NL7905450A - METHOD FOR COATING POLYCARBONATE SHEETS AND POLYCARBONATE FOILS WITH PLASTIC LAYERS. - Google Patents

Description

/ \ N.0.27.833

Rohm GmbH, Darmstadt, Federal Republic of Germany. '

Method for coating polycarbonate sheets and polycarbonate films with plastic layers.

The invention relates to a method for coating polycarbonate sheets and polycarbonate films with plastic layers. !

Polycarbonate articles are distinguished by excellent light transmittance, high mechanical strength and high dimensional stability at elevated temperature, excellent dimensional accuracy and relatively low water absorption. For this reason, polycarbonate sheets are preferably used for particularly impact-resistant translucent construction elements, lamp domes, glazing and the like. 10

However, with polycarbonate glazing and also with other objects, the considerably less scratch resistance of the polycarbonate compared to silicate glass is a major drawback.

Intensive irradiation with ultraviolet light also causes damage to the surface of polycarbonates, which are expressed by the maturing of originally glossy surfaces, which is caused by a large number of particularly fine hair cracks.

Since the processing of the polycarbonates is predominantly by | injection molding and to a small extent by hot molding, that is to say by molding at relatively high temperatures, is carried out! : is the problem by adding ultraviolet light absorbing! ; means to the resins before the resins are incorporated into it! generally cannot be solved. One solution was to protect the surfaces of the polycarbonate front pin of coatings! provided containing an ultraviolet light absorbent

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- £ see W.3F. Christopher and P.W. Pox in "Polycarbonatesa, Reinhold -I- 790 5 4 50 i r * 2 -

Publishing Comp. Hew York (1962).

According to U.S. Pat. No. 3 * 582,398, to enhance the optical properties (air permeability) of polycarbonate articles, transparent coatings of polymethyl methacrylate (EMMA), which preferably contain ultraviolet light absorbers, are applied. The coating process can be carried out technically by dipping, spraying or pouring a solution of the polymethyl methacrylate in an indifferent volatile solvent.

Ultraviolet light-inhibiting coatings can also be obtained by pressing polycarbonate sheets with films of acrylate copolymers while heating. According to the German se * Off enlegungs script "1 .953 * 276, a prefabricated 0.025 - 0.25 mm thick polyacrylate film, preferably consisting of a methyl methacrylave-ethyl acrylate copolymer containing 0.25-5% by weight of an ultraviolet 15 light absorbent contained on the respective plates.

To obtain a strong adhesion, the temperature used should be at least 163 ° C and the pressure at least 1.4 kg / cm. The higher the selected temperature, the smaller the pressure and the residence time under pressure can be set. Possible embodiments have been indicated by applying by pressing in a (heated) roller, achieving the compound by joint deformation under the influence of vacuum of the film of the polymeric acrylate and the polycarbonate film or by injection molding in which the process of injection molding is carried out by spraying the melted polycarbonate against a film of the polymeric acrylate, the two materials being simultaneously bonded and pressed in a single operation step.

The indicated methods of coating with poly (meth) acrylates, especially in combination with ultraviolet light absorbers, may, however, significantly improve the weather resistance of polycarbonate articles; however, a generally applicable method for solving the problem of scratch-resistant polycarbonate coating is not given. 35

The scratch-resistant coating of polycarbonate articles can be carried out according to German Offenlegunsschrift 1,963-278 7905450 5 ft by applying a coating based on methylmelamine cross-linked, hydroxylated, fluorine-containing polymers.

However, it has been found that scratch-resistant coatings of the prior art present adhesion strength and weathering resistance problems. 5

The adhesion of a coating based on methylmelamine cross-linked hydroxylated fluorine-containing polymers to the polycarbonate surface is considerably poorer than that of (meth) acrylate polymers, especially when exposed to weather influences. Already after a relatively short period of exposure to weathering, a tendency to loosen the coating and an increased sensitivity of the surface to damage is observed.

Therefore, also with regard to obtaining scratch-resistant coatings, the problem remained presently of providing a method for coating polycarbonate articles, the coatings of which adhere strongly and otherwise meet the highest requirements.

The methods hitherto known have certain drawbacks.

Coating using an organic solvent is unsatisfactory from a technical and ecological point of view. While the application of a film under pressure and heating approaches the desired goal, this prior art process has remained unsatisfactory with regard to technical production.

The production of the film, the production of the 25l * 6 polycarbonate article and the assembling are separate process steps. Prior art pressing requires a minimum temperature of 163 ° C; however, there is a tendency to increase the temperature so that the time for the pressing process can be shortened. 50

The aforementioned possibilities of the process of the common vacuum forming of a polyacrylate film and a polycarbonate film or the process of injection molding against a polyacrylate film are, of course, limited to objects formed under vacuum or injection molded. In the middle 35 is left or under the conditions of molding under 7905450

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• <r 4 cuum in all cases a uniform, stable and strongly adhering coating can be obtained.

The aim should be that the coating process can be carried out continuously in a relatively simple manner. 5

It has been found that the surface of polycarbonate sheets and polycarbonate films, in particular polycarbonate sheets with one or more plastic layers, in particular those on a poly (meth) acrylate basis, can be coated in such a way that the coatings almost completely meet the requirements of such coatings. 10 things are said if the polycarbonate articles, in particular the polycarbonate sheets, and the plastic layers to be applied in the desired dimensions are placed in an extruder. coextruded by means of a multi-component nozzle and optionally applies a scratch-resistant coating (finishing layer) to the poly (meth) acrylate-based layer obtained in this way as an intermediate layer.

Polycarbonates, as is customary in the art, are to be understood to mean the polycondensation products of carbonic acid with polyhydric alcohols, especially divalent phenols, such as the dioxydiphenylalkanes having a molecular weight greater than about 12,000. Particular to be mentioned are the (4.4 * -dihydroxy-diphenyl) -propane-2.2 polycarbonates and their derivatives substituted in the core by one or more halogen or alkyl groups.

As material for the plastic layer to be applied, polymers or copolymers based on (meth) acrylates firstly come into consideration, insofar as they are suitable for extruding. Particular mention should be made of polymers and copolymers of acrylic or methaeryl acid esters, primarily with methyl methacrylate and methyl acrylate as monomer and, furthermore, with acrylic esters of the homologous alcohols with 2-4 carbon atoms, in particular ethyl and butyl acrylate, further benzyl acrylate, the dimethacrylic esters of diols such as the ethanediol and the 1,4-butane diol methacrylate. Also suitable as monomers for the material to be co-extruded according to the invention are 35 (co) polymers with acrylonitrile, styrene, maleic anhydride, 790 54 50 5 butadiene / styrene, butadian / α-methylstyrene.

The plastic layers to be applied generally have a thickness of 10 - 100 µm, preferably 50 µm. The thickness of the layer to be applied can be of critical importance with regard to the technical application, since from a certain thickness of the coating one has to count with a propagation of cracks in the layer present underneath.

As a particularly interesting embodiment of the coating method according to the invention, the simultaneous application of a number of suitable plastic layers by coextruding in an extruder by means of a multi-component nozzle can be mentioned. In this case, the poly (meth) acy, which is particularly suitable because of the good adhesion to the polycarbonate surface, are used as an intermediate layer. Advantageously, at least one of the plastic layers protecting the polycarbonate core, in particular the poly (meth) acrylate layer, contains suitable ultraviolet light-absorbing agents, for example the agents mentioned in US patent 5 594-264.

As the material for the scratch-resistant coatings, which are optionally applied to the intermediate layer of poly (meth) acrylates prepared by co-extruder and interposed, are the scratch-resistant coatings known per se, for example the coatings which based on varNsiloxane resins, or mention the coatings based on methyl melamine cross-linked hydroxylated, fluorine-containing polymers described in German Federal Legislation, 1,963,278. 25

The application of the scratch-resistant coatings to the intermediate layer of poly (meth) acrylates applied by co-extrusion can be carried out in a manner known per se, for example by applying a solution with the coating agent dissolved therein. 30

The starting materials suitable for coextruding or the starting materials suitable for coating plastics, i.e. polycarbonates and the preferred polymers or copolymers of (meth) acrylates, can be in conventional form and quality suitable for extrusion. are present, for example, as granules or powders.

790 5450 'C 6 -

The execution of the extruding process in the extruder according to the invention can also be carried out in a manner known per se using commercially available extruders and multi-component nozzles of suitable dimensions. 5

The adhesion between the polycarbonate article and the plastic layer or layers to be applied is established during the extruding process, the heat content of the layers developed during the extruding process generally in order to achieve a well-adhering connection between the layers is sufficient.

The extruding process according to the invention is expediently followed by treatment by calibrating.

The ultraviolet light absorbing agent or agents can either be added to the starting material intended for coating the plastic in the most homogeneous distribution and mixed, or be continuously fed during extrusion.

The coatings obtained according to the method of the invention stand out above the products obtained according to the methods of the prior art, in particular with regard to adhesion and especially with regard to the optical properties.

The following example illustrates the invention.

Example for carrying out the coating method according to the invention using a (maximum) four-component nozzle.

The device according to the invention schematically shown in the figure serves for the manufacture of polycarbonate sheets provided with a plastic coating. The parts which are important for the implementation of the method according to the invention are a multi-component nozzle, in which the layer thickness is adjusted by means of show elements (push bars) 1,2,3 and 4. The total thickness of the plates is adjusted by two adjustable lips 5 and 6.

Both the adjustment of the thrust element and the adjustment of the lips can be carried out by means of differentials 7, 8, 9> 10 »11 and 12. The material supply takes place via the flow channels 13, 14, 15 and 16 arranged in the interior of the nozzle in 790 5450 7. The multi-component nozzle is heated by means of resistance heating elements, the individual layers of which are thermally adjustable independently of each other.

With the device according to the figure, for example, 5 polycarbonate sheets of different thicknesses can be coextruded with plastic coatings between, for example, 10 - 100 µm sheets.

A dependence of the different layers on one another does not exist from the viewpoint of manufacture. For example, films or plates on a polycarbonate base layer and polymers or copolymers of (meth) acrylates can be coextruded. This also applies if one or more ultraviolet light absorbers are added to the coextruded polymer or copolymer.

For example, it is possible to perform both the coextruding such that the final layer contains the ultraviolet light absorbing agent or agents on both outer sides of the plate or the films, and the coextruding such that the intermediate layer or layers contain ultraviolet light absorbers as a component. 20

The processing temperatures in the extrusion process depend on the type of molding compound used in each case. In the case of (meth) acrylates, the temperature is generally 240-280 ° C.

For the polycarbonate molding compositions, the mass temperature is generally 260-310 ° C. Within the indicated ranges, attention should be paid to the regulation of the temperature at which optimum bonding and optimal optical quality of the coextruded material is achieved. The optimum temperature or the optimum setting of the thickness is achieved if a homogeneous amount of the material without bubbles is present in the roller groove of the calender connected behind the multi-component nozzle.

t 790 5450

Claims (10)

Method for coating polycarbonate sheets and polycarbonate films with plastic layers, characterized in that the polycarbonate plates and polycarbonate films and the plastic layer to be applied are simultaneously produced by coextruding in an extruder by means of a multi-component nozzle, whereby in the course of the extruding takes place the adhesion process of the plastic layer on the polycarbonate sheets and polycarbonate films. 2. A method according to claim 1, characterized in that the polycarbonate sheets and polycarbonate films are manufactured together with different layers of plastic to be applied, wherein in the course of the extrusion the adhesion process of the plastic layers on the polycarbonate sheets and polycarbonate foils takes place. 15 Method according to claim 1 and / or 2 for coating polycarbonate sheets with plastic layers based on polymers or copolymers of (meth) acrylates, characterized in that the polycarbonate sheets and the plastic layers to be applied are simultaneously co-extruded in a extruder is manufactured by means of a multi-component nozzle, during which the adhesion process of the plastic layers on the polycarbonate sheets takes place during the course of the extrusion. 4. A method according to claims 1-3, characterized in that one or more ultraviolet light absorbing agents are added to the covering plastic layer. 5. Process according to claims 1-4, characterized in that a plastic layer of polymers or copolymers of (meth) acrylates is used as the plastic layer to be applied directly to the polycarbonate sheet or polycarbonate, t-film. 30 6. Process according to claims 1-5, characterized in that calendering is carried out after the extrusion process. 7. Process according to claims 1-6, characterized in that on the plastic layer (intermediate layer) of polymers or intermediate layer of polymer or copolymers of (metb) acrylates yield a scratch-resistant coating as the final layer. 8. Process according to claims 1 - 7, characterized in that the plastic layer (intermediate layer) bonded to the polycarbonate sheet in the course of the extrusion under strong adhesion in a thickness of 10 - 100 µm. Method according to claims 1-8, characterized in that a scratch-resistant coating based on a silicone resin is applied. 10 10. Process according to claims 1 to 90, characterized in that a scratch-resistant coating based on methylamine cross-linked, hydroxylated, fluorine-containing polymers is applied. 7905450 i