DD145079B1 - METHOD FOR PRODUCING MOLDED PARTS FROM THERMOPLASTIC DISPERSIONS AND WOOD PARTICLES - Google Patents

Description

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Title of the invention

Process for the production of molded parts from thermoplastic dispersions and wood particles

Field of application of the invention

The invention relates to a process for the production of molded parts from thermoplastic dispersions and wood particles for the furniture, construction and light industry »

Characteristic of the known technical solutions

Many technical solutions are known, which include processes for the production of press plates or moldings from wood particles with the addition of binders. These differ in each case in the selection of the material components or the binder, the nature of the introduction and mixing of the components and in the formation of the finished parts.

Usually, thermosetting condensation resins are used as binders. The use of such resins has the disadvantages that a Nachhärtezeit (when using phenolic resin) or. Conditioning time (when using melamine or urea-formaldehyde resins) after hot pressing of the wood particle material is necessary. The surfaces of the pressed parts are subsequently ground after the hot pressing in order to obtain a homogeneous, scratch-resistant and as closed as possible surface. But above all, when using

Condensation resins, a subsequent deformation or relief formation of the board materials for special Anwcndungsfälle not possible (US-PS 3,627,864, US-PS 3,649,297, US-PS 3,793,125, AT-PS 295 119).

According to the teaching of US Pat. No. 3,554,856 it is also possible to use polyacrylonitrile (or, copolymers and polymer blends having at least 85% of acrylonitrile units in the total mass of the polymer) in combination with the moisture contained in the particulate material as binder. In the heat and pressure pressing process, a pseudo-melt state is achieved from polymers and water, which leads to binding of the wood particles. The finished, non-deformable board materials produced in this way have a particularly high resistance to heat. "

In addition, methods for the use of powdered or fibrous thermoplastics are known in which special additional operations are provided to produce a workable wood particle-thermoplastic mixture. For example, e.g. a granulation technology or a melt mixing with subsequent comminution required to obtain an aggregated particulate wood-thermoplastic mixture (CH-FS 570 869) · Are also used various plastic parts, with the necessary drying of the wood particle material and the necessary comminution of the Plastic material to finely divided, expediently powdered plastic matrix adversely affect the process performance. However, in this process is just the preparation and the sensible re-use of plastic waste in the foreground (DE-OS 22 06 829) ·

Other processes concern the production of semi-finished products from wood particles and thermoplastics, which can be deformed by extrusion. Again, special facilities for dewatering of the wood particle material are provided (DE-OS 22 45 871).

In order to improve the flexural strength properties of plates made from acetylated wood fibers, SU-PS 489 654 proposes to wet the acetylated fiber material with 2 to 5% polyvinyl acetat emulsions.

Object of the invention

The aim of the invention is to produce a variably shaped, thin-walled, but stable and versatile thermoplastic wood particle molding rationally «

Explanation of the essence of the invention

The invention is based on the object, with little technological effort and using suitable thermoplastic dispersions which are added to the wood particles, stable and deformable moldings whose surface texture is smooth and firm to produce without Nachhärtezeit "invention, the wood particles, preferably wood fibers, with an aqueous , 39 ··· 57% solids contained, plasticizer-free, finely dispersed dispersion of terpolymers based on acrylic acid esters or acrylic acid ester-styrene copolymers or homopolymers of polyvinyl acetate sprayed. The amount of aqueous thermoplastic dispersion used is chosen so that the amount of pesticides, based on dry (atro) wood particles, 10 ».. 4-0 % . The non-woven mixture is then precompacted into coarse nonwovens and formed in the press under pressure and heat to form the molding. The nonwovens are produced in one or more layers, wherein homopolymer dispersion of the polyvinyl acetate or acrylic ester or acrylic acid ester-styrene copolymer according to the respective Layered request be added differently. For special applications, a heat-curable resin is added to the wood-particle / thermoplastic mixture of the middle layer of a multi-layer nonwoven. »Forming is effected directly or by subsequent deformation of the board material by the end user»

The production of these thin-walled Thermoplastic Holzportikel- molded parts is experience possible for a simple technology. The thermoplastic dispersions are advantageously ready to use on delivery, while others

Thermoplastic material must first be prepared and crushed accordingly. The spraying of the wood particles with the aqueous thermoplastic dispersion allows a good dosage, an intimate and all-round wetting and mixing of both components, eliminating the otherwise observed problem of segregation. This has a favorable effect on the characteristic properties and the surface appearance of the moldings.

The present invention further has the cost-reducing advantage that the wood particles to be compressed do not need to be dried again. "Another advantage results from the fact that grinding of the Pormteiloberflachen can be omitted in contrast to the use of condensation resins, as when using thermoplastic dispersions without grinding a good, smooth, firm and closed surface is achieved. A further advantage is that as panels manufactured parts are deformable under simultaneous action of heat and pressure from the end user for its particular application, the deformability depends on the thermoplastic content. At higher thermoplastic content and highly deformed objects can be produced, as they were previously made of press plates only by joining individual parts. It eliminates the necessary in the known use of condensation resins Nachhärte time by multi-day stacking. After cooling, the molded parts can be further processed or used immediately. "Depending on the utility value, the thermoplastic content in the surface can be increased in relation to the middle layer or used depending on the type.

embodiment

The invention will be explained in more detail in the following examples.

example 1

3000 g of wood fibers are sprayed with 2000 g of an aqueous dispersion of an acrylic acid ester-styrene copolymer (solids content on atro plastic 4-0%) and the free-flowing mixture is sprinkled in a felter plant to a coarse non-woven plate or to a shaped body (moisture 3 ··· 7 % solids on atro

Wood 25 ... ЗО%). After transport of the nonwoven fabric, the desired molding is formed by direct molding in the press tool of the press. Pressing conditions: specific pressing pressure 2.5 ··· 5 MPa, temperature I70 ... 200 ⁰ C. Adjustable gross density range: 600 ... 1000 kg / дР.

If no surface effect is envisaged, then silicone release film is used as a supplement during the pressing process. »If still necessary, all molded parts can be processed like usual wood-based materials.

Example 2

Wood fibers are treated analogously to Example 1 when using an aqueous, terpolymeric dispersion based on acrylic ester (solids content on atro plastic 43%) »

Example 3

Wood fibers are treated analogously to Example 1 when using an aqueous homopolymer dispersion of polyvinyl acetate (solids content on atro plastic 55%).

Example 4

Production of the sprayed wood particle-thermoplastic mixtures and nonwovens in a known manner analogously to Examples 2 and 3 · Before entering the press, the stratification of three individual nonwovens takes place.

Composition of the cover layer nonwovens analogously to Example 2, composition of the middle nonwoven analogously to Example 3. The mass of the middle layer is 1 to 6 times the mass of a cover layer nonwoven

 Pressing conditions analogous to Example 1 «

Example 5

Production of the wettable wood particle-thermoplastic mixtures and nonwovens in a known manner analogously to Example 4, wherein the wood fiber-thermoplastic mixture provided for the nonwoven fabric analogously to Examples 1 to 3 additionally comprises a heat-curable resin of 0.5 ··· 30% by weight is sprayed on the total mass. Further treatment analogously to Example 4,

Example б

Production of the low-rise pourable wood particle-thermoplastic mixture and fleece in a known manner analogously to Example 1 to 4. In the press, a transportable fiberboard blank is produced. Pressing conditions analogous to Example 1 using spacer strips (5 ♦ ·· 8 mm) «

This fiber board blank is profiled after re-plasticization (heating to I70. ". 180 ⁰ C) in a preheated pressing tool according to the desired fiber molding in Nachverformungsprozeß. Pressing conditions of the post-deformation see Example 1 _e

For the molded parts produced according to Examples 1 to 6, the average properties listed below are £

Bulk density (ке / пА

(MPa) 690 1000 flexural strength 37 ~ 41 42 Ε module (HPa) 00 1900 1800 - 25ОО Thickness swelling 15 - 18 15 - 18 Thickness (mm) 4, 3.2

Claims (1)

Erfindungsanspruoh Process * for the production of molded parts from thermoplastic dispersions and wood particles, in particular wood fibers, by spraying the wood particles with thermoplastic dispersions, precompacting of sprayed wood particles to coarse nonwovens and pressing of the single or multilayer nonwovens under pressure and v / er .. characterized in that the wood particles with aqueous weiuhmflcfoerfreien, finely dispersed dispersions топ terpolymers AAF eggs based on Acrylsäureestern or sprayed from Acrylsaureesterßtyrol copolymers or Hornopolymeren of Polyvinylacetots, wherein the solid content of the Thernoplastdispersion 39 ·· о 57% and the applied solids fraction, based on atro wood particles, is 10 ... 40% «