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A new fibre-spreading machine developed in Japan makes it possible to manufacture composite products using high-viscosity matrices such as thermoplastic resins. Among other advantages, the new machine yields improved mechanical properties, stable quality and high productivity.
(Published on May 2005 – JEC Magazine #17)
BY HARUKAZU UNO, COMMERCIAL DIVISION MANAGER, TECHNOMAX CORP.
Purpose of development
Around 1995, we tried to understand the future potential of fibre composite materials. Knowing that recyclable raw materials would be required in the future, we were convinced that a composite material made of thermoplastic resin and reinforcing fibre would become important. Therefore, we studied thermoplastic resins and reinforcing fibres.
The study proved that it was difficult to use thermoplastic resins with reinforcing fibres because thermoplastic resins have a fundamentally high viscosity and thus a poor ability to impregnate fibres, not to mention their high melting point. Therefore, in order to improve the impregnability of thermoplastic resins, we concentrated on the idea of spreading the reinforcing fibre and reducing its thickness, and therefore decided to study and develop a fibre spreading technique.
Around the same time in1995, various fibre spreading methods appeared in Japan and throughout the world as a result of research on such techniques. However, no techniques combining high fibre spreading accuracy with practicality and versatility were found. Therefore, in order to improve the conventional fibre spreading technique, we studied the action of ultrasonic waves and attempted to harness them to spread a fibre bundle. However, at normal ultrasonic frequencies, the fibre bundle was cut or could not be spread at all. As a result of trial and error, an ultrasonic method able to spread fibres was completed in about one year. Subsequently, we proceeded to research and develop an improved fibre spreading technique from 1996, launched the improved technique in 1998 and finally succeeded in developing a fibre spreading machine, but the machine had a few practical problems. As a result of continuing further improvement up to the present day, we have now completed a practical fibre spreading machine.
At the same time, we also developed a weaving machine for spread fibre without twists using the above technique. A conventional weaving machine had not become widely used because productivity was low and quality was poor. However, these problems have now been solved and we have created an improved weaving machine for spread carbon fibre, that offers stable quality and high productivity.
Features and advantages of the fibre spreading machine
- Spread width: about 4 times wider than the original fibre. (12K CF: max. 30mm) (24K CF: max. 45mm) - Feed speed of spread fibre: up to 100m/min (for example, 80m/min for 12K (=12,000: number of filaments) and a width of 20mm). - Computer control using a touch panel (for example, control of ultrasonic frequency and tension). - Stable width of spread fibre (for example, an error of ±1mm or less for 12K spread fibre and a width of 20mm). - Types of practicable spread fibres can be increased by improving width stability and straight stability of fibre on the fibre spreading machine. - Fibre can be attached and detached through a one-touch operation at the time of fibre feeding and winding. - The fibre spreading machine is designed to improve workability by the structure of a cantilever roll.
Features and advantages of the weaving machine using spread fibre produced by a fibre spreading machine
- Fabric width: 1,000mm. - Weaving machine revolutions: up to 120 (rpm) (for example, 40 rpm for 12K and a width of 20mm). - Computer control using a touch panel. - Width of fibre capable of being woven: 1mm to 50mm. - The weaving machine is designed to prevent fluctuations in fibre width at the time of weaving. - Fabrics with various textures (plain weave, twill weave, satin weave) can be woven.
Features and advantages of products using spread fibre
- Even for a thick fibre bundle, physical properties more than or equal to those of a thin fibre bundle can be obtained by spreading and thinly forming the thick fibre bundle. - Thinning and flattening of a fibre bundle leads to improved resin impregnability and a significantly decreased occurrence of voids between the resin and the fibre bundle. - Lower void content leads to improved mechanical strength of composite material. - Fibre spreading greatly contributes to improving the specific strength and straightness of filaments. - Ultralight and ultrathin products which could only be made with an expensive, thin fibre bundle (1K, 3K) can now be manufactured using a cheap, thick fibre bundle (12K, 24K). - In the future, our fibre spreading technique will be indispensable for the manufacture of composite products using a high-viscosity matrix such as a thermoplastic resin.
The following tables and photographs show various data and states of spread fibre and products using spread fibre
Mechanical properties obtained during the tensile test
The spread fibre has improved strength and elastic modulus over the original fibre. Since observed differences in the strength and elastic modulus even in C.V. values are within the standard deviation, it may be concluded that the strength improvement is attributable to the fibre spreading treatment.
The figures on the left represent sectional micrographs of UD using spread fibres and spread fabrics. It can be seen from the figures that each filament aligns straight and overlaps.Also, the lower left figures are photographs of destructive tests using spread fibres and normal fibres. As shown in the photograph, spread-fibre FRP does not cause buckling destruction.
Mechanical properties obtained during the compression test
Comparison of fibre characteristics
Spread fibre fabric thickness
Reference Thickness data of fabric using normal-fibre filament
Fibre opening processed products of original fibre manufacturer for 6K and 12K products.
Fabric prepreg characteristics
Prepreg uses 250°F epoxy resin.
Typical modes of compressive fracture in each specimen after the compression test
Stress concentration occurred in the original fibre owing to the presence of resin-rich spots and fibre-bundle dense spots revealed in the cross section observation. However, as the spread fibre was thinned by the fibre spreading treatment, filament straightness was improved, thus leading to uniform stress distribution in the respective filaments and eventually to improved strength and elastic modulus.
Conventionally, for a fabric with a basis weight of 100g/m2, an ultrathin product (for example, 1K) needed to be used. For the first time, fibre spreading now enables weaving of a fabric with a basis weight of 100g/m2 or less using a standard product (for example, 12K, 24K). In addition to basis weight or thickness advantages, improvement in ILSS owing to an increase in fabric smoothness and an improvement in the bending strength of moulded products also provides significant advantages.
In terms of cost, fibre spreading can provide fabric at a lower cost than a normal-fibre fabric product with low basis weight.
Conventional applications include aerospace, vehicles, building materials, energy-related material, sporting goods, general industrial equipment, industrial components, etc. and our fibre spreading technique should become widely used in these applications. In the future, we can expect that the spread fibre obtained by this technique will be used as reinforcement for composite materials with a highviscosity matrix, such as thermoplastic resins or metals. Furthermore, we can expect that new commercial products will be developed using our fibre spreading technique with more common materials.
Future potential and applied technology
We believe that from now on, manufacturers – particularly carbon fibre manufacturers – will tend to use thick fibre bundles to reduce their costs. Therefore, our fibre spreading technique enables the manufacture of fibre composite materials with high-viscosity matrices.
Ultrathin products which cannot be manufactured using thick fibre bundles can also be made, and the fibre composite material can be applied to various applications. Moreover, as an applied technology, resin impregnation can be performed with fibre spreading because an ultrasonic method has been adopted.