SOUND ABSORBING MINERAL WOOL PRODUCT AND METHOD OF MANUFACTURING THE SAME

Abstract: A mineral wool body suited for use as a sound insulating body having the ability of damping or absorbing both high frequence and low frequence sound, and in which at least the largest portion of the surfaces of the mineral wool body which are exposed to said high frequence and low frequence sound is covered with a binder in such amount and by such application method that practically all surface fibres of the mineral wool body are bound to each other and still the binder does not provide an integral, unbroken film of binder. The binder preferably is a solution of an inflammable alkali silicate, especially water glass, and it is applied to the mineral wool body in an amount of 75-150 or preferably 95-140 g dry matter content/m<2> of the mineral wool body, whereupon the solvent is allowed to evaporate or dry, preferably at a temperature of less than 120 DEG C. The binder can be pre-polymerized so that the viscosity at 20 DEG C and a dry matter content of 50% is more than 300 mPa.s, and the binder is applied in a concentration of less than 40% or preferably less than 38% dry matter content.

Description: Sound absorbing mineral wool product and method of manufacturing the same The present invention generally relates to a mineral wool product, and more particularly the invention is directed to a mineral wool product * for sound absorbing purposes and a method of manufacturing such product. Modern buildings, especially large buildings, are often provided with an extensive and sofisticated ventilation system. In buildings having such systems it is important that people in the buildings do not hear sounds from fans or from the flow of air in the ventilation channels. It is also important that sounds, e.g. music or conversation, are not transferred from one room to another over the common ventilation channels. In order to avoid such problems it has mostly been necessary to provide some type of sound insulation in the ventilation system, e.g. by introducing some type of sound absorbing material in the ventilation channels. Basically this can be made in two different ways: - according to one way the ventilation channels or ventilation drums or made of, or are covered with, a sound absorbing material, e.g. felt or board of mineral wool; - according to the second way sound traps are formed in the ventilation channels or ventilation drums', e.g. by providing elements in the channels, the main object of which is to fade out or absorb sounds distributed by the air inside the channels. The sound traps, in turn, mainly can be of two different types, namely a type which deflects the ventilation air once or twice by baffles, or sound traps of in-line type, in which the air flows substantially straight linear through a channel having a substantially constant cross section area, and in which the channel walls are made of or covered with a sound absorbing material. Especially in the latter case there are ery great demands on the efficiency of the sound absorbation. By means of mineral wool it is without difficulties possible to obtain an effective absorbation of sound of fairly high frequencies, e.g. more than 1000 Hz, but a standard type of such sound absorbing material, however, has a restricted possibility of absorbing sound of low frequencies. It is known that the ability of the mineral wool to absorb low frequence sound can be increased by giving the mineral wool a surface layer of a suitable material, e.g. a thin layer of plastic. If the plastic is sufficiently thin and elastic the ability of the mineral wool product to absorb low frequence sound is drastically increased, and still its ability of absorbing high frequence sound is not reduced to any noticable extent. Mineral wool materials of said type having a surface covering, however, have substantial disadvantage. Firstly the plastic foils, by means of which the mineral wool is covered are inflammable, and secondly it is technically difficult to apply the plastic film on the mineral wool, especially in narrow spaces like on the concave inner- surface of a tubular insulation or similar means. Now it has surprisingly proved that it is possible to obtain the same good effect as with the plastic film covering substantially more simple, quicker and more economically, namely by covering the mineral wool insulation with a diluted binder solution which is then allowed to dry. Two circumstances are of determining importance concerning the amount of binder solution and the state of the binder solution: - on one hand the amount of binder etc must be sufficient to interlock practically all fibres on the surface of the mineral wool product, - on the other hand the amount of binder must not be so great that an integral, unbroken film of binder is formed on the surface of the mineral wool product. Generally it is not necessary to cover the surface of the entire mineral wool product, since those surfaces, which do not directly form a part of the ventilation channel are not subjected to sound and therefore cannot absorb or fade out the sound of the ventilation channels. Therefore it is quite sufficient to treat 5 only the surfaces of the mineral wool body which directly define the channel. It may also be suitable that some parts of the surfaces which define the channel are left untreated so that said parts can increase the ability of the material to absorb the highest freuqencies of the sound. 10 According to the invention the actual surfaces of the mineral wool bodies are covered with a non-inflammable material, especially an alkali silicate like water glass. A suitable water glass substance is provided by EKA under the trade name "Bindizil FK10". 15 The water glass preferably also can be pre-polymerized or it can be treated in any other way so as to obtain a viscosity of at least 300 IPa.s at 20 °C and 50 % dry matter content. For application technical reasons the dry matter content must not be too large, and preferably the dry matter content is kept less 20 than 40 %, preferably less than 38 %. The amount of binder applied to the mineral wool surface is of substantial importance. On one hand the amount should be sufficient as to bind all loose surface fibres, on the other hand the amount must not be so large that the binder provides an 25 .integral covering over the mineral wool body. Practical tests have proved that the amount of binder applied to the product should be between 75 and 100 g dry matter/m*- of the mineral wool surface, or preferably between 95 and 140 g/m . Also the temperature during the drying or the evaporation of 30 the solvent is important so that the surface covering substance should keep its pliability. Tests have shown that the temperature should not be higher than 120 °C. -\ There are different ways of applying the binder, e.g. rolling or spraying the binder. When roll ng the binder onto the 35 mineral wool product there is, however, a risk that loose fibres stick to the roller and by time hazard the treatment result. Therefore it is recommended that the binder is sprayed on to the product. It is important that the fibres of the mineral wool material are not of a hydrofobic surface character so that said fibres make it difficult or impossible to apply the binder or to obtain a correct spreading of the binder over the surface fibres. In order to eliminate the said risk the binder therefore preferably can be given a slight amount of a wetting agent, e.g. a water soluable tenside.

Claims: CLAIMS 1. A mineral, wool body suited as a sound insulating body having the ability of damping or absorbing both high frequence and low frequence sound, c h a r a c t e r z e d in that at least the largest amount of the fibres of the mineral wool body which are exposed to the high frequence and low frequence sound or covered with a binder to such an extent and in such way, that practically all fibres at the surface of the mineral wool body are bound to each other and still the binder does not provide an integral unbroken film of binder. 2. Mineral wool body according to claim 1, c h a r a c ¬ te i z e d in that the binder is of an inflammable type and is an alkali silicate, especially water glass and is applied in an amount of 75 - 150 or preferably 95 - 140 g dry matter/π of the mineral wool body. 3. Mineral wool body according to claim 2, c-ti a r a c - t e r i z e d in that the water glass is pre-polymerized. 4. Mineral wool body according to any of claims 1 - 3, c h a r a c t e r z e d in that the binder contains a slight amount of a wetting agent. 5. Mineral wool body according to any of claims 1 - 4, c harac te r i z e d in that the mineral wool body is • formed by disks or semi -tubes and is provided inside the ventilation channel system and covers the entire flow area thereof. 6. Method of manufacturing mineral wool bodies, e.g. plates or semi -tubes, according to any of the preceding claims having the ability of damping or absorbing both high frequence and low frequence sound, c h a r a c t e r i z e d in that a diluted solution of a binder is applied to the mineral wool body, whereupon the solvent of the binder is allowed to evaporate, and whereby the binder is applied in an amount which is sufficient to bind practically all fibres at the surface of the mineral wool body after the solvent is evaporated, and still without forming integral, unbroken film of binder. 7. Method according to claim 6, c h a r a c t e r i z e d in that only one part of the surface of the mineral wool body, which is subjected to sound, is surf ace- treated. 8. Method according to claim 6 or 7, c h a r a c ¬ t e r i z e d in that a binder of an inflammable substance, preferably an alkali silicate like water glass is sprayed or rolled onto the mineral wool body. 9. Method according to claim 8, c h a r a c te r i z e d in that the binder is pre-poly erized to a viscosity of more than 300 mPa.s at 20 °C and a dry matter content of 50 % before the binder is applied to the mineral wool body. 10. Method according to any of claims 6- 9 c harac ¬ t e r i z e d in that the binder before being applied to the mineral wool body, is given a concentration of less than 40 % or preferably less than 38 % dry matter content, and in that the binder is applied in an amount of 75 - 150 or preferably 95 - 140 g dry matter/πr of the mineral wool body. 11. Method according to any of claims 6 - 10, c h a r a c - t e r i z e d in that the solvent of ,the binder is allowed to evaporize or dry at a relatively Tow temperature, preferably less than 120 °C.

Inventors: LUNDQUIST PER-OLOF, LUNDQUIST, PER-OLOF
Applicants: ROCKWOOL AB, ROCKWOOL AKTIEBOLAGET
Application year: 1987
Main classification: E04B1
IPC codes: E04C2