GB2339208A

GB2339208A - Dry-strength agents for mechanical pulp

Info

Publication number: GB2339208A
Application number: GB9813128A
Authority: GB
Inventors: David A Holroyd
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 1998-06-18
Filing date: 1998-06-18
Publication date: 2000-01-19
Also published as: GB9813128D0

Description

Case lq98CH014 2339208 ORGANIC COMPOUNDS This invention relates to a

process of paper manufacture.

In the manufacture of paper products such as paper, cardboard.and the like from pulp, it is a known and well-established practice to improve the dry strength of the final product by adding a cationic starch to the wet-end of a paper machine. VAiile this is effective for many pulps, it is not so effective for pulps with a high level of anionic charge, such as those which are predominantly mechanical in nature. The level of anionic charge in such systems means that an unacceptably high level of cationic starch must be used.

It has now been found that the dry strength of paper prepared from a mechanical pulp can be considerably enhanced by the addition thereto of certain substances. The invention therefore provides a process of increasing the dry strength of a paper product derived from a predominantly mechanical pulp, comprising the addition to the pulp at the wet-end of a paper machine of a mixture of an anionic or non-ionic starch and a water-soluble phenol- or naphthol-forTnaldehyde resin or of a reaction product of starch and a phenol- or naphtholformaldehyde resin.

In this specification, it is to be understood that where a compound or material is referred to in the singular, the use of two or more such compounds or materials is comprehended, unless otherwise stated.

By "predominantly mechanical pulp" is meant a pulp in which most of the content has been produced by mechanical means, as opposed to chemical means. Such pulps include thermomechanical pulp (TN2), chemithermornechanical pulp (CTNT), groundwood pulp, deinked pulp (from recycled paper products) and NSSC pulp. Such pulps are relatively cheap in comparison with chemical pulps, but they have a number of disadvantages which have hitherto confined their use to a relatively narrow range of applications. The use of this invention permits the use of such pulps in a much wider range of paper products.

Any non-ionic or anionic starch is suitable for use in the present invention. A preferred variety of starch is a modified raw starch, that is, a raw starch which has been modified through Case 1998CH014 2 significant molecular scission, molecular rearrangements, oxidation or introduction of substituent chemical groups into the starch molecules (see "Modified Starches: Properties and Uses" by 0. Wurzburg (CRC, 1986) at p.13. Typical examples of such starches include low viscosity starches, crosslinked starches and starch esters, all of them well-known commercial products. The source of the starch is not important and any such starch may be used, for example, maize (corn) starch, potato starch, etc. Particular examples of modified starches which have been found to be useful in the present invention are starch phosphate esters, for example the NYLGUM (trade mark) range of potato and maize starch esters.

By "water-soluble phenol-or naphthol-formaldehyde resin" is meant any of such resins known to the art. Such materials are well-known as, for example, reserving agents, especially in the dyeing of wool, and as tanning agents. A preferred group of resins are those which contain sulphonic acid and/or sulphone groups, however, other types may also be used. A preferred material is the condensation product of dihydroxydiphenylsulphone with 0.2-3.0 moles of formaldehyde. Other suitable materials are the phenol-and naphthol-forrnaldehyde resins described in British Patent 1,525,110, the contents whereof are incorporated herein by reference.

In case a reaction product of starch and a phenol- or naphtholfonnaldehyde resin is used, native starch can be used and the resin is reacted with the starch in the range of 4-10% by weight. The preferred resin is again the condensation product of dihydroxydiphenylsulphone and 0.2-3.0 moles of formaldehyde, especially 0.75 moles of formaldehyde. The resin is reacted with the starch as an aqueous solution in an oven at a temperature of 105'C for 30 minutes. The reaction product can be dried and ground to a fine powder but should be used as an aqueous solution which is prepared by cooking at 90'C for 20 minutes.

The starch and the resin may be added to the pulp at the wet-end in any order. However, it is preferred that they be pre-mixed and added together. In one embodiment of the invention, they may be reacted together, prior to addition to the pulp. The invention therefore also provides a paper dry-strength additive, comprising a modified raw starch or the reaction product of starch and a phenol- or naphthol-forrnaldehyde resin as hereinabove defined and a water-soluble phenol- or naphthol-formaldehyde resin as hereinabove defined. In either case, the proportion of starch to resin is from 60:1 to 6:1, preferably from 30:1 to 15:1 by weight of Case 1998CH014 3 dry materials. The proportion of starch in the pulp (dry material by weight of drypulp) is from 0.5 to 4.0%, preferably from 1.0 to 2.0%.

In a preferred embodiment of the invention, the materials hereinabove described are used in conjunction with a polyethylene oxide (PEO)-based retention aid. The polyethylene oxides useful in this embodiment of the invention are those with a molecular weight (weight-average) in excess of two million. A typical suitable commercial material is "Cartaretin" (Trade mark) E ex Clariant International Ltd. The combination of starch, resin and PEO gives unusually good results. The PEO is used in the same manner and in the same proportions as are conventional retention aids.

The invention may be used with any paper pulp, but it has been found to be particularly beneficial when used in conjunction with pulps which are predominantly mechanical in nature. Paper products produced from such pulps show considerably enhanced dry strength properties. Moreover, the materials are relatively inexpensive and the improved results are therefore achieved at equal or reduced costs. The invention therefore also provides a paper product which is made by a process which comprises a process as hereinabove described.

The invention is now further described with reference to the following examples:

EXAMPLE1

A 2 % (weight) aqueous slurry of "Meritena" (trade mark) NpH, a modified native maize (corn) starch is prepared by adding it to water and heating at 85'C for 15 minutes. This slurry is added with stirring to a paper pulp of 50% old cardboard and 50% old newsprint such that there is present 2% dry starch on dry pulp.

This preparation is repeated except that there is also added to the starch slurry before heating 6.3% (dry material on dry weight of starch) of dihydroxy-diphenylsulphone-formaldehyde resin.

Both pulps are used to prepare hand-sheets. These sheets are pressed on to steel glazing plates for I minute at 8.0 bar pressure and then placed in drying rings and dried for 30 minutes at 100'C in a fan-assisted oven. The sheets are then conditioned at 23'C and 50% relative Case 1998CH014 4 humidity for 12 hours. The sheets are subjected to an automatic burst tester and the Burst Index measured on a number of sheets. The measurements and subsequent calculation of the Burst Index are carried out according to standard test method TAPPI No. T403 om-91. The average results are as follows:

[Burst Index Pulp without starch or resin 2.61 u wi starch 2.78 Pulp with starch and resin 3.01 The improvement in Burst Index can readily be seen.

EXAMPLE2

Use of polyethylene oxide with starch and resin.

Example I is repeated, but with the addition of polyethylene oxide of molecular weight approx. 6,000,000 ("Cartaretin" E is used). This is added after the resin and starch additions. Burst Index is measured as hereinabove described and retention is measured by TAPPI test method T261. The results obtained are shown in the following table (where "ZFN" is the resin and "E" the polyethylene oxide).

Additive Burst Index % Retention Nil 1.63 52.6 2% Starch 1.85 53.1 2% Starch + 6% ZFN 2.12 53.7 2% Starch + 6% ZFN + 0.005%E 2.14 62.8 0.005% E 1.62 54.1 The improvement in both burst index and retention brought about by the combination of starch, resin and PEO can easily be seen.

Case 1998CH014 5 EXAMPLE3

A resin for reacting with starch was prepared as follows:

0.5 moles of dihydroxydiphenolsulphone were reacted with 0.75 moles of formaldehyde at I OO'C for 30 minutes. Aft er cooling this resin was added to a native starch at dosage levels of 0 to 10%. The resin was added with sufficient water to ensure good mixing with the starch. After mixing for 5 minutes the starch/resin blends were allowed to react in an oven at IOTC for 30 minutes. The dry product was then ground to a fine powder. The various samples of starch + resin were then prepared as solutions by cooking at 90'C for 20 minutes. The various starch solutions were then evaluated as strength additives for an all waste furnish.

Results:

Starch dosage 2%, strength determinations were carried out as before and the results expressed as the Burst Index.

No additives 2.04 Starch, no resin 2.21 Starch + 4% resin 2.26 Starch + 6% resin 2.30 Starch + 8% resin 2.34 Starch + 10% resin 2.38 Case 1998CH014 6

Claims

1. A process of increasing the dry strength of a paper product derived from mechanical pulp, comprising the addition to the pulp at the wet-end of a paper machine of a mixture of an anionic or non-ionic starch and a water-soluble phenol-or naphthol-forrnaldehyde resin or of a reaction product of starch and a phenol- or naphthol-forrnaldehyde resin.

2. A process according to claim 1, wherein the starch is a modified raw starch, as hereinabove defined.

3. A process according to claim I or claim 2, wherein the water-soluble phenol- or naphthol-formaldehyde resin is one which contains sulphonic acid and/or sulphone groups.

4. A process according to claim 1, wherein a reaction product of starch and a phenol- or naphthol-formaldehyde resin is used.

5. A process according to claim 4, wherein a reaction product of native starch and a dihydroxydiphenylsulphone-formaldehyde resin is used.

6. A process according to any one of claims 1-5, wherein polyethylene oxide of weightaverage molecular weight of at least 2,000,000 is used as a retention aid.

7. A paper product which is made by a process which comprises a process according to any one of claims 1-6.

Case 1998CH014 7

8. Use of a mixture of an anionic or non-ionic starch and a water-soluble phenol- or naphthol-formaldehyd resin or of a reaction product of starch and a phenol- or naphtholformaldehyde resin to improve the dry strength of a paper product derived from mechanical pulp.