U.S. patent application number 10/505775 was filed with the patent office on 2006-05-18 for microspheres.
This patent application is currently assigned to AKZO NOBEL N.V.. Invention is credited to Ingela Eriksson, Anna Kron, Orjan Soderberg.
Application Number | 20060102307 10/505775 |
Document ID | / |
Family ID | 33542576 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060102307 |
Kind Code |
A1 |
Kron; Anna ; et al. |
May 18, 2006 |
Microspheres
Abstract
The invention relates to a process for the production of paper
or nonwoven fibres comprising the steps of adding thermally
expandable microspheres comprising a thermoplastic polymer shell
and a propellant entrapped therein to a stock comprising fibres or
to a web of fibres, forming paper or nonwoven from the stock or the
web, and applying heat to raise the temperature of the microspheres
sufficiently for them to expand and thereby increase the bulk of
the paper or the nonwoven, wherein said expandable microspheres
comprise from about 17 to about 40 wt % propellant and have a
volume-average diameter from about 17 to about 35 µm. The invention
also concerns certain expandable microspheres and use thereof.
Inventors: |
Kron; Anna; (Sundsvall,
SE) ; Soderberg; Orjan; (Njurunda, SE) ;
Eriksson; Ingela; (Sundsvall, SE) |
Correspondence
Address: |
WHITE, REDWAY AND BROWN LLP
1217 KING STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
AKZO NOBEL N.V.
VAIPERWEG 76, P.O. BOX 9300
ANNHEIM
NL
6800
|
Family ID: |
33542576 |
Appl. No.: |
10/505775 |
Filed: |
June 1, 2004 |
PCT Filed: |
June 1, 2004 |
PCT NO: |
PCT/SE04/00835 |
371 Date: |
September 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60482497 |
Jun 26, 2003 |
|
|
|
Current U.S.
Class: |
162/168.1 ;
162/147; 162/158 |
Current CPC
Class: |
D21H 21/54 20130101;
C08J 9/18 20130101; D21H 27/30 20130101; B01J 13/14 20130101 |
Class at
Publication: |
162/168.1 ;
162/147; 162/158 |
International
Class: |
D21H 21/54 20060101
D21H021/54 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2003 |
EP |
03445085.8 |
Claims
1-17. (canceled)
18. Process for the production of paper or nonwoven from fibres
comprising the steps of adding thermally expandable microspheres
comprising a thermoplastic polymer shell and a propellant entrapped
therein to a stock comprising fibres or to a web of fibres, forming
paper or nonwoven from the stock or the web, and applying heat to
raise the temperature of the microspheres sufficiently for them to
expand and thereby increase the bulk of the paper or the nonwoven,
wherein said expandable microspheres comprise from about 17 to
about 40 wt % propellant and have a volume-average diameter from
about 17 to about 35 .mu.m according to ISO13319:2000.
19. Process as claimed in claim 18, wherein the expandable
microspheres have a volume-average diameter from about 19 to about
35 .mu.m according to ISO13319:2000.
20. Process as claimed in claim 18, wherein the expandable
microspheres comprise from about 19 to about 40 wt %
propellant.
21. Process as claimed in claim 18, wherein the thermoplastic
polymer shell is made of a co-polymer from ethylenically
unsaturated monomers comprising at least one acrylic ester or
methacrylic ester monomer and at least one vinylidene halide
monomer.
22. Process as claimed in claim 21, wherein the thermoplastic
polymer shell is a co-polymer obtained from monomers comprising
methyl methacrylate, vinylidene chloride and acrylo nitrile.
23. Process as claimed in claim 18, wherein the propellant
comprises isobutane.
24. Process for the production of paper comprising the steps of
adding expandable microspheres to a stock containing cellulosic
fibres, dewatering the stock on a wire to obtain paper, and drying
the paper by applying heat and thereby also raising the temperature
of the microspheres sufficiently for them to expand and increase
the bulk of the paper, wherein said expandable microspheres
comprise from about 17 to about 40 wt % propellant and have a
volume-average diameter from about 17 to about 35 .mu.m according
to ISO13319:2000.
25. Process as claimed in claim 24, wherein paper comprising three
or more layers is produced and the expandable microspheres are not
added to the portion of the stock forming any of the two outer
layers.
26. Process as claimed in claim 24, wherein the cellulosic fibres
partly or fully originate from recycled paper.
27. Process as claimed in claim 24, wherein the expandable
microspheres have a volume-average diameter from about 19 to about
35 .mu.m according to ISO13319:2000, comprise from about 19 to
about 40 wt % of isobutane as propellant, and the thermoplastic
polymer shell is a co-polymer obtained from monomers comprising
methyl methacrylate, vinylidene chloride and acrylo nitrile.
28. Process for the production of nonwoven as claimed in claim 18,
comprising the steps of forming a web of fibres, adding to said web
a binder and expandable microspheres, and forming nonwoven and
applying heat to raise the temperature of the microspheres
sufficiently for them to expand and thereby increase the bulk
nonwoven, wherein said expandable microspheres comprise from about
17 to about 40 wt % propellant, and have a volume-average diameter
from about 17 to about 35 .mu.m according to ISO13319:2000.
29. Thermally expandable microspheres comprising a thermoplastic
polymer shell made of a co-polymer obtained by polymerizing
ethylenically unsaturated monomers comprising at least one acrylic
ester or methacrylic ester monomer and at least one vinylidene
halide monomer and from about 17 to about 40 wt % of a propellant
entrapped in said polymer shell, wherein the expandable
microspheres have a volume-average diameter from about 17 to about
35 .mu.m according to ISO13319:2000.
30. Thermally expandable microspheres as claimed in claim 29,
wherein the ethylenically unsaturated monomers comprise acrylo
nitrile.
31. Thermally expandable microspheres as claimed in claim 29,
having a volume-average diameter from about 19 to about 35 .mu.m
according to ISO13319:2000.
32. Thermally expandable microspheres as claimed in claim 29,
comprising from about 19 to about 40 wt % propellant.
33. Thermally expandable microspheres as claimed in claim 29,
wherein the blowing agent comprises isobutane.
34. Thermally expandable microspheres as claimed in claim 29,
wherein the expandable microspheres have a volume-average diameter
from about 19 to about 35 .mu.m according to ISO13319:2000,
comprise from about 19 to about 40 wt % of isobutane as propellant,
and the thermoplastic polymer shell is a co-polymer obtained from
monomers comprising methyl methacrylate, vinylidene chloride and
acrylo nitrile.
Description
[0001] The present invention relates to a process for the
production of paper or nonwoven and thermoplastic expandable
microspheres useful therefore.
[0002] Expandable thermoplastic microspheres comprising a
thermoplastic polymer shell and a propellant entrapped therein are
commercially available under the trademark EXPANCEL.RTM. and are
used as a foaming agent in many different applications.
[0003] In such microspheres, the propellant is normally a liquid
having a boiling temperature not higher than the softening
temperature of the thermoplastic polymer shell. Upon heating, the
propellant evaporates to increase the internal pressure at the same
time as the shell softens, resulting in significant expansion of
the microspheres. The temperature at which the expansion starts is
called T.sub.start, while the temperature at which maximum
expansion is reached is called T.sub.max. Expandable microspheres
are marketed in various forms, e.g. as dry free flowing particles,
as an aqueous slurry or as a partially dewatered wet-cake.
[0004] Expandable microspheres can be produced by polymerising
ethylenically unsaturated monomers in the presence of a propellant.
Detailed descriptions of various expandable microspheres and their
production can be found in, for example, U.S. Pat. Nos. 3,615,972,
3,945,956, 5,536,756, 6,235,800, 6,235,394 and 6,509,384, and in EP
486080.
[0005] It has been disclosed to use microspheres in papermaking,
for example in U.S. Pat. Nos. 3,556,934 and 4,133,688, JP Patent
2689787 and in O. Soderberg, "World Pulp & Paper Technology
1995/96, The International Review for the Pulp & Paper
Industry" p. 143-145.
[0006] It is an object of the invention to provide a process for
the production of paper or nonwoven with low bulk density.
[0007] It is another object of the invention to provide expandable
thermoplastic microspheres that can be used in the production of
paper or nonwoven with low bulk density.
[0008] It has previously been believed that expandable
thermoplastic microspheres of large size would have poor expansion
properties. However, it has now been found that such microspheres,
when also having high content of propellant, give higher expansion
than expected when used in the production of paper or nonwoven for
increasing the bulk thereof.
[0009] The invention thus concerns use of thermally expandable
microspheres comprising a thermoplastic polymer shell and from
about 17 to about 40 wt %, preferably from about 18 to about 40 wt
%, most preferably from about 19 to about 40 wt %, particularly
most preferably from about 20 to about 35 wt % of a propellant
entrapped in said polymer shell, and having a volume-average
diameter from about 17 to about 35 .mu.m, preferably from about 18
to about 35 .mu.m, more preferably from about 19 to about 35 .mu.m,
most preferably from about 20 to about 30 .mu.m, particularly most
preferably from about 21 to about 30 .mu.m, in the production of
paper or non-woven for Increasing the bulk thereof.
[0010] The term expandable microspheres as used herein refers to
expandable microspheres that have not previously been expanded,
i.e. unexpanded expandable microspheres.
[0011] All figures for volume-average diameter given herein refer
to values obtained by measuring according to ISO 13319:2000,
"Determination of particle size distributions--Electrical sensing
zone method". Detailed description of this measuring method can be
obtained from, for example, Swedish Institute For Standards,
Stockholm.
[0012] The invention further concerns a process for the production
of paper or nonwoven from fibres comprising the steps of adding
thermally expandable microspheres comprising a thermoplastic
polymer shell and a propellant entrapped therein to a stock
comprising fibres or to a web of fibres, forming paper or nonwoven
from the stock or the web, and applying heat to raise the
temperature of the microspheres sufficiently for them to expand and
thereby increase the bulk of the paper or the nonwoven. The
expandable microspheres have a volume-average diameter from about
17 to about 35 .mu.m, preferably from about 18 to about 35 .mu.m,
more preferably from about 19 to about 35 .mu.m, most preferably
from about 20 to about 30 .mu.m, particularly most preferably from
about 21 to about 30 .mu.m. The amount of propellant in the
expandable microspheres is from about 17 to about 40 wt %,
preferably from about 18 to about 40 wt %, most preferably from
about 19 to about 40 wt %, particularly most preferably from about
20 to about 35 wt %.
[0013] An embodiment of the invention concerns a process for the
production of paper comprising the steps of adding expandable
microspheres as described above to a stock containing cellulosic
fibres, dewatering the stock on a wire to obtain paper, and drying
the paper by applying heat and thereby also raising the temperature
of the microspheres sufficiently for them to expand and increase
the bulk of the paper. The expandable microspheres may be added
separately or together with one or more other additive used in the
papermaking process.
[0014] The expandable microspheres can be added in any form,
although it from a practical point of view is most preferred to add
them in the form of an aqueous slurry, preferably having a solids
content from about 5 to about 55 wt %, most preferably from about
40 to about 50 wt %. The slurry preferably also comprises a
thickener compatible with paper making, such as anionic or cationic
starch, optionally in combination with a salt such as sodium
chloride. Starch may, for example, be present in the slurry in an
amount from about 0.1 to about 5 wt %, preferably from about 0.3 to
about 1.5 wt %. Sodium chloride, or another salt, may, for example,
be present in the slurry in an amount from about 0.1 to about 20 wt
%, preferably from about 1 to about 15 wt %.
[0015] The amount of expandable microspheres added to the stock is
preferably from about 0.1 to about 20 wt %, most preferably from
about 0.2 to about 10 wt % dry microspheres of the dry content in
the stock. Any kind of paper machine known in the art can be
used.
[0016] The term "paper", as used herein, is meant to include all
types of cellulose-based products in sheet or web form, including,
for example, board, cardboard and paperboard. The invention has
been found particularly advantageous for the production of board,
cardboard and paper board, particularly with a basis weight from
about 50 to about 1000 g/m.sup.2, preferably from about 150 to
about 800 g/m.sup.2.
[0017] The paper may be produced as a single layer or a multi-layer
paper. If the paper comprises three or more layers, the expandable
microspheres are preferably not added to the portion of the stock
forming any of the two outer layers.
[0018] The stock preferably contains from about 50 to about 100 wt
%, most preferably from about 70 to about 100 wt % of cellulosic
fibres, based on dry material. Before dewatering, the stock besides
expandable microspheres, may also contain one or more fillers, e.g.
mineral fillers like kaolin, china clay, titanium dioxide, gypsum,
talc, chalk, ground marble or precipitated calcium carbonate, and
optionally other commonly used additives, such as retention aids,
sizing agents, aluminium compounds, dyes, wet-strength resins,
optical brightening agents, etc. Examples of aluminium compounds
include alum, aluminates and polyaluminium compounds, e.g.
polyaluminium chlorides and sulphates. Examples of retention aids
include cationic polymers, anionic inorganic materials in
combination with organic polymers, e.g. bentonite in combination
with cationic polymers or silica-based sols in combination with
cationic polymers or cationic and anionic polymers. Examples of
sizing agents include cellulose reactive sizes such as alkyl ketene
dimers and alkenyl succinic anhydride, and cellulose non-reactive
sizes such as rosin, starch and other polymeric sizes like
copolymers of styrene with vinyl monomers such as maleic anhydride,
acrylic acid and its alkyl esters, acrylamide, etc.
[0019] At drying, the paper, and thereby also the microspheres, is
preferably heated to a temperature from about 50 to about
150.degree. C., most preferably from about 60 to about 110.degree.
C. This results in expansion of the microspheres and thereby also a
bulk increase of the paper. The magnitude of this bulk increase
depends on various factors, such as the origin of cellulosic fibres
and other components in the stock, but is in most cases from about
5 to about 50% per weight percentage of retained microspheres in
the dried paper, compared to the same kind of paper produced
without addition of expandable microspheres or any other expansion
agent. Any conventional means of drying involving transferring heat
to the paper can be applied, such as contact drying (e.g. by heated
cylinders), forced convection drying (e.g. by hot air), infrared
techniques, or combinations thereof. In the case of contact drying,
the temperature of the contact surfaces, e.g. the cylinders, is
preferably from about 20 to about 150.degree. C., most preferably
from about 30 to about 130.degree. C. The paper may pass a series
of several cylinders, e.g. up to 20 or more, of increasing
temperature.
[0020] The cellulosic fibres in the stock may, for example, come
from pulp made from any kind of plants, preferably wood, such as
hardwood and softwood. The cellulosic fibres may also partly or
fully originate from recycled paper, in which case the invention
has been found to give unexpectedly good results.
[0021] Another embodiment of the invention concerns a process for
the production of nonwoven comprising the steps of forming a web of
fibres, adding to said web a binder and expandable microspheres as
described above, and forming nonwoven and applying heat to raise
the temperature of the microspheres sufficiently for them to expand
and thereby increase the bulk nonwoven. The expandable microspheres
and the binder may be added separately or as a mixture. The amount
of expandable microspheres added is preferably from about 0.1 to
about 30 wt % of dried product, most preferably from about 0.5 to
about 15 wt % of dried product. The amount of binder added is
preferably from about 10 to about 90 wt % of dried product, most
preferably from about 20 to about 80 wt % of dried product
[0022] The term "nonwoven" as used herein is meant to include
textiles made from fibres bonded together by means of a binder.
[0023] The web of fibres can be formed in any conventional way, for
example by mechanical or aerodynamical dry methods, hydrodynamical
(wet) methods, or spunbonded processes. The binder, preferably
pre-mixed with expandable microspheres, can then be added to the
web also in any conventional way, for example by any kind of
impregnation method such as immersion of the web in a bath of
binder or coating the web by kiss roll application or knife coating
with a doctor blade or floating knife.
[0024] The web comprising a binder and expandable microspheres can
then be heated to a temperature sufficient for the microspheres to
expand, preferably from about 70 to about 200.degree. C., most
preferably from about 120 to about i60.degree. C. Preferably,
curing of the binder takes place at the same time. The heating can
be effected by any suitable means, such as contact drying (e.g. by
heated cylinders), forced convection drying (e.g. by hot air),
infrared techniques, or combinations thereof.
[0025] The fibres can be any kind of commercially available fibres,
natural fibres, mineral fibres, as well as synthetic inorganic and
organic fibres. Examples of useful fibres include polypropylene,
polyethylene, polyester, viscose, and polyamide fibres, as well as
fibres made from two or more of the above polymers.
[0026] The binder can be any kind of natural or synthetic adhesive
resin, such as resins of polyacrylates and co-polymers thereof,
polymethacrylates and co-polymers thereof, rubber latexes such as
styrene/butadiene copolymers, acrylonitrilelbutadiene copolymers,
poly(vinyl chloride) and copolymers, poly(vinyl ester) such as
poly(vinyl acetate) and copolymers, e.g. with ethylene, poly(vinyl
alcohol), polyurethane, and aminoplast and phenoplast
precondensates such as urea/formaldehyde,
urea/melamine/formaldehyde or phenol/formaldehyde.
[0027] Preferred expandable microspheres to be used according to
the invention are described below.
[0028] The thermoplastic polymer shell of the expandable
microspheres is suitably made of a homo- or co-polymer obtained by
polymerising ethylenically unsaturated monomers. Those monomers
can, for example, be nitrile containing monomers such as
acrylonitrile, methacrylonitrile, .alpha.-chloroacrylonitrile,
.alpha.-ethoxyacrylonitrile, fumaronitrile or crotonitrile; acrylic
esters such as methyl acrylate or ethyl acrylate; methacrylic
esters such as methyl methacrylate, isobomyl methacrylate or ethyl
methacrylate; vinyl halides such as vinyl chloride; vinyl esters
such as vinyl acetate other vinyl monomers such as vinyl pyridine;
vinylidene halides such as vinylidene chloride; styrenes such as
styrene, halogenated styrenes or .alpha.-methyl styrene; or dienes
such as butadiene, isoprene and chloroprene. Any mixtures of the
above mentioned monomers may also be used.
[0029] Preferably the monomers comprise at least one acrylic ester
or methacrylic ester monomer, most preferably methacrylic ester
monomer such as methyl methacrylate. The amount thereof in the
polymer shell is preferably from about 0.1 to about 80 wt %, most
preferably from about 1 to about 25 wt % of the total amounts of
monomers.
[0030] Preferably the monomers comprise at least one vinylidene
halide monomer, most preferably vinylidene chloride. The amount
thereof in the polymer shell is preferably from about 1 to about 90
wt %, most preferably from about 20 to about 80 wt % of the total
amounts of monomers.
[0031] Most preferably the monomers comprise both at least one
acrylic ester or methacrylic ester monomer and at least one
vinylidene halide monomer.
[0032] Preferably the monomers comprise at least one nitrile
containing monomer, most preferably at least one of acrylonitrile
and methacrylonitrile, particularly most preferably at least
acrylonitrile. The amount thereof in the polymer shell is
preferably from about 1 to about 80 wt %, most preferably from
about 20 wt % to about 70 wt % of the total amounts of
monomers.
[0033] In an advantageous embodiment the monomers comprise at least
one acrylic ester monomer, at least one vinylidene halide and at
least one nitrile containing monomer. The polymer shell may then,
for example, be a co-polymer obtained from monomers comprising
methyl methacrylate in a preferred amount from about 0.1 to about
80 wt %, most preferably from about 1 to about 25 wt % of the total
amounts of monomers, vinylidene chloride in a preferred amount from
about 1 to about 90 wt %, most preferably from about 20 to about 80
wt % of the total amounts of monomers, and acrylontrile in a
preferred amount from about 1 to about 80 wt %, most preferably
from about 20 to about 70 wt % of the total amounts of
monomers.
[0034] It may sometimes be desirable that the monomers for the
polymer shell also comprise crosslinking multifunctional monomers,
such as at least one of divinyl benzene, ethylene glycol
di(meth)acrylate, di(ethylene glycol) di(meth)acrylate, triethylene
glycol di(meth)acrylate, propylene glycol di(meth)acrylate,
1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,
glycerol di(meth)acrylate, 1,3-butanediol di(meth)acrylate,
neopentyl glycol di(meth)acrylate, 1,10-decanediol
di(meth)acrylate, pentaerythritol tri(meth)acrylate,
pentaerythritol tetra(meth)acrylate, triallylformal
tri(meth)acrylate, allyl methacrylate, trimethylol propane
tri(meth)acrylate, tributanediol di(meth)acrylate, PEG #200
di(meth)acrylate, PEG #400 di(meth)acrylate, PEG #600
di(meth)acrylate, 3-acryloyloxyglycol monoacrylate, triacryl formal
or triallyl isocyanate, triallyl isocyanurate etc. The amount
thereof in the polymer shell is preferably from about 0.1 to about
10 wt %, most preferably from about 0.1 to about 1 wt %,
particularly most preferably from about 0.2 to about 0.5 wt % of
the total amounts of monomers.
[0035] The propellant is normally a liquid having a boiling
temperature not higher than the softening temperature of the
thermoplastic polymer shell and may comprise hydrocarbons such as
propane, n-pentane, isopentane, neopentane, butane, isobutane,
hexane, isohexane, neohexane, heptane, isoheptane, octane or
isooctane, or mixtures thereof. Aside from them, other hydrocarbon
types can also be used, such as petroleum ether, or chlorinated or
fluorinated hydrocarbons, such as methyl chloride, methylene
chloride, dichloroethane, dichloroethylene, trichloroethane,
trichloroethylene, trichlorofluoromethane, perfluorinated
hydrocarbons, etc. Preferred propellants comprise isobutane, alone
or in a mixture with one or more other hydrocarbons. The boiling
point at atmospheric pressure is preferably within the range from
about -50 to about 100.degree. C., most preferably from about -20
to about 50.degree. C., particularly most preferably from about -20
to about 30.degree. C.
[0036] Apart from the polymer shell and the propellant the
microspheres may comprise further substances added during the
production thereof, normally in an amount from about 1 to about 20
wt %, preferably from about 2 to about 10 wt %. Examples of such
substances are solid suspending agents, such as one or more of
silica, chalk, bentonite, starch, crosslinked polymers, methyl
cellulose, gum agar, hydroxypropyl methylcellulose, carboxy
methylcellulose, colloidal clays, and/or one or more salts, oxides
or hydroxides of metals like Al, Ca, Mg, Ba, Fe, Zn, Ni and Mn, for
example one or more of calcium phosphate, calcium carbonate,
magnesium hydroxide, barium sulphate, calcium oxalate, and
hydroxides of aluminium, iron, zinc, nickel or manganese. If
present, these solid suspending agents are normally mainly located
to the outer surface of the polymer shell. However, even if a
suspending agent has been added during the production of the
microspheres, this may have been washed off at a later stage and
could thus be substantially absent from the final product
[0037] Some of the microspheres described above are novel. The
invention thus also concerns thermally expandable microspheres
comprising a thermoplastic polymer shell made of a co-polymer
obtained by polymerising ethylenically unsaturated monomers
comprising at least one acrylic ester or methacrylic ester monomer
and at least one vinylidene halide monomer, and from about 17 to
about 40 wt %, preferably from about 18 to about 40 wt %, most
preferably from about 19 to about 40 wt %, particularly most
preferably from about 20 to about 35 wt % of a propellant entrapped
in said polymer shell, wherein the expandable microspheres have a
volume-average diameter from about 17 to about 35 .mu.m, preferably
from about 18 to about 35 .mu.m, more preferably from about 19 to
about 35 .mu.m, most preferably from about 20 to about 30 .mu.m,
particularly most preferably from about 21 to about 30 .mu.m.
Regarding further possible and preferred embodiments of the novel
microspheres, applicable parts of the above description of the
process for the production of paper or nonwoven is referred to.
[0038] The novel expandable microspheres can be prepared by
polymerising the monomers in the presence of the propellant with
the same methods as described in the earlier mentioned U.S. Pat.
Nos. 3,615,972, 3,945,956, 5,536,756, 6,235,800, 6,235,394 and
6,509,384, and in EP 486080.
[0039] In a preferred batchwise procedure for producing expandable
microspheres, the polymerisation is conducted as described below in
a reaction vessel. For 100 parts of monomer phase (suitably
including monomers and propellant, the ratio of which determines
the amount of propellant in the final product), one or more
polymerisation initiator, preferably in an amount from about 0.1 to
about 5 parts, aqueous phase, preferably in an amount from about
100 to about 800 parts, and one or more preferably solid colloidal
suspending agent, preferably in an amount from about 1 to about 20
parts, are mixed and homogenised. The size of the droplets of
monomer phase obtained determines the size of the final expandable
microspheres, in accordance with principles described in e.g. U.S.
Pat. No. 3,615,972 and can be applied for all similar production
methods with various suspending agents. The temperature is suitably
maintained from about 40 to about 90.degree. C., preferably from
about 50 to about 80.degree. C., while the suitable pH depends on
the suspending agent used. For example, a high pH, preferably from
about 6 to about 12, most preferably from about 8 to about 10, is
suitable if the suspending agent is selected from salts, oxides or
hydroxides of metals like Al, Ca, Mg, Ba, Fe, Zn, Ni and Mn, for
example one or more of calcium phosphate, calcium carbonate, chalk,
magnesium hydroxide, barium sulphate, calcium oxalate, and
hydroxides of aluminium, iron, zinc, nickel or manganese. A low pH,
preferably from about 1 to about 6, most preferably from about 3 to
about 5, is suitable if the suspending agent is selected from
silica, bentonite, starch, methyl cellulose, gum agar,
hydroxypropyl methylcellulose, carboxy methylcellulose, colloidal
clays. Each one of the above agents have different optimal pH,
depending on, for example, solubility data.
[0040] In order to enhance the effect of the suspending agent, it
is also possible to add small amounts of one or more promoters, for
example from about 0.001 to about 1 wt %. Usually, such promoters
are organic materials and may, for example, be selected from one or
more of water-soluble sulfonated polystyrenes, alginates,
carboxymethylcellulose, tetramethyl ammonium hydroxide or chloride
or water-soluble complex resinous amine condensaton products such
as the water-soluble condensation products of diethanolamine and
adipic acid, the water-soluble condensation products of ethylene
oxide, urea and formaldehyde, polyethylenimine, polyvinylalcohol,
polyvinylpyrrolidone, amphoteric materials such as proteinaceous,
materials like gelatin, glue, casein, albumin, glutin and the like,
non-ionic materials like methoxycellulose, ionic materials normally
classed as emulsifiers, such as soaps, alkyl sulfates and
sulfonates and long chain quaternary ammonium compounds.
[0041] Conventional radical polymerisation may be used and
initiators are suitably selected from one or more of organic
peroxides such as dialkyl peroxides, diacyl peroxides, peroxy
esters, peroxy dlcarbonates, or azo compounds. Suitable initiators
include dicetyl peroxy dicarbonate, tert-butyl cyclohexyl peroxy
dicarbonate, dioctanoyl peroxide, dibenzoyl peroxide, dilauroyl
peroxide, didecanoyl peroxide, tert-butyl peracetate, tert-butyl
perlaurate, tert-butyl perbenzoate, tert-butyl hydroperoxide,
cumene hydroperoxide, cumene ethylperoxide, dilsopropyl hydroxy
dicarboxylate, azo-bis dimethyl valeronitrile, azo-bis
isobutyronitrile, azo-bis (cyclo hexyl carbonitrile) and the like.
It is also possible to initiate the polymerisation with radiation,
such as high energy ionising radiation.
[0042] When the polymerisation is essentially complete,
microspheres are normally obtained as an aqueous slurry or
dispersion,. which can be dewatered by any conventional means, such
as bed filtering, filter pressing, leaf filtering, rotary
filtering, belt filtering or centrifuging to obtain a so called wet
cake that can be used as such. However, it is also possible to dry
the microspheres by any conventional means, such as spray drying,
shelf drying, tunnel drying, rotary drying, drum drying, pneumatic
drying, turbo shelf drying, disc drying or fluidised
bed-drying.
[0043] The invention will now be further described in connections
with the following Examples, which, however, not should be
interpreted as limiting the scope thereof. If not otherwise stated,
all parts and percentages refer to parts and percent by weight.
EXAMPLE 1
[0044] A three layer paper board with a basis weight of about 180
g/m.sup.2 was produced in a pilot paper machine with a machine
speed of 7 m/min and having recirculated process water. The pulp
was composed of 40 wt % hardwood and 60 wt % softwood pulp and was
beaten to a Schopper-Riegler value of 25.degree. SR and then
dispersed to give a pulp slurry/stock. An aqueous slurry of
expandable microspheres was before the mixing pump added to the
stock used for the middle layer in an amount of about 1 wt % dry
microspheres of the dry substance in the stock. As retention aid
0.1 wt % Polymin.TM. SK was used. In the drying section the paper
web was heated by cylinders having a temperature profile from 30 to
130.degree. C. Different kinds of expandable microspheres were
tested, all having isobutane as propellant and a polymer shell from
vinylidene chloride (VDC), acrylonitrile (ACN) and methyl
methacrylate (MMA) but In various ratios. In order to determine the
retention of the microspheres, paper samples were taken before the
press section for determination of the amount of microspheres
(using GC). The retention was calculated from the microspheres
addition and the content of microspheres in the paper. Moreover,
samples from the dried paper were taken for determination of bulk
and thickness. The results are shown in Table 1. TABLE-US-00001
TABLE 1 VDC/ACN/MMA in Amount of Increased bulk polymer shell
propellant Particle size (% per percentage of (wt %) (wt %) (.mu.m)
retained microspheres) 56/35/9 15.8 13.2 6 56/35/9 24.4 24.6 39
73/24/3 16.5 12.3 19 73/24/3 24.8 28.0 39
EXAMPLE 2
[0045] A single layer paper board with a basis weight of about 200
g/m.sup.2 was produced in a pilot paper machine with a machine
speed of 4 m/min and not having recirculated process water. The
pulp was composed of 50 wt % hardwood and 50 wt % softwood pulp and
was beaten to a Schopper-Riegler value of 25.degree. SR and then
dispersed to give a pulp slurry/stock. An aqueous slurry of
expandable microspheres was before the mixing pump added to the
stock in an amount of about 1.75 wt % dry microspheres of the dry
substance in the stock. As retention aid Compozil.RTM., 0.1%
BMA-O.TM. and 0.75% Raisamy.TM. 135, was used. In the drying
section the paper web was heated by cylinders having a temperature
profile from 65 to 122.degree. C. Expandable microspheres with the
same propellant and same monomers in the polymer shell as in
Exampel 1 were tested. The retention of microspheres and the
bulk/thickness of the paper were determined as in Example 1. The
results are shown in Table 1 TABLE-US-00002 TABLE 2 VDC/ACN/MMA in
Amount of Particle Increased bulk polymer shell propellant size (%
per percentage of (wt %) (wt %) (.mu.m) retained microspheres)
56/35/9 36.2 17.8 47 56/35/9 12.5 12.7 17 56/35/9 14.0 11.2 11
73/24/3 24.5 20.5 34 73/24/3 19.4 19.5 33 73/24/3 20.4 33.5 32
73/24/3 18.4 18.3 29 73/24/3 15.9 26.1 28 73/24/3 23.5 12.8 23
73/24/3 30.9 17.8 21 73/24/3 15.1 17.3 19 73/24/3 15.4 12.1 14
73/24/3 13.4 15.1 14
It appears that the overall trend is that the combination of high
amount of propellant and large particle diameter gives high
increase of the bulk of the paper. However, due to difficulties to
exactly measure the amount of retained microspheres, some
individual results may be inconsistent with the overall trend.
* * * * *