Inorganic substance composition and process for producing same

An inorganic substance composition comprising at least 50% by weight of a finely divided inorganic substance and 2 to 50% by weight of a fiber forming organic polymeric material and having a specific surface area of more than 2 m.sup.2 /g is described. The composition is prepared by preparing a liquid suspension from the inorganic substance, the organic polymeric material and a solvent; heating the liquid suspension to at least 100.degree. C to dissolve the organic polymeric material in the solvent; and then extruding the heated liquid suspension at a pressure equal to or higher than the vapor pressure of the solvent through an orifice into a zone of a lower pressure to evaporate the solvent.

The present invention relates to a novel inorganic substance composition 
composed of a predominant amount of a finely divided inorganic substance 
and a minor amount of a fiber forming synthetic polymeric material wherein 
said finely divided inorganic substance is incorporated so that its useful 
properties may effectively be utilized. It also relates to a process for 
producing such an inorganic substance composition. 
Attempts have been made to improve or modify the properties of organic 
polymeric materials by incorporating finely divided inorganic substances, 
and some of them are widely practiced in the manufacture of rubber, 
fibers, papers, molded articles, films and paints. In these fields finely 
divided inorganic substances are utilized as a reinforcing agent, or for 
the purpose of enhancing dimensional stability, rigidity, heat resistance, 
weatherability or printing properties, or as a filler to reduce the cost 
of the product. Inorganic substances have inherent properties, which 
cannot be seen in organic polymeric materials, such as high resistance to 
thermal distortion, high rigidity and high surface activity. These useful 
properties of inorganic substances have heretofore not been fully utilized 
in many cases. 
It has been found that in order to fully utilize the beneficial properties 
of a finely divided inorganic substance it should be present in the 
product in an amount of at least 50% by weight based on the weight of the 
product, and the product should have a specific surface area of more than 
2m.sup.2 /g. 
Thus, in accordance with one aspect of the present invention there is 
provided an inorganic substance composition comprising at least 50% by 
weight of a finely divided inorganic substance and 2 to 50% by weight of a 
fiber forming organic polymeric material and having a specific surface 
area of more than 2 m.sup.2 /g. 
In accordance with another aspect of the present invention there is 
provided a process for producing an inorganic substance composition which 
comprises the steps of: 
1. PREING A LIQUID SUSPENSION FROM THE FOLLOWING THREE COMPONENTS; 
A. a finely divided inorganic substance, in an amount which equals in 
weight at least 50% of the total weight of this component and component 
(b) below, 
b. a fiber forming organic polymeric material, in an amount which equals in 
weight 2 to 100% of the weight of the component (a), and 
c. a solvent capable of dissolving the component (b) at a temperature of at 
least 100.degree. C.; 
2. heating the liquid suspension a temperature of at least 100.degree. C. 
to dissolve the component (b) in the component (c); and then, 
3. extruding said heated liquid suspension under a pressure equal to or 
higher than the vapor pressure of the component (c) through an orifice 
into a zone of a lower pressure to evaporate the component (c) therefrom. 
The inorganic substance composition of the present invention is 
characterized as having a specific surface area of at least 2 m.sup.2 /g, 
preferably at least 10 m.sup.2 /g, and being usually in the form of a 
fibril-like, fine fibrous, fine flake-like, arborescent or fine web-like, 
porous structure having numerous fine, irregular voids therein. 
The "specific surface area" used herein is the ratio of the surface area 
per unit weight of the inorganic substance composition, determined by BET 
adsorption method. The specific surface area should be at least 2 m.sup.2 
/g and preferably at least 10 m.sup.2 /g. When the specific surface area 
is lower than 2 m.sup.2 /g, the inorganic substance composition is 
restricted in its use. For example, when the inorganic substance 
composition is used as an artificial soil, it is poor in hygroscopic 
property, adsorption of the effective components of fertilizer, and 
promotion in growth of roots. When used as adsorbent, it is poor in 
adsorption capacity. When used as a filter material, it is poor in 
filtration capacity. When used as sheet or paper stock, it is poor in 
dispersibility in a liquid medium, beatability and a paper making 
performance. 
The "finely divided inorganic substance" referred to herein means inorganic 
particles capable of passing through a 100 mesh screen of Japanese 
Industrial Standard and has a maximum size of up to 500 .mu.. 
Illustrations of such inorganic substance include, for example, asbesto, 
alumina, antimony trioxide, barite, calcium carbonate, calcium sulfate, 
kaolin clay, carbon black, diatomaceous earth, feldspar powder, terra 
abla, quartz, graphite, magnesium carbonate, magnesium hydroxide, 
magnesium oxide, mica, molybdenum disulfide, agalmatolite clay, sericite, 
pyrogenic silica, finely divided silicic acid, silica amorphous, silica 
sand, silicate, titanium oxide, whiting, slate powder and the like. These 
inorganic substances may be used either alone or as a mixture of two or 
more of these inorganic substances. 
The "polymeric material" referred to herein means a fiber-forming organic 
linear high molecular weight compound, which may have stabilizers, 
antistatics, flame retardants and other conventional additives. Examples 
of the polymeric materials are polyolefins, such as polyethylene, 
polypropylene, polybutene-1, polystyrene and polyisobutylene; polyamides 
such as polyhexamethylene sebacamide, polycaprolactam and polypyrrolydone; 
polyesters, such as polyethylene terephthalate, poly-.beta.-valerolactone, 
and poly-p(.beta.-hydroxyethoxy) benzoate; polycarbonates, polyurethanes, 
polyethers such as polyoxymethylene and poly-p-(2,6-dimethylphenoxide); 
homopolymers and copolymers of vinyl compounds, such as acrylonitrile, 
vinyl chloride, vinyl acetate, vinylidene chloride, and methyl 
methacrylate; a copolymer of vinyl alcohol and ethylene obtained by 
hydrolysis of a copolymer of vinyl acetate and ethylene. These polymeric 
materials may be used either alone or as a mixture of two or more of these 
polymeric materials. 
Properties of typical polymeric materials and finely divided inorganic 
substances which may be employed in the practice of the invention are 
listed in Tables I and II. 
Table I 
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Specific 
Particle Surface 
Finely Divided Inorganic 
Size V.sub.f V.sub.a 
Area 
Substance (Micron) (cc/g) (cc/g) 
(m.sup.2 /g) 
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Finely Divided Silicic 
Average 
Acid A (SiO.sub.2.nH.sub.2 O) 
0.020 0.50 1.91 150 
Finely Divided Silicic 
Average 
Acid B (SiO.sub.2.nH.sub.2 O) 
0.040 0.51 2.09 80 
Diatomaceous Earth 
95% 
10 or 0.55 1.50 20 
less 
Magnesium Carbonate 
Average 
0.1 0.46 1.81 20 
Clay 98% 
2 or less 
0.38 0.72 20 
Talc 98% 
4 or less 
0.37 0.87 13 
Calcium Carbonate A 
Average 
1.4 0.38 1.10 6 
Calcium Carbonate B 
Average 
4.0 0.40 0.70 2 
Magnesium Carbonate/ 
Calcium Carbonate 
-- 0.43 1.39 14 
(4/3 by weight) 
Finely Divided Silicic 
Acid B/Calcium Carbonate 
-- 0.46 1.49 50 
(3/2 by weight) 
Diatomaceous Earth/ 
Calcium Carbonate 
-- 0.40 1.31 14 
(4/3 by weight) 
Magnesium Carbonate/ 
-- 0.42 1.29 12 
Talc (4/3 by weight) 
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Table II 
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Polymer V.sub.p (cc/g) 
Softening point (.degree. C.) 
______________________________________ 
High Density Polyethylene 
1.05 135 
Law Density Polyethylene 
1.10 100 
Crystalline polypropylene 
1.09 160 
Polyacrylonitrile 
0.86 232 
Polyethylene Terephthalate 
0.77 200 
Polyvinyl Chloride 
0.70 150 
Polystyrene 0.95 160 
Nylon-66 0.88 240 
Polymethyl Methacrylate 
0.84 140 
______________________________________ 
In Table I, V.sub.a is the bulkiness of the finely divided inorganic 
substance and is measured under a load of 10 kg/cm.sup.2 in a manner as 
noted below. 
The measurement is carried out at a temperature of 25.degree. C. and under 
dry conditions using a cylinder of 15 cm in height and 2/.BECAUSE..pi. cm 
inner diameter having a removable flat bottom and equipped with a plunger 
movable up and down by means of an air-cylinder and capable of applying a 
load of 10 kg/cm.sup.2. A predetermined portion (Wg) of the finely divided 
inorganic substance to be measured is weighed and placed in the cylinder. 
The sample in the cylinder is then leveled by gently knocking the cylinder 
with a wood hammer. A load of 10 kg/cm.sup.2 is then applied on the 
plunger via the air-cylinder and allowed to stand for 1 minute. The 
plunger is then lifted. Another portion (Wg) of the sample is introduced 
to the cylinder and the general procedure as described above is repeated. 
The procedure is repeated 10 times in total. The volume of the sample (10 
.times. Wg) stacked in the cylinder is measured, and the bulkiness of the 
sample is calculated therefrom. The value of W employed in this 
measurement depends on the particular finely divided inorganic substance 
and the process for preparing the substance and is determined in a manner 
as follows. An appropriate portion of the sample is weighed and placed in 
a scaled glass cylinder of an inner diameter of 2/.fwdarw..pi. cm and a 
length of 30 cm and having a flat bottom so that the cylinder may be 
filled to a depth of about 20 cm with the sample. The cylinder is then 
caused to fall a distance of 2 cm onto a fixed surface at a rate of 60 
times per minute. The height of the sample in the cylinder is gradually 
lowered to an equilibrium value. From this value and the weight of the 
sample the bulk density of the sample is calculated and adapted as W in 
the above measurement. 
Values of V.sub.f given in Table I were determined by a method in 
accordance with JIS-K-5101. Values of softening point and V.sub.p given in 
Table II were determined by methods in accordance with ASTM-D-1526 and 
JIS-K-6760, respectively. 
The inorganic substance composition of the present invention is prepared by 
the steps of: 
1. dispersing a stated amount of a finely divided inorganic substance 
(component a) and a stated amount of a polymeric material (component b) in 
a solvent (component c) capable of dissolving said polymeric material at a 
temperature of at least 100.degree. C. to produce a liquid suspension; 
2. heating the liquid suspension to a temperature of at least 100.degree. 
C. to dissolve the polymeric material in said solvent; and then, 
3. extruding the heated liquid suspension under a pressure equal to or 
higher than the vapor pressure of said substance through an orifice into a 
zone of a lower pressure to evaporate said solvent therefrom. 
In the preparation of a liquid suspension from the three components a, b 
and c, mentioned above, both the manner and the order in which the three 
components are blended with each other are not critical. It is possible 
that water contained in the component a and/or component b will cause 
problems when the resulting composition is used in certain fields. In such 
a case, the water contained therein should preferably be removed, for 
example, by drying prior to the preparation of a liquid suspension of the 
three components. 
Component c, i.e., a solvent capable of dissolving component b, i.e., a 
polymeric material at a temperature of least 100.degree. C., should have a 
boiling point lower than the softening point of the polymeric material, 
employed and should be capable of dissolving the polymer material, under 
the extrusion conditions, i.e., at elevated temperature and pressure. The 
solvent should be substantially inert to the polymeric material, and 
construction materials of which the employed equipments are composed. 
Illustrative of suitable solvents, one can mention, for example, 
hydrocarbons such as butane, hexane, cyclohexane, pentene, benzene and 
toluene; halogenated hydrocarbons such as methylene chloride, chloroform, 
methyl chloride, propyl chloride, trichloroethylene, trichloroethane, 
tetrachloroethylene, tetrachloroethane, chlorobenzene, 
fluorotrichloromethane and 1,1,2-tricycloro-1,2,2-trifluoroethane; 
alcohols such as methanol, ethanol, propanol and butanol; ketones such as 
acetone, cyclopentanone, methyl ethyl ketone and hexafluoroacetone; esters 
such as methyl acetate, ethyl acetate and .gamma.-butyrolactone, ethers 
such as ethyl ether, tetrahydrofuran and dioxane; nitriles such as 
acetonitrile and propionitrile; and trifluoroacetic acid, carbon 
tetrachloride, carbon disulfide, nitromethane, water, and sulfur dioxide; 
and a combination thereof. Depending on the nature of the particular 
polymeric material, a suitable solvent should be selected. 
The liquid suspension of the three components is prepared in a closed 
vessel and heated to a temperature of at least 100.degree. C. in the 
vessel to dissolve the polymeric material in said solvent. The proportion 
of the solvent employed to the mixture of the finely divided inorganic 
substance and the polymeric material should desirably be such that the 
resulting heated suspension having the polymeric material dissolved 
therein will be flowable enough to be pumped. The heated suspension is 
maintained under an autogenous pressure of at least 5 kg/cm.sup.2, 
preferably at least 10 kg/cm.sup.2, and is extruded under this autogenous 
pressure or higher pressures through an orifice into a zone of a lower 
pressure and a lower temperature, preferably into an ambient atmosphere, 
to suddenly evaporate the solvent thereby leaving the desired porous 
structure. The last mentioned operation may be referred to as "spurting". 
In the practice of the manufacture of such a structure, any suitable 
apparatus, including a conventional autoclave, may be employed, provided 
that they are equipped with an orifice through which the heated mixture 
may be extruded or ejected under elevated temperature and pressures. 
Conveniently, a continuous extruder can be employed, comprising a pressing 
zone, compressing zone, heating zone, metering zone and an extrusion head 
having an orifice or orifices. 
The porous structure so obtained can be beaten in a liquid medium incapable 
of dissolving the polymeric material contained in the porous structure to 
be formed into a uniform slurry containing so-called fibrid. A sheet or 
paper may be prepared from the fibrid containing slurry by a conventional 
paper making procedure. 
Even if the polymeric material used for the preparation of the porous 
structure is a hydrophobic polyolefin, the porous structure can be 
successfully beaten and/or disintegrated in an aqueous medium by blending 
a minor amount, e.g., 10% by weight based on the weight of the porous 
structure, of hydrophilic cellulose pulp therewith to provide a slurry, in 
which fibrid-like structure elements are well dispersed, from which sheets 
can be made. 
The inorganic substance structure of the present invention may also be 
dispersed in a liquid medium incapable of dissolving the inorganic 
substance structure, such as, for example, methylene chloride and 
trichloroethylene, from which dispersion sheets can be made. 
Sheet-like structures made from the inorganic substance composition of the 
present invention exhibits enhanced postprocessability when compared with 
similar products obtained by prior art processes, since the former 
structure has lower densities and contains more voids therein, and in 
consequence can absorb various treating agents applied thereto to a 
greater extent. Thus, antistatic agents, flame retardants and other 
additives may readily be applied to the sheet-like structure of the 
invention. 
The sheet-like structure may be calendered at an appropriate temperature. 
It has been found that the calendered products have a surprisingly high 
initial modulus. They also have enhanced tenacity and dimensional 
stability. By way of an example, a calendered sheet obtained by a process 
in accordance with the invention and comprising 10 parts by weight of high 
density polyethylene and 90 parts by weight of calcium carbonate undergoes 
little or no shrinkage when heated to temperatures slightly below the 
melting point of the polyethylene. When fired, it goes on burning with 
little or no shrinkage. These results are surprising and quite unexpected 
from the behaviours of the comparable sheetlike products of polyolefin 
prepared by prior art processes, which undergo shrinkage to a great extent 
when merely approaching a heating source. The calendered sheet of the 
invention is superior to cellulose paper in the hydrophobic property. 
If desired, the inorganic substance composition of the present invention 
may be used as a filler in a paper-making process. This is advantageous 
because, firstly, the inorganic substance composition provides a yield 
higher than conventional fillers and, secondly, the composition exercises 
no harmful influence on the characteristics of the resulting paper even if 
the inorganic substance composition is used in a greater amount. 
If desired, a sheet-like structure may be prepared from a blend of the 
inorganic substance composition and a fibrous material such as natural 
fibers, synthetic fibers, semi-synthetic fibers, glass fibers, metal 
fibers and carbon fibers. The sheet-like structure generally has an 
improved tear strength and a good feel. 
The inorganic substance composition of the present invention has several 
used besides the sheet-like structure illustrated above. For example, it 
can be used as a molding material, a heat-insulation material, a packing 
material, a sound-proofing material and other construction materials. 
The invention will be further described in the following Examples, in which 
finely divided inorganic particle and polymer components are those 
indicated in Tables I and II, unless otherwise specified, and all parts 
are by weight.