EP0000022A1 - Scratch and weather resistant composite material based on polycarbonate - Google Patents

Abstract

The present invention relates to a clear, highly impact-resistant, scratch and weatherproof composite system made of a polycarbonate layer which has a coating of polyacrylate on at least one of its surfaces, which is coated on its outer surface with a scratch and weatherproof coating made of hydroxylated fluoropolymer, which is crosslinked with methylmelamine and / or polysilicic acid.

Description

The present invention relates to a clear-transparent, high-impact, scratch and weatherproof composite system made of a polycarbonate layer which has a coating of polyacrylate on at least one of its surfaces, which is coated on its outer surface with a scratch and weatherproof coating made of hydroxylated fluoropolymers which is cross-linked with methyl melamine and / or polysilicic acid.

Molded parts made of polycarbonate have a combination of excellent properties; high light transmission, high impact strength and high heat resistance. A disadvantage of molded parts made of polycarbonate - like molded parts made from all other thermoplastics - is their relatively low scratch resistance. Due to the low scratch resistance, there are many fine scratch marks in the surface during practical use, which cause optical opacity and reduce transparency.

It is known to make molded parts. To provide polycarbonate with a coating of a polyacrylate. Technically, this can be done by coating the molded parts made of polycarbonate with a varnish based on polyacrylate. This is described

ir. of DT-OS 1,694,273. The coating can also be made by pressing polycarbonate sheets with films; Polyacrylate can be made. This is described in DT-05 1.953.276.

Such a coating of molded parts made of polycarbonate makes the system weatherproof, especially when the polyacrylate film applied to polycarbonate contains a UV absorber; these coatings practically do not change the scratch resistance.

It is also known that molded parts made of polycarbonate can be coated with a scratch-resistant coating based on methylmelamine-crosslinked, hydroxylated fluoropolymers. According to one embodiment, this polymer can have up to 60% by weight of silicon dioxide, based on the combined weight of silicon dioxide and crosslinked polymer. This is described in DT-OS 1.963.278.

A disadvantage of these polycarbonate moldings coated in this way is the poor weather stability of these coatings. After a short period of weathering, the scratch resistance and the adhesive strength of the coating decrease. The silicon dioxide-modified coatings are somewhat more weatherproof than the silicon dioxide-free coatings. Nevertheless, the weather stability must also be described as poor.

It is also known that molded parts made of polyacrylate can be coated with a scratch-resistant coating made of a methylmelamine-crosslinked hydroxylated fluoropolymer. This is described in DT-OS 1.963.278. These coatings on molded parts made of polyacrylate are scratch-resistant and weather-resistant. However, the disadvantage of this composite system is its low impact strength.

The present invention now relates to a clear-transparent, high-impact, scratch and weatherproof composite system made of polycarbonate as a substrate, which has a film made of polyacrylate on at least one of its surfaces, which has a coating based on methylmelamine-crosslinked hydroethylated fluoropolymer.

Uncoated molded parts made of polycarbonate have high impact strength. According to DIN 53 453, the test specimens remain "unbroken". In contrast, molded parts made of polyacrylate have a significantly lower impact resistance. When testing the impact strength, values of 14-26 kJ / m ² are obtained. Moldings made of polycarbonate coated with polyacrylate have an impact resistance that is significantly lower than that of the uncoated polycarbonate moldings.

It has now surprisingly been found that such molded parts made of polycarbonate which are coated with polyacrylate have a very high impact resistance if the polyacrylate coating has an additional coating of melamine-modified hydroxylated fluoropolymer on its outer surface.

The polyacrylate film can have a thickness of 0.010 to 1.25 mm. The face seal made from methyl melamine cross-linked h ^y -hydroxylated fluoropolymer can have a thickness of 0.005 to 0.5 mm.

This invention further relates to a method for producing a scratch-resistant composite system, in which a coating of polyacrylate is applied either continuously or discontinuously to the molded parts made of polycarbonate, and then a coating of methylmelamine-crosslinked hydroxylated fluoropolymer on this acrylate layer. This can be done by first coating the polycarbonate moldings with a polyacrylate varnish and treating them with a fluoropolymer coating solution after curing. Alternatively, the polycarbonate substrate can also be connected on one or both sides with polyacrylate films and the polyacrylate layer can then be coated with fluoropolymer. The composite system according to the invention can also be produced by connecting a film of polyacrylate coated on one side with fluoropolymer to the substrate polycarbonate at elevated pressure and temperature such that the fluoropolymer coating points outwards.

The bond between polyacrylate film and polycarbonate substrate can be achieved in a press under heat and pressure. The polyacrylate film can optionally be applied to polycarbonate sheets by pressing the acrylic sheet and the polycarbonate sheet through the nip of a pair of rolls, the rolls of which are heated. For an effective connection, the temperature used should be at least 160 ° C and the pressure at least 1.4 kg / cm ² . The higher the temperature, the shorter the time required and the lower the pressure required.

Suitable polycarbonates for the purposes of the invention are polycondensates obtainable by reacting diphenols, in particular dihydroxydiarylalkanes, with phosgene or diesters of carbonic acid, of which unsubstituted dihydroxydiarylalkanes are also suitable whose aryl radicals in the o- and / or m-position to the hydroxyl group Wear methyl groups or halogen atoms. Branched polycarbonates are also suitable.

Polycarbonates have average weight average molecular weights Mw between 10,000 and 100,000, preferably between 20,000 and 40,000, determined by measurements of the rel. Viscosity in CH ₂ C1 ₂ at 25 oC and a concentration of 0.5% by weight.

Suitable diphenols are, for example, hydroquinone, resorcinol, 4,4'-dihydroxydiphenyl, bis (hydroxyphenyl) alkanes such as, for example, C ₁ -C ₈ alkylene or C ₂ -C ₈ alkylidene bisphenols, bis (hydroxyphenyl) cycloalkanes such as C ₅ -C ₁₅ cycloalkylene or C ₅ -C ₁₅ cycloalkylidene bisphenols, bis (hydroxyphenyl) sulfides, ethers, ketones, sulfoxides or sulfones; Furthermore, α, α 'bis (hydroxyphenyl) diisopropylbenzene and the corresponding ring-alkylated or ring-halogenated compounds. Polycarbonates based on bis- (4-hydroxyphenyl) propane-2,2 (bisphenol A), bis- (4-hydroxy-3,5-dichlorophenyl) propane-2,2 (tetrachlorobisphenol A), bis are preferred - (4-hydroxy-3,5-dibromophenyl) propane-2,2 (tetrabromobisphenol A), bis- (4-hydroxy-3,5-dimethylphenyl) propane-2,2 (tetramethylbisphenol A) , Bis- (4-hydroxyphenyl) -cyclohexane-1,1 (bisphenol Z) and based on trinuclear bisphenols such as α, α'-bis- (4-hydroxyphenyl) -p-diisopropylbenzene.

Further diphenols suitable for the production of polycarbonate are described in US Patents 2,970,131, 2,991,273, 2,999.d35, 2,999,846, 3,014,391, 3,028,365, 3,062,731, 3,148,172, 3,271,367. 3,271,368 and 3,280,078.

The polyacrylate film used according to the invention or the polyacrylate-based lacquer used according to the invention can consist of any polyacrylate or polymethacrylate. Polyacrylates and polymethacrylates include homopolymers and copolymers of Acrylsäureesters and methacrylic acid ester having molecular weights from 103 to 107 and having from 4 to 13 carbon atoms in the monomer such as polyacrylic acid isobutyl ester, polymethacrylic acid methyl ester, Polymethacrylsäureäthylhexylester, Polyacrylsäureaethylester, copolymers of various Acrylsäureestern and / or methacrylic esters such as for example, methacrylic acid, methyl acrylate, cyclohexyl ester copolymers, and also copolymers of acrylic acid esters and / or methacrylic acid esters with crosslinking agents, such as, for example, 1,4-butanediol dimethacrylate, glycol dimethacrylate, triglycol dimethacrylate, trimethylolpropane trimethacrylate, allyl methacrylate and acrylate, and triallyl ester / methacrylate with / / or α-methylstyrene and the graft polymers and copolymers and copolymers and polymer mixtures composed of acrylic esters, methacrylic acid esters, styrene and butanediene. The aforementioned molecular weights of the polyacrylates and polymethacrylates. are as a number average M To understand n, determined for example by end group analysis.

wobei wenigstens zwei der CH₂-Gruppen an das Sauerstoffatom in der vernetzten Sauerstoff/Methylmelamin-Bindung gebunden sind.The methyl-melamine-crosslinked coating composition of hydroxylated fluoropolymer according to the invention is a crosslinked polymer, which contains fluorine-containing polymer chains which carry a multiplicity of oxygen / methylmelamine bonds, the oxygen being bound to a carbon am in the skeleton of the fluorine-containing polymer chain or a side chain and the carbon atom having at least one hydrogen atom, the chains being at least 20% by weight of fluorine contain and are crosslinked by the oxygen-methylmelamine bonds, characterized in that fluorine is arranged in the skeleton of the polymer chain, each polymer chain having a unit weight of not more than 700 per oxygen atom in the crosslinked O-methylmelamine bond and the methylmelamine being oxygen melamine bond has the following formula:

wherein at least two of the CH ₂ groups are attached to the oxygen atom in the crosslinked oxygen / methylmelamine bond.

The hydroxylated fluoropolymers can be crosslinked with polysilicic acid instead of methylmelamine. Both networking options can also be used side by side. The fluoropolymers crosslinked with polysilicic acid should contain a maximum of 60% by weight of silicon dioxide, based on the total weight of crosslinking agent and crosslinked polymer.

The polymer chain of the methylmelamine-crosslinked polymer results from fluorine-containing monomer units, preferably tetrafluoroethylene or chlorotrifluoroethylene and, if appropriate, from copolymerized fluorine-free, ethylenically unsaturated monomer units, the units having oxygen-bound methylmelamine.

Preferably, the fluorine-free, ethylenically unsaturated monomer unit is derived from a hydroxyalkyl vinyl ether, e.g. Hydroxybutyl vinyl ether, 2-hydroxypropyl vinyl ether or 6-hydroxyhexyl vinyl ether or vinyl acetate.

The methylmelamine in the sense of the invention is preferably derived from hexa- (methoxy-methyl) -melamine or hexa- (cyclohexyloxymethyl) -melamine.

The composite system according to the invention can either contain clear, colorless, transparent, translucent or opaque colored individual components or can be constructed from appropriate layers.

The present invention is described in more detail below with the aid of the examples:

Example A

• a) Herstellung des hydroxylierten Fluorpolymer In einem 8 1-Reaktor wurden 5500 ml tert. Butylalkohol, 26 g wasserfreies Kaliumcarbonat, 330 g 4-Hydroxybutylvinyläther, 0,9 g Azoisobutvrodinitril und 390 kg Tetrafluoräthylen gegeben und unter Rühren während 3,5 h auf 65 °C erhitzt, wobei währenddessen der Druck von einem Anfangswert von etwa 9,8 kg/cm2 auf 3,9 kg/cm² abfiel.
  • Nach dem Abkühlen wurde aus der klaren farblosen Lösung das weiße feste Copolymere durch Zugabe von Wasser ausgefällt. Nach Abfiltrieren, Waschen mit Wasser und Trocknen an der Luft wurde ein weißes festes Copolymeres mit einem Fluorgehalt von 35,5 % erhalten. Das Copolymere war in Methanol löslich.
• b) Herstellung der Uberzugslösung aus hydroxyliertem Fluorpolymer gemäß a) und Hexamethoxymethylmelamin.
  • Zu 3.000 g einer 14,65 %igen Lösung des oben beschriebenen Copolymeren (a) in Methanol gab man 500 g Methylisoamylketon, 500 g Toluol, 1000 g Essigsäure, 146 g Hexamethoxymethylmelamin und 12 g einer 20 %igen p-Toluolaulfonsäurelösung in Isopropanol. Ferner wurden dieser Lösung 5 g Siliconöl zur Verhinderung des Orangenschaleneffektes und 20 g 2(2'-Hydrozy-5'-methylphenyl)-benzotriazol zur Stabilisierung gegen die Einwirkung von UV-Licht gegeben.

Preparation of a coating solution of a hydroxylated fluoropolymer crosslinked with methylmelamine.

• a) Preparation of the hydroxylated fluoropolymer 5500 ml of tert were in an 8 1 reactor. Butyl alcohol, 26 g of anhydrous potassium carbonate, 330 g of 4-hydroxybutyl vinyl ether, 0.9 g of azoisobutvrodinitrile and 390 kg of tetrafluoroethylene were added and the mixture was heated to 65 ° C. with stirring for 3.5 h, during which time the pressure rose from an initial value of about 9.8 kg / cm2 dropped to 3.9 kg / cm ² .
  • After cooling, the white solid copolymer was precipitated from the clear colorless solution by adding water. After filtering, washing with water and drying in air, a white solid copolymer with a fluorine content of 35.5% was obtained. The copolymer was soluble in methanol.
• b) Preparation of the coating solution from hydroxylated fluoropolymer according to a) and hexamethoxymethylmelamine.
  • To 3,000 g of a 14.65% solution of the copolymer (a) described above in methanol was added 500 g of methyl isoamyl ketone, 500 g of toluene, 1000 g of acetic acid, 146 g of hexamethoxymethylmelamine and 12 g of a 20% solution of p-toluenesulfonic acid in isopropanol. Furthermore, 5 g of silicone oil to prevent the orange peel effect and 20 g of 2 (2'-hydrozy-5'-methylphenyl) benzotriazole to stabilize against the action of UV light were added to this solution.

Example B

Preparation of a coating solution from hydroxylated fluoropolymer crosslinkable with polysilica.

A hydrolyzed ethyl silicate solution was prepared by treating 100 g of tetraethyl orthosilicate with 69.5 g of anhydrous ethanol and 22.5 g of 0.1 N hydrochloric acid. After aging for 24 hours, a 120 g portion of this solution was mixed with 102 g of methyl isoamyl ketone and heated at 32 ^° under reduced pressure until the weight of the residue was 120 g.

This measure removed most of the ethanol, leaving a solution of polysilicic acid in methyl isoamyl ketone. The silicon dioxide content was calculated to be 15%.

A (tetrafluoroethylene / 4-hydroxybutyl vinyl ether) / silicon dioxide coating composition (ratio 60:40) was prepared by mixing 200 g of the above polysilicic acid solution with 164 g of tetrahydrofuran and 136 g of a 33% solution of the hydroxylated fluoropolymer (a) in methanol.

Example 1: Polymethyl methacrylate

Plates of polymethyl methacrylate with a layer thickness of 4.0 mm were immersed for two minutes in the solution described above under Example A, pulled out at about 15 cm / min and treated with heat for one hour at 135 °. The coating obtained was hard, colorless, glossy and transparent.

The coating had a thickness of about 8 _/ u after curing. The adhesive strength, measured using the cross-cut method, was 100%. The data are listed in Table 1.

For comparison, uncoated sheets of 4.0 mm thickness made of polymethyl methacrylate were also measured. The data are in Table 1.

Example 2: Polycarbonate

• 2.1 Polycarbonate coated with a coating solution according to Example A
  • Sheets of polycarbonate based on bisphenol A were coated with a relative solution viscosity (η rel.) According to DIN 7746 of 1.31 and a layer thickness of 4.0 mm. The coating solution according to Example A was applied using a film applicator at a speed of ₄₀ cm / min. The coating was cured at 135 ° C for 17 hours.
  • After curing, the coating had a thickness of approximately 12 _/ u. The properties are shown in Table 1.
• 2.2 Polycarbonate coated with 1.) a coating solution according to Example A as a primer and 2.) with a coating solution according to Example B as a finish.
  • Polycarbonate sheets based on bisphenol A (η _rel = 1.31) with a thickness of 4.0 mm were immersed in the coating solution according to Example A for 2 min, and were drawn out at 30 cm / min pulled and cured to a primer coat at 160 ° C for 30 min. After cooling to room temperature, the plates were immersed in the coating solution according to Example B for 2 min, taken out at a speed of 30 cm / min and cured at 160 ° C. for 2 h. The test results are shown in Table 1.
  • For comparison to Examples 2.1 and 2.2, similar uncoated polycarbonate sheets were also investigated (see Table 1 for the result).

Example 3: Polycarbonate coated with a coating based on polymethyl methacrylate

• 25 Gew.% Polymethylmethacrylat
• 30 Gew.% Toluol
• 30 Gew.% 1,2-Dichloräthan
• 15 Gew.% Methyl-äthyl-keton.

Polycarbonate sheets based on bisphenol A (η _rel = 1.31) of 4.0 mm layer thickness were 2 min. long immersed in the following coating solution:

• 25% by weight of polymethyl methacrylate
• 30% by weight toluene
• 30% by weight 1,2-dichloroethane
• 15% by weight of methyl ethyl ketone.

After slowly pulling the plates out of the solution, they were allowed to flash off at room temperature for 24 hours and then cured at 105 ° C. for 2 hours. After cooling, the properties were determined. They are listed in Table 1.

Example 4: Polycarbonate coated with a coating based on polymethyl methacrylate as a primer and with a coating according to Example _A as a finish.

Polycarbonate sheets coated according to Example 3 were immersed in the coating solution according to Example A for 2 minutes, removed from the solution at a rate of 40 cm / min and cured at 135 ° C. for 1 hour. The coating obtained was hard, colorless, transparent and of high gloss. The test results are in Table 1.

Example 5: Polycarbonate, laminated on both sides with polymethyl methacrylate and then coated on the coating from Example A.

The laminate made of polymethyl methacrylate / polycarbonate / polymethacrylate was produced during the extrusion of polycarbonate based on bisphenol A (q rel. 1.31) at a melting temperature of 2 ° C via a slot die. Polymethyl methacrylate films with a layer thickness of 0.025 mm were applied to the surfaces of the extruded polycarbonate sheet with the aid of rollers in such a way that continuous production was possible. This was achieved in that the 4.0 mm thick PC plate and the two polymethyl methacrylate films were passed through the nip of a pair of rolls in such a way that the films covered the two outer surfaces of the polycarbonate plate. The temperature of the rollers was set at 60 ° C; the temperature of the extruded polycarbonate sheet at the confluence was 160 ° C. and the pressure of the two rollers against each other was 1.4 kg / cm.

The laminates produced in this way were tested. The results are shown in Table 1.

Laminates as described above were immersed in the coating solution according to Example A for 2 minutes, removed from the solution at a rate of 15 cm / min and cured at 135 ° C. for 1 hour.

The test results are shown in Table 1.

Example 6: Polycarbonate, laminated on one side with polymethyl methacrylate and then coated with a coating from Example A.

Such a laminate of polycarbonate based on bisphenol A (ηrel. = 1.31) was produced as described in Example 5. The extruded polycarbonate sheet was 4.0 mm thick; the polymethyl methacrylate film had a thickness of 0.05 mm. The plate and film were passed through the same nip.

Plates produced in this way were coated on the polymethyl methacrylate side with the coating solution of Example A using a film applicator. The peeling speed was 40 cm / min. The coating was then cured at 135 ° C. for 1 hour.

The laminated uncoated and the laminated coated plates described above were examined. The results are shown in the table.

Example 7: Polycarbonate laminated with a film of polymethyl methacrylate coated on one side

A film of polymethyl methacrylate 1.0 mm thick was coated with the coating solution of Example A using a film applicator. The peeling speed was 15 cm per min. The coating was then cured at 135 ° C. for 1 hour. The films coated in this way were cut into 15 × 20 cm pieces. Polycarbonate sheets with a thickness of 4.0 mm and the same area dimensions were connected on one side to the acrylate foils in a heat sealing press in such a way that the coating was facing outwards.

The bond was achieved under the following conditions: temperature: 160 ° C; Pressure: 35 kg / cm2; Duration: 5 min.

After cooling, the properties of the composite panels were checked. The values are shown in Table 1.

• 1. Kratzfestigkeit - Stahlwolletest
  • Die Kratzfestigkeit der Überzüge gegenüber Stahlwolle wurde dadurch bestimmt, daß ein kleiner Bausch (1-2 cm²) Stahlwolle 20mal über die gleiche Fläche des Überzugs unter Anwendung einer Kraft von 250-300 g je Quadratzentimeter des Stahlwollebausches hin und her gerieben wird. Der Überzug wird dann hinsichtlich der Verkratzung untersucht und wie folgt bewertet:
    
• 2. Kratzfestigkeit - Siliciumcarbid-Falltest (ASTM-D-613-44)
  • Die Kratzfestigkeit nach dem Siliciumcarbid-Falltest wurde dadurch bestimmt, daß zunächst die Trübung nach ASTM D 1003 gemessen wurde und nach Berieselung der Probekörper-Oberflächen mit 1000 g Siliciumcarbidkörnern aus 63 cm Höhe die Trübung nochmals ermittelt wurde. Angegeben in der Tabelle ist die Differenz der Trübungs-Werte.
• 3. Die Haftfestigkeit der Überzüge wurde mit Hilfe des Gitterschnitt-Testes ermittelt (DIN 5315).
  
• 4. Die Wetterfestigkeit der Überzüge wurde mit Hilfe eines Kohlebogen-Bewitterungsgerätes (ASTM E-42-57) ermittelt. Vor und nach einer 2.000ständigen künstlichen Bewitterung wurden Kratzfestigkeit und Haftfestigkeit der Überzüge gemessen.
• 5. Die Lichtdurchlässigkeit wurde nach DIN 5036 ermittelt.
• 6. Die Schlagzähigkeit wurde nach DIN 53 453 an 6 mm breiten Prüfkörpern gemessen, die aus den 4 mm dicken Platten herausgearbeitet wurden. Je 12 Prüfkörper wurden gemessen und die Werte ermittelt. Bei einseitig beschichteten Prüfkörpern lag die Beschichtung während der Prüfung in der Zugzone.

Explanations of the information in Table 1

• 1. Scratch resistance - steel wool test
  • The scratch resistance of the coatings against steel wool was determined by rubbing a small pad (1-2 cm ² ) of steel wool back and forth 20 times over the same area of the coating using a force of 250-300 g per square centimeter of the steel wool pad. The coating is then examined for scratching and rated as follows:
    
• 2. Scratch Resistance - Silicon Carbide Drop Test (ASTM-D-613-44)
  • The scratch resistance after the silicon carbide drop test was determined by first measuring the haze according to ASTM D 1003 and, after sprinkling the specimen surfaces with 1000 g of silicon carbide grains from a height of 63 cm, the haze was determined again. The difference in the turbidity values is given in the table.
• 3. The adhesive strength of the coatings was determined using the cross cut test (DIN 5315).
  
• 4. The weather resistance of the coatings was determined using a carbon sheet weathering device (ASTM E-42-57). The scratch resistance and adhesive strength of the coatings were measured before and after 2,000 hours of artificial weathering.
• 5. The light transmission was determined according to DIN 5036.
• 6. The impact strength was measured according to DIN 53 453 on 6 mm wide test specimens which were worked out from the 4 mm thick plates. 12 test specimens each were measured and the values determined. With test specimens coated on one side, the coating lay in the tensile zone during the test.

Claims (6)

1. Composite system of polycarbonate and polyacrylate layers, characterized in that the polycarbonate layer carries a polyacrylate layer on at least one of its surfaces, which is coated on its outer surface with a crosslinked fluoropolymer. 2. Composite system according to claim 1, characterized in that the polyacrylate layer consists of polymethyl methacrylate. 3. Composite system according to claim 1, characterized in that the polycarbonate layer is coated on both sides. 4. A composite system according to claim 1, characterized in that the crosslinked fluoropolymer is crosslinked with methylmelamine and / or polysilicic acid, the content of Si0 _{2 being} at most 60% by weight, based on the crosslinked fluoropolymer and crosslinking agent. 5. A method for producing the composite systems according to claims 1 to 4, characterized in that a polyacrylate film of 0.010 to 1.25 mm thick is applied to the polycarbonate layer and then the polyacrylate layer is coated with fluoropolymers. 6. A method for producing the composite systems according to claims 1 to 4, characterized in that a film coated on one side with fluoropolymer Polyacrylate is applied to a polycarbonate layer so that the fluoropolymer coating forms the outer surface of the composite system.