AU2014301105A1

AU2014301105A1 - Process for producing a gypsum fiber board

Info

Publication number: AU2014301105A1
Application number: AU2014301105A
Authority: AU
Inventors: Jurgen Burczeck; Vanya Stancheva IVANOVA-TSANEVA; Lothar Scheller; Vladimir Stefanov TSVETANOV
Original assignee: Knauf Gips KG
Current assignee: Knauf Gips KG
Priority date: 2013-06-26
Filing date: 2014-06-26
Publication date: 2015-12-17
Anticipated expiration: 2034-06-26
Also published as: AU2014301105B2; EP3013768B1; EP3013768A1; DK3013768T3; NO3013768T3; WO2014207098A1

Abstract

The invention relates to a method for producing a hydrophobized gypsum fiber board comprising the steps of: - providing of gypsum stucco, - providing fibers, - introducing the gypsum stucco together with fibers in a main mixer, - spreading the mixture of gypsum stucco and fibers on a moving sieve belt, - humidifying the mixture of gypsum stucco and fibers with a moisture water, - compressing the moistened mixture in order to obtain a gypsum fiberboard strand. The invention is characterized in that at least the gypsum stucco is put into liquid form with a hydrophobizing agent.

Description

-1 Process for producing a gypsum fibre board The subject-matter of the present invention is a process for producing a hydrophobised gypsum fibre board. Hydrophobised gypsum fibre boards are gypsum fibre boards with a reduced water absorption capacity. To comply with standard EN 15283-2, type GFH, the increase in mass of the board must not exceed 5 wt.% during two hours' storage in water at 230. Such boards are used for example in humid rooms such as bathrooms, rear-ventilated facade systems and as facade panels. A variant for the production of hydrophobised gypsum fibre boards is subsequently to hydrophobise gypsum fibre boards produced in the usual way. Since the board core is not hydrophobised with this variant, increased water absorption of the board can arise in the event of damage to the surface of the board as well as to the saw edges arising during processing. A further variant for production is to mix a powdery hydrophobising agent into the dried gypsum fibre mixture. The homogeneous distribution of the hydrophobising agent is not guaranteed here. The problem of the present invention was to make available an alternative method for producing a hydrophobised gypsum fibre board. This problem is solved by a process for producing a hydrophobised gypsum fibre board in the dry or semi-dry process, comprising the steps - provision of stucco gypsum - provision of fibres - 2 - introduction of stucco gypsum together with fibres in a main mixer - spreading the mixture of stucco gypsum and fibres on a moving sieve belt - moistening the mixture of stucco gypsum and fibres with moistening water - pressing the moistened mixture in order to obtain a gypsum fibre board strand, characterised in that at least the stucco gypsum is mixed with a hydrophobising agent in liquid form. Stucco gypsums within the meaning of this application are forms of calcium sulphate hemihydrate, which correspond to the approximate formula CaSO 4 x '- H 2 0, which set with the addition of water to gypsum - calcium sulphate dihydrate. As a stucco gypsum, stucco gypsum has proved particularly favourable that has a grain size of 0.001 mm to 3 mm. The fraction of stucco gypsum that lies in this grain size range preferably stands at at least 50 wt.% of the stucco gypsum, more preferably at 70 wt.%, still more preferably 90 wt.%. The grain size of at least 80 wt.% of the stucco gypsum fraction preferably lies at < 2 mm or < 1 mm or < 100 pm. Corresponding grain sizes can easily be obtained from sieve lines. According to the invention, at least the stucco gypsum is mixed with a hydrophobising agent in liquid form. In an embodiment of the invention, the stucco gypsum is mixed for this purpose in a pre-mixer with the hydrophobising agent.

- 3 In another embodiment, the stucco gypsum together with the fibres is mixed in the main mixer with the hydrophobising agent. In a further embodiment, stucco gypsum and fibres are first mixed together in a main mixer and the addition of hydrophobising agent then takes place in a subsequent mixer. The introduction of the hydrophobising agent preferably takes place by an injection process, i.e. the hydrophobising agent is pressed under pressure through one or more nozzles of preferably 0.5 - 3.0 mm diameter. Alternatively, the introduction can also take place by spraying-in or suchlike. As fibres within the meaning of this application, consideration is given in particular to cellulose fibres and synthetic mineral fibres. Suitable cellulose fibres can be obtained particularly easily from paper and cardboard waste. As synthetic mineral fibres, consideration is given in particular to vitreous fibres, so-called textile glass fibres or wools. Mineral fibres based on rock wools and/or glass wools are particularly suitable. In principle, organic synthetic fibres, natural fibres, metal fibres etc. can also be used. Sizes in the range from 0.001 mm to 2 mm are particularly well suited as fibres. At least 50 wt.% of the fibre content preferably lies for in this range, more preferably 70 wt.%, still more preferably 90 wt.% of the fibre content lies within the claimed limits.

Mixtures of different fibres can also be used. Preferred mixers used as a pre-mixer, main mixer or post mixer are continuous mixers. In parallel with the horizontal mixer shaft, the mixing stock is mixed by means of the mixing tools fitted to the mixer shaft and then conveyed onwards. The mixer preferably comprises a metering device, with which water and/or hydrophobising agent can be metered. In a preferred embodiment, the stucco gypsum - if appropriate together with the fibres - is mixed with relatively small quantities of water before it comes onto the moving sieve belt. This serves in particular for the treatment of anhydrite III contents, which are to be found in stucco gypsum. The stucco gypsum is still "dry" and does not stick together after this treatment. In this case, the water is chemically bound. The introduction of the water preferably takes place by injection. The introduction of the anhydrite water preferably takes place in the pre-mixer or post-mixer. In preferred embodiments of the invention, the hydrophobising agent is added together with the water which is used for the treatment of the anhydrite III contents. A preferred embodiment of the invention is a method, wherein an anhydrite III treatment takes place in the pre mixer and a hydrophobising agent is introduced at the same time. In another preferred embodiment, the hydrophobising agent is introduced together with water to the anhydrite III treatment in the post-mixer. The dry mixture comprising fibres and, as appropriate, treated stucco gypsum is then spread onto the moving sieve belt. Moistening of the mixture of stucco gypsum and fibres - 5 takes place on the sieve belt with further water, which is referred to as moistening water. This is followed by pressing of the moistened mixture in order to obtain a gypsum fibre board strand. As a result of the pressing, part of the water is already removed from the gypsum/fibre mixture. On the one hand, it is necessary to select the quantity of moistening water sufficiently large such that complete moisture penetration of the gypsum/fibre mixture is ensured. On the other hand, it is desirable to keep the quantity of moistening water as small as possible in order to achieve rapid drying of the board. Complete moisture penetration is typically achieved only during the pressing, because the water is pressed through the gypsum fibre mixture and exits downwards through the sieve belt. The gypsum fibre board strand is then cut and dried. After the surface grinding and the milling of the desired edges, the boards can, if required, be impregnated and palettised. According to the invention, the liquid hydrophobising agent can be added without auxiliary materials to the stucco gypsum or the mixture of stucco gypsum and fibres. It is preferable, however, for it to be added to the water in the anhydrite III treatment or to the moistening water or if need be to both. Embodiments are particularly preferred in which hydrophobising agent is also added at least to the water for the anhydrite treatment. Although the quantities of water added there are relatively small, the effect can surprisingly be that the hydrophobising agent is distributed for the most part uniformly in the stucco - 6 gypsum and thorough hydrophobisation of the board is thus achieved. As a ratio of fibres to stucco gypsum, quantities of 0.1 to 0.3 parts by weight of fibres per part by weight of stucco gypsum have proved to be particularly suitable. Quantities of 0.005 to 0.1 kg of water per kg of stucco gypsum have proved particularly suitable for the anhydrite treatment, the range from 0.01 to 0.05 being more preferable. With regard to the quantity of the moistening water, 0.6 to 1 kg of moistening water per kg of the mixture of stucco gypsum and fibres is usually suitable. As a hydrophobising agent, use can in principle be made of hydrophobising agents which have already been used for the treatment of gypsum plaster boards. In particular, it can be organic silicon compounds, in particular siliconates and polisiloxanes. Examples of this are the commercially available potassium methyl siliconate solutions or methyl hydrogen polisiloxanes. Mixtures of hydrophobising agents are also possible. Liquid means that it concerns a substance which offers little resistance to a change in shape, but offers great resistance to a change in volume. It is important that the hydrophobising agent is liquid in the temperature range in which it is used. Typical ranges of use for the application of the hydrophobising agent lie between 10 and 40'C. The temperature of use preferably lies between 15 and 30 0 C. The viscosity of the liquid hydrophobising agent preferably lies in the range from 0.5 to 2000 mPas at the temperature of use.

Injection is preferred for the introduction of the liquid hydrophobising agent - alone or with the anhydrite treatment water. In the case of introduction together with the moistening water, mixing-in is sufficient on account of the large quantity of water. In some embodiments, it is preferable for suspensions or emulsions to be first prepared from the hydrophobising agents, which are then combined with the water for the continuous mixer or moistening water. 0.002 to 0.015 kg per kg of the mixture of stucco gypsum and fibres has proved to be suitable as the quantity of hydrophobising agents, any water contained in the hydrophobising agent, for example when use is made of a suspension or emulsion, not being included in this calculation. It is common practice to the person skilled in the art that, apart from the constituents stucco gypsum, fibres and hydrophobising agent, other standard auxiliary agents, in particular setting accelerators, setting retardants, detergents, dyes, can be included in the production of the gypsum fibre boards. The subject-matter of the invention is also a gypsum fibre board which can be obtained by the process according to the invention. It differs from gypsum fibre boards in which a surface impregnation takes place, in particular by the fact that the complete board is hydrophobised. Such a gypsum fibre board preferably conforms to the typing GF-H according to EN 15283-2. The invention is explained in greater detail by the following examples.

-8 Example A fine-particle stucco gypsum was provided, which has a mass through-pass of 85% on the 63 pm serve. The fine-particle stucco gypsum is conditioned for the reduction of the AIII content in a continuous mixer with a device for water injection and a metering device, wherein water metered with 0.03 kg per kg stucco gypsum is injected into the continuous mixer. In order to achieve the desired hydrophobisation of the complete gypsum fibre board, liquid methyl hydrogen polysiloxane in a quantity of 0.01 kg per kg of stucco gypsum is added to the water for the anhydrite treatment. Cellulose fibres were obtained from paper waste and were processed in such a way that 40% of the fibres were smaller than 90 pm. 100 kg of a fine-particle pre-treated stucco gypsum was mixed intimately with 18 kg of cellulose fibres in a main mixer. The dry gypsum fibre mixture thus obtained was spread uniformly onto be moving sieve belt. The moistening of the mixture with moistening water in the ratio 1 to 0.8 was carried out on the sieve belt. The moistened gypsum fibre mixture was pressed to the desired board thickness in the press working line. During this process, the mixture was completely moistened and a major part of the excess water was expelled. The continuous gypsum fibre board strand thus obtained was brought to the desired board format by means of water-cutting.

- 9 The still moist gypsum fibre boards were transported on the setting belt to a multistage dryer and dried here to a residual moisture of < 1%. After the drying, the board surfaces were ground and the formation of the desired edges took place. Finally, the gypsum fibre boards were palettised. The boards met the conditions of the GF-H board.

Claims

1. A process for producing a hydrophobised gypsum fibre board, comprising the steps - provision of stucco gypsum - provision of fibres - introduction of the stucco gypsum together with fibres into a main mixer - spreading the mixture of stucco gypsum and fibres on a moving sieve belt - moistening the mixture of stucco gypsum and fibres with moistening water - pressing the moistened mixture in order to obtain a gypsum fibre board strand, characterised in that at least the stucco gypsum is mixed with a hydrophobising agent in liquid form.

2. The process according to claim 1, wherein the stucco gypsum is mixed with the hydrophobising agent in a pre-mixer.

3. The process according to claim 1 or 2, wherein the stucco gypsum together with fibres is mixed with the hydrophobising agent in the main mixer.

4. The process according to any one of claims 1 to 3, wherein the mixture comprising stucco gypsum and fibres is mixed with the hydrophobising agent in a post-mixer. - 11

5. The process according to any one of claims 1 to 4, wherein water is additionally added in order to convert anhydrite III into stucco gypsum.

6. The process according to claim 5, wherein the hydrophobising agent is introduced together with the water.

7. The process according to any one of claims 1 to 6, wherein the hydrophobising agent is added as solutions, suspension or emulsion.

8. The process according to any one of claims 1 to 7, wherein 0.1 to 0.3 parts by weight of fibres per part by weight of stucco gypsum are prepared.

9. The process according to any one of claims 1 to 8, wherein the fibres are cellulose fibres, synthetic mineral fibres or mixtures thereof.

10. The process according to any one of claims 1 to 9, wherein the quantity of moistening water lies at 0.6 to 1.0 kg per kg of the mixture of stucco gypsum and fibres.

11. The process according to any one of claims 1 to 10, characterised in that the hydrophobising agent is an organic silicon compound, in particular a potassium methyl siliconate solution or a methyl hydrogen polisiloxane, which is preferably used in the form of an emulsion.

12. The process according to any one of claims 1 to 11, characterised in that the quantity of hydrophobising agent amounts to 0.002 to 0.015 kg per kg of the mixture of stucco gypsum and fibres. - 12

13. The process according to any one of claims 1 to 12, characterised in that further additives are added.