U.S. patent application number 10/345140 was filed with the patent office on 2003-07-24 for plasterboard composition, preparation of this composition and manufacture of plasterboards.
Invention is credited to Leclercq, Claude.
Application Number | 20030138614 10/345140 |
Document ID | / |
Family ID | 8852622 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030138614 |
Kind Code |
A1 |
Leclercq, Claude |
July 24, 2003 |
Plasterboard composition, preparation of this composition and
manufacture of plasterboards
Abstract
A plasterboard composition includes from 55 to 92% of hydratable
calcium sulphate; from 0.1 to 5% of mineral and/or refractory
fibres; from 3 to 25% of a mineral additive; from 1 to 5% of
unexpanded vermiculite; and from 3 to 15% of hydrated alumina.
Inventors: |
Leclercq, Claude; (Pernes
Les Fontaines, FR) |
Correspondence
Address: |
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
8852622 |
Appl. No.: |
10/345140 |
Filed: |
January 16, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10345140 |
Jan 16, 2003 |
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PCT/FR01/02125 |
Jul 3, 2001 |
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Current U.S.
Class: |
428/292.1 ;
428/292.4; 428/299.4 |
Current CPC
Class: |
C04B 14/26 20130101;
C04B 14/10 20130101; C04B 28/14 20130101; Y10T 428/249946 20150401;
Y10T 428/249924 20150401; C04B 2111/28 20130101; C04B 2111/0062
20130101; C04B 2111/10 20130101; Y10T 428/249925 20150401; C04B
28/14 20130101; C04B 14/10 20130101; C04B 14/202 20130101; C04B
14/26 20130101; C04B 14/303 20130101; C04B 14/42 20130101; C04B
22/0013 20130101 |
Class at
Publication: |
428/292.1 ;
428/299.4; 428/292.4 |
International
Class: |
D04H 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2000 |
FR |
00 09 392 |
Claims
What is claimed is:
1. Plasterboard composition comprising: from 55 to 92% of
hydratable calcium sulphate; from 0.1 to 5% of mineral or
refractory fibres; from 1 to 5% of unexpanded vermiculite; and from
3 to 15% of hydrated alumina; from 3 to 25% of a mineral additive
consisting essentially of a clayey material, the mineral additive
includes an amount of crystalline silica which is at most about 15%
by weight of the mineral additive, and an inert mineral supplement
compatible with the clayey material and dispersible in the plaster
board composition.
2. The plasterboard composition according to claim 1, in which a
nature and an amount of the mineral additive are chosen so that the
plaster composition contains at most 2% crystalline silica.
3. The plasterboard composition according to claim 1, in which the
nature and the amount of the mineral additive are chosen so that
the plasterboard composition contains at most 1% cellular
crystalline silica.
4. The plasterboard composition according to claim 1, in which the
mineral additive comprises kaolin, illite, quartz and dolomite.
5. The plasterboard composition according to the claim 4, in which
the mineral additive comprises, in percentages by weight: 25%
kaolin; 10% illite; 15% quartz; and 50% dolomite.
6. The plasterboard composition according to claim 1, in which the
unexpanded vermiculite is micronized.
7. The plasterboard composition according to claim 1, which
furthermore includes up to 4% boric acid.
8. The plasterboard composition according to claim 2, which
furthermore includes up to 4% boric acid.
9. The plasterboard composition according to claim 5, which
furthermore includes up to 4% boric acid.
10. The plasterboard composition according to claim 1, comprising:
70 to 80% of hydratable calcium sulphate; 1% of glass fibres; 10 to
15% of the mineral additive consisting essentially of kaolin,
illite, quartz and dolomite; 2 to 4% of micronized unexpanded
vermiculite; 6 to 10% of hydrated alumina; and 0 to 2% of boric
acid.
11. A plasterboard consisting essentially of a hardened composition
according to claim 1.
12. A plasterboard consisting essentially of a hardened composition
according to claim 6.
13. A plasterboard consisting essentially of a hardened composition
according to claim 7.
14. A plasterboard consisting essentially of a hardened composition
according to claim 10.
15. A plasterboard consisting essentially of a hardened composition
according to claim 1, in which the density is between 800 and 1,000
kg m.sup.3.
16. The plasterboard according to claim 11, in which at least one
of its sides is coated with a reinforcing material based on mineral
and/or refractory fibres, or based on cardboard.
17. The plasterboard according to claim 16, in which each of its
two sides is coated with a reinforcing material based on glass
fibres.
18. The plasterboard according to claim 12, in which at least one
of its sides is coated with a reinforcing material based on mineral
and/or refractory fibres, or based on cardboard.
19. The plasterboard according to claim 18, in which each of its
two sides is coated with a reinforcing material based on glass
fibres.
20. The plasterboard according to claim 13, in which at least one
of its sides is coated with a reinforcing material based on mineral
or refractory fibres, or based on cardboard.
21. The plasterboard according to claim 20, in which each of its
two sides is coated with a reinforcing material based on glass
fibres.
22. The plasterboard according to claim 14, in which at least one
of its sides is coated with a reinforcing material based on mineral
or refractory fibres, or based on cardboard.
23. The plasterboard according to claim 22, in which each of its
two sides is coated with a reinforcing material based on glass
fibres.
24. A method of preparing a composition according to claim 1,
comprising mixing the constituents of the composition together in
any order.
25. A method of preparing a composition according to claim 6,
comprising mixing the constituents of the composition together in
any order.
26. A method of preparing a composition according to claim 7,
comprising mixing the constituents of the composition together in
any order.
27. A method of preparing a composition according to claim 10,
comprising mixing the constituents of the composition together in
any order.
28. A continuous process for manufacturing plasterboards,
essentially comprising the following steps: mixing the various
constituents of the composition according to claim 1 with water to
form a slurry; depositing the slurry on a reinforcing material,
followed by shaping and covering an upper face of the slurry using
a second reinforcing material; where appropriate, shaping edges of
the board by moulding the board on profiled bands; setting the
composition on a manufacturing line that runs along a conveyor
belt; cutting the set composition at the end of the line into
predetermined lengths; and; drying of the boards obtained.
29. A continuous process for manufacturing plasterboards,
essentially comprising the following steps: mixing the various
constituents of the composition according to claim 6 with water to
form a slurry; depositing the slurry on a reinforcing material,
followed by shaping and covering an upper face of the slurry using
a second reinforcing material; where appropriate, shaping edges of
the board by moulding the board on profiled bands; setting the
composition on a manufacturing line that runs along a conveyor
belt; cutting the set composition at the end of the line into
predetermined lengths; and; drying of the boards obtained.
30. A continuous process for manufacturing plasterboards,
essentially comprising the following steps: mixing the various
constituents of the composition according to claim 7 with water to
form a slurry; depositing the slurry on a reinforcing material,
followed by shaping and covering an upper face of the slurry using
a second reinforcing material; where appropriate, shaping edges of
the board by moulding the board on profiled bands; setting the
composition on a manufacturing line that runs along a conveyor
belt; cutting the set composition at the end of the line into
predetermined lengths; and; drying of the boards obtained.
31. A continuous process for manufacturing plasterboards,
essentially comprising the following steps: mixing the various
constituents of the composition according to claim 10 with water to
form a slurry; depositing the slurry on a reinforcing material,
followed by shaping and covering an upper face of the slurry using
a second reinforcing material; where appropriate, shaping edges of
the board by moulding the board on profiled bands; setting the
composition on a manufacturing line that runs along a conveyor
belt; cutting the set composition at the end of the line into
predetermined lengths; and; drying of the boards obtained.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of PCT
International Application No. PCT/FR01/02125, filed in France on
Jul. 3, 2001, which claims the priority of French Patent
Application No. 00 09 392, filed in France on Jul. 18, 2000, the
entire contents of both applications are hereby incorporated herein
by reference.
BACKGROUND OF THE APPLICATION
[0002] The present invention relates to a plasterboard composition,
a method of preparing this composition and a process for
manufacturing plasterboards having a greatly improved fire
resistance.
[0003] It is well known to use plasterboards for producing
partitions, coverings of vertical or inclined elements, or for
producing ceilings, whether suspended or not.
[0004] These boards generally consist of a core, essentially made
of plaster, covered on each of its sides with a sheet which serves
both as reinforcement and as facing and which may be made of
paperboard or of mats of mineral fibres.
[0005] U.S. Pat. No. 3,616,173 describes a fire-resistant board of
low density (between 0.64 and 0.8 g/cm.sup.3), the core of which is
based on plaster, glass fibres, a mixture or not, of clay,
colloidal silica and/or colloidal aluminium oxide, and optionally
of unexpanded vermiculite.
[0006] In that patent, it is specified that silicon and aluminium
oxides, in dry powder form, are difficult to disperse and also
expensive. For this reason in particular, that patent recommends
the use of clays. The plasterboard according to that patent has a
high-temperature shrinkage, which is quite low, but its fire
resistance is limited. Such a board therefore does not have the
properties needed to constitute good fire protection.
[0007] European Patent Application No. 0 470 914 of the Applicant
disclosed in 1992 a plasterboard intended for fire protection, the
faces of which are covered with a reinforcing material based on
yarns and/or fibres of a mineral and/or refractory material. The
core of this boards comprises:
[0008] 55 to 94% of plaster;
[0009] 0.1 to 5% of mineral and/or refractory fibres;
[0010] 2 to 25% of silica;
[0011] 1 to 15% of talc and/or mica; and
[0012] optionally, aluminium hydroxide and/or expanded
vermiculite.
[0013] Since then, the Applicant has continued its research in the
field of plasterboards with a view to improving both the hot
mechanical strength, the shrinkage behaviour and the heat transfer
of its plasterboards.
[0014] It has now achieved its objectives by developing a
plasterboard composition comprising:
[0015] from 55 to 92% of hydratable calcium sulphate;
[0016] from 0.1 to 5% of mineral and/or refractory fibres;
[0017] from 3 to 25% of a mineral additive;
[0018] from 1 to 5% of unexpanded vermiculite; and
[0019] from 3 to 15% of hydrated alumina.
[0020] According to a preferred embodiment of the invention, the
nature and the amount of mineral additive are chosen so that the
plasterboard composition contains at most 2% crystalline silica
and/or at most 1% cellular crystalline silica, that is to say
silica having crystals of less than 5 microns in size. Such a
composition therefore has the advantage of having a crystalline,
especially cellular, silica content in accordance with the
recommendations of the International Agency for Research on Cancer,
according to which it is recommended to reduce the use of cellular
crystalline silica as far as possible since this compound is
assumed to have a maximum toxicity.
[0021] The second subject of the invention is a method of preparing
a plasterboard composition, in which the constituents of the
plasterboard composition defined above are mixed in any order.
[0022] Finally, the third subject of the invention is a continuous
process for manufacturing plasterboards, essentially comprising the
following steps:
[0023] preparation of a slurry by mixing the various constituents
of the composition with water in a mixer;
[0024] deposition of the slurry thus prepared on the reinforcing
material, followed by shaping and covering of the upper face of the
slurry using a second reinforcing material;
[0025] where appropriate, shaping of the edges of the board
obtained previously by moulding the fresh board on profiled bands,
this forming consisting especially in tapering the edges of the
board;
[0026] hydraulic setting of the hydratable calcium sulphate on a
manufacturing line while the ribbon of hydratable calcium sulphate
board runs along a conveyor belt;
[0027] cutting of the ribbon at the end of the line into
predetermined lengths; and;
[0028] drying of the boards obtained.
[0029] Further characteristics and advantages of the invention will
now be described in detail in the description, which follows and is
given with reference to the drawings in which:
[0030] FIG. 1 shows the variation in shrinkage as a function of
time for the control board and boards A and B;
[0031] FIG. 2 shows the variation in the shrinkage as a function of
time for the control board and the boards B, C and D during another
test;
[0032] FIG. 3 shows the temperature rise on the unexposed side of
the control plasterboard and plasterboards A and B;
[0033] FIG. 4 shows the temperature rise on the unexposed side of
the control plasterboard and plasterboards B and C, during another
test; and
[0034] FIG. 5 shows the temperature rise on the unexposed side of
the control plasterboard and plasterboard D during another
test.
[0035] The subject of the invention is therefore a plasterboard
composition that can be used to manufacture a plasterboard having a
greatly improved fire resistance.
[0036] This composition comprises (in % with respect to the entire
dry mix)
[0037] from 55 to 92% of hydratable calcium sulphate;
[0038] from 0.1 to 5% of mineral and/or refractory fibres;
[0039] from 3 to 25% of a mineral additive;
[0040] from 1 to 5% of unexpanded vermiculite; and
[0041] from 3 to 15% of hydrated alumina.
[0042] The term "hydratable calcium sulphate" should be understood
to mean, within the present context, an anhydrous calcium sulphate
(anhydrite II or III) or a semihydrated calcium sulphate
(CaSO.sub.4.times.1/2H.sub.2O) in its a or b crystalline form. Such
compounds are well known to those skilled in the art and are
generally obtained by baking a gypsum.
[0043] The mineral and/or refractory fibres are preferably glass
fibres. They may be short (3 to 6 mm on average) or else long (10
to 24 mm on average) or of intermediate lengths. Preferably, glass
fibres having a single length of 13mm .+-.5 mm are used.
[0044] In particular, fibres coming from an E-type glass are used,
these possibly being in two forms, one being in a form called a
"roving" comprising glass strands supplied on reels and cut before
they are introduced into the usual circuit for mixing the
hydratable calcium sulphate with water, or else in the form of
precut strands which are metered before mixing the hydratable
calcium sulphate with water.
[0045] Preferably, fibres having a length of about 13 mm (.+-.5 mm)
and a diameter of about 13 microns (.+-.5 .mu.m) are used.
[0046] The essential function of the glass fibres is to impart
high-temperature mechanical strength, allowing the cohesion of the
calcined plaster to be maintained.
[0047] As mineral additive, numerous clays may be used. The
advantages afforded by clays are, on the one hand, the fact that
they release the water that they contain (water of constitution)
when they are heated to a temperature between 100 and 600.degree.
C. and, on the other hand, the fact that they compensate for the
shrinkage of the plaster in a fire because of their ability to
exfoliate.
[0048] Preferably, the nature and the amount of mineral additive
are chosen so that the plaster composition contains at most 2%
crystalline silica and/or at most 1 % cellular crystalline
silica.
[0049] It is therefore advantageous to use a mineral additive
comprising at most 7.5% of cellular crystalline silica.
[0050] As mineral additive, it is possible to use a mineral
additive comprising essentially a clayey material, the amount of
crystalline silica of which is at most equal to about 15% by weight
of the mineral additive, and an inert mineral supplement compatible
with the clayey material and dispersible in the hardened plaster
substrate.
[0051] For example, it is possible to use a mineral additive
comprising, as clayey material, kaolin, illite, quartz and, as
mineral supplement, dolomite. In particular, a mineral additive is
used which has the following composition (in percentages by weight
with respect to the total weight of mineral additive):
[0052] 25% of kaolin;
[0053] 10% of illite;
[0054] 15% of quartz; and
[0055] 50% of dolomite.
[0056] The calcined chemical composition of this additive is the
following (in %)
[0057] SiO.sub.2:43
[0058] TiO.sub.2:1.1
[0059] Al.sub.2O.sub.3:15
[0060] Fe.sub.2O.sub.3:1.6
[0061] K.sub.2O:1.2
[0062] CaO:23
[0063] MgO:14
[0064] Its particle size is expressed by a 63 .mu.m screen oversize
of less than 15%.
[0065] Its loss on ignition at 900.degree. C. is 26.5%.
[0066] The composition according to the invention comprises
unexpanded vermiculite, which is an aluminium-iron-magnesium
silicate in the form of flakes, which expand at a temperature above
200.degree. C., thereby making it possible to compensate for the
shrinkage of the plaster. Furthermore, the unexpanded vermiculite
improves the thermal resistance of the plaster.
[0067] Preferably, a micronized unexpanded vermiculite is used,
that is to say one in which all the particles are less than 1 mm in
size. This has the advantage of making it possible for the
vermiculite to be better distributed within the plaster and of
avoiding an abrupt expansion causing structural disorders.
[0068] Hydrated alumina (aluminium trihydroxide) is preferably used
with a fine particle size (median diameter of about 10 microns). It
has the effect of giving rise to an endothermic reaction
complementary to that of gypsum, especially by having a water of
crystallization content of about 35%, the water being releasable
between 200 and 400.degree. C. (gypsum containing about 20% of
water releasable at about 140.degree. C.).
[0069] The composition according to the invention may furthermore
possibly include up to 4%, especially from 1 to 4%, of boric acid,
as this product advantageously loses its water of constitution
above 100.degree. C., thereby contributing to the fire resistance
of the plasterboard. Moreover, boric acid modifies the crystalline
structure of the hydrated calcium sulphate in a manner favourable
as regards shrinkage on ignition.
[0070] The composition according to the invention may be prepared
by mixing, per 100 parts by weight of composition:
[0071] from 55 to 92 parts by weight of hydratable calcium
sulphate;
[0072] from 0.1 to 5 parts by weight of mineral and/or refractory
fibres;
[0073] from 3 to 25 parts by weight of a mineral additive;
[0074] from 1 to 5 parts by weight of unexpanded vermiculite;
and
[0075] from 3 to 15 parts by weight of hydrated alumina.
[0076] The manufacture of the plasterboards may be carried out
essentially according to the following steps:
[0077] preparation of a slurry by mixing the various constituents
of the composition with water;
[0078] deposition of the slurry thus prepared on the reinforcing
material, followed by forming and covering of the upper face of the
slurry using a second reinforcing material;
[0079] where appropriate, shaping of the edges of the board
obtained previously by moulding the fresh board on profiled
bands;
[0080] hydraulic setting of the hydratable calcium sulphate on a
manufacturing line while the ribbon of hydratable calcium sulphate
board runs along a conveyor belt;
[0081] cutting of the ribbon at the end of the line into
predetermined lengths; and
[0082] drying of the boards obtained.
[0083] After this treatment, the plasterboards are ready for
use.
[0084] According to an embodiment, the density of the hardened
composition which constitues the core of the boards is between 800
and 1,000 kg/m.sup.3.
[0085] The reinforcing material may be based on mineral or
refractory fibres. It may be in the form of a web, a fabric or a
mat of mineral fibres, preferably glass fibres. The web, fabric or
mat may be combined with a sheet of mineral and/or refractory,
entangled continuous yarns or yarn meshes, or in another form.
[0086] The reinforcing material may also be made of cardboard.
[0087] Preferably, a reinforcing material made of glass yarns or
fibres is used.
[0088] The plasterboard according to the invention has the
following advantages:
[0089] the composition can be easily formulated in the form of a
fluid slurry which is then converted, advantageously continuously,
into a plasterboard in conventional plants used for this type of
manufacture;
[0090] by virtue of the presence of an outer reinforcing material,
the edges of the plasterboard may be advantageously shaped,
particularly tapered, during manufacture of the board;
[0091] it provides effective fire protection; thus boards according
to the invention, having a thickness of around 12.5 mm and a
density of around 0.88 g/cm.sup.3, guarantee fire resistance for
longer than 2 hours;
[0092] by virtue of their good dimensional stability, the boards
according to the invention after the fire resistance test maintain
a good overall appearance without any deep cracking and exhibit
mechanical integrity (this behaviour is important for applications
requiring a very high level of fire protection, such as air ducts
for ventilation and for smoke venting, in which there is a
requirement for them to seal against hot gases under high
pressure);
[0093] the results of the reaction-to-fire tests on plasterboards
according to the invention are very good: when these boards are
exposed to the action of a radiating source and/or a specific
burner under defined conditions (for 20 minutes), capable of
igniting the gases released and of propagating the combustion, it
has been found that there is no ignition and that the deterioration
of these boards is merely superficial; after this test, the
plasterboards according to the invention are therefore still
capable of stopping the spread of a fire;
[0094] because of its lightness and its ability to be worked (cut,
nailed, screwed, stapled, screwed/bonded, etc.), it is very easy to
install; advantageously, it has tapered edges with which it is
possible to produce reliable joints between the boards using
plasterboard jointing compounds, for example of the type of those
used for plasterboards faced with paperboard, and preferably
fire-resistant jointing compounds; in addition, there are various
possible ways of finishing off the construction elements produced
with boards according to the invention, especially with paint,
wallpaper, etc.;
[0095] it has the application characteristics required in the
construction field: such as flexural stiffness, high impact
strength, moisture resistance and no creep in the presence of
moisture or under its own weight when it is mounted as a ceiling;
and
[0096] finally, given that it can be manufactured using a simple
process well known in the plasterboard field and that, in addition,
the raw materials of which it is composed are quite inexpensive,
the plasterboard according to the invention has the advantage of
having a moderate manufacturing cost.
[0097] The best performance is achieved with boards obtained from
the following composition:
[0098] 70 to 80% of a hydratable calcium sulphate semihydrate;
[0099] 1 % of glass fibres
[0100] 10 to 15% of the clay described above, consisting of 25%
kaolin,
[0101] 10% illite, 15% quartz and 50% dolomite;
[0102] 2 to 4% of unexpanded micronized vermiculite;
[0103] 6 to 10% of hydrated alumina; and
[0104] 0 to 2% boric acid.
[0105] Of course, provided that the proportions assigned to each of
the essential constituents are respected, it is possible to
introduce, into the composition according to the invention, by way
of secondary ingredients, additives normally used to facilitate the
processing of the other constituents or for imparting additional
particular properties on the composition. By way of examples of
such additives, mention may be made of fluidizing agents, foaming
agents, setting accelerators and water-repellent agents.
Examples
[0106] The following examples are given purely by way of
illustration and are in no way limiting in character.
Example 1
[0107] A control board was prepared according to the aforementioned
European Patent Application No. EP-A-0470914 and four boards A, B,
C and D according to the invention.
[0108] The composition of the boards is given in the following
table:
1 Composition (%) Control A B C D Plaster 76 76 76 76 74 Glass
fibres 1 1 1 1 1 Clay -- 18 13 10 13 Vermiculite -- 2 4 3 2
Hydrated alumina 10 3 6 10 8 Boric acid -- -- -- -- 2 Quartz 9 --
-- -- -- Talc 4 -- -- -- --
[0109] The hydratable calcium sulphate used came from the
industrial baking of desulphurized gypsum (FGD).
[0110] The clay used consisted of 25% kaolin, 10% illite, 15%
quartz and 50% dolomite.
[0111] The vermiculite used was a micronized unexpanded
vermiculite.
Example 2
[0112] The hot mechanical strength (also called the
high-temperature core cohesion) of the control board and boards A,
B, C and D prepared in Example 1 were measured.
[0113] The test used combined a thermal stress, exerted on both
sides of the test sample by means of a Mecker burner delivering a
flame having a constant temperature of 1020.degree. C., with a
tensile mechanical stress of 0.2 kg/cm.sup.2.
[0114] The parameters recorded were the failure time and the final
shrinkage.
[0115] The results are given in the following table:
2 Board Control A B C D Failure time (min) >100 >120 >120
109 93.5 Shrinkage (%) 4.4 2.1 2.95 1.5 1.3
[0116] It may be seen that failure of the control, A and B test
specimens was reached after two hours of stressing. Moreover, all
the formulations lasted at least 1 hour 30 minutes.
[0117] In the case of all the plasterboard test specimens according
to the invention, it may be seen that the combination of micronized
unexpanded vermiculite combined with clay allows the final
shrinkage to be reduced to less than 3%.
[0118] Test specimen D containing boric acid has the least
shrinkage.
Example 3
[0119] The shrinkage behaviour of the control board and boards A,
B, C and D prepared in Example 1 was measured.
[0120] The test involved consisted in simply exerting the same
thermal stress as in Example 2, in the absence of any mechanical
stress.
[0121] The recorded parameter was the shrinkage after 15, 30, 45
and 60 minutes.
[0122] The results are given in the following table:
3 Shrinkage of the boards in % Time (min) Control A B C D 15 3.0
1.3 1.4 0.3 0.9 30 3.0 1.4 1.1 0.5 1.2 45 3.2 1.6 1.7 0.8 1.1 60
3.6 1.5 2.5 1.2 0.7
[0123] FIG. 1 shows the variation in the shrinkage as a function of
time for the control board and boards A and B.
[0124] FIG. 2 shows the change in shrinkage as a function of time
for the control board and boards B, C and D, during another
test.
[0125] The difference between the control and the test specimens
according to the invention is very marked, particularly in the
initial phase (up to 30 minutes. The micronized unexpanded
vermiculite/clay pair reduces the shrinkage by a factor of about 2
compared with the control.
[0126] Again, it is found that the shrinkage is minimal with test
specimen D containing boric acid.
Example 4
[0127] The heat transfer of the control board and boards A, B, C
and D prepared in Example 1 was measured.
[0128] The test consisted in exerting a thermal stress on one side
of the by means of a Mecker burner delivering a flame with a
constant temperature of 1020.degree. C.
[0129] The parameters recorded were the temperature of the
unexposed test specimen, the time to reach values corresponding to
the Fire Wall and insulation classification criterion according to
the French Decree of August 1999 and the EN 1361-1 and EN 13 501-2
standards, in which dt=140.degree. C. on average or a maximum of
180.degree. C. at any point.
[0130] In addition, the time to reach a temperature of 400.degree.
C. was also recorded, as this time is a significant measure of the
heat transfer after dehydration.
[0131] The results are given in the following table:
4 Time(s) to reach temperature Boards Temperature Control A B C D
160.degree. C. 595 525 655 640 570 200.degree. C. 645 615 710 690
635 400.degree. C. 945 930 1035 1105 1020
[0132] FIG. 3 shows the temperature rise on the unexposed side of
the control plasterboard and plasterboards A and B.
[0133] FIG. 4 shows the temperature rise on the unexposed side of
the control plasterboard and plasterboards B and C, during another
test.
[0134] FIG. 5 shows the temperature rise on the unexposed side of
the control plasterboard and plasterboard D, during another
test.
[0135] All the tests were carried out under the same
conditions.
[0136] It may be seen that the shape of the curves are similar,
with a first vaporization plateau around 100.degree. C. and then
another one around 120.degree. C.
[0137] Moreover, heat transfer through the calcined board takes
place up to a maximum point at 450.degree. C.
[0138] The results on test specimen A are comparable to those on
the control test specimen.
[0139] The results of all the other test specimens according to the
invention are better than those of the control board, especially
both from the standpoint of the duration of the vaporization
plateau, thus guaranteeing that a fire-wall criterion is met for a
longer time, and reduced heating in the 200 to 400.degree. C.
region.
[0140] Although only preferred embodiments are specifically
illustrated and described herein, it will be appreciated that many
modifications and variations of the present invention are possible
in light of the above teachings and within the purview of the
appended claims without departing from the spirit and intended
scope of the invention.
* * * * *