FI63086B - ABSORBER PAPER OCH FOERFARANDE FOER DESS FRAMSTAELLNING - Google Patents

Description

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Patent- och ragittantyralaan '7 Arasta »utl» * d och mUkrifun publlcarad 31.12.82 (32) (33) (31) The requested «cuoikuut —- fegtrd prlorltat (71) Imperial Chemical Industries Limited, Imperial Chemical House,

Millbank, London SW1, England-England (GB) (72) Richard George Cleveland Henbest, Stockton on Tees, Cleveland,

The present invention relates to absorbent papers: such papers have a wide range of uses, such as face or other hygienic wipes, and absorbent papers, such as facial or other hygienic wipes, Depending on the desired application, other factors besides absorbency, such as bulk, softness and strength, may be important.

Generally, paper is made by a wet process in which a pulp slurry in water is converted to a sheet, e.g., by applying the pulp to a moving porous surface, e.g., a cylinder paper machine wire, and removing water by first draining through the porous surface and then passing the drained fibrous web through a suitable dryer. In general, to produce satisfactory paper, the average length of the fibers should be less than 10 mm. The fibers used to make paper are usually cellulose: there are two main types of cellulose pulps: namely lignin-free, e.g. e.g., a mechanical pulp in which Crude cellulose, e.g., wood, is ground to the required fiber size by removing lignin. Semi-chemical and thermomechanical pulps are produced by methods that remove little or no lignin, so they are classified here as mechanical pulps. Papers made from lignin-free e.g. chemical pulp have significantly different properties compared to lignin-containing e.g. mechanical pulps. In some cases, the paper can be made from a mixture of lignin-free and lignin-containing pulps to achieve the desired balance of properties.

One parameter that has a significant effect on the properties of the paper is the degree of grinding or refining of the pulp: In general, the higher the degree of grinding of the cholester, the stronger and less fluffy the resulting paper. The degree of grinding is suitably determined by measuring the degree of grinding of the pulp. The degree of grinding as defined herein means the degree of grinding as measured by the standard Canadian degree of grinding test method: the higher the degree of grinding, the less well the pulp is ground. The degree of grinding also affects the absorbency of the paper: In general, the higher the degree of grinding, i.e. the less ground, the higher the absorbency.

It has been found that absorbent papers can be obtained by making paper from certain blends of cellulosic pulp and fibers formed from an amino-formaldehyde resin such as urea-formaldehyde (UF) resin.

Paper made from blends of UF resin fibers and cellulosic pulps is described in English Patent Application 10404/77. The pulp grade of the cellulosic pulp according to said application was less than 400 ml with chemical pulp or 120 ml with mechanical pulp.

It has now been found that absorbent papers can be made from cellulosic pulps with lower degrees of grinding.

The term absorbent paper means that the water absorption capacity of the paper is greater than 3: this can be determined by impregnating a weighed amount of air-dry paper with water, shaking it gently to remove excess water, and reweighing it.

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Absorption capacity is calculated as the weight of water absorbed per unit weight of air-dry paper. The absorbent papers of the present invention generally have a higher water absorption capacity than most absorbent papers that can be made from the cellulosic pulp used under the same papermaking conditions. For example, unground or very lightly ground chemical wood pulp may have a degree of grinding of about 600 ml and a water absorption capacity of paper made therefrom of about 3. By adding 20% UF fibers to the same wood pulp, the water absorption opacity can be increased to about 3.4. Alternatively, stronger papers can be made: thus, by grinding a cellulosic pulp of about 450 ml with a degree of grinding before mixing with 20% UF fibers, a paper stronger than most absorbent pulp papers made of pure cellulose can be made, which can be obtained from this pulp but however, it has similar absorption properties.

In order to obtain absorbent papers from cellulose pulps which have been ground fairly well, it is necessary to add such an amount of amino-formaldehyde resin fibers that the resulting mixture has a high degree of grinding. The ratio of the degree of grinding of a mixture of lignin-containing and lignin-free, e.g. mechanical and chemical pulp, to the degree of grinding of individual pulps is sufficiently linear for the purposes of this invention, which can be expressed by: F = fc x + fm (1 - x) fc is the degree of grinding of the lignin-free mass fm is the degree of grinding of the lignin-containing mass x is the weight fraction of lignin-free mass in the mixture.

On the other hand, the relationship between the degree of grinding of the amino-formaldehyde resin fibers and the cellulose pulp and the individual degree of grinding of the amino-formaldehyde resin fibers and the cellulose pulp is not linear. However, as a guideline, if lignin-free, e.g. chemical pulp with a degree of grinding of 400 ml, is mixed with the same amount of UF fibers, the degree of grinding of the resulting mixture will be about 600 ml. Similarly, a lignin-containing, e.g. mechanical pulp with a degree of grinding of 120 ml, when mixed with the same amount of UF fibers, gives a degree of grinding of the mixture of about 380 ml.

4,63086 According to the present invention, there is provided an absorbent paper product formed from a blend of fibrous materials comprising 5-95% by weight of amino-formaldehyde resin fibers insoluble in cold water and having a mean length of between 1 and 10 mm and a mean diameter of between 1 -30 μm, and 95-5% by weight of cellulose pulp, respectively, provided that when the Canadian standard grinding rate of the cellulosic pulp is less than 310 x 140 ml (where x is the weight fraction of lignin-free pulp in said cellulose pulp), the proportion of amino-formaldehyde resin fibers in the mixture is is above 220 x + 400 ml.

Thus, considering the case where the cellulose pulp is completely lignin-free, e.g. chemical pulp, i. x = 1, the degree of grinding of the pulp should exceed 450 ml. However, when the pulp has a degree of grinding of less than 450 ml, absorbent papers can be prepared with blends containing sufficient amino-formaldehyde resin fibers to give the blend a degree of grinding of more than 620 ml. Similarly, when the cellulose is completely lignin-containing, e.g. mechanical pulp, i. x = 0, the pulp should have a degree of grinding greater than 140 ml, but if it is less than this value, absorbent papers can be made with blends containing enough amino-formaldehyde resin fibers to give a blend degree of more than 400 ml.

The amino-formaldehyde resin used in the preparation of the fibers is a condensate of an amino compound, preferably a polyamine such as urea or melamine, with formaldehyde. The amino compound is preferably urea, alone or in a mixture of up to 5% by weight of melamine. The molar ratio of formaldehyde to amino groups is preferably between 0.6: 1 and 1.5: 1, in particular between 0.7: 1 and 1.3: 1.

Amino-formaldehyde resin fibers can be prepared by any suitable fiber formation technique, such as wet or dry spinning, and are preferably formed by a centrifugal spinning method, as described, for example, in German OLS Publication 2,810,535, which gives, as is preferred, substantially straight and unbranched fibers. .

The fibers of the amino-formaldehyde resin should have an average length, weighted by length, of 1-10 mm, preferably 2-6 mm. Preferably, substantially all of the fibers of the amino-formaldehyde resins should have a length of 1-10 mm. The fibers of the amino-formaldehyde resin should have an average diameter of 1 to 30, preferably 2 to 20, and especially 5 to 15. Preferably, substantially all of the formaldehyde resin fibers should have a diameter of 1 to 30.

The fibers of the amino-formaldehyde resin preferably have an average strength of -2 -1 at least 50 MNn (corresponding to approximately 33 Nmg).

The fibers of the amino-formaldehyde resin should be sufficiently hardened so that they are insoluble in water: thus their solubility in water at 25 ° C should not exceed 1.5% by weight.

Cellulosic fibers that can be used include mechanical wood pulp, chemical wood pulp made by sulfate or sulfite cooking methods, thermomechanical, and semi-mechanical wood pulp. Alternatively, the cellulosic pulp may be cotton linen, flax fibers recovered from rags, or other cellulosic fiber suitable for use in papermaking. Depending on their origin or method of preparation, they may contain different amounts of lignin. Thus, for example, cotton linters are substantially free of lignin.

Absorbent papers can be prepared by the conventional wet process, as described above, after the fibrous materials have been prepared and blended into the aqueous papermaking pulp. The absorption capacity and bulk of the paper can be increased if compression of the wet sheet of paper before drying is omitted.

Papers containing a large proportion of amino-formaldehyde resin fibers tend to be relatively weak in strength. The strength of such papers can be increased by attaching a binder to the paper: the binder can be added to the water of fibrous materials or can be incorporated at a later stage of impregnation or coating. In this case, the binder can be sprayed on a wet web or it can be coated on dry or partially dried paper. Different methods are suitable for different binder systems, as is well known to those skilled in the art of papermaking.

Binders can also be advantageously added to papers containing smaller amounts of amino-formaldehyde resin fibers.

Examples of suitable binders include starch or modified starch, chain polymers, water-soluble polymers such as polyethyleneimine, polyacrylamide, and polyvinylpyrrolidone. The binder is preferably treated to make it cationic in water. Particularly preferred are cationic binders added in addition to the fibers - including, in addition to said additives, cationic starch and urea - or in addition to melamine-formaldehyde resins, as is usually done to increase the wet strength of the paper. A typical amount of additive used is 0.01 to 10% by weight, preferably 0.1 to 5% by weight of the amount of fibrous materials.

The paper products of this invention contain 5-95% by weight of amino-formaldehyde resin fibers and 95-5% by weight of cellulose fibers, respectively. The properties of the paper vary considerably as the proportions of the respective fibers vary: thus, as the proportion of amino-formaldehyde resin fibers increases, the absorbency and bulk increase. In general, as the proportion of amino-formaldehyde resin fibers increases, the degree of grinding of the cellulosic pulp should be reduced to achieve sufficient strength, although it is understood that strength is not important in some applications, such as high absorbency products.

The paper products preferably contain at least 15%, and preferably less than 80% by weight of amino-formaldehyde resin fibers.

Paper products can be creped by conventional methods to increase their bulk and, incidentally, to improve their elongation. Creping may not be necessary for papers containing mainly amino-formaldehyde resin fibers, but in such a case it may be desirable to add one or more of the above additives. When the amount of amino-formaldehyde resin fibers is relatively low, i. less than about 35% by weight, the paper becomes soft and bulky, and may require creping with conventional equipment to produce acceptable paper for absorption purposes. However, due to the greater magnitude provided by the amino-formaldehyde resin fibers, the efficiency of the creasing process can be reduced compared to ordinary papers.

At medium amounts of amino-formaldehyde resin fibers (i.e., 35-75% by weight), the papers may be acceptable for some absorbent purposes, but for other purposes they may require creasing.

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At high concentrations of amino-formaldehyde resin fibers, i. more than 75% by weight, is made of a very bulk absorbent paper that requires little, if any, creping. However, it may be desirable, and especially for papers containing more than 90% by weight of amino-formaldehyde resin fibers, to use a binder as described above.

The advantages of the papers of this invention provided by the presence of amino-formaldehyde resin fibers are improved absorbency, softness, porosity and bulkiness, often with little or no sacrifice in strength, allowing a combination of useful properties not possible with pure cellulosic pulps.

In addition, the rapid flow properties of the amino-formaldehyde resin fibers also provide advantages in manufacturing. It is also possible, for example, to increase the dilution of the pulp without reducing the speed of the machine and thus to improve the sheet formation. This can be especially important with light towel products.

The invention is illustrated by the following examples in which all percentages are by weight. The amino-formaldehyde resin fibers used in the examples were urea-formaldehyde (UF) fibers prepared by centrifugal spinning. An aqueous solution of urea-formaldehyde resin having a molar ratio of formaldehyde: urea of 2: 1, a solids content of 65% and a viscosity of 45 poise was continuously mixed with 10% of a solution containing 1.66% polyethylene oxide having an average molecular weight of 600,000 and 6.66% ammonium sulfate. The resulting mixture was fed at a speed of 200 g / min into a 13 cm diameter spinning jug rotating at 10,000 rpm. The resin was spun as fibers from the jug into the atmosphere at 150 ° C and then the fibers were removed and cured by heating at 120 ° C for 3 h to render them insoluble in cold water. The resulting fibers were torn and further decomposed in a Valley laboratory grinder. The average fiber length of the torn, ground fibers was about 3 mm and the average diameter was 10 μm. Essentially all fibers had a length in the range of 1-10 mm and a diameter in the range of 3-20 μm. The strength of the fibers, measured by the short-distance test of the loose-fiber mat, was about 120 NMm

In the examples, UF fibers were blended in the indicated amounts, expressed on a dry fiber basis, with cellulosic pulps ground to 63086 to the degrees of grinding indicated in the Valley mill. The resulting mixtures were prepared as hand sheets weighing about 60 g m, using a British standard hand sheet machine. Except when specifically reported, the papers were wet-pressed.

The papers were tested as follows:

Absorption Capacity: A small amount of paper was weighed, soaked in water, gently shaken to remove excess water, and reweighed. The absorption capacity was calculated as the weight of water absorbed per gram of air-dry paper.

Absorption time: Pin according to Bibulous paper test T432. The time taken for 1 ml of water to be absorbed was measured.

Klemm Absorption Test: This experiment was modified to match the sizes of the paper samples prepared, and based on the fact that highly absorbent materials were tested. A paper strip, 150 mm x 15 mm in size, was held upright with a 10 mm sample immersed in water. The height of water rise in this strip was measured for 5 min. after. (Normally 10 minutes is recommended for the Klemm test).

oil absorption: According to the Patra test using oil S-600.

Outbreak Index: The burst pressure is measured by the pin T403 method -2 and the result expressed in kNm is divided by the amount of substance -2 expressed in gm to give the burst index.

Example 1 In this example, commercially available birch sulphate, i.e. chemical wood pulp. In order to obtain the maximum absorbability achievable with this pulp, the pulp was dispersed in water in a laboratory chopper without any prior grinding or refining. Because in the absorption capacity test, the paper sample tended to decompose when completely immersed in water, making it impractical to obtain a meaningful value, the paper was also made from the same pulp after it was lightly ground.

Papers were also made from blends of cellulosic pulp that had been ground to varying degrees with varying amounts of UF fibers. The results are shown in the following table.

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Grinding degree (mi) Kuoh_ Rest- Absorp- Abs. Klenrn o / ^ kfius ^ A ^ o / ° UF - irdete:

Mass Sequence cm-2 / g kNg (sec) (mm).

1.1 * 0 + + - 0.44 - 146 70 1.2 * 0 604 604 - 0.65 2.98 145 56 1.3 * 20 284 384 2.06 1.78 2.70 376 40 1.4 20 452 510 2.09 1.11 3.03 177 68 1.5 20 604 612 2.22 0, 30 3.38 60 90 1.6 50 452 621 2.69 0.33 3.42 54 101 1.7 50 604 690 2.78 0.11 3.52 25 126 1.8 75 284 691 3.20 0.11 4.01 29 106 1.9 75 452 692 3.37 0.01 4.23 21 118 1.10 75 604 735 3.49 - 5.20 17 112 x comparative + unground mass

Run 1.1 and 1.2 show that the maximum absorbability achieved with birch sulphate pulp alone is: absorption capacity approx. 3, absorption time about 145-146 sec, and Klemm rise approx.

56-70 mm.

This example shows that although the absorption properties of paper containing 20% UF (run 1.4) are similar compared to the maximum values achievable with birch sulfate pulp alone, the burst index is much better. It also shows that absorbent papers can be made using low pulping pulps if sufficient UF fibers are added cf. times 1.3 and 1.8.

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Example 2

To demonstrate the effect of the binder, starch was added to the fiber mixture from which the papers were made. The cellulose pulp was birch-sulfate pulp ground to a degree of grinding of 484 ml.

% starch- Mixture Kuch- Tel. Absorpt. Klami lys milling degree keus index kapas. increase in fiber m.

Driving gp weight starch. (ml) kNg ”(mm) 2.1 * 0 0 484 1.46 2.50 2.95 41 2.2 * 0 5 411 1.42 4t50 2.69 58 2.5 50 5 616 2.90 0 , 62 5.87 158 2.4 75 10 696 46 0.12 5.19> 140 x comparative

Comparing starch-free systems with similar mixing, degree of grinding and UF content as in Example 1, e.g. run 2.3 to run 1.6 and run 2.4 to run 1.9, it can be seen that the addition of starch improves both the absorbency and the burst index .

Example 3

The procedure of Example 1 was repeated using commercially available unbleached mechanical wood pulp instead of birch sulphate pulp. In one case, a running 3.7 paper was prepared omitting the wet pressing step. The results are shown in the following table.

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Grinding (mi) Kuoh- Puhk. Absorption- Absorp- Terminal misaste keus index capacitance. tio. rise

Driving -] time

Mass Mixture cmV «(sec.) ^ 3.1 * 0 437 4 37 - - 3.32 205 45 3.2 * 20 69 110 2.59 0.84 3.01 758 32 3.3 20 437 503 2.90 0.27 3.84 195 6o 5.4 50 145 423 3.24 0.20 3.82 75 69 3.5 50 437 548 3.46 0.11 3.94 138 59 5.6 75 69 544 3.54 0.10 4.2 21 108 3.7+ 75 69 544 4.8 0.08 5.49 13 122 3.8 75 87 570 4.51 0.11 4.47 34 100 3.9 75 145 613 3.46 0.06 4.61 49 85 x comparative + not wet-pressed Again, it is seen that if sufficient UF fibers are added, absorbent papers can be made from low milling pulp.

Example 4

The procedure of Example 1 was repeated using a mixture of 70% bleached pine sulphate and 30% bleached birch sulphate as cellulose pulp. In a few cases, 3% of the fiber weight was added to the starch, and in all these times the wet pressing step was omitted. The indicated water absorption time is the time required to absorb 0.1 ml of water, in contrast to 1 ml in the previous examples.

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Grinding (ml) Fluffy- Rest. oil water terminal degree of index

Ajo% W si. bointi bointi cnr / g kNg »time (am) 5608 '' (sec.) 4.1 * 0 587 587 3.25 1.83 0.4 5.8 99 4.2 * 0 638 658 3.50 1, 21 0.6 6.5 94 4.3 * 0 650 650 3.62 0.97 0.8 4.6 108

4.4 20 587 675 3.53 1.03 0.2 5.5 HO

4.5 20 638 700 3.48 0.76 <0.1 6.1 103 4.6+ 20 640 705 3.72 1.60 0.2 8.6 90 4.7 20 650 675 3.68 0.55 0, 3 4.4 106 4.8 40 587 712 3.95 0.45 <0.1 3.9 109 4.9 40 638 725 3.88 0.34 <0.1 4.6 112 4.10+ 40 640 728 3, 76 0.85 0.1 5.3 94 4.11 40 650 725 3.97 0.29 <0.1 3.5 114 x comparative + starch added

Example 5

The procedure of Example 1 was repeated using birch sulphate wood pulp with a degree of grinding of 425 ml as cellulose pulp. The results are shown in the following table along with the values for commercial blotting paper and commercial absorbent paper towel fabric.

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The mixture has a powder fluff index. Terminal brewed degree _i ^

Ajo% UI * (“1) (cm g) kNg (sec.) ^ 5.1 10 460 1.72 2.26 44 43 5.2 20 500 1.92 1.93 42 46 5.3 30 535 2.15 1.40 21 64 5.4 40 570 2.28 1.00 18 70 5.5 50 605 2.48 0.80 9 86 5.6 60 642 2.81 0.40 9 102 5.7 70 680 5.06 0.23 6 113 5.8 80 715 3, 29 0.11 1 * 115 5.9 90 752 4.42 0.06 3 * 82 5.10 Absorbent paper 1.78 0.73 44 48 5.11 Absorb, towel. fabric 4.12 0.56 20 * 2.5 x the time taken for 0.1 ml of water to be absorbed.

The papers of runs 5.1-5.9 all had an absorption capacity of more than 3.