FR2916382A1 - Thermoplastic polymer based object fabricating method for forming furniture, involves adjusting temperature of extruder to value greater than melting temperature, and dividing flow from extruder into two flows supplying die from cooling jig - Google Patents

Abstract

The method involves utilizing a twin-screw extruder composed of supply, compression and pumping zones. An adjuvant polymer compound reinforced with natural vegetable fibers and wood flour is introduced. The set point temperature of the extruder at the level of the compression zone is adjusted to a value lower than or equal to melting temperature of thermoplastic polymers. The temperature of the extruder at the level of the pumping zone is adjusted to a value greater than melting temperature of the polymers. A flow from the extruder is divided into two flows supplying die from a cooling jig. An independent claim is also included for a thermoplastic polymer based object comprising irregular surface.

Description

The present invention relates to a method of manufacturing objects

  Finished extrusions, in particular thermoplastic, fibrous and wood-fiber profiles of the wood There are processes for the extrusion of thermoplastic polymers with adjuvants and colorants, to imitate wood, but the veined aspect does not imitate not properly wood and gives a plastic appearance.

  Thus, French Pat. No. 2,101,956 describes a process for extruding a composition into a closed-cell, shock-resistant, sliceable, and nailable cell-like cellular structure, and having a skin forming an integral part thereof. This composition comprises a particular vinyl resin, a lubricant, an expanding agent and an activator system consisting of organotin thioglycolate and a barium salt of a saturated fatty acid having from 14 to 18 carbon atoms. This composition is premixed in a conventional high intensity mixer, by introducing the abovementioned raw materials in a predetermined order and then cooled. The pulverulent premix obtained is then introduced into an extruder. This extrusion process, which involves hot premixing the raw materials to prepare a composite material (most often referred to as compounds) in the pulverulent state, is complicated. In addition, the extrusion process described in French Patent No. 2,101,956 does not provide a profile having the veined and fibrous appearance of the wood, surface and heart.

  In the European Patent No. 46 579, to obtain a profiled veined profile, it is recommended to start from a mixture of polyvinyl chloride, a particular polymer such as chlorinated polyethylenes and various adjuvants, in particular dyes, d homogenize this hot mixture at a temperature below the plasticization temperature, generally up to 120 C, then cool the mixture to room temperature and finally, conventionally, injection molding or extruding the mixture. This extrusion process also involves hot premixing the raw materials to prepare a composite material (or compounds).

  This multi-step process is complicated and therefore expensive. In addition, it allows to manufacture only profiles compact structure. Another major flaw of the process described in this European patent lies in the fact that these profiles generally have a relatively homogeneous color in the mass. As a result, the veins are barely visible, if at all. More recently, it has been described in Japanese Patent JP 7214631, a method of manufacturing by extrusion of a synthetic wood comprising the following main steps: feeding an extruder with a raw material consisting of a synthetic thermoplastic resin colored, a part of this resin having colored shades corresponding to the summer wood and the other part being of minor color, having colored shades corresponding to the winter wood, extrusion of this raw material and passage of the molten stream between the outlet the extruder and the die, through an annular member having a plurality of passages. The process described in this Japanese patent is provided for only one type of thermoplastic starting resin formula.

  None of the aforementioned patents discloses a method for manufacturing extruded objects with a veined and fibrous appearance.

  The subject of the present invention is a process which does not have the drawbacks of the abovementioned processes.

  Thus, a main object of the invention is a method of manufacturing extruded objects whose color intensity, density and structure can be continuously varied to obtain either a homogeneous cellular structure or a compact structure, extruded objects obtained having in addition a fibrous appearance well marked, surface and in the mass, mimicking the external and internal appearance of the wood.

  Another important object of the invention is a method for producing extruded objects with a well-marked surface and mass-shaped vein and fibrous appearance which is simple and reproducible, in particular which can be implemented from raw materials available on the market.

  Another important object of the invention is a method of manufacturing finished or semi-finished extruded articles, which can be formed and / or thermoformed and worked under the same conditions as wood, for example, cut, nailed, screwed, glued, painted, varnished, etc. In accordance with the present invention, there has been found a process for the extrusion manufacture of objects, in particular profiles and tubes, based on thermoplastic polymers, having a veined and fibrous appearance at the surface and in the mass, allowing achieve the above objectives. This process consists of a combination of the following four essential characteristics (1) and (4):

  (1) using a twin-screw extruder composed of at least three successive functional zones: a feed or inlet zone, a central compression zone (setting temperature 150) and a pumping or outlet zone, the twin-screw extruder being followed by a die, then by conformers,

  (2) continuously, a homogeneous mixture is prepared at room temperature and the homogeneous mixture obtained is introduced into the feeding zone of the extruder, the homogeneous mixture comprising: • a thermoplastic polymer matrix, • hemp fibers • spruce flour The extruder set point temperature in the zone is about 150 to155.

  (3) The set point temperature of the extruder at the compression zone is set at a value less than or equal to the melting temperature of the thermoplastic polymers, and at the pump zone at a value greater than the melting temperature of the thermoplastic polymers, the residence time of the mixture in the extruder being adapted to obtain a heterogeneously mixed and melt mixture at the outlet of the extruder, (4) Then the flow coming out of the extruder is divided the extruder in at least two streams that feed the die and the conformers.

  All the above operating conditions (1) to (3) contribute to obtaining a heterogeneously melted and kneaded mixture at the outlet of the extruder.

  Step (4) of the process makes it possible to obtain the fibrous appearance. The twin-screw extruder has either of the following two technical characteristics (a) and (b): (a) the length (L) of the twin-screw varies from about 20 to about 28 diameters (D), (b) The compression ratio in the compression zone of the twin screw varies from about 1.5 to about 2.5. The compression ratio corresponds to the ratio of the diameter of the twin-screw core in the feed zone.

  Preferably, the twin-screw satisfies both the above-mentioned characteristics (a) and (b).

  The introduction of the homogeneous mixture into the extruder is carried out continuously, without interruption in time, in order to limit or even eliminate the segregation phenomena in the homogeneous mixture.

  Preferably, in the context of the process according to the invention, no raw material is introduced separately from the other raw materials in the twin-screw extruder. Therefore, the introduction of raw materials into the extruder is preferably provided only at the feed zone.

  The homogeneous mixture comprises a matrix based on thermoplastic polymers, being adjuvanted and of different color, a reinforcement composed of hemp fiber and wood flour.

  The colors of the polymer may vary from white to black (by the way, especially yellow, ocher, green, red, blue, brown, etc ...). The quantities and the colors are adapted according to the colored nuances that one seeks to obtain to imitate a natural wood.

  For thermoplastic polymers suitable for carrying out the process according to the invention, mention may be made of polyvinyl chlorides and acrylonitrile-butadiene-styrene copolymers (ABS).

  The choice of the thermoplastic polymer is determined according to the desired mechanical properties for the extruded objects. The preferred thermoplastic polymers are polyvinyl chlorides.

  The dyes and any adjuvants provided are selected from those capable of withstanding the extrusion conditions, particularly those which do not decompose at the temperatures expected in the different areas of the twin screw extruder.

  For polyvinyl chlorides, the adjuvants which are generally provided in the bulk of the components are stabilizers, lubricants, dyes and possibly plasticisers. One can also have an anti-UV agent. The set temperature of the extruder is set below the melting temperature of the thermoplastic polymers. In the case of polyvinyl chloride, this temperature advantageously varies from 150 to 155 C.

  The set temperature of the extruder, at the level of the compression zone, is less than 25 ° C. or substantially equal to the melting temperature of the thermoplastic polymers, and the set temperature of the extruder, at the level of the pumping zone, is: • Greater than 25 ° C. at the melting point of the thermoplastic polymers, in most of the pumping zone, • at least 25 ° C. above the temperature of the pumping zone; melting the thermoplastic polymers in the final part of the pumping zone, close to the exit of the extruder.

  In the case where the components are based on polyvinyl chloride, the target temperature of the extruder advantageously varies: from about 150 ° C to about 155 ° C in the feed zone - from about 150 ° C to about 160 C in the compression zone, from about 170 C to about 180 C in most of the pumping zone from about 185 C to about 195 C in the final part of the pumping zone, close to the outlet of the extruder.

  Also, in this particular case, the residence time of the polyvinyl chloride mixture in the extruder advantageously varies from about 2 minutes to about 5 minutes and is a function of the geometry and dimensions of the extruded object. According to a fourth essential characteristic of the invention, at the outlet of the extruder, the outgoing flow, consisting of the melt and heterogeneously kneaded mixture, is divided and divided into two streams which feed a die and then a shaper.

  To do this, provision is made between the end of the twin-screw extruder and the die means for dividing the stream of molten mixture. These means may be constituted by a finned ring or by a ring pierced with openings of sufficient size not to significantly curb the flow, and a number equivalent to the desired number of flows.

  Preferably, a fixed-finned ring is chosen, the fins having a shape suitable for guiding and dividing the stream of molten mixture without appreciably braking it. The industrial plant useful for implementing the method according to the invention is simple.

  This installation preferably comprises: means for dosing raw materials in the solid state and means for homogenizing these raw materials. For example, there can be provided a metering and mixing apparatus connected to independent hoppers each containing one of the materials necessary for the preparation of the homogeneous mixture, the metering and mixing apparatus being adjusted according to the preprogrammed composition of the desired homogeneous mixture; connected directly to the metering device and mixer, a twin-screw extruder whose preferred characteristics have been described above; At the outlet of the extruder, means for dividing the flow of molten and heterogeneously mixed mixture leaving the extruder, in at least two streams that feed a die and a shaper of the extruded object. Preferably, these flow splitting means are a fixed finned ring. In the context of the invention, no distribution grid is used as dividing means or any other equivalent means favoring the homogenization of the melt flow. For the manufacture of solid extruded objects, we use a die called torpedo without punch. For the manufacture of extruded objects (circular section tubes, square, ...), using a conventional die with punch. For the manufacture of plates or sheets, a flat die is used.

  In order to obtain an extruded object with a veined and fibrous surface appearance, a conventional die with a punch is indispensable, having a lower section with respect to the entry of the shaper. The shaper may be provided immediately after the exit of the die or the first shaper is close to the die 10 to 12 mm.

  The process according to the invention makes it possible to prepare thermoplastic extruded objects having a veined and fibrous aspect, having the following characteristics: they are obtained from a polymer mixture, wood flour, hemp fiber, adjuvanted and different colors. They have an average density that can be varied from 1, 2 to 0.8. They can be subjected to forming and thermoforming operations.

  As the case may be, the extruded objects are advantageously hollow or solid.

  The extruded objects obtained by the process according to the invention can be used wherever the wood is used, for example for making furniture, both outside and inside, and in general, pieces of furniture. common section of any kind usually made of wood or plastic profiles. The invention will be further illustrated, without being limited in any way, by the following description of a particular embodiment given by way of example.

  Example: manufacture of a profile 25mm in diameter.

  The compound of polymers reinforced with natural plant fibers and wood flour is introduced into a twin-screw extruder.5 In addition, the industrial plant used has an extruder comprising a twin-screw 60mm in diameter and length equal to 28 times the diameter. The compression ratio in the compression zone is equal to 2. The extruder temperatures are: at the feed zone: 150 C at the compression zone 155 C at the pumping zone: 175 C and 195 C near the exit of this zone at the level of the sector: 187 C.

  The flow rate of materials in the extruder is 40kg per hour. The die comprises, in the direction of flow of the molten stream: • A ring of 4 fixed fins • A die 25mm diameter 25 mm diameter tubular shaper is less than 0.1 mm away from the die.

  The raw materials and their dosing in the homogeneous mixture are as follows: 60% of rigid polyvinyl chloride (PVC) 10% of hemp fiber 30% of spruce flour 0.1% of chlorinated polyethylene This mixture comes under the pellet form.

  The mixture used has a VICAT softening temperature of about 74 C (ISO 306 standard).

  The final product obtained, at the output of the shaper, is a solid section of 25 mm in diameter, having a mean density equal to 0.898, with a veined and fibrous appearance, reproducing very satisfactorily the appearance of the wood.

Claims (7)

  1. Process for the extrusion manufacture of objects based on thermoplastic polymers with a veined and fibrous appearance, this process being characterized in that: (1) a twin-screw extruder composed of at least three successive functional zones is used: a feed zone, a central compression zone and a pumping zone, the twin-screw extruder being followed by a die and then by conformers, (2) an adjuvanted polymer compound and different colors reinforced with fibers are introduced. natural vegetables and wood meal. The set temperature of the extruder in the feed zone is set to a value below the melting temperature of the thermoplastic polymers, (3) the set temperature of the extruder at the compression zone is adjusted to a value less than or equal to the melting temperature of the thermoplastic polymers, and, at the level of the pumping zone, to a value greater than the melting point of the thermoplastic polymers. (4) The flow exiting the extruder is divided into two streams which supply the die and then the formers.   2. Method according to claim 1, characterized in that the mixture comprises a mixture of an adjuvanted and colored polymer, hemp fibers and wood flour.   3. Method according to claim 1 or 2, characterized in that: - the set temperature of the extruder at the compression zone is less than 25 C or substantially equal to the melting temperature of the polymers thermoplastics - the extruder set point temperature at the pumping zone is: • Greater than 25 C at the melting temperature of the thermoplastic polymers, in most of the pumping zone, • Upper than at least 25 ° C. at the melting temperature of the thermoplastic polymers, in the final part of the pumping zone, close to the exit of the extruder.   4. Method according to one of the preceding claims, characterized in that the compression ratio in the compression zone varies from about 1.5 to about 2.5. -10-   5. Method according to one of the preceding claims, characterized in that at least one component consists essentially of polyvinyl chloride.   6. Method according to claim 5, characterized in that the components consist essentially of polyvinyl chloride.   7. Process according to claim 6, characterized in that the target temperature of the extruder varies: from about 150 ° C. to about 155 ° C. in the feed zone, from about 150 ° C. to about 160 ° C. in the feed zone. compression zone, - from about 170 C to about 180 C in most of the pumping zone - from about 185 C to about 195 C in the final part of the pumping zone, close to the exit of the extruder. 10. The method of claim 7, characterized in that the residence time of the polyvinyl chloride-based mixture in the extruder varies from about 2 minutes to about 5 minutes. 11. Extruded thermoplastic material objects with a veined and fibrous appearance, characterized in that: they are obtained from a polymer mixture, wood flour, hemp fiber, adjuvanted and of different colors. - They have an average density that can be varied from 1.2 to 0.8. - They may be subjected to forming and thermoforming operations. - They are hollow or full and have an irregular, fibrous surface.