WO1996000763A1

WO1996000763A1 - Fire protecting agent

Info

Publication number: WO1996000763A1
Application number: PCT/NO1995/000113
Authority: WO
Inventors: Arve VALSØ; Egil Kleven; Kalman Nagy
Original assignee: Fireguard Scandinavia A/S
Priority date: 1994-06-28
Filing date: 1995-06-27
Publication date: 1996-01-11
Also published as: SE9604745D0; NO942438D0; SE510143C2; DE19581683T1; SE9604745L; FI965112A0; FI965112A; DK146496A; AU2899795A

Abstract

Fire and smoke retarding water based composition and a method for one-step impregnation of water absorbable and normally combustible materials, such as wood or timber, paper or textiles, said composition comprising ammoniumphosphates, water soluble metal salts and optionally other additives, such as fungicides. The composition comprises in combination: 0.5-40 weight % monoammoniumphosphate and/or diammoniumphosphate, 5-30 weight % water soluble and dissociatable ammonium compound, 10-60 % water soluble metal salt with ability to form water insoluble salts with phosphate ions and/or ammoniumphosphate ions, 0-30 weight % phosphoric acid (85 %), 1-20 weight % acetic acid, and optionally maximum 5 weight % additives in a total concentration of from 1 to 55 weight % with respect to the total weight of the water solution.

Description

Fire protec ting agent

The present invention concerns a fire retarding agent and a method for protecting impregnable and normally combustible material, such as wood and textiles.

Background

There are a lot of known fire retarding agents for impregnating of combustible material. The problem with known agents is in general sweating of the impregnating agent and discoloring of the impregnable material, the time and cost involved in multi step impregnation, toxicity, and ineffective fire protection and smoke retardation. NO Patent 167400 describes a fire and smoke retarding agent comprising mono ammoniumphosphate and/or diammoniumphosphate and/or ammoniumsulphate, NaHCO₃, EDTA, phosphoric acid (85%), and optionally common additives. This agent is used to impregnate wood, among other things. A drawback of this agent is the occurence of sweating of the impregnated agent from the substrate material due to the influence of humidity. This is particularly relevant with timber, which requires a high content of fire protecting agent, which again requires impregnation by means of relatively large volumes of a liquid carrier (water). The absorbed fire protecting compounds will by the external influence of humidity migrate in the substrate material to even out the concentration gradient. The substrate material can then after a certain period of time lose at least part of its fire protection.

GB Patent 1.171.475 (Blunt) describes a method for providing fire protecting impregnation of timber. According to this publication, the timber is impregnated in a first step by a buffered (pH 5-6) solution of diammonumphosphate, and in a second step by a solution of magnesium sulphate, thus forming an insoluble magnesium- ammoniumphosphate. Moreover, in the introductoion of the patent specification it is mentioned that it is known to impregnate timber by precipitation of an insoluble metal phosphate at acidic conditions. However, this method is said to cause problems with for example corrosion defects on metal components located adjacent to impregnated timber or wood caused by remaining acidic impregnating solution, including leaching of impregnating material. The originators of this british invention have consequently chosen to impregnate in the absence of acid. A first drawback with Blunt¹ s method is that the process steps including a first impregnation, draining, second impregnation and subsequent drying will hardly secure a sufficient depth of impregnation of large sized material. Material impregnated in accordance with this method will therefore in many cases not fulfil Norwegian requirements for fire technical classification. A second and at least equally important disadvantage is that the impregnation must be performed in two steps to avoid precipitation of the metal phosphates prior to penetration into the material. If one nevertheless should obtain a fairly acceptable non-hygroscopic result with Blunt¹ s method, the draining after the first impregnation step would have to be replaced by a time consuming drying step. A two-step drying process involves risk of loss caused by increased handling of the material. These factors may again impose increased price of impregnated material.

Object

The main object of the present invention is to provide an agent and a method for the impregnation of water absorbable and normally combustible material, which despite a one-step impregnation achieves a proper retention of fire and smoke retarding agent even at influence of external humidity, and fulfil the highest fire technical classification requirements according to the Norwegian Standard.

Another object of the invention is to provide such an agent which avoids the problems with discoloring of impregnated timber or wood.

The invention The objects above are fulfilled by a method according to the characterizing part of claim 5 and an agent according to the characterizing part of claim 1. Further favourable features appear from the corresponding dependent claims. According to the invention there is provided a fire, and smoke, retarding water, based composition for use in a one-step impregnation of water absorbable and normally combustible materials, such as wood or timber, paper, and textiles such as rayon, cotton and wool, said composition comprising ammoniumphospates, water soluble metal salts and optionally additives, such as fungicides. The composition is characterized by comprising:

0.5-40 weight% monoammoniumphosphate and/or diammoniumphosphate, 5-20 weight % of a water soluble and dissociateable ammonium compound,

10-60% water soluble metal salt with ability to form water insoluble salts with phosphate ions and/or ammonium phosphate ions, 0-30 weight% phosphoric acid (85%), 1-20 weight % acetic acid, and optionally maximum 5 weight % additives in a total concentration from 1 to 55 weight % with respect to the total mass of the water based solution.

The materials are impregnated in a manner known per se which secures, a sufficient absorption of the agent in accordance with the invention, such as dipping or pressure- vacuum impregnation.

After impregnation, the material is dried at conditions securing remowal of water and acetic acid (HAc) from the impregnation solution. The gradual removal of HAc results in a gradual change of pH of the impregnated solution, which in turn effect a precipitation of water insoluble metal phosphates and/or metal ammoniumphosphates from the ammoniumphosphates and the phosphoric acid. The impregnated material will in this way exhibit a high and uniformly distributed content of fire retarding water insoluble salts, such as metal ammoniumphosphate and metal phosphate, without presence of corrosive acid. In addition, the impregnated material fulfils the highest requirements with regard to the Norwegian Standard of fire technical classification, and is neutral with respect to colour change of the impregnated material. The present fire and smoke retarding composition also enables one-step impregnation, which particularly in the production of fire retardant timber or wood results in substantial savings in cost and time. In further detail, the agent of the present invention can be prepared by blending two separate components a) and b): component a) comprising water, mono- and/or diammoniumphosphate, optionally phosphoric acid and an ammonium compound having the ability to dissociate in water, such as ammoniumacetate, ammoniumsulphite, ammoniumsulphate, ammoniumchloride and ammoniumnitrate, preferably ammoniumacetate, wherein the content of and the ratio between water and the ammonium salts and optionally phosphoric acid, is selected to obtain a pH of 3-6, component b) water, acetic acid and at least one water soluble metal salt having the ability to form water insoluble salts with phosphate ions and/or ammoniumphosphate ions, such as magnesiumsulphate and/or magnesiumacetate, the content of and the ratio between water and acetic acid is selected to obtain a pH in the range 1.5-3.2, and component a) and b) are blended preferably at ambient temperature and pH-adjusted with ammoniumacetate or an acid, preferably 50% phosphoric acid, and optionally supplied with additives, thus forming a one-component fire and smoke retarding impregnation solution having a pH in the range 1.5-4.3. In cases where the requirements of corrosion inhibition are less stringent, phosphoric acid can be replaced by other inorganic acids, such as HC1 or H₂SO₄.

Topical metal salts for use in the present invention are salts that form insoluble phosphates or ammoniumphosphates in the impregnated material. Examples of such metals are the earth alkaline metals Ba, Ca and Mg, and metals from group IV of the periodic system, such as Fe, Cu and Zn. Examples of suitable metal salts for use with the present invention are chlorides of Cu, Zn, Ba, Ca, Mg and Fe, sulphates or Cu, Zn, Fe, Mg, and acetate of Ca, Cu, Zn and Mg. Magnesiumsulphate is preferred for several reasons: low price, low toxicity, good solubility in the parent solution prior to impregnation, and low solubility after impregnation and drying, e.g. in the form of magnesiumammonium-phosphate. However, persons skilled in the art would be able to reveal other metal salts suitable for use with the present invention with support from the present description and their ordinary knowledge.

Suitable ammonium compounds for use in component a) above can be any compound which dissociates in the water based solution and forms ammonium ions. Preferred ammonium compounds are ammoniumacetate and/or ammoniumsulphate, which by a change of pH during the drying step are included in the formation of insoluble metal ammonium phosphates.

The impregnated solution may have a varying content of salts, according to the material absorbed and the extent of desired fire retardant effect. Timber requires for example a relatively high content of salts, e.g. at least 20 weight% (in the timber), whereas other materials often require less salts. Dependent on the content of for example Mg salts, at least a portion of the magnesiumsulphate can be substituted by magnesiumacetate to decrease the sulphate concentration in the solution. The impregnation solution can be incorporated into the substrate material in a manner known per se. With regard to timber, for example conventional pressure impregnation processes are suitable.

In the preparation of material which is hard to impregnate or material having a relatively large thickness, such as timber, it is preferred to dry the impregnated material in an atmosphere with a gradually decreasing humidity content. If e.g. impregnated timber is dried in an atmosphere with a low humidity content, an increased drying temperature must be used, or a disproportionately long time will have to be used to remove the substantial part of the acetic acid remaining in the timber, if at all possible. However, high drying temperatures weaken the timber strength substantially, for example about 50% at a drying temperature of 120° C. In order to avoid weakening of the timber strength and effect removal of the acetic acid component, it is preferred to dry the timber for 1-3 weeks at about 60 °C and in an atmosphere having a gradually decreasing humidity content, for example from 100% RH at the beginning and down to 20% RH at the end of the drying step. Moreover, it is preferred to dry the timber with exhange of air in order to keep the partial pressure of acetic acid at an acceptable low level in view of the concentration gradient during the stripping of the same from the timber. Time, temperature, and humidity conditions may vary from one type of material to another, and may vary with the dimension of the material. Without wish to be bound by any particular theory or explanation, it is believed that drying in an atmosphere having a gradually decreasing humidity content will prevent concentration of HAc and strip off the binary system water/acetic acid with an accompanying increase of pH, e.g. to 4.5, and gradually precipitate fire protecting phosphates and ammoniumphosphates. The resulting impregnation will in this way be uniformly distributed in the material, and will also be water insoluble and non- hygroscopic. Moreover, experiments carried out in connection with the present invention show that timber impregnated and dried in this manner is practically free from residual acetic acid.

The timber impregnated in this way fulfil, thanks to the high solid content after drying, the highest classification for organic material according to the Norwegian Standard 3919, and do not involve drawbacks with regard to discoloring of the timber or corrosion of metal components located inside or adjacent to the impregnated timber.

The invention is described in further detail in the following in view of the attached figure, which illustrates the results from fire technical tests performed on pinewood impregnated with a composition according to the invention. A preferred composition according to the present invention for timber, without additives, comprises:

Monoammoniumphosphate 0.5 20 Weight%

Ammoniumsulphate 0.5 20 Weight %

Ammoniumacetate 10.0 - 20 Weight% Magnesiumsulphate 5.0 40 Weight%

Magnesiumacetate 10.0 - 20 Weight %

Phosphoric acid 85% 15.0 - 30 Weight %

Acetic acid 10.0 - 20 Weight %

This composition has the benefit that the impregnated wood exhibits good fire protection, low hygroscopisity, good basis for applying e.g. varnishes and stain, including low corrosion of nails and similar located inside or adjacent to the wood.

Supply of magnesium salts is performed to tie up the magnesium ions to water insoluble magnesium phosphates and magnesium ammonium phosphates. In addition, a lattice-forming substance can be added, for example in the form of a polymer- forming organic monomer, which also improves fixation of the salts and renders wood based products and other combustible water absorbant materials more resistant to leaching after impregnation.

Preparation of a preferred solution for impregnation As stated above, the impregnation solution is prepared from the preferred composition above in two separate batches, which then are combined and pH adjusted to a range of 1.5 to 4.3. However, the blending of the respective components may also occur in one step, but with regard to possible precipitation at preparation of concentrated solutions, it is usually preferred to divide the preparation of the composition in two steps or batches.

Composition A.

To an appropriate volume of water and a suitable container of plastic or stainless steel provided with a stirrer and pH gauge is added: a) monoammoniumphosphate with constant stirring until all have been dissolved b) ammoniumsulphate with continued stirring, and the stirring is continued until all has been dissolved c) magnesiumsulphate with continued stirring, and the stirring is continued until all has been dissolved.

Composition B.

To an appropriate volume of water and a suitable container of plastic or stainless steel provided with stirrer and pH gauge is added: a) magnesiumacetate with constant stirring until all have been dissolved, and b) acetic acid during constant stirring until a pH of 1.5 - 3.2 is obtained, preferably pH 2.0.

The composition B is added to composition A with constant stirring. The pH is adjusted to 3.5-3.7 with ammoniumacetate to increase pH if required, or phosphoric acid to decrease pH if required. After a certain period of time with stirring, the stirring is terminated, and the solution is allowed to rest for settling. Alternatively, the pH of the solution can be decreased with sulphuric acid, hydrochloric acid and/or acetic acid, and increased with alkaline compounds such as ammonium hydroxide. However, ammoniumacetate is preferred because of its fire retardant effect after precipitation in the impregnated material.

Impregnation of timber or wood

Impregnation of timber or wood is best performed in a conventional impregnation plant for wood. After the wood has been placed in the impregnation plant, the wood is subjected to a low pressure of 50 mbar for at least 20 minutes. Impregnation solution is supplied into the impregnation plant, and the wood is pressurized, preferably to 16 bar until the desired amount of liquid has penetrated the wood (2-10 hours).

The solution should contain from 5 to 55 weight percent of solids with regard to the total weight of the solution, e.g. having the preferred composition as stated above. The wood is dried in a conventional wood dryer preferably at 60° C, and in an atmosphere having a gradually decreasing humidity content and continous or batchwise removal of acetic acid from the drying atmosphere to maintain a concentration gradient of acetic acid during the stripping of the same, whereby the acetic acid is stripped off the wood. After drying the wood should contain 15-40 weight percent of the impregnated composition (solids) with respect to the mass of dry wood.

Impregnation of textiles Textiles of rayon, cotton, wool, composite textiles or textiles of other combustible and water absorbant materials are dipped in the impregnation solution, or the impregnation solution is sprayed onto the same. The concentration of the impregnation solution will be dependent on the mode of treatment, and will typically be within the range from 5 to 25 weight percent solids on the basis of the total mass of the liquid. Particles having a diameter above 100 micrometer are removed by filtration. After dipping, the excess liquid is pressed out, followed by drying of the textiles. After drying the textiles should exhibit weight increase of 10-15% in the form of solids from the impregnation solution. Impregnation of textiles in accordance with the present invention results in an impregnated material having small sized and uniformly distributed fire retardant metal salts, for example <20 micrometer, and in this way the material will have the same consistency, e.g. softness, even after impregnation. The present invention, contrary to comparable prior art methods, also secures a well controllable impregnation with regard to the amount of fire retardant components absorbed in the textile material.

Impregnation of paper and paper products. Paper and paper products are impregnated in a way similar to impregnation of textiles.

Fire tests In order to demonstrate the effectiveness of the liquid as a fire retardant and smoke retardant agent, a bate of pinewood wainscot having a thickness of 12 mm was impregnated with a liquid prepared in accordance with the method described above with the following compositions:

Table 1

Composistion of different impregnation solutions AA BB CC

(weight %) (weight %) (weight %)

Monoammoniumphosphate 22.20 15.18 Diammoniumphosphate 7.24 Ammoniumsulphate 2.90 3.03 Ammoniumacetate 4.52 0.20 5.06 Magnesiumsulphate ^• 7H₂O 15.38 6.76 8.09 Magnesiumacetate ^• 4H₂O 2.90 3.03 Phosphoric acid (85%) 18.57 6.92 Acetic acid (60%) 7.24 6.76 Additives 4.19 3.03 Water 47.00 54.10 56.64 The wainscot was then tested in accordance with the Nord test-method, which is identical with the standard NS-INSTA 412. The results from this test are shown in Fig. 1-3 for sample AA-CC, respectively, which illustrate that the impregnated pinewood wainscot fulfils the fire technical requirements in NS-INSTA 412 with good margins, both with respect to temperature and in particular with respect to smoke development which in practice is zero. After ten minutes testing time, the measured temperature was about 100°C lower than the accepted temperature limit. During the test period as a whole it no smoke development of importance was detected and far below the acceptable limit.

Hygroscopisity test

Sample pieces of pinewood having a dimension of 230x114x14 mm and impregnated with the solution above, were dried to a humidity content of 20 weight percent and then placed horizontally in an air conditioning chamber with an angle of about 10° and for about 5 days. The air conditioning chamber had a relative humidity xof about 100% and a temperature of about 25°C. Observations and measurements were performed once a day. The samples were then conditioned at ambient temperature until the humidity content of the wood remained stable. The test results did not show any salt expulsion during or after the test period, and the humidity absorption was below the limit level according to ASTM-D3201-86.

The present invention accordingly provides a novel agent for impregnation of normally combustible material, which offers impregnation in one step and fulfils the requirements with respect to hygroscopisity, toxicity, discoloring of impregnated material including corrosion of metal components mounted inside or adjacent to impregnated material.

Claims

Claims.

1. A fire and smoke retarding water based composition for use in one-step impregnation of water absorbant and normally combustible materials, such as wood or timber, paper and textiles, said composition comprising ammoniumphosphates, water soluble metal salts and optionally other additives, characterized in that the composition in combination comprises:

0.5-40 weight% monoammoniumphosphate and/or diammoniumphosphate, 5-30 weight % water soluble and dissociateable ammonium compound, 10-60% water soluble metal salt with ability to form water insoluble salts with phosphate ions and/or ammoniumphosphate ions, 0-30 weight % phosphoric acid (85%), 1-20 weight % acetic acid, and optionally maximum 5 weight % additives in a total concentration of from 1 to 55 weight % with respect to the total mass of the water solution.

2. A Composition in accordance with claim 1, characterized in that the metal salt comprises chlorides of Cu, Zn, Ba, Ca, Mg, Fe, sulphates of Cu, Zn, Fe, Mg, acetates of Ca, Cu, Zn, Mg, or mixtures of such.

3. A composition in accordance with claim 1, characterized in that the metal salt comprises magnesiumsulphate and/or magnesiumacetate.

4. A composition in accordance with any one of claims 1 to 3, characterized in that the water soluble ammonium compound comprises ammoniumacetate and/or ammoniumsulphate.

5. A method for impregnation of water absorbant and normally combustible materials, such as wood or timber, paper and textiles with a composition comprising ammoniumphosphates, water soluble metal salts and optionally other additives, for the formation of water insoluble and fire retardant salts, particularly metal ammoniumphosphates and metal phosphates, characterized in: a) providing a fire retardant water based impregnation solution comprising

0.5-40 weight% ammoniumphosphate and/or diammoniumphosphate, 5-30 weight% water soluble and dissociateable ammonium compound, 10-60% water soluble metal salt with the ability to form water insoluble salts with phosphate ions and/or ammoniumphosphate ions, 0-30 weight% phosphoric acid (85%), 1-20 weight % acetic acid, and optionally maximum 5 weight % additives in a total concentration of from 1 to 55 weight % with respect to the total weight of the water solution, b) impregnating the material in question in one step by means of a method known per se, such as dipping, sputtering or pressure-vacuum impregnation, c) drying said impregnated material to remove acetic acid and water from the impregnation solution.

6. The method of claim 5, characterized in that said metal salt comprises at least one of the salts selected from the group consisting of chlorides of Cu, Zn, Ba, Ca, Mg, Fe, sulphates of Cu, Zn, Fe, Mg, and acetates of Ca, Cu, Zn, Mg.

7. The method of claim 5, characterized in that said metal salt comprises magnesiumsulphate and/or magnesiumacetate.

8. The method of any one of claims 5 to 7, characterized in that said water soluble ammonium compound comprises ammoniumacetate and/or ammoniumsulphate.

9. The method of any one of claims 5 to 8, characterized in drying material having large thickness in an atmosphere with a gradually decreasing humidity content.