Note: Descriptions are shown in the official language in which they were submitted.
1153161
BACKROVND OF THE INVENTION
Field of the invention
The present invention relates to a method for
the production of greaseproof paper or greaseproof pulp
by refining a bleached sulphate pulp.
DESCRIPTION OF THE PRIOR ART
Greaseproof paper, which is a special paper for
packing fatty products, is traditionally produced from
sulphite chemical pulp. For the desired quality of the
paper to be obtained, the chemical pulp must be refined
until it obtains the properties required by a greaseproof
pulp. The chemical pulp must therefore be easy to refine,
and additionally should be pure and contain only small
amounts of odourous and tasting ingredients.
As small and medium sulphite pulp factories are
closed down because of pollution problems, it has been
: tried to use bleached sulphate;chemical pulp in the
production of greaseproof paper. Since ordinary sulphate
pulp is difficult to refine, it consumes considerably
more refining energy and additionally requires expensive
chemical aids to obtain approximately the same greaseproof
properties as sulphite pulp.
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SUMMARY OF THE INVENTION
The object of the present invention is to provide
a method for the production of a satisfactory greaseproof
paper from a s~lphate pulp, while obtaining advantages
compared with both sulphite pulps and previously used
sulphate pulps.
In the method according to the invention a known
oxygen-alkali delignified high yield sulphate pulp is
bleached with chlorine, alkali and hypochlorite and
the bleached pulp is refined. In other words, the inven-
tion consists in the use of a delignified high yield
sulphate pulp for the production of greaseproof paper
after chlorine-alkali-hypochlorite bleaching and refi-
ning of the pulp.
DETAILED DESCRIPTION OF THE INVENTION WIT~ PREFERRED
EMBODIMENTS
The sulphate pulp used as a starting material
for the production of the greaseproof pulp according
to the invention, is a known high yield sulphate pulp
which has been delignified as described in US patent
specification 4 093 Sll and TAPPI 59 (11) : 77 (1976).
This sulphate pulp is produced with a hemicellulose
preserving cooking liquor, preferably a polysulphide :
liquor having a polysulphide content of 2 to 12 grams
per liter and produced by the Moxy process, to a relati-
vely high lignin content corresponding to a kappa number
of about 60, see TAPPI 58 (8) : 172 (1972). After a
partial washing, the pulp was further delignified to
a kappa number of about 30 with oxygen and alkali at
about 110C in a suitable reactor. The pulp was then
further bleached in three stages with chlorine, alkali
and sodium hypochlorite, respectively, to a brightness
of 80 to 85~ SCAN. If the bleaching of the sulphite
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pulp in the hypochlorite stage is cond~cted so that
the pH value of the pulp at the end of this stage is
7.0 to 8.5, it has turned out that the obtained pulp
is particularly easy to refine to greaseproof properties.
The pH value at the end of the hypochlorite bleaching
stage,should preferably be within the range 7.0 to 8.0
and particularly between 7.0 and 7.5. These are exeptio-
nally low values. On the other hand it is preferred
to refine the pulp in alkaline surroundings, i.e. at
a pH value of at least 7.0 and possibly as high as 10Ø
A testing of this pulp in the laboratory showed
that it was considerably better suited for the production
of greaseproof paper than ordinary sulphate pulp marketed
for this purpose. Compared with greaseproof paper from
sulphite pulp, the high yield sulphate pulp produced
a more pure product having satisfactory greaseproof
properties. The paper further had better wet strength
properties than the sulphite pulp, and thus produced
fewer breaks in the paper machine with a correspondingly
higher paper production. The refining energy demand
was approximately as for sulphite pulp, i.e. substan-
tially lower than for the sulphate pulp presently marke-
ted for greaseproof purposes.
Also the strength properties of the finished product
were considerably better than what is usual with a sul-
phite pulp as a starting material. The high strength
resulted in a better convertability of the paper produced
in the pilot period. Convertability is a property which
becomes more and more important due to present demands
for advanced pressures and high speed packing machines.
The content of odourous and tasting ingredients
and resin in the sulphate pulp used is at such a low
level compared with sulphite pulp that no problems
are to be expected. On the contrary, sulphite pulp from
pine wood may give inconveniences with respect to taste
and odour in the product and also acute resin problems,
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llS3161
but also sulphite pulp from fir wood may give problems
in this respect.
Further features of the invention will be apparent
from the following description and the claims. The inven-
tion will be further illustrated by means of examples.
Example 1
A high yield sulphate pulp was produced in a conti-
nuous vapour phase Kamyr digester from a mixture of
fir and pine chips. The production was approximately
350 tons per day. 19.5~ effective alkali calculated
as NaOH was added per ton dry chips. The white liquor
had a content of about 6 to 8 grams polysulfide sulphur
per liter and was produced by the Moxy process. The
white liquor sulfidity was about 40% before the oxyda-
tion in the Moxy reactor. For a more detailed descrip-
tion of the Moxy process, see US patent specification
4 308 313. The temperature in the cooking zone was about
160C and the cooking time was about 2.5 hours.
From the blowing conduit of the digester a pulp
flow of about 70 tons per day was branched out and passed
to a reactor through an in-line refiner. In the refiner
liquor, oxygen and steam were admixed. The addition
of oxygen and alkali corresponded to 35 kg 2 and 50
kg NaOH, respectively, for each ton of pulp. The steam
demand corresponded to a temperature increase from about
85C to 110C at 10% pulp consistency. The residence
time of the pulp in the reactor was about 30 minutes
at 5 at pressure before the pulp was diluted and blown
to a tank.
The oxygen-alkali delignification res~lted in
a reduction of the kappa number of the pulp from about
60 to about 30. A sample of this pulp was further bleached
in the laboratory in three stages with chlorine, alkali
and sodium hypochlorite (6.5% chlorine, 2.5% NaOH and
2.7% hypochlorite ~ 0.2% NaOH, the pH value being about
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7.0 at the end of the hypochlorite stage) to a bright-
ness of 83% SCAN. The pulp thus obtained was compared
with a conventional sulphate pulp for the produc tion
of greaseproof. The result of the comparison is shown
in table 1.
It appears from table 1 that the oxygen-alkali
delignified high yield sulphate pulp was considerably
easier to refine to a low freeness and greaseproof proper-
ties than the conventional sulphate pulp sold to various
producers of greaseproof paper. The conventional sulphate
pulp is so difficult to refine that the paper requires
an addition of expensive chemicals such as carboxy methyl
cellulose in order to give satisfactory greaseproof
properties.
Example 2
From the blowing conduit of a continuous Kamyr
digester in which a high yield sulphate pulp as described
in example 1 was produced, a flow of about 50 tons per
day was branched from the pulp. In total about 400 tons
such pulp were bleached in the oxygen reactor at the
same conditions as described in example 1, and then
pressed in a screw press to about 27% dry matter. The
pulp entering the reactor had an average kappa number
of 51.1, whereas the kappa number in the outlet from
the reactor was 30.7. The pulp was then shipped to a
sulphite factory. Here the chemical pulp production
was interrupted, and both the bleaching plant and the
paper factory were fed with the supplied oxygen bleached
pulp for about 5 days.
In the bleaching plant about 6.5% chlorine was
added to the pulp in the first stage, about 2.5% NaOH
was added in the second stage, and about 3% active chlo-
rine as sodium hypochlorite was added in the third stage
at 40 to 42C. The pH value was about 7.0 at the end
of the third stage.
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Table 1
Pulp acc. to Conventional sulphate
Example 1 pulp (bleached)
Refining time,
rev. on PFI
refiner 7000 9000105001050013500 15000
SR 77 82 86 60 74 77
Freeness, s74 118 244 17 37 47
Wear index,
Nm/g 120.5 124.5121.5123.5122.5 125.5
Air perme-
ability, nm/Pa14.6 4.6 0.94 206 45.4 37-9
Blister
formation Trace Trace Heavy NoNo No
Prior to refining the pùlp was buffered with a
mixture of sodium bicarbonate and NaOH, so that the
pulp after refining still had a pH value of at least
7Ø
The ordinary greaseproof products of the factory
were produced with excellent quantitative and qualitative
results. As an example of the results obtained, table
2 states results for the greaseproof pulp according
to the invention compared with the demands made to a
greaseproof pulp having a base weight of 34 (55 g/m2)
and high quality.
The paper described in example 2 has been examined
for odour and taste at Sentralinstitutt for industriell
forskning, Oslo, and Verpackungslabor fur Lebensmittel
und Getranke, Vienna. At SI the paper was analysed on
a gas chromatograph and compared with a corresponding
analysis of ordinary greaseproof paper from sulphate
pulp. The analysis showed a substantially smaller area
below the chromatographic curve for the product accor-
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Table 2
Demands to greaseproof Analysis data forpulp having a base 2 greaseproof pulp
weight of 34 (55 g/m ) having a base weight
and high quality of 34, produced in
accordance with the
invention
Opacity, phV ~ 60 61
Tappi number, s ~21800 1800
Air permeability ~ 0
Burst strength ~ 26 31
Longitudinal tear
strength ~ 19 22
Transverse tear
strength ~ 22 25
Bentzen ~ 300 500
Wet strength, % ~ 30 34
Number of spots ~ 20 4
Area of spots, mm ~ 1 0,18
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ding to the invention, which means that there should
be no danger of odour and taste problems. At the said
laboratory in Vienna, a taste panel compared a vegetable
parchment paper and a greaseproof paper produced accor-
ding to the invention. The conclusion was that after
covering of a butter surface with the two types of paper,
no difference in taste of the butter could be established,
so that both papers could be regarded as equivalent
with respect to transferring taste to fatty products.
Vegetable parchment paper is the material which is at
present used as a packing paper for butter in most coun-
tries.
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The paper according to the invention described
in this example was also sent to three different custo-
mers for conversion on the paper machines of their factories.
All the customers found the paper to be easily convertable.
It will thus be seen that according to the invention
a greaseproof paper having a very high quality can be
produced from sulphate pulp with a substantially reduced
energy demand for the refining operation compared with
previously used sulphate pulps, and without addition
of expensive chemicals.
