DE102004010461A1 - Extrusion of plastic profiles containing natural fillers involves extrusion of a plastic and filler mixture through a die and cooling in a temperature gradient which solidifies the outer area then cools remaining bulk - Google Patents

Abstract

A mixture(11) of additives based on natural materials and a plastic binder matrix are compressed and plasticized in an extruder(12), continuously extruded through a die(13) and immediately cooled on the surface with a predetermined temperature gradient along the extrudate length. The outer area of the extruded profile(17) cools and holds the profile shape and then the remaining cross-section solidifies. A mixture(11) of additives based on natural materials and a plastic binder matrix are compressed and plasticized in an extruder(12). The molten mixture is continuously extruded through a die(13) and immediately cooled on the surface with a predetermined temperature gradient along the extrudate length. The outer area of the extruded profile(17) cools and holds the profile shape and then the remaining cross-section solidifies. An independent claim is included for the process equipment which includes an extruder(12) with profiling die(13) immediately followed by a cooling zone with a temperature gradient along the profile.

Description

The Invention is to methods and apparatus and material uses directed according to the independent claims.

From the EP 0 908 281 A1 For example, non-continuous recovery of a rope-shaped molding from wood-based material in the form of a non-flowable mixture of shavings and thermosetting resins is known as thermosetting binders. For this purpose, a plunger is guided in a tubular mold, the length of which is a multiple of the Preßhubes. The mixture to be pressed is introduced transversely into the tube in front of the piston and so easily compressed in the first pressing stroke that the tube is closed in front of the piston. Heat is then added to initiate the curing of the binder contained in the mixture. Now, a second Preßhub for final compression of the further curing molding, which is to connect with the already located in the pipe and thereby further pushed forward in the pipe molding front side. The inner wall of the pipe, for example provided with longitudinal grooves, determines the cross-sectional geometry of the applied strand. This running in fairly slow double step sequence method of molding a wood material under heat and pressure is suitable because of the forming Rohrpreßform in which the strand-shaped molded part under the action of Kolbenhubes from a succession of short compacts, only for the production of little bending resistant rods with easier Cross-sectional geometry. This is then usually mechanically rework to measure, because the pending at the output of the tube internal pressure in the not yet full block cured compact inevitably leads to a relaxation under diameter increase. However, the surface of such a compact is not waterproof, the compact for outdoor use therefore not suitable. This seems to be due to the fact that the Spanversiegelung by the binder in the course of mere Rohrverpressung is not sufficiently perfect, so that moisture can penetrate easily under the surface of the compact and swell there chips, causing blistering and tearing of the surface of the compact ,

In particular, for technologically difficult to control molded parts, such as along an edge L-shaped steeply angled panels for cladding, the only lower throughput ausbringende technology of the single-mold press is used, as they are approximately in the EP 0 646 442 B1 is described. But undercut and other complicated cross-sectional geometries such as varied angled window frame or fair construction profiles can not be molded.

The DE 199 21 458 A1 does not describe the use of wood-like feedstocks in the compact, but the production of hollow chamber profiles made of thermoplastic material in the so-called cooling nozzle method by pressing the plastic melt through a heated profile tool and an immediately following cooled calibration with internal and external cooling. In order to achieve a desirable extrusion rate, the plastic melt is first pressed out of the profile tool in the form of mutually independent open sub-profiles of spaced-opening sub-profile channels, after which a transition of the sub-profiles in a hollow chamber profile channel takes place only in the calibration. Here in the calibration tool only so the closed hollow profile missing connections are created from inflowing plastic melt. This requires, however, that until then by appropriately restrained cooling a block cooling, ie a rapid solidification over the entire cross-section of the extruded profile must be avoided.

From the DE 195 10 944 C1 is the extrusion of plastic melts to hollow sections under pressure through a profile tool with internal profile mandrel known, which projects from the profile tool in an immediately subsequent calibration and cooling unit; which is quite complex in terms of apparatus and yet hardly allows any loss of dimensional stability due to swelling at the outlet of the strand from the pressure range to be avoided.

Of the On the other hand, the invention is based on the technical problem in a fast-moving process from a readily available renewable Material as feedstock in the binder for immediate outdoor use suitable surface properties a stretched profile with virtually any cross-sectional geometry at to gain high dimensional accuracy.

These Task is inventively by the Combinations of the specified in the independent main claims Characteristics solved.

Thereafter, in the interest of sufficient surface quality so far only compression-molded mixture, for example, the type described above, ie with wood particles as feedstock in the binder, now highly compressed by means of the screw of an extruder, and optionally involuntarily crushed, as well as plasticized, from it by a profiling tool issued thereafter and immediately thereafter to be intimately cooled with a preferably influenced temperature gradient over a certain longitudinal extent of the profile. This cooling of the already profiled from the tool but still under pressure exiting strand is carried out by a, to avoid pressure loss directly attached to the tool, profile-holding cooling station with a dense sequence of plates, which also each have an opening of the cross-sectional geometry of the extruded profile and to be flowed through by a cooling medium such as in particular water at different temperatures. This ensures that immediately after the profiling tool directly on solidification of the surface a targeted stabilizing block cooling takes place substantially over the entire cross section of the extruded profile and thus the due to the high Extrusionspreßdruckes of typically 300 bar still pending in the cooling station high density in the extrusion profile remains stably maintained over the entire cross-section after dispensing. Otherwise, there would be a risk that in a tubular casing in the form of the already solidified surface still unbound yet viscous, after the exit from the cooling station due to elimination of the prevailing therein profile-containing external pressure would be re-inflated mass.

ever more intense the cooling leads to cross-sectional hardening, the higher is the pressure. extending from the extruder through the mold into the shape-retaining cooling station builds up in it. Therefore, it is appropriate to the cooling gradient over the Route through the cooling station pressure dependent to change to then behind the cooling station a due to block consolidation in cross section dimensionally stable workpiece with above the Length of constant To spend compaction.

The Cross-sectional shape of this issued from the cooling station highly solidified After all, Extrusionsprofiles does not need any final fixation in a usual during extrusion, only at a distance behind the tool arranged profile-determining Calibration distance to learn more. But if, for example, for precision profiles, After all, a calibration follows, then this is expediently with the opposite Air irradiation particularly effective water cooling connected. A direct one water cooling is applicable here because the profile already tempered with his quasi, namely waterproof compacted surface of the cooling station Coming into the calibration line occurs and therefore herein Rip the surface as a result of adhesion of the plastic, so also one Moisture control of the wood chips inside the strand, can not occur anymore.

Around optionally the already solidified profile through the calibration path behind it is a common deduction in extrusion technology arranged, which detects the strand between two conveyor belts. These but only needs to go into action when the in the calibration distance incoming strand due to lower proportion of chips in the mixture too soft to pull without support to be pushed through the calibration. On the other hand is at Use of a deduction device whose traction control in accordance with already solidification of the profile, so the pressure at the entrance the calibration route appropriate.

The output profile can be edited like natural wood. The inner one Solidification due to the high Extrusionspreßdruckes leads in the initial profile to a Density, of the order of magnitude from 30% (for hardwood as input) to 50% (for spruce) above that of the wood material used is and accordingly higher Provides strength as a pure plastic extrusion product. The strand material is fully recyclable after crushing or grinding. Wood, in particular the resinous wood of the coniferous trees, points as feedstock the advantage of particularly willing connection to polyethylene and to polypropylene as the adhesive binders, so that then im extruding mixture only of the order of 20% by weight Binders are required and yet already at the beginning of the run through the cooling station so that even the waterproof surface is achieved. The amount On the other hand, the starting materials in the mixture can amount to up to 80 percent by weight. in general, it is expediently chosen between 40 and 60 weight percent.

The Wood as a resource can be used in any form between flour and Span be introduced into the mass to be extruded, with large particles like shavings be crushed anyway during pressing in the extruder screw. But almost every other renewable, possibly in The third world richer than wood available, especially cellulosic Raw material fibrous structure is well usable as a feedstock, especially corn, flax, barley and straw, rice straw and rice husk, as well as pine cones and the skins of almost all nuts. The Fibers in peanut and in rice husks are characterized by their hairy consistency special Verkettungsfreudigkeit in the compressed state and leave Therefore, with otherwise the same parameters lighter and still very high claimable wood-like Achieve extrusion profiles.

Adhesive binders for the starting materials are all customary plastics which react under pressure and heat, such as thermosets and thermosetting plastics and mixtures thereof. This is Poly ethylene, polypropylene and polystyrene because of their low purchase price, while the UV-resistant PVC is not only a mechanically higher loadable and firmer, but also a better weather-resistant structure can be achieved. To promote the rapid cooling in the interest of a durable solid surface additives are useful, can be promoted by the more color-stable and UV-resistant surface properties.

further developments The invention will become apparent from the other claims and from the description below of a preferred apparatus embodiment to the solution according to the invention. Based the one in the single figure of the drawing not shown to scale Schematic diagram of an apparatus for exercising the method is the Invention closer explained.

The mixture 11 from particular fibrous natural product as a feedstock in curable plastic binder is in an extruder 12 mechanically compacted and at the same time thermally plasticized, then from a round opening as a continuous strand in a profilgebendes heated tool 13 convert. This indicates the fluidic transformation of the strand shape to the profile 17 a succession of heated plates with coaxial openings of the desired cross-sectional geometry for the extrusion profile to be dispensed 17 on, as it is known from the technology of plastic extrusion.

Immediately behind this profiling tool 13 is from the still under extrusion pressure profile 17 a cooling station 15 go through the poorly heat-conductive mounting structures 14 directly on the output of the tool 13 is mounted. The cooling station 15 shows a tightly packed package of again profiling perforated plates 15a on. The hollow, in particular with channels for passing a cooling fluid such as water configured. By means of differently tempered of these cooling plates 15a can the on the fresh, still under extrusion pressure profile strand 17 acting temperature gradient can be set so that first solidifies the strand surface holding shape, and immediately before it leaves the cooling station 15 a blockage solidification over the entire remaining cross-section of the profile 17 entry. As a result, the large extrusion compression forces are effectively hermetically and rigidly into the profile by means of the initially solidified surface 17 locked in. A caused by this internal pressure radial inflation of the strand cross-section after exiting the cooling station 15 can therefore no longer occur, the starting materials remain intimately bonded and rigidly wrapped in their Kunststoffeinbettung. Also, as a result of these early, even under pressing pressure surface hardening no surface bonding of plastics to the profile openings in the tool plates more occur, which could otherwise lead to damage when torn from the tool to surface damage.

It can then, for example, for delicate precision profiles, after the cooling station 15 in one of them set calibration distance 16 a final definition of the cross-sectional dimensions after already solidified surface and blockage solidification done. For this, a series of plates standing in the cooling water bath has openings of the final cross-sectional geometry of the extrusion profile 17 on. The serve no more profiling, only the profile determination. The length of the calibration path 16 becomes proportional to the strength of the strand 17 and selected at the output speed.

Usually the profile is 17 due to the relatively high solids content in the mixture 11 and due to its block cooling under pre-solidified surface behind the profile hold the cooling station 15 already strong enough, even without additional pulling action evenly through the calibration 16 to be pushed through. But it can be the continuous strand of Extrusionsprofiles 17 also through this route 16 by means of the band pair 18 a withdrawal facility 19 be drawn through, with the considerable for such a feed, as otherwise only found in pure plastic extrusion speed.

Ultimately, this finished extrusion profile 17 then in a cutter 20 cut to size and spent for shipping.

The drawing takes into account that (preferably as outlined at the entrance) at the cooling station 15 or on the tool 13 and optionally also on the calibration path 16 pressure sensors 21 to tax breaks 22 on the extruder 12 as well as at the cooling station 15 and optionally at the deduction facility 19 can be provided. This is to illustrate that it is convenient to the Temperaturgradierenten in the cooling station 15 to go through with constant pressure and therefore either the subsequent delivery of the mixture 11 or correspondingly controlling the cooling hardening; while optionally the drive of the deduction device 19 is accelerated by faster removal of an input jam on the calibration line 16 counteract.

A bonded to under very high pressure fibrous natural materials such as wood as a feedstock in the plastic binder-based material can thus be inventively in complicated cross Sectional geometry with the surface quality of a molded wood part suitable for outdoor use as an uninterrupted extrusion profile 17 Produce at high speed, when directly on the profiling extrusion tool 13 a profile-preserving surface cooling with block consolidation takes place over the entire profile cross section under a temperature gradient which can be set in the direction of the line. In the context of the present invention, the term material for the feedstock extends beyond (wood) shavings also to (wood) flour and to other - in particular fibrous - renewable natural products. As plastic binder in addition to polypropylene and polyethylene or polystyrene, but also all common other thermoplastics in terms of price, PVC in terms of its strength and UV resistance are particularly suitable. By mixtures of different starting materials and binders, including thermosetting plastics, it is possible to obtain particular physical or chemical material properties of the wood-like extruded profile 17 targeted setting within wide limits.

Claims (13)

A process for producing strand molds from plastic-bonded starting materials, characterized in that a mixture of natural materials as the starting materials and plastic as a binder in an extruder compacted and plasticized and then issued by a profiling tool as a continuous strand of an extrusion profile and immediately thereafter with a longitudinal direction Profile-oriented temperature gradient is cooled profilhaltend on the surface and block-solidified over its cross-section. Method according to claim 1, characterized in that the existence subsequent profile-determining calibration, with function-critical If necessary, pressure increase under mechanical tension. Method according to one of the preceding claims, characterized characterized in that as Starting materials span-shaped, floury, grainy or in particular fibrous natural substances, preferably based on wood, be used. Method according to one of the preceding claims, characterized characterized in that as Binder besides polypropylene, polyethylene, polystyrene or PVC Other thermoplastics or thermosets, even in mixtures used be, optionally with additives. Method according to one of the preceding claims, characterized characterized in that Proportion of starting materials in the mixture between 20 and 80, preferably between 40 and 60 weight percent is chosen. Method according to one of the preceding claims, characterized characterized in that profile-preserving cooling dependent on from the pressure at the entrance of the profiling tool or at the entrance the profile-following cooling immediately following it takes place. Method according to one of the preceding claims, characterized characterized in that Construction of the extrusion pressure before the profiling tool in dependence from the pressure at the entrance of the profile-holding cooling takes place. Method according to one of the preceding claims, characterized characterized in that Pull on the calibrated strand as a function of the pressure at the entrance the calibration takes place. Apparatus for carrying out the method according to one of the preceding claims, characterized in that for a in an extruder ( 12 ) to be compacted, plasticized mixture ( 11 ) of preferably fibrous, naturally renewable resources and plastic binder directly on a profiling tool ( 13 ) following a profile-holding cooling station ( 15 ) with a longitudinal direction of the Extrusionsprofiles ( 17 ) oriented temperature gradient is provided. Device according to the preceding claim, characterized in that the cooling station ( 15 ) with a package of profile-holding cold plates ( 15a ) for rapid surface and block consolidation of the extrusion profile ( 17 ) just behind the output of the profiling tool ( 13 ) is arranged. Device according to the preceding claim, characterized in that the cooling plates ( 15a ) can be flowed through by different temperature cooling fluids. Device according to one of the three preceding claims, characterized in that a distance to the cooling station ( 15 ) following calibration distance ( 16 ), if necessary with a withdrawal device ( 19 ), is provided. Use of fibrous natural substances as starting materials in a highly compressed one obtained according to at least one of the preceding method claims plastic-bound wood-like Extrusion profile with water-resistant surface.