Fire-retardant cellulose insulation and process for making same

A fire-resistant, cellulose insulation and method, the cellulose insulation including a predetermined quantity of talc to impart the desired degree of fire-resistant characteristics to the cellulose. If desired, limited quantities of boron compounds can be added with the talc. The method includes directing ground cellulose from the primary grinding stage into a surge bin to accommodate metering the talc with the cellulose to thereby assure the appropriate distribution ratio of talc in the cellulose.

BACKGROUND 
1. Field of the Invention 
This invention relates to a cellulose insulation product and method and, 
more particularly, to a fire-resistant, cellulose insulation product and 
method wherein talc is intimately blended with the cellulose to impart the 
necessary fire-resistant characteristics to the cellulose. 
2. The Prior Art 
Recent events relating to the availability and cost of fuels has resulted 
in an increased interest in structural insulation products. The primary 
feature of any insulation is the ability to impede conductive and 
convective heat losses by forming minute air pockets in a nonconductive or 
low thermal conductive matrix. The air pockets form an effective dead air 
space or barrier against the conductive and convective heat losses. A 
finely divided cellulose material has been found to be extremely useful as 
an insulation product since the cellulose has very low thermal 
conductivity and can be shredded or otherwise finely divided to provide 
the desirable air entrapment characteristics. Suitably treated, the 
cellulose also maintains a desired degree of dimensional stability 
referred to in the trade as "loft". Additionally, insulation quality 
cellulose is readily available from recycled cellulose products such as 
newsprint, cardboard and kraft paper. These raw materials are readily 
recoverable from the waste disposal systems of most communities. 
However, cellulose is carbonaceous and a finely divided cellulose product 
is, therefore, extremely flammable in view of the enormous surface area 
exposed for combustion. Accordingly, it has been conventional to mix a 
predetermined quantity of a fire-resistant material such as a boron 
compound with the cellulose. The boron compounds generally include boric 
acid, borax and borates. 
Additionally, certain cellulose insulation products have included ammonium 
sulfate as the fire-resistant material. However, recent governmental 
regulations have required the discontinuance of cellulose insulation 
products incorporating ammonium sulfate as the fire-resistant material. 
Ammonium sulfate is believed to be deleterious since it combines with 
moisture to form acidic byproducts which have been found to cause 
corrosive damage to electrical wiring, etc. 
Although cellulose insulation is used only in sheltered locations, exposure 
to atmospheric moisture is of considerable importance. Conventionally, the 
insulation is incorporated in a dwelling as an overlayment in the attic 
above the ceiling and is blown in while, simultaneously, being fluffed by 
the action of the blowing process. Most attics are ventilated and exhaust 
systems from bathrooms, range hoods and the like are directed into the 
attic space for subsequent dispersal to the atmosphere through the attic 
ventilation system. Accordingly, moisture in the heavily moisture-laden 
air from a bathroom or range hood tends to condense on the exposed 
insulation on cold days. This condensation has been found to form the 
acidic byproducts with ammonium sulfate resulting in their being 
proscribed by governmental regulations. 
Additionally, other fire-resistant compounds that are soluble are known to 
"migrate" under the effect of moisture. This migration results from the 
periodic solubilization upon moisture condensation and recrystallization 
upon moisture evaporation of the soluble compounds with the result that 
the solubilized compounds are removed from portions of the cellulose. The 
exposed cellulose is thereby deprived of its fire-resistant protection 
with a resulting, potentially dangerous condition. 
The production of fire-resistant, cellulose insulation material also 
requires extensive grinding and mixing of the fire-resistant materials 
with the cellulose insulation. While various fire-resistant materials have 
been tried, they tend to be abrasive to the grinding equipment resulting 
in excessive equipment wear, downtime, and corresponding production loss. 
In view of the foregoing, it would, therefore, be a significant advancement 
in the art to provide a fire-resistant, cellulose insulation material 
which is (1) relatively available as a raw material and, therefore, 
relatively inexpensive to obtain, (2) inert to occassional contact with 
condensation, and (3) low in abrasion of grinding equipment. Such a 
fire-resistant cellulose insulation material and method is disclosed and 
claimed herein. 
BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
The present invention relates to any novel, fire-resistant, cellulose 
insulation product wherein talc is incorporated with the cellulose to 
impart the desired fire-resistant characteristics to the cellulose. The 
talc is introduced into the cellulose during the grinding process to 
impart the desired fire-resistant characteristics to the cellulose. The 
relatively low hardness of the talc minimizes machinery abrasion. Talc is 
also abundantly available as earthen deposits so that it is less expensive 
to use than the conventional boron compounds. 
It is, therfore, a primary object of this invention is to provide 
improvements in fire-resistant, cellulose insulation. 
Another object of this invention is to provide an improved method for 
producing a fire-resistant, cellulose insulation material. 
Another object of this invention is to provide a fire-resistant, cellulose 
insulation material wherein talc provides the primary fire-resistant 
characteristic to the insulation. 
Another object of this invention is to provide a fire-resistant cellulose 
insulation material wherein the fire-resistant material has low abrasive 
characteristics to reduce equipment wear. 
These and other objects and features of the present invention will become 
more fully apparent from the following description and appended claims 
taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention is best understood by reference to the drawing wherein like 
parts are designated with like numerals throughout. 
General Discussion 
Talc is a naturally occuring magnesium silicate (3MgO.4SiO.sub.2.H.sub.2 O) 
and is frequently referred to by various names including, for example, 
talcum, soapstone, rensselaerite, potstone, steatite and French chalk. 
Advantageously, talc is one of the softer minerals and has a hardness of 
between 1.0 and 1.5 in terms of the Mohs' Scale. Furthermore, talc is 
relatively insoluble in water. A finely divided talc will tend to float on 
water and resist wetting. Since talc is a combination of the oxides of 
magnesium and silicon, talc will not support combustion. A representative 
analysis of the composition of talc obtained from a commercial mining 
operation is set forth in Table I, below. 
TABLE I 
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ANALYSIS OF MINE GRADE TALC 
Compound Weight % 
______________________________________ 
MgO 29.0 
SiO.sub.2 62.5 
Al.sub.2 O.sub.3 
1.9 
Fe.sub.2 O.sub.3 
1.9 
TiO.sub.2 0.15 
K.sub.2 O 0.09 
CaO 0.005 
Weight Loss 5.5 
On Heating 
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The weight loss on heating is believed to represent water loss. Water loss 
does not interfere with the fire-resistant characteristics imparted by the 
talc. On the contrary, it is believed that the water loss on heating 
contributes to the fire-resistant characteristics since the water absorbs 
a portion of the thermal energy which would otherwise tend to char or coke 
the cellulose. Surprisingly, it was discovered in the development of the 
present invention that talc, when intimately mixed with a highly 
combustible material such as finely divided cellulose, was found to be 
even more effective as a fire-resistant material than the conventional 
boron compounds or ammonium sulfate. This is believed to be a result, in 
part, of the tendency for the water molecule portion of the talc to absorb 
and remove a portion of the thermal energy which would otherwise char the 
cellulose. This was experimentally demonstrated when a sample of the 
fire-resistant, cellulose of this invention was subjected to the flame of 
a blow torch with minimal thermal degradation. This latter characteristic 
is particularly useful since any carbonaceous material will tend to coke 
upon the application of heat, the coking process producing highly 
combustible gases such as carbon monoxide, methane and the like. 
Accordingly, a fire-resistant material such as talc is particularly 
advantageous when incorporated with a highly combustible material such as 
finely divided cellulose. 
Another surprising discovery made as a result of this invention is that the 
talc is not only insoluble but appears to impart a desirable degree of 
hydrophobicity to the cellulose insulation material. Being insoluble, talc 
has a very low tendency to migrate or otherwise leave the cellulose 
without fire-resistant protection while, to a lesser extent, the finely 
divided talc also assists in forming a limited, water-repellant coating on 
the cellulose. 
Additionally, it was discovered at the inherent softness of the talc 
contributed greatly toward its intimate dispersion throughout the 
cellulose material while minimizing abrasive wear on the grinding 
machinery. On the other hand, siliceous materials such as perlite tended 
to cause excessive machinery wear. 
The cellulose material useful in this invention may be readily supplied 
from various sources although the principle source consists of recycled 
newsprint, cardboard, kraft paper and the like. Newsprint is especially 
desirable since it provides a certain degree of uniformity to the raw 
material and may be obtained for a relatively nominal cost per ton. 
The Embodiment of the Drawing 
With particular reference to the drawing, a flow diagram, shown generally 
at 10, is schematically illustrated and includes a waster paper feed 12, a 
primary grinder 14, a surge bin 16, a talc supply 18, a secondary grinder 
22, and, where desirable, a tertiary grinder 24. Cellulose from waste 
paper feed 12 is directed into the primary grinder 14 which reduces the 
waste paper to a substantially uniform mass of cellulose. Primary grinder 
14 is substantially a conventional grinder and is adapted to receive 
newsprint, cardboard, kraft paper and the like. The ground cellulose from 
primary grinder 14 is introduced into a surge bin 16. 
The function of surge bin 16 is to accommodate the controlled admixing of 
talc from talc supply 18 with cellulose from primary grinder 14. Surge bin 
16 provides a particularly useful function since cellulose is discharged 
from primary grinder 14 in relatively nonuniformed clumps or masses and in 
surges. An outlet 20 is provided for surge bin 16 and may be configurated 
in the form of a screw conveyer or the like for the purpose of directing a 
predetermined quantity of cellulose from surge bin 16 into secondary 
grinder 22. The rate of feed from talc supply 18 is coordinated with 
regulator of outlet 20 so as to admix talc with the cellulose on a ratio 
generally between about 5-25%, by weight, talc to cellulose. 
Secondary grinder 22 and tertiary grinder 24 are each configurated as 
high-speed grinders. In one presently preferred embodiment of this 
invention secondary grinder 22 and tertiary grinder 24 were each 
configurated as high-speed hammer mills having a tip speed of the hammers 
of 20,000 feet per minute. Conventional hammer mills were modified and 
suitably balanced to accommodate this high speed. Advantageously, the 
relatively softness of the talc did not induce excessive wear of the 
mechanical equipment of grinders 22 and 24. 
Introduction of talc from talc supply 18 prior to the secondary grinder 22 
has the additional advantage in that the talc greatly reduces the fire 
hazard present during the grinding process. For example, newsprint, 
cardboard, and kraft paper from the waste paper feed contains stones or 
metallic debris such as staples and the like which encourage spark 
formation during the high-speed grinding process. However, with the talc 
present in the grinder, the opportunities for ignition are substantially 
minimized thereby contributing significantly to the safety of the grinding 
process. 
In one experimental sample, boric acid in an amount of up to 10% by weight 
was introduced with the talc from talc supply 18 making the total 
fire-resistant material in the cellulose approximately 25% by weight. 
Although boric acid is known for its fire-resistant properties, no 
increased fire resistance capability could be ascertained by the inclusion 
of boric acid therein. Although boric acid is not determined to be 
detremental, it could not be adequately determined whether the boric acid 
contributed any fire-resistant properties to the insulation material other 
than that which was obtainable by the use of talc according to this 
invention. However, where necessary to comply with existing code 
requirements, it may be necessary to include known boron compounds with 
the talc until the use of talc alone has met with sufficient acceptance. 
In light of the relatively high grinding speeds, particularly in secondary 
grinder 22 and tertiary grinder 24, as one phase of the experimental 
procedure, a non-flammable oil was introduced into the grinding process as 
a dust suppressant. For example, a commercially available silicone oil was 
introduced into the grinding process in amounts up to 5% by weight and was 
found to suppress dust formation. Silicone oil is known also for its 
resistance to wetting. The silicone oil also appeared to enhance the 
adhesion between the talc and the cellulose material. Excessive dust 
suppression is not necessarily indicated as being an ultimate goal since a 
certain amount of talc dust in each of grinders 22 and 24 appears to be 
desirable for suppression of ignition. 
Fire-resistant, cellulose insulation is discharged through outlet 26 from 
tertiary grinder 24 and was found to have a desirable degree of intermix 
between the talc and the cellulose. The cellulose was also found to be 
very finely divided as a result of the high-speed grinding process. Both 
the intimate dispersion and fine division are a direct result of the 
high-speed grinding process which is obtainable, in large part, as a 
result of the very soft nature of talc. 
The invention may be embodied in other specific forms without departing its 
spirit or essential characteristics. The described embodiments are to be 
considered in all respects only as illustrative and not restrictive and 
the scope of the invention is, therefore, indicated by the appended claims 
rather than the foregoing description. All changes that come within the 
meaning and range of equivalency of the claims are to be embraced within 
their scope.