Note: Descriptions are shown in the official language in which they were submitted.
CA 022~6398 1998-11-27
FiLF.puLl~T~J~
PCT/EP 97/ 02780 i ~ .
P 4818/97-PCT
April 23, 1998
Description
The invention relates to a fire-protection
agent for sheets or moldings made from chips or fibers
which have been obtained from timber or from
constituents of annual plants, and also to such boards
and moldings which comprise a fire-protection agent of
this type. The invention also relates to a process for
providing fire resistance to such sheets or moldings.
Sheets or moldings of the type described are
generally very flammable. However, their material
properties give them a variety of applications as
working materials, for example in furniture
construction and the interior fitting of buildings, and
also in motor vehicles. In many of the possible uses,
however, the ready flammability of the particle boards
or fiberboards and moldings, deriving from the ready
combustibility of the organic raw materials used, is a
disadvantage. Especially in the building industry, it
is desirable on safety grounds to use only working
materials which have low flammability or are fire-
resistant.
Attempts have continually been made in the past
to provide fire retardancy or fire resistance to boards
of timber materials and boards made from sustainable
raw materials. For example, DE 31 44 773 A1 proposes
applying an aqueous solution of inorganic salts to
wood-chip granules which are to be press-molded to give
a wood-chip molding, and then applying glue to the
granules and press-molding these. However, it is also
necessary according to this prior art additionally to
apply a fire-resistant layer to the surfaces of the
wood-chip moldings in order to be able to produce wood-
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chip moldings which are not just fire-retardant but
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A process for providing fire resistance to a
cellulose material has been described in DE 29 23 587
Al. In this it is claimed that the cellulose material
is impregnated with phosphoric acid and with an aqueous
solution which comprises at least one amonium [sic]
salt, for example amonium [sic] sulfate. Other
substances, such as borax and trisodium phosphate, may
be added here. The main constituent of this known
impregnating solution is phosphoric acid, to which the
desired flame-retardant effect is primarily attributed.
An impregnating solution of this type is, however, not
usable when producing particle boards or fiberboards,
since the phosphoric acid gives them an acid reaction
and the binders used when producing particle boards and
fiberboards would precure before the compression
procedure, and this would be extremely disadvantageous.
An example of the provision of flame retardancy
to timber is given in CN 1 100 592. This prior art,
however, likewise does not concern itself with the
provision of fire resistance to particle boards and
fiberboards or to moldings in which the chips and/or
fibers have already been impregnated with a fire-
protection agent during the production process.
The object on which the invention is based is
therefore to propose a fire-protection agent which can
be used to provide fire resistance to sheets or
moldings made from
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The objcct on ~h;ch thc invcntion ~ ,
therefore to propose a ~ t which can
be used to ~rovid~~~~ire resistance to boards or
~ g~ m~dc -f- ~ chips or fibers which have been
obtained from timber or from constituents of annual
plants. A further object of the invention is to provide
boards and moldings of the type described which are
fire-resistant or highly fire-resistant, and also to
propose a process for providing fire resistance to
boards or moldings of the type described. The fire-
protection agent proposed here must be compatible with
the usual binders for gluing the chips or fibers and
when exposed to a flame must not evolve any smoke gases
hazardous to health.
According to the invention, this object is
achieved by means of a fire-protection agent which
comprises from 65 to 85 parts by weight, preferably 74
parts by weight, of ammonium sulfate, from 10 to 25
parts by weight, preferably 19 parts by weight, of
borax and from 4 to 10 parts by weight, preferably 7
parts by weight, of trisodium phosphate. The moldings
and boards proposed according to the invention comprise
this fire-protection agent.
The process according to the invention for
providing fire resistance to boards or moldings of the
type described at the outset includes the following
steps:
- the chips or fibers are impregnated with the
proposed fire-protection agent in a solution,
- the impregnated chips or fibers are dried to a
moisture content of from about 1 to about 12%,
preferably from 1 to 4%,
- a glue in the form of a binder is applied to the
impregnated and dried chips or fibers,
- the impregnated and dried chips or fibers, to
which a glue has been applied, are compressed to
give pressed mats and then press-molded to give
boards or moldings.
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The proposed fire-protection agent is a mixture
of inorganic salts which do not comprise any chlorides
and are nontoxic. It is compatible with all known
condensation resins and polymerization resins, for
example urea resins, melamine resins and phenol-
formaldehyde resins, epoxy resins, novolak resins, PMDI
resins, etc. In addition, it does not give rise to any
volatilization of harmful gases from the finished sheet
or molding.
The ammonium sulfate present in the proposed
fire-protection agent promotes the surface-
carbonization of cellulose via formation of sulfuric
acld .
Borax swells on heating and additionally acts
as a disinfectanti it also serves as an agent for melt
flow during press-molding of the pressed mats. The
trisodium phosphate which is also present in the fire-
protection agent decomposes from 75~C to give NaOH and
P2Os; it has emulsifying, water-softening and buffering
properties.
Mixing these three salts in the ratio given
produces a fire-protection agent which can be used to
provide fire resistance to boards or moldings made from
chips or fibers which have been obtained from wood or
from constituents of annual plants.
An advantageous further development of the
novel fire-protection agent consists in admixing
additionally from 0.5 to 2 parts by weight, preferably
1 part by weight, of sodium metasilicate. Sodium
metasilicate has a water-softening effect and acts as a
wetting agent, and also as a disinfectant, and on
heating releases water. If it is admixed with the fire-
protection agent in a solution it serves as a wetting
agent and thus promotes the wetting of the chips or
fibers with the fire-protection agent. An advantageous
side effect consists in the fungicidal and insecticidal
properties which the fire-protection agent obtains as a
result of admixing of the sodium metasilicate.
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The proposed fire-protection agent is most
advantageously used if it is present in an aqueous
solution, where the concentration of the solution may
be from 20 to 50%, preferably from 30 to 35%. The chips
or fibers may be saturated and thus impregnated with an
aqueous solution of this type before the glue is
applied and before press-molding to give boards or
moldings.
To achieve the other objects the invention
proposes boards or moldings made from chips or fibers
which have been obtained from timber or from
constituents of annual plants and which comprise the
abovementioned novel fire-protection agent. This fire-
protection agent may include ammonium sulfate, borax
and trisodium phosphate in the mixing ratios given
above or, as an advantageous further development,
additionally comprise sodium metasilicate.
The boards or moldings have the best flame-
retardant properties if the ratio of the dry weight of
the proposed fire-protection agent to the dry weight of
the chips or fibers is from 0.1 to 0.4, preferably 0.2.
According to the invention, fire-resistant
boards or moldings made from chips or fibers are
produced using the process described in Claim 11. A
solution of the proposed fire-protection agent is
therefore used to preimpregnate the chips or fibers,
the chips or fibers being saturated with the solution.
The fire-protection agent here may comprise the mixture
of salts given in Claim 1 or the mixture of salts
described in Claim 2. The fire-protection agent is
preferably present in an aqueous solution with a
concentration of from 20 to 50%, preferably from 30 to
35%. The preimpregnation of the chips or fibers with
the fire-protection agent may take place in a dip bath
or else by injecting the fire-protection agent into a
continuous mixer or into a screw mixer. The density of
the solution used of the fire-protection agent is
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preferably about 1.2 g/cm3, and its pH is slightly
alkaline, preferably about 8.5.
For the application of glue to the chips or
fibers, their moisture content must not usually exceed
about 12%. It is therefore necessary, after the
impregnation with an aqueous solution of the fire-
protection agent, to dry the impregnated chips or
fibers. After the drying, the impregnated chips or
fibers have a pH of from about 3.5 to 4.5.
Urea resins or melamine resins are preferably
used for the glue application to the chips or fibers
impregnated with the fire-protection agent. A great
advantage of this is that the ammonium sulfate present
in the fire-protection agent dissociates during the
press-molding of the chips or fibers due to the heating
which occurs during that process, and functions as a
curing agent for the binder. This means that it is not
necessary to add a separate substance as a curing
agent. In the case of chips or fibers made of straw,
however, PMDI resins are preferably used as binders.
Using the novel process it is possible to
produce boards or moldings made of chips or fibers,
which are fire-resistant to highly fire-resistant
without the need to apply an additional fire-retardant
coating.
The invention is further explained below using
two examples.
Example 1:
Pine chips were obtained in a known manner by
chipping logs in such a way that their length was from
5 to 15 mm, their width from 2 to 4 mm and their
thickness from 0.2 to 0.5 mm. These chips were predried
to a moisture content of about 30%.
A solution of the fire-protection agent of the
following composition was added to the predried chips
in a continuous mixer:
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50 parts by weight of water,
37 parts by weight of ammonium sulfate,
9.5 parts by weight of borax,
3.5 parts by weight of trisodium phosphate.
The ratio of the weight of the solution added
of the fire-protection agent to the dry weight of the
chips was 0. 6.
The impregnated chip material was then dried in
a drum drier to a residual moisture of about 1% and fed
into a mixer for applying glue. In the mixer for
applying glue, an aqueous binder of the following
composition was added to the impregnated chip material:
82.5 parts by weight of liquid urea-formaldehyde resin
(65% strength),
5 parts by weight of paraffin emulsion (50% strength),
12.5 parts by weight of water.
In this step there was no need to add a
substance as a curing agent, since the dried
impregnated chip material had a pH of from 3.5 to 4 and
the fire-protection agent added therefore functioned as
a curing agent on compression. The ratio of the weight
25 of the aqueous binder to the weight of the dried,
impregnated chip material was about 0. 2
The chips to which glue had been applied were
then spread out to form a mat and press-molded for
3.4 min at a temperature of 180~C with a press time
30 factor of 10 sec/mm to give a particle board. The
resultant particle board had the following parameters:
Thickness: 20.4 mm
Density: 650 kg/m3
Weight per m2: about 13.3 kg
Flexural strength: about 24 N/mm2
Transverse tensile strength (V 20): about 0. 42 N/mm2
Transverse tensile strength (V 100): about 0.18 N/mm2
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Thickness swelling (2 h): about 5.5%
The finished particle board can be used as a
furniture board in dry and damp areas, and also
externally as in the DIN Standards 68761 (Parts 1 and
4), 68762, 68763 and 68800.
The fire resistance of the particle board was
tested by directing the full flame of a bunsen burner
at a distance of 13.5 cm onto the surface of the board,
as a result of which the temperature prevailing there
was from 800 to 1000~C. Flame application for 5 min did
not ignite the particle board. All that was observed
was surface carbonization; very little smoke was
generated. The particle board fulfilled the
requirements of the DIN 4102 Standard.
Example 2:
Wheat straw was comminuted and separated into
fibers with a length of from 4 to 8 mm, a width of from
0.5 to 2 mm and a thickness of about 0.15 mm. These
straw fibers were mixed in a screw mixer with a fire-
protection agent in a solution of the following
composition:
21 parts by weight of ammonium sulfate,
5.4 parts by weight of borax,
3 parts by weight of trisodium phosphate,
0.6 parts by weight of sodium metasilicate,
70 parts by weight of water.
The ratio of the weight of the added solution
of the fire-protection agent to the dry weight of the
straw fibers was 0.67.
The impregnated straw fibers were then freed
from excess solution of the fire-protection agent in a
dewatering screw device and then dried to a residual
moisture content of about 4%.
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PMDI resin was sprayed onto these straw fibers
in such a way that the ratio of the weight of the PMDI
resin to the dry weight of the straw fibers was 0. 06.
The impregnated and glued straw fibers were
spread out to form a mat, heated in a preheating
station to a core temperature of about 60~C and then
press-molded for 4.4 min at a temperature of 200~C and
with a press time factor of 15 sec/mm, to give a
fiberboard. The finished fiberboard had the following
parameters:
Thickness: 17.5 mm
Density: 550 kg/m3
Weight per m2: 9. 6 kg
The flame of a bunsen burner was also applied
to this fiberboard at a distance of 13.5 cm in such a
way that the temperature at the surface of the board
was from 800 to 1000~C. After the flame had been
applied for 5 min the board had not undergone any
change other than surface carbonization, which
developed without generation of flames. Very little
smoke generation was observed during this. The DIN 4102
Standard was again complied with.
