JPS634767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite material of plastic and wood flour, and in particular provides a method for easily and inexpensively manufacturing a polypropylene composite board containing a large amount of wood flour. .

Attempts have been made for quite some time to replace a portion of plastic, particularly polypropylene resin, with inexpensive wood flour and to use it in fields that do not require much strength such as impact resistance. The advantages of this type of composite material are that it has a woody feel and weight, and is excellent in rigidity, writability, paintability, adhesiveness, and processability.
One advantage is that it can be molded using general plastic molding methods such as extrusion molding, vacuum molding, injection molding, and press molding.

Conventionally, when producing a material that is a mixture of plastic and wood flour, the method used is to first make plasticized composite pellets using a twin-screw extruder or single-screw extruder, and then perform injection molding or extrusion molding. . The reason for this is that high blends of wood flour have poor extrusion stability and the extrusion rate fluctuates, making it impossible to obtain sheets or plates of a constant thickness. This is because if this is not done sufficiently, problems such as the surface becoming extremely rough and the formation of cavities inside occur. Therefore, the current practice is to once create resin pellets containing wood flour and then pass them through an extruder or injection molding machine again to shape them.

These methods require two extrusion steps, which increases the processing cost and eliminates the advantage of mixing inexpensive wood flour.

The present inventors have devoted themselves to research into a method for easily and inexpensively manufacturing polypropylene plates containing a high proportion of wood flour by eliminating the drawbacks of this conventional method. They discovered a method for efficiently producing a beautiful composite plate with a constant thickness and no roughness or cavities, and completed the present invention.

In the present invention, a third substance is added in addition to the polypropylene resin and wood flour in the production of polypropylene composite boards. This substance can be called a type of mediator that promotes miscibility between the resin and wood flour, and research has shown that low molecular weight polyethylene or atactic polypropylene are suitable for this purpose. The average molecular weight of the mediator varies depending on the fineness of the wood flour used and the wood flour blending ratio, but it ranges from 1000 to
It can be limited to a relatively narrow range of 4000. If the average molecular weight exceeds 4,000, it will not penetrate into the extruder very well, resulting in an extremely low extrusion rate, and will also cause extrusion patterns and irregularities on the surface of the extruded plate, making it impossible to obtain a high-quality plate. Furthermore, if the average molecular weight is less than 1000, the penetration will be similarly poor and the effect as a miscibility mediator cannot be exhibited. The appropriate addition rate of the mediator was 20 to 40 parts by weight per 100 parts by weight of the polypropylene resin.

The polypropylene resin used in the present invention is preferably in powder form, and pellet form is unsuitable because it has poor stability when biting into an extruder. Further, the lower the fluidity of the resin, the better, and good results were obtained with a melt index of about 5.

In the present invention, the wood powder to be mixed with the polypropylene resin is regardless of the tree species, and if ordinary wood sawdust can be used, sawdust from processed materials such as boards and particle boards can also be used. The grain size of the wood flour should be finer than 25 mesh screen passes;
If the particle size is coarser than 25 mesh, extrusion stability will be poor.
The extrusion rate also decreases. It is also desirable to dry the wood flour before use; air drying will result in a decrease in the throughput. Although the blending ratio of wood flour can be increased or decreased in the range of 50 to 150 parts by weight per 100 parts by weight of polypropylene resin depending on the use of the composite board, the present invention is particularly directed to a high blending of wood flour. Furthermore, when blending the resin and wood flour, adding 1 part by weight or less of a low melting point substance such as calcium stearate as a lubricant and mixing while heating at a temperature that does not melt the resin will further improve extrusion stability and increase the extrusion amount. can also be increased.

As is clear from the above explanation, when a mixture of polypropylene resin and wood flour is extruded using an extruder, the stability of biting in the hopper of the extruder,
Furthermore, the extrusion rate is an important factor and can be improved by adding a miscibility mediator such as low molecular weight polyethylene or atactic polypropylene and a lubricant such as calcium stearate, but it is possible to improve the extrusion rate by thoroughly kneading in the extruder. In order to perform smooth extrusion, it is necessary to make some modifications to the extruder itself. That is, in a single-screw extruder, (1) the inner diameter of the extruder barrel is changed between the supply section and the metering section, and a two-stage barrel system is used in which the inner diameter of the metering section is made thinner.

(2) Add a tapered groove to the barrel wall of the supply section.

(3) It is necessary to make the gap between the screw shaft of the metal ring part and the barrel wall to an appropriate depth.

FIGS. 1 and 2 show longitudinal and transverse sections of a single screw extruder barrel in which the present invention is practiced. In the figure, 1 is a hopper, 2 is a supply part barrel, 3 is a metering part barrel, 4 is a screw, 5 is a tapered groove made on the supply part barrel wall,
6 indicates the gap between the metal ring screw shaft and the barrel wall.

Among the above three modifications, (1) is a known method used in ordinary extruders, but in the present invention, the barrel inner diameter ratio of the feeding section and the metering section is particularly changed to 1:0.6.
~0.8. As a result of research, it was found that extrusion becomes difficult if the barrel inner diameter of the metering section is less than 0.6 times that of the supply section. (2) By forming shallow tapered grooves on the barrel wall of the supply section, the penetration of the mixture of resin and wood flour supplied from the hopper is improved, resulting in an increase in the extrusion rate. The groove may be shallow, with a width of 5 to 20 mm and a depth of 1 to 5 mm, but the length should be approximately 1.5 to 3 times the inner diameter of the supply barrel, and should be provided vertically parallel to the screw axis, from the hopper side. It gradually becomes shallower toward the extrusion side,
Make it disappear eventually. The number of grooves may be one, but it is more preferable to provide about three grooves. (3) is a measure to improve the kneading of the mixture of resin and wood flour and smooth extrusion by maintaining an appropriate gap between the screw shaft and the barrel wall in the metal ring part, and this gap is too wide. If kneading is not sufficient, surface roughness and internal hollowing of the composite plate will be induced. Furthermore, if the gap is too narrow, gas is likely to be generated due to overheated decomposition of the wood flour, making it impossible to obtain a satisfactory board. The appropriate size of the gap was 5 to 10 mm.

Using an extruder modified as above and adding the above-mentioned miscibility promoter, polypropylene resin 100
A beautiful plate-like product containing 50 to 150 parts by weight of wood flour can be easily extruded.

By further sandblasting the obtained plate-like product, a plate with significantly improved paint applicability, printability, antistatic properties, etc. can be obtained.

According to the manufacturing method of the present invention, there is no need to make resin and wood flour into pellets in advance and extrude and shape the pellets again.
Since the desired polypropylene composite plate can be obtained in the process, it not only reduces processing costs but also requires less equipment investment for extruders, making it extremely economically advantageous compared to conventional methods. There is no doubt.

Further explanation will be given below with reference to Examples.

In the examples, all "parts" mean "parts by weight."

Example 1 Powdered polypropylene resin (trade name, Yucalon TA
-5, manufactured by Mitsubishi Yuka) 100 parts wood flour, 25 pieces of mesh paste (manufactured by Sanyo Kokusaku Pulp)
100 parts low molecular weight polyethylene (trade name, Mitsui Hiwax 110P, manufactured by Mitsui Petrochemicals), 20 parts calcium stearate, 0.5 parts were mixed well, and the barrel inner diameter ratio of the supply part and the metering part was 1:0.75 (130φ). -98φ) extruder,
The material is fed into a single-screw extruder that has three tapered grooves with a length three times the inner diameter of the barrel on the barrel wall of the supply section, and the gap between the screw shaft of the metering section and the barrel wall is adjusted to 8 mm to form a plate. Extruded objects. The extrusion stability was good and it was possible to obtain the desired product without surface roughness or internal voids for a long time.

The surface of this plate-shaped article was sandblasted, and the paint coating was good, and the plate had a beautiful woody feel.

Example 2 Powdered polypropylene (trade name, Yucalon TA-
5. Mitsubishi Yuka Co., Ltd.) 100 parts wood flour, 100 parts mesh paste (Mitoyo Kakoki Co., Ltd.) 150 parts atactic polypropylene (Sumitomo Chemical Co., Ltd.)
40 parts were mixed well and fed to the same single-screw extruder as in Example 1 for continuous extrusion for a long time. 0.5mm
It was below. The obtained composite plate had no surface roughness and no cavities were formed inside.

The surface of this plate-like product was sandblasted in the same manner as in Example 1, and the plate had a woody feel and had good coating and adhesive properties.

[Brief explanation of the drawing]

FIG. 1 shows a longitudinal cross-section of a single-screw extruder barrel, and FIG. 2 shows a cross-section thereof. In the diagram, 1...hopper, 2...supply barrel, 3
...metalling part barrel, 4...screw, 5
...Tapered groove on the barrel wall of the engaging part, 6...
...Gap between the screw shaft of the metal ring and the barrel wall.

Claims (1)

[Claims] 1 A mixture of 100 parts by weight of polypropylene resin and 50 to 150 parts by weight of wood flour of 25 mesh
1000-4000 low molecular weight polyethylene or atactic polypropylene as miscibility mediator 20-40
part by weight, the barrel inner diameter ratio of the supply part and the metering part is 1:0.6 to 0.8, the supply part barrel wall has a tapered groove with a length of 1.5 to 3.0 times the barrel inner diameter, and the metering part has a tapered groove of 1.5 to 3.0 times the barrel inner diameter. A method for producing a polypropylene board mixed with wood flour, which is characterized by extrusion molding using a single-screw extruder having a two-stage barrel in which the gap between the screw shaft and the barrel wall is adjusted to 5 to 10 mm.