EP0694094B1

EP0694094B1 - Fibrous products and a process for preparing flame retardant fibrous products

Info

Publication number: EP0694094B1
Application number: EP94911975A
Authority: EP
Inventors: Reijo Louko; Heikki Ahonen
Original assignee: EKOVILLA Oy
Current assignee: EKOVILLA Oy
Priority date: 1993-04-15
Filing date: 1994-04-15
Publication date: 1997-09-03
Anticipated expiration: 2014-04-15
Also published as: ATE157716T1; WO1994024359A1; EP0694094A1; FI931721A0; FI95401B; DE69405385T2; DE69405385D1; AU6431294A; FI931721A; FI95401C

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 suited for manufacturing fibrous products made from organic fibers.
According to said method, the fibrous raw material is defibered to a desired degree of defibering and a fire-retardant agent is admixed with it to the end of manufacturing a product of essential flame-retardancy.
The invention also concerns an essentially fire-retardant organic fiber-based material according to claim 8.
Such a material is comprised of organic fibers milled to a desired degree of defibering and admixed with a fire-retardant agent.
The material according to the invention is suited for use particularly as a thermal insulation and also as an aggregate in, e.g., road pavement materials and similar materials applied in hot form.
Recycling and reuse of waste materials have gained a wide importance in today's industrialized world. To utilize recycled paper, methods have been developed permitting the reuse of such fibers in the manufacture of, e.g., thermal insulation materials. These insulation materials include products called, among other names, as cellulosic blow wool or Ecowool, are widely marketed and a plurality of patents related thereto are known. In fact, since 1977 in the USA alone, the patents granted cover 50 types of thermal insulation materials made from wood fiber, the composition of fire retardant agents used with such materials and manufacturing methods thereof, as well as binding agent compositions used for spray-bonding of the said fibers. Some of the patents also teach the sterilization of said cellulosic wool insulation material to the end of improving its resistance against decay in the insulation cavity.
The thermal insulation capability of materials used for thermal insulation of buildings is based on the fact that the insulation material prevents air circulation in the insulation cavity. An ideal insulation material would be characterized by also to a certaing extent being capable of preventing the random movement of molecules in the air. The latter category includes insulation materials termed aerogels in which the pore size is in the order of a few nanometers. The insulation performance can also be improved by filling the voids in the insulation material with a gas of low thermal conductivity or such materials that provide a high reflectance to IR radiation and are inferior heat conductors. Obviously, the most effective thermal insulation is a vacuum complemented with a plurality of high-reflectance surfaces spaced from each other. However, such exotic materials cannot be economically used in these days for the thermal insulation of a conventional building or similar structure.
The thermal conductivity of air is 0.0253 W/m°C, which value can be closely attained by expanded polystyrene having a plurality of reflecting surfaces and a small pore size. The best material available from natural sources which is cork that has a thermal conductivity in the order of 0.045 W/m°C at a density of 140 kg/m³.
The thermal conductivities of typical cellulosic insulation wool, or Ecowool, are approx. 0.034 - 0.036 W/m°C at best. Correspondingly, the thermal conductivity of, e.g., mineral wool is in the order of 0.040 W/m°C, sometimes 0.038 W/m°C. Respectively, the advantageous densities are 30 - 36 kg/m³ for cellulosic wool and 30 - 80 kg/m³ for mineral wool. The difference is related to the different values of thermal conductivity. As for many other materials, the best insulation results are obtained using a density of 40 - 60 kg/m³ for the mineral wool.
The benefits of thermal insulation products made from organic fibers in regard to, e.g., mineral wool insulation materials are their high thermal insulation capability and advantageous production costs. Owing to the possibility of using recycled paper as the raw material, the competitive edge of these products will be further improved in the future.
Typically, cellulosic insulation wool is made by shredding paper and milling the shreds by means of, e.g., a hammer mill and admixing the milled fibers with a fire-retardant agent to render the insulation wool noncombustible and nonsmouldering. Simultaneously, a great number of the fire-retardant agents used therein also act as fungicidal and antimicrobial agents that inhibit the growth of such microorganisms. Typical of such agents are boron compounds, salts of phosphoric acid, antimony compounds, urea etc., that is the same agents that are conventionally used in all other applications of fire resistance improvement.
As an example of the prior art, reference is made to US patent publication 4,804,695 comprising milling fibrous raw material, which can be either wood or (recycled) paper, together with pulverized boric acid (adding boric acid by 14 % of the weight of the fibers) using a hammer mill for the milling step.
Concurrent processing techniques of cellulosic wool have some drawbacks. Namely, the hammer mill crushes the fibers but does not defiber them in the same manner as purpose-designed refiners. Such crushing of the fiber converts it to a form which is disadvantageous in terms of the thermal insulation function.
Further, it would be advantageous in terms of production to blend all required chemicals such as the fire-retardant agents and preservation chemicals already prior to the milling step in order to ensure their homogeneous mixing with the base material. This, however, is not possible when using defibering refiners. The reason is as follows:
Typical fire-retardant agents such as borax or boric acid or soda or mixtures thereof are used in hydrated form to exploit their fire-retardant capability. In fact, borax and other similar chemicals are preferably used as fire-retardant agents particularly in their hydrated forms as then the water of hydration is released at the lowest possible temperature thus absorbing heat and capturing oxygen from the surroundings of the fiber in a fire situation. Alternatively, if admixed with the base material in anhydrated form, anhydrated borax or other similar chemical capable of absorbing water of hydration can later absorb the water of hydration assuming that the required water of hydration is available from, e.g., the humidity of the surrounding air.
The ten waters of hydration bound by hydrated borax are first released at 60.8 °C temperature when the borax is converted into pentahydrate and/or tetrahydrate, and later at 95 °C to dihydrate. When milling recycled paper, for instance, the dry milling step is conventionally carried out using a specific input energy of approx. 100 kWh per ton of raw material. Already at such a relatively low level of specific input energy, the internal temperature of the fibrous material and the temperature of entrained air and additives are elevated so much as to cause the "melting" of hydrated chemicals in their contained water of hydration, whereby plugging of all grooves in the refiner bars results.
In addition to the actual production costs of insulation materials, the in situ installation of the insulation material forms a significant factor in the thermal insulation costs of buildings.
The lowest-cost installation method of thermal insulation is blowing by means of an air flow to the insulation cavities. Cellulosic wool and other blowable insulation materials are conventionally best suited for use in applications involving insulation of such horizontal surfaces on which a certain degree of long-term self-compressive settling is not crucial. Due to this reason, the major market for these insulation materials has principally been in the insulation of attic floors of buildings, and also to some extent, of ground floors. By contrast, these insulation materials which tend to settle under self-compression have rarely been used as such in the insulation of wall cavities.
When blowing a loose-fill material such as cellulosic wool or mineral wool into a cavity to be insulated in the wall of a building, the above-described reasons have invariably necessitated the coapplication of a binder suited to bind the fibers together so as to prevent the settling of the installed insulation.
However, such addition of binding agents brings about several drawbacks including:

unavoidable introduction of moisture into the space to be insulated,
higher consumption of fire-retardant agent(s) due to added binding agents,
problems incurred by volatile chemicals contained in the binding agents or from the acting of such agents as a favoured nutrient for microbes and fungal hyphae.

It is an object of the present invention to overcome the disadvantages of the prior-art technology and to achieve an entirely novel method of manufacturing such organic fiber-based products which are suited for use as, e.g., blowable thermal insulation materials and aggregates in various compositions applied in hot form.
The invention proposes a method as claimed in claim 1.
According to the present invention, a fibrillated fibrous product is produced by milling a suitable cellulosic or lignocellulosic raw material in the manner described below. The cheapest product is achieved by defibering recycled paper, while the method is also suited for making products directly from wood or virgin pulp/paper.
The recycled paper can be either groundwood-containing, that is, newsprint essentially consisting of paper made from mechanical pulp, or groundwood-free paper which is printing paper essentially made from chemical pulp, or alternatively, paper containing both of these pulp types such as LWC paper principally made from mechanical pulp with chemical pulp admixed as a strength-imparting component. Furthermore, the recycled paper may contain fillers and pigments, or alternatively, be essentially free from these.
All the above-listed raw material grades are termed as "fibrous raw material" in the context of the present invention. The term "paper" is defined to include all grades of paper, paperboard, cardboard and board with a basis weight in the range of 50 - 500 g/m² typical.
In a preferred embodiment of the invention, in which recycled paper is processed into a thermal insulation material, a particularly suitable fibrous raw material is formed by paper at least essentially made from lignocellulosic (wood-containing) pulp. An example of such raw material is recycled 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 containing besides pulp, also mineral fillers such as clay and/or talc. This kind of paper includes, e.g., archive-proof copying papers, magazine papers, art printing papers, etc. The end product contains after milling approx. 1 - 50 % clay, talc or similar mineral-based filler used in printing papers.
The fibrous raw material is ground to desired degree of defibering. In this context, "desired degree of defibering" refers to fibrillation of the fibrous raw material in smaller particles. The target size of the particles varies according to the application.
Accordingly, in the first preferred embodiment of the invention mentioned above, the raw material is ground to a particle size of approx. 0.1 - 50 mm, advantageously approx. 1 - 10 mm. In the second preferred embodiment of the invention, the raw material is ground to a much smaller particle size of typically approx. 0.01 - 10 mm, advantageously approx. 0.1 - 5 mm.
For the end result of the milling step it is essential that an attrition action is attained which leads to the defibering of the raw material fibers, whereby a product resembling fluff (or ripped pulp) is obtained.
Accordingly, suitable mills are disk or conical refiners and similar refiner types having rotary refining plates or knives. Particularly advantageously the refiners are equipped with grooved or tipped bars. As will be described below, a particularly advantageous embodiment employs for the defibering of recycled paper such grooved bars in which the grooves are approx. 5 mm deep and the ridges are 3 - 5 mm high. Milling with grooved bars can provide a product of finer degree of defibering than, e.g., tipped bars. In the refiner used herein, the typical bar clearance is in the order of 0.1 - 0.5 mm for defibering recycled paper.
In conjunction with the present invention it has been found that disk and conical refiners can also be employed for admixing the raw material to be milled with the fire-retardant agents such as borax, boric acid, soda, urea, alkali metal salts of phosphoric acid, etc., provided that these agents are introduced in anhydrated or almost anhydrated form. Particularly advantageous fire retardants are borax, soda or a mixture thereof. Agents advantageously suited for use as fire retardants are salts occurring in forms including at least five waters of hydration, advantageously ten waters of hydration, as well as also in anhydrated forms or forms with a lesser amount of waters of hydration. An essential portion of said waters of hydration of said salts is released at a temperature above 30 - 120 °C.
"Fire retardancy" in this context refers to reduction of the inflammability of a material, that is, conversion of the material to a form which is at least essentially noncombustible and nonsmouldering.
The fire-retardant action of agents mixed in dry form is not as effective as that of compounds containing water of hydration. Consequently, according to the present invention, it has been found advantageous to introduce the fire-retardant agent in two portions: in its anhydrous form and hydrous form. Accordingly, a portion which is 1/4 - 1/2 of the fire-retardant material is introduced in anhydrous form to the fibrous base material prior to defibering, and the other portion which is 1/2 - 3/4 of the fire-retardant material is introduced in hydrous form to the fibrous base material after defibering.
If the entire amount of fire-retardant agents is admixed in dry form with the base material fibers in conjunction with the milling step, a greater amount of the fire-retardant agent(s) is required to ensure the initial fire retardancy of the thermal insulation material. Moreover, it must be noted that not all of the fire-retardant agent can be admixed in anhydrous form with the fibrous material, because such a procedure makes it difficult to prevent plugging of the grooved bars. In fact, it has been found that, e.g., anhydrous borax can be maximally admixed with the fibers prior to the milling step by only approx. 8 % of the weight of the fibrous raw material and still keep the bars clean and unplugged. Of course, several different types of refiner bars are used, but the above-given guideline is valid for bars having an approx. 5 mm deep groove and a 3 - 5 mm high ridge that have been found to render an optimal result in the dry-defibering of recycled paper. The advantageous choice of this bar type is evidenced in that such bars make it possible to produce thermal insulation material having a density of 30 kg/m³, while thermal insulation material produced using tipped bars or a hammer mill gives a density of 36 kg/m³ for the insulation material.
As a general rule, the upper limit for the admixed amount of anhydrous borax or similar fire-retardant agent is approx. 10 - 15 % of the weight of the fibers.
During the milling step, the raw material is advantageously admixed with another material, particularly such that also itself becomes milled. Hence, the fire-retardant agents are complemented or augmented preferably using other anhydrous or hydrous salts to the end of fixing other materials to the raw material fibers.
The method according to the invention achieves the following benefits and others:

A portion of the fire-retardant agent can be better dispersed between the fibers.
A disk or conical refiner equipped with grooved or tipped bars can be used.
The dry fibrous material will later become moist, that is, accumulate water of hydration, whereby the insulation material swells and undergoes mutual binding of the fibers thus providing a nonsettling insulation structure.
The dry, well-dispersed material, which initially is anhydrous but later becomes hydrous through absorbing water of hydration, forms a good substrate also for other agents that can be easily bound to the fibers.

In the present context, the last item above particularly refers to activated carbon.
Namely, elimination of radon hazard can be advantageously achieved according to the present invention. As the thermal insulation of buildings is improved resulting in greater tightness of the building, a growing problem arises from the isolation of radon gas entering the building. When the ground floor isolation of a building is made according to the invention, the thermal insulation material is advantageously complemented with activated carbon, whose function is to adsorb the radon gas emanating from the ground and retain it until the radioactivity of the radon gas has decayed to an insignificant level. Advantageously, the activated carbon is dispersed as homogeneously as possible among the base material fibers to maximize the statistical possibilities of adsorbing radon atoms.
The activated carbon is advantageously admixed with the fibers by approx. 1 - 20 %, advantageously 1 - 5 %, of the base material fiber weight, while the anhydrous inorganic agent capable of later accumulating water of hydration is used by 2 - 8 % of the base material fiber weight, and both of these agents are admixed with the fibrous base material prior to the milling step. Subsequent to the milling step, the hydrous portions of the fire-retardant agents can be admixed with the material in a conventional manner.
Owing to its nonsettling structure, the thermal insulation material according to the invention can also be used for insulating vertical walls by, e.g., blowing the organic fiber-based insulation material into the wall cavity.

Example

Organic fiber-based products suited for use as thermal insulation were manufactured from recycled paper chiefly comprising newsprint. The recycled paper was first ripped into coarse shreds, after which to the paper-based material was added anhydrous borax by 2 - 8 % of the fibrous base material weight. The admixed material was defibered in a disk refiner equipped with grooved bars into a relatively coarse fluff having a particle size of approx. 1 - 5 mm. Subsequently the fluff was admixed with hydrous borax by 12 - 20 % of the fibrous base material weight.
For comparison, a reference fluff was prepared in which all the borax was admixed in hydrous form after the milling step.
Tests performed on the materials indicated that fire-retardant agents introduced in dry, anhydrous, fine-pulverized form later absorbed water of hydration, and resultingly, the settling of these insulation materials in vertical cavities was as little as only approx. 5 - 20 % of the settling of the comparative insulation material in which all of the fire-retardant agent was admixed in hydrous form after the milling step of the fibrous base material.

Claims

A method of manufacturing an essentially fire-retardant product from a fibrous base material, according to which method
- the base material is defibered to a desired degree of defibering and

- a fire-retardant agent is admixed with it,
characterized by
- milling the fibrous base material in a refiner equipped with grooved bars in order to defiber the fibers,

- using as fire-retardant agents inorganic salts which absorb water of hydration in them and occur in both hydrous and anhydrous forms, and

- introducing 1/4 to 1/2 of the fire-retardant agent in anhydrous form prior to defibering and introducing 1/2 to 3/4 of the fire-retardant material to the fibrous base material after defibering in hydrous form.
A method as defined in claim 1, characterized by using at borax, soda or a combination thereof as fire-retarding material.
A method as defined in claim 1, characterized by performing the milling with a disk or conical refiner.
A method as defined in claim 1, characterized by complementing or augumenting the fire-retardant agents by other salts occurring in anhydrous and hydrous forms to the end of bonding other substances to the fibers.
A method as defined in claim 1, characterized by admixing the anhydrous fire-retardant agent with the fibrous base material by not more than approx. 10 to 15 %, advantageously not more than 8 %, of the base material fiber dry weight.
A method as defined in claim 1, characterized by complementing the defibering of the anhydrous agent to the base material with the milling of activated carbon to the fibers by approx. 1 to 20 % of the base material fiber weight.
Use of the method defined in claim 1 in the production of thermal insulation materials or aggregates for asphalt and similar coatings to be applied in hot form.
A thermal insulation material, characterized in that it has been prepared acccording to claim 1.
A thermal insulation material as defined in claim 8, characterized in that the fire-retardant agents are comprised of salts capable of absorbing at least five waters of hydration as well as occurring in anhydrous form or forms of a smaller amount of water of hydration.
A thermal insulation material as defined in claim 8, characterized in that the salts used as fire-retardant agents are capable of releasing an essential fraction of their water of hydration at a temperature higher than 30 °C yet lower than 120 °C.
A thermal insulation material as defined in claim 8, characterized in that it contains 1 to 20 % pulverized activated carbon based on the dry weight of the fibers.
A thermal insulation material as defined in claim 8, characterized in that it contains besides salts acting as fire-retardant agents also other anhydrous and hydrous salts capable of bonding other materials to the fibers.
A thermal insulation material as defined in claim 8, characterized in that it comprises recycled paper shredded to a fluff with a particle size of approx. 0.1 to 50 mm, advantageously 1 to 10 mm, admixed with borax, soda or a mixture thereof.
A thermal insulation material as defined in claim 13, characterized in that the fibers are defibered from at least essentially wood-fiber-containing recycled paper.
An aggregate for asphalt and similar coatings applied in hot form, characterized in that is has been prepared according to claim 1.
An aggregate as defined in claim 15, characterized in that the fibers are essentially comprised of defibered organic fibers milled to a particle size of approx. 0.01 to 10 mm, advantageously 0.1 to 5 mm, said organic fibers being defibered from recycled paper containing mineral fillers.
An aggregate as defined in claim 16, characterized in that it incorporates as mineral fillers approx. 1 to 50 % clay and/or talc.