DE102005052440A1 - Two or three dimension product manufacture from wood and plastic composite material involves heating composite material, forming to shape and cooling - Google Patents

Abstract

A composite material, consisting mainly of lignocellulose particles from wood and agricultural fibers, and a polymer matrix are heated until formable, then shaped or molded and finally cooled. Heating of the composite base material may be achieved in a variety of ways, e.g. with hot air, radiant heat, hot plates, heated tools and molds, infra-red lamps, hot fluids or open flame. When heated to a suitable forming temperature the material can be shaped or molded by rolling, clamping and twisting along the length, hand forming, vacuum or compressed air forming, pressing in mechanical or hydraulic presses, bending around patterns or cylindrical tools or stretching. The shaped product can be cooled in artificial or natural air flows, in liquids or atomized liquids or in cooled molding tools.

Description

Since there is still no valid standard in Germany for the definition of wood-plastic composite materials, the version of the Austrian Standard (ÖNORM 2005) which is generally used on the day of the application applies:
"Wood-plastic composite material
Wood plastic composite (WPC)
Material that is made of predominantly lignocellulosic particles (eg wood, agrofibres), as well as of polymers as a matrix by a molding process to form a composite material.
The achievable mass fractions of the finished product of lignocellulosic material are usually between 25% and 85%. "

typically, consist of wood-plastic composites in Germany and Central Europe from a wood fiber or flour content of 50% to 90% and one Plastic matrix of semi-crystalline polypropylene (PP) or less often made of polyethylene (PE). Blends with other plastics (e.g. PVC and ABS) and bio-plastics are technically possible, however little common.

The Advantages over Solid wood is the free, three-dimensional formability of the material and the greater moisture resistance. Across from Synthetic plastics provide wood-plastic composites higher rigidity and a significantly lower coefficient of thermal expansion.

The reduced dependence from the finite resource crude oil shapes that natural Image of the material and accelerates with rising raw material prices the conventional plastics market entry for wood-plastic composites.

One generally accepted German term has not yet can establish therefore, becomes more common Way the English abbreviation WPC (wood-plastic composite) used. (see nova 2005)

It is known, wood-plastic composites of granules or loose components in shaping processes to final products or To process semi-finished products. The usual methods are extrusion and injection molding.

By Extrusion are only profile-limited, straight-line sections produced. injection molding however, allows the production of almost all body shapes. The sizing However, the tools and the press-in process set early technical limits. In addition, the tooling costs are very high. Production of individual pieces and small series is uneconomical. Large-sized components are not feasible. Small wall thicknesses can be due to limited production of the processing process.

The described method is in the plastic processing as thermoforming described (see Michaeli 1999). New is the transition and modification of the process from the plastic technology in the wood technology for the novel Wood-plastic composite material.

Two- and three-dimensional transformations are for many applications in construction, in furniture but also in the interior and interior of motor vehicles, Ships and planes indispensable. These applications are so far the wood-plastic composites and above In addition, all wood materials made of fibers or chips closed. It come either molded or damp-hot bent veneers and solid woods (e.g. Beech), or conventional plastics and metals.

the The method specified in the claim is based on the problem the limited ones Forming processes of the previous production processes of wood-plastic composites to expand and so new applications for wood-plastic composites and wood-based materials in general.

• a) Zuführen von Wärmeenergie
• b) Umformen des Holz-Kunststoff-Verbundwerkstoffs
• c) Auskühlen des Werkstoffs

gelöst.This problem is due to the features listed in the claim

• a) supplying heat energy
• b) reshaping the wood-plastic composite material
• c) cooling the material

solved.

The Hot forming of wood-plastic composites allows completely new Applications for this group of materials and for Wood materials in general, which were previously semi-finished metal or metal were reserved for conventional plastic.

The particular advantages of this method are that instead of a variety of thin ones Veneers or strips only a single plate or bar reshaped must become. More time-consuming and labor-intensive processes for connecting the individual layers, as with traditional wood materials, solid wood strips and veneer usual, are no longer necessary.

Tabelle: Verarbeitungstemperaturen von Kunststoffen (Franck 2000) Furthermore, the lower pressures are advantageous over injection molded or extruded workpieces during the manufacturing process. In the above methods, pressure is built up only in one flow direction of the material, while hot working applies the entire surface. The structure of the wood components is significantly less damaged and the positive properties, in particular mechanical strength, are retained. A greater degree of damage to the wood components than in injection molding or extrusion by (re) heating is not to be expected: the processing temperatures for hot working of the commonly used plastics PE and PP are significantly lower than those for injection molding and extrusion:

Table: Processing temperatures of plastics (Franck 2000)

Several technical implementations of the method are in the claims 2 to 4 described. In particular, the described deformation means Forming techniques with hot desire and with preheated tools leaves the standard, industrial Expect production. The heating by means of hot air and manual Deforming or bending over a roller allows Wide application areas in the wood and plastic processing trade.

Further notes on the procedure are given below:
The wood-plastic composite is heated to the specific softening temperature of the contained plastic, but not unnecessarily higher so as not to damage the wood components. Because of their low thermal conductivity, the workpieces must be heated slowly and evenly. If a complete workpiece is to be heated and reshaped, heating cabinets or tempering furnaces are suitable, and in the case of tabular materials also heated plates. For forming in individual areas, a hot air blower is sufficient. When bending and folding, the heated zone should be at least six times as wide as the plate is thick; The minimum bending radius is two to three times as large as the plate thickness to choose.

Problematic can the sudden Leakage of water vapor from 100 ° C be, depending on the outdoor climate stored in the wood components. Too much moisture must be the wood-plastic composite first be dried. In addition, the moisture bound in the material to cloudiness or Cause blistering in the reshaped area.

in the Range of softening temperatures is the wood-plastic composite soft and rubber-elastic. The elasticity goes through the wood content However, not as far as it is from conventional thermoplastic Plastics is known. The forming process must therefore be slower and done with less train.

Of the Material can mechanically within the softening temperature zone or by hand be deformed. The polymer molecules are at this time able to make segmental change of location and get under Entanglement strain. At discharge, however, they endeavor to restore the original Position again, which can lead to the provision of the workpiece. To this recovery efforts To counteract, the workpiece must after loading in loaded Stay in condition and cool.

The spray with water mist or other cooling measures Although they speed up the process, they carry certain risks can lead to cooling voltages to lead, at least for higher quality Applications should be avoided. To the water absorption through To avoid the wood components, must be surface water with pulp or Textiles are included.

citation

• Franck, Adolf (2000): Plastics compendium, 5th new edition. u. ext. Aufl., Würzburg, Vogel, 2000, p. 304
• Michael, Walter (1999): Introduction to plastics processing, 4th erw. Aufl., Munich / Vienna, Hanser, 1999, page 179 ff
• nova (2005): Study Wood-Plastic Composites (WPC) Markets in North America, Japan and Europe with emphasis on Germany; Technical Properties - Application areas - Prices - Markets - Actors, June 2005, Hürth
• ÖNORM (2005): Austrian Standard, B3030 (draft), 01.08.2005, Chapter 3: Terms, page 3

• 1) Um 90° gebogene Leiste (1): Eine 6 mm starke Leiste aus Holz-Kunststoff-Verbundwerkstoff wird beidseitig mittels Heißluft erwärmt, über eine Walze mit glatter Oberfläche gebogen und anschließend durch Wassernebel abgekühlt. Die Feuchtigkeit wird sofort mit Zellstoff aufgenommen. Anwendungsgebiete liegen unter anderem im Möbelbau (z.B. gebogene Möbelfronten oder -seiten).
• 2) Über die Länge um 90° verdrehte Leiste (2): Eine 3 mm starke Leiste aus Holz-Kunststoff-Verbundwerkstoff wird einseitig in ein festes Lager eingespannt, auf der anderen Seite in einem losen Lager fixiert, mittels Heißluft allseitig erwärmt, mechanisch verwunden und anschließend in dieser Position langsam abgekühlt. Anwendungen finden sich in aussteifenden Konstruktionselementen.
• 3) Zweidimensional verformtes Modell eines Stuhles (3): Eine 2,5 mm starke Leiste aus Holz-Kunststoff-Verbundwerkstoff wird gemäß Entwurf eingeschnitten, mittels Heißluft punktuell erwärmt, händisch verformt, durch Wassernebel abgekühlt und an den weiteren Punkten wieder erwärmt und umgeformt. Die Übertragung auf die Fertigung tatsächlicher Sitzmöbel ist zu erwarten, zumindest für Elemente wie Sitzschalen, Armlehnen und anatomisch geformte Rückenlehnen. Einsatzbereiche im Architektur- und Möbel-Modellbau sind offensichtlich.
• 4) Dreidimensional verformte, schalenförmige Platte (4): Eine 2,5 mm starke Platte aus Holz-Kunststoff-Verbundwerkstoff wird in einem Ofen temperiert, auf eine Hohlform aufgelegt, durch Druck mit einer zylindrischen Gegenform langsam mechanisch verformt und in diesem Zustand abgekühlt. Das Verfahren lässt sich auf viele Anwendungen in der Serienfertigung übertragen.

Some embodiments of the method are shown below:

• 1) 90 ° bent bar ( 1 ): A 6 mm thick strip made of wood-plastic composite material is heated on both sides by means of hot air, bent over a roller with a smooth surface and then cooled by water mist. The moisture is absorbed immediately with pulp. Areas of application include furniture construction (eg curved furniture fronts or sides).
• 2) Over the length by 90 ° twisted bar ( 2 ): A 3 mm thick strip made of wood-plastic composite material is clamped on one side in a fixed bearing, fixed on the other side in a loose bearing, heated by hot air on all sides, mechanically wound and then slowly cooled in this position. Applications are found in stiffening construction elements.
• 3) Two-dimensionally deformed model of a chair ( 3 ): A 2.5 mm thick strip made of wood-plastic composite material is cut according to the design, selectively heated by hot air, deformed by hand, cooled by water mist and reheated at the other points and reshaped. The transfer to the production of actual seating is expected, at least for elements such as seats, armrests and anatomically shaped backrests. Applications in architectural and furniture model making are obvious.
• 4) Three-dimensionally deformed, cup-shaped plate ( 4 ): A 2.5 mm thick plate made of wood-plastic composite material is tempered in an oven, placed on a mold, slowly mechanically deformed by pressure with a cylindrical counter-mold and cooled in this state. The process can be transferred to many applications in mass production.

Claims (4)

Method for producing two- or three-dimensionally hot-formed workpieces made of wood-plastic composite material which has been produced from predominantly lignocellulose-containing particles (for example wood or agrofibres) and from polymers as matrix by a shaping process to form a composite material, characterized that a) thermal energy is supplied, b) the wood-plastic composite material is formed, c) the workpiece cools down. Method according to claim 1, characterized that heat energy a) by means of hot air supplied becomes. b) by means of heat radiator supplied becomes. c) is supplied by means of heated plates. d) by means of heated Tools or heated forms is supplied. e) by means of infrared radiation supplied becomes. f) is supplied by means of a heated liquid. G) is supplied by means of an open flame. Method according to claim 1, characterized that the wood-plastic composite a) about a Roller is reshaped. b) clamped in a device and twisted along becomes. c) manually is transformed by muscle power. d) by vacuum or compressed air is deformed. e) by means of a mechanical press and a Form is reshaped. f) by means of a hydraulic press and a shape is transformed. g) formed by means of bending template becomes. h) by means of a cylindrical shape (e.g., drawing punch) is formed over. i) in Forming process we stretched. Method according to claim 1, characterized that the workpiece a) by a natural one Air flow cools. b) through an artificial Air flow cools. c) through an atomized liquid chilled becomes. d) through a liquid chilled becomes. e) by a cool Cooled form becomes.