FIELD OF INVENTION
This invention relates to a process of preparing polymer coated glass fiber mat. Further this invention also relates to a process of preparing the novel precursor.
Background of invention
Generally, in the foundries, inclusion and inclusion related defects are commonly found. The occurrence of inclusions in the casting has deleterious effect on its mechanical and physical properties. In order to achieve inclusion free casting, filtration of metal is required and normally effected by the following materials:
a. Refractory cloth filter;
b. Cellular sieve core;
c. Ceramic foam filter.
Refractory cloth filter is a refractory fibre mesh available in various pore sizesand generally employed for separation of coarse slag and dress particles.
Cellular sieve cores are extruded ceramic shapes having straight holes. These are found to be more efficient than the cloth filter.
Ceramic foam filter is a reticulated ceramic open structure having interconnected pores. It is available in different porosities. This type of filtration system is found to be the most efficient in trapping non-metallic impurities.
Ceramic foam filters are used for bulk filtration of molten aluminium. It is used in extrusion plants, sheer caster units, slab casting and pressure die casting units. The main drawback
of these filters is that they are not flexible and cannot be
reused.
U.S.Patent No. 5,698,304 describes polymer coated glass fiber mat. A facer sheet is provided which is adapted to receive a pre foam mixture during a structural laminate forming process. The facer sheet comprises a first predominantly glass fiber mat having first and second outer surfaces and a polymeric material applied to the first outer surface of the mat. The polymeric material acts as a substantially impervious barrier to the liquid prefoam mixture received at the second outer surface of the mat during the structural laminate forming process. A similar type of work i.e. a coating for fiberglass insulation is disclosed in U8 Patent No. 4,968,556. The coating composition for fiberglass articles comprising an aqueous dispersion containing a mixture of at least two polymeric binders, as well as aluminium^xrihydrate, antimony oxide, and also defoaming agents, biocides, thickeners, color pigments, dispersants and the like, has now been discovered. The dried coating composition of this invention, made by applyng the aqueous coating composition to fiberglass insulation and drying the coating in a drying oven has been found to impart an exceptionally advantageous balance of properties to the fiberglass insulation. Another U.S.Patent No. 5,112,678 describes a method and composition for coating mat and articles produced therewith . A method of producing a non-porous mat includes coating a predominantly glass fiber porous web
substrate. The coating comprises an aqueous mixture of a mineral
pigment; a first binder material comprised of a polymer latex
adhesive material; and, a second binder material comprised of an
inorganic adhesive material.
Besides these there are some related works on the process of
preparing the precursors, which are incorporated herein as
reference. A related application entitled as "Precursors for
boron nitride ceramic coating" (Patent No. US 9082693) describes
that polymeric B— aminoborazene compounds are suitable for
pyrolytic conversion to boron nitride. The B—aminoborazene
compounds are preferably mixed with an organic solvent and a
cross-linking agent to form a polymeric gel. The polymeric gel is
then pyrolyzed to form boron nitride. The polymeric gel is
useful to coat various forms and materials.
In somewhat related chemistry, Kato and co—workers Chem.
Lett.691 (1985) reported the formation of a spinnable
condensation product from the reaction of boric acid and 1,2,3-
o propanetriol. This material was then heated at 1300—1400 C
for 2-4 hr. Powder X—ray diffraction analysis of the resulting
powder gave evidence of the formation of h-BN and B C,although
4 the XRD patterns suggested limited crystallinity in the samples.
Later on Kato (Yogyo Kyosaishi, 95,130 (1987) reported reactions
between boric acid and diethanolamine as well as triethanolamine.
They suggested that a glassy polymer was formed which on
pyrolysis under N at 1400 C gives boron nitride and a small
2 amounts of boron carbide. None of these studies provided data on
ceramic powder quality ,or the utility of the intermediate polymers to
form fibers or coatings.
liayaCJ. Electrochem, Soc,135,1278 (1988) f J. Am Ceram.Soc, 71,
1104 (1988) has reported on reactions of triethylborane and tris
(dimethylamino) borane with polyfunctional amines and on the
subsequent pyrolysis of resulting polymers.Rees and Seyferth CJ.Am
Ceram.Soc.,71,C194C1988)fCeram.Eng. Sci.Proc., 9,1009 (1988);
Ibid, 9, 1021 (1988 )3 have developed new preceramic polymers
-(B H .L-L) , which are produced by the reaction of
10 12 n decaborane-14 (B H ) with varous diamines (iL Li) such
10 14 as H NCH CH NH , Me NCH CH Nile ,
2222 2 22 2 HN< CH CH ) NH, and N(CH CH ) N in diethyl
2 2 2 2 2 3
ether.The polymers are converted to ceramic powders by pyrolysis in
o the temperature range from 1000 to 1500 C at a heating rate of
o 10 C/min in a stream ofammonia.
(lira belli and Sneddon C J.Am.Chem.Soc., 110,3305 (1998 > 3 have
found that 2—vinylpentaborane undergoes polymerization with the
formation of soluble poly(2-vinylpentaborane). Subsequently,
o they observed that pyrolysis of this material in NH at 1000 C
3 produced amorphous BN containing a small amount of carbon,

Inorg.Chem, 27,3271 (1988)] .The amorphous BN was converted to h-BN
in high overall ceramic yield by further heating of the residue
o at 14S0 C.
In the past few years, Paciorek and co-workers [Polym. Prepr., Am
Chem.Soc.,Div.Polym.Cheat.25,15 (1984); U.S.Pat,4531468 (1986);
Ceram.Eng.Sci.Proc.,9,993 (1988); U.8.Pat,4707556 (1987)3 and Rice
and co-workers ECeram.Eng. Sci.Proc.,6,1171(1985); J.Am.Ceram
Soc.,70,C-58 (1987)3 have examined syntheses and processing of a
number of borazine monomers and polymers as boron nitride
precursors.
It was reported Chem.Mater.,Vol. 7, No.10, p.1942,(1995) that
borazine readily dehydropolymerizes in the liquid state at

moderate temperatures (70—110 ºC) to give a soluble polymer,
polyborazylene, in excellent yields of 81-91%. The polymer is
isolated as a white solid that is soluble in ethers such as glyme
and THF. The polymer can be precipitated by slowly adding ether
solutions of the polymer to pentane which has a molecular weight
of M =849.Elemental analysis indicates that compositions range
n from B N H to B N H for crude polymers
3 3 3.4 3 3 3.9 and from B N H to B N H for preci-
3 3 2.65 3 3 3.8 pitated samples. Pyrolysis studies show that the polymer converts
to boron nitride in excellent chemical (89-99X) and ceramic
yields (84-9 3%). Solutions of polyborazylene were also used to
coat carbon and ceramic fiber yarn bundles, which when pyrolyzed
under argon or ammonia, produced excellent boron nitride
coatings as characterized by AES spectroscopy.
Mideman C Cheat.Hater., Vol. 10,No. 1, p.412, (1998)] et al . reported
second-generation polymeric precursors to BN ceramics by the
reaction of polyborazylene (PB), CB N H 1 ,with
3 3 3.5 n diethylamine (DEA), dipentylamine (DPA), and hexamethyldisilazane
(HMD). A recent patent application entitled as "Heat resistant glass fiber mat and manufacture of the mat" (Patent No. JP-2003089953) describes that the mat is manufactured by the process involving impregnating of long glass fibers with a mixture of a ceramic sol and an organic resin, drying, disintegrating, and needle punching. The mat is useful for as a muffer, an engine cover, etc., in an automobile.
As evident from the foregoing discussions, decarboranes, borazenes, and their derivatives are used as polymeric precursors for synthesis of boron nitride. Problems associated with borazenes and decaboranes are that they are highly toxic and expensive materials. So it was necessary to develop low cost precursors, to synthesize a variety of boron containing polymeric precursors from inexpensive non-toxic and readily available starting materials.
OBJECTS OF THE INVENTION
An object of this invention is to produce a pyrolytic polymer
coated glass fiber mat for filtration of molen metals, such as
aluminium.
Another object of this invention is to propose a process for
the preparation of a novel precursor which is used to coat glass
fiber mats.
Yet another object of this invention is to propose a

precursor which is sable upto 800 ºC, both in air and inert
atmosphere.
Yet another object of this invention is to propose a precursor which is extremely hard and can withstand the rigors of hot metal (aluminium) which filtration without any damage to the coated filter. BRIEF DESCRIPTION OF THE INVENTION
According to this invention there is provided a process of preparing polymer coated glass fiber mat by dip coating polymer/ oligomeric precursor such as herein desc ribed on glass fiber mats comprising;
a. cleaning the glass fiber mats, with a suitable solvent such as herein described.
b. prefiring the said cleaned glass fiber mats at a temperature
ranging from 300-500 ºC for 1-3 hrs.

c. cooling the said mats to room temperature;
d. immersing the said cooled mats in 15—40% polymer/oligomer-precursor solution;
e. drying the said coated mats;
f. firing the dried coated mats for 3 hours at 400 ºC.
g. cooling the said coated mats slowly to the room temperature. In accordance with this invention the glass fiber mats arc cleaned with a suitable solvent e.g., aliphatic alcohol (ethanol)
or aliphatic ketone (acetone) which is preferably used to prepare the precursor solution. The cleaned mats are then prefired between 300-500°C for approximately 1-5 hours duration.
These prefired mats are then cooled to room temperature and have been immediately immersed in a 15-40% precursor solution preferably 30% and kept therein for a fixed duration (12-24 hours) of time. The mats are then taken out and dried in flowing air at 100°C. These mats are again fired at 400°C for 3 hours followed by slow cooling to room temperature.
Further, according to this invention there is also provided a process of preparing the novel precursor by condensing stoichiometric ratios of boric acid and a compound selected from
Glycerol or other polyols(including diols)
Diethanol amine
Triethanol amine
Ethanol amine
Urea and related compounds
Urea/formaldehyde and/or aliphatic alcohol
Melamine/formaldehyde and/or aliphatic alcohol
Melamine/benzoguanamine and related compounds
Aniline/guanidine and related compounds
in the presence of a suitable solvent.Then filtering the solid product thus obtained and purifying the said solid product by recrystallization for a solvent.
Further, in accordance with this invention the novel precursor is prepared by refluxing structure stoichimetric ratio of boric acid and a compound selected from
Glycerol or other polyols(including diols)
Diethanol amine
Triethanol amine
Ethanol amine
Urea and related compounds
Urea/formaldehyde and/or aliphatic alcohol
Melamine/formaldehyde and/or aliphatic alcohol
Melamine/benzoguanamine and related compounds
Aniline/guanidine and related compounds
in a resin kettle fitted with a stirrer and Dean-Strak trap in the presence of a solvent at atmospheric pressure. Water evolved during the course of the reaction is removed as an azeotrope and the progress of the reaction is monitored by measuring the amount of water of reaction collected through the Dean-Stark trap. The required temperature range is between 100-150°C and the time required is 4-6 hours.
Filtering the solid product from thus obtained and purifying the same by recrystallization from 95% ethyl alcohol. The reaction is carried until completion (when the liberation of water is completely stoped). The yield of the oligomer is 90%.
Examples
Filtration of Molten Meta, such as Aluminium using coated glass fiber mat:
Pyrolytic polymer coated glass fiber mat has been used to filter molten aluminum. No visual or microscopic evidence of the coating subsequent to filtration of the molten metal has been found. Any other metal (T < 800°C) can be filtered by these fiber mats.
Method 1. Synthesis of Triethanol amine-Boric Acid(poly) condensates: Equimolar quantities of triethanol amine and boric acid are taken in a resin kettle fitted with a stirrer and Dean-
Stark trap. The mixture is heated to reflux in presence of toluene or xylene at atmospheric pressure for 6 hours. Water evolved during the course of the reaction has been removed as an azeotrope. The progress of the reaction has been monitored by measuring the amount of water of reaction collected through the Dean-stark trap. The reaction is carried until completion (when the liberation of water is stopped). A light yellow colored solid (i.e., polyborate ester) is formed and is separated by filtration. The oligomer/polymer is purified by recrystallization from 95% ethyl alcohol (yield=90%).
Method 2. Synthesis of Urea-Boric Acid (poly) condensates: Three moles of urea and four moles of boric acid are taken in a resin kettle fitted with a stirrer and Dean-Stark trap. The mixture is heated to reflux in presence of toluene or xylene at atmospheric pressure for 4 hours. Water evolved during the course of the reaction has been removed as an azeotrope. The end-point of the reaction is monitored by measuring the amount of water of reaction collected through the Dean-Strak trap. The reaction is continued until the liberation of water is stopped. A white glassy solid is formed which is separated by filtration. The oligomer/polymer is purified by recrystallization from 95% ethyl acohol (yield=90%).
ME CLAIM:
1. A process of preparing polymer coated glass fiber mat by dip coating polymer/ oligomeric precursor such as herein described on glass fiber mats comprising:
a. cleaning the glass fiber mats, with a suitable solvent such as herein described.
b. prefiring the said cleaned glass fiber mats at a
temperature ranging from 300-500 ºC for 1-5 hrs.
c. cooling the said mats to room temperature ;
d. immersing the said cooled mats in 15-40% polymer/oligomer—precursor solution;
e. drying the said coated mats;
f. firing and dried coated mats for 3 hours at 400 ºC.
g. cooling the said coated mats slowly to the room temprature.
2. A process as claimed in claim 1, wherein said solvent is selected from aliphatic alcohol such as ethanol and aliphatic ketone such as acetone.
3. A process as claimed in claim 1, wherein said mats of
step (b) are prefired preferably at a temperature of 400 ºC for
3 hours.
4. A process as claimed in claim 1, wherein in step (d) the mats are immersed preferably in 30% precursor solution.

5. A procss as claimed in claim 1, wherein in step (e) the
step of drying is preferred in the presence of air at 100 ºC.
6. A process for preparing the polymer/oligomeric precursor by condensation comprising;
refluxing stoichiometric ratio of boric acid and a compound selected from Glycerol or other polyols (including diols)
Diethanol amine
Triethanol amine
Ethanol amine
Urea and related compounds such as herein described.
Urea/ formaldehyde and/or aliphatic alcohol
Melamine/formaldehyde and/or aliphatic alcohol
Melamine/benzoguanamine and related compounds such as herein described
Aniline/guanidine and related compounds such as herein
described, in the presence of a suitable solvent such as herein

described at a temperature of 100—150 ºC for 4-6 hours to produce
a solid product, separating said solid product from the reaction
mixture by filtration, purifying said solid product by
recrystallization.
7. A process as claimed in claim 6, wherein the solid product is recrystallized from 93% ethyl alcohol.

A process of preparing polymer coated glass fiber mat by dip
coating polymer/oligomeric precursor such as herein described on
glass fiber mats comprising: cleaning the glass fiber mats, with
a suitable solvent such as herein described, prefiring the said

cleaned glass fiber mats at a temperature ranging from 300—500 ºC
for 1-5 hrs, coaling the said mats to room temperature; immersing
the said cooled mats in 15—40% polymer/oligomer—precursor
solution, drying the said coated mats, firing the dried coated

mats for 3 hours at 400 ºC, cooling the said coated mats slowly
to the room temperature.