GB1591322A - Method of papermaking - Google Patents

Description

(54) A METHOD OF PAPERMAKING (71) We, MOBIL OIL CORPORATION, a Corporation of the State of New York, United States of America of 150 East 42nd Street, New York, New York 100A, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of papermaking particularly for improving the effect of optical brighteners.

For the purpose of achieving a maximum degree of whiteness the paper industry has various methods at its disposal, such as selecting highly white paper half stuff, bleaching the raw material, and using fillers or white pigments, shading dyes and/or optical brighteners.

The high demands for quality that the final product has to meet nowadays particularly in the field of printing paper necessitate increasing demands for quality in the fillers and pigments employed. For a limitation of the addition of fillers and pigments the increasing use of both sides of the paper, the increasing sieve wear, but above all the decrease of the strength properties are responsible. The strength properties are impaired by the addition of fillers or pigments as the surface bonds of the fibers towards one another are disturbed.

When selecting the fillers and pigments for addition to the pulp, particle size and particle shape, covering power and whiteness, low abrasion, uniformity and purity of the material supplied, and other factors have to be considered.

For brush pigments also the binder requirements, dispersion properties and favourable rheological behaviour are of additional significance.

In view of these limitations for the admixture of fillers and pigments, so-called optical brighteners have been increasingly employed in recent years to improve the degree of whiteness in the paper pulp as well as in brush pulp or brush paint.

The optical brighteners do not cover the conventional yellow tinge of the paper by subtraction but substitute for the lack of remission an additional light caused by their fluorescence. Optical brighteners shift the tint of the brightened material e.g. from yellow towards blue, and the increase in remission results in an increase in brightness. The brighteners fluoresce sufficiently only when mounted in substance on material such as cellulose, starch, casein, polyvinyl alcohol, plastics such as polyvinyl acetate, or the like.

In the use of optical brighteners there arises the difficulty that fillers and pigments quite generally reduce the effect of the brighteners in the paper because they absorb in the UV range or have a yellow tinge. In addition, the influence of fillers or pigments decreasing the effectiveness appears to be connected with their refractive index and with covering properties.

It is the object of this invention to provide a process for improving the effect of optical brighteners in paper industry wherein the undesired influence of fillers or pigment on the optical brighteners is decreased or essentially eliminated and an increase of the degree of whiteness and at the same time of the retention properties of the materials used and the strength properties in the papers are achieved.

The problem underlying the invention is solved by a method of papermaking in which a polypiperidine halide, adsorbed on a finely divided particulate carrier, is added to the pulp composition. According to a special embodiment the polypiperidine halide used is polypiperidine chloride or polydimethyl diallyl ammonium chloride, but the respective bromide may be used as well.

Surprisingly it was found that the effectiveness of optical brighteners can be considerably increased by minor quantities of the cationic polymer, polypiperidine chloride, and that when fillers and/or pigments are used the previous admixture of the cationic polymer improves or even makes possible the substantive mounting of the optical brightener, thus making the brightener highly effective.

The carriers employed for the polypiperidine halide can be either finely divided inorganic materials, e.g. fillers, such as kaolin or talcum, and white pigments, such as calcium carbonate, magnesium silicate, aluminium silicate, calcium silicate or silica gel; or organic fillers, such as starch, carboxymethyl cellulose, fine-particle cellulose fiber of various degrees of pulping or fine-particle mechanical wood pulp. lt has proved particularly advisable to slurry a filler or a pigment or an organic carrier and a polypiperidine halide in aqueous solution and to add such slurry to the paper pulp e.g. in the tub or the beater before the optical brightener is added.

According to a special embodiment of the invention, a polypiperidine halide in aqueous solution can be added directly to a paper pulp, particles of which serve as a carrier for the polymer, before the optical brightener is added.

The optical brighteners employed in paper industry are anionic substances, derivatives of the diamino stilbene disulphonic acid, preferably condensation products containing triazine ring compounds, being used particularly.

Special advantages will result when the polypiperidine halide is employed in the presence of starch, particularly in such quantities that the starch is cationized or partially cationized.

In order to achieve the effect according to the invention, it is sufficient to use minor quantities of polypiperidine halide, particularly of polypiperidine chloride. Quantities of e.g. 0.05 to 1 % by weight, particularly 0.1 to 0.3 weight % polypiperidine halide, based on pigment or filler, have proved suitable.

In case starch is used simultaneously, the following quantites can be employed: 0.1 to 1.0 weight %, particularly 0.5 to 1 weight % starch and 0.05 to 1 weight % polypiperidine halide, based on pigment or filler; the substances being heated in aqueous medium to temperatures of between 40 and 70"C, the inorganic or organic carrier being added after cooling and the anionic optical brightener being brought into contact with the materials thus treated.

The invention will now be explained in more detail by means of Examples. The polypiperidine halide employed in the Examples was polypiperidine chloride or polydimethyl diallyl ammonium chloride (cf. M.Fred Hoover and Hugh E.Carr: "Performance Structure Relationships of Electro-conductive Polymers", Tappi, The Journal of the Technical Association of the Pulp and Paper Industry, vol. 51 No. 12, December 1968, pages 552 to 559; and U.S. patent 3.228.770), hereinafter called "cationic polymer". The above article by Tappi discloses the use of such polymers in coating formulations but does not suggest the process of the present invention in which the polypiperidine halide adsorbed on a carrier is added to a paper pulp composition. Likewise U.S. Patent 3,288,770 mentions the use of such polymers as wet strength improvement agents for papers but makes no mention of the addition of such polymers to pulp compositions.

Example 1 The cationic polymer was allowed to mount on pigment surfaces by dispersing various pigments, which were slurried in water of room temperature (solids content 20 to 60 weight %) and which are listed in Table I below, in an aqueous solution of 1 to 10 weight % of the cationic polymer. After the cationic polymer was mounted on the pigment surface, tne optical brightener, a commercial brightener (derivative of the diamino stilbene disulphonic acid, BLANKOPHOR of Bayer A.G.) was added. In addition, where required, the starch quantities stated in Table I were added after previous treatment with the cationic polymer.

In the practical performance the procedure was as follows: The pigments were dispersed in water in a beaker with stirring. The solids content was adjusted depending on the kind of pigment and the viscosity resulting therefrom to be between 20 and 60 weight % solids. Under constant stirring an aqueous solution of the cationic polymer or a mixture of an aqueous solution of the cationic polymer with a starch addition was then slowly and dropwise - with interruptions - added to the pigment suspension. In order to ensure even adsorption, the mixture was stirred for about 10 minutes before the optical brightener was added. Then the previously dissolved anionic optical brightener was also slowly added under constant stirring.

After further stirring for 10 minutes the brightening effect is clearly recognizable under UV light. The product thus prepared can be employed directly as a slurry in the paper factory, e.g. in the tub or the beater, or can first be dried and then ground and employed in the production or upgrading of paper.

The following results were obtained: TABLE I Sample % cationic polymer % optical brightener WG +) based on pigment based on pigment Pulp kaolin A - - 0.15 84.2 Pulp kaolin A 0.5 % starch 0.3 % cat.polymer 0.15 88.3 Brush clay B - - 0.15 87.6 Brush clay B 0.2 % starch 0.2 % cat.polymer 0.15 88.5 Al-silicate C - - 0.15 77.5 Al-silicate 0.5 % cat.polymer 0.15 79.3 Al-silicate C 0.7 % starch 0.5 % cat.polymer 0.15 80.9 CaCO3 D - - 0.15 92.8 CaCO3 D 0.2 % cat.polymer 0.15 97.8 CaCO3 D 0.1 % starch 0.1 % cat.polymer 0.15 97.6 CaCO3 D 0.5 % starch 0.2 % cat.polymer 0.15 98.4 +) WG = degree of whiteness measured with the "Elrepho" apparatus with xenon lamp From Table I can be seen that by employing the cationic polymer both with and without the use of starch an increase in whiteness of from 3 to 5 points can be achieved.

From the following Table II the characteristics of the pigments and fillers employed can be seen.

TABLE II Sample chem.composition degree of particle size spec.weight refractive spec.surface whiteness (micron) index (n) m/g Pulp-kaolin A Al2O3.SiO2.H2O 84.2 1 - 5 2.6 1.56 6.8 Brush clay B Al2O3.SiO2.H2O 87.6 0.5 - 2 2.6 1.56 11.5 Al-silicate C - - 77.5 1 - 2 2.1 1.48 140.0 Chalk D CaCO3 92.8 0.5 - 2 2.7 1.56 8.0 Example 2 According to the method described in Example 1 calcium carbonate treated with the cationic polymer was brought into contact with various optical brightener types and concentrations.

TABLE III Sample % cat.polymer % opt.brightener degree of whiteness based on pigment based on pigment CaCO3 0.2 0.05 opt.brightener I1) 94.8 CaC03 0.2 0.1 dto. 96.5 CaCO3 0.2 0.15 dto. 97.8 CaCO3 0.2 0.1 opt.brightener II2) 96.3 CaCO3 0.2 0.15 dto. 97.4 CaCO3 - - 0.15 dto. 93.3 ') "Tinopal" of Ciba-Geigy A.G. derivative of an amino stilbene sulphonic acid 2) "Blankophor P" of Bayer A.G.

(derivative of a stilbene disulphonic acid) Surprisingly it was found that by the use of minor quantities of the cationic polymer (polypiperidine halide, particularly polypiperidine chloride) additionally the retention properties of the filler pigments and fibers as well as the strength characteristics of the paper were substantially improved.

Furthermore native starch can be economically - partially or entirely - cationized with the cationic polymers. Cationized starch has better retention and strength properties.

The advantages achieved by the use of the cationic polymer are apparent from the following Examples.

Example 3 In order to carry out sheet formation tests on the RK (Rapid-Koethen) sheet former the following pulp composition was prepared: 50 weight % sulphate cellulose, bleached 30 weight % sulphite cellulose, bleached 20 weight % beech cellulose, bleached SR degree+) about 35 SR filler kaolin, calcium carbonate, untreated in either case and pretreated with cationic polymers pH value 5.5 in the tests with kaolin pH value 7.8 in the tests with CaCO3 +) SR degree = Schopper-Riegler degree of beating (freeness).

In each case identical starting quantites of filler were added (about 30 weight % based on the dry fiber weight).

The results obtained in the sheet formation tests are presented in Table IV.

TABLE IV filler retention tear length (m) (ash %) longitud. transverse kaolin untreated 14.4 2450 2100 kaolin with 0.2 % cat.polymers 16.1 2590 2250 kaolin with 0.5 % cat.polymers 17.5 2350 2080 CaCO3 untreated 11.0 2620 2190 CaCO3 with 0.2 % cat.polymers 13.1 2710 2250 Table IV shows that because of the positive charge of the filler, caused by the cationic polymer, better adsorption or retention at the negative fiber will occur. In mixtures of untreated filler and treated filler, the untreated kaolin is likewise better retained because of a charge equalisation. Among the known consequences of the better retention properties are the longer sieve passage periods.

Treatment of the filler or pigment respectively with the cationic polymer was carried out in accordance with the method described in Example 1 for the practical performance.

The strength characteristics are normally adversely influenced by the addition of fillers because the surface bonds (bridging hydrogen bonds) among the cellulose fibers will be disturbed, that is to say the strength decreases considerably with increasing filler content.

But surprisingly, by pretreating the fillers with the cationic polymer a certain increase in strength will occur in spite of an increase in filler content. This can possibly be caused by an interaction between the fibers and the polymer at the surface of the filler, contrary to the untreated filler. Since especially with the low-gramme papers there arise great difficulties in upgrading and processing with regard to the strength properties, this result is of special significance.

The improvements obtained in the use of the cationic polymer through cationisation of native starch are shown in the following Example 4.

Example 4 (a) Sheet formation experiments on the RK sheet former Pulp composition: 70 weight % mechanical wood pulp, bleached 30 weight % sulphate cellulose, bleached pH value: 7.0 SR degree: about 40 SR The following was added to the pulp mixture: A 5 ml 10 weight % of native potato starch B 5 ml 10 weight % of native potato starch mixed with 1 % of the cationic polymer and heated C 5 ml 10 weight % of native potato starch mixed with 3 % of the cationic polymer and heated D 5 ml 10 weight % of native potato starch mixed with 5 % of the cationic polymer and heated The weight of the sheets formed was 2.4 g in each case.

Strength test: Load at rupture according to DIN 53112 paper sample A 2.8 kp paper sample B 3.2 kp paper sample C 3.5 kp paper sample D 3.5 kp From the. test results a marked strength increase with the cationized starches as compared with the native starch is apparent.

(b) Sheet formation experiments on the RK sheet former Pulp composition: 50 weight % mechanical wood pulp, bleached 50 weight % sulphonic cellulose, bleached pH value: 7.0 SR degree: about 40 SR The following was added to the pulp mixture: A 1 ml 10 weight % of native potato starch B 0.5 ml 10 weight % of native potato starch mixed with 5 weight % of the cationic polymer and boiled for a short time C 1 ml 10 weight % of native potato starch mixed with 5 weight % of the cationic polymer and boiled for a short time 1 weight % of optical brightener (based on the 2.4 g sheet weight) was added to each of the three different compositions.

Degree of whiteness: measured with the "Elrepho" apparatus with xenon lamp.

Paper sample degree of whiteness A 79.2 B 80.5 C 82.5 By the cationisation of the starch, as in the fillers and coating pigments, the degree of whiteness is improved.

When the cationized starch and the optical brightener are mixed beforehand, a major reduction of the brightening effect occurs. The same was noted with the paper strengths.

The application of adhesive layers on papers which are dried and can be made to stick by moistening and contacting with another material such as e.g. also paper, is called "gumming".

Claims (13)

WHAT WE CLAIM IS:

1. A method of papermaking in which a polypiperidine halide, adsorbed on a finely divided particulate carrier, is added to the pulp composition.

2. A method according to Claim 1, wherein the composition comprises an anionic optical brightener.

3. The method according to Claim 1 or 2, wherein the polypiperidine halide used is polypiperidine chloride or polydimethyl diallyl ammonium chloride.

4. The method according to Claim 1, 2 or 3, wherein said carrier comprises a filler or white pigment.

5. The method according to any of Claims 1, 2 or 3, wherein said carrier comprises starch, carboxy methyl cellulose, cellulose fiber or mechanical wood pulp.

6. The method according to any of Claims 1 to 5, wherein a filler or pigment or an organic carrier, and a polypiperidine halide in aqueous solution, are slurried to produce said adsorbed halide and said slurry is added to the paper pulp before adding an optical brightener.

7. The method according to Claim 1, 2 or 3, modified in that a polypiperidine halide is added directly to a paper pulp, constituents of which serve as adsorbent carrier for said halide, before an optical brightener is added.

8. The method according to any of Claims 2 to 7, wherein the anionic brightener used is a derivative of diamino stilbene disulphonic acid.

9. The method according to any of Claims 1 to 8, wherein the polypiperidine halide is employed in the presence of starch.

10. The method according to any of Claims 4 to 9, wherein from 0.05 to 1 per cent by weight of polypiperidine halide based on pigment or filler, are employed.

11. The method according to any of Claims 5 to 10, wherein from 0.1 to 1.5 per cent by weight of starch are employed.

12. The method according to any one of Claims 9 or 11, wherein the starch and the polypiperidine halide are subjected to heating in aqueous medium to temperatures of between 40 and 70"C, and after cooling the inorganic or organic carrier is added, and then an anionic optical brightener is brought into contact with the materials thus treated.

13. A method of papermaking according to Claim 1 substantially as described in the Examples.