Note: Descriptions are shown in the official language in which they were submitted.
~5~
~FN 6732 -1-
Bac~ground Of The Invention
The present invention relates to thermal insul-
ation material and more particularly to insulation made
from cellulosic ~ibers having high flame-retardant prop-
erties.
Fiberized wood or other fibrous cellulosic ~
material serves as an excellent insulating material when
blown into the walls, floors, or attic of a home or other
type of building that must be protected against heat
losses. Cellulosic insulating materials are light in
weight and inexpensive. The R value per inch of such
insulating material is quite high and in many cases may
equal or exceed the R value per inch of fiberglass
batting.
The use of fiberized wood or other cellulosic
material as insulation is known in the art. For example,
Heritage, U.S. patent No. 2,325,055, teaches forming
a thermal insulation material by refining wood chips
at elevated temperatures in the presence of steam.
Various bonding, fire-proofing, and mold-preventing
agents are added to the material prior to its entry
into the refiner. Portz, U. S. patent No. 2,470,641,
adds dry boric acid to disintegrated newsprint to form
a fire-resistant insulating material.
However, there has been a reluctance in the
past to use cellulosic insulating matcrials because of
problems with insuring adequate fire resistance of the
material. To meet stringent fire regulation standards
the insulating material must not be ignitable in the
presence of heat. Present federal regulations require
cellulosic insulating material to have a critical
radiant flux of at least 0.12 watts/cm .
Accordingly, the need still exists in the art
for a process of preparing wood or other cellulosic
fiber insulating material which meets or exceeds the
. 1,
~L~.s~
~FN 6732 -2-
regulated fire resistance standards.
S~mnar~ Of The Invention
The present invention meets that need by pro-
yiding a cellulosic fiber insulating material and process
of preparing it which has excellent fire resistance
properties and yet is inexpensive to manufacture and
easy to use. In accordance with the process of the
present invention, hard and/or soft wood chips or other
celiulosic material such as bagasse, straw, and the like
are loaded into a pressurized steaming chamber. There
the chips are pretreated with steam under pressure and
at elevated temperatures for a sufficient period of time
to soften the chips and moisturize them by steam impreg-
nation. The steam pressures may be from about 60-150
psig, the temperatures from about 270-370F and the time
of pretreatment fairly short, i.e. on the order of
3-6 minutes.
The softened chips are then passed to a refiner
or other fiberizing device where they are refined under
pressure. Preferably, a single or double disc refiner
or one having bar-type grinding segments is used. A
fire-retardant chemical such as borax or boric acid is
added directly fnto the refiner immediately prior to the
grinding disc or discs where it is uniformly dispersed
throughout the wood fibers due to the mixing and fiber-
izing action oE the refiner. ~ charge of 20 - 30 percent
by weight of borax (based on bone dry cellulose fiber)
is preferred. [t may be added as a concentrated aqueous
solution or on a dry basis.
The fiberized material exits from the refining
stage and is immediately brought down to atmospheric
pressure. Because of the rapid depressurization, a
considerable amount of steam is flashed off of the
material leaving a lower moisture content for drying.
The material is then conventionally dried and baled.
When used as insulation, the bales are shredded at the
building site to fluff up the material and blown into
l~LS~4;2
~FN 6732 -3-
the walls, floors, and attic.
Although the pretreatment steps of heating
and so~tening of the cellulose fibersare important to
the process, it has been found that the point of injec-
tion of fire-retardant chemical is critical to the
production of an insulating material having superior
fire and flame resistant properties. Thus, it is
essential to the practice of the present invention that
the fire-retardant chemical, preferably borax, is added
directly into the eye of the refiner immediately prior
to the grinding disc or discs.
Accordingly, it is an object of the present
inven~ion to provide a highly fire and flame resistant
cellulosic insulating material and process for its
preparation. This and other ob~ects and advantages of
the invention will become apparent from the following
description and appended claims.
Description Of The Preferred Embodiments
Several fibrous cellulosic materials can be
utilized as starting materials for the process of the
present invention including straw and bagasse although
it is preferred that hard or soft wood chips be used.
The cellulosic materials are first loaded into a
pressurized chamber whcre they are softened under the
application of ileat and pressure. In a prcferred arrange-
sent, wood chips are supplicd to the chamber rom a
chip storage bin via a hopper and screw fccder which
forces a dense plug of chips into the pressurized
chamber.
The cellulosic materials are then exposed to
saturated steam at from about 60 to about 150 psig and
at temperatures of about 270 to 370F for three to si~
minutes. Treatment times, pressures, and temperatures
will vary somewhat depending upon the nature of the
material being treated. Generally, the upper limit of
BFN 6732 -4-
pressure and temperature will correspond to the lesser
treatment time and vice versa. In a preferred embodiment,
wood chips are steamed at from 60 - 100 psig and 277-
309F for 3 - 5 minutes.
The softened fibrous cellulosic material is then
transferred by suitable means such as a screw conveyor
to a refiner or other fiberizing device. Preferably,
a refiner having single or double discs or bar-type
grinding segments is utilized. At this point in the
process, a fire-retardant chemical such as borax, boric
acid, or a borate is added directly into the re~iner
immediately prior to the grinding discs or segments.
By adding the fire-retardant chemical at this point,
rather than during pretreatment or after fiberization,
the chemical is uniformly dispersed throughout the
cellulosic fibers due to the mixing and fiberizing action
of the refiner yielding a superior flame and fire
resistant thermal insulation material. It has been
found that the addition of the fire-retardant chemical
to the fibers immediately prior to fiberization is
critical in obtaining superior fire resistance properties.
The fire-retardant chemical may be added in a
dry, powdered state or may be injected as a ccncentrated
a~ueous solution. In a preferred embodiment, borax is
injected into the refiner at a chargc o~ about 20 - 30
percent by weight borax to dry fiber wei~ht. If an
a~ueous solution of borax is used, it has been found
that a 20 pcrc~nt by wei~ht borax solution yields
excellent results.
The treated fiberized material is then blown
from the pressurized refiner to atmospheric pressure.
Because of the rapid depressurization, a considerable
amount of moisture present in the fiberized material
is flashed off as steam, lowering the moisture content
of the material and rendering easier and less expensive
to dry. If the fire-retardant chemical has been added
~3LS~4~
~FN 673~ _5_
in a dr~v st~te at the re~ining sta~e, here is even less
moisture in the material which has to be driven off
by drying.
~ he material may then be dried in a conventional
manner such as by blowing heated air through it and
packed in bales. When needed for use as insulation,
the bales may be easily transported to the building
site, shredded, and blown into walls and attics and
under floors.
In order to better understand the invention,
reference is made to the following nonlimiting examples.
EXAMPLE I
Thermal insulation was prepared according to
the process of the present invention by treating wood
chips in a pressurized chamber with approximately
100 psig saturated steam at about 277 - 309F for five
minutes. It was then refined with borax being added
directly into the refiner immediately before the grinding
segments as a 20 percent by weight concentrated aqueous
solution. A total of 20 - 25 percent by weight borax
was added based on the original dry weight of the wood
chips. After fiberization, the insulation material
was dried.
The insulation was then tested for flame spread
(per ASTM designation ~-84) and flame resistance (per
ASTM designation C-739). Both the flame spread and flame
resistance ratinc3s were well within fcdcral specification
HH-1-515C for Type I insulation. Other tests were
performed showing that the insulation has no objectionable
odors, does not corrode metals, has an average 4.6 percent
moisture absorption, a starch content of less than
l percent, and a thermal resistance (R) value of 3.38/
inch.
~5~2
FN 6732 -6-
EXAMPLE II
Three different samples o~ insulation were
prepared by treating wood chips in a pressurized chamber
with lO0 psig saturated steam graduall~ lowered to 60
psig by the end of a five minute treatment period.
Temperatures in the chamber ranged from 309F to 277F.
The wood chips were then refined in a bar-type grinding
segment refiner. Borax was added as a 20 percent by
weight concentrated aqueous solution; total borax
added amounted to 20-25 percent by weight of the original
dry weight of the wood chips~ The only difference in
the samples prepared was that Sample A was prepared in
accordance with the practice of the present invention
by injecting the borax into the eye of the refiner
immediately before the grinding segments. Borax was
injected into Sample B in the blow line as the material
exited the refiner. Borax was added to Sample C during
the steaming and preheating stage of the process.
All of the samples were tested in compliance
with federal specification HH-I-515D. That specification
requires a critical radiant flux of a-t least 0.12 watts/
cm for cellulosic thermal insulation. The results of
the tests are reported in Table I below.
TABLE I
. _
Critical ~adiant Flux
Run l Run 2 Run 3 Avera~e
Sample Watts/cm2 Watts/cm2 Watts/cm2 Watts/cm2
A 0.92 0.82 0~86 0.86
B 0.55 0.5~ 0.5~ 0.55
C <0.0~ <0.09<0.09 <0.09
~ s can be seen, Sample A, prepared in accordance
with the process of the present invention exhibits sup-
erior results of a magnitude of 60 percent greater than
Sample B and 950 percent greater than Sample C. The
critical radiant flux values for Sample A are over
llS~4z
BFN 6732 -7-
seven times greater than federal standards require.
While the process and product herein described
constitute preferred embodiments of the invention, it
is to be understood that the invention is not limited
thereof and that changes may be made therein without
depar~ing from the scope o~ the invention.
What is claimed is:
