|Title of Invention||
"PROCESS FOR THE PRODUCTION OF A MULTI-LAYER MULTI-WALL SHEET AND A MULTI-LAYER MULTI-WALL SHEET"
|Abstract||Process for the production, by coextrusion, of a multi-layer multi-wall sheet comprising a base layer and at least one coextruded layer, characterized in that part of the material flow forming the base layer is diverted and fed directly in to the multi-wall mould (14) to form the multi-walls.|
|Full Text||The present invention relates to a process for the production of a multi-layer multi-wall sheet and a multi-layer wall sheet.
The present invention relates to a process for the production of gussetless multi-wall sheets coated by coextrusion, to special extrusion dies for the production of such sheets, to their use for the production of such sheets, to multi-layer coextruded multi-wall sheets comprising at least one layer containing a thermoplastic and at least one coating, without the triangle effect, and to other products containing this multi-layer multi-wall sheet.
Multi-wall sheets are often provided on one or both of the outer sides with a coextruded layer capable of performing different functions. For example, it can be a UV protective layer for protecting the sheet from damage (e.g. yellowing) by UV radiation, but other functions, e.g. IR reflection, are also performed in this way.
The state of the art relating to such multi-wall sheets is summarized below.
EP-A 0 110 221 discloses sheets consisting of two layers of polycarbonate, one layer containing at least 3 wt.% of a UV absorber. These sheets can be produced by coextrusion according to EP-A 0 110 221.
EP-A 0 320 632 discloses mouldings consisting of two layers of thermoplastic, preferably polycarbonate, one layer containing special substituted benzotriazoles as UV absorbers. EP-A 0 320 632 also discloses the production of these mouldings by coextrusion.
EP-A 0 247 480 discloses multi-layer sheets in which there is a layer of branched polycarbonate as well as a layer of thermoplastic, the polycarbonate layer containing special substituted benzotriazoles as UV absorbers. The production of these sheets by coextrusion is also disclosed.
EP-A 0 500 496 discloses polymer compositions stabilized against UV light with special triazines, and their use as the outer layer in multi-layer systems. The polymers mentioned are polycarbonate, polyester, polyamides, polyacetals, polyphenylene oxide and polyphenylene sulfide.
However, all the coated multi-wall sheets known from the state of the art exhibit the problem of the so-called "triangle effect", i.e. the coextrusion process gives rise to gussets consisting of the material of the coextraded layer, coupled with a certain unevenness of the sheet surface.
Fig. 1 is a diagram of a section through a multi-wall sheet, showing how these gussets are formed. The arrows show the flow of the polymer melt in the multi-wall mould of the multi-wall sheet (1) that causes gusset formation in the coextruded layer (2).
Given the state of the art, the object is therefore to produce a multi-wall sheet optionally coated with several layers by coextrusion, which, in contrast to the state of the art, no longer exhibits the triangle effect.
This object forms the basis of the present invention.
In the case of sheets coated on one side, this problem could be solved with a modified feed of the coextrusion material by increasing the material feed from the uncoated side, making it possible to avoid gusset formation on the coated side.
Fig. 2 is a diagram of a section through a multi-wall sheet, showing how this process could work:
An increased polymer flow from the uncoated side allows a distribution of the melt in the direction of the coated side of the multi-wall sheet (3) such that the coextruded layer (4) remains gussetless.
In the case of sheets coated on both sides, however, this process would no longer work. Here, for example, the increased feed from the bottom side would produce a thicker gusset on the bottom side, so the gain on one side would be offset by a loss on the other side.
Fig. 3 is a diagram of a section through a multi-wall sheet, showing what this effect would look like (feed at (5)): While the top coextruded layer (6) remains gussetless, the bottom coextruded layer (7) has a thick gusset.
It has now been found, surprisingly, that the gusset formation or triangle effect on each side can be virtually completely avoided by modifying the material flows during extrusion in such a way that a partial flow is tapped from the conventional material flow around the die comb, said partial flow being fed directly into the multi-wall mould of the die that forms the walls of the sheets. The material flow through the comb is normally divided into an upper and a lower stream which flow together at the multi-wall moulds, from above and below, to produce the walls. However, this flowing of material from the upper and lower streams creates a typical "draining funnel", which is filled on the coextrusion side with coextrusion material flowing in afterwards. A gusset is formed, as shown in Fig. 1. To enable part of the material to be fed directly into the multi-wall moulds, according to the invention, the material flow from the upper and lower streams is reduced or even prevented, as shown in Fig. 4, and the funnel formation and hence the gusset formation or triangle effect is minimized, or preferably even completely avoided, on both sides of the sheet. The process according to the invention is therefore suitable for the production of multi-wall sheets coated on one or both sides.
Fig. 4 is a diagram of a section through a multi-wall sheet, showing how the process according to the invention works:
Both coextruded layers (9) and (10) remain gussetless due to an additional feed of polymer melt at (8), for example through a channel into the multi-wall mould.
It is totally surprising that a problem which had existed for so long could be solved so successfully by such a simple measure.
The present invention thus provides a special process for the production of coatings on multi-wall sheets by coextrusion, and the gussetless sheets, or sheets free of the triangle effect, obtainable by this process. These sheets are distinguished by a particularly smooth surface and uniform, i.e. gussetless, coextruded layers. A multi-wall sheet coated on both sides is a preferred embodiment.
This patent application therefore also provides a special extrusion die for carrying out the process according to the invention.
hi addition to the conventional channels, sections and moulds required for various purposes, the die comb contains channels which feed part of the inflowing material directly into the multi-wall mould. In a preferred embodiment, the material is fed directly forwards into the multi-wall mould from a region at the back of the die.
A diagram of a possible embodiment of the die according to the invention, at a multi-wall mould, is shown as a cross-section in Figure 5:
The polymer melt flows in at (12). The melt is fed into the multi-wall mould (14) through the channels (13). (15) denotes the top side or bottom side mould. The sheet exits at (16).
The present invention also provides a product containing said sheets. This product, which contains e.g. said multi-layer multi-wall sheet, is preferably selected from the group comprising glazing, greenhouses, winter gardens, verandas, car ports, bus shelters, canopies, partitions, cash kiosks and solar collectors.
The process according to the invention has the substantial advantage of avoiding the triangle effect, which otherwise has noticeable adverse consequences due to gusset
formation and the associated wastage of material, and by an uneven sheet surface. The coating material wasted in the gusset generally consists of valuable thermoplastic containing expensive additives. It can be of considerable financial advantage to save such material.
The process according to the invention is suitable for the production of a very wide variety of coextruded layers and mainly for any conceivable functional layers, including in combination (UV protection and functional layer, e.g. IR reflection on the top and UV protection on the bottom), and is particularly suitable for the production of multi-wall sheets provided with UV protection on both sides.
The multi-layer products according to the invention, such as multi-wall sheets, have further advantages over the state of the art. The multi-layer products according to the invention, such as the multi-wall sheet, can be produced by coextrusion, affording advantages over a product produced by lacquering. Thus, in contrast to lacquering, no solvents volatilize during coextrusion.
Moreover, lacquers cannot be stored for long periods. Coextrusion does not have this disadvantage.
Also, lacquers demand expensive technology. For example, they require explosion-proof machines and solvent recycling, i.e. high investment in plants. Coextrusion does not have this disadvantage.
A preferred embodiment of the present invention is said multi-layer multi-wall sheet wherein the base layer and the coextruded layer can be made of identical or different thermoplastics. Preferably, both layers are based on the same material.
Suitable thermoplastic moulding compounds are any moulding compounds containing e.g. polycarbonate and/or polyester and/or polyestercarbonates and/or polyesters and/or polymethyl methacrylates and/or polystyrenes and/or SAN and/or
blends of polycarbonate and polyesters and/or polymethyl methacrylates and/or polystyrenes and/or SAN.
Preferred moulding compounds are those containing transparent thermoplastics such as polycarbonate and/or polyester, as well as blends containing at least one of the two thermoplastics. It is particularly preferable to use polycarbonate and polymethyl methacrylates and very particularly preferable to use polycarbonate.
The preparation of these thermoplastics is well known to those skilled in the art and is carried out by the known processes.
According to the invention, the preferred multi-layer products are those in which the coextruded layer additionally contains 1 to 20 wt.% of UV absorbers and has a thickness of 5 to 200 jam, preferably 30 to 100 µm.
The multi-wall sheets can be twin-wall sheets, triple-wall sheets, quadruple-wall sheets, etc. The multi-wall sheets can also have different profiles, e.g. X profiles or XX profiles. The multi-wall sheets can also be corrugated.
A preferred embodiment of the present invention is a multi-wall sheet with coextruded layers on both sides, the base material and the two coextruded layers being made of polycarbonate.
Depending on the type of thermoplastics used and the additives they contain, the multi-layer products according to the invention can be translucent, opaque or transparent.
Li one particular embodiment, the multi-layer products are transparent.
Both the base material and the coextruded layer(s) of the multi-layer multi-wall sheets according to the invention can contain additives.
In particular, the coextruded layer can contain UV absorbers and demoulding agents.
The UV absorbers or mixtures thereof are present in concentrations of 0-20 wt.%, preferably 0.1 to 20 wt.%, particularly preferably 2 to 10 wt.% and very particularly preferably 3 to 8 wt.%. If two or more coextruded layers are present, the proportion of UV absorbers in these layers can differ.
Examples of UV absorbers that can be used according to the invention are described below:
a) Benzotriazole derivatives of formula (I)(Formula Removed)
hi formula (I), R and X are identical or different and are H, alkyl or alkylaryl.
Preferred representatives are Tinuvin 329, where X = 1,1,3,3-tetramethylbutyl and R = H, Tinuvin 350, where X = tert-butyl and R = 2-butyl, and Tinuvin 234, where X = R = 1,1 -dimethyl- 1-phenyl.
b) Dimeric benzotriazole derivatives of formula (II): (Formula Removed)In formula (IT), R1 and R2 are identical or different and are H, halogen, C1-C10-alkyl, Cs-Cio-cycloalkyl, C7-Ci3-aralkyl, C6-C14-aryl, -OR5 or -(CO)-O-R5, where R5 = H or Ci-C4-alkyl.
In formula (II), R3 and R are also identical or different and are H, Ci-C4-alkyl, Cj-Ce-cycloalkyl, benzyl or C
In formula (IT), m is 1, 2 or 3 and n is 1, 2, 3 or 4.
Preference is given to Tinuvin 360, where R1 = R3 = R4 = H, n = 4, R2 = 1,1,3,3-tetramethylbutyl and m = 1 .
bl) Dimeric benzotriazole derivatives of formula (TTf):
wherein the bridge is(Formula Removed)
R1, R2, m and n are as defined for formula (IT), p is an integer from 0 to 3, q is an integer from 1 to 10,
Y is -CH2-CH2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6- or CH(CH3)-CH2-and R3 and R4 are as defined for formula (II).
Preference is given to Tinuvin 840, where R1 = H, n - 4, R2 = tert-butyl, m = 1, R2 is in the ortho position to the OH group, R3 = R4 = H, p = 2, Y - -(CH2)5-and q = 1.
c) Triazine derivatives of formula (IV):
herein R1, R2, R3 and R4 are identical or different and are H, alkyl, CN or halogen and X is alkyl.
Preference is given to Tinuvin 1577, where R1 = R2 = R3 = R4 = H and X = hexyl, and Cyasorb UV-1164, where R1 = R2 = R3 = R4 = methyl and X = octyl.
d) Triazine derivatives of formula (IVa) below:
R2 is H or Ci-alkyl to C4-alkyl, and
n is 0 to 20.
e) Dimeric triazine derivatives of formula (V):
R1, R2, R3, R4, R5, R6, R7 and R8 can be identical or different and are H, alkyl, CN or halogen and X is alkyl or -(CH2CH2-O-)n-C(=O)-.
f) Diaryl cyanoacrylates of formula (VI):
R to R can be identical or different and are H, alkyl, CN or halogen. Preference is given to Uvinul 3030, where R1 to R40 = H.
Very particularly preferred UV absorbers are selected from the group comprising Tinuvin 360, Tinuvin 1577 and Uvinul 3030.
(Formula Removed)Tinuvin 1577(Formula Removed)
Uvinul 3030(Formula Removed)
Said UV absorbers are commercially available.
In addition to or in place of the UV absorbers, the layers can also contain other conventional processing aids, especially demoulding agents and flow regulators, as well as the additives conventional for the polycarbonates used, such as stabilizers, especially heat stabilizers, and also colorants, optical brighteners and inorganic pigments.
All the 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 average molecular weights Mw preferably of 18,000 to 40,000, particularly preferably of 26,000 to 36,000 and very particularly preferably of 28,000 to 35,000, determined by gel permeation chromatography calibrated against polycarbonate.
For the preparation of polycarbonates, reference may be made for example to "Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964", to "D.C. PREVORSEK, B.T. DEBONA and Y. KESTEN, Corporate Research Center, Allied Chemical Corporation, Morristown, New Jersey 07960, 'Synthesis of Poly(ester)carbonate Copolymers' in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 19, 75-90 (1980)", to "D. Freitag, U. Grigo, P.R. Muller and N. Nouvertne, BAYER AG, 'Polycarbonates' in Encyclopedia of Polymer Science and Engineering, Vol. 11, Second Edition, 1988, pages 648-718" and finally to "Dres. U. Grigo, K. Kircher and P.R. Muller, 'Polycarbonate' in Becker/Braun, Kunststoff-Handbuch, Volume 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Manser Verlag, Munich, Vienna 1992, pages 117-299".
The polycarbonates are preferably prepared by the interfacial polycondensation process or the melt transesterification process and the preparation is described below using the interfacial polycondensation process as an example.
The compounds that are preferably to be used as starting compounds are bisphenols of the general formula(Formula Removed)
wherein Z is a divalent organic radical having 6 to 30 carbon atoms and containing one or more aromatic groups.
Examples of such compounds are bisphenols belonging to the group comprising dihydroxybiphenyls, bis(hydroxyphenyl)alkanes, indanebisphenols, bis(hydroxy-phenyl) ethers, bis(hydroxyphenyl) sulfones, bis(hydroxyphenyl) ketones and 1,3- or l,4-bis(hydroxyphenylpropyl)benzenes.
Particularly preferred bisphenols belonging to the above groups of compounds are bisphenol A, terraalkylbisphenol A, l,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene (bisphenol M), l,4-bis-[2-(4-hydroxyphenyl)-2-propyl]benzene, l,l-bis(4-hydroxy-phenyl)-3,3,5-trimethylcyclohexane (bisphenol TMC) and optionally mixtures thereof.
Preferably, the bisphenol compounds to be used according to the invention are reacted with carbonic acid compounds, especially phosgene, or, in the case of the melt transesterification process, with diphenyl carbonate or dimethyl carbonate.
Polyestercarbonates are preferably obtained 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'- or 4,4'-diphenyldicarboxylic acid and benzophenonedicarboxylic acids. Up to 80 mol%, preferably from 20 to 50 mol%, of the carbonate groups in the polycarbonates can be replaced by aromatic dicarboxylic acid ester groups.
Examples of inert organic solvents used in the interfacial polycondensation process are dichloromethane, the various dichloroethanes and chloropropane compounds, carbon tetrachloride, chloroform, chlorobenzene and chlorotoluene. It is preferable
to use chlorobenzene or dichloromethane or mixtures of dichloromethane and chlorobenzene.
The interfacial polycondensation reaction can be accelerated by catalysts such as tertiary amines, especially N-alkylpiperidines, or onium salts. It is preferable to use tributylamine, triethylamine and N-ethylpiperidine. In the case of the melt transesterification process, it is preferable to use the catalysts mentioned in DE-A4238123.
The polycarbonates can be intentionally branched in a controlled manner by using
small amounts of branching agents, some suitable branching agents being
phloroglucinol, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)-2-heptene, 4,6-dimethyl-
2,4,6-tri(4-hydroxyphenyl)heptane, 1,3,5-tri(4-hydroxyphenyl)benzene, 1,1,1 -tri(4-
hydroxyphenyl) ethane, tri(4-hydroxyphenyl)phenylmethane, 2,2-bis[4,4-bis(4-
hydroxyphenyl)cyclohexyl]propane, 2,4-bis(4-hydroxyphenylisopropyl)phenol, 2,6-
dihydroxyphenyl)propane, hexa(4-(4-hydroxyphenylisopropyl)phenyl) ortho-terephthalate, tetra(4-hydroxyphenyl)methane, tetra(4-(4-hydroxyphenylisopropyl)-phenoxy)methane, 1,3,5-tris[2-(4-hydroxyphenyl)-2-propyl]benzene, 2,4-dihydroxy-benzoic acid, trimesic acid, cyanuric chloride, 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole and 1,4-bis(4',4"-dihydroxytriphenyl)methyl)benzene, especially l,l,l-tri(4-hydroxyphenyl)ethane and bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.
The branching agents or mixtures of branching agents optionally to be used concomitantly in an amount of 0.05 to 2 mol%, based on the diphenols used, can be introduced together with the diphenols or else added at a later stage of the synthesis.
The chain terminators used are preferably phenols, such as phenol, alkylphenols like cresol and 4-tert-butylphenol, chlorophenol, bromophenol, cumylphenol or mixtures
thereof, in amounts of 1-20 mol%, preferably 2-10 mol%, per mol of bisphenol. Phenol, 4-tert-butylphenol and cumylphenol are preferred.
The chain terminators and branching agents can be added to the syntheses separately or else together with the bisphenol.
The preparation of the polycarbonates by the melt transesterification process is described by way of example in DE-A 42 38 123.
Polycarbonates that are preferred according to the invention are the homopoly-carbonate based on bisphenol A, the homopolycarbonate based on l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, the copolycarbonates based on the two monomers bisphenol A and l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and the copolycarbonates based on the two monomers bisphenol A and 4,4'-dihydroxybiphenyl (DHB).
The homopolycarbonate based on bisphenol A is particularly preferred.
The polymer used can contain stabilizers, examples of suitable stabilizers being phosphines, phosphites, stabilizers containing Si, and other compounds described in EP-A 0 500 496. Examples which may be mentioned are triphenyl phosphites, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris(nonylphenyl) phosphite, tetrakis(2,4-ditert-butylphenyl)-4,4'-biphenylene diphosphonite and triaryl phosphite. Triphenylphosphine and tris(2,4-ditert-butylphenyl) phosphite are particularly preferred.
These stabilizers can be present in all the layers of the multi-wall sheet according to the invention, i.e. both in the base layer and in the coextruded layer(s). It is possible for different additives or concentrations of additives to be present in each layer.
Furthermore, the multi-wall sheet according to the invention can contain 0.01 to 0.5 wt.% of esters or partial esters of monohydric to hexahydric alcohols, especially glycerol, pentaerythritol or guerbet alcohols.
Examples of monohydric alcohols are stearyl alcohol, palmityl alcohol and guerbet
alcohols. Glycol is an example of a dihydric alcohol.
Glycerol is an example of a trihydric alcohol.
Pentaerythritol and mesoerythritol are examples of tetrahydric alcohols.
Arabitol, ribitol and xylitol are examples of pentahydric alcohols.
Mannitol, glucitol (sorbitol) and dulcitol are examples of hexahydric alcohols.
The esters are preferably the monoesters, diesters, triesters, tetraesters, pentaesters and hexaesters or their mixtures, especially random mixtures, of saturated CIQ to Cae aliphatic monocarboxylic acids and optionally hydroxymonocarboxylic acids, preferably saturated CH to €32 aliphatic monocarboxylic acids and optionally hydroxymonocarboxylic acids.
The commercially available fatty acid esters, especially of pentaerythritol and glycerol, can contain Examples of saturated aliphatic monocarboxylic acids having 10 to 36 C atoms are capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid and montanic acids.
Examples of preferred saturated aliphatic monocarboxylic acids having 14 to 22 C atoms are myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachidic acid and behenic acid.
Saturated aliphatic monocarboxylic acids like palmitic acid, stearic acid and hydroxystearic acid are particularly preferred.
The saturated C10 to C36 aliphatic carboxylic acids and the fatty acid esters are either known as such in the literature or can be prepared by processes known in the literature. Examples of pentaerythritol fatty acid esters are those of the particularly preferred monocarboxylic acids mentioned above.
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 esters can be present both in the base layer and in the coextruded layer(s). Different additives or concentrations can be present in each layer.
The multi-wall sheets according to the invention can contain antistatic agents.
Examples of antistatic agents are cationic compounds, e.g. quaternary ammonium, phosphonium or sulfonium salts, anionic compounds, e.g. alkylsulfonates, alkylsulfates, alkylphosphates or carboxylates in the form of alkali metal or alkaline earth metal salts, and non-ionic compounds, e.g. polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters or ethoxylated fatty amines. Preferred antistatic agents are non-ionic compounds.
These antistatic agents can be present both in the base layer and in the coextraded layer(s). Different additives or concentrations can be present in each layer. The antistatic agents are preferably used in the coextruded layer(s).
The multi-wall sheets according to the invention can contain organic dyes, inorganic coloured pigments, fluorescent dyes and, particularly preferably, optical brighteners.
These colorants can be present both in the base layer and in the coextruded layer(s). Different additives or concentrations can be present in each layer.
All the moulding compounds and their additives and solvents used to produce the multi-wall sheet according to the invention can be contaminated with respective impurities as a result of their preparative processes and storage, the aim being to work with the cleanest possible starting materials.
The individual constituents can be mixed in known manner, either successively or simultaneously, either at room temperature or at elevated temperature.
The additives, especially the UV absorbers and other additives mentioned above, are preferably incorporated in known manner into the moulding compounds for the multi-wall sheets according to the invention, by mixing polymer granules with the additives at temperatures of about 200 to 330°C in conventional machines, such as internal kneaders, single-screw extruders and double-shaft extruders, for example by melt compounding or melt extrusion, or by mixing solutions of the polymer with solutions of the additives and subsequently vaporizing the solvents in known manner. The proportion of additives in the moulding compound can vary within wide limits and depends on the desired properties of the moulding compound. The total proportion of additives in the moulding compound is preferably up to about 20 wt.%, preferably 0.2 to 12 wt.%, based on the weight of the moulding compound.
The UV absorbers can also be incorporated into the moulding compounds e.g. by mixing solutions of the UV absorbers, and optionally other additives mentioned above, with solutions of the plastics in suitable organic solvents such as CEbCk, halogenoalkanes, halogenoaromatics, chlorobenzene and xylenes. The mixtures of substances are then preferably homogenized in known manner via extrusion; the mixtures of solutions are preferably removed, for example compounded, in known manner by vaporization of the solvent followed by extrusion.
It is possible to work the multi-wall sheets according to the invention e.g. by deep drawing or by means of surface treatments, such as the application of scratch resistant lacquers, water spreading layers, and the like, and the products produced by these processes are also provided by the present invention.
Coextrusion as such is known in the literature (cf. for example EP-A 0 110 221 and EP-AO 110238). In the present case the procedure is preferably as follows: Extruders for producing the core layer and covering layer(s) are connected to a coextrusion adapter. The adapter is constructed so that the melt forming the covering layer(s) is applied as a thin layer adhering to the melt for the core layer. The multi-layer melt strand produced in this way is then converted to the desired shape (multi-wall sheet) in the die connected downstream. The melt is subsequently cooled under controlled conditions in known manner by means of vacuum sizing (multi-wall sheet) and then cut into lengths. Optionally, an annealing furnace can be used after sizing in order to remove stresses, hi place of the adapter arranged upstream from the die, it is also possible for the die itself to be designed so that the melts are brought together at that point.
In the process according to the invention, the illustrated process is carried out using a die modified as described above, i.e. with a channel for feeding the material directly into the multi-wall mould. Accordingly, the present patent application also provides the use of a die according to the invention for the production of a gussetless coated multi-wall sheet.
The invention is illustrated in greater detail by the following Examples, which do not imply a limitation. The Examples according to the invention merely represent preferred embodiments of the present invention.
The machines and equipment used for the production of multi-layer solid sheets are described below. They comprise:
- the main extruder with a screw of length 25 to 36 D and a diameter of 70 mm
to 200 mm, with and without venting,
- one or more coextruders for applying the covering layers, with a screw of
length 25 to 36 D, D being the diameter of the extruder, and a diameter D of
25 mm to 70 mm, with and without venting,
- a coextrusion adapter,
- a special multi-wall sheet die,
- a sizer,
- a take-off device,
- a roller conveyor,
- a cutting device (saw),
- a delivery table.
'he polycarbonate granules of the base material were fed into the hopper of the main xtruder and the coextrusion material was fed into the hopper of the coextruder. each material was melted and conveyed in its own cylinder/screw plasticizing ystem. Both material melts were brought together in the coextrusion adapter and ne multi-wall sheet die and formed a composite after leaving the die and cooling in ne sizer. The other devices served to transport the extruded sheets, cut them into engths and deliver them.
he sheets obtained were then assessed visually.
olycarbonate multi-wall sheets of the following dimensions were produced:
vin-wall sheet 10 mm thick, 11 mm wall separation, 2100 mm wide, 1.7 kg/m2
N2 10/11-2100 1.7 kg/m2
vin-wall sheet 10 mm thick, 11 mm wall separation, 2100 mm wide, 2.0 kg/m2
S2 10/11-2100 2.0 kg/m2
vin-wall sheet 8 mm thick, 11 mm wall separation, 2100 mm wide, 1.5 kg/m2
N2 8/11-2100 1.5 kg/m2
twin-wall sheet 8 mm thick, 11 mm wall separation, 2100 mm wide, 1.7 kg/m2 SS2 8/11-2100 1.7 kg/m2
They contained no obvious gussets and accordingly did not exhibit the triangle effect.
The following polycarbonates were used as coextrusion materials in these experiments:
- Makrolon® 1243, a branched bisphenol A polycarbonate containing 0.3 mol%
of isatin biscresol as branching agent and having a Mw of 29,234 and a relative solution viscosity of 0.5 g/100 ml, and
- Makrolon® 3103, a linear bisphenol A polycarbonate having a Mw of 31,887
and a relative solution viscosity of 0.5 g/100 ml,
as base materials, and
- DP1-1816, another linear bisphenol A polycarbonate having a Mw of 33,560
and containing UV stabilizing additives.
1. Process for the production, by coextrusion, of a multi-layer multi-wall sheet comprising a
base layer and at least one coextruded layer, characterized in that part of the material flow forming
the base layer is diverted and fed directly in to the multi-wall mould (14) to form the multi-walls.
2. Process as claimed in claim 1, wherein the partial flow is diverted through a multi-wall sheet die having at least one channel (13) that leads to a direct feed of part of the material, forming the base layer, into the multi- wall mould.
3. Process as claimed in claim 2, wherein the partial flow is diverted from a region at the back of the multi-wall sheet die.
4. Process as claimed in claim in any one of the preceding claims, wherein the multi-layer multi-wall sheet comprises a base layer, a first coextruded layer on the top side of the base layer and a second coextruded layer on the bottom side of the base layer.
5. Process as claimed in claim in any one of the preceding claims, wherein the base layer and the coextruded layer (s) each contain a transparent thermoplastic.
6. Process as claimed in 5, wherein the base layer and the coextruded layer(s) each contain the same transparent thermoplastic.
7. Process as claimed in claim 6, wherein the base layer and the coextruded layer(s) each contain polycarbonate.
8. Process as claimed in claim in any one of the preceding claims, wherein at least one coextruded layer contains at least one UV absorber.
|Indian Patent Application Number||4961/DELNP/2005|
|PG Journal Number||07/2013|
|Date of Filing||28-Oct-2005|
|Name of Patentee||BAYER SHEET EUROPE GMBH|
|Applicant Address||OTTO-HESSE-STR. 19/T9, 64293 DARMSTADT, GERMANY|
|PCT International Classification Number||B29C 47/20|
|PCT International Application Number||PCT/EP2004/004704|
|PCT International Filing date||2004-05-04|