DE69405385T2 - FIBROUS PRODUCTS AND METHOD FOR THE PRODUCTION OF FLAME-RETARDANT FIBROUS PRODUCTS - Google Patents

Abstract

The invention relates to organic fiber-based products and a method of manufacturing such products. According to the method, the fibrous raw material is milled together with a fire-retardant agent to a desired degree of defibering to the end of producing an at least essentially fire-retardant product. According to the invention, the fibrous raw material is admixed with at least a portion of the amount of the fire-retardant agent to be used, after which the material is milled to a desired degree of defibering using a refiner capable of exerting a milling action. Accordingly, when making a product suited for use as thermal insulation, 1/4 - 1/2 of the fire-retardant material is introduced to the fibrous base material prior to defibering in anhydrous form and 1/2 - 3/4 of the fire-retardant material is introduced to the fibrous base material after defibering in hydrous form. According to the invention, recycled paper can be used in the production of an at least essentially fire-retardant organic fiber-based material in which the anhydrous component incorporated therein swells during moisturizing, binds the fibers to each other and thus achieves a structure free from self-compressive settling.

Description

The present invention relates to a method according to the preamble of claim 1, which is suitable for producing fibrous products from organic fibers.

According to said method, the fibrous base material is defibrated to a certain degree of defibration and a fire retardant is mixed in so that a substantially flame retardant product is obtained.

According to claim 8, the invention further relates to a substantially flame-retardant organic material based on fibers.

Such a material comprises organic fibres which have been shredded to a desired level of defibration and to which a fire retardant has been added.

The material according to the invention is particularly suitable for use as thermal insulation (insulation) and also as an aggregate for for example road building materials and similar materials which are used in hot form.

Recycling and the reuse of waste materials have become very important in the industrialized world today. Processes have been developed for the use of recycled paper that allow the reuse of these fibers to produce insulation materials, for example. These insulation materials include products known as cellulose blown wool or ecowool, which are widely marketed and a large number of patents are known that relate to them. Since 1977 Patents granted in the United States alone protect 50 types of insulation materials made from wood fibers, the compositions of the fire retardants used with these materials and the manufacturing processes thereof, as well as the composition of the binders used to spray-bond said fibers. Some of the patents further teach the sterilization of said cellulose wool insulation materials so as to improve their resistance to decomposition in the cavity to be insulated.

The insulating properties of materials used to insulate buildings are based on the fact that the insulating materials prevent air circulation in the cavity to be insulated. An ideal insulating material can therefore also be characterized by being able to prevent, to a certain extent, the random movement of air molecules. The latter class includes insulating materials called aerogels, whose pore size is in the order of a few nanometers. The insulating properties can be further improved by filling the cavities of the insulating materials with a gas of low thermal conductivity or materials that provide high IR reflection and are poor heat conductors. The best thermal insulator is obviously a vacuum filled with a multitude of highly reflective surfaces separated from each other. However, these exotic materials cannot be used today for economic reasons to insulate conventional buildings or similar structures.

The thermal conductivity of air is 0.0253 W/mºC, and this value can be almost achieved by expanded polystyrene with a large number of reflective surfaces and a small pore size. The best material that can be obtained from natural sources is cork, which has a thermal conductivity of the order of 0.045 W/mºC at a Density of 140 kg/m³. The thermal conductivities of typical cellulose insulation wool, or ecowool, are at best about 0.034-0.036 W/mºC. The corresponding thermal conductivity of mineral wool, for example, is in the order of 0.040 W/mºC, sometimes 0.038 W/mºC. The advantageous densities are 30-36 kg/m³ for cellulose wool and 30-80 kg/m³ for mineral wool, respectively. The difference relates to the different values of thermal conductivity. The best insulation results for mineral wool, as for many other materials, are achieved using a density of 40-60 kg/m³.

The advantage of insulation materials made from organic fibers compared to insulation materials made from mineral wool, for example, is their high insulation and advantageous production costs. Since it is possible to use recycled paper as a raw material, the competitiveness of these products will be further improved in the future.

Typically, cellulose insulation wool is made by tearing up paper and shredding the paper pieces using, for example, a hammer mill and adding a fire retardant to the shredded fibers to obtain a non-combustible and non-smoldering insulation wool. At the same time, a large number of fire retardants used for this purpose also act as fungicidal and antimicrobial agents, preventing the growth of microorganisms. Typical agents are boron compounds, salts of phosphoric acid, antimony compounds, urea, etc., i.e. they are the same agents that are conventionally used for all other applications to improve fire resistance.

As an example of the prior art, US Patent 4 804 695 is cited, which describes the grinding of a fibrous raw material, which can be either wood or (recycled) paper, together with powdered boric acid (addition of 14% boric acid based on the weight of the fibers) using a hammer mill for the grinding step.

The processes used to produce cellulose wool have some common disadvantages. Namely, the hammer mill that crushes the fibers does not defiber them in the same way as refiners designed for this purpose. This means that the fibers are converted into a form that is detrimental to use as insulating material.

Furthermore, it would be advantageous for the production to mix all the required chemicals, such as fire retardants and preservative chemicals, before the grinding step to ensure that they are mixed homogeneously with the base material. However, this is not possible if defibering refiners are used. The reason for this is as follows:

Typically, fire retardants such as borax or boric acid or soda or mixtures thereof are used in hydrated form to take advantage of their flame retardant ability. In fact, borax and other similar chemicals are most preferably used as flame retardants in their hydrated form because the water of hydration is then released at the lowest possible temperature so that in a fire the heat is adsorbed and the oxygen from the environment of the fibers is captured. Alternatively, if the anhydrous form is mixed with the base material, the anhydrated borax or a similar chemical capable of absorbing water of hydration can later absorb the water of hydration, it being assumed that the required water of hydration is available from the environment, i.e. from the humidity of the surrounding air.

The zelm hydration water, which binds the hydrated borax, is first released at a temperature of 60.8ºC, whereby the borax is converted into the pentahydrate and/or tetrahydrate and later at 95ºC to the dihydrate. When the recycled paper is refined, for example, the dry refining step is carried out using a specific energy input of about 100 kWh per tonne of raw material. Even with these relatively small amounts of specific energy input, the internal temperature of the fibrous material and the temperature of the admixed air and additives are raised to such an extent that a "melting" of the hydrated chemicals in their hydration water is caused, clogging all the grooves in the refiner bars.

In addition to the actual production costs of the insulation materials, the installation of the insulation materials on site is a significant factor in the costs of insulating buildings.

The most cost-effective method of applying insulation is to blow the insulation into the cavities using a stream of air. Cellulose wool and other blowable insulation materials are traditionally best suited to applications involving the insulation of horizontal surfaces where a certain degree of long-term self-compression is not critical. For this reason, the main market for these insulation materials is the insulation of attics of buildings and, to some extent, the insulation of ground floors. In contrast, these insulation materials, which tend to sag due to self-compression, are rarely used for the insulation of wall cavities.

If a loose filling material, such as cellulose wool or mineral wool, is blown into a cavity in a wall of a building, it is essential, for the reasons described above, to use an additional binding agent that is suitable for binding the fibres together so that the subsidence of the insulation is prevented.

However, the addition of these binders brings with it some disadvantages, including:

- unavoidable introduction of moisture into the room that is to be insulated,

- higher consumption of fire retardants, as these bind to the binder,

- Problems related to the volatility of chemicals present in the binder or the action of these agents as a preferred food source for microbes and fungi.

It is an object of the present invention to overcome the disadvantages of the prior art and to provide an entirely new process for producing products based on organic fibers, the products being suitable for use, for example, as blow-in thermal insulation material and as an aggregate in various compositions applied in hot form.

The invention proposes a method as claimed in claim 1.

According to the invention, a fibrillated fibrous product is produced by grinding a suitable raw material of cellulose or lignocellulose in the manner described below. The product is most inexpensively obtained by defibrating recycled paper, but the process is also suitable for producing these products directly from wood or original pulp/paper.

The recycled paper may either contain wood, which means that the newsprint consists mainly of paper made from mechanically obtained pulp, or may be wood-free, which means that the printing paper consists mainly of chemically obtained pulp, or alternatively the paper may contain both of these pulp types, such as LWC paper, which is basically made from mechanically obtained pulp to which chemically obtained pulp has been added as a reinforcing component. Furthermore, the recycled paper may also contain fillers and pigments or may alternatively be substantially free of these.

All the raw material qualities listed above are referred to as "fibrous raw material" in the context of the present invention. The term "paper" is defined to include all paper, cardboard, solid board, and carton qualities with a typical weight in the range of 50-500 g/m².

In a preferred embodiment of the invention, in which the recycled paper is converted into an insulating material, a particularly suitable fibrous raw material is formed from paper which is made at least essentially from lignocellulose pulp (containing wood). An example of such a raw material is newsprint. According to a second preferred embodiment of the invention, in which an aggregate for e.g. asphalt is produced, a particularly suitable fibrous raw material is coated paper which, in addition to pulp, also contains mineral fillers such as clay and/or tallow. This type of paper includes, for example, archival copy paper, magazine paper, art paper, etc. The end product, after shredding, contains approximately 1-50% clay, talc or similar mineral-based fillers which have been used in printing paper.

The fibrous raw material is ground to the desired degree of defibration. In this context, "desired degree of defibration" refers to the fibrillation of the fibrous raw material into smaller pieces. The target size of the pieces depends on the application. According to the first preferred embodiment of the invention mentioned above, the raw material is ground to a particle size of about 0.1-50 mm, advantageously about 1-10 mm. In the second preferred embodiment of the invention the material is ground to a much smaller particle size of typically about 0.01-10 mm, advantageously 0.1-5 mm.

It is essential for the end result of the refining step that attrition of the material is achieved so that defibration of the raw material fibers is achieved, thereby obtaining a fluff-like product (or shredded pulp). Accordingly, disc or cone refiners and similar types of refiners with rotating refiner disc or knives are suitable mills. Particularly suitable refiners are equipped with grooved bars or tipped bars. As described below, a particularly preferred embodiment for defibrating recycled paper uses grooved bars, the grooves being about 5 mm deep and the elevations about 3-5 mm high. Refining with grooved bars can provide a product with a finer degree of defibration than, for example, refining with tipped bars. The typical clear bar spacing used for the refiner for this purpose is in the range of 0.1-0.5 mm for defibrating recycled paper.

In connection with the present invention it has been found that disk and cone refiners can also be used to mix the raw materials to be ground with the fire retardants such as borax, boric acid, soda, urea, alkali metal salts of phosphoric acid, etc., provided that these agents are added in an anhydrous or almost anhydrous form. Particularly advantageous flame retardants are borax, soda or mixtures thereof. Agents advantageously suitable for use as flame retardants are salts which occur as hydrates with at least 5 waters of hydration, advantageously 10 waters of hydration, and also in anhydrous form or in forms with smaller amounts of hydration water. A substantial part of the waters of hydration of the salts is released at a temperature above 30-120°C.

"Flame retardancy" in this context refers to the reduction of the flammability of material, i.e. the conversion of material into a form that is at least substantially non-combustible and non-smoldering.

The flame retardant effect of agents that are added in dry form is not as great as that of compounds that contain water of hydration. According to the invention, it was therefore found that the flame retardant should be added in two parts: in its anhydrous form and its hydrated form. Accordingly, the anhydrous form of the flame retardant, the proportion of which is 1/4 to 1/2, is added before the defibration of the fibrous base material and the other part of the flame retardant, which is 1/2 to 3/4, is added in the hydrated form after the defibration of the fibrous base material.

If the entire amount of flame retardant is added in dry form to the fibrous base material in connection with the refining step, a larger amount of flame retardant is required to ensure initial flame retardancy of the insulation material. In addition, it must be noted that not all of the flame retardant can be added to the fibrous material in anhydrous form because it is difficult to prevent clogging of the groove bars in such a process. In fact, it has been found that anhydrous borax, for example, can be added to the fibers before the refining step at only about 8% of the weight of the fibrous raw material and the bars remain clean and unclogged. Of course, different types of refiner bars are used, but the guideline presented above is valid for bars having grooves of about 5 mm deep and 3-5 mm elevations, which have been found to give an optimal result in dry defibration of recycled paper. The correct choice of this type of rod is important because these rods are able to produce an insulating material that has a density of 30 kg/m³, while an insulation material produced with loaded rods or a hammer mill has an insulation density of 36 kg/m³.

The upper limit for the amount of anhydrous borax or similar flame retardant to be added is generally about 10-15% of the weight of the fibers.

During the milling step, the raw material is advantageously mixed with other materials, in particular those which are themselves to be milled. Therefore, the flame retardants are preferably supplemented or augmented using other anhydrous or aqueous salts so that other materials adhere to the fibrous raw material.

The method according to the invention achieves the following advantages, among others:

- Part of the flame retardant can be better distributed among the fibers.

- A disc or cone refiner equipped with grooved or tipped rods can be used.

- The dry fibrous material later becomes moist, i.e. hydration water is collected, causing the insulation material to swell and the fibers to bond to one another, thus forming a non-settling insulation structure.

- The dry, well-dispersed material, which is initially anhydrous but later becomes aqueous by absorption of water of hydration, forms a good substrate also for other agents which are easily bound to the fibers.

In this context, the last point refers in particular to activated carbon.

Advantageously, the removal of dangerous radon can be achieved by the present invention. As the insulation of buildings is improved, making the buildings more airtight, an increasing problem arises from the entrapment of radon gas entering the buildings. When the floor insulation of the building is carried out according to the invention, the insulation material is advantageously supplemented with activated carbon, the function of which is to adsorb the radon gas escaping from the ground and to hold it until the radioactivity of the radon gas has decayed to an insignificant level. Advantageously, the activated carbon is dispersed as homogeneously as possible under the fibrous base material in order to maximize the statistical probability of adsorbing radon atoms.

The activated carbon is advantageously added to the fibers in an amount of 1-20%, advantageously 1-5%, based on the weight of the fibrous base material, while the anhydrous inorganic agent, which is able to collect later hydration water, is mixed in an amount of 2-8%, based on the weight of the fibrous base material, and both agents are mixed with the fibrous base material before the milling step. After the milling step, the hydrated parts of the fire retardant agent can be mixed into the material in a conventional manner.

Thanks to its non-settling structure, the insulating material according to the invention can also be used to insulate vertical walls, for example by blowing the insulating material based on organic fibers into the cavities of the wall.

Example

Organic fibre-based products suitable for use as insulation have been manufactured from recycled paper, consisting mainly of newsprint. The recycled paper was first torn into coarse pieces, then 2-8% anhydrous borax, based on the weight of the fibrous material, was added to the paper-based material. The mixed material was defatted in a disc refiner equipped with grooved bars to relatively coarse flakes with a particle size of about 1-5 mm. Then 12-20% hydrated borax, based on the weight of the fibrous base material, was mixed into the flakes.

For comparison, reference flakes were prepared to which all the borax was added in hydrated form after the milling step.

Tests carried out on the materials show that flame retardants introduced in dry, anhydrous and finely powdered form later absorb hydration water, resulting in this insulation material settling in vertical cavities only to a small extent of about 5-20% compared to the settling of a comparable insulation material in which all of the flame retardant was added in hydrated form after the milling step of the fibrous base material.

Claims (17)

1. A process for producing a substantially fire-resistant product from a fibre-based material, which process comprises - the base material is defibrated to a certain degree and - a fire retardant is added, characterized in that - the fibre-based material is refined in a refiner equipped with corrugated rods for defibering the fibres, - an inorganic salt is used as a fire retardant, which absorbs water of hydration and occurs in both hydrate and anhydride form, and - 1/4 to 1/2 of the fire retardant in anhydride form is added before defibration, and - 1/2 to 3/4 of the fire retardant material in hydrate form is added to the fiber-based material after defibering. 2. Process according to claim 1, characterized in that borax, soda or a combination thereof is used as the fire-retardant material. 3. Process according to claim 1, characterized in that the grinding is carried out with a disc or cone refiner. 4. A process according to claim 1, characterized in that the fire retardants are replaced by other salts which are present as hydrate in Anhydride form, can be supplemented or improved after incorporating other substances into the fibers. 5. A method according to claim 1, characterized in that the anhydrous fire retardant is mixed with the fiber-based material to not more than 10 to 15%, advantageously not more than 8% of the fiber dry weight of the base material. 6. Process according to claim 1, characterized in that the defibration of the anhydrous agent to the base material is supplemented by the grinding of activated carbon to the fibers in about 1 to 20% by weight of the base fiber material weight. 7. Use of the process according to claim 1 for the production of thermal insulation material or aggregates for asphalt and similar coatings which are applied in hot form. 8. Thermal insulation material, characterized in that it was manufactured according to claim 1. 9. Thermal insulation material according to claim 8, characterized in that the fire retardants consist of salts which are capable of absorbing at least 5 molecules of water of hydration and also of occurring in anhydride form or in a form with smaller amounts of water of hydration. 10. Thermal insulation material according to claim 8, characterized in that the salts used as fire retardants are capable of releasing a substantial amount of their hydration water at a temperature above 30ºC but lower than 120ºC. 11. Thermal insulation material according to claim 8, characterized in that it contains 1 to 20% powdered activated carbon, based on the dry weight of the fibers. 12. Thermal insulation material according to claim 8, characterized in that, in addition to the salts acting as fire retardants, it also contains other anhydrous or hydrous salts which are capable of binding other materials to the fibers. 13. Thermal insulation material according to claim 8, characterized in that it contains recycled paper which has been shredded into a fluff with a particle size of about 0.1 to 50 mm, advantageously 1 to 10 mm, and mixed with borax, soda or a mixture thereof. 14. Thermal insulation material according to claim 13, characterized in that the fibers are defibrated from recycled paper containing at least substantially wood fibers. 15. Aggregate for asphalt and similar coatings applied in hot form, characterized in that it was manufactured according to claim 1. 16. Aggregate according to claim 15, characterized in that the fibers consist essentially of defatted organic fibers which have been ground to a particle size of about 0.01 to 10 mm, advantageously 0.1 to 5 mm, wherein the said organic fibers have been defatted from recycled paper containing mineral precipitants. 17. Aggregate according to claim 16, characterized in that it contains about 1 to 50% clay and/or tallow as mineral filler.