Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
  • D21H13/36—Inorganic fibres or flakes
  • D21H13/38—Inorganic fibres or flakes siliceous
  • D21H13/40—Inorganic fibres or flakes siliceous vitreous, e.g. mineral wool, glass fibres
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
  • D21H13/10—Organic non-cellulose fibres
  • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H13/22—Condensation polymers of aldehydes or ketones
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/08—Filter paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H5/00—Special paper or cardboard not otherwise provided for
  • D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
  • D21H5/20—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of organic non-cellulosic fibres too short for spinning, with or without cellulose fibres

Definitions

• This invention relates to fibrous materials and in particular to sheet-like articles containing amino-formaldehyde resin fibres.
• Amino-formaldehyde resin fibres are useful as the fibrous constituents in sheet like articles such as paper where they are generally used in admixture with cellulosic fibres.
• Papers made wholly from amino-formaldehyde resin fibres tend to have little or no strength because generally the fibres exhibit little or no self adhesion. When blended with cellulosic fibres, the latter donate strength to the paper but in many cases it would be desirable to improve the strength still further.
• One way of improving the strength is to employ partially cured (degree of cure 50-90%) amino-formaldehyde resin fibres.
• paper is made from partially cured amino-formaldehyde resin fibres made by employing only mild curing conditions, i.e. weak curing catalysts, low curing temperatures and/or short curing times.
• Partially cured amino-formaldehyde resin fibres can also be made as described in US Patent 4172057 by conducting the reaction of the amino compound with the formaldehyde in the presence of certain carbohydrates.
• the degree of cure of amino-formaldehyde resin fibres is measured by digesting an accurately weighed sample (about 5 g) of the dry fibre in 200 ml of water for 2 hours at 50°C. The undissolved fibre is recovered by filtration, dried at 100°C in air for 2 hours, and then reweighed. The degree of cure is the ratio between the weight of the recovered fibre and the original weight of fibre, and is expressed herein as a percentage.
• amino-formaldehyde resin fibres that have only been partially cured may exhibit some self adhesion and so be used as the sole fibrous component of paper, they suffer from the disadvantages that some of the fibre may be lost during the conventional wet-laid paper production process because of the partial water solubility of the partially cured resin and also that free formaldehyde may be evolved during the paper making process thus constituting a health hazard.
• the processing conditions are such as to cause welding of the amino-formaldehyde resin fibres to each other and/or to other fibrous materials present at at least some of the points where the fibres contact one another.
• Such welding is referred to herein as inter-fibre bonding.
• Inter-fibre bonding can be observed using a microscope: thus if a sample of the article, e.g. paper, is observed using a magnification of x 100 or greater, welds between at least some of the fibres can be seen. It will be appreciated that it is not necessary, in order to obtain useful improvements in strength, that every fibre should be welded to another fibre.
• the degree of inter-fibre bonding should preferably be such that less than 50% by weight of the amino-formaldehyde resin fibres can be removed from the sample as individual fibres without any fibres adhering thereto when the sample is probed with a fine probe.
• inter-fibre bonding is achieved with highly cured amino-formaldehyde resin fibres, i.e. those having a degree of cure above 93%, by heating the sheet material in the presence of water under specified conditions.
• FR-A-2373617 It has been proposed in FR-A-2373617 to dry paper made from certain amino-formaldehyde resin fibres by heating at above 60°C and to improve the cohesion of the paper by heating at over 90°C.
• the fibres are made from an amino-formaldehyde resin that has been modified by the incorporation of certain inorganic oxyacid, e.g. sulphite, radicals.
• certain inorganic oxyacid e.g. sulphite
• Inter-fibre bonded articles made in accordance with the present invention differ from the products of GB-A-1574344 in various respects.
• the incorporation of the UF fragments gives rise to little or no increase in bulk of the paper: the bulk is said to increase by less than 0.1 cm 3 g-' for each 10% by weight of UF fragments incorporated.
• inter-fibre bonded articles containing amino-formaldehyde resin fibres and cellulose fibres exhibit a significant increase in bulk: the bulk increases by at least about 0.15 cm 3 g-' for each 10% by weight of amino-formaldehyde resin fibres incorporated.
• the enhancement in bulk generally becomes more pronounced as the degree of beating of the cellulose pulp increases.
• the amino-formaldehyde resin is in the form of fibres that have been hot cured to a high degree before the shaped article is formed therefrom.
• the present invention provides a process for making a sheet-like article comprising
• inter-fibre bonding in water-sensitive articles can also be assessed by measuring the wet strength of the sample: if inter-fibre bonding has occurred the wet strength of the sample will be increased. It is preferred that the wet strength is increased by at least 25% compared with a similar sample in which no inter-fibre bonding exists.
• the wet strength of a sample in the form of paper may be measured by Tappi Standard Method T456.
• the wet strength measurement and probing may not be indicative of the presence of inter-fibre bonding but such inter-fibre bonding can be detected by microscopy.
• the article contains little or no cellulose fibres, there may be little difference between the wet and dry strengths of the article.
• the article in order to generate inter-fibre bonding, the article is subjected to the action of water at an elevated temperature.
• the fibrous material may be formed into the desired sheet form and then wetted and subjected to the elevated temperature or the article may be formed from an aqueous slurry of the fibrous materials and subjected to the elevated temperature as part of the drying process used to remove the water.
• the paper may be made by a conventional wet-laid process and then subjected to inter-fibre bonding conditions in the drying stages of paper manufacture.
• the conditions required to generate inter-fibre bonding vary with the degree of cure of the amino-formaldehyde resin fibres.
• the degree of cure increases above 93% by weight, the minimum amount of water in the article required to get inter-fibre bonding increases.
• the drying time required decreases.
• the temperature should be at least 80°C and is preferably in the range 90 to 180°C.
• the application of pressure before, or preferably during, the heating step promotes inter-fibre bending.
• the pressure may vary from just sufficient to ensure good contact between adjacent fibres, typically 0.1 to 50 kg cm- 2 (0,01 to 4,9 MPa) or more depending upon the water content and the drying conditions. As the applied pressure increases, less water is required. While the application of pressure greater than that, that is just sufficient to ensure good contact between adjacent fibres is not always necessary, its application enables inter-fibre bonding to be obtained in some borderline cases where, in the absence of applied pressure, no inter-fibre bonding is achieved.
• the time required may vary from about 30 seconds to 10 minutes or more: it will be appreciated that longer times than the minimum required to achieve inter-fibre bonding may be employed.
• the minimum water content required to achieve inter-fibre bonding varies from about 10% by weight of the fibrous material (at low degrees of cure, high temperature and pressure) to over 300% (at low pressures and temperature and high degree of cure). Again it will be appreciated that more water than the minimum required to achieve inter-fibre bonding may be employed. Preferably at least 200% by weight of water is used, based on the dry weight of the fibrous material.
• the amino-formaldehyde resin used to make the amino-formaldehyde resin fibres 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 admixture with 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 particularly between 0.7:1 and 1.3:1.
• the amino-formaldehyde resin fibres may be made by any suitable fibre forming technique such as wet or dry spinning and are preferably formed by a centrifugal spinning process, for example as described in US Patent Specification 4178336, which gives, as is preferred, substantially straight and unbranched fibres.
• the amino-formaldehyde resin fibres preferably have an average length, weighted by length, of between 1 and 10 mm, particularly between 2 and 6 mm. Preferably substantially all the amino-formaldehyde resin fibres have a length within the range 1 to 10 mm.
• the amino-formaldehyde resin fibres preferably have an average diameter between 1 and 20 pm, particularly between 2 and 15 pm, and most particularly between 3 and 10 1 1m. Preferably substantially all the amino-formaldehyde resin fibres have a diameter between 1 and 30 pm.
• the amino-formaldehyde fibres should have a degree of cure of at least 93%, preferably 94 to 99% by weight.
• these degrees of cure are achieved by incorporating a suitable curing catalyst, e.g. ammonium sulphate, ammonium chloride, formic acid, dihydrogen ammonium phosphate, or phosphoric, sulphuric, sulphamic, or hydrochloric acids into the resin prior to spinning into fibres and then heating the fibres after spinning at above 100°C, particularly above 120°C for e.g. up to 3 hours: in general the higher the curing temperature, the shorter the time required.
• 3 hours at 120°C may give a degree of cure of about 94% by weight, only 5 minutes may be required at 180°C to give a degree of cure of about 97%.
• the sheet-like article may be made from the amino-formaldehyde resin fibres as the sole fibrous constituent or may be made from the amino-formaldehyde resin fibres in admixture with other fibrous materials, which may be cellulosic or non-cellulosic.
• the amino-formaldehyde resin fibres should constitute at least 5% by weight of the total fibrous material in the article.
• Particularly useful sheet materials may be made from blends of amino-formaldehyde resin fibres and cellulose fibres containing 5 to 100%, preferably 10 to 50%, by weight of amino-formaldehyde resin fibres.
• Cellulose fibres that may be used include the lignin-free fibres such as cotton linters or chemical wood pulp e.g. paper making pulp made from the raw cellulose by treatment by chemical means such as the well known sulphate or sulphite processes, or lignin-containing fibres such as mechanical, semi-chemical, or thermomechanical wood pulp. Mixtures of lignin-containing and lignin-free cellulose fibres, e.g. mixtures of mechanical and chemical pulps, may be used.
• the cellulose fibres may be lightly beaten or well beaten, depending on the intended use of the article.
• the invention is of particlar merit in the production of sheet like products such as paper and board from fibrous materials comprising amino-formaldehyde resin fibres alone or in admixture with up to 90% by weight, based on the total weight of fibrous material, of cellulose fibres.
• Such products have improved mechanical properties compared to those in which there is no inter-fibre bonding and, in particular, have superior wet strengths.
• inter-fibre bonded amino-aldehyde resin fibre containing papers have superior wet strengths to the 100% cellulose papers which have not been otherwise treated to promote wet strength, e.g. by the inclusion of a wet strength resin binder.
• the use of the amino-resin fibres in admixture with cellulose fibres gives a significant increase in bulk.
• An increase in bulk is generally desirable as it enables less raw materials to be used, with consequent economic advantages, to obtain a paper of given volume. While the bulk of an all-cellulose paper can be increased by reducing the degree of beating of the cellulose, this results in a reduction in paper strength.
• the incorporation of the amino-formaldehyde resin fibres enables an increase in bulk to be achieved without such a large decrease in paper strength.
• the inter-fibre bonded papers of the present invention have improved wet strength compared to papers in which there is no inter-fibre bonding: this renders paper made in accordance with the invention particularly suited to applications such as filter papers. Increased bulk is desirable in such applications as the porosity increases with an increase in bulk.
• the increase in bulk given by the incorporation of the amino-formaldehyde resin fibres becomes greater as the degree of beating of the cellulose fibre increases: thus where the cellulose fibre is lightly beaten, so as to give a paper of high bulk, the increase in bulk may be little more than about but with a more highly beaten cellulose pulp, particularly one giving a paper of bulk below about 2 cm 3 g -1 when made wholly from the cellulose fibre, the increase in bulk is generally at least
• Articles made in accordance with the present invention from a mixture of cellulose fibres and amino-formaldehyde resin fibres are preferably made from fibre mixtures containing 5 to 95, particularly 10 to 50, % by weight of amino-formaldehyde resin fibres and, correspondingly, 95 to 5, particularly 90 to 50%, by weight of cellulose fibres.
• Articles may also be made in accordance with the present invention from fibrous material containing only amino-formaldehyde resin fibres or amino-formaldehyde resin fibres in admixture with non-cellulosic fibres. These mixtures may, if desired, also contain cellulosic fibres.
• the non-cellulosic fibres may be synthetic organic fibres such as polyester, e.g. polyethylene terephthalate, fibres; polyolefin, e.g. polypropylene, fibres; or polyamide fibres; or inorganic fibres such as glass or asbestos fibres.
• the fibrous material contains at least 5% by weight of amino-formaldehyde resin fibres and, correspondingly, up to 95% by weight of the non-cellulosic fibres or mixture of cellulosic and non-cellulosic fibres.
• the amount of non-cellulosic fibres is preferably at least 10% by weight of the total weight of fibres in the article.
• the fibrous material, other than the amino-formaldehyde resin fibres preferably comprises 10 to 100% by weight of non-cellulosic fibres and, correspondingly, 90 to 0% by weight of cellulosic fibres.
• Paper or other sheet like products made in accordance with the present invention from amino-formaldehyde resin fibres alone or from mixtures containing non-cellulosic fibres have a significant strength whether or not they also contain cellulose fibres.
• they may have a burst index (bursting pressure measured according to the TAPPI standard procedure divided by the weight per unit area) of at least 0.2 kPa m2g-1..
• the amino-formaldehyde resin fibres may also be welded to the cellulosic fibres.
• Particularly preferred fibre compositions comprise 10 to 90, especially 20 to 60, % by weight of amino-formaldehyde resin fibres, 10 to 90, especially 20 to 50, % by weight of non-cellulosic fibres, and 0 to 75, especially 10 to 50, % by weight of cellulosic fibres.
• a commercially available aqueous urea/formaldehyde resin having a U:F molar ratio of 1:2 of solids content 67% was diluted with water to a viscosity of 30 poise (3 Pa - s).
• 10%, based on the solids, of an aqueous solution containing 1.6% poly(ethylene oxide) and 6.7% ammonium sulphate was mixed continuously with the resin solution as it was fed to a spinning cup of a centrifugal spinning apparatus.
• the resin was spun by the process described in US Patent Specification 4178336 using a spinning cup of 12.7 cm diameter having 24 rectangular holes and rotating at 7000 rpm.
• the resin was spun at a rate of 100 g min-'.
• the fibres were continuously removed from the spinning apparatus and their cure was continued by heating in air at 150°C for 40 minutes.
• the resultant fibres which had an average diameter of 8.5 pm, had a degree of curing of 94.6%.
• the fibres were cut to a nominal length of 3 mm and dispersed in a standard laboratory pulp disintegrator in water (consistency 1.2%) for 17 minutes.
• Paper handsheets (100% UF resin fibres) were made by the standard procedure using the British Standard Handsheet former with the replacement of the standard pressing step with pressing in a press heated to 110°C. Prior to pressing water was sprayed on to the handsheets and the moisture content was determined by weighing the handsheets before and after pressing.
• Burst Index (burst pressure in kPa divided by the substance in gm- 2 ) was determined according to the standard TAPPI procedure.
• the Breaking Lengths were measured on an Instron tensile tester (table top model) using samples 15 mm wide with a gauge length of 100 mm.
• the crosshead speed was 0.5 cm/min.
• Inter-fibre bonding was assessed microscopically. Its presence is indicated in the following table by a tick.
• Example 1 was repeated using resin fibres cured for 120 minutes at 150°C to give a degree of cure of 96.6%.
• Example 1 was repeated using resin fibres cured for 170 minutes at 150°C to give a degree of cure of 97.9%.
• Example 1 was repeated using resin fibres cured at 150°C for 330 minutes to give a degree of cure of 99.0%.
• Example 1 was repeated using resin fibres cured for 30 minutes at 150°C to give a degree of cure of 96.4%. In each case the pressing time was 3 minutes at 110°C.
• Example 1 was repeated using fibres cured for 30 minutes at 150°C to give a degree of cure of 95.9%.
• the moist sheets were pressed at a pressure of about 0.1 kg cm- 2 for varying times at various temperatures.
• paper handsheets were made from 80% birch sulphate pulp and 20% urea-formaldehyde resin fibres similar to those used in Example 1. Some of the handsheets were wetted and dried under inter-fibre bonding inducing conditions and the wet breaking length was measured.
• a similar handsheet made wholly from the birch sulphate pulp had wet breaking length of 0.09 km.
• Example 7 was repeated but using a 50/50 mixture of the birch sulphate pulp and the urea- formaldehyde resin fibres.
• Papers were made on a pilot paper making machine from mixtures of lightly beaten bleached hardwood sulphate cellulose pulp and urea-formaldehyde resin fibres made by the procedure described in Example 1 and having a degree of cure of 94.6%.
• the paper was dried under light pressure against cylinders heated to about 100°C. The drying time and moisture content were sufficient to give inter-fibre bonding.
• Paper was also made and dried under the same conditions from the lightly beaten cellulose pulp alone.
• the tensile strengths (wet and dry) in the transverse direction of the paper, i.e. at right angles to the machine direction, and the wet burst index was measured and are quoted in the table as a percentage of the corresponding properties of the all-cellulose paper. It is seen that the bulk increases by over 0.017 cm 3 g -1 for each percent of urea-formaldehyde fibres incorporated.
• Example 1 was repeated using urea-formaldehyde resin fibres of average diameter 9 11m and 94.9% degree of cure, in admixture with glass or polyethylene terephthalate (PET) fibres, and also, in some cases with softwood sulphate cellulose pulp.
• PET polyethylene terephthalate
• the glass fibres had a mean diameter of 20 ⁇ m while the PETfibres were 1.5 denier, drawn, uncrimped fibres that had been washed in warm water to remove any spin finish from their surfaces.
• the glass, PET, and urea-formaldehyde fibres were cut to provide a length distribution between 1 and 5 mm by passing the fibres twice through a paper shredding machine with the cutters spaced at a nominal 3 mm.
• the sheets were couched from the wire of the sheet former, placed on a non-stick plate, weighed, sprayed evenly with a little deionised water, reweighed and then pressed on each side for 30 seconds using a domestic ironing press at 170°C giving an applied pressure of about 0.1 kg cm- 2 .
• the weight of the dried paper was determined.
• the solids content of each sheet entering the press was thus determined, and so the moisture content as a percentage of the total fibre content was calculated.
• Example 6 of UK Patent Specification 1573115 the production of paper from a mixture of urea-formaldehyde resin fibres and cellulose pulp on a Fourdrinier paper making machine is described. Examination of a sample of the paper produced in that Example revealed no inter-fibre bonding.
• Urea-formaldehyde resin fibres made by the procedure described in Example 1 and having a degree of cure of 94% were mixed, in various proportions with a beaten cellulose pulp and made into handsheets by the British Standard method (which involves air drying at room temperature and does not promote inter-fibre bonding).

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Materials For Medical Uses (AREA)

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• 1981
  • 1981-03-27 EP EP81301359A patent/EP0038136B1/en not_active Expired
  • 1981-03-27 DE DE8181301359T patent/DE3170814D1/de not_active Expired
  • 1981-04-02 NZ NZ196721A patent/NZ196721A/xx unknown
  • 1981-04-03 AU AU69086/81A patent/AU540107B2/en not_active Ceased
  • 1981-04-06 NO NO811169A patent/NO811169L/no unknown
  • 1981-04-15 FI FI811181A patent/FI66946C/fi not_active IP Right Cessation

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