Process for production of paper using thioether compounds

Details Process for production of paper using thioether compounds Process for production of paper using thioether compounds

1999-04-30

2001-07-31

Nguyen, Dean T. (Department: 1731)

Paper making and fiber liberation

Processes and products

Non-fiber additive

C162S168400, C162S177000

Reexamination Certificate

active

06267844

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the reduction of brightness reversion in paper products, particularly those made from high-yield pulps and to compositions for achieving same.
A “high-yield” pulp is a pulp in which the papermaking fibres are separated by means which are mainly mechanical action (optionally with some chemical treatment). As the name indicates, there is relatively little waste with such a pulp, in contrast to the so-called “chemical” pulps where the fibre separation is achieved by purely chemical means. Paper made from high-yield pulp (for example, groundwood pulp, refiner pulp, thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP)) is considerably cheaper than that made from chemical pulp, even when the high-yield pulp is bleached. The problem which has restricted the use of high-yield pulps to non-archival uses such as newsprint and corrugated paper is the tendency of such paper to undergo brightness reversion (yellowig) with time, this being believed to be caused by the instability to ultraviolet light of the lignin component of high-yield pulps.
SUMMARY OF THE INVENTION
The present invention provides a process for the production of paper, comprising the steps of: (a) providing a paper pulp, and (b) forming a paper sheet therefrom, the process further including the process step of providing to the paper at some point in the said production process a thioether compound of formula I
in which
m is an integer of from 2-4;
n is an integer of at least 2;
p is an integer of from 1-4;
X is a bridging member and A is alkylene or arylene, optionally substituted;
R
1
is (a) alkyl (C
1
-C
6
), optionally substituted but not containing fluorine or silicon, (b) phenyl or benzyl, both optionally substituted or (c) a heteroaromatic residue, and if p is equal to 1 and R
2
is hydrogen or alkyl (C
1
-C
6
), then R
1
can also be another residue R
3
O[(CH
2
)
m
O]
n
X—A—S—Z— where R
3
is hydrogen or alkyl (C
1
-C
6
), and Z is selected from (CH
2
)
2
, (CH
2
)
3
, (CH
2
)
4
, CH
2
CH(CH
2
OH), CH
2
CH(OH)CH(OH)CH
2
, CH
2
CH
2
OCH
2
CH
2
, 1,2-phenylene, 1,3-phenylene, 1,4-phenylene, 2,5-(1,3,4-thiadiazolyl), 1,3-xylylene, 1,3,5-triazinyl (optionally substituted), and
R
2
is hydrogen or alkyl (C
1
-C
6
), optionally substituted, or another residue R
1
—S—A—X—.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has now been found that the use of certain compounds allows the light-induced yellowing of paper to be considerably reduced, often to levels where papers not previously thought suitable for archival material may be used for such applications. The invention therefore provides a paper production process, comprising the process steps of (a) providing a paper pulp, and (b) forming a paper sheet therefrom, the process further including the process step of providing to the paper at some point in the said production process a thioether compound of formula I
in which
m is an integer of from 2-4;
n is an integer of at least 2;
p is an integer of from 1-4;
X is a bridging member and A is alkylene or arylene, optionally substituted;
R
1
is (a) alkyl (C
1
-C
6
), optionally substituted but not containing fluorine or silicon, (b) phenyl or benzyl both optionally substituted or (c) a hetaromatic residue, and if p is equal to 1 and R
2
is hydrogen or alkyl (C
1
-C
6
) then R
1
can also be another residue R
3
O[(CH
2
)
m
O]
n
X—A—S—Z— where R
3
is hydrogen or alkyl (C
1
-C
6
), and Z is selected from (CH
2
)
2
, (CH
2
)
3
, (CH
2
)
4
, CH
2
CH(CH
2
OH), CH
2
CH(OH)CH(OH)CH
2
, CH
2
CH
2
OCH
2
CH
2
, 1,2-phenylene, 1,3-phenylene, 1,4-phenylene, 2,5-(1,3,4-thiadiazolyl), 1,3-xylylene, 1,3,5-triazinyl (optionally substituted), and
R
2
is hydrogen or alkyl (C
1
-C
6
), optionally substituted, or another residue R
1
—S—A—X—.
Examples of X are —C(═O)—, —CH
2
C(═O)O—, —C(═O)NH—, —S(═O)
2
— or a direct bond.
Examples of suitable groups R
1
include methyl, ethyl, CH
3
OC(═O)CH
2
—, CH
3
CH
2
OC(═O)CH
2
—, HOCH
2
CH
2
—, CH
3
CH(OH)CH
2
— and HOCH
2
CH(OH)CH
2
—.
Examples of suitable groups R
2
include H—, methyl, ethyl and HOCH
2
CH
2
SCH
2
CH
2
C(═O).
The heteroaromatic residue is selected from 2-thienyl, furfuryl, 2-pyridinyl (optionally substituted), 4-pyridinyl (optionally substituted), 2-(5-methyl-1,3,4-thiadiazolyl), 2-pyrimidyl, 2-(4-hydroxypyrimidyl), 2-(4-hydroxy-6-methylpyrimidyl), 2-(4-hydroxy-6-propylpyrimidyl), 2-(4,6-dihydroxypyrimidyl), 2-benzoxazolyl and 2-benzothiazolyl (optionally substituted).
Preferably and independently of each other
m is 2;
n is at least 4, more preferably 4-50;
p is 1;
X is —C(═O)— or —CH
2
C(═O)O—;
A is methylene or ethylene;
R
1
is methyl, ethyl, HOCH
2
CH
2
—, phenyl, benzyl or 1,3,5-triazinyl;
R
2
is hydrogen, methyl or HOCH
2
CH
2
SCH
2
CH
2
C(═O)—.
Compounds of formula I can be produced for example by addition of a compound of the formula II
HS—R
1
  (II)
to mono- or diacrylate esters of polyalkylene glycols of the formula III
R
2
—[—O—[—(CH
2
)
m
—O—]
n
—C(═O)—CH═CH
2
]
p
  (III)
or by reaction of polyalkylene glycols with compounds of the formula IV
HOC(═O)—A—S—R
1
  (IV)
and optionally further reaction with bridging reactants.
The invention further provides a method for reducing the tendency of a paper to yellow on exposure to light, comprising the incorporation thereinto, at some stage in the manufacture thereof, of a compound according to formula I.
The invention further provides a paper additive which comprises a compound of formula I.
The invention further provides paper produced by a process incorporating a compound of formula I.
In this description of the invention, unless otherwise stated, the description of a component in the singular also includes the possibility that more than one such component may be used.
The paper may also contain other additives known in the art to control brightness reversion. Examples of such additives include ultraviolet absorbers, for example, 2,4-dihydroxybenzophenone, benzotriazole UV absorbers such as “FADEX” (trade mark) F liquid and “TINUVIN” (trade mark) 1130, ascorbic acid, sodium ascorbate, ethylene glycol bisthioglycolate, S-methyl-1-thioglycerol, sodium hypophosphite, poly(ethylene glycol), and poly(tetrahydrofuran). Such additives may be added either together with, or separately from, the thioether compound as hereinabove described. More preferably, the thioether is added together with an ultraviolet absorber.
The paper may further contain other additives commonly employed in the papermaking industry. Examples of such additives include sizing agents (for example, rosin, starch, alkyl ketene dimer, alkenyl succinic anhydride), wet strength resins (for example, polyaminoamide-epichlorohydrin resins), retention- and drainage aids (for example, polyaluminum chloride, polydiallyldimethylammonium chloride), and optical brightening agents. Such additives may be added either together with, or separately from, the thioether.
The invention is performed by adding the thioether to the pulp or paper sheet at some point in the paper production process, and preferably at the size-press. There are a number of possibilities, namely,
(a) addition to the pulp, prior to sheet formation;
(b) application to a sheet formed on the wire of a paper machine, for example by spraying or coating;
(c) addition at a size-press;
(d) application to the sized sheet at a stage later than the size-press.
The preferred possibility is (c). In all cases, the total quantity of compound lies between 0.02% and 20% (preferably between 0.1% and 10%) by weight on dry fibre.
The invention may be used with paper made from any kind of pulp, but gives especially good results with papers which are formed from high-yield pulps, whereby, with the use of the invention, the tendency to yellow is reduced to a surprising and considerable degree. This permits the use in paper of much higher quantities of high-yield pulp than was previously the case, with consequent potential for consid

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