Note: Descriptions are shown in the official language in which they were submitted.
1 ~7875~ `
- 2 - HOE 81/F 308
Fibrids are understood as meaning small fibers
~hich are oriented in longitudinal direction and have a
cellulose-like structure, i.e. which have a finite but
non-uniform length, ;rregular thickness, fissured surface
and a high degree of twinning.
The preparation of such fibrids is known, for
example from German Patent 1,290,040. In this patent,
the first step is to prepare plexus filaments, which are
then cut into staple lengths, the staple fiber particles
are suspended in a l;quid, and the particles present in
the suspension are fibr;llated in a way which is in itself
known. The term plexus filament is used here to describe
a filamentous product which is made from a crystalline
plastic and has a three-dimensional network which is
virtually free of tunnel-like channels and voids and con-
sists of a large number of molecularly oriented film- or
tape-l;ke fibrids which have a th;ckness of less than 2 ~m
and wh;ch co~b;ne w;th and separate from one another at
irregular intervals along their length and are preferably
2û oriented in the direction of the longitud;nal axis.
These plexus filaments, and their preparation, are
described in more detail in 8elgian Patent 568,524. In
this patent, a solution which is under its autogenous pres-
sure or under an elevated pressure of a synthetic polymer
25 tS ex~ruded at a temperature which ;s above the atmos-
pher;cally measured bo;ling point of the solvent through
an orifice into a space under a low pressure, to prcpare
l 178757
-- 3
the plexus filaments. This preparation of plexus filaments
is also called flash spinning or relaxation spinning.
Polyoxymethylene can also be used to prepare
plexus filaments in this way and then to fibrillate them
to give fibrids. The solvents used in Belgian Patent
568,524, to prepare the plexus filaments, are aprotic
solvents, namely methylene chloride, ethylene chloride,
acetonitrile and methyl ethyl ketone. As experiments
have shown, the process does not produce fibrids, but only
plexus filaments, even at extremely low polymer concen-
trations of, for example, 1X by weight in methyl ethyl
ketone. However, since plexus filaments are unsuitable
for producing paper and for use as an additive for build-
ing materials, they must be processed in a second process
step in accordance with German Patent 1,290,~40 above to
g;ve fibrids, the process becoming more involved as a
result. The polyoxymethylene fibrids thus obtained have,
in particular, a relatively small specific surface area
and a low degree of beating, and papers made therefrom
have relatively low strengths.
In contrast, U.S. Patent 2,988,782 proposes the
preparation of fibrids by precipitatin~ polymers under
certain precipitation conditions. Fibrids of this type
are suitable for preparir)g sheet-like structures on a
paper machine~ Ho~lever, in this patent fibrids are
understood as meanin~ particles which are fiber-like or
film-like~ ~he film-like constituents are troublesome in
industrial paper manufacture, since some of ~hem pass
throuyh the sieve. They also render the resulting paper
1 1~87~7
to be of low quality, since on printing film-like con-
stituents are picked out and white defects form. In
building materials, film-(ike constituents contribute
virtually nothing to the thickening action desired and
are therefore quality-reduc;ng.
Further, German Auslegeschrift 1,241,116 describes
the formation of long- or short-fibrous polyoxymethylene
by precipitating polyoxymethylene from its solutions (cf.
Examples). The products characterized as short-fibrous
are, however, those which are severely contaminated uith
film-like constituents. The long-fibrous product is found
to be unsuitable for making paper and for use as a thicken-
ing agent in building materials due to its excessive
length of 10 to 50 cm and its thickness of more than 1 mm.
Neither can the products described be dried without des-
troying their fibrid structure.
Finally, German Offenlegungsschrift 2,947,490 has
for the first time disclosed a one-stage process for pre-
paring polyoxymethylene fibrids using the flash spinning
2D method and which is characterized by a specific choice of
solvent mixture. However, this process has the disadvan
tage that the mixture claimed, of a low alcohol and water,
changes its composition during the evaporation step and
that expensive measuring and control devices therefore
become necessary for the continuous recycling of the
evaporated solvent mixture in order to maintain the sol-
vent composition at a constant value. The fibrids obtained
in this process also tend to stick together on drying
with substantial loss of their fibrid structure; their
1 1787~
bulk density is also relatively high.
The object of the present invention, then, was to
provide polyoxymethylene fibr;ds and a process for their
preparation which are free, or at least largely free, of
the disadvantages of the state of the art and, in par-
ticular, the abovementioned disadvantages.
Accordingly, the invention relates to polyoxy-
methylene fibrids which have a reduced specific viscosity
of 0.5 and 2.0 dl . 9-1, preferably 0.6 to 1.20 dl . 9-1
(measured in butyrolactone which contains 2% by weight of
diphenylamine, at 140C in a concentration of 0.5 9/100 ml)
and a specific surface area (by BET with argon) of 30 to
200 m2/g, preferably 50 to 120 m2/g, which are comprised
of at least 95% of fiber-like particles the average length
of which is between 0.2 and 5 mm and have a bulk density
which does not exceed 150 g/liter (air-dispersed s~ate).
The invention also relates to a process for pre-
paring polyoxymethylene fibrids by extruding a solution
of the polymer in a solvent mixture of lower alcohol and
water through a nozzle into a Drecipitation bath which is
kept in motion, wherein the temperature in the precipi-
tation bath is 0-100C and the solvent mixture contains
3-25X by weight of water, relative to the total mixture.
Known polyoxymethylenes are a suitable material
for preparing fibrids according to the invention. These
polyoxymethyLenes may be understood as incLuding homo-
polymers of formaldel7yde or of a cyclic oligomer of form-
aldehydef for example trioxane, the terminal hydro>yl
groups of which are stabilized against degradation in a
l 178757
- 6 -
kno~n ~ay by chemical means, for example by etherification
or esterification.
Furthermore, according to the invention, the term
polyoxymethylenes also embraces copolymers of formaldehyde
or of a cyclic oligomer of formaldehyde, preferably trioxane,
the copolymers having, in addition to oxymethylene units,
oxyalkylene un;ts in the primary valency chain which have
at least two, preferably two to eight, and specifically
two to four, adjacent carbon atoms and possess terminal
primary alcohol groups. The comonomer content in the
copolymers is advantageously 0.1 - 20, preferably 0.5-10,
% by weight and, in particular, 0.7 - 5X by ~eight.
Compounds which are suitable for copolymerizing
with formaldehyde or cyclic oligomers of formaldehyde,
preferably trioxane, are in particular cyclic ethers pre-
ferably having 3, 4 or 5 ring members and/or cyclic acetals
which differ from trioxane, namely preferably formals
having 5 - 11, preferably 5, 6, 7 or 8, ring members and/
or l;near polyacetals, preferably polyformals.
Suitable comonomers for trioxane are in particular
compounds of the formula
C~2 ~ ~CR1H]X - tO - (CR2~) ] -0
L z y
in which (A) R1 and R2 are identical or different and
each deno.es a hydrogen atom, an aliphatic alkyl radical
having 1 - 6, preferably 1, 2, 3 or 4, carbon atoms or a
phenyl radical and ~a) x is equal to 1, 2 or 3 and y is
equal to zero or (b) x is equal to zero, y is equal to
1, 2 or 3 and z is equal to 2 or (c) x is equal to zero,
y is equal to 1 ar,d z is equal ~o 3, 4, 5 or 6, or ~e) R1
l 178757
- 7 -
denotes an alkoxymethyl radical having 2 - 6, preferably
2, 3 or 4, carbon atoms or a phenoxymethyl radical, and
x is equal to 1 and y is equal to zero or y and z are
equal to 1 and R2 has the abovementioned meaning.
Epoxides, for example ethylene oxide, propylene
oxide, styrene oxide, cyclohexene oxide, oxacyclobutane
and phenyl glycidyl ether, in particular, are used as
cyclic ethers.
Suitable cyclic acetals are in particular cyclic
formals of aliphatic or cycloaliphatic a,~ -diols having
2 - 8, preferably 2, 3 or 4 carbon atoms and the carbon
chain of ~hich can be interrupted by an oxygen atom at
intervals of 2 carbon atoms, for example glycol formal
(1,3-dioxolane), propanediol formal (1,3-dioxane), butane-
diol formal ~1,3-d;oxepane) and diglycol formal (1,3,6-
trioxocane) and 4-chloromethyl-1,3-dioxolane and hexane-
diol formal ~1,3-dioxonane). Unsaturated formals, such
as butenediol formal (1,3-dioxacyclohept-5-ene), are also
possible.
Not only homopolymers but also copolymers of the
cyclic acetals defined above and also linear condensates
of aliphatic or cycloaliphatic a ,~ -diols ~ith aliphatic
aldehydes or thioaldehydes, preferably formaldehyde, can
be used as linear polyacetals. In particular, homopoly-
mers of l;near formals of aliphatic a,~ -diols having 2 -
8, preferably 2 - 4, carbon atoms, for example poly(1,3-
dioxolane), poly(1,3-dio%ane) and poly(1~3-dioxepane),
are used.
Conlpoul1ds having several polymeri~able qroups in the
1 17875~
-- 8 --
molecule, for example alkylglycidyl formals, polyglycol
diglycidyl ethers, alkanediol diglycidyl ethers or bis-
(alkanetriol) triformals, may also be used as addit;onal
comonomers for trioxane, in an amount of O.OS - 5, pre-
ferably 0.1 - 2, X by weight, relative to the total amount
of monomer. Such additional comonomers have been des-
cr;bed, for example, in German Auslegeschrift 2,101,817.
The values for the reduced specific viscosity
(RSV values~ of polyoxymethylenes used according to the
invention, and hence also of fibrids obtained therefrom,
are in general between 0.5 and 2.0 dl.g 1, preferably
between 0.7 and 1.20 dl.g 1 (measured in butyrolactone
which contains 2X by weight of diphenylamine, at 140C in
a concentration of 0.5 9/100 ml).
The crystallite melting points of the polyoxy-
methylenes are within a range of 140 - 180C, preferably
150C - 170C, and their densities are between 1.38 and
1.45 g.ml 1, preferably 1.40 and 1.43 g.ml~1 (measured
;n accordance with DIN 53,479).
lf polymers are used which have an RSV value which
is lower than those indicated above, fibrids are admittedly
also formed; but they are relatively short and mixed ~o
an increasing extent with non-fibrous fractions. By means
of the RSV value of the polymer it is thus possible to
control the fiber length, the degree of slenderness and the
degree of branching of the fibrids, so that preferable
ranges depend on where the fibrids are to be used. At
higher RSV values, in particular dissolving the polymer
proves increasingly troublesome and therefore nore expensive.
l 1787~7
The preferably binary or ternary oxymethylene co-
polymers used according to the invention are prepared in
a known ~ay by polymerizing the monomers in the presence
of cationically active catalysts at temperatures between
0 and 100C, preferably between 50 and 90C (cf. for
example U.S~ Patent 3,027,352). Examples of catalysts
used here are Lewis acids, for example boron trifluoride
and antimony pentafluoride, and complex compounds of Lewis
acids, preferably etherates, for example boron trifluoride
diethyl etherate and boron trifLuoride di-tert.-butyl
etherate. Protonic acids, for example perchloric acid,
and salt-like compounds, for example triphenylmethyl hexa-
f luorophosphate, triethyloxonium tetrafluoroborate or
acetyl perchLorate, are also suitable. The polymerization
can be ~arried out in water~ a suspension or a solution.
To remove unstable fractions, the copolymers are advan-
tageously subjected to partial controlled thermal or
hydrolytic degradation down to terminal primary alcohol
groups (cf. U.S. Patents 3,103,499 and 3,119,623).
2U Homopolymers of formaldehyde or of trioxane which
are used according to the invention are also prepared in
a known manner by catalytically polymerizing the r,onomer
(c~. for example U.S. Patents 2,768,994 and 2,989,505).
Fibrids according to the invention are comprised
of at least 95%, preferably o, at least 97% and in par-
ticular of 98 to 100% of fiber-like particles. They thus
contain either no or only an extremely small fraction of
film-like consti uents. The content of film-like con-
stituents is determined microscopically on moist, r,ot yet
I ~87~7
-- ~o --
dried, product. Their content is defined as the number
of film-like constituents in proportion to the total
number of par~icles in an area of the microscope slide.
Particles are called film-like if their ratio of length
to diameter is belo~ 5 : 1. The measurement area, and
also the concentration of particles in this measurement
area, must of course be chosen in such a way that an
adequate number of particles can be seen and hence the
accuracy of measurement is correspondingly high.
Since the content of fiber-like particles is high,
the bulk density is low and is at most 150 g/liter, pre-
ferably between 10 and 100 g/liter and in particular
' between 20 to 80 g/liter. To measure the bulk density
~;thin the meaning of the ;nvention, 10-50 9 of fibrids
dried at room temperature are whipped up at level II
~about 1,000 rpm) in a kitchen mixer, for example "Starmix"
from Messrs. Elektrostar Schottle GmbH and Co., Reichenbach,
with 1 liter capacity, until all fibrids are freely mobile;
this usually takes about 10 seconds. They are then dis-
charged by means of an earthed wire to eliminate theinfluence of an electrostatic charge which may be present.
The ~eight of the loose material is determined in a 250 ml
graduated rylinder, ~hich, before the reading is taken,
is repeatedly tapped firmly until the volume of the loose
material remains constant.
Fibrids according to the invention also have a
non-uniform length the mean of which is between 0.2 and
5 mm, preferably 0~2 to 2 mm and in particular betweon
0.5 and 1.5 mm. 1'he cross-sec~ion is also non-uniform in
~ vt~s tr~
1 178757
shape and size; the thickness ~the apparent diameter) is
predominantly about 1 - 2ûO ym~ preferably 2 - 50 ,um. The
mean length of the fibrids is determined as CFL (classi-
fied fiber length) in accordance with the TAPPI method
T 233, and the thickness of the fibrids is determined in
accordance with TAPPI method T 234 (coarseness). A method
which is suitable for rapidly determining th;s mean length
and the thickness of the fibrids is a measurement by
~ microscope, in which the most frequently occurring lengths
and thicknesses are visually determined. Only the longest
fibrils (branches) on the fibrids enter into this measure-
ment of len~th.
Since fibrids according to the invention are
highly branched, they have a large specific surface area
(by 8ET using ar~on) of usually 30 - 200 m2/g, prefer-
ably 50 - 120 m2/g.
The degree of beating is also correspondingly high
and amounts to 20 to 80 SR, preferably 25 to 50 SR. The
degree of beating is determined as the Schoppcr-Riegler
value in accordance with leaflet V/7/61 (old version 107)
of the Verein der Zellstoff- und Papier-Chemiker und
Ingenieure CAssociation of Cellulose and Paper Chemists
and ~ngineers] (issued on 1st July 1961).
Polyoxymethylene fibrids according to the invcntion
have hydrophilic surface properties and are therefore
readily dispersible in ~ater - usually even without a
wetting agent. Filters prepared therefrom have improvcd
adsorptive properties. In spccial cases it can even be
advisable to produce hydrophobic surface properties by
l 178757
- 12 -
adding suitable hydrophobing agents.
Fibrids according to the invention can contain the
additives described below, namely functional additives,
for example nucLeating agents, colored pigments, stabil~
izers, antistatic flame retardants, lubricants, optical
brighteners and the like as well as fillers. This can
affect the properties of the fibrids, for example in res-
pect of the morphology, the degree of beating or the bulk
density. Thus, certain heavy fillers will correspond-
ingly raise the bulk density; if such fillers are presentin high percentages, the limit specified above, of
150 g/liter, can be exceeded. However, the range accord-
ing to .he invention, of the bulk density, is maintained
if the dens;ty difference between filler and polymer ;s
allowed ~for.
The additives content is generally up to 75X by
weight, in the case of functional additives, preferably 0.1
to 10X by weight, relative to the total mixture; for fil-
lers the preferable range extends from 30 to 65% by weight.
Owing to their branched morphology, fibrids accord-
ing to the ;nvention can be very readily processed in a
known way, for example as described in German Patent
1,290,040, to give paper having good properties.
Excellent papers, which can be glazed, coated,
laminated and printed in a customary way, can be prepared
from these fibrids even when mixed w;th other fiber
materials, such as cellulose, cellulose fibers and synthetic
fibers.
Fibrids according to the invention can also be
1 1787S7
- 13 -
used, for example, for wallpapers, filters, labels,
metallic papers and other special papers and the like.
Polyoxymethylene fibrids can also be processed on board
machines, the resulting cardboards having an excellent
resistance to water. Polyoxymethylene fibrids according
to the invention can also be used in non-wovens and as
a thickening agent in rapid-curing asphalt, paints,
renders, adhesives, sealing compositions and coating
materials based on unsaturated polyesters, epoxide resins,
bitumen pastes and PVC plastisols. Finally, they are
also highly suitable as an additive to building materials,
such as cement, if appropriate together with other fiber-
forming materials, for example for manufacturing cement-
fiber boards and the like.
In the process according to the invention for pre-
paring polyoxymethylene fibrids, a solution of the polymer
is forced through one or more nozzles into a moving
precipitation bath. To carry out this process, first a
preferably homogeneous solution of the polymer is prepared,
starting from a dry or solvent-moist powder or granules,
depending on the method of preparation of the polymer,
and mixing the polymer ~ith the solvent and heating the
mixture, for example in pressure autoclaves with stirring,
for example by steam jacket heating or by blowing in steam.
~f in the polymer;zation or the subsequent stabilizing
and working-up processes the polyoxymethylenes are obtaincd
as a solution or suspension in an alcoholtwater mixture
of the composi' ion according to the invention, it is
possible to use this solut-ion or susper~sion d;rectly in
1 17875~
- 14 -
the process according to the invent;on.
According to the invention - as already mentioned -
~he solvent used is a mixture of 75 - 97X by weight
of a lower alcohol having 1 - 4 carbon atoms and 3 - 25X
by weight of water, each relative to the total solvent
mixture. Examples of lower alcohols which are possible
for this purpose are methanol, ethanol, isopropanol,
n-propanol, n-butanol and i-butanol and mixtures of these
alcohols. If higher alcohols, of more than 4 carbon atoms,
for example n-hexanol, are used fibrids are admittedly also
formed, but ;n this case the temperature which is neces-
sary for preparing the solution is relatively high.
Methanol and isopropanol are preferably used.
The mixing rat;o of alcohol and water is of con-
siderable importance for the preparation of the fibrids.If, for example, less than about 75% by ~eight of the
lower alcohol and more than about 25X by weight of water
are used, fibrids are obtained which, on drying not only
at room temperature, but also at elevated temperatures,
2~ stick together to form a more or less granular product
and lose their fibrid structure. The fibrid structure
can no longer be recovered by means of dispersing equip-
ment using customary mechanical forces. The tendency to
stick together can be monitored by measuring the bulk
Z5 density in the manner described above. A further disad-
vanta~e if the a~cohol content in the solvent mixture is
too low is that in this case the fibrids end up rela-
tively short.
~ f, on the other hand, a solvent mixture is used
~ 1787~7
- 15 -
which contains a relatively large amount of alcohol and
a relatively loh amount of water, the result is increasing
difficulties in dissolving the polymer. The range of
85 - ~SX by veight of the lo~er alcohol and 5 - 15X by
weight of water is preferable, since at these values the
dissolution properties of the polymer and the stability
of the fibrid morphology on drying and the producible
length of the fibrids are particularly well balanced.
The concentration of .he polymer in the solvent
mixture is as a rule between 10 and 300 9 per liter of
soLution, preferably bet~een 50 and 200 9 per liter.
Lower concentrations are usually uneconomicaL, since they
require a large amount of circulating solvent; higher
concentrations frequently harbour the risk that two-
1~ dimensional film-like constituents are formed. The upper
limit of the polymer concentration also depends to a certain
extent on the molecular weight; the h;gher the molecular
weight, the lower is the concentration permissible in this
process. If the process is carried out in a continuous
manner, the polymer concentration used must also be har-
monized with the amount of solvent in the precipitation
bath ;n order for the resulting fiber suspension to remain
pumpable, which requires a fibrid concentration of less
than 5% by weight. Depending on the length of the fibrids,
a final concentration of 1 - 3% by weight is as a rule
desirable. The longer the fibrids the more the suspension
has to be diluted.
There i a relationship between the polymer con-
centration and the fiber length, so that an expert can
l 1787~7
~ 16 -
use the polymer concentration (and - as mentioned - the
amount of alcohol) to set the desired fiber dimensions.
Thus, the fibrids become shorter the lower the polymer
concentration (and the lower the amount of alcohol).
The temperature of the solutiGn of the polyoxy-
methylene depends on the molecular weight of the polymer,
the nature and amount of the comonomer and the composition
of the solvent. If homogeneous solutions are used the
temperature necessary for d;ssolution must be considered
the lower temperature limit, while the upper temperature
limit is essentially only restricted by economic consider-
ations. The dissolution temperature is known for many
examples and can otherwise be easily experimentally
determined or interpolated from known data by an expert.
This temperature range ;s between 150 and 190C for the
preferred alcohols in their preferred mixing ratios with
~ater. The solution is as a rule under the autogenous
Yapor pressure of the solvent mixture at this temperature,
but the pressure can be considerably increased by inert
gas pressure or by means of a pump. The pressure is in
general between 20 and 60 bar, preferabLy between ZO and
30 bar.
In addition to the polymer, the solution can also
contain auxiliaries from the polymerization, for example
decomposition products of the catalys~s for the cationic
polymerizat;on, which products are described in 8ritish
Patent 1,i46,649~ ~erman Offenlegungsschriften 1,595,7U5
and 1,595,668 and German Ausle~eschriften 1,199,504 and
1,175,~2. These auxiliaries also include compounds which
I ~ 787~7
have a basic reaction and are used for removing unstable
fractions down to the terminal pr;mary aLcohol group, for
example lo~er tertiary aliphatic amires, such as tri-
ethylamine or triethanolamine, or a secondary alkali metal
phosphate, such as disodium hydrogenphosphate (cf. U.S.
Patents 3,174,948, 3,219,6Z3 and 3,666,714), and the
resulting reaction products, for example methylal, tri-
oxanc, tetroxane, formic acid and methyl formate.
The polymer solution can also contain a very wide
variety of known additives. Examples of such additives
are customary nucleating agents, which accelerate the
crystallization and by means of which the morphology of
the fibrids can be influenced, such as, for example,
branched or crosslinked polyoxymethylenes, taLc or boron
nitride (cf. German Patent 2,101,817 and German Offen-
legungsschrift 1,940,132).
Fillers can also be suspended ;n the solution.
Suitable fillers are all naturally occurring or synthetic-
ally prepared inorganic materials in unmodified or surface-
modified form, in particular metal powders, antimony tri-
oxide, carbon black, graphite, ground rock, quartz powder,
mica, slate po~der, feldspath powder, diatomaceous earth,
finely d;vided asbestos, sparingly soluble oxides, hy-
drated oxides, hydroxides, silicates, aluminates, borates,
2~ ferrites, sulfates, carbonates, basic salts and double
salts~ preferably containing aluminum and/or magnesium,
calcium, sodium, titaniuM or iron as the metal component.
Particularly prefer2ble fillers are t;tanium dioxide,
alumina, calcium carbonate, talc, dolornite, wollastor,ite,
1 1787~
- 18 -
silica, hydrated aluminum oxide and calcium sulfate. Of
these clay, calcium carbonate, talc and silica are par-
ticularly preferable.
These fillers can have been treated in a known
manner, for example ~ith silanes, and generally have a
mean particle size between 0.1 and 50 ~m, preferably
between 0.5 and 10 ~m.
The amount of additive in the polymer solution
depends on the field of application and on the nature of
the additive and is sufficiently high for the abovementioned
contents in the fibrids to be obtained. In general, the
amount ;s thus up to 80X, in the case of functional
additives preferably between 0.1 and 10X by weight, rela-
tive to the total solids comprised of polymer and additive.
In the case of a filler, a concentration of 30 - 70X by
~eight, relative to total sol;ds, is advantageously used
in most fields of applicat;on.
Further additives to be mentioned are kno~n stabil-
;zers against the influence of heat, oxygen and/or air,
as described, inter alia, in German Offenlegungsschrift
2,043,498. Compounds particularly suitable for this pur-
pose are bisphenol compounds, alkaline earth metal salts
of carboxylic acids and guanidine compounds. The bis-
phenol compounds used are chiefly esters of monobasic 4-
hydroxyphenylalkanoic ac;ds which conta;n 7 - 13, prefer-
ably 7, ~ or 9, carbon atoms and are mono- or di-ring-
substituted by an alkyl radical containing 1 - 4 carbon
atoms. The alcohol components in these esters are ali-
phatic dihydric, trihydric or tetrahydric alcohols which
~ ~787~7
_ 19 _
contain 2 - 6, preferably Z, 3 or 4, carbon atoms. Examples
uhich may be mentioned of such esters are esters of ~-(3-
tert.-butyl-4-hydroxyphenyl)-pentanoic acid, ~-(3-methyl-5-
5-tert.-butyl-4-hydroxyphenyl)-propionic acid, ~3,5-di-
tert.-bu.yl 4-hydroxyphenyl)-acetic acid, ~-(3,4-di-tert.-
butyl-4-hydroxyphenyl)-propionic acid or ~3,5-di-isopropyl-
4-hydroxyphenyl)-acetic acid with ethylene glycol, propane-
1,2-d;ol, propane-1,3-diol, butane-1,4-dioL, hexane-1,6-
d;ol, 1,1,1-trimethylolethane or pentaerythritol.
The alkaline earth metal salts of carboxylic acids
which are used are in particular alkaline earth metal
sa;ts of aliphatic, preferably hydroxyl-containing mono-
bas;c, dibac;c or tribasic carboxylic acids having 2 - 20,
preferably 3 ~ 9, carbon atoms, for example the calcium
or magnesium salts of stearic acid, ricinoleic acid,
lactic acid, mandelic acid, malic acid or citric acid.
Suitable guanidine compounds are compounds of the
formula
NC - NH - C - NH - R
NH
in which R denotes a hydrogen atom, a cyano group or an
alkyl radical having 1 - 6 carbon atoms, for e~ample
cyanoguanidine, N-cyano-N'-methylguanidine, N-cyano-N'-
ethylguanidine, N-cyano-N'-isopropylguanidine, N-cyano-N'-
tert.-butylg~anidine or N,N'-dicyanoguanidine. The guan-
idine compound, if used, is used in an amount ~f 0.01 -
1, preferably 0~02 - 0.5, X by weight, relative to the
total weight.
The solution can also contain other additives,
1 1787~
- 20 -
such as known antistatic agents, flame-retardants or lubri-
cants and the like.
Colored polyoxymethylene fibrids can be obtained
by dissolving or dispersing dyestuffs in the polymer
solution. The addition of optical brighteners is also
interestin~ for some applications.
To improve the dispersibility of the polyoxy-
methylene fibrids, surface-active agents, such as ethoxyl-
ated alcohols, carboxylic acids or amines, alkanesulfonates
or hydroxyl-bearing polymers such as polyvinyl alcohol
or carboxymethylcellulose, can also be added to the solution.
The polymer solution is then forced through one
or more nozzles which, although their design (size, shape
and length) affects the dimensions of the resulting fib-
rids, are not essential to the invention. Suitablenozzles have been described, for example in Belgian Patent
568,52~. Examples which may be mentioned here are simple
ho'e nozzles having a diameter of, for example, 0.5 - 5 mm,
tubes having a diameter of 1 - 10 mm and a length of 1 -
1,000 cm and conical nozzles having an annular gap witha width of ~.02 - 5 mm, preferably 0.05 - 0.5 mrn~ Valves
w;th an adjustable circle-shaped annular gap, where the
fiber dimensions can be affected by varying the annular
gap, are part;cularly preferable. A valve of this type
is shown in the attached Figure. In this Figure (1)
denotes a pipe through which the precipitation bath flows.
The valve (2), through which the polymer solution is added,
is mounted at right angles to the pipe; (3) represents
the valve housing and (4) represen~s the valve cone, ~ith
~ ~787~7
- 21 -
~hich the circle-shaped annular gap can be variably
adjusted. (a), (b), (c) and (d) indicate the valve cone
position actually used in the present IlLustrative Embodi-
ment 1.
The narrower the gap or the orifice of the nozzle,
the shorter and more slender are the resulting fibrids.
The linear speed at the narrowest point of the nozzle
is in general between 1 and 200 m/s, preferably 5 - 30 m/sec
The polymerization product passes through the
nozzle and then into a cold moving precipitation bath,
where the polymer prec;pitates with the formation of
fibrids. The precipitation bath is preferably comprised
of the same solvent mixture as that of the polymer solution,
s;nce if the process is carried out in a continuous manner
t~is enables solvent recycling to take place without
expensive measuring and control equipment. However, in
principle the process according to the invention can also
be operated without this advantage, using mixtures of a
lo~er alcohol and ~later of a different composition. Also,
other solvents which are not acidic, for example ketones,
esters, ethers and the like, can also be used in principle
as the precipitation bath.
The temperature of the precipitation bath is,
according to the invention, advantageously between 0 and
100C, preferably between 30 and 70C. The temperature
of the precipitation bath is measured downstream of the
nozzle, after complete and thoroucJh mixing of solvent and
pr~cipitating medium. Although the polymer also precipi-
tates a~ eleva~ed ~emperatures, very short fibrids or
l ~78757
- 22 -
two-dimensional film-like structures are increasingly
produced - according to the other process conditions.
This tendency can be opposed to a certain extent by using
~ solvent mixture with a correspondingly higher alcohol
5- content. The use of relatively low temperatures is tech-
nically more involved, since this requires using expensive
refrigerants, without the quality of the resulting fibrids
being significantly improved. To obtain the preferred
ranges of the precipitation temperature, the temperature
of the precipitating so(vent before the nozzle, depending
on the intensity of agitation, the temperature of the
solution and the throughput speed is between 20 and 60C.
If the process is carried out in a continuous manner, this
solvent is obtained by cooling down the filtrate after
the fibrids have been separated off or by cooling the fib-
rid suspension and subsequently separating off the fibrids,
cooling ~ater be;ng normally used for the cooling down.
According to the invention, the precipitation
bath must be adequately agitated to enable the formation
of the fibrids aimed at according to the invention. The
exact extent of this necessary agitation can be readily
determined by a small number of experiments, but, naturally,
the intensity of agi.at,on must be chosen to be hi~her the
greater the throughput through the nozzle in order to
avoid damming in front of the nozzle and to generate rapid
mi~;ng. It can also be stated in general that a low
degree of agitation favors the formation of film-like
constituents. If, thus, there ;s the risk of forming such
short-fibered film~like cons~ituents even due to the other
l 1787$~
- 23 -
process conditions, such as low alcohol content, high
concentration of the dissolved polymer or high temperature
of the precipitation bath, then th;s risk can be opposed,
to a certain extent, by more thorough agitation of the
5- prec;pitation bath. In general, this agitation should be
such that the linear speed is at least 0.1 m/s, preferably
0.1 - 30 m/s and part;cularly preferably 0.3 - 10 m/s.
Lower speeds can produce sheet-shaped constituents with-
out fibrid characteristics or continuous filament-like
1~ structures. In contrast, speeds higher than 30 m/s re-
quire an unnecessarily high mechanical energy. To
obtain this linear speed, the precipitation bath, if
contained in a cylindrical vessel, can be stirred or, if
contained in a closed tube, circulated. It is essentially
;mmater;al for the formation of dryable fibrids without
f;lm-l;ke constituents whether the flow ;s l;near or
turbulent.
The angle between the direction of motion of the
solut;on in the nozzle and of the cold solvent has no
sign;ficant influence on the properties of the product.
An angle between 30 and 90 ;s preferable for technical
reasons. In particular in the case of conical nozzles,
th;s angle may not be the same for all parts of the nozzle.
If necessary, the fibrids can be ground and/or
Z5 classified by known methods to affect the degree of fibril-
lation, the fiber length or the distribution of fiber
lengths. However, grindiny is in principle not necessary
in order to set free discrete particles.
The fibrids are then rernoved frorn the precipitation
l 1~87S~
- 24 -
bath by freeing them from a large proportion of non-
evaporated solvent, by known mechanical methods, for
example by filtering with suction, squeezing oft, centri-
fuging and the like, and, if necessary, washed with water
and dried. The fibrids can be loosened up mechanically
by means of suitable mills, a bulk density of 10 -
150 g/liter being obtained.
A significant advantage of the process according
to the invention, over known methods of preparing fibers
by precipitating, is that highly branched fibrids which
are almost or completely free of sheet-shaped film-like
constituents are solely formed. The process according to
the invention, by the choice of suitable parameters such
as polymer concentration in the solution, size of the
nozzle orifice and speed of the solution and of the pre-
cipitation bath, also produces fibrids which ~hile having
a high degree of slenderness have a mean length within the
millimeter range. Fibrids prepared according to the
invention do not stick together on drying, unlike
polyoxymethylene fibrids prepared by flash evaporation,
so that the fibrid structure is fully retained on drying.
This feature makes these fibrids very highly suitable even
for dry mixtures of building materials, into which the
filler-containing fibrids can be mixed particularly ~ell
owing to their higher specific density. The process
according to the invention is also technically less
involved, since the condensation of the vapors and the
correction of the solvent composit;on by dis~illation
and the associated-measurin~ and con~rolling effort are
~ 1787~
- 25 -
eliminated.
The examples which follow illustrate in more
detail the fibrids according to the invention and the
process for their preparation:
Example 1
A solution of 3.8X by weight of a copolymer of
98X by weight of trioxane and 2X by weight of ethylene
oxide and which had an RSV value of 1.0 dl/g and 0.1% by
weight of triethylamine in a mixture of 95-~ by weight of
methanol and 5% by weight of water was prepared with
st;rring at 180C in a pressurized storage vessel. The
solution, under a pressure of 27 b2r, was forced through
an annular nozzle as in the Figure. In th;s nozzle, the
valve cone had a position which was such that a = 7 mm,
b = 0.15 mm, c = 0.07 mm and d = 7.2 mm. the diameter
of the valve housing was 12.4 mm. A throughput of 280
liter~h was obtained under the above conditions.
After passing through the nozzle this solution then
flowed immediately into a pipe which was located at right-
angles to the nozzle and had a diameter of 40 mm and inwhich the above solvent mixture flowed by with a speed of
0.35 m/s. The temperature of the precipitation bath was 40C
in front of the nozzle and 59C after mixing had been
effected. The resulting fibrids were filtered off with
suction on a drum filter, washed with water until methanol-
free, dried at room temperature and mechanically loosened
up by stirring for 5 minutes in a Henschel mixer. Micro-
scopic inspection in polarized light showed that the
fibrids were free of film-like constituents. The data
1 ~787~
- 26 -
measured are listed in Table 1.
3.0 g of the fibrids obtained in accordance with
this example were used, together with 10 liters of water,
to form a sheet of paper on the Rapid-Kothen manual sheet
S former; no losses occurred.
50 g of these fibrids were also used to prepare a
t~ ~(tile) adhesive comprising 40 parts of cement, 6~
, . . . .. . . . . . .
parts of sand, 5 parts of an ethylene/vinyl acetate co-
polymer powder prepared ~ith po~yvinyl alcohol as a pro-
tective colloid (88% by weight of vinyl acetate, and 12Xby weight of ethylene), 0.5 part of methylhydroxyethyl-
cellulose (viscosity of 2% strength solution in water at
20C: 6,000 mPa.s) and 0.4 part of polyoxymethylene
fibrids. After stirring with 33 parts of water the mix-
ture produced a thin-bed adhesive which had a creamy con-
sistency and which could be smoothly spread out by means
of a doctor blade.
10 9 of these fibrids were also used to prepare
a fiber-cement board, by being dispersed in 800 ml of
water in a kitchen mixer and the dispersion being stirred
into 200 9 of Portland cement. The evenly dispersed
suspension was then used, this time together with 6
liters of water, to form a fiber-cement board on the
Rapid-Kothen manual sheet former. This board was com-
25 pressed overnight under a pressure of 200 kp/cm2 C2,850
psi~ at room temperature using wire screens. After stor-
age for four weeks, the board had a weight of 201~ 9 and
a density of 1.63 g/cm3.
1 1 787~7
- 2~ -
Example 2
Corresponding to Example 1, a solution of 3.0X
by weight of a copolymer of ~7.94% by weight of trioxane,
2X by weight of ethylene oxide and 0.06% by weight of
butanediol diglycidyl ether and which had an RSV value
of 0.99 dl/g and 0.1% by weight of triethylamine was pre-
pared at 180C in a mixture of 90X by weight of iso-
propanol and 10% by weight of water and forced through a
nozzle as in the ~igure, but the valve was adjusted so
as to produce a throughput of 250 liter~h. The precipi-
tation bath of 90X by weight of isopropanol and 10X by
~le;ght of water ;n this case flowed with a speed of 0.55
m/s at rightangles past the mouth of the nozzle. The
precipitation bath had a temperature of 42C in front
of the nozzle and a temperature of 55C after rixing
had been effected. In isolating the fiber the vater
wash of Example 1 was dispensed with. The data measured
are summarized in Table 1.
A filter sheet of 3 mm thickness was prepa ed
from the fibrids obtained, bleached fir sulfite pulp with
40 SR and kieselguhr in a weight ratio of 40~0/20 in
a Rapid-Kothen manual sheet former. This sheet was in-
serted into a laboratory pressure filter. On filtering
turbid cider, all materials responsible for this turbid-
ity were retained. The filtrate was clear.Example 3
Corresponding to Example 1, a solution of 4.3'~
by weigh~ of a homopolymer of trioxane and the .erminal
groups of which had been blocked wi~h acetate groups and
l 178757
- 28 -
She RSV value of which was 0.81 dl/g was used. The flow
rate of the prec;p;tation bath was in th;s case 0.60 m/s
and the precipitation temperature was 50C. The data
measured are summarized in Table 1.
6 Example 4
Corresponding to Example 1, a mixture of 97X by
weight of a solvent mixture comprising 85X by ~eight of
methanol and 15X by weight of water and 3% by weight of
solids compr;sing 33 1/3% by weight of alumina (English
china clay with a mean particle size of 3 ~m and the
analysis of which produces 46.2X of SiO2, 3~.7X of
- Al2G3 and 13.1% of loss on ignition) and 66 2/3X by
we;ght of the copolymer in accordance with Example 2 was
prepared at 182C, and the copolymer dissolved. As
for the rest, Example 1 was followed, but the water wash
was dispensed with. The fibrids contained 31.2X of alumina,
uhich corresponds to a pigment incorporation rate of 93X.
The remaining data are listed in Table 1.
Example 5
Example 4 was repeated using a solvent mixture
of ~0% by weight of methanol and 10X by weight of water
and as sol;ds a mixture of 70X by weight of calcium car-
bonate with an orthorhombohedral particle shape and a
mean particle size of 0.6 ~m and 30% by weight of the
copolymer used in Example 2. The resulting fibrids con-
tained 63.6% of calcium carbonate, which corresponds to
a pîgment incorporation rate of 91% by weight~ The
remaining data are listed in Table 1.
~ ~787~
- 29 -
Example 6
Corresponding to Example 2, a solution ~as prepared
of 10.0X by weight of the copolymer specified there in a
m;xture of 90X by weight of methanol and 10X by weight
of water, at 182C and, as described in Example 2,
forced through a nozzle into a precipitation bath. The
product was ~orked up as described in Example 1. The
data measured are shown in Table 1.
~ Morphology moist fibrids
dry f;brids
Specific surface area 53 m2/g
Fraction of fiber-like particles ~9.5 %
Bulk density 25 g/liter
Mean fiber length 1.4 mm
Example 7
Example 1 was modified in such a way that the
precipitation bath was not a methanol/water mixture but
pure water. The data measured are shown in Table 1.
Morphology moist fibrids
dry fibrids
Specific surface area 61 m2/g
Fraction of fiber-like particles 99.5 X
8ulk density 44 g/liter
Mean fiber length 0.6 mm
Example 8
Example 1 was modified in such a way ~hat the
copolymer used comprised 96.6X of trioxane and 3.4X of
dioxolane and was emplGyed in a concentration of 2.0% by
weight, relative to the poly~er solu~ion. ~he data
~ 178~
- 30 -
measured can be seen ,ro~ Table 1.
Morphology moist fibrids
dry fibrids
Specific surface area 79 m2/g
Fraction of fiber-like particles 99.5 X
Bul~ density 31 g/liter
Mean fiber length 0.3 mm
A coating composition was prepared from 3.0X by
weight of the dried fibrids and 98% by weight of an un-
saturated polyester having a viscosity of 1,000 mPa.s,by dispersing the mixture in a toothed disk disperser.
Applied in a thickness of 1 mm, this composition did not
run off from a glass plate mounted so as to be vcrtical.
Comparative Example 1
Corresponding to Example 1, a solvent mixture
co~prising 6~X by weight of methanol and 40% by weight
of water was used. The resulting fibrids were extremely
short and severely contaminated with film-like material.
On drying at room temperature, the fibrids stuck to-
gether to form a crumbly product. If the moist product
;s used to prepare paper as in Example 1, 16% by weight
of the product pass through the sieve.
If the dried product is used to prepare a thin-
bed adhesive in accordance with Examplc 1, the adhesive,
after having been made up with water and applied with a
doctor blade, does not have a hold-out (it flows without
the action of shear forces) and its sur,ace is not smooth
due to grainy constituents. Thin-bed adhesives contain-
ing dried f;~rids produced by the flash process in
~ 178757
- 31 -
accordance with German Offenlegungsschrift 2,947,490
behave in the same way. The data measured are listed in
Table 1. The fibers were classified before the drying
step.
Comparative Example 2
~ xample 1 was followed, but the precipitation
temperature was adjusted to 132C. Th;s did not pro-
duce any fibrids but only a grainy product having a mean
particle size of about 0.45 mm.
Comparative Example 3
Example 1 of German Offenlegungsschrift 2,947,490
was repeated. The fibrids formed were filtered off and
dr;ed at room temperature. In this step, fibr;ds became
stuck together with the formation of an essentially
crumbly and grainy product having a bulk density of 190
g/liter.
1 1787~7
-- 32 --
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