HK1093039A - Grouser plate coated by coextrusion without any triangle effect - Google Patents

Description

Multiwall sheet coated by coextrusion without triangular effect

The present invention relates to a method for producing a wedge-free multiwall sheet (Stegplatte) coated by coextrusion, a special extrusion nozzle for producing such a sheet, its use for producing such a sheet, as well as a multilayer coextruded multiwall sheet comprising at least one layer comprising a thermoplastic material and at least one coating layer without trigonometric effect, and other products comprising the multilayer multiwall sheet.

Multiwall sheets typically have coextruded layers on both sides on one or both outer sides that can perform different functions. For example, it may be a UV protective layer to protect the sheet from UV radiation (e.g. yellowing), but also to perform other functions as such, such as IR reflection.

The following is a summary of the prior art relating to such multiwall sheets.

EP-A0110221 discloses sheets consisting of two layers of polycarbonate, one of the layers containing at least 3% by weight of UV absorber. These sheets can be produced by coextrusion according to EP-A0110221.

EP-A0320632 discloses moldings composed of two layers of thermoplastics, preferably polycarbonates, one of the layers containing a specifically substituted benzotriazole as UV absorber. EP-A0320632 also discloses the production of these moldings by coextrusion.

EP-A0247480 discloses multilayer sheets which have a structure which, in addition to a thermoplastic layer, also has a layer of branched polycarbonate which contains a specifically substituted benzotriazole as UV absorber. The production of these sheets by coextrusion is also disclosed.

EP-A0500496 discloses polymer compositions UV-light stabilized with special triazines and their use as outer layers in multilayer systems. The polymers mentioned are polycarbonates, polyesters, polyamides, polyacetals, polyphenylene ethers and polyphenylene sulfides.

However, all coated multiwall sheets known from the prior art show the problem of the so-called "trigonometric effect", i.e.a wedge (Zwickel) consisting of the material of the coextruded layers is obtained during coextrusion, with a certain unevenness of the sheet surface.

Figure 1 schematically shows how a wedge is formed by means of a cross-section of a multiwall sheet. The arrows show the flow of the polymer melt in the multiwall die of the multiwall sheet (1), which causes wedge formation in the coextruded layer (2).

Starting from the prior art, the object of the present invention is therefore to produce multiwall sheets, optionally covered with multilayers by coextrusion, which no longer have a triangular effect compared with the prior art.

This object forms the basis of the present invention.

In the case of single-coated sheets, this problem can be solved by increasing the material feed of the uncoated side using a modified feed of co-extruded material, so that the formation of wedges at the coated side can be avoided.

Figure 2 shows schematically, by means of a section of a multiwall sheet, how the process works:

the melt can be distributed in the direction of the coated side of the multiwall sheet (3) by enhancing the polymer flow of the uncoated side, so that the coextruded layer (4) remains wedge-free.

But in the case of double-coated sheets, the process is no longer effective. Here, for example, adding a charge to the floor will create a thicker wedge at the floor, so that the benefit on one side will be offset by the loss on the other side.

Figure 3 shows this effect schematically by means of a section of a multiwall sheet (charge at (5)): while the upper coextruded layer (62) remains wedge-free, the bottom coextruded layer (7) has thick wedges.

It has now surprisingly been found that the formation of wedges or the trigonometric effect on each side can be substantially completely avoided by changing the material flow during extrusion, so that around the comb of the nozzle a partial flow is guided out of the conventional material flow, said partial flow being guided directly into the middle of the multiwall die of the nozzle forming the sheet wall. Typically, the material flow is divided by a comb into an upper flow and a lower flow, which converge up and down at the multi-wall die and thereby create a wall. This outflow of material from the upper and lower streams results in a typical "discharge funnel" on the coextrusion side that is filled with the subsequent inflow of coextrusion material. As shown in fig. 1, a wedge is formed. By feeding part of the material directly into the multiwall mould by the method according to the invention, material loss from the upper and lower streams is reduced or even avoided, as in fig. 4, and funnel formation and thus wedge formation, i.e. the triangular effect, is minimized, preferably even completely avoided, on both sides of the sheet. The process according to the invention is therefore suitable for producing multiwall sheets coated on one and both sides.

Figure 4 shows schematically, by means of a section of a multiwall sheet, how the process according to the invention works:

coextruded layers (9) and (10) are kept free of wedges by additionally feeding the polymer melt at (8), for example, through a channel into a multi-wall die.

It is entirely surprising that the long-standing problem can be successfully solved by this simple measure.

The subject of the invention is therefore a particular process for producing coatings on multiwall sheets by coextrusion, and sheets free of wedges or of trigonometric effects obtainable by this process. These sheets are characterized by a particularly smooth surface and a uniform, i.e. wedge-free, co-extruded coating. A preferred embodiment is a double-coated multiwall sheet.

The subject of the present application is therefore also a special extrusion nozzle which can carry out the process according to the invention.

In addition to the conventional channels, sections and dies used for different purposes, the comb of the nozzle also includes channels for feeding a portion of the flow-in material directly into the multi-walled die. In a preferred embodiment, the material is fed forward from the area behind the nozzle directly into the multi-wall die.

One possible embodiment of a nozzle according to the invention at a multi-wall die is schematically shown as a cross-section in fig. 5:

the polymer melt flows in at (12). The melt stream is fed through a channel (13) into a multi-wall die (14). (13) Representing either the upper or lower mold. The sheet emerges at (16).

The invention also relates to products containing said sheet. Products comprising, for example, the multi-layered multiwall sheet are preferably selected from the group consisting of glazes, greenhouses, warm coats, balconies, parking stalls, bus stops, skylights, partition walls, spot kiosks, and solar collectors.

The method according to the invention has the great advantage of avoiding the trigonometric effect, which would otherwise be significantly adversely affected by the formation of wedges and the corresponding material waste and uneven sheet surfaces. The coating material wasted in the wedge generally comprises valuable thermoplastic materials, including expensive additives. Saving these materials can be economically significant.

The process according to the invention is suitable for producing a wide variety of coextruded layers and mainly any functional layer that is conceivable includes combinations thereof (UV protection and functional layers, such as IR reflection on the top and UV protection on the bottom) and is particularly suitable for producing multiwall sheets with UV protection on both sides.

The multilayered product according to the invention, such as a multiwall sheet, has other advantages over the prior art. The multilayer product according to the invention, such as a multiwall sheet, can be produced by coextrusion. Thereby being superior to products produced by painting. Thus, unlike painting, no solvent is volatilized during coextrusion.

In addition, the lacquer cannot be stored for a long time. Coextrusion does not have this disadvantage.

In addition, lacquers require expensive techniques. For example, they require explosion-proof equipment, solvent recycling and thus high capital investment. Coextrusion does not have this disadvantage.

A preferred embodiment of the present invention is the multilayer multiwall sheet wherein the base layer and the coextruded layer can be made of the same or different thermoplastic materials, preferably both layers are based on the same material.

Suitable thermoplastic molding materials are any molding materials which comprise, for example, polycarbonates and/or polyesters and/or various polyester carbonates and/or polyesters and/or polymethyl methacrylates and/or polystyrenes and/or SANs and/or blends of polycarbonates and polyesters and/or polymethyl methacrylates and/or polystyrenes and/or SANs.

Preferred molding compounds comprise transparent thermoplastics such as polycarbonates and/or polyesters, and those comprising a blend of at least one of the two thermoplastics. Particularly preferably, polycarbonates and polyesters are used, and most preferably polycarbonates are used.

The preparation of these thermoplastics is well known to the person skilled in the art and is carried out by known processes.

Preferred multilayer products according to the invention are those in which the coextruded layers additionally comprise from 1 to 20% by weight of a UV absorber and have a thickness of from 5 to 200. mu.m, preferably from 30 to 100. mu.m.

The multiwall sheet can be a double wall sheet, a triple wall sheet, a quadruple wall sheet, or the like. Multiwall sheets can also have different profiles, such as an X profile or an XX profile. The multiwall sheet can also be a corrugated multiwall sheet.

One preferred embodiment of the present invention is a multiwall sheet having coextruded layers on both sides, wherein the substrate and the two coextruded layers are made of polycarbonate.

Depending on the type of thermoplastic used and their additives, the multilayer products according to the invention are translucent, opaque or transparent.

In a particular embodiment, the multilayer product is transparent.

Both the substrate and the monolayer or multilayer coextruded layer of the multiwall sheet according to the invention can comprise additives.

In particular, the coextruded layer may comprise a UV absorber and a release agent.

The UV absorber or mixture thereof is present in a concentration of 0 to 20% by weight. Preferably from 0.1 to 20% by weight, particularly preferably from 2 to 10% by weight and most particularly preferably from 3 to 8% by weight. If two or more coextruded layers are present, the amount of UV absorber in these layers may vary.

Examples of UV absorbers which can be used according to the invention are described below:

a) benzotriazole derivatives of formula (1):

in formula (I), R and X are the same or different and represent H, alkyl or alkylaryl.

Preferred for this purpose are Tinuvin 329, where X ═ 1, 1, 3, 3-tetramethylbutyl, R ═ H, Tinuvin 350, where X ═ tert-butyl, R ═ 2-butyl, Tinuvin 234, where X ═ R ═ 1, 1-dimethyl-1-phenyl.

b) Dimeric benzotriazole derivatives of formula (II):

in the formula (II), R¹And R²Are identical or different and represent H, halogen, C₁-C₁₀Alkyl radical, C₅-C₁₀Cycloalkyl radical, C₇-C₁₃Aralkyl radical, C₆-C₁₄Aryl, -OR⁵Or- (CO) -O-R⁵Wherein R is⁵H or C₁-C₄An alkyl group.

In the formula (II), R³And R⁴Also identical or different and denoted H, C₁-C₄Alkyl radical, C₅-C₆Cycloalkyl, benzyl or C₆-C₁₄And (4) an aryl group.

In formula (II), m represents 1, 2 or 3, and n represents 1, 2, 3 or 4.

Preferred is Tinuvin 360, wherein R¹＝R³＝R⁴＝H，n＝4，R²1, 1, 3, 3-tetramethylButyl, m ═ 1.

b1) Dimeric benzotriazole derivatives of formula (III):

wherein the bridge is

R¹、R²M and n are as defined in formula (II), and wherein p is an integer from 0 to 3, q is an integer from 1 to 10,

y is equal to-CH₂-CH₂-、-(CH₂)₃-、-(CH₂)₄-、-(CH₂)₅-、-(CH₂)₆-or CH (CH)₃)-CH₂-，R³And R⁴As defined in formula (II).

Preferred for this purpose are Tinuvin 840, in which R is¹＝H，n＝4，R²T-butyl, m 1, R²In ortho position to the OH group, R³＝R⁴＝H，p＝2，Y＝-(CH₂)₅-，q＝1。

c) Triazine derivatives of formula (IV):

wherein R in formula (IV)¹，R²，R³And R⁴Are identical or different and are H or alkyl or CN or halogen, and X is equal to alkyl.

Preferred for this is Tinuvin 1577, where R¹＝R²＝R³＝R⁴H, X ═ hexyl; cyasorb UV-1164, wherein R¹＝R²＝R³＝R⁴Methyl and X octyl.

d) Triazine derivatives of formula (IVa):

wherein

R¹Is represented by C₁Alkyl to C₁₇An alkyl group, a carboxyl group,

R²represents H or C₁Alkyl to C₄Alkyl, and

n is 0 to 20.

e) Dimeric triazine derivatives of formula (V):

wherein

R in the formula (V)¹、R²、R³、R⁴、R⁵、R⁶、R⁷、R⁸May be the same or different and represents H or alkyl or CN or halogen, X is alkyl or- (CH)₂CH₂-O-)_n-C(＝O)-。

f) A diaryl cyanoacrylate of formula (VI):

wherein

R¹To R⁴⁰May be the same or different and represents H, alkyl, CN or halogen.

Preferred for this is Uvinul3030, wherein R is¹To R⁴⁰＝H。

Particularly preferred UV absorbers are selected from Tinuvin 360, Tinuvin 1577 and Uvinul 3030.

Tinuvin 360：

Tinuvin 1577

Uvinul 3030

The UV absorbers are commercially available.

In addition to or instead of the UV absorbers, these layers may also comprise other conventional processing aids, in particular mould release agents and flow control agents, and also conventional additives for polycarbonates, such as stabilizers, in particular heat stabilizers, and also colorants, optical brighteners and inorganic pigments.

All known polycarbonates are suitable as preferred thermoplastics for the multilayer products according to the invention:

these are homopolycarbonates, copolycarbonates and thermoplastic polyester carbonates.

They have a weight-average molecular weight M_wPreferably from 18000 to 40000, particularly preferably from 26000 to 36000 and particularly preferably from 28000 to 35000, as determined by gel permeation chromatography corrected for polycarbonate.

For the preparation of Polycarbonates, reference may be made, for example, to "Schnell, Chemistry and Physicsof Polycarbonates, Polymer Reviews, volume 9, Interscience Publishers, New York, London, Sydney 1964", and "D.C.PREVORSEK, B.T.DEBONA and Y.KESTEN, Corporation Research Center, Allied chemical Corporation, Morristown, New Jersey 07960," "Synthesis of Polymer company Copolymers, Journal of Polymer Science, Polymer Edition, volume 19, 75-90 (1980)", "D.Freetag, U.G.G., P.R.Muverr and N.BAYEtR" Polycarbonates, polyester Polycarbonates, polyolefin Polycarbonates, WO 19, 75-90(1980), and "D.Freetag", U.G.G.R.Muverner and N.S.S.R.S.S.S.S.S.A.S.A.S. Pat. No. and No. polyester Polycarbonates, polyolefin Polycarbonates, polyolefin Polycarbonates.

The polycarbonates are preferably prepared by the phase interface process or the melt transesterification process and are described below as exemplary using the phase interface process.

Preferred compounds for use as starting compounds are bisphenols having the general formula:

HO-Z-OH，

wherein Z is a divalent organic group having 6 to 30 carbon atoms and comprising one or more aromatic groups.

Examples of such compounds are bisphenols belonging to the following group: dihydroxybiphenyl, di (hydroxyphenyl) alkane, indanbisphenol, bis (hydroxyphenyl) ether, bis (hydroxyphenyl) sulfone, bis (hydroxyphenyl) ketone, and 1, 3-bis (hydroxyphenylpropyl) benzene or 1, 4-bis (hydroxyphenylpropyl) benzene.

Particularly preferred diphenols belonging to the above group of compounds are bisphenol A, tetraalkylbisphenol A, 1, 3-bis [2- (4-hydroxyphenyl) -2-propyl ] benzene (bisphenol M), 1, 4-bis- [2- (4-hydroxyphenyl) -2-propyl ] benzene, 1-bis (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane (bisphenol TMC) and optionally mixtures thereof.

Preferably, the bisphenol compounds used according to the invention are reacted with carbonic acid compounds, in particular phosgene, or in the case of the melt transesterification process diphenyl carbonate or dimethyl carbonate.

The polyester carbonates are preferably prepared by reacting the above-mentioned bisphenols, at least one aromatic dicarboxylic acid and optionally carbonic acid equivalents. Examples of suitable aromatic dicarboxylic acids are phthalic acid, terephthalic acid, isophthalic acid, 3, 3 '-diphenyldicarboxylic acid or 4, 4' -diphenyldicarboxylic acid and benzophenonedicarboxylic acids. A proportion of up to 80 mol%, preferably from 20 to 50 mol%, of the carbonate groups in the polycarbonate may be replaced by aromatic dicarboxylic acid ester groups.

Examples of inert organic solvents used in the phase interface process are dichloromethane, the various dichloroethane and chloropropane compounds, carbon tetrachloride, chloroform, chlorobenzene and chlorotoluene, preference being given to using chlorobenzene or dichloromethane or mixtures of dichloromethane and chlorobenzene.

The phase interface reaction can be accelerated by catalysts such as tertiary amines, in particular N-alkylpiperidines, or onium salts. Preference is given to using tributylamine, triethylamine and N-ethylpiperidine. In the case of the melt transesterification process, preference is given to using the catalysts mentioned in DE-A4238123.

Some suitable branching agents which the polycarbonates can be deliberately branched in a controlled manner by using small amounts of branching agents are phloroglucinol, 4, 6-dimethyl-2, 4, 6-tris (4-hydroxyphenyl) -2-heptene, 4, 6-dimethyl-2, 4, 6-tris (4-hydroxyphenyl) heptane, 1, 3, 5-tris (4-hydroxyphenyl) benzene, 1, 1, 1-tris (4-hydroxyphenyl) ethane, tris (4-hydroxyphenyl) phenylmethane, 2-bis [4, 4-bis (4-hydroxyphenyl) cyclohexyl ] propane, 2, 4-bis (4-hydroxyphenyl-isopropyl) phenol, 2, 6-bis (2-hydroxy-5' -methylbenzyl) -4-methylphenol, 2- (4-hydroxyphenyl) -2- (2, 4-dihydroxyphenyl) propane, hexa (4- (4-hydroxyphenylisopropyl) phenyl) o-phthalate, tetrakis (4-hydroxyphenyl) methane, tetrakis (4- (4-hydroxyphenylisopropyl) phenoxy) -methane, 1, 3, 5-tris [2- (4-hydroxyphenyl) -2-propyl ] benzene, 2, 4-dihydroxybenzoic acid, 1, 3, 5-tribenzoic acid, cyanuric chloride, 3-bis (3-methyl-4-hydroxyphenyl) -2-oxo-2, 3-dihydroindole and 1, 4-bis (4', 4 "-dihydroxytriphenyl) methyl) benzene, especially 1, 1, 1-tris (4-hydroxyphenyl) ethane and bis (3-methyl-4-hydroxyphenyl) -2-oxo-2, 3-indoline.

The branching agents or branching agent mixtures optionally used concomitantly in amounts of from 0.05 to 2 mol%, based on the diphenols used, may be introduced together with the diphenols or added at a later stage of the synthesis.

The chain terminators used are preferably phenols, such as phenol, alkylphenols, such as cresol and 4-tert-butylphenol, chlorophenol, bromophenol, cumylphenol or mixtures thereof, in amounts of from 1 to 20 mol%, preferably from 2 to 10 mol%, per mol of bisphenol. Phenol, 4-tert-butylphenol and cumylphenol are preferred.

Chain terminators and branching agents may be added to the synthesis system either separately or together with the bisphenols.

The preparation of polycarbonates by the melt transesterification process is described, for example, in DE-A4238123.

Preferred polycarbonates according to the invention are homopolycarbonates based on bisphenol A, homopolycarbonates based on 1, 1-bis (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane, copolycarbonates based on two monomers, namely bisphenol A and 1, 1-bis (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane, and copolycarbonates based on two monomers, namely bisphenol A and 4, 4' -dihydroxybiphenyl (DOD).

Homopolycarbonates based on bisphenol a are particularly preferred.

The polymers used may comprise stabilizers. Examples of suitable stabilizers are phosphines, phosphites or Si-containing stabilizers, and further compounds as described in EP-A0500496. Examples which may be mentioned are triphenyl phosphite, diphenylalkyl phosphites, phenyldialkyl phosphites, tris (nonylphenyl) phosphite, tetrakis (2, 4-di-tert. -butylphenyl) -4, 4' -biphenylene diphosphonite and triaryl phosphites. Triphenylphosphine and tris (2, 4-di-tert-butylphenyl) phosphite are particularly preferred.

These stabilizers can be present in all layers of the multiwall sheet according to the present invention, i.e., in both the base layer and the coextruded layer or layers. Different additives or different concentrations of additives may be present in each layer.

In addition, the multiwall sheet according to the invention can comprise 0.01 to 0.5 wt.% of esters or partial esters of mono-to hexahydric alcohols, in particular glycerol, pentaerythritol or guerbet alcohols.

Examples of monohydric alcohols are stearyl alcohol, palmityl alcohol and Guerbet alcohol.

An example of a glycol is ethylene glycol.

Glycerol is an example of a triol.

Pentaerythritol and meso-erythritol are examples of tetrahydric alcohols.

Arabitol, ribitol and xylitol are examples of pentahydric alcohols.

Mannitol, glucitol (sorbitol) and galactitol are examples of hexahydric alcohols.

The ester is preferably saturated C₁₀To C₃₆Aliphatic monocarboxylic acids and optionally hydroxymonocarboxylic acids, preferably saturated C₁₄To C₃₂Monoesters, diesters, triesters, tetraesters, pentaesters and hexaesters of aliphatic monocarboxylic acids and optionally hydroxymonocarboxylic acids or mixtures thereof, in particular random mixtures.

Commercially available fatty acid esters of pentaerythritol and glycerol, in particular, may contain < 60% of various partial esters as a result of the preparation process.

Examples of saturated aliphatic monocarboxylic acids having from 10 to 36 carbon atoms are capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid and montanic acid.

Examples of preferred saturated aliphatic monocarboxylic acids having 14 to 22 carbon atoms are myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachidic acid and behenic acid.

Saturated aliphatic monocarboxylic acids such as palmitic acid, stearic acid and hydroxystearic acid are particularly preferred.

C₁₀To C₃₆Saturated aliphatic carboxylic acids and fatty acid esters are those which are known per se in the literature or can be prepared by processes known in the literature. Examples of pentaerythritol fatty acid esters are those of the above-mentioned particularly preferred monocarboxylic acids.

Esters of pentaerythritol and glycerol with stearic acid and palmitic acid are particularly preferred.

Esters of Guerbet alcohols and glycerol with stearic acid and palmitic acid and optionally hydroxystearic acid are also particularly preferred.

The ester may be present in both the base layer and the one or more coextruded layers. Different additives or concentrations may be present in each layer.

Multiwall sheets according to the invention can comprise an antistatic agent.

Examples of antistatic agents are cationic compounds, such as quaternary ammonium salts, phosphonium salts or sulfonium salts, anionic compounds, such as alkylsulfonates, alkylsulfates, alkylphosphates or carboxylates in the form of alkali metal or alkaline earth metal salts, and nonionic compounds, such as polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters or ethoxylated fatty amines. Preferred antistatic agents are nonionic compounds.

These antistatic agents may be present in both the base layer and the coextruded layer or layers. Different additives or concentrations may be present in each layer. Antistatic agents are preferably used in one or more of the coextruded layers.

The multiwall sheet according to the invention can comprise organic dyes, inorganic colored pigments, fluorescent dyes, and particularly preferably optical brighteners.

These colorants can be present in both the base layer and the coextruded layer or layers. Different additives or concentrations may be present in each layer.

All moulding compounds used for the multiwall sheet according to the invention and their additives and solvents can be contaminated with corresponding impurities as a result of their preparation process and storage, for which the aim is to use starting materials which are as clean as possible.

The individual components can be mixed in a known manner either sequentially or simultaneously, and can be mixed both at room temperature and at elevated temperature.

The additives, in particular the UV absorbers and the other additives mentioned above, are preferably incorporated in a known manner into the molding compounds for the multiwall sheets according to the invention by mixing the polymer particles with the additives at temperatures of about 200 to 330 ℃ in conventional apparatuses, such as internal kneaders, single-screw extruders and twin-screw extruders, for example by melt compounding or melt extrusion, or by mixing solutions of the polymers with solutions of the additives and subsequent evaporation of the solvents in a known manner. The proportion of additives in the molding compound can vary within wide limits and depends on the desired properties of the molding compound. The total content of additives in the molding compound is preferably up to about 20% by weight, preferably from 0.2 to 12% by weight, based on the weight of the molding compound.

The UV absorber can also be produced, for example, by reacting a solution of the UV absorber and, if desired, the abovementioned further additives with the plastic in a suitable organic solvent, for example CH₂Cl₂The halogenated alkanes, halogenated aromatics, chlorobenzene and xylene are mixed and introduced into the molding mass. The mixture is then preferably homogenized by extrusion in a known manner; the mixture of solutions is preferably removed in a known manner by distilling off the solvent and subsequent extrusion, for example compounding.

The multiwall sheets according to the invention can be treated, e.g., by deep drawing or with a surface treatment, such as the application of a scratch-resistant lacquer, a water-spreading layer, etc., and the products produced by these processes are also subject matter of the present invention.

Co-extrusion is known per se from the literature (see, for example, EP-A0110221 and EP-A0110238). In the present case, the following treatment is preferred: an extruder for producing the core layer and the one or more cover layers is attached to the coextrusion joint. The joint configuration is such that the melt forming the coextruded layer is applied as a thin layer adhered to the melt for the core layer. The multilayer melt strand thus produced is subsequently converted into the desired shape (multiwall sheet) in adjacently connected nozzles. The melt (multiwall sheet) is then cooled under controlled conditions in a known manner using vacuum calibration and then cut to the desired length. If desired, an annealing furnace may be used after calibration to remove stress. Instead of a joint arranged upstream of the nozzle, the nozzle itself can also be designed such that the melts are brought together at this point.

In the method according to the invention, the process shown is carried out using a modification as described above, i.e. a nozzle with a channel for feeding the material directly to the multiwall die. The subject matter of the present application is therefore also the use of a nozzle according to the invention for producing a wedge-free coated multiwall sheet.

The present invention is described in more detail by the following examples, which are not intended to limit the invention. The examples according to the invention represent only preferred embodiments of the invention.

The machinery and equipment used to produce the multilayer solid sheet are described below. They include:

a main extruder with a screw of length 25 to 36D and diameter 70mm to 200mm, with and without degassing device,

one or more co-extruders for applying the cover layer, having a screw length of 25 to 36D, D being the diameter of the extruder, and a diameter D of 25mm to 70mm, with and without degassing devices,

-a co-extrusion joint,

special multiwall sheet nozzle

-a collimator for collimating the light beam,

-a drawing-off device for drawing off the material,

-a roller conveyor,

-a cutting device (saw),

-a storage station.

The polycarbonate granules of the substrate were fed into the hopper of the main extruder and the coextrusion material was fed into the hopper of the coextruder. Melting and conveying each material was carried out in a separate barrel/screw plasticizing system. The two material melts were flowed together in a coextrusion adapter and a multiwall sheet nozzle and formed a composite after exiting the nozzle and cooling in a calibration unit. Other devices are used to transport, cut, and store extruded sheets.

The resulting sheet was then visually evaluated.

A polycarbonate double wall sheet was produced having the following dimensions:

10mm thick, 11mm wall spacing, 2100mm wide, 1.7kg/m² SN2 10/11-21001.7kg/m²Double-walled sheet of

10mm thick, 11mm wall spacing, 2100mm wide, 2.0kg/m² SS2 10/11-21002.0kg/m²Double-walled sheet of

8mm thick, 11mm wall spacing, 2100mm wide, 1.5kg/m2 SN² 8/11-2100 1.5kg/m²Double-walled sheet of

8mm thick, 11mm wall spacing, 2100mm wide, 1.7kg/m² SS2 8/11-21001.7kg/m²Double-walled sheet of

They contain no significant wedges and therefore have no triangular effect.

The following polycarbonates were used as coextrusion materials in these experiments:

Makrolon^*1243 containing 0.3 mol% of isatin dimethyl phenol as branching agent and having M_wA branched bisphenol A polycarbonate of 29234 and a relative solution viscosity of 0.5g/100ml, and

Makrolon^*3103 having M_w31,887 and relative solution viscosity0.5g/100ml of a linear bisphenol A polycarbonate,

as a substrate, and

DP1-1816 with M_w33560 and another linear bisphenol a polycarbonate comprising a uv blocking additive.

Claims (10)

1. A method for producing a coated multiwall sheet without wedges by coextrusion, characterized in that a part of the material flow of a substrate is fed directly into a multiwall die.

2. The method of claim 1, characterized in that the material is fed through at least one channel in a comb of nozzles, which material is fed directly onwards to the multi-wall mould from the area behind one or more of said nozzles.

3. Multiwall sheet nozzle, characterized in that at least one channel in a nozzle comb results in feeding part of the material directly to a multiwall mould.

4. Use of the nozzle of claim 3 for producing a coextruded multiwall sheet without wedge formation.

5. Coated by coextrusion, without wedge formation.

6. Multiwall sheet according to claim 5, characterized in that it comprises a transparent thermoplastic material.

7. Multiwall sheet according to claim 5, characterized in that all layers are based on the same thermoplastic material.

8. Multiwall sheet according to claim 5, characterized in that it consists of polycarbonate.

9. Multiwall sheet according to claim 5, characterized in that the coextruded layers provide UV protection.

10. A product comprising the multiwall sheet of claims 5 to 9.