WO2021191264A1

WO2021191264A1 - Molded article providing an electromagnetic shielding

Info

Publication number: WO2021191264A1
Application number: PCT/EP2021/057549
Authority: WO
Inventors: Timo Alexander PRENZER; Volker Zeiher; Thomas Bayerl; Simon Kniesel
Original assignee: Basf Se
Priority date: 2020-03-25
Filing date: 2021-03-24
Publication date: 2021-09-30

Abstract

A molded article providing an electromagnetic shielding, comprising i) a polymer substrate comprising at least one polymer having a contact angle θ with water of at most 95°; and ii) a metal coating coated directly on at least a part of the surface of the polymer substrate by thermal layering. By appropriate selection of polymer substrate, a metal coating can be applied to the surface thereof by thermal layering techniques without the need of a chemical surface pre-treatment or modification, or the application of a primer layer, even if the polymeric substrate contains significant proportions of reinforcing fillers or flame retardants. The invention also relates to a process for manufacturing a molded article providing an electromagnetic shielding, comprising i) providing a polymer substrate comprising at least one polymer having a contact angle θ with water of at most 95°; and ii) directly coating at least a part of the surface of the polymer substrate with a metal coating by thermal layering.

Description

Molded Article Providing an Electromagnetic Shielding

This invention relates to a molded article providing an electromagnetic shielding. Further, the invention relates to a process for manufacturing a molded article providing an electromagnetic shielding.

Electromagnetic interference (EMI), radio frequency interference (RFI) and electrostatic discharge (ESD) are terms often used synonymously, especially in the context of electromagnetic compatibility (EMC) and electromagnetic shielding. It is well-known that electronic devices are both sources and receptors of EMI, which creates a two-fold problem. Electromagnetic radiation penetrating a device may be detrimental to the operational integrity of such a device, e.g., by causing cause electronic failure. Furthermore, the amount of electromagnetic radiation emitted by a device is typically subject to regulations. It is therefore desirable to prevent the disruption of devices sensitive to electromagnetic radiation by external emissions, and to minimize the electromagnetic emission of devices themselves.

Hitherto, housings accommodating electronic components steel are often made of aluminum or steel to shield electromagnetic waves. Metal housings are however relatively heavy and expensive. Currently, housings for electronic devices are increasingly of a polymeric nature, rather than metallic. Polymeric housings offer increased design flexibility and productivity with decreased cost. Flowever, polymers are typically insulators, so EMI waves pass freely through unshielded polymers without substantial impedance or resistance. The use of polymeric housings has thus raised concern with regard to EMI shielding. Moreover, ever increasing device miniaturization and the increase in clock speeds of microprocessors used in computing devices makes it more difficult to control the EMI pollution generated by such devices.

While a metal housing is inherently an effective EMI barrier, plastic enclosure parts must be made electrically conductive in order to function as an EMI shield. This has typically been achieved by a conductive layer, such as a paint, metal-filled elastomer, or a metal foil or coating, which may be provided by fastening, laminating, lining, transferring, over molding, spraying, dipping, cladding, plating, or metallizing, or otherwise which may be applied or deposited across the interior or exterior surfaces of the housing. Although each method may offer certain advantages to the designer, there is almost always a cost-performance tradeoff necessary in the selection. DE 100 37 212 A1 relates to a process for producing a coating on a plastic surface by means of thermal spraying methods, wherein the process comprises the application of a primer layer on the plastic surface and subsequently applying a coating.

WO 2007/045217 A1 describes a process for coating a fiber-reinforced composite material, wherein a primer layer comprising organic and metallic components is applied, subsequently a layer comprising predominantly metallic components is applied, and finally a functional layer consisting of metal, a metal-carbide composite, oxide ceramics or mixtures thereof is applied by thermal or kinetic spraying.

US 6,570,085 B1 describes an EMI shield for electronic devices constructed from thermoformable polymeric materials metallized on all surfaces by vacuum metallization.

Thermal layering techniques such as thermal spraying have been conventionally utilized for applying metal coatings. The coating layer so formed is self-adherent and conforms to ribs, wall, and other structures, irregularities, or discontinuities which may be formed on the housing part surface. However, many polymeric substrates need chemical surface treatment or modification prior to the metallizing, such as chemical or solvent etching, grit-blasting, such as with aluminum oxide or another abrasive, or other known surface treatment such as corona discharge or plasma ionization. Alternatively, a chemical bond coat or primer layer, must be applied to the surface to form an intermediate tie layer between the surface and the metallized layer.

Adhesion problems may occur or are aggravated when the polymeric substrate contains reinforcing members or flame retardants. The presence of flame retardants is often required due to regulatory provisions. The presence of reinforcing members is required to achieve the stability demands. Blasting of the surface may expose the reinforcing members such as glass fibers, so that the metallized layer must not only adhere to the treated polymeric surface but also to the exposed reinforcing member.

It is an object of the present invention to provide molded articles which are light-weight and easy to manufacture, while providing sufficient electromagnetic shielding.

The object is achieved by providing a molded article providing an electromagnetic shielding, comprising i) a polymer substrate comprising at least one polymer having a contact angle Q with water of at most 95°; and ii) a metal coating coated directly on at least a part of the surface of the polymer substrate by thermal layering.

Further provided is a process for manufacturing a molded article providing an electromagnetic shielding, comprising i) providing a polymer substrate comprising at least one polymer having a contact angle 0 with water of at most 95°; and ii) directly coating at least a part of the surface of the polymer substrate with a metal coating by thermal layering.

It has now been found that by appropriate selection of polymer substrate, a metal coating can be applied to the surface thereof by thermal layering techniques without the need of a chemical surface pre-treatment or modification, or the application of a primer layer, even if the polymeric substrate contains significant proportions of reinforcing fillers or flame retardants.

The molded article may be used as an electronic component box for a vehicle or parts thereof such as a housing half or bottom part, side walls or top cover.

The following discussion relates to embodiments of both the molded article and the process of the invention, unless noted otherwise.

According to the invention, the polymer substrate constituting the molded article comprises at least one polymer having a contact angle Q with water (at 25 °C) of at most 90°, preferably at most 85°, particularly at most 80°, such as at most 75° or at most 70°. For example, the polymer has a contact angle Q with water of 50 to 90°, preferably 50 to 85°, particularly 55 to 80°, such as 60 to 75° or 60 to 70°. The contact angle 0 quantifies the polarity of the polymer substrate. Without wishing to be bound by theory, it is believed that high polarity polymers (i.e. hydrophilic polymers) exhibit high surface energy that allows for a particularly beneficial interaction of the thermally coated metal with the surface of the polymer substrate.

The water contact angle may be measured with a static contact angle measurement device, such as the Video Contact Angle System: DSA100 prop Shape Analysis System from Kruess GmbFI (Flamburg, Germany). In this particular system, a machine is equipped with a digital camera, automatic liquid dispensers, and sample stages allowing a hands-free contact angle measurement via automated placement of a drop of water (where the water drop has a size of approximately 5 pi). The drop shape is captured automatically and then analyzed via prop Shape Analysis by a computer to determine the static, advancing, and receding water contact angle. Static water contact angle may be generally understood as the general “water contact angle” described and claimed herein.

In a preferred embodiment, the polymer substrate comprises a polyamide and/or a polyester. The functional groups of these polymers, i.e. amide and ester groups, are polar and thus increase the hydrophilicity of the polymer substrate. Suitable polyamides typically have an amide group concentration of at least 8000 mmol/kg, preferably at least 8500 mmol/kg such as at least 8800 mmol/kg. The amide group concentration is understood to be the number of amide groups (in mmol) per kg of polyamide. The higher the amide group concentration, the higher the polarity of the polyamide.

Polyamides may be designated using abbreviations, which consist of the letters PA followed by numbers and letters. Some of these abbreviations are standardized in DIN EN ISO 1043-1. Polyamides which can be derived from aminocarboxylic acids of the H2N-(CH2)_x-COOH type or the corresponding lactams are identified as PA Z, wherein Z denotes the number of carbon atoms in the monomer. For example, PA 6 represents the polymer of e- caprolactam or of w-aminocaproic acid. Polyamides which can be derived from diamines and dicarboxylic acids of the H2N- (CH2)_X-NH2 and HOOC-(CH2)_y-COOH types are identified as PA Z1Z2, wherein Z1 denotes the number of carbon atoms in the diamine and Z2 denotes the number of carbon atoms in the dicarboxylic acid. Copolyamides are designated by listing the components in the sequence of their proportions, separated by slashes. For example, PA 66/610 is the copolyamide of hexamethylenediamine, adipic acid and sebacic acid. For monomers having an aromatic or cycloaliphatic group, the following letter abbreviations are used: T = terephthalic acid,

I = isophthalic acid, MXDA = m-xylylenediamine, I PDA = isophoronediamine, PACM = 4,4'-methylenebis(cyclohexylamine), MACM = 2,2'-dimethyl-4,4'-methylenebis(cyclo- hexylamine).

In one embodiment, the polyamide is an aliphatic polyamide. In this case, the polyamide is preferably selected from PA 4, PA 5, PA 6, PA 7, PA 8, PA 9, PA 10, PA 11, PA 12, PA 46, PA 66, PA 6/66, PA 66/6, PA 69, PA 610, PA 612, PA 96, PA 99, PA 910, PA 912, PA 1212, and copolymers and mixtures thereof.

In one embodiment, the polyamide is a semi-aromatic polyamide. In this case, the polyamide is preferably selected from PA 6.T, PA 9.T, PA 8.T, PA 10.T, PA 12.T, PA 6.1,

PA 8.1, PA 9.1, PA 10.1, PA 12.1, PA 6.T/6, PA 6.T/10, PA 6.T/12,

PA 6.T/6.I, PA 6.T/8.T, PA 6.T/9.T, PA 6.T/10T, PA 6.T/12.T, PA 12.T/6.T, PA 6.T/6.I/6, PA 6.T/6.I/12, PA 6.T/6.1/6.10, PA 6. T/6.1/6.12, PA6.T/6.6, PA 6.T/6.10, PA 6.T/6.12, PA 10.T/6, PA 10.T/11 , PA 10.T/12, PA 8.T/6.T, PA 8.T/66, PA 8.T/8.I, PA 8.T/8.6, PA 8.T/6.I, PA 10.T/6.T, PA 10.T/6.6, PA 10.T/10.I, PA 10T/10.I/6.T, PA 10.T/6.I,

PA 4.T/4.I/46, PA 4.T/4.I/6.6, PA 5.T/5.I, PA 5.T/5.I/5.6, PA 5.T/5.I/6.6, PA 6.T/6.I/6.6, PA MXDA.6, PA IPDA.I, PA IPDA.T, PA MACM.I, PA MACM.T, PA PACM.I, PA PACM.T, PA MXDA.I, PA MXDA.T, PA 6.T/IPDA.T, PA 6.T/MACM.T, PA 6.T/PACM.T, PA 6.T/MXDA.T, PA 6.T/6.1/8.T/8.1 , PA 6.T/6.I/10.T/10.I, PA 6.T/6.I/IPDA.T/IPDA.I, PA 6.T/6.I/MXDA.T/MXDA.I, PA 6.T/6.I/MACM.T/MACM.I, PA 6. T/6. I/P ACM. T/P ACM. I, PA 6.T/10.T/IPDA.T, PA 6.T/12.T/IPDA.T, PA 6.T/10.T/PACM.T, PA 6.T/12.T/PACM.T, PA 10.T/IPDA.T, PA 12.T/IPDA.T and copolymers and mixtures thereof. More preferably, semi-aromatic polyamide is selected from PA 6.T, PA 9.T, PA 10.T, PA 12.T, PA 6.I, PA 9.I, PA 10.1, PA 12.1, PA 6.T/6.I, PA 6.T/6, PA 6.T/8.T, PA 6.T/10T, PA 10.T/6.T, PA 6.T/12.T, PA12.T/6.T, PA IPDA.I, PA IPDA.T, PA 6.T/IPDA.T, PA 6.T/6.I/IPDA.T/IPDA.I, PA 6.T/10.T/IPDA.T, PA 6.T/12.T/IPDA.T, PA 6.T/10.T/PACM.T, PA 6.T/12.T/PACM.T, PA 10.T/IPDA.T, PA 12.T/IPDA.T and copolymers and mixtures thereof.

In a preferred embodiment, the polyamide is selected from polycaprolactam (PA 6), poly(hexamethylene adipamide) (PA 66) and copolymers and mixtures thereof. In an especially preferred embodiment, the polyamide is selected from polycaprolactam (PA 6) and poly(hexamethylene adipamide) (PA 66). Their amide group concentration and contact angle 0 with water, respectively, are as follows:

Suitable polyesters typically have a high ester group concentration. The ester group concentration is understood to be the number of ester groups (in mmol) per kg of polyester. The higher the ester group concentration, the higher the polarity of the polyester.

Suitable polyesters include terephthalates, especially polyalkylene terephthalates such as polyethylene terephthalate (PET), poly (butylene terephthalate) (PBT), and polypropylene terephthalate (PTT), or copolymerized polyalkylene terephthalates such as polyethylene naphthalate polyethylene terephthalate (PEN). Preferably, the polyester is a polyalkylene terephthalate, most preferably polybutylene terephthalate.

Polybutylene terephthalate (PBT) has an ester group concentration of 0.2 and a contact angle Q with water of 73°.

The preparation of polyesters and polyamides is well-known in the literature. For example, conventional preparation processes for PA 6 and PA 66 are described in Kunststoffhandbuch, 3/4 Technische Thermoplaste: Polyamide, Carl Hanser Verlag, 1998, Munich, p. 42-71. Suitable polyesters and polyamides are typically also commercially available.

The polymer substrate preferably comprises a total amount of 25 to 100 wt.-%, more preferably 30 to 75 wt.-%, such as 35 to 65 wt.-% of polymers having a contact angle 0 with water of at most 90°, relative to the total weight of the polymer substrate.

Besides the polymer as described above, the polymer substrate may comprise further components. The polymer substrate typically comprises:

A) 25 to 100 wt.-%, preferably 25 to 99 wt.-%, more preferably 25 to 98 wt.-%, of at least one polymer having a contact angle 0 with water of at most 90°, as defined above,

B) 0 to 75% wt.-%, preferably 1 to 50 wt.-%, more preferably 1 to 50 wt.-%, of at least one filler and reinforcer,

C) 0 to 50 wt.-%, preferably 0 to 25 wt.-%, more preferably 1 to 25 wt.-%, of at least one additive, where components A) to C) add up to 100% wt.-%.

The term “filler and reinforcer”, i.e. component B, is understood in a broad sense in the context of the invention and comprises particulate fillers, fibrous substances and any intermediate forms. In a preferred embodiment, the polymer substrate comprises at least one fibrous substance selected from

- inorganic reinforcing fibers, such as boron fibers, glass fibers, carbon fibers, silica fibers, ceramic fibers, potassium titanate fibers and basalt fibers;

- organic reinforcing fibers, such as aramid fibers, polyester fibers, nylon fibers, polyethylene fibers; and

- natural fibers, such as wood fibers, flax fibers, hemp fibers and sisal fibers.

It is especially preferable to use glass fibers, carbon fibers, aramid fibers, boron fibers, metal fibers or potassium titanate fibers.

In one embodiment, the polymer substrate comprises chopped glass fibers, preference being given to short fibers having a length in the range from 2 to 50 mm and a diameter of 5 to 40 pm. Alternatively, it is possible to use continuous fibers (rovings). Suitable fibers are those having a circular and/or noncircular cross-sectional area. In the latter case, the ratio of dimensions of the main cross-sectional axis to the secondary cross- sectional axis is typically > 2, preferably in the range from 2 to 8 and more preferably in the range from 3 to 5.

In a specific embodiment, the polymer substrate comprises so-called “flat glass fibers”. These specifically have a cross-sectional area which is oval or elliptical, or elliptical and provided with indentation(s) (called "cocoon" fibers), or rectangular or virtually rectangular. Preference is given to using glass fibers with a noncircular cross-sectional area and a ratio of dimensions of the main cross-sectional axis to the secondary cross- sectional axis of more than 2, preferably of 2 to 8, especially of 3 to 5.

For reinforcement of the polymer substrate, it is also possible to use mixtures of glass fibers having circular and noncircular cross sections. In a specific implementation, the proportion of flat glass fibers, as defined above, predominates, meaning that they account for more than 50% by weight of the total mass of the fibers.

If rovings of glass fibers are used, these preferably have a diameter of 10 to 20 pm, preferably of 12 to 18 pm. In this case, the cross-section of the glass fibers may be round, oval, elliptical, virtually rectangular or rectangular. Particular preference is given to flat glass fibers having a ratio of the cross-sectional axes of 2 to 5. More particularly, E-glass fibers are used. However, it is also possible to use all other glass fiber types, for example A-, C-, D-, M-, S- or R-glass fibers or any desired mixtures thereof, or mixtures with E- glass fibers. In a preferred embodiment, the molded article comprises i) a polymer substrate comprising

A) 25 to 99 wt.-% of polyamide 6, polyamide 66 or polybutylene terephthalate (having a contact angle Q with water of 50 to 80°),

B) 1 to 50% wt.-% of at least one fibrous substance as defined above,

C) 0 to 25% wt.-% of at least one additive, preferably a flame retardant, where components A) to C) add up to 100% wt.-%, and ii) the metal coating comprises aluminum or zinc.

Specifically, it was found that polymeric compositions comprising PA 66, PA 6 or PBT show increased adhesion to metal applied by thermal layering in comparison to polypropylene (PP) and polyethylene (PE). A polymer substrate comprising the polymer and a fibrous substance can be produced by known processes for producing long fiber-reinforced rod pellets, especially by pultrusion processes, in which the continuous fiber strand (roving) is fully saturated with the polymer melt and then cooled and cut. The long fiber-reinforced rod pellets obtained in this manner, which preferably have a pellet length of 3 to 25 mm, especially of 4 to 12 mm, can be processed by the customary processing methods, for example injection molding or press molding, to give moldings.

Particulate fillers may have a wide range of particle sizes ranging from particles in the form of dusts to large grains. Useful filler materials include organic or inorganic fillers and reinforcers. For example, it is possible to use inorganic fillers, such as kaolin, chalk, wollastonite, talc, calcium carbonate, silicates, titanium dioxide, zinc oxide, graphite, glass particles, e.g. glass beads, nanoscale fillers, such as carbon nanotubes, carbon black, nanoscale sheet silicates, nanoscale alumina (AI₂O₃), nanoscale titania (T1O₂), graphene, permanently magnetic or magnetizable metal compounds and/or alloys, sheet silicates and nanoscale silica (S1O₂). The fillers may have been surface treated.

Examples of sheet silicates used in the polymer substrate compositions include kaolins, serpentines, talc, mica, vermiculites, illites, smectites, montmorillonite, hectorite, double hydroxides or mixtures thereof. The sheet silicates may have been surface treated or may be untreated.

The polymer substrate preferably comprises a total amount of 15 to 75 wt.-%, more preferably 20 to 60 wt.-%, such as 20 to 55 wt.-% of at least one filler or reinforcer B), relative to the total weight of the polymer substrate. Suitable additives C) include heat stabilizers, flame retardants, light stabilizers (UV stabilizers, UV absorbers or UV blockers), lubricants, dyes, nucleating agents, metallic pigments, metal flakes, metal-coated particles, antistats, conductivity additives, demolding agents, optical brighteners, and defoamers.

The polymer substrate preferably comprises at least one flame retardant in a total amount of 0.01 to 30 wt.-%, more preferably 0.1 to 20 wt.-%, relative to the total weight of the polymer substrate. Useful flame retardants include halogenated and halogen-free flame retardants and synergists thereof (see also Gachter/M uller, 3rd edition 1989 Hanser Verlag, chapter 11).

Preferred halogen-free flame retardants are red phosphorus, phosphinic or diphosphinic salts and/or nitrogen-containing flame retardants such as melamine, melamine cyanurate, melamine sulfate, melamine borate, melamine oxalate, melamine phosphate (primary, secondary) or secondary melamine pyrophosphate, neopentyl glycol boric acid melamine, guanidine and derivatives thereof known to those skilled in the art, and also polymeric melamine phosphate (CAS No.: 56386-64-2 or 218768-84-4, and also EP 1095030), ammonium polyphosphate, trishydroxyethyl isocyanurate (optionally also ammonium polyphosphate in a mixture with trishydroxyethyl isocyanurate) (EP584567). Further N-containing or P-containing flame retardants, or PN condensates suitable as flame retardants, can be found in DE 10 2004 049 342, as can the synergists likewise customary for this purpose, such as oxides or borates. Suitable halogenated flame retardants are, for example, oligomeric brominated polycarbonates (BC 52 Great Lakes) or polypentabromobenzyl acrylates with N greater than 4 (FR 1025 Dead sea bromine), reaction products of tetrabromobisphenol A with epoxides, brominated oligomeric or polymeric styrenes, Dechlorane, which are usually used with antimony oxides as synergists (for details and further flame retardants see DE- A-102004 050025).

Heat stabilizers are preferably selected from copper compounds, secondary aromatic amines, sterically hindered phenols, phosphites, phosphonites and mixtures thereof. The polymer substrate typically comprises at least one heat stabilizer in a total amount of 0.01 to 3 wt.-%, more preferably 0.02 to 2 wt.-% and especially 0.1 to 1.5 wt.-%, relative to the total weight of the polymer substrate. If a copper compound is used as a heat stabilizer, the amount of copper is preferably 0.003 to 0.5 wt.-%, especially 0.005 to 0.3 wt.-% and more preferably 0.01 to 0.2 wt.-%, relative to the total weight of the polymer substrate. If stabilizers based on secondary amines are used as heat stabilizers, the amount of these stabilizers is preferably 0.2 to 2 wt.-%, more preferably from 0.2 to 1.5 wt.-%, relative to the total weight of the polymer substrate.

If stabilizers based on sterically hindered phenols are used as heat stabilizers, the amount of these stabilizers is preferably 0.1 to 1.5 wt.-%, more preferably from 0.2 to 1 wt.-%, relative to the total weight of the polymer substrate.

If stabilizers based on phosphites and/or phosphonites are used as heat stabilizers, the amount of these stabilizers is preferably 0.1 to 1.5 wt.-%, more preferably from 0.2 to 1 wt.-%, relative to the total weight of the polymer substrate.

Compounds of mono- or divalent copper are, for example, salts of mono- or divalent copper with inorganic or organic acids or mono- or dihydric phenols, the oxides of mono- or divalent copper or the complexes of copper salts with ammonia, amines, amides, lactams, cyanides or phosphines, preferably Cu(l) or Cu(ll) salts of the hydrohalic acids or of the hydrocyanic acids or the copper salts of the aliphatic carboxylic acids. Particular preference is given to the monovalent copper compounds CuCI, CuBr, Cul, CuCN and CU2O, and to the divalent copper compounds CuCh, CuSC , CuO, copper(ll) acetate or copper(ll) stearate.

The copper compounds are commercially available, or the preparation thereof is known to those skilled in the art. The copper compound can be used as such or in the form of concentrates. A concentrate is understood to mean a polymer, preferably of the same chemical nature as component A), which comprises the copper salt in high concentration. The use of concentrates is a standard method and is employed particularly frequently when very small amounts of a feedstock have to be metered in. Advantageously, the copper compounds are used in combination with further metal halides, especially alkali metal halides, such as Nal, Kl, NaBr, KBr, in which case the molar ratio of metal halide to copper halide is 0.5 to 20, preferably 1 to 10 and more preferably 3 to 7.

Particularly preferred examples of stabilizers which are based on secondary aromatic amines and are usable in accordance with the invention are adducts of phenylene- diamine with acetone (Naugard® A), adducts of phenylenediamine with linolenic acid, 4,4'- bis (a, a-dimethylbenzyl)diphenylamine (Naugard ® 445), N,N'-dinaphthyl-p- phenylenediamine, N-phenyl-N'-cyclohexyl-p-phenylenediamine or mixtures of two or more thereof.

Particularly preferred examples of stabilizers which are based on sterically hindered phenols and are usable in accordance with the invention are N,N'-hexamethylenebis-3- (3,5-di-tert-butyl-4-hydroxyphenyl)propionamide, bis(3,3-bis(4'-hydroxy-3'-tert- butylphenyl)butanoic acid) glycol ester, 2,1 '-thioethyl bis(3-(3,5-di-tert-butyl-4-hydroxy- phenyl)propionate, 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), triethylene glycol 3- (3-tert-butyl-4-hydroxy-5-methylphenyl)propionate or mixtures of two or more of these stabilizers.

Preferred phosphites and phosphonites are triphenyl phosphite, diphenyl alkyl phosphite, phenyl dialkyl phosphite, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythrityl diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecyl pentaerythrityl diphosphite, bis(2,4-di-tert-butylphenyl) penta erythrityl diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythrityl diphosphite, diisodecyloxy pentaerythrityl diphosphite, bis(2,4-di-tert-butyl-6-methylphenyl) penta erythrityl diphosphite, bis(2,4,6-tris(tert-butylphenyl)) pentaerythrityl diphosphite, tristearylsorbitol triphosphite, tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylene diphosphonite, 6-isooctyloxy-2,4,8,10-tetra-tert-butyl-12H-dibenzo-[d,g]-1 ,3,2-dioxa- phosphocin, 6-fluoro-2,4,8,10-tetra-tert-butyl-12-methyldibenzo-[d,g]-1 ,3,2-dioxa- phosphocin, bis(2,4-di-tert-butyl-6-methylphenyl)methyl phosphite and bis(2,4-di-tert- butyl-6-methylphenyl) ethyl phosphite. More particularly, preference is given to tris[2-tert- butyl-4-thio(2'-methyl-4'-hydroxy-5'-tert-butyl)phenyl-5-methyl]phenyl phosphite and tris(2,4-di-tert-butylphenyl) phosphite (Hostanox ® PAR24: commercial product from BASF SE).

A preferred embodiment of the heat stabilizer consists in the combination of organic heat stabilizers (especially Hostanox PAR 24 and Irganox 1010), a bisphenol A-based epoxide (especially Epikote 1001) and copper stabilization based on Cul and Kl. An example of a commercially available stabilizer mixture consisting of organic stabilizers and epoxides is Irgatec NC66 from BASF SE. More particularly, preference is given to heat stabilization exclusively based on Cul and Kl. Aside from the addition of copper or copper compounds, the use of further transition metal compounds, especially metal salts or metal oxides of group VB, VIB, VI I B or VIIIB of the Periodic Table, is ruled out. In addition, it is preferable not to add any transition metals of group VB, VIB, VI I B or VIIIB of the Periodic Table, for example iron powder or steel powder, to the polymer substrate. Suitable antistats include carbon black and carbon nanotubes. The use of carbon black may also serve to induce a black color of the polymer substrate. Preferably, the amount of antistats, such as carbon black, is in the range of 0.01 to 10 % by weight based on the total weight of the polymer substrate.

The polymer substrate is preferably provided in the desired shape of the molded article or a part thereof and may be provided by any suitable process known in the art. Preferably, the polymer substrate is provided by injection molding including a demolding step. The process of injection molding is well known in the art and not especially limited in the context of this invention. Injection molding allows for considerable breadth of design possibilities and generally allows for a high versatility of shapes of the obtained molded body.

Advantageously, the present process allows for the polymer substrate to be coated subsequently to demolding without chemical surface pretreatment. Preferably, mechanical pretreatments such as grit-blasting are carried out before thermal layering.

At least a part of the surface of the polymer substrate is directly coated with a metal coating by thermal layering. Thermal layering techniques are coating processes in which melted or heated materials are applied onto a surface, for example via spraying. The “feedstock”, also known as the “coating precursor”, is heated by electrical or chemical means. Electrical heating means comprise plasma and arc heating. Chemical heating means include combustion flaming. WO 00/29635 A2 discloses suitable thermal layering techniques. In general, thermal layering involves the steps of: (i) providing a feed material comprising a metal or metal alloy; (ii) heating said feed material of step (i) into a molten state; (iii) atomizing said feed material of step (ii) while in said molten state; (iv) spraying the atomized feed material of step (ii) while in said molten state on at least a portion of the surface of the polymer substrate to form a self-adherent coating of metal thereon; and (v) solidifying the coating of step (iii) to form a metallic layer.

The metal coating is coated directly on at least a part of the surface of the polymer substrate by thermal layering. In one embodiment, the outer surface of the polymer substrate is partially or completely coated with the metal. In another embodiment, the inner surface of the polymer substrate is partially or completely coated with the metal. In yet another embodiment, both the inner surface and the outer surface of the polymer substrate are partially or completely coated with the metal. The terms “outer surface” and “inner surface” are understood to relate to the surfaces of the molded article relative to an object placed within the molded article.

In a preferred embodiment, the molded article comprises a metal coating coated directly on the outer surface of the polymer substrate by thermal layering. Preferably, the outer surface of the polymer substrate is completely coated with the metal.

Preferably, the metal coating comprises a metal selected from aluminum, aluminum alloys, zinc, zinc alloys, copper, silver, steel, steel alloys and nickel. It is especially preferred that the metal coating comprises a metal selected from aluminum and zinc. The coating metal or alloy does not have to be thermomechanically workable and can be specifically formulated for thermal coating.

The metal coating of the molded article provides an electromagnetic shielding. In order to achieve sufficiently high electromagnetic shielding, the metal coating preferably has a thickness of at least 1.0 pm, such as at least 2.0 pm or 5.0 pm, for example a thickness in the range of 1.0 to 200 pm or 1.0 to 100 pm such as 2.0 to 10 pm, and furthermore has a surface impedance of less than for example 1 Q/sq. The molded articles of the present invention may be suitably used wherever molded articles providing an electromagnetic shielding are required. For example, the molded articles may be used as components for the automotive sector, especially as housings for charge air coolers, heat exchangers, circuit boards, relays, resistors, capacitors, diodes, transistors, connectors, regulators, processors, controllers, memory elements and/or sensors.

The invention is illustrated by the following examples. The examples relate to practical and in some cases preferred embodiments of the invention, which do not limit the scope of the invention.

Examples

Materials: Sample 1

A) 50 wt.-% of polyamide 66 compound with flame retardance additive

B) 50 wt.-% of glass fiber Sample 2

A) 70 wt.-% of polyamide 6 compound with flame retardance additive

B) 30 wt.-% of glass fiber

The molded articles of sample 1 and sample 2 comprise an aluminum coating.

Tests: 1) Thermal Shock Test

For molded articles 1 and 2, the following conditions were applied:

- 224 cycles, each cycle with the conditions 30 min. -40°C // 30 min. 120 °C, and afterwards

68 cycles, each cycle with the conditions 30 min. -40°C // 30 min. 150 °C

A molded article passed the test when no lamination was observed at the end of the test. 2) Adhesion Test after Thermal Shock Test

After the thermal shock test of 224 cycles, each cycle with the conditions 30 min. -40°C // 30 min. 120 °C, the following adhesion test was conducted: - Gluing a round (diameter 150 mm) planar holding device on the metal surface of the substrate with an epoxy glue;

Pulling off the holding device and measuring the breaking force [N]

A molded article passed the test at values of equal or more than 200 N as breaking force with adhesive fracture in the metal-plastic interface.

Results:

1 ) Thermal Shock T est Molded article 1 : test passed Molded article 2: test passed

2) Adhesion Test after Thermal Shock Test

Molded article 1 : test passed Molded article 2: test passed It is evident that molded articles with the compositions described above, which were tested with thermal shock conditions of 224 cycles, each cycle with the conditions 30 min. -40°C // 30 min. 120 °C, unexpectedly still show breaking force values of more than 200 N in a subsequent adhesion test.

Claims

1. A molded article providing an electromagnetic shielding, comprising i) a polymer substrate comprising at least one polymer having a contact angle Q with water of at most 95°; and ii) a metal coating coated directly on at least a part of the surface of the polymer substrate by thermal layering.

2. The molded article according to claim 1 , wherein the polymer substrate comprises a polyamide and/or a polyester.

3. The molded article according to claim 2, wherein the polyamide is polycaprolactam or poly(hexamethylene adipamide).

4. The molded article according to claim 2, wherein the polyester is a polyalkylene terephthalate, preferably polybutylene terephthalate.

5. The molded article according to any one of the preceding claims, wherein the metal coating comprises a metal selected from zinc, zinc alloys, aluminum or aluminum alloys, preferably from aluminum and zinc.

6. The molded article according to any one of the preceding claims, wherein the polymer substrate comprises at least one fibrous substance selected from

- inorganic reinforcing fibers, such as boron fibers, glass fibers, carbon fibers, silica fibers, ceramic fibers and basalt fibers;

7. The molded article according to any one of the preceding claims, wherein the polymer substrate comprises at least one flame retardant.

8. The molded article according to claim 6 or 7, wherein i) the polymer substrate comprises A) 25 to 99 wt.-% of polyamide 6, polyamide 66 or polybutylene terephthalate,

B) 1 to 50% wt.-% of at least one fibrous substance,

9. A process for manufacturing a molded article providing an electromagnetic shielding, comprising i) providing a polymer substrate comprising at least one polymer having a contact angle Q with water of at most 95°; and ii) directly coating at least a part of the surface of the polymer substrate with a metal coating by thermal layering.

10. The process according to claim 9, additionally comprising an injection molding step including a demolding step, to provide the polymer substrate.

11. The process according to claim 10, wherein the polymer substrate is coated subsequently to demolding without chemical surface pretreatment.

12. The process according to any one of claims 9 to 11 , wherein the polar polymer substrate comprises a polyamide, such as polycaprolactam or poly(hexamethylene adipamide), and/or a polyester, such as a polyalkylene terephthalate, preferably polybutylene terephthalate.

13. The process according to any one of claims 9 to 12, wherein the metal coating comprises a metal selected from zinc, zinc alloys, aluminum and aluminum alloys, preferably from aluminum and zinc.

14. The process according to any one of claims 9 to 13, wherein the polymer substrate comprises at least one fibrous substance selected from

- organic reinforcing fibers, such as Aramid fibers, polyester fibers, nylon fibers, polyethylene fibers; and - natural fibers, such as wood fibers, flax fibers, hemp fibers and sisal fibers.

15. The process structure according to any one of claims 9 to 14, wherein the polymer substrate comprises at least one flame retardant.