KAERKI TIMO (FI)
KAERKKAEINEN OLAVI (FI)
KAERKI TIMO (FI)
| FR2609927A1 | 1988-07-29 | |||
| US5516472A | 1996-05-14 | |||
| EP1815956A1 | 2007-08-08 | |||
| US6337138B1 | 2002-01-08 |
| CLAIMS 1. A method for manufacturing composite material, in which method, as wood material is used heat-treated wood material which is ground fine, the fine heat- treated wood material is mixed with plastic material such that the ratio of wood material in the wood-plastic composite material is about 55-95 weight percentages of the mixture weight, and the mixture is manufactured into wood-plastic composite material, characterised by grinding the heat-treated wood material such that the particle size of ground heat-treated wood material is 0.8 mm or less. 2. A method according to claim 1, characterised by the particle size of about 70- 85% of the volume of ground heat-treated wood material being about 0.5-0.8 mm and the particle size of about 15-30% of the volume of wood being less than 0.1 mm. 3. A method according to claim 1, characterised by the particle size of about 75- 80% of the volume of ground heat-treated wood material being about 0.5-0.8 mm and the particle size of about 20-25% of the volume of wood being less than 0.1 mm. 4. A method according to any one of claims 1-3, in which the wood material is heat-treated before grinding, characterised by adjusting the treatment temperature to 180-210°C with the thermal-modification technique. 5. A method according to claim 4, in which the wood material is heat-treated before grinding, characterised by adjusting the treatment temperature to 180-190°C with the thermal-modification technique. 6. A method according to claim 4, in which the wood material is heat-treated before grinding, characterised by adjusting the treatment temperature to 200-210°C with the thermal-modification technique. 7. A method according to claim 4, in which the wood material is heat-treated before grinding, characterised by adjusting the treatment temperature to 190-200°C with the thermal-modification technique. 8. A method according to claim 1, characterised by the ratio of wood material in the plastic composite material being about 65-95 weight percentages of the mixture weight. 9. A method according to claim 1, characterised by the ratio of wood material in the plastic composite material being about 75-95 weight percentages of the mixture weight. 10. A method according to claim 1, characterised by the ratio of wood material in the plastic composite material being about 5-35 weight percentages of the mixture weight. |
The invention relates to a method for manufacturing composite material, in which method, as wood material is used heat-treated wood material which is ground fine, the fine heat-treated wood material is mixed with plastic material such that the ratio of wood material in the wood-plastic composite material is about 55-95 weight percentages of the mixture weight, and the mixture is manufactured into wood- plastic composite material.
As raw materials of wood-plastic composite materials, wood material, plastic and binders are used. The materials and agents are mixed together and the mass formed is treated in a suitable way in a temperature appropriate for the purpose into a desired product.
The purpose is to create various weather- and wear-resistant products of the wood- plastic composite materials to replace, inter alia, products manufactured of impregnated wood. Advantages of the wood-plastic composite material are good durability against both moisture and dents, being environmentally- friendly and recyclability.
As the wood material of the wood-plastic composite material, normal wood as chips or dust is commonly utilised. As the plastic material, plastic materials suitable for the purpose, such as e.g. polyethylene or polypropylene plastic, are usually employed. It is known that the moisture-durability and hardness of the wood-plastic composite are affected by the properties and proportions of both wood material and plastic material.
It is also known to use as the wood material of the wood-plastic composite material the so-called heat-treated wood as dust or chips. When manufacturing thermally- modified wood material i.e. heat-treated wood, the wood material is treated in a high temperature and introduced to various pressures. The purpose is to effectively dry the wood material and remove its moisture without substantially changing the dimensions of wood. In the process, wood obtains valuable properties. The moisture of thermally-modified wood material is low and it can absorb almost no moisture, and it is well suited for use in, inter alia, various humid environments. The properties of thermally-modified wood differ greatly from the ones of the so-called normally dried wood.
A disadvantage of recent wood-plastic composite materials is that the material or their components can react to varying moisture conditions and other external conditions, whereby the end result obtained does not retain its shape and dimensions adequately enough in demanding conditions of use.
An object of the invention is to introduce a method for manufacturing composite material, which eliminates disadvantages related to recent methods and products. A particular object of the invention is to introduce a method which is inexpensive of its material costs, more cost-effectively manufacturable than earlier and which provides a product which is more stable and wood-like than earlier. Furthermore, an object of the invention is to introduce a method which can affect the properties of end products in accordance with the purpose and requirements of use. The object of the invention is achieved with the method for manufacturing composite material which is characterised by what is presented in the claims.
In the method according to the invention, heat-treated wood material is ground such that the particle size of ground heat-treated wood material is 0.8 mm or less.
In an advantageous embodiment according to the invention, heat-treated wood material is ground such that the particle size of about 70-85% of the volume of ground heat-treated wood material is about 0.5-0.8 mm and the particle size of about 15-30% of the volume of wood is less than 0.1 mm.
In an advantageous embodiment according to the invention, the particle size of about 75-80% of the volume of ground heat-treated wood material is about 0.5-0.8 mm and the particle size of about 20-25% of the volume of wood is less than 0.1 mm.
It has been proved that the key properties of composite material obtained with the method can be substantially improved by affecting the particle size of heat-treated wood raw material and by retaining its particle size as 0.8 mm at the most. Furthermore, the key properties of composite material can be improved by using two or more different particles exactly determined and by varying their mutual mixing ratio. Some of the particles are extremely fine, less than 0.1 mm, and these operate as a binder in the processing of particle material of larger size and plastic.
In the method, wood material is heat-treated before grinding. In an advantageous embodiment of the invention, the treatment temperature is adjusted to 180-210°C with the thermal-modification technique. In a further advantageous additional embodiment of the invention, the treatment temperature is adjusted to 180-190°C with the thermal-modification technique. When the treatment temperature is adjusted to 180-190°C, good breaking and bending resistance are obtained according to tests. In a next advantageous additional embodiment of the invention, the treatment temperature is adjusted to 200-210°C with the thermal-modification technique. When the treatment temperature is adjusted to 200-210°C, good moisture resistance and product raw material almost non-swelling are obtained.
In a yet further advantageous additional embodiment of the invention, the treatment temperature is adjusted to 190-200°C with the thermal-modification technique. Then, it is possible to optimise the technique and provide good breaking and bending resistance, good moisture resistance and product raw material almost non- swelling in the same end product.
In the above ways, studies show that exceptionally good hardness is obtained in the products being manufactured and their other key properties can also be accurately optimised in accordance with the purpose of use. According to studies, when manufactured in a way according to the method, the passing through of the wood- plastic mass is improved, it retains its profile shape and the number of shutdowns decreases, which directly affect the manufacturing capacity. By varying the mutual ratios of particles and the thermal modification of wood, the properties of end products can be affected according to the purpose and requirements of use. Thus, it is possible to substantially decrease the volume of plastic material used without weakening the properties of the end product and retain its wood-like nature. It should be noted that, by means of the heat-treatment and grinding of heat-treated wood and by means of controlling its process and treatment, a fine mass is obtained which cannot be achieved of ordinary wood with normal methods and normal costs.
The properties of heat-treated wood are well applicable to this purpose, because the heat-treated wood is of uniform quality and uniformly distributed and does not change almost at all in this form due to moisture and other external factors. An advantage is also the fact that it is possible to manufacture wood-plastic composite material by using heat-treated wood material generated as a by-product in the production of heat-treated wood and flour formed of it. Then, the flour generated in the manufacture of heat-treated wood can be utilised advantageously directly on the by-product line in the production of heat-treated wood as such extremely cost- effectively. Furthermore, it is possible that the production employs non-marketable material oddments of the production of heat-treated wood by grinding them to suitable flour. It is also possible to utilise such wood material, the so-called weed tree, which would not otherwise be heat-treated, to treat it normally in the heat- treated wood process, ground it to flour and use it in the method according to this invention as wood material. Then, all raw materials can be employed.
The method according to the invention produces a mass based on heat-treated wood in which a required volume of plastic material or other equivalent materials is inserted as a binder, by suitably combining which and with various treatment ways, it is possible to obtain optimal raw material for different purposes for which it has not traditionally been possible to utilise wood. When manufacturing test pieces, wood-like products with a clean surface, resistant to weather, retaining their dimensions and shape have been provided with a small volume of plastic material. It is also possible to feed the extractives of wood released in the heat-treatment into the mass as the binder. Flour can be manufactured of solid heat-treated wood which yields good cost-efficiency. A further advantage is that, with the method which employs raw material with good properties according to the invention, it is possible to manufacture various products which replace current products. The method utilises plastic materials known as such and earlier utilised in wood- plastic composite materials.
In the method according to the invention, the volume of plastic material used is advantageously about 5-35 weight percentages of the mixture weight depending on the purpose of use. The content of additional binder can be advantageously 0-20 weight percentages. Then, the method according to the invention offers considerable benefit in costs, because the ratio of cheaper fibre material is considerably larger than earlier, but still provides the same good properties for the part of moisture resistance and dimension stability as when using a common fibre material and a greater ratio of plastic. The price of plastic raw material is about tenfold the one of fibre material. Thus, the price of the product is obtained inexpensive and the manufacture cost-effective. The wood-like nature of the product is retained, its appearance is natural and ecological and the colour of the product can be changed in the heat-treatment in accordance with the level of heat- treatment without the use of colourings. Additionally, the product is durable and easily machinable and its surface can be obtained smooth. The disposal of the product after use does not cause such a great problem as products having a higher plastic content. A further advantage is also that, when the ratio of wood in the end product is large, the heat- and cold-conductivity of the product is closer to the thermal conductivity properties of common wood than those of a product having a high ratio of plastic material. For specific purposes of use, it is possible to use, inter alia, polyethylene and such equivalent swelling agents/binding agents as the binder.
In solid wood production in an LW process, the treatment can be performed acceleratedly without weights, ignoring the deformation of wood and ground without moisturising and steadying. Then, even weed trees can be the raw material. In various embodiments of the invention, the volume of wood material and plastic material can vary as above in accordance with the purpose and requirements of use.
In various embodiments of the method, the ratio of wood material can vary between about 55-95 weight percentages, the ratio of plastic material can vary between about 5-35 weight percentages and the content of additional binder can vary between about 0-20 weight percentages.
In advantageous embodiments of the invention, the ratio of wood material can vary between about 65-95 weight percentages, the ratio of plastic material can vary between about 5-30 weight percentages and the content of additional binder can vary between about 0-15 weight percentages. In advantageous additional embodiments of the invention, the ratio of wood material can vary between about 75-95 weight percentages, the ratio of plastic material can vary between about 5-25 weight percentages and the content of additional binder can vary between about 0-10 weight percentages.
A workable example is an embodiment which includes 80 weight percentages of heat-treated wood material flour, 18 weight percentages of polyethylene or polypropylene plastic and 2 weight percentages of coupling agent maleic anhydride and/or maleated polypropylene. It has been verified in comparison tests that the workability of the material mixture with this mixture ratio is at a totally different level and much better than the one of material mixture manufactured of the common wood mass. Another embodiment employs 90 weight percentages of heat-treated wood material flour, 9 weight percentages of plastic raw material and 1 weight percentage of additional binder. When the wood material content is high (e.g. 80-95 weight percentages), the properties and the appearance of the product are more wood-like compared to a one having a low wood material content.
Another embodiment is a mixture which includes about 65-70% of wood fibre, about 18-27% of plastic material and about 8-12% of talc used as the additional binder. According to a study, adding about 10% of talc in the mixture enables improving all of the mechanical properties and the moisture strength (inter alia, water absorption) of the product. Therefore, excellent consistency for terrace boards, among others, can be obtained.
The method according to the invention employs wood material suitable for the purpose.
In the heat-treatment process, wood material is heated for periods of various duration in different temperatures. In a method, wood is placed in a heat-treatment space the temperature of which is quickly risen to about 100°C, then the temperature is slowly risen up to about 120-130°C. At the next step, the temperature is increased to about 190-200°C and kept there for some time. At the final step, wood is cooled down and the temperature is controllably decreased to normal temperature. This process requires about 36 hours. When wishing to obtain high-quality thermally-modified wood material, the wood has to be treated carefully and the temperatures and treatment times have to be continuously monitored. After the heat-treatment process, the thermally-modified wood is inspected and broken or discoloured wood is removed. Then, the thermally-modified wood is treated in a desired way in accordance with the purpose of end use. This step produces wood pieces, cutter chips and sawdust.
In the method according to the invention, these production residues of thermally- modified wood, i.e. wood pieces, cutter chips, sawdust, broken wood, discoloured wood, are employed as the raw material of the method and are utilised being thermally-treated wood of their properties. In the method, the wood in question is ground into fine powder, plastic material and/or other mixture material is added, the mixture is heated into a temperature fit for the purpose and products of desired shape are formed of it.
It is also possible to heat-treat so-called difficult-to-use wood i.e. such wood of which no purposeful products can be obtained. Such wood are, inter alia, sawing waste, branches, tops. When such wood is heat-treated, it is substantial that the wood is effectively obtained dry, but splits or deformations can be formed in it during drying. Then, the heat-treatment period can be considerably decreased and the heat-treatment can be performed e.g. in about 18 hours, which is about half of the duration of the above heat-treatment process. This way, wood material to be used as the raw material of the method according to this specification is obtained cost-effectively and quickly.
The invention is not limited to the described advantageous embodiments, but it can vary within the scope of the inventive idea presented in the claims.
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