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
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
  • D21H11/04—Kraft or sulfate pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D1/00—Methods of beating or refining; Beaters of the Hollander type
  • D21D1/20—Methods of refining
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
  • D21F11/006—Making patterned 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/28—Starch
• • 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
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents
• • 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
  • D21H27/02—Patterned 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
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/10—Packing paper

Definitions

• the present invention relates to the field of kraft paper and more specifically to a new method for making such paper, which method has been found to provide kraft paper with a unique combination of physical properties. Accordingly, the invention also relates to this new paper as well as to so-called valve sacks made of such a kraft paper .
• Kraft paper is a general term for paper with above all good strength properties, for which an important application area is the manufacture of sacks.
• a representative example of such sacks are so-called valve sacks, e.g. for cement, which must meet high standards primarily with respect to tensile strength (an important part of tensile energy absorption) and porosity (high air permeability) .
• High porosity is required in paper intended for such sacks to enable the sack to let out the air which accompanies the filling material when the sack is being filled. In other words, the sack should retain, and be strong enough to hold, the filling material and at the same time let out said air.
• valve sacks in this context, the air can only escape through the paper, which to this end is provided with perforations.
• this high porosity is not required in open sacks, such as garbage bags and the like, since air can escape through the opening at the top while the sack is being filled.
• kraft paper in connection with the manufacture of kraft paper, one has been aware of the desirability of a good combination of high strength and high porosity, but in general, in this respect, these two properties have been considered to be mutually opposite, so that measures taken to increase the strength have led to a corresponding reduction in porosity and vice versa.
• the measures taken according to the prior art for the purpose of achieving an optimisation of the above- mentioned primary properties of kraft paper can, in short, be described as follows.
• the pulp intended for kraft paper has been subjected to a first fibre processing with energy being supplied to the fibres when the fibre suspension has a high consistency, generally over 15 % by weight, (HC refining) followed by a second beating with energy being supplied at a low fibre consistency, typically about 4% by weight (LC beating) , the energy supplied in connection with said LC beating being at least 100 k h/tonne of paper.
• HC refining is an opera- tion which provides kneading of fibre against fibre and micro compressions in the fibre and consequently imparts good stretching properties to the fibre
• LC beating provides shredding of the fibre wall and consequently improves its tensile strength.
• starch for example, has been added as a strengthening agent to the stock obtained from the beating at one or more points in the process, before the stock is fed onto the wire of the paper machine.
• the total amount of strengthening agent added has been up to a maximum of approximately 6 kg/tonne of finished paper, in order to maintain satisfactory porosity in the finished paper.
• the normal combination of tensile strength and porosity has generally been a tensile energy absorption index of 2.9 J/g both in the machine direction (longitudinally) and in the cross direction (transversely) , distributed over a tensile index of 75 Nm/g longitudinally and 60 Nm/g transverse- ly with a stretching of up to 8.0%. It has been possible to achieve this at a Gurley value of 18 seconds. Higher tensile strength or higher porosity has been achievable only at the cost of an unacceptable value for the latter of these two properties.
• the paper provided according to the invention exhibits both high porosity and a high tensile energy absorption index, which properties can, in addition, be combined with e.g. good runnability in connection with the production of sacks.
• a more detailed definition of these properties is given below.
• a first object of the invention is thus to provide a method for making kraft paper with an exceptional combination of tensile energy absorption index and porosity.
• Another object of the invention is to provide a method which produces kraft paper which, in addition, exhibits good runnability in connection with sack production.
• a further object of the invention is to reduce, with the aid of the above-mentioned beneficial properties, the grammage of the kraft paper made by means of the method according to the invention, which in turn can lower costs to the manufacturer and the end consumer and which, more- over, reduces environmental impact with better utilisation of raw materials and fewer shipments.
• the invention also has for its object to provide finished kraft paper exhibiting in itself the above-mentioned beneficial properties.
• a further object of the invention is to provide valve sacks made or formed of the above-mentioned kraft paper, a major advantage of the good porosity or air permeability being that the sacks do not need be provid- ed with perforations. This means, first of all, one less operation in the manufacturing of the sack itself and, secondly, a better work environment for the customer when filling and handling the sack in question.
• Another of object of the invention is to provide valve sacks of the above-mentioned type, wherein the improved tensile strength can be utilised for making the sacks smaller and/or for manufacturing sacks formed of fewer layers than was previously the case.
• the method according to the present invention is a method for making kraft paper comprising the steps of subjecting sulphate or kraft pulp to high consistency refining (HC refining) only or HC refining in combination with low consistency beating (LC beating) , wherein, if LC beating is utilised, the energy supply in connection with LC beating is maintained at a value below 80 k h per tonne of finished paper, calculated as 100% dry paper, and adding a strengthening agent to the stock obtained in this connection at one or more separate points in the process, before the stock is fed onto the wire of the paper machine, so that the total amount of strengthening agent added will correspond to at least 8 kg of strengthening agent (calculated as starch with DS 0.035) per tonne of paper (calculated as 100% dry paper) .
• HC refining high consistency refining
• LC beating low consistency beating
• the method as it will be described herein is a method for making kraft paper with a grammage which is generally within the 50 - 140 g/m 2 range. Where one chooses to be within this range in connection with kraft paper production depends primarily on the application area intended for the paper.
• a major advantage of the method according to the invention is, of course, that it is possible to make kraft paper exhibiting good tensile strength and good porosity despite a very low grammage, e.g. in the order of 50 - 70 g/m 2 , while in other cases it may, for example, be of great value to have paper with a relatively high grammage, e.g. in the order of 120 - 140 g/m 2 , and to utilise it as a single layer in a bag rather than having to make a similar sack with a plurality of layers of a different grammage with equally good physical properties.
• a preferred application area for the method according to the invention is for making sack kraft paper, since this represents a very large market and since the paper obtained according to the invention exhibits a unique combination of properties which are particularly advantageous in connection with sacks. Primarily, this applies to valve sacks, in which good air permeability is required, as described above, and where the method according to the invention has even made it possible to omit the perforations which previously had to be used in sacks of this type.
• kraft paper in connection with the invention this refers to bleched or unbleched paper made primarily of sulphate pulp (kraft pulp) .
• kraft pulp kraft pulp
• it may refer to unbleached sulphate softwood pulp.
• the sulphate pulp which forms the starting point, is subjected to HC refining only, which is generally carried out at an energy supply in the range of 150 - 400 kWh per tonne of finished kraft paper, which in this case as in every other case in connection with the invention is calculated as 100% dry paper, unless otherwise indicated.
• a particularly preferred range for HC refining is 200 - 300 kWh per tonne of paper.
• HC refining is generally carried out at a fibre sus- pension consistency exceeding 15% by weight and usually at an upper limit of 40% by weight, i.e. suitably in the range of 15 - 40% by weight.
• a preferred consistency of the fibre suspension in connection with HC refining is 28 - 40% by weight, most preferably 30 - 34% by weight.
• HC refining can be combined with low consistency beating (LC beating) , provided that the energy supply in connection with the LC beating is maintained at a value below 80 kWh per tonne of paper.
• LC beating low consistency beating
• LC beating With respect to LC beating, it should preferably be carried out at a maximum energy supply of 50, more prefer- ably a maximum of 30, most preferably a maximum of 20, kWh per tonne of finished paper.
• LC beating refers to a fibre suspension consistency in the range of 2 - 10% by weight, preferably 3 - 6% by weight, a specially preferred value being about 4% by weight.
• these operations can be carried out independently of one another with the aid of conventional refining and beating apparatus, such as refiners. Nevertheless, a preferred embodiment of the invention involves carrying out at least one, or both, of said operations in a refiner.
• HC refining and LC beating in connection with the method according to the invention also comprise the cases where either or both of these operations are carried out in several sequentially arranged refining or beating devices.
• energy supply values stated for these operations refer to net values with the idling effect for the respective device having been sub- tracted.
• starch is a suitable strengthening agent, the term starch being interpreted broadly as comprising all conceivable types or fractions of starch which provide the desired effect.
• this agent is chosen among charged polymers in accordance with common practice.
• the adding of a strengthening agent to the stock can be carried out at any point in the process from the time the latter leaves the refining or the beating until it is fed onto the wire of the paper machine.
• it can be carried out at one or more sepa- rate points, the use of two points having been found particularly advantageous.
• An advantageous point for the second addition of a strengthening agent has been found to be at or in connection with the mixing pump utilised for the paper machine, preferably on its suction side.
• the function of the strengthening agent at the latter point is not only strength enhancing but the agent in question is also, as is known per se in the field, active in retaining and distributing the fine material in the sheet .
• the total minimum amount of the strengthening agent in question is 8 kg per tonne of paper and the maximum amount is usually a total of at most 20 kg per tonne of paper, the amount being calculated on the basis of starch with DS 0.035, as can be seen above .
• 4-10 kg of strengthening agent per tonne of paper are preferably added in a first addition and an amount of the agent in question in the same range, i.e. 4-10 kg per tonne of paper, is added in a second addition.
• Particularly preferred ranges in both of these cases are 5-8 kg per tonne of paper.
• a variant of the method according to the invention comprises the adding of essentially an equal amount by weight of the strengthening agent, within the range stated above, in connection with two additions of said agent.
• Another embodiment of the method comprises adding a maximum of 6 kg per tonne of paper in a first addition and more than 6 kg per tonne of paper in a second addition, i.e. a greater amount of strengthening agent in the second addition than in the first.
• a particularly preferred range for the first addition is
• the kraft paper obtained in connection with the above method exhibits a unique combina- tion of above all tensile strength and porosity or more specifically tensile energy absorption index and porosity.
• the tensile energy absorption index is defined as energy absorbed per weight of paper during stretching to initial rupture in connection with tensile testing, (at standard testing conditions) .
• the porosity is measured in the Gurley unit, which is defined as the time required for 100 ml of air to pass a circle of the sample with a diameter of 28.7 mm.
• tensile energy absorption index and porosity tensile energy absorption index 2.5-3.5 J/g, especially 2.7-3.5 J/g, at a Gurley porosity of less than 10 seconds, preferably less than 7 seconds. More specifically, at a Gurley value of 5 seconds, a paper having a tensile energy absorption index of 3.1 longitudinally and 3.0 transversely has been achieved.
• the reference to a single tensile energy absorption index value means the average of the longitudinal and transverse values, i.e. MD(machine direction) -value + CD (cross direction) -value divided by 2.
• a kraft paper is provided with the aid of the method according to the invention, which in itself exhibits good runnability in connection with sack production.
• runnability refers to the fact that the sack manufacturer' s tube and bottom machines can be run at a high speed and produce high quality sacks. If the paper is flimsy, pulls to one side, etc., one talks of poor runnability.
• the embossing wire utilised is driven separately in rela- tion to the paper web, the embossing wire preferably being driven slower or faster than the paper web.
• the embossing is carried out by the wire being pressed against the paper and resulting in a pattern.
• the paper is lying against a soft under- lay, which means that the pattern being pressed into the paper increases the thickness of the same.
• the pattern redistributes tensions in the paper and makes it more "tensionless” . Because of the high strength and the high porosity of the paper according to the invention, the embossing can be utilised to a maximum extent on lower grammages; i.e. to lower the grammage of the paper utilised by the customer.
• the invention since the invention has made it possible to provide kraft paper with a new, unique combination of properties, the invention also relates to this new paper per se.
• This new paper is characterised by the following combination of physical data: tensile energy absorption index 2.5-3.5 J/g at a Gurley porosity of less than 10 seconds, preferably less than 7 seconds. More preferably, especially for unbleched paper, the tensile energy absorption index is 2.7-3.5 J/g at said Gurley porosity of less than 10 seconds, preferably less than 7 seconds. Most preferably, said tensile energy absorption index is about 3 J/g at a Gurley value of about 5 seconds. Generally, it can also be added that the tensile energy absorption index value is somewhat lower for a bleched than for an unbleched kraft paper, such as approximately 10% lower.
• this kraft paper preferably exhibits equally good runnability as previously known 70 g/m 2 paper, most preferably as 80 g/m 2 paper.
• the above-mentioned kraft paper according to the invention is producible with the aid of the method described above.
• the invention obviously relates to this new paper per se, irrespective of how it is produced.
• a third aspect of the invention relates to a valve sack made of one or more layers of the kraft paper defined above, since valve sacks in particular have proven an exceptionally advantageous application of the new kraft paper because of its combination of properties.
• valve sack for e.g. 50 kg cement, means that it can be made entirely without perforations.
• valve sack is the kind formed of a single layer of the kraft paper in question with a relatively low grammage value for such a single layer construction, specifically not exceeding 120 g/m 2 .
• Fig. 1 shows a flow chart relating to the part of the method comprising the essential features of refining/beating and addition of a strengthening agent, more specifically, starting with a sulphate pulp and up to the operation where the stock is to be fed to a paper machine (not shown) ; and
• Fig. 2 shows an outline diagram of an embodiment of an embossing device in connection with a drying cylinder included in the drying section of a paper machine.
• Fig. 1 shows an arrow 1 indicating the feeding of sulphate pulp into a so-called HC (high consistency) tower 2, in which the pulp is stored before being fed into an HC press 3 for adjusting (increasing) its consistency to the desired value. From this press 3, the pulp moves on to an HC refiner 4 for high consistency refining.
• the pulp suspension is then fed by the intermediary of a buffer vat 5 to a first set of LC refiners 6 in which it is subjected to a first LC beating.
• a second buffer vat 7 By the intermediary of a second buffer vat 7, a new LC beating follows in a second set of LC refiners 8 (machine beaters) .
• the purpose of the storing in the buffer vats 5 and 7 is to enable equalisation of any flow fluctuations from prior steps in the process.
• the beaten pulp leaving the second set of LC beaters 8 then goes to a machine chest 9, in which the pulp is mixed with starch added at the arrow 10.
• sulphuric acid is also added for pH regulation according to prior art.
• the pulp is then conducted to a mixing pump 14, on whose suction side further starch is added (indicated by the arrow 15) .
• the stock is fed onwards by the intermediary of a pressurised screen 16 to a paper machine (indicated by the arrow 17) .
• This paper machine is of the conventional type for making kraft paper for e.g.
• the Figure shows the addition of, in this context, the conventional additives alum (auxiliary chemical) at 18, rosin size (hydrophobising) at 19 and WS agent (wet strength) at 20.
• the embossing device shown in Fig. 2 comprises an embossing roller 21 with an associated embossing wire 22.
• the figure also shows a number of drying cylinders 23 included in the drying section of the paper machine.
• a drying wire 24 and a paper web 25 resting thereupon run above these drying cylinders.
• the embossing wire 22 is driven separately in relation to the paper web 25 and preferably with a speed which deviates from the speed of the paper web.
• the paper is given the desired embossing pattern, which in connection with the invention has been found to provide exceptionally good runnability when producing sacks from the kraft paper according to the invention.
• the test conditions were as follows (with the reference numerals for the respective devices indicated in brackets) . Table 1
• the table shows that the paper made according to the invention exhibits a unique combination of tensile energy absorption index and Gurley value in relation to the comparative examples at otherwise comparable proper- ty values.
• a lowering of the Gurley value from about 18 s to about 5 s at comparable, or even somewhat enhanced, values for the tensile energy absorption index thus represents an exceptionally valuable development in this field.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Paper (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Bag Frames (AREA)
• Making Paper Articles (AREA)

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• 1997
  • 1997-07-09 SE SE9702656A patent/SE510506C2/sv not_active IP Right Cessation
• 1998
  • 1998-07-07 BR BRPI9810569-8A patent/BR9810569B1/pt not_active IP Right Cessation
  • 1998-07-07 EP EP98934054A patent/EP1012377B1/de not_active Expired - Lifetime
  • 1998-07-07 HU HU0003123A patent/HU222668B1/hu not_active IP Right Cessation
  • 1998-07-07 AT AT98934054T patent/ATE219536T1/de not_active IP Right Cessation
  • 1998-07-07 ES ES98934054T patent/ES2147169T3/es not_active Expired - Lifetime
  • 1998-07-07 CZ CZ0476399A patent/CZ297129B6/cs not_active IP Right Cessation
  • 1998-07-07 WO PCT/SE1998/001340 patent/WO1999002772A1/en active IP Right Grant
  • 1998-07-07 PL PL33797298A patent/PL187952B1/pl unknown
  • 1998-07-07 RU RU2000102887/12A patent/RU2208079C2/ru active
  • 1998-07-07 AU AU83658/98A patent/AU8365898A/en not_active Abandoned
  • 1998-07-07 PT PT98934054T patent/PT1012377E/pt unknown
  • 1998-07-07 EE EEP200000009A patent/EE04531B1/xx unknown
  • 1998-07-07 CA CA002295075A patent/CA2295075A1/en not_active Abandoned
  • 1998-07-07 DE DE1012377T patent/DE1012377T1/de active Pending
  • 1998-07-07 DE DE69806168T patent/DE69806168T2/de not_active Expired - Fee Related
  • 1998-07-09 ZA ZA986082A patent/ZA986082B/xx unknown
• 1999
  • 1999-12-23 BG BG104046A patent/BG63849B1/bg unknown

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