[0001] The present invention relates to paper sizing methods and is more particularly concerned
with the sizing of paper using rosin-based sizing compositions at relatively high
pH values. The invention also relates to sizing compositions per se, for use in carrying
out such methods, and the resultant sized paper products.
[0002] Conventional paper sizing methods, using rosin in either its emulsified or soaped
forms, involve the separate addition to one or more selected points in the paper machine
wet-end of the rosin-based sizing composition and of an aluminium salt. This technique
operates satisfactorily at pH values lying generally in the range from 4 to 6. When
the pH is higher than about 6, to any significant extent, for example in the case
where chalk is added to the paper pulp, sizing by this technique becomes erratic and
very difficult to control. In view of these difficulties, when attempting to make
sized paper or to surface size paper already made, using a pH value above the normal
4 to 6 range, it is common practice to resort to the use of non-rosin sizes, such
as those based on alkyl ketene dimers.
[0003] Attempts to size generally at neutral or alkaline pH values or to use specific aluminium
salts (e.g. polyaluminium chloride) in the two-shot mode in the presence of chalk
have only given very poor results.
[0004] It is also known that if a one-shot mode of operation is used, namely a method involving
use of a pre-mix of rosin and aluminium salt, made a considerable time before addition
of the pre-mix to the machine, again only spasmodic control of sizing in an alkaline
environment is obtainable. Such one-shot systems, operated so as to avoid these difficulties,
are disclosed for instance in our pending Application No. 88304405.9 (Publication
Number EP-A-0293119) and also in US-A-4333795.
[0005] It has now surprisingly been found that if a pre-mix of a rosin-based size and an
aluminium salt is made, on an in-line basis just before its addition to the paper
machine, much better and more controlled sizing is obtained with rosin, when the stock
contains chalk or otherwise has a neutral or alkaline pH value. Thus, the present
invention is based upon the unexpected discovery of a difference in behaviour if a
pre-mix of rosin and an aluminium salt is made when or just before it is in fact used,
as compared with known methods where it is made a considerable time before its use.
[0006] According to one aspect of the present invention therefore, a paper sizing method
is provided, in which paper is made from a pulp system containing chalk or otherwise
having a neutral or alkaline and therefore high pH, in which a pre-blended composition
containing a rosin-based size and an aluminium compound is used or the rosin-based
sizing composition and the aluminium compound are added separately but simultaneously
and are pre-mixed just prior to addition at an appropriate selected point in the paper
machine wet-end.
[0007] According to another aspect of the present invention, a pre-blended paper sizing
composition, comprising a rosin-based size and an aluminium compound and suitable
for use on or immediately after its formulation, is also provided. Particular optional
but preferred features of the proposed one-shot paper sizing composition of the present
invention may include the incorporation into the composition of a higher than normal
amount of aluminium salt, a higher than normal amount of the rosin-based size or the
inclusion of at least one polyelectrolyte.
[0008] According to a further preferred feature of the method and the composition of the
invention, the weight ratio of the rosin size to the aluminium compound, used in carrying
out the method and accordingly present in the one-shot composition, on a dry basis,
lies in the ratio 1:0.01 to 5. According to a further preferred feature of the invention,
the ingredients added to the paper machine wet-end in carrying out the method of the
invention, either during operation or as a one-shot pre-mix, include at least one
urea-based extender.
[0009] In addition to the stock sizing of paper, according to the invention, another aspect
consists in the use of pre-mixed compositions and techniques, of the kind indicated
above, in the surface sizing of paper which has already been manufactured, whether
or not a rosin-based sizing composition has been used in its manufacture up to that
stage. A further aspect of the present invention consists of any paper or paper-like
product made by a method according to the present invention or made using a paper-sizing
composition according to the invention.
[0010] In accordance with a preferred embodiment of the invention, a pre-mixed rosin-based
sizing composition for use in carrying out the present invention may contain, in addition
to the rosin and the aluminium compound, one or more other additives useful in the
making of paper, for instance for optimising the sizing function of the rosin-based
component per se. Such additional and optional additives include cationic and anionic
polyelectrolytes, and also cationic starches. For example, the pre-mix can contain
one or more of cationic and anionic polyacrylamides, polyethyleneimine, polydialkyl
dimethyl ammonium chloride (DADMAC) or polyamide/epichlorohydrin condensates, as well
as dicyandiamide/formaldehyde condensation products.
[0011] According to a further aspect of the invention, despite the fact that pre-mixed one-shot
sizing products, such as are available commercially, in the form of products made
and supplied by chemical companies, are difficult to use, particularly in neutral
or alkaline pH circumstances, it is possible according to another aspect of the invention
to effect modification of the in-line mixing technique indicated above, optionally
with the addition of further aluminium salt and/or polymers, so that such pre-mixed
commercial products can also be employed, in accordance with the principles of the
present invention, whereby greater control and effectiveness than has previously been
possible with such one-shot products.
[0012] In order to carry out the method of the invention in practical terms, it is necessary
to employ some form of mixing device, so as to control the degree of dispersion of
the aluminium salt and the rosin size, which in turn affects its distribution amongst
the paper fibres, with optimisation of sizing efficiency. The mixing device is suitably
associated with the wet-end of the paper machine and its proper use ensures that
the dispersion serves to control the degree of agglomeration of the fibres in the
pulp.
[0013] In carrying out the invention, the rosin-based size component employed, by being
formulated into a pre-mix with an aluminium compound, can be based on rosin or rosin
modifications, prior to conversion into a stable emulsion form. Thus, use can be made
for this purpose of gum rosin, formaldehyde-treated gum rosin or tall oil rosin, fumaric
acid-treated gum rosin or tall oil rosin, disproportionated rosin, maleic anhydride-treated
gum rosin or tall oil rosin such as the compounds or any combination of untreated
or treated rosin, such as the compounds of the kinds just mentioned. In addition,
esters or part esters of any of any of the above-mentioned forms of rosin, formed
with straight chain or polyhydric alcohols, can also be used. A third possibility
is to use any appropriate mixture of any of the aforementioned untreated or treated
forms of rosin, including disproportionated rosin and tall oil rosin, together with
any one or more of the esters or part esters just described.
[0014] As a further aspect of the invention, it is possible to use resinous materials other
than rosin per se or chemically-modified rosin compounds. For example, hydrocarbon
resins, both of the aromatic and aliphatic varieties, can be used when suitably formulated,
in order to carry out the paper-making methods of the present invention.
[0015] Paraffin waxes and microcrystalline waxes may be used in conjunction with any of
the above-mentioned rosin or resin-based types of sizing compositions, the particular
use of one or other of the possible waxes depending largely upon the properties which
may be required in the eventual paper product.
[0016] Furthermore, any appropriate rosin-based sizing emulsion, derived from any one or
more of the above-mentioned materials, may incorporate one or more extenders. By way
of example, urea-based extenders may be employed for this purpose. Such extenders
are disclosed for example in US-A-4022634, 4093779, 4141750, 4025354, 4437894 and
4605445. Any appropriate rosin emulsion may also be extended with emulsions of alkyl
ketene dimers, prior to or subsequent to pre- mixing with the aluminium compound.
The alkyl ketene dimer emulsions may be stabilised with either cationic starch or
cationic or anionic polymers.
[0017] According to another aspect of the invention, the aluminium compound incorporated
in the one-shot pre-mix of the invention or otherwise employed in carrying out paper
sizing methods according to the present invention is selected from polyaluminium chlorides,
aluminium chlorohydrate, aluminium sulphate (paper makers alum) and any mixture of
two or more of the foregoing.
[0018] In putting the invention into practice, it is desirable to incorporate in the paper
sizing composition, when made up in a one-shot form, at least one stabilising agent,
which may take the form of one or more surface active agents or surfactants. Mixtures
of stabilising agents or surfactants also can be used. A very wide range of possibilities
is available as to the nature of such materials, which can be anionic, non-ionic,
cationic or amphoteric.
[0019] One particular class of stabilised emulsion comprises essentially a rosin soap and
a protective colloid. The rosin-based component, namely the rosin soap, can be a sodium,
potassium or ammonium soap of rosin or of a modified rosin, together with amine salts
of rosins or modified rosins, for instance the amine salts formed with mono-, di-
or triethanolamine. These stabilisers can be added separately or formed in situ when
making up the rosin-based emulsion composition. Colloids which can be used to stabilise
the resultant product include casein, starch, soya protein and cellulose derivatives,
the former being the most preferred, as well as certain polymers, such as polyvinyl
pyrrolidone or polyvinyl alcohol (PVA). A preferred form of stabilised emulsion consists
essentially of the potassium or sodium soap of the rosin or rosin derivative and casein
as the stabilising colloid.
[0020] According to a further feature of the invention, surface active agents or surfactants
which can be used in formulating the compositions of this invention include:
(i) salts of sulphonic acids having the general formula:

where R′ represents a hydrocarbon residue having from 4-18 carbon atoms, m is an
integer having a value of 1 or 2, n is an integer having a value of 4 to 25, X represents
a hydrogren atom or a hydroxyl group and M represents a monovalent cation and
(ii) salts of sulphuric acid half esters having the general formula:

wherein R² represents a hydrogen atom or an alkyl group having from 1 to 4 carbon
atoms, A represents a straight chain or branch chain alkylene group having 2 or 3
carbon atoms, p is an integer having a value of 4 to 25 and Q is a monovalent cation,
including all those compounds described in US-A-4309388.
(iii) alkyl-benzene sulphonates wherein the alkyl substituent comprises from 8 to
24 carbon atoms, including all those compounds described in US-A-4157982.
(iv) sulphosuccinate half esters of fortified rosin having the formula:
H(3-m). R. [(CH₂CH₂0)n- OC.C₂H₃SO₃Na.- C00Na]
wherein R is a fortified rosin acid tricarboxylate group, m has an average value of
1.5 to 3 and n has an average value from 4.5 to 25 including all those described in
EP-A-159794.
(v) compounds having one or other of the formulae:

wherein R represents an alkyl group comprising from 4 to 18 carbon atoms, and R′
represents an alkyl or alkenyl group comprising from 4 to 18 carbon atoms and n is
an integer having a value of 4 to 25, including all those described in US-A-4199367.
(vi) sulphosuccinate salts of ethylene oxide condensates having the general formula:-

wherein R represents an alkyl group comprising from 4 to 18 carbon atoms and n is
an integer having a value of 4 to 25 including all those compounds described in US-A-4203776.
(vii) organic phosphate esters having one or other of the general formulae:

and mixtures thereof,
wherein R represents an alkyl or an alkyl-phenol, alkenyl or alkaryl group comprising
from 5 to 20 carbon atoms, n has a value of 5 to 20 and X represents a monovalent
cation or hydrogen.
[0021] Cationic resin dispersant systems may also be used to stabilise the rosin dispersions
of this invention. Examples of suitable materials include water-soluble polyaminopolyamide/epichlorohydrin
resins, water-soluble alkylene-polyamine/ephichlorohydrin resins and poly(diallylamine)/epichlorohydrin
resins.
[0022] In order that the present invention may be fully understood and appreciated, the
following examples of use of the paper sizing methods and compositions of the present
invention are given, by way of illustration only. In the examples, all amounts are
given as percentages by weight, unless otherwise indicated. In example 1, part A represents
use of the invention, while part B represents use according to the prior art.
Example 1
Part 1
[0023] A pilot Fourdrinier paper machine was used which was operated to produce paper of
85 gsm at 16 kg per hour from softwood/hardwood Kraft furnish loaded with 10% chalk.
[0024] Pre-mixes of the rosin size and aluminium salt were made using a laboratory mixer
and were metered just prior to the flow box.
[0025] The following results were obtained:-
Rosin Size Solids/fibre % |
Polyaluminium chloride (as received) |
1 min Cobb gsm |
pH at Flow Box |
1.0 |
0.5 |
68 |
7.8 |
1.0 |
1.0 |
29 |
7.6 |
1.0 |
1.5 |
29 |
7.6 |
Part B
[0026] For comparison with the practice exemplified in Part A, sheets were made using Kraft
pulp containing 10% of chalk. The size and the PAC were added separately to the pulp
and held for 30 minutes before sheets were made.
[0027] The following results were obtained:-
Rosin size Solids/fibre % |
Polyaluminium chloride (as received) |
1 min Cobb gsm |
pH at Flow Box |
1.0 |
0.5 |
146 |
7.4 |
1.0 |
1.0 |
156 |
7.2 |
1.0 |
1.5 |
154 |
7.3 |
2.0 |
0.5 |
154 |
7.4 |
2.0 |
1.0 |
144 |
7.3 |
2.0 |
1.5 |
137 |
7.2 |
Example 2
[0028] A commercial paper machine producing envelope paper at the rate of 6.8 tonnes per
hour with a chalk content varying from 5.8 to 7.8 per cent was sized by pre-blending
free rosin size and alum and adding the pre-mix to the forward side of the thick stock
head-box. Throughout the run, the amount of size used (dry basis) was 0.45% and the
amount of alum used (dry basis) was 1.93%.
Time |
1 Min Cobb |
Flow Box pH |
12.30 |
26 |
8.0 |
12.45 |
20 |
8.0 |
13.45 |
20 |
8.0 |
13.50 |
22 |
7.5 |
14.25 |
21 |
7.7 |
14.59 |
21 |
7.6 |
15.34 |
21 |
7.7 |
[0029] Referring to example 1 above, it will be noted that, in part B, the Cobb values indicate
that the sheets were close to saturation. Referring to the last three results in part
B of example 1, double the amount of rosin size on a percent solid/fibre basis was
used, as compared with the first three, but this made very little difference to the
Cobb values obtained and none of those obtained in part B came anywhere near the much
better results in terms of levels of sizing achieved in carrying out the invention,
according to part A of example 1. A very satisfactory range of sizing is given by
the last two results of example 1 part A in particular and throughout example 2. In
these examples, "as received" in relation to the polyaluminium chloride means that
it contained 10 percent Al₂0₃.
[0030] The invention thus represents a substantial and surprising advance on previous paper
sizing methods and compositions.
1. A method of sizing paper using paper-making stock to which a rosin-based or resin-based
sizing agent and an aluminium compound are added, characterised in that
(a) sizing is carried out at a neutral or alkaline pH and
(b) the sizing agent and the aluminium compound are added simultaneously to the paper-making
stock at a selected point in the paper machine wet-end.
2. A method according to claim 1, wherein the paper pulp system contains chalk in
an amount sufficient to produce a pH above 6.
3. A method according to claim 1 or 2, wherein a pre-blended composition comprising
the rosin-based or resin-based sizing agent and the aluminium compound is added to
the paper-making stock in the paper machine.
4. A method according to claim 1 or 2, wherein the rosin-based or resin-based sizing
agent and the aluminium compound are added separately but simultaneously to the paper-making
stock in the paper machine.
5. A method according to claim 3, wherein the sizing agent and the aluminium compound
are pre-mixed just prior to addition to the paper machine.
6. A method according to any preceding claim, wherein a higher than normal amount
of aluminium compound or a higher than normal amount of the sizing agent is incorporated
in the composition.
7. A method according to any preceding claim, wherein the weight ratio of the sizing
agent to the aluminium compound used in carrying out the method, on a dry basis, lies
in the range from 1:0.01 to 5.
8. A method according to any preceding claim, wherein the ingredients added to the
paper machine wet-end, either during operation or as a one-shot pre-mix, include
at least one urea-based extender.
9. A method according to any preceding claim, wherein at least one polyelectrolyte
is incorporated into the composition.
10. A method according to claim 9, wherein a pre-mixed rosin-based sizing composition,
used in carrying out the method, also contains in addition to the rosin and the aluminium
compound, one or more other additives for optimising the sizing function of the rosin-based
component per se.
11. A method according to claim 10, wherein the one or more additives are selected
from cationic and anionic polyelectrolytes and cationic starches.
12. A method according to claim 11, wherein the additives are selected from cationic
and anionic polyacrylamides, polyethyleneimine, polydialkyl dimethyl ammonium chloride
(DADMAC), polyamide/epichlorohydrin condensates and dicyandiamide/formaldehyde condensation
products.
13. A method according to any preceding claim, wherein a pre-mixed composition comprising
the sizing agent and the aluminium compound is used, at a neutral or alkaline pH,
in the surface sizing of paper which has already been manufactured, whether or not
a rosin-based sizing composition was used in its manufacture up to that stage.
14. A method according to any preceding claim, wherein the sizing agent is based upon
rosin or a rosin modification selected from gum rosin, formaldehyde-treated gum rosin
or tall oil rosin, fumaric acid-treated gum rosin or tall oil rosin, disproportionated
rosin, maleic anhydride-treated gum rosin or tall oil rosin, esters or part esters
of any such rosin or rosin modification with straight chain or polyhydric alcohols,
and mixtures of such untreated and treated forms of rosin with any one or more of
such esters or part esters.
15. A method according to any of claims 1 to 13, wherein the sizing agent is based
upon resinous materials selected from aromatic and aliphatic hydrocarbon resins.
16. A method according to any preceding claim, wherein the aluminium compound is selected
from polyaluminium chlorides, aluminium chlorohydrate, aluminium sulphate and mixtures
thereof.
17. A method according to any preceding claim, wherein at least one stabilizing agent
selected from anionic, nonionic, cationic and amphoteric surfactants is incorporated
into the paper sizing composition.
18. A pre-blended paper sizing composition comprising a rosin-based or resin-based
paper sizing agent and at least one aluminium compound, characterised in that the
composition is suitable for use in the manufacture of sized paper on or immediately
after its formulation by combination of the paper sizing agent and the aluminium compound
and that the composition is effective to size paper-making stock or to surface-size
paper under conditions including a neutral or alkaline pH.
19. Sized paper, when made by a method according to any of claims 1 to 17.
20. Sized paper, when made using a sizing composition as defined in claim 18.