WO2002004192A1

WO2002004192A1 - Bi-material process

Info

Publication number: WO2002004192A1
Application number: PCT/EP2001/008089
Authority: WO
Inventors: Stéphane MENIO; Eric Lafranche; José PABIOT; Claude Ollive
Original assignee: Menzolit S.A.
Priority date: 2000-07-12
Filing date: 2001-07-12
Publication date: 2002-01-17
Also published as: AU2001287609A1; WO2002004192B1; FR2811607A1

Abstract

The invention refers to a process for the production of moulded pieces made from plastic materials by injection moulding or injection compression moulding thereby using at least two different types of plastics materials in the same mould whereby at least one material is used for the formation of the core of the piece and at least one material is used for the formation of the skin of the piecewhereby the skin envelopes the core of the piece at least partially whereby at least one material for the formation of the core of the piece is a thermoset material and whereby at least one material for the formation of the skin is a thermoset material.

Description

"Bi-Material Process"

Process for the manufacture of pieces by injecting at least two different polymeric materials as well as use of these pieces

FIELD OF THE INVENTION:

The invention refers to a process for the manufacture of pieces made from plastic materials by injection moulding or injection compression moulding from at least two different types of plastics materials as well as to the use of these pieces.

BACKGROUND OF THE INVENTION:

Bulk moulding compounds (BMC) are used in large amounts for the manufacture of products made out of plastic materials. Most of them are produced on the base of curable unsaturated. polyester (UP) resins. By undergoing cross-linking and/or curing (hardening) - partially or completely - they form thermoset plastics.

BMC are manufactured in series for production e.g. of head lamp reflectors for automobiles. Head lamp reflectors in automobiles are subjected to temperatures in the range of from 120 to 240 °C when spending light, the temperature depending for example on the type and size of the reflector, the type of the lamp and the ventilation inside the lamp reflector. Furtheron, they have to fulfil a very high degree of reflection as may be measured according to the ASTM standard E430 or according to the European standard ISO 2813 which sets requirements similar to the ASTM standard E430. Therefore, the curving has to be quite exact and the surface of these reflectors has to have a very smooth surface with an extraordinary low surface roughness not to loose too much light into undesired directions.

BESTATIGUNGSKOPIE Head lamp reflectors are manufactured by the steps of

1.) mixing the raw materials and several additives together to generate a BMC ready to be injected,

2.) injection moulding of the BMC,

3.) cleaning operations like removing the sprues, deflashing, and removing the dust,

4.) a UV light treatment to optimize adhesion of the clear coat on the surface of the BMC chemically and physically to the chemical substance(s) of this clear coat,

5.) overcoating the surface of the formed piece with a varnish which is called "clear coat" by immersing or by spraying to generate a much smoother surface which has a very low surface roughness,

6.) metallizing the surface of the clear coat e.g. with aluminium or an aluminium alloy in a vacuum chamber and

7.) coating the metallized surface to protect it against oxidation and tarnishing e.g. by a clear thin varnish layer, which may be a layer of polysiloxan. The appliance of the clear coat necessitates great care to avoid e.g. runs, drips and other disturbing irregularities.

EP-A-0 790 115 teaches a process for the production of high-quality optical components primarily made from thermoset materials whereby only one material is used having a content of pre-cured moulding material as well as a very high fibre and filler content and whereby the mould surface temperature should be above 170 °C (360 °F). The target of this process is to avoid the clear coat by manufacturing pieces with a very smooth injection moulded surface. This process requires surfaces of the mould with an excellent surface quality as well as the strictly complying with several narrow requirements of the process conditions to generate moulded pieces where a very thin skin is formed of a fibre-free material having a very low filler content which is pressed out after separation of the phases of the moulding material. Therefore, this process requires a nearly perfect process control within several very narrow ranges which is hardly to be fulfilled in series production and which is expensive. It is expected that this process causes a high abrasion at all walls getting in contact with the moulding material.

As the manufacturing of the clear coat including the UV treatment causes production costs in the range of about 25 to 30 % of the completed head lamp reflector, it is one object of the invention to propose a less expensive manufacturing process by avoiding the clear coat. It is a further object of the invention to propose a process which may be used in series production and which may be controlled relatively easy. Furtheron, it is another object of the invention to propose a process in which skins of excellent colour, gloss, antistatic behaviour, scratch resistance etc. can be produced in series on the outer parts of the plastic pieces.

The BMC will be called "moulding material" or often shortened "material" in the following, partly being used as "core material" or partly being used as "skin material".

SUMMARY OF THE INVENTION:

According to the present invention, there is provided a process for the production of moulded pieces made from plastic materials by injection moulding or injection compression moulding thereby using at least two different types of plastics materials in the same mould whereby at least one material is used for the formation of the core of the piece and at least one material is used for the formation of the skin of the piece whereby the skin envelopes the core of the piece at least partially whereby at least one material for the formation of the core of the piece is a thermoset material and whereby at least one material for the formation of the skin is a thermoset material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

It has been discovered that if e.g. two different but similar moulding materials for injection moulding are put one after the other into a channel or into an open space standing in pressure contact with the pressure inducing moulding machine or plug system and if these two materials are then injected into a mould in such way that the first material must not fill the whole space most far from the entrance of the mould where the moulding material entered the open space of the mould but that the first moulding material primarily envelopes the second material which generates the core of the piece to be formed. Therefore, a skin may be formed from the first material which is called furtheron the skin material and a core may be formed from the second material which is called furtheron the core material.

It was astonishing that it was possible that the skin material may surround the core material partially or totally depending on the composition, the volume and the condition of the two moulding materials as well as on the geometry and surface condition of the mould and of the channels which lead to the open space of the mould.

Furtheron, it was discovered that it is possible to use even three, four or even more different moulding materials for manufacturing a piece according to the invention. In such a case the second and perhaps even a third moulding material may form a layer being partially or totally below the layer of the first resp. second moulding material, so that the skin materials may more or less form onion like shells from the outer skin layer to the inner skin layer.

Surprisingly it has been found that the way a first moulding material is and sometimes even one to three additional moulding materials are lead to the open space of the mould to form a skin and the conditions of these materials and of the process decide if a skin enveloping a core of the piece develops.

Furtheron, it was astonishing that the quality of the surface of the skin may look quite fine, but that it is necessary to measure the surface quality exactly. This may be done e.g. by atomic force microscopy for measuring the roughness of the surface and/or by an instrument for determining the quality of the gloss to optimize the surface quality of the skin which cannot be done by visual inspection only. It was observed that the roughness occurs in such a microscale that it cannot be measured good enough with conventional measuring systems with a touching diamond top like a Perthometer or by visualizing the topography with a scanning electron microscope as many surface faults and inhomogeneities are smaller than 0.1 μm.

As a machine for the injection moulding or for the injection compression moulding, an injection moulding machine may be used. Alternatively, although no longer used nowadays for injecting of moulding materials into a mould, a cylinder press machine might be used instead of the injection machine. In the following, the process is described as used for an injection moulding machine, although a similar process might be used for a cylinder press machine. The expert in the art knows what to do as nearly all actions and conditions for both types of machines are generally known to the expert in the art.

As raw materials as the main base for the moulding materials, e.g. unsaturated dicarboxylic acids and/or saturated dicarboxylic acids together with diols, may be used for forming the resin of a moulding material. To these raw materials may be added monomers like vinyl, allyl, and/or acrylic compounds for cross-linking, a free radical polymerization initiator like t-butyl perbenzoate or any peroxide, a releasing agent like zinc or calcium stearate, an inhibitor to prevent premature polymerization and/or to modify the reaction times, an optical brightener to slightly coloured resins, a blue dye as a curing indicator, a light stabilizer to prevent yellowing in the light of the sun, an antistatic agent, a flame retardant like a chlorinated paraffin, an aluminium hydroxide and/or an antimony trioxide, a soluble dye and/or an insoluble pigment for colouring, a filler like calcium carbonate and/or kaolin and/or mica and/or dolomite, a thickening agent as required for a moulding material like calcium and/or magnesium oxide/hydroxide which may be mixed with a filler and used to impregnate the fibres and thereby converting the moulding compound into a highly viscous state, a low shrink and low-profile additive like a solution of thermoplastics in styrene to reduce volume shrinkage during curing, especially polystyrene, poly(vinyl acetate), poly(methyl methacrylate), saturated polyesters, cellulose acetobutyrate, and polycaprolactams, fibres especially made of an „E" glass in the form of chopped fibres and sometimes even further additives.

The moulding materials may be used in a pre-cured stage, especially when used with anjsocyanate. As the use of the terms "curing" resp. "cross-linking" depends on the chemical constitution as well as on the profession of the expert using these words, there will not be differentiated in this text if it is a curing and/or a cross-linking.

The moulding material to be used for moulding the skin resp. the core of the piece may be fed e.g. into a hopper and under the simultaneous action of pressure applied on the moulding material by a piston and/or by the backward or forward movement of an injection screw. The quantity of the moulding material may be fed from the front of the injection screw into a barrel which can be heated at a temperature in the range e.g. of from 15 to 50 °C, whereby the level of the temperature depends on the catalytic system of the moulding material. If needed, the system with the plug and piston used may be heated, too. Generally, it is preferred that the injection screw is equipped with a non return valve to avoid a return of the moulding material into the screw after injection into the mould. The fed moulding material is then injected into the mould with the aid of the screw which behaves like a piston or with the aid of the plug transfer system.

Generally, the injection time may vary between 0.5 and 3 seconds, preferably between 0.5 and 1.5 seconds. When the mould is filled with the moulding material, a hold pressure is applied to avoid defaults brought about by the shrinkage of the moulding material during its curing/cross linking. The time during which the hold pressure is applied depends on the curing/cross linking time and on the geometry of the gate of the tool. The hold pressure time may vary between 3 and 15 seconds, preferably between 5 and 10 seconds.

The mould may be hold at a temperature in the range of from 130 to 180 °C, preferably of from 135 to 175 °C. This temperature depends on the catalytic system of the moulding material. The whole process from starting filling the open space of the mould until the opening of the mould and ejection of the moulded part(s) may take 30 to 90 seconds, preferably 40 to 60 seconds. This time depends primarily from the maximum thickness of the parts and from the polymerisation speed of the moulding material.

There are only few differences in the use of a machine for the injection moulding or a machine for the injection compression moulding. When using injection compression moulding it has to be taken care that the slits standing necessarily open between the different parts of the mould are not opened too wide, so that the moulding material(s) may fill and close these slits. If these gaps/slits between the different parts of the mould can be closed with the moulding material as the openings of the different parts of the mould are standing not too wide open, then it is possible to build up a hold pressure for a certain short time so that the moulding materials can be cured/cross- linked under this relatively high pressure.

The details for handling such a moulding machine as well as the injection processes itself are well known to the expert in the art so that it is not necessary to describe most of the steps of these well-known processes.

For the process according to the invention it is desirable to have a mould and channels which lead to the mould of a high surface quality of the inner surfaces. It is necessary to have at least one container for the skin material with the equipment to inject the skin material(s), in many cases such that this material is in front of the core material. Furtheron, it is necessary to have at least one container for the core material(s) with the equipment to inject the core material(s) into the mould and which equipment is independent from the equipment to inject the skin. If there should be used even a third or possibly even a fourth material, these materials may be injected between the (first) skin material and the (last) core material in a way that all the different materials can stand in pressure contact with the pressure inducing machine for the injection; then it is favourable to have even one or two further containers for the third resp. fourth moulding material together with the equipment to inject these materials. The third resp. fourth moulding material may be located in the formed piece in between the outer skin and the inner core; if the skin material should surround the core material only partially, it may be favourable that at least one further moulding material forms a further layer of the piece, especially there where the skin material is still missing.

In most of the cases it will be the target to produce a skin which has an essentially constant layer thickness. The term "essentially" shall hereby indicate that the layer thickness cannot be produced strictly constant but may vary according to the process and piece selected. On the other hand it may be intended to produce a piece having a skin which shows a continuous change of the layer thickness. Preferably, there may be used only two or three different moulding materials for all the injection, more preferred only one material for the formation of the core of the piece and only one material for the formation of the skin surrounding the core at least partially whereby the two materials must not be separated sharply after injection. The two different materials may show a zone of a mixture, even with a gradient, between the core material and the skin material after being injected and before being cured/cross-linked in a zone at about the interface between the core and the skin. If there should be used a third or even a fourth different moulding material the second and the third material will be located between the inner core and the outer skin of the piece.

The pieces to be manufactured with such a skin may fulfil different tasks. One task may be that the skin is formed having a surface roughness measured similarly to and calculated as the average peak-to-valley-height value R_a of not more than 50 nm as measured by atomic force microscopy, preferably of not more than 25 nm, more preferred of not more than 16 nm, much more preferred of not more than 10 nm, especially of not more than 6 nm. R_a has been measured and calculated according to ISO 4287/1 over a measuring field of 20 μm x 20 μm with an atomic force microscope of the type Nanoscope E from Digital Instrument on the functional face of the surface of the piece resp. of the mould or channel.

Another task of the skin may be that it is formed having after curing/cross-linking at least partially a colour different from the colour of the core material after curing/cross- linkage, preferably a coloured skin on a white or naturally coloured core material. Or it may be formed being after curing/cross-linking at least partially naturally coloured or transparent or clear on a core material being after curing/cross-linking white, of natural colour or of any other colour.

Another task of the skin may be that it is formed surrounding the core at least partially after curing/cross-linking having a high electrical resistance and/or preventing from static electrical load. A further task of the skin may be that it is formed at least partially having after curing/cross-linking a high chemical resistance against acidic and/or basic media and/or solvents.

A further task of the skin may be that it is formed at least partially having after curing/cross-linking a high scratch resistance. The scratch resistance should show after standard testing a scratch with a width lower than 100 μm for a load of at least 2 Newton. Preferably, a scratch with a width lower than 100 μm is generated with a load of at least 2.3 Newton. More preferably, the load may be between 2.5 and 3 Newton for this kind of scratch. The testing may be done with a measurement according to German standard DIN 53799.

The skin may be formed at least partially surrounding the core of the piece having after curing/cross-linking a thickness of from 0.01 to 0.8 mm, preferably of from 0.02 to 0.7 mm, more preferred of from 0.05 to 0.6 mm, much more preferred of from 0.08 to 0.5 mm. The skin may have a layer thickness of essentially the same thickness, which may be preferred as this process may be easier to be controlled and which process allows to control shrinkage and deformation of the piece much more easily. But alternatively, the skin may show an (intended) gradient of the layer thickness of the skin, too.

The core material may have - in comparison with the skin material - nearly the same or similar rheological properties and a slightly or strongly different chemical composition; preferably the skin material has a slightly lower viscosity than the core material.

The core material may contain fibres in a range of from 5 to 30 % by weight as well as fillers in a range of from 30 to 85 % by weight as calculated before curing/cross- linking.

Preferably the fibre content of the core material varies in the range of from 7 to 25 % by weight, more preferred of from 9 to 20 % by weight, much more preferred of from 10 to 15 % by weight and preferably the filler content varies in the range of from 38 to 78 % by weight, more preferred of from 50 to 75 % by weight and much more preferred of from 58 to 70 % by weight. Nevertheless, for certain purposes moulding materials may be selected which favour a fibre content of from 2 to 12 % by weight, especially of from 4 to 9 % by weight, and/or a filler content in the range of from 25 to 48 % by weight, especially of from 30 to 45 % by weight.

As fibres usually glass fibres are used, especially fibres of glass E. A high fibre content causes a high strength and a high modulus of elasticity, but the more or less important orientation of these fibres during injection may strongly affect these properties as well as the quality of the surface as can be observed from the quality of the surface (roughness vs. smoothness, gloss, homogeneity). A low fibre content causes a relatively low strength and a relatively low modulus of elasticity, but the quality of the surface may be influenced positively.

A high filler content causes a high viscosity as well as a high modulus of elasticity and may positively influence the quality of the surface, but may affect the impact properties, too. A low filler content causes a relatively low strength and a relatively low modulus of elasticity, but the quality of the surface may be increased favourably; furtheron, a low filler content allows to introduce a higher amount of glass fibres. A skin material having a low fibre content and/or having a low filler content should undergo a chemical reaction in order to modify the viscosity level of the unsaturated polyester resin. This may be obtained at least partially with an oxide and/or hydroxide, especially with an oxide and/or hydroxide of an alkaline earth element. If for example MgO reacts with carboxylic acid, then the viscosity of the material is increased which allows to further reduce the content of fillers, sometimes even down to zero.

The viscosity of the unsaturated polyester resin for a core material or for a skin material may also be modified by a chemical reaction between the hydroxyl group of the unsaturated polyester resin and the constituents containing at least one isocyanate group, like toluene diisocyanate (TDI) or methylene diphenyl diisocyanate (MDI). The viscosity of the material may also be increased through the use of a high viscosity unsaturated polyester resin, containing for example a small quantity of monomer, and more particularly of a high viscosity monomer or even a high fusion point monomer like the "triallyl cyanurate". In these cases, the viscosity of the material is increased which allows to further reduce the content of fillers in the skin material, sometimes even down to zero. In many cases, it is favourable to have a skin material of another viscosity than the core material.

The skin material may contain fibres in a range of from 0 to 10 % by weight as well as fillers in a range of from 0 to 50 % by weight as measured before curing/cross-linking. Preferably, the content of fibres may vary in a range of from 0.5 to 8 % by weight, more preferred of from 1.5 to 6 % by weight or being essentially free of fibres, whereas the content of fillers may vary in the range of from 1 to 46 % by weight, more preferred of from 5 to 42 % by weight, much more preferred of from 15 to 38 % by weight, but it may also be possible to use a material being essentially free of fillers. The fibres are usually of the same or similar type as for the core material.

It may be preferred that the filler of a core material or of a skin material has a very small grain size, e.g. the average grain size as may be measured with a Sedigraph 5100 from the company of Micrometrics. The average grain size of the filler may be in the range of from 0.05 to 5 μm, preferably in the range of from 0.1 to 3 μm, more preferred in the range of from 0.3 to 1.5 μm. It may be desirable not to control the average grain size but the maximum grain size of the filler. In such a way it may be desired that the maximum grain size may be not greater than 20 μm, preferably not greater than 15 μm, more preferred not greater than 10 μm, much more preferred not greater than 6 μm.

Furtheron, it may be preferred that glass fibres are used in a core material or in a skin material which have an average length in the range of from 3 to 12 mm in general, but which may show an average length in the range of from 3 to 6 mm for normal requirements, preferably of from 4.5 to . 6 mm; but for cases where excellent mechanical properties are required an average length of at least 6 mm is preferred and for cases where mechanical properties are fundamental an average length in the range of 12 mm is preferred.

On the other hand, it may be preferred that glass fibres are used in a skin material or in a third and/or fourth material which have an average length in the range of from 0.05 to 4.5 mm, preferably of from 0.08 to 3 mm, more preferred of from 0.1 to 1.5 mm or of about 0.1 mm; in such a case, it concerns milled fibres, when an excellent surface smoothness is required.

The material for the skin may be injected into a channel which leads to an entrance of the mould or may be injected into the very first beginning of the open space of the mould which is the entrance area which forms part of the moulded piece and which part will be separated from the piece after ejection. The material for the skin may be injected either at essentially the same time or of from 0.01 to 5 seconds before the injection of the material for the core material, preferably of from 0.2 to 2.5 seconds before, much more preferred of from 0.4 to 1.8 seconds. If a third and/or fourth moulding material is used it may be preferred that it is injected at essentially the same time or shortly after the first skin material and shortly before the last core material. The skin material as well as the third resp. fourth moulding material may be pushed with a weak impulse into a channel leading to or into the mould or into the entrance of the mould so that the skin material is located in front of the core material and in that the core material is pushed with a strong impulse forward thereby moving the skin material in front of it into the open space of the mould. If a third resp. a fourth moulding material is used then it may be placed with a weak impulse in between the skin material and the beginning of the core material. It is important that these moulding materials are located in such a way one after the other that e.g. the injection moulding machine can inject all these materials into the open space of the mould without causing any considerable injury to the moulding materials and to the moulded piece e.g. by enclosing gases or by mixing of the different materials or by diesel effect as a consequence of the local start of burning at the surface or by porosities or by dull areas which do not have an excellent gloss. Table 1 : Parameters of the injection moulding and of the injection compression moulding

* preferably with a temperature gap in the range of about 15 °C between male and female parts

All the ranges indicated with "about ..." have to be interpreted as being relatively broad. Table 2: Influence of the effect of parameters varied within the range of Table 1 with respect to the invention

The skin material may be distributed at least partially along the inner surface(s) of the mould reducing its open space to create a thin layer along the surface(s) of the mould and so that the core material is distributed then in the remaining space in the mould, preferably that the whole core region of the piece is filled with the core material and that the core of the piece is enveloped essentially around the whole core with a thin layer of the skin material.

It has been observed that it may be helpful that the moulding materials get into close contact to the walls of the channel resp. to the walls of the open space of the mould. The channel between the nozzle for the core material and the open space of the mould for forming the entrance may be bent, curved, twisted and/or changing its cross section and/or in such a way that the very first part of the surface(s) of the mould for forming the entrance shows at least one step, projection, bending and/or curving. Such a bending, curving, twisting, changing of the cross section, step, projection etc. shall cause a closer contact of the skin material(s) resp. the core material(s) so that the materials shall keep a closer contact to the inner surfaces of the mould resp. to the interfaces of the remaining open space formed by other moulding materials. In such a case, the skin material(s) will form a better and wider skin resp. layer resulting in a more homogeneous layer thickness.

The end of the nozzle for a skin material or the end of the system with the piston and plug for a skin materialjnay be directed to and connected with the beginning or the middle of the nozzle for the core material or may be directed to and connected with the mould itself. If more than one end of such systems/machines should be directed to and connected with the mould, this might be done from one end to the other end of these systems/machines right opposite or nearly opposite to another such end or directed to the open space in a right angle or in another angle and/or may be directed to the same or to nearly the same or a distant location within the open space. Preferably, these nozzles lead into the same channel or into connected channels which lead to the open space of the mould for forming the entrance and/or directly into the open space of the mould for forming the entrance.

Preferably, a plug transfer system 1 comprising a plug and a piston (Figures 1 and 2) or a nozzle (not shown in the Figures) may be used to move a skin material 2 forward with pressure. This may be a total volume of e.g. 5 to 20 cm³ of at least one skin material 2. The non return valve 3 ensures that this material cannot be driven backwards.

Preferably, the plug transfer system 1 may be directly connected with the very first part - the entrance - of the mould 6 (Figure 2). The entrance of the mould shall be the very first part of the mould forming part of the formed body which does not belong to the piece itself and which will be removed from the formed body before selling the piece. In this case, the skin material 2 will be collected in the system 1 and will be pushed directly into the mould 6.

In another preferred embodiment, the end of the system 1 collecting and pushing forward a skin material is directed to and connected with a nozzle 4 of an injection unit which may be used for at least one core material 5 (Figure 1). Then it is favourable that the end of the system 1 is connected with the nozzle 4 at the front part or medium part of the nozzle 4. The end of the nozzle 4 of the injection unit is connected with the entrance of the mould 6.

Preferably, the thickness of the skin amounts to 7 to 11 % of the thickness of the piece in the moulded as well as in the cured/cross-linked stage.

According to the invention, the moulding material pushed in front of all the moulding materials starts to fill the total volume of the first part of the open space of the mould having a contact to the surfaces of the mould. By further pushing the moulding materials according to the invention, the first moulding material which enters the open space will cover the walls of the mould and will fill no or only a small part of the open space opposite from the entrance. The quantity of material to cover all the surface of the mould represents the so-called skin material. The following moulding material(s) will enter and fill the remaining space in the midst of the other moulding materials and represents the so-called core material.

The skin material and/or the core material may be already completely compounded to be used without further additions and without further adapting the rheological properties ready to be injected.

The surface(s) of the mould and/or the channel which leads to the entrance of the mould may favourably have a roughness R_a of not more than 50 nm on the functional faces of the surface; preferably of not more than 25 nm, more preferred of not more than 16 nm, much more preferred of not more than 10 nm, especially of not more than 6 nm.

The roughness R_a was measured by atomic force microscopy (AFM) on samples with a functional surface to be measured of 20 x 20 μm. The microscope used was of the type Nanoscope E from Digital Instrument.

The surface(s) of the mould and/or the channels which lead to the entrance of the mould may be polished before starting work for the first time and may be polished from time to time or may be coated with a material of very high hardness, e.g. with titanium nitride. Preferably, the roughness R_a of the surface of the skin material minus the roughness R_a of the surface of the mould, shows a value of not more than 5 nm calculated from atomic force microscopy measurements, favourably not more than 3 nm.

A metallization may be applied to the functional face(s) of the piece, upon which a protective layer may additionally be applied.

The metallization may be formed in a vacuum chamber by sublimation, especially of aluminium or an aluminium containing substance. The protective layer shall shelter the reflective layer from oxidation.

According to an embodiment, a thermoset material is generated showing a flow of the moulding material with a fountain flow effect.

The metallized pieces manufactured according to the process of the invention may be used as lamp reflectors or as any other reflectors or as mirrors. Or they may be used for housings, as optical elements, as elements with a high brilliance and/or excellent colour and glance, as elements with excellent scratch resistance, excellent water resistance, excellent weathering resistance, excellent chemical resistance, excellent thermal properties and/or excellent electrostatic behaviour.

EXAMPLES:

The following examples illustrate, in detail, embodiments of the invention. The following examples shall help to clarify the invention, but they are not intended to restrict its scope.

The quality of the surface of the moulded pieces was characterized by the roughness

R_a of the surface as measured by atomic force microscopy.

For metallized applications which require a very high reflection of light, a close correlation between the ratio D/(D+B) for haze and gloss and the roughness on the other hand was observed.

The optical properties of the surfaces of the materials were measured with a Haze -

Gloss Instrument from BYK-GARDNER under an angle of 20 °. The lower the value of the haze, the better are the smoothness of the surface and the lower the roughness of the surface. The higher the value of the gloss, the better is the shine of the surface.

The resulting data were calculated such to give a first ratio R₁ between the value of the measured haze (D) for the numerator and the value of the gloss (B) for the denominator and to give a second ratio R₂ with the value of the calculated haze (d) for the numerator and with the sum of the values for gloss and calculated haze (B+d) for the denominator. These ratios gave a good evaluation of the surface quality of the moulded parts. The lower the value of these ratios are, the better is the quality of the surface. The calculated haze (d) was established with the relation D = 1285,1 log ((d/20)+1).

According to the present invention (example 2), the following results were obtained in comparison to the state of the art (example 1 ):

Table 3: Examples concerning coloured materials:

Table 4: Results of the haze - gloss measurements on the surface of the moulded parts:

There is a significant difference for the haze and gloss values of the surfaces as well as for the ratios R₁ and R₂ between example 1 and 2. It seems that the data of table 4 gained for example 2 cannot be reached without using a skin material. It was astonishing that recovering the core material by a skin material improved the surface quality of the moulded part.

The recipes 1 and 3 had been used for example 1 , whereas the recipes 4 and 6 had been used for example 2.

Example 3:

The recipes 1 and 2 shall illustrate the chemistry and viscosity of the skin material used in the pre-cured stage.

The recipes 1 ,2 and 3 shall illustrate the differences on chemistry and viscosity between core and skin material.

The recipes 4,5 and 6 shall illustrate chemistry and surface quality of the skin and of the core material, especially for examples of the tables 3 and 4. Table 5: Examples showing some recipes correlated with the properties of these materials and of the surfaces of moulded pieces

(1 ): viscosity 5.5 Pa«s - solid content 74 %

(2): viscosity 20 Pa»s - solid content 76 %

(3): viscosity 1.6 Pa»s - solid content 65 %

(4): viscosity 3 Pa«s - solid content 67 %

(5): viscosity 0.3 Pa«s - solid content 65 %

(6): viscosity 2.9 Pa»s - solid content 35 %

BHT: butyl hydroxy toluene

PBQ : para-benzoquinone

SR 350: trimethylol propane trimethacrylate

BPIC-C75: isopropylcarbonate tertio butylperoxide

TBPEH pur: ethyl-2 perhexanoate tertio butylperoxide

Marinco H: magnesium hydroxide

Gasil 23D: synthetic amorphous silica

OL 107: aluminium hydroxide

Claims

CLAIMS:

1. A process for the production of moulded pieces made from plastic materials by injection moulding or injection compression moulding thereby using at least two different types of plastics materials in the same mould whereby at least one material is used for the formation of the core of the piece and at least one material is used for the formation of the skin of the piece whereby the skin envelopes the core of the piece at least partially characterized in that at least one material for the formation of the core of the piece is a thermoset material and that at least one material for the formation of the skin is a thermoset material.

2. The process as claimed in claim 1 characterized in that only two or three different materials are used, preferably one material for the formation of the core of the piece and one material for the formation of the skin surrounding the core at least partially whereby the two materials must not be separated sharply.

3. The process as claimed in claim 1 or 2 characterized in that a skin is formed having a surface roughness R_a of not more than 50 nm as measured by atomic force microscopy.

4. The process as claimed in one of the preceding claims characterized in that a skin is formed having after curing/cross-linkage at least partially a colour different from the colour of the core material after curing/cross-linkage, preferably a coloured skin on a white or naturally coloured core material.

5. The process as claimed in one of the claims 1 to 3 characterized in that a skin is formed being after curing/cross-linkage at least partially naturally coloured or transparent or clear on a core material being after curing/cross-linkage white, of natural colour or of any other colour.

6. The process as claimed in one of the preceding claims characterized in that a skin is formed surrounding the core at least partially after curing/cross-linkage having a high electrical resistance and/or preventing from static electrical load.

7. The process as claimed in one of the preceding claims characterized in that a skin is formed at least partially having after curing/cross-linkage a high chemical resistance against acidic or basic media and/or solvents.

8. The process as claimed in one of the preceding claims characterized in that a skin is formed at least partially having after curing/cross-linkage a high scratch resistance.

9. The process as claimed in one of the preceding claims characterized in that a skin is formed at least partially having after curing/cross-linkage a thickness of from 0.01 to 0.8 mm.

10. The process as claimed in one of the preceding claims characterized in that the core material has - in comparison with the skin material - nearly the same or similar rheological properties and a slightly or strongly different chemical composition.

11. The process as claimed in one of the preceding claims characterized in that the core material contains fibres in a range of from 5 to 30 % by weight as well as fillers in a range of from 30 to 85 % by weight as measured before curing/cross-linking.

12. The process as claimed in one of the preceding claims characterized in that a skin material with a low fibre and/or with a low filler content is used to modify the level of the viscosity of the unsaturated polyester (UP) resin at least partially with an oxide and/or hydroxide, especially of any alkaline earth elements.

13. The process as claimed in one of the preceding claims characterized in that the skin material contains fibres in a range of from 0 to 10 % by weight as well as fillers in a range of from 0 to 50 % by weight as measured before curing/cross-linking.

14. The process as claimed in Claim 12 or 13 characterized in that the filler has an average grain size in the range of from 0.05 to 5 μm.

15. The process as claimed in one of the preceding claims characterized in that the material for the skin is injected into the channel which leads to the entrance of the mould or into the entrance of the mould either at the essentially same time or of from 0.01 to 5 seconds before the injection of the material for the core material.

16. The process as claimed in one of the preceding claims characterized in that the skin material is pushed with a weak impulse into a channel leading to or into the mould so that the skin material is located in front of the core material and in that the core material is pushed with a strong impulse forward thereby moving the skin material in front of it into the open space of the mould.

17. The process as claimed in one of the preceding claims characterized in that the skin material is distributed at least partially along the surface(s) of the mould to create a thin layer along the surface(s) of the mould and that the core material is distributed in the remaining space in the mould, preferably that the whole core region of the piece is filled with the core material and that the core of the piece is enveloped essentially around the whole core with a thin layer of the skin material.

18. The process as claimed in one of the preceding claims characterized in that the nozzle for the skin material or the piston with the plug for the skin material leads the skin material pushed forward into the channel between the nozzle for the core material and the open space of the mould for forming the entrance.

19. The process as claimed in one of the preceding claims characterized in that the channel between the nozzle for the core material and the open space of the mould for forming the entrance is bent, curved, twisted and/or changing its cross section and/or that the very first part of the surface(s) of the mould for forming the entrance shows at least one step, projection, bending and/or curving.

20. The process as claimed in one of the preceding claims characterized in that the end of the nozzle for the skin material or the piston with the plug for the skin material is located to the beginning or the middle of the nozzle for the core material right opposite or directed to the same open space in an angle or nearly opposite or nearly directed to nearly the same open space in an angle, preferably these nozzles lead into the same channel or into connected channels which lead to the open space of the mould for forming the entrance and/or directly into the open space of the mould for forming the entrance.

21. The process as claimed in one of the preceding claims characterized in that the skin material and/or the core material are already completely compounded to be used without further additions and without further adapting the rheological properties.

22. The process as claimed in one of the preceding claims characterized in that the mould surface(s) has a roughness R_a of not more than 50 nm measured by atomic force microscopy.

23. The process as claimed in one of the preceding claims characterized in that the roughness R_a of the surface of the skin material minus the roughness R_a of the surface of the mould shows a value of not more than 5 nm measured by atomic force microscopy.

24. The process as claimed in one of the preceding claims characterized in that a metallization is applied upon the functional face(s) of the piece, upon which a protective layer may be applied additionally.

25. The process as claimed in one of the preceding claims characterized in that a thermoset material is generated showing a flow of the moulding material with a fountain flow effect.

26. A method of use of a metallized piece manufactured according to one of the claims 1 to 25 as a lamp reflector or as any other reflector or as a mirror.

27. A method of use of a piece manufactured according to one of the claims 1 to 25 for a housing, a lamp reflector, any other reflector, a mirror, an optical element, an element with a high brilliance, excellent colour and/or excellent glance, an element with excellent scratch resistance, excellent water resistance, excellent weathering resistance, excellent chemical resistance, excellent thermal properties and/or excellent electrostatic behaviour.