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
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
• • 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
  • D21H21/28—Colorants ; Pigments or opacifying 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
  • D21H27/30—Multi-ply
  • D21H27/40—Multi-ply at least one of the sheets being non-planar, e.g. crêped

Definitions

• the invention relates to a method for producing a multi-layered paper liner web, and multi-layer paper liner.
• Paper-based packaging is used widely nowadays, with ever increasing amounts for various product packaging purposes. For reasons of better ecological but also economical sustainability, considerable effort is made to use paper-based packaging products wherever possible, thereby for example replacing plastic packaging or other types of packaging.
• liners or paper liners which can be used as stand-alone paper packaging or as part/component of a paper packaging, for example as one paper-ply in such multi-component paper packaging.
• While several types of paper liners are known in the art of paper technology, the most widely used type of paper liners are multilayer products.
• One prominent example is a two-layer paper liner with a top layer made of good quality, virgin cellulose material which often is also bleached, and a bottom or support layer made of comparatively lower quality cellulose material, for example recycled paper and/or broke.
• Such layered, cellulose material combinations are for example used as top layers in paper packaging applications.
• Such top layer which in packaging applications is the layer visible to the eye, commonly comprises a high share of Kraft pulp or is basically made from Kraft pulp, such type of paper liner is also referred to or designated as Kraft liner or Kraft top.
• Liners facing the outside of a paper packaging product of course have particular high requirements regarding optical appearance.
• the top layer of such liners is desired or required to be essentially white, having a high degree of brightness.
• optical appearance may have to be met. If the packaging for example is to be printed, certain surface smoothness levels may have to be fulfilled to provide for sufficient printability and print quality of a paper-based packaging comprising a paper liner to be printed for example. Other requirements on optical appearance may pertain to brightness or whiteness or specific coloration of a paper-based packaging.
• a paper packaging showing highly uniform, optical appearance usually is considered as having higher quality, regardless of the actual colour of the paper itself.
• Irregularities in the optical appearance of paper liners often originate from the differences in shades between the cellulose fibre materials selected for the top and support layers of typical paper or Kraft liners. Since it is desirable to use as little virgin fibre material as possible for the top layer/ply, said top layers are sought to be produced as thin as possible. This however causes the bottom or support layer being made of lower quality cellulose material to at least partially shine through the top layer, thereby causing a stained optical appearance of the liner due to the mentioned different shades of the cellulose materials. Such ununiform, optical appearance commonly is referred to as mottling in paper making technology.
• An objective of the invention was to address the deficiencies still existing in the prior art and to provide an improved method for producing a multi-layer paper liner web with reduced mottling in a more ecological and economic sustainable way.
• Another objective of the invention was to provide a multi-layer paper liner with reduced mottling, which can be produced in an improved, more ecological and economic sustainable way.
• the method for producing a multi-layer paper liner web comprises
• a dye exhibiting a blackish colour is added to the first pulp.
• the method hereby comprises all the steps listed above. However, the sequence of method steps listed above and in claim 1 does not need to be executed strictly in the order as provided above and in claim 1. As long as it makes sense in technical regard, the sequence of the individual process steps listed above and in claim 1 can be swapped or carried out in an interchanging manner. For example, it may be convenient to apply the method step of dewatering and drying the first and second paper webs at least partially, i.e. to a certain degree of dryness or to a certain water content, before carrying out the method step of joining the first and second webs to one another.
• first and the second webs may be dewatered and dried at least almost fully to a desired water content, and then joined to one another without subsequent drying.
• a binder may for example be used for the joining.
• the first web and the second web may be dewatered/dried in the multiple drying steps either separately from one another or in the already joined state at any stage within the method, wherein the step of joining the first and second webs can be carried out before dewatering/drying of the first and second webs is commenced, after dewatering/drying of the first and second webs is completed, or after the first and second webs are partially dewatered/dried with further drying after the joining.
• the optical appearance of liners for many liner applications is required to be essentially white, with high brightness. Therefore, an actual removal of colour is desirable for such applications, and that is why processes such as bleaching are often used for production of such white top Kraft liners, to remove or lighten colour and to whiten materials of the liners.
• a dye exhibiting a blackish colour is very effective in reducing mottling of a multi-layer paper or paper web.
• the term black dye may be used instead of the term dye exhibiting a blackish colour.
• the dye exhibiting a blackish colour may be a black dye.
• any dye exhibiting a blackish colour suitable for paper making can be used.
• a water-soluble dye exhibiting a blackish colour may be added to the first pulp.
• Such water-soluble dyes are also referred to as direct dyes.
• an anionic, water-soluble direct dye exhibiting a blackish colour may be added to the first pulp.
• a suitable dye exhibiting a blackish colour the product sold under the name Pergasol TM Black 18 Lna by Solenis TM can be mentioned.
• wastepaper have proven to be cost-effective and readily available raw materials, but these wastepaper types also provide for multi-layer paper liners with good mechanical strength when present in the support layer.
• a brightness of the multi-layer paper liner as viewed from the side of the top layer can be adjusted as desired.
• An optical brightening agent present in the above noted range thereby allows for adjustment of the brightness of the top layer to a value common for multi-layer paper liners.
• suitable optical brightening agents the Tetrasulfo or Disulfo classes of optical brightening agents can be mentioned.
• the support layer may comprise 15 wt.% to 35 wt.% precipitated and/or ground calcium carbonate as another second component other than water of the support layer, based on 100 % total weight of all second components other than water.
• an optical brightening agent may be added to the first pulp in an amount of 0,03 wt.% to 0,5 wt.%, based on 100 % total weight of all first components other than water.
• Optical brightening agents of the Tetrasulfo or Disulfo classes can be mentioned as examples for suitable optical brightening agents.
• precipitated and/or ground calcium carbonate may be added to the first pulp in an amount of 10 wt.% to 25 wt.%, based on 100 % total weight of all first components other than water.
• Either such optical brightening agent or precipitated and/or ground calcium carbonate, or all of them, may be added to the first stock flow, and thus to the first pulp 1 as additives 8 by feeding into the first mixing chest 7 shown in Fig. 1 .
• these additives 8 may also be added at another stage of preparing the first pulp 1. In other embodiments however, such additives 8 may not be used at all, or other additives 8 as mentioned in conjunction with the embodiment disclosed with reference to the figures may be used alternatively or in addition.
• the dye 12 exhibiting a blackish colour is shown to be added after the first stock solution has passed the first machine chest 9, respectively in course of the diluting and cleaning of the first stock flow in the first dilution and cleaning unit 10.
• the dye 12 exhibiting a blackish colour or black dye 12 may however also be added at another stage of the first pulp preparation line 5, for example together with other additive(s) 8 added to the first stock flow in the first mixing chest 7.
• the first pulp 1 can be fed to a first headbox 13 to be fed into a paper machine 14 for forming a web and further processing.
• the method in all cases also comprises a multiple-step dewatering and drying of the first web 25 and the second web 26 in multiple dewatering/drying steps to form the multi-layer paper liner web 30 having a first paper web layer 31 formed from the dewatered/dried first web 25 and a second paper web layer 32 formed from the dewatered/dried second web 26, the first paper web layer 31 and the second paper web layer 32 being connected with each other.
• the first web 25 and the second web 26 are formed in a forming section 33 of the paper machine 14.
• a so-called hybrid former 34 may for example be used to form the first web 25, and a so-called gap former 35 may be used to form the second web 26 in parallel.
• both the first web 25 and the second web 26 may thus be formed and also be dewatered in a first dewatering/drying step within the forming section 33 of the paper machine 14 configuration to a desired water content or consistency.
• the initial dewatering of the webs 25, 26 may be conducted by means of wire meshes and suction means of the hybrid former 34 and gap former 35 respectively, thus by means commonly known in the art.
• first web 25 and the second web 26 having been dewatered to a desired water content are then joined at the end of the forming section 33.
• a consistency of both the first web 25 and the second web 26 may be set to 8 % to 14 % respectively, more preferably to 10% to 12%, immediately before joining the first web 25 and the second web 26 to one another and forming the multi-layer web 27.
• both the first pulp 1 and the second pulp 2 may for example be fed to one single headbox for forming the first web 25 and the second web 26.
• a so-called multi-ply or multi-layer headbox may be used for forming the webs 25, 26 out of the pulps 1, 2, wherein the such formed webs 25, 26 may be joined immediately after web formation without significant dewatering of the webs 25, 26.
• the first web 25 and the second web 26 may be dewatered and dried almost fully to a desired, final water content, and then joined to one another without subsequent drying.
• the first web 25 and the second web 26 may be dewatered/dried in the multiple drying steps separately from one another and/or in the already joined state at any stage within the method, wherein the step of joining the first and second webs 25, 26 can be carried out before dewatering/drying of the first and second webs 25, 26 is commenced, after dewatering/drying of the first and second webs 25, 26 is completed, or after the first and second webs 25, 26 are partially dewatered/dried with further drying after the joining.
• the multi-layer web 27 respectively the joined first and second webs 25, 26 may then be for example subjected to surface treatment by means of a surface processing unit 38 as illustrated by the example depicted in Fig. 2 .
• surface treatment may involve an application of one or more surface treatment substance(s) to the surface of the first web 25 respectively the first layer 28, and/or the second web 26 respectively the second layer 29.
• Common substances/chemicals applied to the surface(s) of the multi-layer web 27 include resins, glues or starch. Since these substances are often referred to as sizing agents, such surface treatment unit 38 often is denoted as size press in paper making technology.
• such surface treatment of the multi-layer web 27 may also be carried out elsewhere in the paper machine 14, for example after the multi-layer web 27 has partially or completely passed the dryer section 40 described next, or surface treatment may be omitted completely.
• the final drying step In paper making is commonly carried out by means of a dryer section 40, wherein such dryer section may be configured as two-part dryer section 40 having a pre-drying section 41 and a post-drying section 42 as illustrated in Fig. 2 . Between such pre-drying section 41 and post-drying section 42, a surface treatment unit 38 may be arranged for surface treatment of the multi-layer web 27. Independent thereof, the dryer section 40 may comprise a variety of cylinders 43, which may be steam-heated cylinders as is commonly known.
• the multi-layer paper liner web 30 may be wound up onto a carrier-roll 44 after finishing, for example for transport to an intended application location.
• the multi-layer paper liner web 30 may be subjected to an additional surface treatment prior to winding up or otherwise assembling.
• the multi-layer paper liner web 30 may be processed by means of a calender 45 to smoothen the surfaces of the of the multi-layer paper liner web 30 as illustrated in Fig. 2 .
• the arrangement of the first pulp preparation line 5 and second pulp preparation line 15, and thus also the arrangement of the headboxes 13, 24 and hybrid former 34 and gap former 35 may be swapped, such that the multi-layer web 27 is transported through the various stages of the paper machine 14 with the first layer 28 and the second layer 29 also being swapped, or upside-down respectively as compared with or in contrast to the embodiments shown in Fig. 1 and Fig. 2 .
• the multi-layer paper liner web 30 may be produced comprising one or more additional paper layers attached to the second paper web layer 32.
• the multi-layer paper liner web 30 may be cut to multi-layer paper liners 45 for further use, for example as component of a packaging product or as stand-alone packaging product, which cutting typically is done at the production or application location.

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Citations (8)

• 2024
  • 2024-01-16 EP EP24152004.8A patent/EP4589068A1/de active Pending

Patent Citations (8)

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