Method for manufacturing a mat-like product containing mineral fibres and a binding agent; and obtained product

Abstract: In the method for manufacturing a mat-like product containing mineral fibres and a binding agent, the binding agent is mixed with the fibres before the formation of the product. The material used as the binding agent is thermo-plastic particles, such as fibres, a powder, or particles in a dispersion, which are supplied in connection with the manufacture of fibres to the fibres forming of melted material supplied in the air. The fibres and the binding agent are carried by a turbulent air flow, in which the heat contained in the solid material and the fibres forming thereof is used for melting or softening thermoplastic particles into a state, in which they effect the binding of fibres to each other. The invention relates also to the use of products manufactured by the method and containing mineral fibres and a solidified thermo-plastic binding agent for the manufacture of compression-moulded mineral fibre products.

Description: The invention relates to a method for manufacturing a mat-like product containing mineral fibres and a binding agent as presented in the preamble of claim 1. In the manufacture of mats formed of mineral fibres, the fibres are produced by conveying melted material on centrifugal wheels or inside perforated drums which sling the material by the centrifugal force outwards as thin fibrous pieces. At the same time, air is blown from the side of the centrifugal wheels in a direction perpendicular to the slinging direction, whereby the pieces are simultaneously directed to a certain direction and cooled down by air. The fibres are carried by the air flow onto an air-permeable support, through which the air flow passes, and on this support they form a felt which is conveyed by the support to aftertreatment devices. Production methods of this kind are described e.g. in Finnish Patents No. 76842 and 77272 as well as in CH-410747. For binding mineral fibres into a homogeneous mat, a suitable liquid binding agent, which will harden, is sprayed to the fibres in fluid form before the settling of the fibres into a mat. At the same time as the fibres are formed, a suitable cooling agent, such as water, is mixed with them for ensuring a sufficiently quick cooling of the fibres. Next, the matting formed on the support is usually subjected to treatment with heat by raising its temperature again for hardening the binding agent, at which stage the final density and thickness of the product is determined. After this, the product can be worked further in a number of ways, e.g. by sawing, cutting, etc. In the present application, the term mineral fibres is used to denote stone fibres, glass fibres, ceramic fibres, or slag fibres. In the methods of prior art mentioned above, the binding agent in general use is phenol-based resin which is sprayed on the surface of the fibres and used for hardening the mat at the later stage of heat treatment. A problem with the use of such resin lies in the environmental and health risks involved. Furthermore, a long heating time and, correspondingly a long heating oven is required for hardening the resin, thus increasing the costs on investment and energy in the lines of mat manufacture. It is an aim of the invention to present a method by which it is possible to achieve quick binding of the product by a binding agent and, on the other hand, exploitation of the heat contained in the melted raw material of mineral fibres in the formation of the product. This aim is attained according to the invention with a method as presented in the appended claim 1. In the method, thermoplastic particles constituted by bicomponent fibres are used as the binding agent, which are mixed with the fibres to be formed of a melted material. The fibres and the binding agent are formed into a mixture passing forward in a turbulent air flow, i.e. a dispersion of air, fibres and binding agent particles, in which the heat of fibre formation, i.e. the heat content of the melted material forming the raw material of the fibres, is used for bringing the thermoplastic particles into a state where they glue the fibres to each other. The fibres that are solidified from the melted state in connection with the fibre formation emit the melting heat to the surrounding air, wherefrom it is transferred to the thermoplastic particles. At the same time, the turbulent air flow mixes the fibres and the binding agent particles into a homogeneous mixture, and at the time of settling of the mixture into a solid mat on a support, the binding agent particles are readily in a state in which they glue the fibres to each other. As the formed mat is cooled down, the binding agent particles are hardened, and a finished bound product is achieved.The binding agent is environmentally safe, and the stage of heat treatment in the process remains short. Some advantageous embodiments of the method are presented in the appended dependent claims 2 to 8. The invention relates also to the use of products manufactured by the method in the manufacture of compression-moulded mineral fibre products. In the following, the invention is described in more detail by reference to the appended drawing, which shows a side view of the apparatus in which the method according to the invention can be applied. The drawing shows an apparatus comprising a fibre-forming centrifuge 4 for mineral fibres, to which the melted material is supplied in a known manner and which will be surrounded by slung fibrous pieces which will be next solidified. A group of centrifuge wheels or a perforated drum can be used as the fibre-forming centrifuge. By means of fibre-forming air blown from a pipe 2 around the centrifuge, the fibres are directed to a certain direction, in this case to a special chamber 5 closed from surrounding air, opposite end is provided with a collecting drum 8 with an air-permeable surface, functioning as the suport for mat-formation. For accelerating the cooling of the melted fibre material, water serving as a cooling agent can be sprayed from the pipe 1 to the chamber 5. The thermoplastic binding agent to be used according to the invention, which may consist of thermoplastic fibres, is fed with the flow of air or liquid conveyed by a pipe 3. This flow is mixed with the fibre-forming air in a way that a turbulent air flow is formed forward in the chamber 5 towards the suction drum 8 functioning as the support for mat formation, the binding agent and the fibres being mixed well together in the air flow. At the same time, heat released during the solidification of the fibres is transferred to the thermoplastic material with the results described above.The said air flow is directed by the suction effective inside the suction drum 8 as the air flow, which conveys fibres and binding agent to the surface of the suction drum, passes through the shell of the drum. The drum is rotatable, whereby the finished mat-like product exits as a continuous mat through a gap between the drum and one wall limiting the chamber. The binding agent can be fed to a suitable part of the chamber from the pipe 3 so that it is carried away by the fibre-forming air and mixed into the fibres, preferably as close to the fibre-forming centrifuge 4 as possible at the proximal end of the chamber. The figure shows also how the temperature of the air in the chamber 5 can be adjusted to be suitable for the material used as the binding agent. At the point of mat exit, there is a temperature sensor giving a signal by means of which a control means 15 controls the quantity of the water used as the cooling agent or the relative flow rates of the air returned from the end of the process and the fresh fibre-forming air taken from the outside, which determine the temperature of the air entering the chamber 5. The adjustment can be performed by changing either one or both of the flow rates. Alternatively, it is possible to regulate the temperature by keeping the quantity of the cooling agent supplied from the pipe 1 constant and adjusting only its temperature. The material used as the binding agent, which is supplied as fibres, can be a polymer which, at a suitable temperature range, e.g. between 100°C and 200°C, comes to a glueing state, such as polyethylene, polypropylene, polyester, polyamide, or some other thermoplastic polymer. Use is made of staple fibres which can be carried by an air flow, either as such or using opening means, to the chamber 5. The temperature of the air in the chamber 5 is adjusted to a suitable range by one of the methods described above. Bicomponent fibres are used; such as polyethylene-polyester fibres, polyethylene-polyproplene fibres, or fibres containing polyamide and another polymer. In bicomponent fibres, part of the fibre consists of a binding material melting or softening at the temperature used, the part of the second material, e.g. the core of the other half, remaining in a solid state. Thermoplastic binding agents also give the product good elasticity and flexibility, and this can be influenced by the choice of the proportion of the binding agent. The content of the binding agent can be e.g. 1.0 to 50.0 wt-%, preferably 5 to 30 wt-% of the total weight of the product. It is also possible to use mixtures of different binding agent particles, for example fibres of different lengths or binding agent particles of different materials. The figure shows also some structural details of the apparatus. For example, on the bottom of the chamber 5, a compartment 11 is arranged at the end near the fibre-forming centrifuge 4 for collecting the heavier beads being formed in connection with the fibre formation. By adjusting the height of the wall separating the compartment, it is also possible to have an effect on the turbulence in the chamber and to remove a certain proportion of the beads for regulating the purity of the product. There are plates 8a inside the suction drum 8 for adjusting the extent of the suction sector of the drum and consequently the orientation of the fibres influencing the thickness of the mat. The feed rate of the fibres being constant, the weight per square metre of the product can be regulated by adjusting the speed of rotation of the suction drum 8. Furthermore, it is possible to regulate the orientation of the fibres by arranging the position of the upper or lower wall 6 of the chamber 5 to be adjustable. It is also possible to equip the chamber with a diffuser structure which is generally known. At the point of mat exit, there is also a press cylinder 7, whereby its position can be adjusted for regulating the density of the mat exiting from the gap between it and the suction drum 8, because the mat can still be well compressed at this stage. After the drum 8, the mat passes to the conveyor, at which point cooling air 9 is supplied across the mat for solidifying the thermoplastic binding agent. Usually only a 10...20°C cooling is sufficient for quick hardening of the particles of the binding agent. The final shaping to a certain density can still be performed after this stage by conveying the mat between cooled press rolls 10. For giving the product a surface pattern, rolls with a surface pattern can be used. Alternatively, the product can be pressed by press rolls only, in which case the press cylinder 7 is not needed. The drawing shows also the possibility that air discharged from the chamber 5 through the suction drum 8 is ciculated through a pipe 12 to the fibre-forming air pipe 2 for controlling the temperature in the chamber 5 by proportioning the quantities of air, as described above. As an alternative or parallel means, a desired proportion of circulating air can be conducted through the pipe 12 also to the pipe 3 in the case where thermoplastic material is supplied through it by air. Hot exhaust air can also be utilised elsewhere, as illustrated by a pipe 14 leaving the pipe 12. The air circulation may also incorporate the mat cooling air 9 through a pipe 13 connected to the pipe 12. The obtained mat can also be subjected to further processing by a number of ways. For example, it can be re-pressed to a certain shape by using temperature and pressure, whereby the material used as the binding agent is softened and hardened again, hardening the product into a new shape. By doing so, the thermoplastic properties of the material used as the binding agent are utilised in an optimal way. The method can be used for the manufacture of e.g. the following products: compression-moulded thermoplastic products, flexible insulating sheets, dense sound-proofing felts, mineral wool mats which are thinner than the conventional products.

Claims: Method for manufacturing a mat-like product containing mineral fibres and a binding agent, according to which the material used as the binding agent is thermoplastic particles which are, in connection with the manufacture of mineral fibres, mixed with the mineral fibres formed of melted material and supplied into air, and the fibres and the binding agent are carried away by a turbulent air flow, in which the heat contained in the melted material and in the mineral fibres formed of it is utilized for melting or softening the thermoplastic particles into a state, in which they effect the binding of the mineral fibres to each other, characterized in that the thermoplastic particles used as the binding agent are bicomponent fibres where part of the fibre consists of a binding material melting or softening at the temperature used, the part of the second material remaining in a solid state. Method according to claim 1, characterized in that the quantity and/or the temperature of a cooling agent (1) which is supplied to the mixture of the mineral fibres and the bicomponent fibres in the air is used to adjust the temperature of the air surrounding the bicomponent fibres to a suitable level. Method according to claim 1 or 2, characterized in that the bicomponent fibres are mixed with the mineral fibres by conveying them by a separate flow (3), such as a gas flow. Method according to one of the claims 1 to 3, characterized in that the mixture of mineral fibres and bicomponent fibres is formed in a chamber (5) substantially closed from the surrounding air. Method according to claim 4, characterized in that the mineral fibres and the bicomponent fibres are collected into a mineral fibre mat at the distant end of the chamber (5), as seen in the main direction of the air flow, on a movable, air-permeable support (8), through which the air flow having carried the mixture in the chamber is passed. Method according to claim 5, characterized in that the mat is cooled down e.g. by an air flow (9) blown through it, whereby the bicomponent fibres are hardened and bind the mineral fibre mat in its shape. Method according to claim 6, characterized in that the mat is calendered at the end of the cooling stage for compressing the mixture of mineral fibres and the bicomponent fibres into its final density and/or for pressing the surface of the mat into a pattern. Method according to one of the claims 1 to 7, characterized in that the air flow having carried the mineral fibres and the bicomponent fibres and/or the air flow (9) having cooled the mat formed thereof is conducted (12) to the beginning of the process and used for adjusting the temperature of the air surrounding the bicomponent fibres. Use of products manufactured by the method according to one of the claims 1 to 8 and containing mineral fibres and solidified bicomponent fibres for the manufacture of compression-moulded mineral fibre products.

Inventors: LE BELL JEAN, SIMOLA JARMO, WESTERLUND ULF, LE BELL, JEAN, SIMOLA, JARMO, WESTERLUND, ULF
Applicants: ROCKWOOL INT, ROCKWOOL INTERNATIONAL A/S
Application year: 1993
Main classification: D04H1
IPC codes: D04H1