as long as possible so that it presents a fully profitable industrial interest.

The inventors of the present invention have sought to overcome all the drawbacks detailed above relating to molds and mold inserts, the molding surface of which has texturing patterns and which are intended for injection molding of parts made of polymeric material. .

More particularly, the inventors of the present invention have sought to develop molds and mold inserts, the use of which during injection molding prevents the bimetallic effect mentioned above from occurring. , and this while not requiring to slow down the rates of injection molding with the implementation of relatively long and tedious cooling steps.

In fact, the inventors have developed a new insert for an injection mold intended for the manufacture of parts made of polymeric material, which is characterized in that it comprises:

- A first part made of a resin, said first part comprising a molding surface which comprises at least one texturing pattern;

- a second part made of a metallic material, said second part of the insert having at least one surface which is in contact with the first part of the insert.

Preferably, the metallic material has a high thermal conductivity, namely that it is at least 150 Wm ^_1 K ^-1 , and preferably at least 200 Wm ^_1 K ^-1 .

The metallic material can be chosen from aluminum, copper, silver, gold and beryllium, taken alone or as an alloy. For example, it can be an alloy of copper and beryllium.

Advantageously, the surface of the second part of the insert which is in contact with the first part of the insert has grooves which are configured so as to secure the first part and the second part of the insert by a mechanical grip. The resin from which the first part of the insert is made fills said grooves; which secures the first and second parts of the insert.

The insert according to the invention may have a generally parallelepiped shape. For example, its thickness can be between 3 mm and 100 mm, preferably between 10 and 20 mm, its length and width can be between 10 mm and 500 mm, preferably between 20 and 80 mm.

The texturing pattern that includes the molding surface of the first part of the insert according to the invention can have micrometric and / or nanometric dimensions. In one embodiment of the invention, the texturing pattern reaches a few tens of nanometers. For example, the height of the pattern can be between 0.01 micrometers and 100 micrometers, the width of the pattern can be between 0.01 micrometers and 100 micrometers and the spacing between each pattern can be between 0.01 micrometers and 100 micrometers.

The second part of the insert of metallic material is located behind the first part of the insert made of resin which has the molding surface comprising the texturing pattern and on which the polymeric molten material is injected during of an injection molding process.

By using an insert according to the invention, the molding surface of which is made of resin, it is however freed from the bimetallic effect which one might have expected when the counter-mold is made of steel.

The bimetallic stripe effect is a thermal phenomenon which occurs when two blades of a material, for example of a polymeric material, having different expansions or shrinkages are joined together. The shrinkage of a polymeric material is linked to its cooling rate. The faster the solidification of the polymeric material, the less there will be shrinkage.

A polymeric material injected during an injection molding process behaves like a bimetallic strip in its cooling phase. Indeed, a skin effect occurs when the molten polymeric material comes into contact with the mold and the counter-mold of the molding tool. This skin effect gradually increases during the entire filling phase of the mold and the counter-mold and during cooling, until the complete solidification of the polymeric material. The skin effect corresponds to the almost instantaneous solidification of the surfaces of the polymeric material in contact respectively with the mold and the counter-mold as soon as the molten polymeric material is injected. This is why two skins (or in other words two blades) are formed. The extent of this skin effect is characterized by the importance of the thicknesses of the skins formed.

During cooling, the two skins in the course of solidification will therefore stiffen the wall of the molten polymeric material which has been injected and will modify the shrinkage in the thickness of this polymeric material.

If the mold and the counter mold are not stabilized at the same temperature during an injection molding process, which is the case for molding tools in which the mold and the counter mold do not are not made of an identical material, the skins formed are not identical. The skin is thinner on the surface of the polymeric material which was in contact with the part of the molding tool (mold or counter-mold) whose stabilization temperature was the highest. The skin being thinner, it is less rigid, and thus the thickness of the polymer material remaining in fusion is thicker; which requires more time to cool and which induces a greater shrinkage. Consequently, the deformation of the piece of polymeric material thus obtained is greater on the side which was in contact with the part of the tooling whose stabilization temperature is the highest.

This is why, when the mold and the counter mold are not stabilized at the same temperature during an injection molding process, the thicknesses of the two skins (or in other words of the two blades) of the material injected polymer are not identical. This has the consequence that the shrinkage is not symmetrical in the thickness of said polymeric material and therefore induces a deformation of the part made of polymeric material obtained after injection molding.

The inventors have developed an insert which, although its molding surface is not made of steel but of a resin, has a stabilization temperature during an injection molding process almost identical to that of a counter-mold made of steel, so that the shrinkage of the polymeric material is symmetrical on the side of the mold and of the counter-mold made of steel, and thus the molded part obtained does not exhibit any deformation.

In other words, the inventors have developed an insert which, although comprising a molding surface made of a resin, does not induce a bimetallic strip effect when it is used in a molding tool with a steel counter mold. The experimental part described below testifies to these remarkable characteristics of the insert according to the invention.

In addition to the fact that the insert according to the invention makes it possible to avoid the bimetallic strip effect, it has the following other advantages:

- The insert according to the invention makes it possible to obtain, in a reliable and precise manner, injected parts having on the surface texturing patterns of excellent quality which correspond perfectly, by complementarity of shapes, to the molding surface of said insert, and even at the nanometric scale, because its molding surface is made of a resin which prevents the skin effect from occurring during the molten injection of the polymeric material.

- In addition, the insert according to the invention can be perfectly used for the injection of series greater than 10,000 pieces. In other words, the life of the insert is extended compared to that of inserts made of thermoplastic material known in the state of the art.

- The use of the insert according to the invention is perfectly integrated into the conventional industrial processes of plastics processing by injection of polymeric material, and this without needing to modify the industrial installations and devices, as well as the parameters of the injection stages. polymeric material. Indeed, the insert according to the invention does not require modifying the injection cycles of parts made of polymeric material which are usually used in this field of plastics processing. The use of an insert according to the invention is perfectly profitable from an industrial point of view.

- In addition, the use of the insert according to the invention in an injection molding process has the advantage of eliminating certain means such as vacuum injection, thermal cycling with a more or less increase important of the cycle time, electromagnetic induction heating, which can be implemented to overcome different problems such as the skin effect which arise with other molding tools known from the state of the art. This last point shows, once again, the profitability of the insert according to the invention compared to the state-of-the-art molding tools.

The resin of the first part of the insert according to the invention can be chosen from:

- thermosetting resins such as epoxy, polyurethane, polyester, vinyl ester, phenolic, bis-maleimide resins;

- thermoplastic resins such as polycarbonate of bisphenol A, polyetherketone, polyaryletherketone, polyphenylene bisphenol A, polysulfone, polyphenylsulfone, poly-2,6-phenylene dimethyloxide, polyetherimide, polyether sulfone, polyamide- imide and polypyromellitimide;

- organic-inorganic hybrid resins;

- sol-gel resins.

By "sol-gel resin" means a resin which has been obtained according to a sol-gel process, namely a process producing a glassy inorganic polymer by simple chemical reactions from precursors in solution, at a temperature close to room temperature (around 20 ° C) and not exceeding 150 ° C.

The precursors in solution of these sol-gel resins can be chosen from zirconium tetra-n-butanolate, zirconium butoxide, isopropyl titanate, tri- (3- (trimethoxysilyl) propyl) isocyanurate, gamma-methacryloxypropyltrimethoxysilane, n- phenyl-gamma-aminopropyltrimethoxysilane, taken alone or in mixtures.

For example, the sol-gel resin may be an acrylic resin modified with nanoparticles of silicon dioxide which has been obtained by a sol-gel process.

“Organic-inorganic hybrid resin” means networks of polymers composed of an organic matrix (for example a polymethyl methacrylate) and an inorganic matrix comprising, for example, silica, titanium, zirconia or zinc.

An example of an organic-inorganic hybrid resin is the resin sold under the trade name ORMOCER® by the company Micro Resist Technology GmbH. This resin has good thermal resistance, at least up to 270 ° C.

Preferably, the resin is a thermosetting resin which is an epoxy resin.

In one embodiment of the invention, the resin further comprises fillers.

The charges can be chosen from:

- mineral fillers such as calcium and / or magnesium carbonate, silicas and sulfates,

- metallic charges such as aluminum, copper and iron.

The charges detailed above can be taken alone or in mixtures.

For example, the resin may comprise a mixture of metallic fillers and mineral fillers.

When the resin comprises metallic charges, it is advantageously charges in the form of powder with a particle size less than 100 μm, more preferably around ten micrometers.

In a preferred embodiment of the invention, the resin is a thermosetting resin comprising metallic fillers. For example, this is the RenCast® CW 47 / Ren® HY 33 system sold by the company HUNTSMAN.

Advantageously, the mass percentage of fillers in the resin is between 30% and 70%.

The fact that the resin includes fillers improves the mechanical strength of the first part of the insert according to the invention. By improving the mechanical strength, it is meant that the first part of the insert according to the invention is more resistant to compression, impact and creep.

In this embodiment of the invention, the first part of the insert according to the invention which is made of a charged resin is perfectly suitable for the injection molding of parts made of polymeric material.

Advantageously, the resin of the first part of the insert has excellent thermal resistance, preferably greater than 200 ° C., even more preferably greater than 210 ° C., as regards the deflection temperature under measured load. according to ISO standard 75. By excellent thermal resistance of the resin, it is meant that the resin from which the first part of the insert according to the invention is made up does not degrade in any way at the temperatures of use of the insert, namely at during an injection molding process.

Excellent thermal resistance of the resin provides an insert according to the invention which is perfectly suitable for injection molding of most polymeric materials which are commonly used in plastics, or even polycarbonate which is a more delicate material to inject. Indeed, if one molds by injection of polycarbonate which has a glass transition temperature of approximately 150 ° C, it is necessary that the mold is made of a material whose glass transition temperature is equal to or greater than 150 ° C, otherwise the mold may be degraded during the injection.

In one embodiment of the invention, the resin has a glass transition temperature equal to or greater than 150 ° C. Thus, the insert according to the invention has the advantage of being intended for injection molding of very diverse polymeric materials.

For example, these polymeric materials can be chosen from polycarbonates, styrenics, polyolefins, polyamides, polyvinyls, elastomeric thermoplastics and silicones.

The resin advantageously has a thermal conductivity less than 2 Wm ^_1 K ^-1 , preferably about 1 Wm ^_1 K ^-1 (for example 1.17 Wm ^_1 K ^-1 ).

When the resin comprises fillers, the fillers being diluted in the resin, they do not modify the conductivity of the resin, even if they are metallic fillers.

Due to the low thermal conductivity of the resin from which the first part of the insert is made according to the invention, during injection molding of parts made of polymeric material, the skin effect mentioned above is not not produce. Thus, the molten polymer material does not freeze prematurely before having filled the cavities of the texturing pattern of the molding surface of the first part of the insert. This guarantees an excellent quality of the duplication of the texturing pattern, even if this texturing pattern is on a nanometric scale.

In one embodiment of the invention, the resin has a hardness of around 90 Shore D measured according to ISO standard 868.

In one embodiment of the invention, the resin has a compressive strength measured according to ISO 868 which is greater than 150 MPa.

The present invention also relates to a mold for injection molding of parts made of polymeric material which is characterized in that it comprises at least one insert according to the invention as described above.

In one embodiment of the invention, said mold consists of the insert according to the invention. By "mold made up of the insert" is meant that the insert according to the invention constitutes the body of said mold and that the fact remains that said mold can include other elements such as fixing means. , perfectly within the reach of the skilled person and which are necessary for the use of the mold in an injection molding process.

In another embodiment of the invention, said mold includes a cavity which is configured to house the insert according to the invention.

The present invention also relates to a molding tool which comprises at least one mold according to the invention as described above and a counter-mold. In one embodiment, the counter mold is made of steel.

The insert, the mold and the molding tool according to the invention can be used to produce by injection molding parts made of polymeric material having at least one texturing pattern on the surface, preferably a texturing pattern with micrometric or nanometric scale, said parts being intended for very varied applications, among which we can for example quote:

- holograms in the field of labeling to improve traceability and avoid counterfeiting,

- parts with self-cleaning and super-hydrophobic surfaces,

- parts made of polymeric material for consumer articles such as packaging parts, in particular packaging for cosmetic, food, stationery or even toys.

The present invention also relates to a method of manufacturing an insert according to the invention, the first part of which is made of a resin chosen from thermosetting resins, hybrid organic-inorganic resins and sol-gel resins, said method manufacturing process includes at least the following steps:

a) there is a master mold comprising a molding surface which comprises at least one texturing pattern;

b) a resin chosen from thermosetting resins, organic-inorganic hybrid resins and sol-gel resins is poured onto said molding surface of the master mold and onto at least one surface of an element made of a metallic material so as to securing the resin with said element to obtain an insert comprising two parts, the first part being made of resin and comprises a molding surface comprising a texturing pattern which is the negative of the texturing pattern of the molding surface of the master mold and a second part which is made of metallic material.

The texturing pattern of the molding surface of the master mold can have dimensions of the order of a micrometer and / or a nanometer. In one embodiment of the invention, the texturing pattern reaches a few tens of nanometers.

In one embodiment of the invention, the master mold is a silicon, quartz, fused silica, silicone mold, a semiconductor material, a metal oxide or even a metal nitride.

Preferably, the master mold is a silicone mold which has the advantage of producing texturing patterns on the surface of the insert according to the invention in 2, 2.5 and 3 dimensions.

The manufacture of the insert according to the invention is therefore easily implemented, and at low cost.

The insert according to the invention can easily be replaced if it were to be damaged during its use during an injection molding or else during any mishandling thereof (namely accidental deterioration) .

In addition, unlike the inserts known from the state of the art which have been described above, it does not require the carrying out of minute and tedious steps such as the deposition of a thin metallic layer or of engraving.

The manufacturing method according to the invention has the following other advantages:

- An insert is obtained, the molding surface of which comprises a texturing pattern which is made of a resin as described above and which gives said insert a longer service life than that of inserts made of thermoplastic materials. In fact, the insert according to the invention can perfectly be used for at least 10,000 injection cycles;

- From a master mold, for example made of an expensive and fragile material such as silicon, copies can be produced so as to obtain inserts according to the invention made of a less expensive material and which will be used during the molding process of parts made of polymeric material. In other words, we make copies of the master mold at low cost that we will use for the injection molding process.

- the inserts according to the invention being easily achievable and at low cost, it is then easy to manufacture inserts with very varied texturing patterns; which will make it possible to obtain pieces of polymeric material having various texturing patterns on the surface; and this by the simple fact that it will be easy to replace an insert according to the invention by another during the injection molding of series of parts made of polymeric material.

The texturing pattern presented by the master mold on its molding surface may have been obtained by different texturing techniques which are perfectly within the reach of those skilled in the art.

In this regard, mention may be made of the techniques which are photolithography, optical lithography by amplitude or phase mask, electron beam lithography, interference lithography, nanosphere / microsphere lithography, lithography by nano-printing (also known under the English name “Nano Imprint Lithography” and its acronym “NIL”), For example, photolithography is a technology which is perfectly known and suitable for carrying out nanostructures between 10 nm and a few tens of micrometers on a master mold, in particular a silicon master mold.

The NIL technique has the advantage of reproducing patterns obtained in a complex manner by other means of lithography, more quickly and on a very fine scale of the order of 10 nanometers.

In other words, it is perfectly within the reach of those skilled in the art to have a master mold as described above which has a molding surface comprising at least one texturing pattern. The materials and techniques for producing texturing patterns described above are examples given by way of illustration which do not limit the scope of the invention. Indeed, other materials and other techniques making it possible to obtain a master mold having a molding surface which has at least one texturing pattern could perfectly well be envisaged.

In one embodiment of the invention, the master mold has a diameter greater than 100 mm, preferably greater than 200 mm and a thickness of a few micrometers to several centimeters, preferably greater than 500 μm.

The master mold comprises on its molding surface a texturing pattern whose dimensions are from a few nanometers to a few tens of micrometer. These dimensions will depend on the desired properties of the desired texturing.

When the master mold is made of silicon, due to the physical characteristics of this material, this requires that the master mold be flat. In addition, it can be brittle when it is subjected to pressures, for example when we are going to pour the resin and / or turn it out. In addition, its cost is high due to the texturing processes used to structure its surface.

This is why, in view of these drawbacks of silicon, it is preferable to use a silicone master mold. The silicone may be Sylgard 184 sold by the company DOW CORNING.

When the master mold is made of silicone, this has the advantage that the molding surface can include texturing patterns in two dimensions, but also in 2.5 and 3 dimensions.

The silicone master mold may have been manufactured from a first mold, for example a silicon mold, which has a molding surface comprising at least one texturing pattern. In this embodiment, the molding surface of the silicone master mold will have a texturing pattern which will therefore be the negative of the texturing pattern of the molding surface of this first mold, for example of the silicon mold, and the insert. according to the invention obtained from this silicone master mold will present on its molding surface a texturing pattern which will be identical to that of said first mold (for example of the silicon mold).

Obtaining a silicone master mold is perfectly within the reach of those skilled in the art. Thus, the parameters for pouring silicone onto a mold are known to a person skilled in the art. In addition, after casting, the silicone hardening step (thermally) is also part of the knowledge of a person skilled in the art.

The choices of texturing patterns on the master mold and the insert according to the invention will be oriented according to the desired texturing pattern on the piece of polymeric material which is injection molded from the insert according to the invention. 'invention. Those skilled in the art have a perfect mastery of molding techniques so that they will be able to develop without difficulty:

- the manufacture of an insert according to the invention with the desired texturing patterns from a master mold,

- the use of the insert according to the invention for the injection molding of parts made of polymeric material.

Before the casting step, the resin was advantageously prepared by mixing, preferably under vacuum, its various constituents (namely the resin and the hardener) in the proportions prescribed by the manufacturer and left to degas for a period sufficient so that the mixture no longer has bubbles.

Preferably, step b) of casting the resin under vacuum is carried out. This has the advantage that degassing of the resin continues during casting.

The casting of the resin can be carried out at room temperature. Then, the resin is brought back to atmospheric pressure and it is:

- left to crosslink at room temperature for the time prescribed by the manufacturer, or

- heated to a temperature and for a time recommended by the manufacturer to promote crosslinking.

The crosslinking of the resin can be followed by a heat treatment at a higher temperature to allow it to have better temperature resistance, the temperature and the duration of this heat treatment also being indicated by the manufacturer of the resin.

In one embodiment, the casting of the resin is carried out at a temperature of approximately 120 ° C. and it is cured for approximately 16 hours at 180 ° C.

Of course, the implementation of step b) of the manufacturing process is perfectly within the reach of the skilled person who masters the casting of a resin on a master mold. This is why, the example described above of the casting of resin in no way limits the scope of the present invention.

As mentioned above, the element made of a metallic material may have grooves which are configured so that the cast resin fits perfectly in it so that the first part and the second part of the insert are integral.

The resin casting step is carried out in a molding tool perfectly within the reach of those skilled in the art. In addition, the casting parameters of the resin are part of the general knowledge of a person skilled in the art.

When the first part of the insert according to the invention is made of a thermoplastic resin, said insert may have been obtained in the following manner:

- A texturing pattern is stamped on a surface of an element made of a thermoplastic resin so as to obtain a first part of the insert comprising a molding surface which comprises said texturing pattern;

- This first part is fixed on the surface of a second element made of a metallic material and which constitutes a second part of the insert so as to secure said first part with the second part of the insert.

The joining of the first part with the second part of the insert can be carried out with any mechanical means within the reach of the skilled person. For example, it can be a collage.

Other advantages and characteristics of the present invention will emerge more clearly from the description which follows of an embodiment of an insert according to the invention given by way of nonlimiting example, as well as from experimental results which are shown in the accompanying drawings, in which:

Fig. 1 shows schematically and in section a tool for the manufacture of an insert according to the invention before being assembled, as well as a part of said insert according to the invention.

Fig. 2 shows schematically and in section the tool shown in FIG. 1 after being assembled and in which said part of the insert has been housed.

Fig. 3 shows schematically and in section the insert according to the invention obtained with the tool shown in Figs. 1 and 2.

Fig. 4 shows schematically and in section the part of the insert surrounded in FIG. 3.

Figs. 5a to 5d show schematically and in section inserts made of different materials.

Fig. 6 is a graph of the rise in temperature over an injection cycle as a function of the time of the inserts shown in FIGS. 5a to 5d.

Fig. 7 is a graph of the temperature as a function of time of the inserts shown in FIGS. 5a to 5d for more than 25 injection cycles.

[0102] FIG. 1 shows schematically and in section a tool 17 for the manufacture of an insert 6 according to the invention.

This tool 17 comprises a first metal element 1 in which is formed a cavity 19 intended to house a block 2 of aluminum which constitutes a second part of the insert 6 according to the invention.

In the first element 1 is also formed a channel 16 which is arranged to bring an epoxy resin 9 loaded with aluminum at a mass content of 60% to the cavity 19.

In block 2, a channel 18 is also formed in which said resin 9 will flow.

The first element 1 further comprises a first fixing means 5a.

The tool 17 includes a second element 3 made of metal. This second element 3 comprises a mold 4 made of silicone which has texturing patterns 8 on its surface.

The second element 3 comprises a second fixing means 5b which is configured to cooperate with the first fixing means 5a so as to fix the first element 1 on the second element 3 of the tool 17 so as to be able to pour the resin 9 .

To manufacture the insert 6 according to the invention, the block 2 is housed in the cavity 19 as can be seen in FIG. 2. The channel 16 of the first element 1 of the tool 17 and the channel 18 of the block 2 are arranged in such a way that when the block 2 is housed in the cavity 19, the channel 18 is in the extension of the channel 16. The second element 3 is fixed to the first element 1 with the first and second fixing means 5a, 5b so as to assemble the tool 17.

Next, the resin 9 is poured under vacuum into the cavity 19 passing through the channel 18 of the block 2.

After the casting of said resin 9, an insert 6 is obtained according to the invention which comprises a first part made of said resin 9 which is integral with a second part consisting of the block 2 of aluminum.

As can be seen in FIG. 4, this insert 6 has in the first part made of resin 9 a molding surface 20 which includes texturing patterns 7. These texturing patterns 7 are of nanometric dimension.

The texturing patterns 7 are the negative of the texturing patterns 8 of the silicone mold 4.

[0114] FIGS. 5a to 5d show schematically and in section inserts 15a to 15d which were used during the experiments described below.

The inserts 15a to 15d comprise first and second fixing means 14a, 14b which are configured to use these inserts 15a to 15d in an injection molding tool (not shown but more fully described below).

More specifically:

- the insert 15a is made of steel 10;

- the insert 15b is made of epoxy resin 11 loaded with aluminum at a mass content of 60%;

- The insert 15c consists of a first part made of epoxy resin 11 loaded with aluminum at a mass content of 60% and a second part made of aluminum 12;

- the insert 15d is made of polycarbonate 13.

Experimental part During the experiments, a molding tool was used which included:

- an ENGEL injection molding machine marketed under the trade name e-max 200/100;

- a mold with a carcass in XC48 steel in which were housed a mold and a counter-mold made of 40 CMD8 steel, pretreated to 110 kg / cm ² according to an AFNOR standard.

A cavity was formed in the mold in which the inserts 15a to 15d were successively arranged.

The inserts 15a to 15d included a molding surface. In addition, the inserts 15b and 15c had a texturing pattern on their molding surface.

The experiments were carried out according to standard injection conditions in the plastics industry.

The molten injected polymeric material was polystyrene sold by the company STYRON under the trade name STYRON® 678E.

Regulation of the mold temperature was obtained with a circulation of water at room temperature.

The injection temperature was 230 ° C and the holding pressure corresponded to 70% of the injection pressure.

The injection speed was 0.53 seconds.

The total injection cycle time was 20 seconds.

During these experiments, temperatures were measured with a thermocouple which had been inserted in the molding tool so as to be located 3 mm from the molding surface of the insert 15a to 15d tested which was therefore in contact with molten polystyrene during the injection molding process. A type J thermocouple isolated from the company BMS marketed under the trade name TI04J2100 coupled to a thermometer marketed by the company TESTO under the trade name 735-2 were used.

During the experiments, the thermocouple was directly connected to the control system of the injection molding machine.

The temperatures were recorded every 0.5 seconds.

The inserts 15a, 15b and 15d made of steel, epoxy resin loaded with aluminum and polycarbonate are comparative inserts of the insert 15c according to the present invention and which has two parts, one being made of resin and the second being made of a metallic element.

This is why, from the temperature measurements of the insert 15c over time during the injection cycles and compared with those of the inserts 15a, 15b and 15d, it was possible to deduce the quality of reproduction. texturing patterns with an insert according to the invention.

First, we studied the temperature rise of the inserts 15a to 15d during the first polystyrene injection cycle.

In FIG. 6 is a graph of the temperature rise as a function of time, more precisely during an injection cycle of the inserts 15a to 15d.

It is noted that the steel insert 15a is the one whose temperature rise is the fastest. In other words, insert 15a reacts almost immediately upon molten injection of the polystyrene.

The insert 15b (consisting only of epoxy resin 11 loaded with aluminum) and the insert 15c according to the invention have a rise in temperature offset with respect to the insert 15a of steel. Knowing that the injection time of a molten polymer material is generally less than one second during an injection molding process, this offset in temperature rise of approximately 2 seconds is very beneficial, because it leaves a acceptable time to fill the cavities of the texturing patterns of the inserts 15b and 15c before the polymeric material (such as polystyrene) injected in the melt freezes (in other words cools). This guarantees good quality reproduction of the texturing patterns. Indeed, the longer the reaction time of the insert to the temperature of the molten polymeric material, the better the quality of reproduction of the texturing patterns of the molding surface of the insert on the molded part of polymeric material.

Thus, with the inserts 15b and 15c, the skin effect is avoided.

With the insert 15d made of polycarbonate, there is no rise in temperature during the ^1st injection cycle. However, as will be demonstrated below with the graph in FIG. 7, with such a polycarbonate insert 15d, after more than 25 injection cycles, there is a rise in temperature of said insert 15d which is greater than 100 ° C.

In conclusion, the graph of FIG. 6 shows that the inserts 15b and 15c are suitable for quality duplication of the texturing patterns that they include on a polymeric material during an injection molding process.

The graph of FIG. 7 represents the temperature as a function of time of the inserts 15a to 15d during several injection cycles (at least 25 cycles; each sinusoid corresponding to an injection cycle) of polystyrene with the injection molding tool described above above.

From graph 7, after a certain number of injection cycles, it can be noted that the temperature tends to stabilize for each of the inserts 15a to 15d. This stabilization temperature is:

- slightly higher than 100 ° C for the insert 15d made of polycarbonate-this high stabilization temperature of the polycarbonate is explained by the fact of its low thermal conductivity of about 0.2 Wm ^_1 K ^-1 ;

- around 90 ° C for insert 15b made of epoxy resin loaded with aluminum;

- About 35 ° C for the insert 15c according to the invention and the insert 15a made of steel.

It should be recalled that the counter-mold of the molding tool is made of steel; which is generally the case in injection molding tools.

In view of the stabilization temperature difference between that of the steel counter-mold which is therefore also about 35 ° C. and that of the polycarbonate insert 15d which is greater than 100 ° C., when the part polystyrene is molded with this insert 15d, there is a bi-blade effect which will have the consequence of deforming it.

Because the difference between the stabilization temperatures of the steel counter-mold and of the insert 15b of epoxy resin loaded with aluminum is smaller than with the insert 15d of polycarbonate, the bimetallic effect occurs to a lesser extent for a molded part with the insert 15b compared to the molded part with the insert 15d made of polycarbonate. In FIG. 7 in view of the quasi-superposition of the curves of the steel insert 15a and of the insert 15c according to the invention, it should above all be noted that the bimetallic effect does not occur when the polystyrene part is molded with an insert 15c according to the invention. Indeed, the insert 15c has a rise in temperature and a stabilization of the temperature which are very similar to those of the steel counter-mold.

Thus, the graph of FIG. 7 demonstrates that in order to avoid the bimetallic strip effect which has the consequence of deforming the molded part made of polymeric material (for example made of polystyrene), it is particularly advantageous to use an insert 15c according to the invention, and this while :

- implementing a perfectly standard injection molding process, namely one which does not require relatively long and tedious cooling steps which slow down the production rate by increasing the duration of the injection cycles;

- using standard molding tools, namely whose counter mold is made of steel.

Claims (10)

claims 1. Insert (6) for an injection mold intended for the manufacture of parts made of polymeric material which is characterized in that it comprises: a first part (9) made of a thermosetting resin, said first part of the insert (6) comprising a molding surface (20) which comprises at least one texturing pattern (7); a second part (2) made of a metallic material, said second part (2) of the insert (6) comprising at least one surface which is in contact with the first part (9) of the insert (6). 2. Insert (6) according to claim 1, characterized in that the resin has a glass transition temperature equal to or greater than 150 ° C. 3. Insert (6) according to one of claims 1 to 2, characterized in that the at least one surface of the second part (2) of the insert (6) which is in contact with the first part (9 ) of the insert has grooves which are configured so as to secure the first part (9) and the second part (2) of the insert (6) by a mechanical hook. 4. Insert (6) according to one of claims 1 to 3, characterized in that the metallic material (2) has a thermal conductivity of at least 150 Wm ^_1 K ^-1 . 5. Insert (6) according to one of claims 1 to 4, characterized in that the resin is an epoxy resin. 6. Insert (6) according to one of claims 1 to 5, characterized in that the resin comprises fillers. 7. Insert (6) according to claim 6, characterized in that the mass percentage of fillers in the resin is between 30% and 70%. 8. Mold for injection molding of parts made of polymeric material, characterized in that it comprises at least one insert (6) according to one of claims 1 to 7. 9. Method of manufacturing an insert (6) according to one of claims 1 to 7, the first part (9) of which is made of a thermosetting resin, characterized in that it comprises at least the following steps: a) there is a master mold (4) comprising a molding surface which comprises at least one texturing pattern (8); b) a thermosetting resin (9) is poured onto said molding surface of the master mold (4) and onto at least one surface of an element (2) made of a metallic material so as to secure the resin (9) with said element (2) for obtaining an insert (6) comprising two parts, the first part (9) being made of said resin (9) and comprising a molding surface (20) comprising a texturing pattern (7) which is the negative the texturing pattern (8) of the molding surface of the master mold (4) and a second part (2) which is made of the metallic material. 10. Method of manufacturing an insert (6) according to claim 9, characterized in that the joining of the first part (9) with the second part (2) of the insert (6) is carried out by bonding.