Note: Descriptions are shown in the official language in which they were submitted.
WO93/11300 PCT/Fl92/0030
A method for reducing the p2rmeability of paper and board
and a substance for the method
The object of this invention is a method for reducing the
permeability of paper and board in which state the treat-
ed product possesses sufficiently good barrier prop-
erties against gases and vapours such as water vapour as
required in the packaging industry, for example. Despite
possessing this property, paper or board treated in ac-
cordance with this method is readily disposable as wasteby, for example, composting or recycling the product back
as raw material for the fibre-consuming industry (i.e.
the product can be re-pulped; i.e~ disintegrated into fi-
brous material without causing problems when used again
in papermaking). The invention also involves the
substance by means of which the aforementioned properties
are achieved.
Increasingly strict regulations pertaining to environ-
mental protection have led to a situation in which the
manufacturers of packaging materials, for example, are
required to organize the post-consumption treatment of
the resultant waste in an environment-friendly manner. In
other words, packaging waste has to be either recycled to
provide industrlàl raw material or it has to be disposed
of by composting, for example. If the latter option is
resorted to, then the material as a whole must be biode-
gradable without releasing any environmentally hazardous
chemicals.
The above re~uirements mean that the continued use of
conventionai solutions (e.g. papers whose non-permeabi-
lity has been achieved by a plastic film lamination) lead
- to high costs because of the material's poor degradabili-
ty and unsuitability for recycling. This is so in packag-
ing situations where the package is required to possess
barrier properties against water vapour, for instance.
Certain commonly used polymers that possess good barrier
WO93/11300 ~ PCT/Fl92/0030
properties (e.g. products containing polyvinyl chloride)
cannot be disposed of by burning because of the hazard
caused by hydrogen chloride gas and dioxin.
The purpose of this invention is to eliminate the above
shortcomings and to make available a paper product which,
while offering adequate barrier properties, can be re-
cycled as raw material for the paper industry or disposed
of by composting or left to decompose in landfills, for
instance.
The method in accordance with the invention is based on
spreading onto the surface of paper or board a dispersion
product containing a component that includes modified
starch. The said dispersion product can also be spread
between the layers making up paper or board in which case
the polymer layer formed when the dispersion dries pro-
vides the required barrier protection. When spread be- ;
tween the layers, the dispersion also forms an adequate
adhesion between the layers and thus no actual gluing
treatment is needed.
It is known that papers can be treated with products con-
taining wax dispersions in order to provide them with
protection against moisture. It is also known that the
said products usually contain commonly used synthetic
polymer dispersions such as styrene butadiene, acrylate
or polyvinyl acetate latexes that provide the products
with adequate adhesion. The proportion of latexes in the
total polymer dispersion's solid matter content is qene-
rally high. Examples of the above technology are to be
found in patent literature; e.g. GB 1 593 331 (J. Vase,
Kemi Oy) and the Finnish patent application 901928 (Neu-
siedler AG) contain descriptions of this technology.
The technology in accordance with these inventions pro-
vides an adequate barrier against water vapour. However,
WO 93/11300 PCI /F192/0030:~
3 '- ~ i r.~ J ~
seeing as the proportion of latex composed entirely of
synthetic substances is high, the product's recyclabili-
ty is impaired as a result of the latex-based disturban-
ce substance accumulation when such material is made into
pulp. On the other hand, if the proportion of wax disper-
sion is in the vapour barrier substance is raised excess-
ively, the dispersion's adhesive and gluing properties
are impaired as is also the print~bility of the treated
surface due to its ink repelling property.
,,
The present invention's point of departure has been to
avoid the aforementioned shortcomings by preparing the
dispersion so that it contains components that promote
the disintegration of the synthetic product in nature and
during the various stages of recycling processes. This -
has been executed either (A) by joining natural polymer
chains (especially starch) to the latex polymer at the
manufacturing stage or (B) by replacing a significant
part of the latex polymer with a combination polymer ~
starch graft copolymer - consisting of starch and a syn-
thetic substance. It has been observed that paper prod-
ucts treated with thus manufactured dispersions are more
readily made into pulp than papers treated with latexes
made according to conventional recipes. Moreover, the
dispersion resid~ls formed in conjunction with pulping
to be considerabiy less likely to form disturbance resid-
uals that cause serious problems in the recycling of pa-
per products treated with synthetic adhesives. In extreme
cases, the amount of synthetic monomers can be low - even
nil. Actually! the properties of a dispersion manufac-
tured in this manner are impaired in that the coater sub-
stance's adhesion is low but still such a dispersion may
find use in less demanding situations.
' 35 As is pointed out in the above, applications for disper-
s~ons manufactured in accordance with the invention are -
mainly in conjunction with packaging materials and wrap-
4 1 ~ L~
WO93/ll300 ' PCT/Fl92/0030
pings that are required to possess certain moisture and
vapour barrier properties. In these cases the dispersion
can be used in place of conventional plastic/paper la-
mination solutions that are non-recyclable as well as
being very slowly degradable in nature on the part of
their plastic component.
When dispersions manufactured in accordance with the pre-
sent invention are used, the resultant paper products
degrade relatively quickly in nature. When compared to
products made using fully synthetic latexes, the degra-
dability of products treated with dispersions manufac-
-tured in accordance with this invention is also better
because the starch components contained by the dispersi-
on and polymer structure offer a natural substrate for
naturally occurring decomposing hydrolytic enzymes. A
polymer dispersion offering better recycling and degra-
ding properties, and manufactured in the manner descri-
bed in the above, has reasonable barrier properties to
offer as such. When necessary, the vapour barrier pro-
- perties can be further modified by means of additives
such as a wax dispersion.
The following is a description of ways according to which
polymers forming the structure of the dispersion can be
manufactured.
-
(A) Manufacturing of latex containing starch in a poly-
mer structure.
~
The principle hère is that the reaction medium used in
the manufacturing of latex by means of the emulsion
polymerization method is a water solution containing con-
ventio~al additives such as initiators acting as cata-
lysts (persulphates, peroxides) and surface-active sub-
stances and starch dissolved into the water phase by
heating. When this is the case, the initiators cause
WO93/11300 PCT/F192/0030~
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radicals to form onto the starch structure and these rad-
icals then act as the initial centres of the polymeri-
zation reaction. In other words, in addition to the fully
synthetic material formed in normal emulsion polymeri-
~ation, one obtains starch graft copolymer material inwhich the polymer chains formed of the synthetic monomers
used are covalently attached to the starch structure.
Since native starch - regardless of its origin - is a
macromolecular compe~nd and water solutions of it have
very high viscosities even in very low solid matter con-
centrations, one must first reduce the molecular size of
the starch or better still use commercially available
starch qualities which have usuali~ been split up by
means of oxidization. In the event that the user wishes
to carry out the oxidization-based splitting up in con-
junction with the reaction, this can be done using a
known art method advantageously as the first stage in the
reaction by using the oxidizing initiators acting as
polymerization catalysts.
In order that the viscosity of the polymer dispersion
obtained as the end product might fall within the appro-
priate range and that it might be a replicable constant,
one must take great care to ensure that the degree of
splitting of the starch is always precisely that which is
required. This can be done by means of viscosity determi-
nation, end group analysis or gel permeation chromatogra-
phy. The initial starch used in the following examples is
either a commercial, hydroqen peroxide oxidized potato
starcb Raisamyl 302P with a viscosity of 20-30 mPas when
used as a 10% solution at a temperature of 60 ~C or na-
; tive potato starch that has been split up enzymatica ly
by alpba-amylase possessinq temperature stability with
respect to Bacillus licheniformis in the manner described
in the example.
WO93/l1300 PCT/Fl92/00
~. tl~ J 6
Example l:
(Al) 34.30 g of oxidized starch Raisamyl 302P were added
to 150 g of water and then transferred into a pressure-
proof reactor vessel. The temperature of the mixture was
raised to 100 C for a period of 20 minutes in order to
dissolve the grains of starch. Following this the mixtu-
re was cooled down to 70 C after which a solution con-
taining 2~5 g of sodium lauryl sulphate in 50 ml of wa-
ter. A monomer mixture containing 116.8 g of styrene,
73.9 g of butadiene washed with a solution of lye and 3.0
g of acrylic acid were then gradually added to the mix-
ture over a period of two hours. Initiator solution con-
taining 3.o g of ammonium persulphate in 70 g of water
was ad~ed from another pressure burette. The polymerizat~
ion reaction was then allowed to proceed for 12 hours.
The end product was a white dispersion with a solid mat-
ter concentration of 45.8% and a viscosity of 890 mPas as
measured by a Brookfield LVT viscometer using measuring
head no. 2 at 2100 r/min. The measurements were conducted
after the product had been neutralized with NaOH to a pH
of 6.8. The product's calculatory starch concentration
was 13%.
Example 2:
(A2) 34.5 g of oxidized starch were added to 150 g of
water and boiled for 20 minutes in order to dissolve the
grains of starch. Following this 2.5 g of sodium lauryl
sulphate in 50 ml of water were added to the solution as
was the catalyst solution and the monomer solution as
mentioned in connection with Example l. The composition
of the monomer solution in this case was 146 g of vinyl
acetate and 22 g of butyl acrylate. The reaction was
allowed to proceed for 14 hours. The dry matter concent-
ration of the neutralized product was 40.8% and its vis-
cosity was 600 mPas at a temperature of 25 C.
W093/ll3~0 , .~.~ ;'i PCr/FI92/~
~xample 3: 49.4 g of oxid_~ed starch were added to 370 g
.f water and boiled for 20 minutes in order to dissolve
the grains of starch. The reaction mixture was provided
with an inert atmosphere by means of a flow of nitrogen.
Next, 0.1 g of CUSO4 was added followed by the addition
during a period of 1.5 hours of a monomer mixture com-
posed of 75 g of acrylic acid and 53 g of acrylic nitri-
te in drops. This was accompanied by the concurrent ad-
dition to the reaction mixture of 6 g of 30% hydrogenperoxide given over a period of 2 hours. The reaction was
allowed to proceed for 11 hours at a temper.ature of 70
C. The product thus obtained was a white dispersion with
a dry matter concentration of 26.3%.
1~ :
Example 4:
(B1) Starch copolymer production. 250 g of native potato
starch with a moisture content of 16~ were mixed into 220
g of water~ This was followed by adding 0.05 U/g of
starch of alpha-amylase possessing a temperature stabi-
lity with rec.pect to B. lichenif~rmis and with an acti-
vity value of 984 U/ml. While mixing the suspension vi-
gorously, its temperature was raised to 90 C and kept
2 there for 30 minutes. As a mean of stopping enzymatic
activity 0.5 ml of 30~ hydrogen peroxide was added and
the temperature was brought down to 60 ~C. A flow of ni-
trogen was led into the reaction mixture, 0.2. g of CuS04
were added, and 38 g of styrene and 6 g of 30% hydrogen
peroxide were administered in drops at the same time for
a period of 1.5 hours. The re~ction was allowed to pro-
ceed ~ ~ another 2 hours at tne end of which the result-
ant whlte dispersion was cooled down to room temperature.
The dispersion's viscosity at 25 C was 670 mPas and its
solid matter concentration was 51.8%.
Example 5:
W093/11300 l~CT/Fl92/0~)3~h
(B2) Starch graft polymer was produced in the manner
described in Example 3 above using butyl acrylate (75 g)
as the monomer to be grafted. The amount of starch was
209 g and it was added to 217 g of water. The resultant
product was a yellowish dispersion with a room tempera-
ture viscosity of 610 mPas and a solid matter concentra-
tion of 50.5~.
Example 6:
This example describes the compositions of the formula-
tions finally spread onto paper surface, containing dis-
persions according to examples 1-4 and control formula-
tions and the properties of papers treated with them.
LD460 is a styrene butadiene latex, manufactured by Rai-
sion Lateksi Oy, RN11~5 is a vinyl acetate acrylate la-
tex, manufactured by Rasional Oy, vahad is a wax disper-
sion containing paraffin with a melting range of c. 50-
70 C.
Using a laboratory coater machine (Endupapp), the dis-
persion was spread onto board (grammage 190 g/m2). The
board was then measured for its water vapour permeability
(WWP) in accordance with the IS0 258~1974 method (unit:
g/m2/24h). PM= amount of dispersion spread (g/m2)O
The value PA in the table depicts the pulpability pro-
perties of treated board. The value is obtained as fol-
lows: the treated board was broken down in accordance
with the method SCAN-C 18:65. The pulped material was
made into laboratory sheets (grammaqe: c. 100 g/m2). The
sheet quality was assessed using a scale of 0 - 5 in
which 0 indicates good pulpability ~no accumulations of
surface treatment material observed) and 5 indicates poor
pulpability (numerous accumulations of surface treatment
substance or unevenness due to incomplete breaking down
WO93/11300 ~ I Z i~ 4 PCT/F192/0030~
g .
of materi ).
Table 1.
RlR2 R3 R4 R5 R6 R7 R8 R9R10 R11
LD460 100~ 70 70 60 90 - -
RN1125 -- 100 -- -- -- -- -- -- -- -- --
Al - -- 100 90 - - - - - - -
A2 - - - - 100
A3 - - - - - 100 - -- - - -
Bl - - - - - - 30 - 30
B2 - - - - - - - 30
vahad - - - 10 - - - - 10 10
PM 17.8- 20.219.918.721.020.319.4 20.320.118.0 0
WWP 29 98 32 7 36 4 27 38 ~ 5 151
PA 5 3 2 2 0 O 1 1 i 4 0
Example 7: -
In this example two pieces of board are made into a lami-
nated pro~ct by means of a dispersion manufactured in
accordance wi~h *he invention. Dispersions R3, R6 and R8
were spread onto boards using amounts that correspon~ed
to c. 20 g/m2 of solid matter. Immediately aft~- th - ;
step anot~er sheet of the same board was press~. aga~nst
the treated surface and the thus formed laminated product
was then allowed to dry. The outcome of the gluing oper-
ation wa-~ assessed on the basis of the fibre tear pro-
duced when the two layers were separated from one another
(total fibre tear = ex~ellent adhesion). The laminates :~.
were also measured for their vapour barrier values.
:
Table 2.
. .
Fibre tear WWP (g/m2/24h)
.
R3 Total 29
R6 Total g
R7 Total 28
R9 Almost total 12
