SE514466C2 - Method for improving sorption properties in cellulose fibres - Google Patents

Abstract

The treated fibres are natural cellulose fibres. The polymers are selected from a group which comprises polyethylene glycols, polypropylene glycols, polyethylene oxide, polytetrahydrofuran, or alkoxylated derivs., polyvinylpyrrolidone or halogen hydroxylated, ethylhydroxylated or hydropropyl derivs., polyvinyl alcohol, hydroxypropyl starch, ethylhydroxyethylcellulose, etc.. The solution of polymer containing water is sprayed onto the fibres or the fibres can be suspended in a solution containing water during treatment. The absorbent material containing cellulose fibres can be fluff, hygiene paper, paper impregnated with heat-hardening resin, the paper being used as an overlay in a decorative laminate.

Description

30 514 4661 2 is, inter alia, that it is only applicable to regenerated cellulose fibres, which are produced by processes involving toxic chemicals, such as carbon disulfide, and that it must be utilized in the actual process of producing the fibres, which makes it difficult for a manufacturer of absorbent products, such as a purchaser of fibres, to modify the sorption properties of the fibres if he has to do so in order to meet the requirements of a specific absorbent product he intends to produce.

Another area in which the sorption capacity of cellulosic materials is important is laminates, especially so-called decorative laminates, as described in US-A-3 373 071. Such laminates conventionally comprise at least three layers: a wear layer, a print or pattern layer below the wear layer, and a core layer supporting the wear layer and the print layer. All the layers consist of paper sheets impregnated with thermosetting resin. The wear layer usually consists of semi-transparent paper impregnated with melamine resin. The impregnation is carried out by immersing the paper in an aqueous solution of the resin. It is obvious that the sorption capacity of the paper is a critical parameter for the effectiveness of the impregnation.

There is thus a need for a simple method to improve the sorption capacity of already existing natural and regenerated cellulose fibers, which method does not involve toxic substances.

This problem is solved by the method defined in the appended claims.

In more detail, the present method includes a step in which cellulose fibers are treated with a water-soluble, nonionic polymer.

"Treating" the fibers with a water-soluble, nonionic polymer means that the polymer is brought into proximity to, or in contact with, the fibers. Preferably, the polymer is kept in proximity to, or in contact with, the fibers for at least about 1 minute, preferably at least about 30 seconds, and especially at least about 5 seconds. Preferably, the treatment is carried out when the dry matter content of the fibers is at least about 20%, preferably at least about 35%, and most preferably at least about 50%.

It is believed that water-soluble, nonionic polymers of the type indicated create improved sorption properties of cellulose fibers by "neutralizing" surfactants, which have been found to occur naturally in the fibers. These surfactants appear to include fatty acids, and the "neutralizing" effect can be explained by the formation of micelles, which have cores of fatty acid and shells of water-soluble nonionic polymer.

Examples of useful water-soluble nonionic polymers are polyethers, e.g. polyethylene glycols (PEG), polypropylene glycols (PPG), polyethylene oxide, polytetrahydrofuran, or alkoxylated derivatives thereof; polyketones, e.g. polyvinylpyrrolidone (PVP) or halogenohydroxylated, ethylhydroxylated, or hydroxypropyl derivatives thereof; polyols, such as polyvinyl alcohol (PVA); starch or derivatives thereof, e.g. hydroxypropyl starch; cellulose or derivatives thereof, e.g. ethylhydroxyethyl cellulose, or copolymers thereof.

Preferably, the polymers have a number average molecular weight of at least about 1500, especially at least about 3000.

Although the water-soluble, nonionic polymer can be added to the fibers in a substantially pure form, it is preferred that the polymer be included in an aqueous mixture, where appropriate optionally in the form of a dispersion or slurry. The mixture is conveniently applied to the formed pulp sheet, conveniently by spraying. The amount of polymer added is conveniently about 0.140 kg/metric ton of dry pulp, preferably about 0.5-5 kg/ton. Optionally, the treatment can be carried out when the fibers are suspended in an aqueous solution, e.g. in the stock in the pulping process prior to sheet formation.

The amount of polymer in the stock is suitably about 0.1-10 kg/ton of dry pulp, preferably about 0.5-5 kg/ton.

The absorbent material may be, for example, fluff, i.e. fibres which have been separated by mechanical means from dry pulp. Although the polymer may remain in the fluff after shredding, this is not considered essential to the invention. Even if less than about 65%, e.g. less than 30% or even as little as 1% of the polymer used in the treatment is actually present in the fluff after shredding, the sorption effect is very significantly improved when compared with fluff produced from untreated pulp.

In another embodiment of the present invention, the absorbent material is tissue paper, which term includes cellulose wadding, tissue and crepe paper, all of which are useful in the household and sanitary fields. It is well known that the liquid absorption rate and the liquid retention capacity of tissue paper are important in use in these fields. Tissue paper can be produced by any suitable papermaking process. Tissue and cellulose wadding grades are usually produced by means of a so-called Yankee machine, i.e. a paper machine in which the drying is accomplished essentially on a Yankee cylinder or Yankee dryer, which is a drying cylinder with a large diameter and a polished surface, which is mainly responsible for the drying of the paper web.

In yet another embodiment, the absorbent material is paper which is to be impregnated with thermosetting resin and used in the manufacture of laminates, especially as an overlay in decorative laminates. . . « i . _ lO 15 20 25 514 466 4 The present invention also relates to absorbent non-cellulosic materials obtainable by the present method, especially hygiene paper or fluff. As will be seen from the examples below, such absorbent cellulose material exhibits surprisingly good sorption properties in comparison with untreated absorbent cellulose material.

The present invention also relates to absorbent products, such as diapers, sanitary napkins, panty liners, tampons, bandages, adult incontinence products, toilet paper, handkerchiefs, kitchen towels, towels, facial tissues, napkins, and similar products comprising such paper or fluff.

The invention also relates to the use of a water-soluble, nonionic polymer of the present type for treating cellulose fibers to improve the sorption capacity of absorbent materials comprising the fibers, such as fluff or hygiene paper, such as tissue. It further relates to a process for producing absorbent materials, including, for example, dry-formed fiber fluff or tissue, comprising cellulose fibers treated with a water-soluble, nonionic polymer.

The fibers forming the pulp sheet are preferably natural cellulose fibers, which are usually obtained by breaking down wood, conventionally in the form of chips, into fibers or fiber bundles. In the present context, the term "fiber bundle" is considered to be equivalent to the term "fibers". The separated fibers can be obtained by any pulping method known to a person skilled in the art, for example by a method for producing mechanical pulp (MP), stone ground pulp (SGW), pressure ground pulp (PGW), refiner pulp (RMP), thermomechanical pulp (TMP), chemimechanical pulp (CMP) or chemithermomechanical pulp (CTMP), although the preferred pulps are chemical pulps, such as sulphate and sulphite pulps. However, the cellulose fibers can also advantageously be cotton fibers. Another likely fiber source is recovered fibers from waste paper.

The present invention is illustrated in more detail below with the aid of examples. Unless otherwise stated, parts and percentages are by weight. In the examples, the polymers according to Table 1 are used. Table 1 Water-soluble nonionic Polymer Average molecular weight 35,000 10,000 6,000 4,000 1,500 600 400 24,000 1,1500 -"- 72,000 glycerol-based propyl- - 4,000 A B C D E F G H l J K 1 I" hydroxypropyl- starch In the examples, absorbent structures are tested with respect to uptake rate, rewetting, wicking height, or a combination of these parameters.

The test method for determining the absorption rate is SCAN-C 33:80, in which samples of 3 g and with a diameter of 50 mm are arranged vertically and a weight of 500 g is loaded on top. The sample is allowed to absorb water from below, the time taken for water to penetrate to the upper surface of the sample being determined automatically by means of an electronic detector. The shorter the time required to penetrate to the upper surface, the higher the absorption rate of the absorbent structures. In the test method for determining rewetting, a sample of 3 g and with a diameter of 50 mm is arranged vertically and a weight of 1 kg is loaded on top for 30 s and then released. 10 ml of water is added to the sample over a period of 10 s, maximum, and the liquid is allowed to drain from the sample for 30 s, after which the sample is loaded with a weight of 1 kg for 4 min. Fifteen weighed sheets, 8.8 cm of filter paper are placed on top of the sample, and the sample and sheet combination is loaded with a weight of 5 kg for a further 1 min., after which the 15 sheets are reweighed.

The weight gain of the sheets is due to rewetting, whereby a low weight gain indicates low rewetting. The absorption height is determined by means of the standard test method SCAN-P 13:64, "Absorption height according to Klemmï, whereby samples of conditioned paper sheets are arranged vertically with the lower end immersed 10 mm in water and the absorption height of the water is determined after 10 min. Higher absorption heights indicate higher sorption capacity.

Examples 1-5: 109 g of sulphate pulp was dissolved in 500 ml of water in a laboratory disintegrator for 10 min. The resulting slurry was dewatered through a wire cloth of a wire mold, thereby producing a pulp sheet with a diameter of 210 mm. 15 g of aqueous solutions containing 0.2% water-soluble nonionic polymer were sprayed onto the sheets in all examples, except for example 1, which is a comparative example. The amount of water-soluble nonionic polymer added to each sheet corresponded to 3 kg of water-soluble nonionic polymer/metric ton of dry pulp. The sheets were dried at 60°C for 120 min. and then dried to fluff in a hammer mill.

The fluff was formed into three samples, each weighing 3 g. The fluff samples thus obtained were tested at ambient conditions of about 23°C and 50% RH for rewetting. The sheets were tested for wicking height according to Klemm. The test results are given in Table 11.

Table 11 Sulfate pulp, 3 kg water-soluble nonionic polymer/metric ton pulp Polymer added by spraying Polymer Example Rewetting, g Absorbency height, mm Ref 1 5.0 106 D 2 4.1 122 G 3 4.8 122 H 4 4.3 112 K 5 4.2 122 The absorbent structure produced according to the present method clearly has a better liquid retention capacity than the corresponding untreated structure.

Example §-1§: The procedure used in Examples 1-5 was repeated, except that the water-soluble nonionic polymer was added during whipping instead of spraying. Here, Example 6 is the comparative example, i.e. without the addition of water-soluble nonionic polymer. The resulting fluff samples were tested for rewetting, as indicated in Table III. 514 466 Table III no isk P added 50 45 43 43 10 41 11 45 12 49 13 4.7 14 4.5 15 - 4.6 rxm¶moom>§ The fluff prepared according to the present method clearly has a higher uptake rate and a better liquid retention capacity than untreated fluff. Example 15-12: The procedure set forth with respect to Examples 1-5 was repeated, although applied to sulfite pulp. Example 16 is a comparative example without any water-soluble nonionic polymer added. The results are given in Table IV.

Table IV Sulphite pulp, 3 non-ton pulp Water-soluble nonionic polymer added through non-ionic Example Ref 16 5 15 D 17 4.55 H 18 4 99 K 19 4.60 The fluff prepared according to the present method clearly has a better 10 in liquid retention foam than untreated fluff.

Example: 10 g of chemithermomechanical pulp (CTMP) was dissolved in 500 ml of water in a laboratory disintegrator for 10 min. The resulting slurry was dewatered through the wire cloth of a wire mold, thereby producing pulp sheets with a diameter of 210 mm. 15 g of aqueous solutions containing 0.2% water-soluble nonionic polymer were sprayed onto the sheets in all examples, except example 20, which is a comparative example. The sheets were dried at 60°C for 120 min. and then dried to fluff in a hammer mill. The fluff was formed into three samples, each weighing 3 g. The fluff samples thus obtained were tested at ambient conditions of about 23°C and 50% RH with respect to rewetting. The test results are given in Table V, in which the amounts of water-soluble nonionic polymer added to each sheet are also given.

Table V CTMP water-soluble nonionic polymer added by spraying Water-soluble nonionic polymer Example Absorption Rewetting, g polymer rate, s Ref 20 10.1 4.90 D 3 kg/ton pulp 21 6.4 3.74 D 6 kg/ton pulp 22 6.4 3.66 K 3 kg/ton pulp 23 5.2 3.70 K 6 kg/ton pulp 24 5.4 3.69 The absorbent structure prepared according to the present method clearly has a higher absorption rate and a better liquid retention capacity than untreated absorbent structure.

Examples 25-27: The procedure set forth in Examples 1-5 was repeated, although applied to cotton. Example 25 is a comparative example without any water-soluble nonionic polymer added. The results are set forth in Table VE.

Table VI Cotton, 3 kg water-soluble nonionic polymer/metric ton pulp Water-soluble nonionic polymer added by spraying Water-soluble nonionic polymer Example Absorption rate Rewetting, g I" ner ty, s Ref 25 5.1 6.54 D 26 4.7 6.04 K 27 4.5 5.59 10 The fluff produced by the present method clearly has a higher absorption rate and a better liquid retention capacity than untreated fluff.

Claims (15)

10 15 20 25 30 35 '514 466 9 PATENT CLAIMS 1. Ways to improve the sorption capacity of cellulose fibers, characterized in that the bromines are treated with an aqueous solution comprising a water-soluble, nonionic polymer. , 2. A method according to claim 1, characterized in that the water-soluble, nonionic polymer has a number average molecular weight of at least about 3000. 3. A method according to claim 1 or 2, characterized in that the treated fi brems are natural cellulose fi bres. 4. A method according to any one of the preceding claims, characterized in that the polymer is selected from the group consisting of polyethers, polyketones, polyols, starch or derivatives thereof, cellulose or derivatives thereof, or copolymers thereof. 5. A method according to any one of claims 1-3, characterized in that the polymer is selected from the group consisting of polyethylene glycols (PEIS), polypropylene glycols (PPG), polyethylene oxide, polytetrahydrofuran, or alkoxylated derivatives thereof; polyvinylpyrrolidone (PVP) or halohydroxylated, ethylhydroxylated or hydropropyl derivatives thereof; polyvinyl alcohol (PVA); hydroxypropyl starch; ethyl hydroxyethylcellulose, or copolymers thereof. i _ 6. A method according to any one of the preceding claims, characterized in that an aqueous solution of polymer is sprayed on the fi brema. 7. A method according to any one of the preceding claims, characterized in that the bremines are suspended in an aqueous solution during the treatment. Cellulose fibers obtainable by a method according to any one of the preceding claims. Absorbent material containing cellulose fibers according to claim 8. Absorbent material according to claim 9, characterized in that it is fl uff. Absorbent material according to claim 9, characterized in that it is hygiene paper. An absorbent product comprising an absorbent material according to any one of claims 9-11. Paper impregnated with thermosetting resin, characterized in that the paper comprises cellulose fibers according to claim 8. 14. Paper according to claim 13, characterized in that the paper is an overlay for use in a decorative laminate. Laminate, which includes paper according to claim ~ 1 3 or 14.