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
  • D21H27/10—Packing 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
  • D21H19/00—Coated paper; Coating material
  • D21H19/80—Paper comprising more than one coating
  • D21H19/82—Paper comprising more than one coating superposed
• • 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
  • D21H19/00—Coated paper; Coating material
  • D21H19/80—Paper comprising more than one coating
  • D21H19/82—Paper comprising more than one coating superposed
  • D21H19/822—Paper comprising more than one coating superposed two superposed coatings, both being pigmented

Definitions

• the present disclosure relates to the field of paper for use in a sack, such as a cement sack.
• the paper sacks need to hold a considerable material weight, i.e. have high tensile strength.
• kraft paper is a suitable sack wall material.
• the sacks typically have two or more walls, i.e. layers of paper material, to further strengthen the sack construction.
• a wall layer of a sack is often referred to as a ply. Production of ply material (i.e. sack paper) is for example disclosed in WO 99/02772.
• a material such as cement is sensitive to moisture contamination during storage.
• the contents of sacks often require protection against atmospheric water vapor that may penetrate the sack plies.
• a moisture barrier incorporated as an intermediate layer in the sack, i.e. between two plies.
• the moisture barrier is typically a plastic film (“free film”), e.g. of polyethylene (PE), that is impermeable to water vapour.
• the free film may also improve resistance to grease and prevent contamination by microorganisms.
• the paper sack should vent air during filling.
• the air that accompanies the powdered material shall efficiently vent from the sack since the filling machines that delivers the material run at high throughput rates.
• the venting capacity of the sack is often the factor limiting for the filling rate. Efficient venting also prevents that air is trapped in the sack and causes under-weight packs, sack rupture and problems when sacks are stacked for transportation.
• WO 2016/ 001029 the free film is replaced by two coating layers provided on the outer paper ply: first a pre-coating layer and then a moisture barrier coating layer.
• the moisture barrier layer is formed from latex and hyper-platy clay.
• the two-layer coating structure of WO 2016/001029 not only provides a barrier against moisture/ water vapour, but it also facilitates disintegration of the sack in a cement mixer.
• the hyper-platy clay used in WO 2016/ 001029 is expensive and may be complicated to handle in the paper mill.
• an objective of the present disclosure is to provide a barrier concept of reduced cost that still runs well in a coating station and provides sufficient protection against water vapour. While it is not necessary that this coating concept facilitates disintegration in a cement mixer, it should allow for recycling of the coated paper according to industry standards.
• a coated paper comprising a kraft paper substrate, a precoating layer provided on the kraft paper substrate and a water vapour barrier coating layer provided on the pre-coating layer, wherein the grammage according to ISO 536:2019 of the coated paper is 65-155 g/m 2 , the pre-coating layer comprises inorganic filler and binder in a dry weight ratio of between 100:25 and 100:5 and the water vapour barrier coating layer comprises clay pigment and styrene-butadiene copolymer (SBR) binder in a dry weight ratio between 100:30 and 100:80, wherein the particle size distribution (% ⁇ 2 pm) of said clay pigment is above 90 and the shape factor of said clay pigment is below 20, such as below 10.
• SBR styrene-butadiene copolymer
• Fig 1 shows a sack according to the present disclosure configured to allow
• Fig 2 shows the sack of Fig 1 provided with a top patch for reinforcement.
• a coated paper comprising a kraft paper substrate, a precoating layer provided on the kraft paper substrate and a water vapour barrier coating layer provided on the pre-coating layer.
• the kraft paper substrate (also referred to as base paper) is preferably formed from a pulp comprising at least 75% by dry weight of virgin fibres. These virgin fibres are typically softwood fibres.
• the kraft paper substrate may be bleached or unbleached.
• the geometric tensile energy absorption (TEA) index of the coated paper is preferably at least 2.0 J/g.
• TEA is measured according to ISO 1924-3:2005.
• the TEA index is obtained by dividing the TEA value by the grammage.
• the geometric TEA index is the geometric mean of the TEA index in the machine direction and the TEA index in the cross direction.
• the grammage of the coated paper is 65-155 g/m 2 . Preferably it is 65-135 g/m 2 , such as 75-115 g/m 2 . In the present disclosure, grammage is measured according to ISO 536:2019.
• the coat weight of the pre-coating layer is preferably 4-20 g/ m 2 , such as 4- 12 g/m 2 , such as 5-10 g/m 2 and the coat weight of the water vapour barrier coating layer is preferably 4-20 g/m 2 , such as 4-12 g/m 2 , such as 5-10 g/m 2 .
• the grammage of the kraft paper substrate is typically 50-140 g/m 2 and preferably 50-120 g/m 2 , such as 60-100 g/m 2 .
• the Cobb 60s value of both sides of the kraft paper substrate may be below 40 g/m 2 , such as below 35 g/m 2 . Accordingly, the Cobb 60s value of the side the coated paper that is not provided with the pre-coating and the barrier coating is preferably below 40 g/m 2 , such as below 35 g/m 2 .
• the Cobb 60s values of the present disclosure are measured according to ISO 535:2014. To obtain lower Cobb 60s values, hydrophobic size, such as AKD, ASA and/or rosin size maybe added in the wet end during production of the kraft paper substrate.
• the kraft paper substrate comprises a wet strength agent. However, the amount of the wet strength agent should be controlled such that the coated paper is still recyclable.
• the pre-coating layer comprises inorganic filler and binder in a dry weight ratio of between 100:25 and 100:5, preferably between 100:20 and 100:8, and more preferably between 100:16 and 100:8. In one embodiment, the dry weight ratio is between 100:16 and 100:10.
• the binder of the pre-coating layer may for example be a styrene-butadiene co-polymer (SBR).
• SBR styrene-butadiene co-polymer
• the SBR is typically provided in the form of a latex when the coating composition is prepared and coated onto the kraft paper substrate.
• the inorganic filler of the pre-coating layer is preferably a relatively coarse pigment, such as a pigment having a particle size distribution (% ⁇ 2 pm) below 70.
• the inorganic filler is a calcium carbonate pigment having a particle size distribution (% ⁇ 2 pm) below 70.
• % ⁇ 2 pm particle size distribution
• the person of skill in the art of pigments for paper coating layers understands here means percent by weight and is familiar with particle size distribution values expressed as the percentage of particles having a size below 2 pm. As an example, this type of values is frequently found on data sheets for pigment products. Particle size distribution values can be determined using a SediGraph 5100 or 5120 device from the company Micromeritics, USA.
• the water vapour barrier coating layer comprises clay pigment and styrene-butadiene co-polymer (SBR) binder in a dry weight ratio between 100:30 and 100:80, wherein the particle size distribution (% ⁇ 2 pm) of said clay pigment is above 90, preferably above 95. Again, as understood by the skilled person, means percent by weight.
• SBR styrene-butadiene co-polymer
• the shape factor of the clay pigment of the water vapour barrier coating layer is preferably below 20, more preferably below 10.
• the dry weight ratio of clay pigment to SBR binder in the water vapour barrier layer is preferably between 100:40 and 100:70, more preferably between 100:40 and 100:60.
• a sack comprising a ply formed from the coated paper of the first aspect.
• the sack is preferably a sack for a hydraulic binder, such as cement.
• the contents of the sack is typically used in mortar or tile fix.
• the sack comprises at least two plies and the ply formed from the coated paper of the first aspect is an outer ply.
• a sack may comprise an inner ply formed from a kraft paper having a Gurley permeance (also referred to as Gurley value or air permeance) of 2-10 s, such as 4-8 s, such as 4-7 s, such as 5-6 s.
• Gurley permeance is measured according to ISO 5636-5:2013.
• the kraft paper of the inner ply typically has a grammage of 60-90 g/m 2 , preferably 60-85 g/m 2 , such as 60-80 g/m 2 .
• the coated paper of the sack typically has a grammage of 75-105 g/ m 2 , such as 75-95 g/m 2 . Accordingly, the paper substrate of the coated paper of the sack typically has a grammage of 60-90 g/m 2 , such as 60-80 g/m 2 .
• the sack is typically configured to allow air to escape from an interspace between the inner paper ply and the outer paper ply during filling of the sack.
• the sack design is such that air can escape from the interspace between the inner paper ply and the outer paper ply through a top end of the sack during filling of the sack.
• a top end of the sack may be formed by folding and gluing the plies such that a portion of the top end is not sealed and air can escape from the interspace through the non-sealed portion during filling of the sack.
• the sack of the present disclosure is preferably a valve sack.
• Valve sacks are well known to the skilled person.
• a valve sack is provided with a valve through which it maybe filled. Such a valve is normally provided at a folded top end of the sack.
• a valve is further discussed below with reference to figures i and 2.
• Figure 1 illustrates an embodiment of a multi-ply sack 100 having a top end 111 and a bottom end 112.
• the sack comprises an inner paper ply 101 and an outer paper ply 102.
• the paper of the outer ply 102 is coated as described above.
• the Gurley permeance of the inner paper ply 101 is 10 s or less.
• the sack 100 is configured to allow air to escape (the air escape is illustrated by the arrow 103) from an interspace between the inner paper ply 101 and the outer paper ply 102 through the top end 111 of the sack 100 during filling of the sack 100.
• air escape is illustrated by the arrow 103
• Such a deaeration is achieved by a non-sealed portion 104 forming an opening between the inner paper ply 101 and the outer paper ply 102 at the top end 111.
• the non-sealed portion 104 maybe flanked by sealed portions 105, i.e. portions in which the outer paper ply 102 is sealed (preferably glued) to the inner paper ply 101.
• the width of the non-sealed portion may for example be 150-160 mm and for a 35 kg having a width of 440-460 mm, the width of the non-sealed portion maybe 190-200 mm.
• the top end 111 of the sack 100 of figure 1 further has a filling valve 106 into which a filling spout may be inserted.
• the arrow 107 illustrates how the filling spout is inserted into the valve 106.
• a ceiling of the valve 106 is reinforced by a valve reinforcement 108, which preferably is composed of paper. Because of the reinforcement provided by the valve reinforcement 108, the sack 100 can hang on the filling spout during filling without breaking. When fully opened, the opening of the valve 106 maybe approximatively diamond-shaped.
• Figure 2 illustrates the sack 100 of figure 1 onto which a top patch 201 has been applied.
• the top patch reinforces top end 111 of the sack 100.
• a slit 202 in the top patch 201 ensures that the air still can escape through the non-sealed portion 104 during filling.
• the slit 202 is thus substantially aligned with the non-sealed portion 104.
• the width of the slit 202 is preferably approximately the same as the width of the non-sealed portion 104.
• parts means parts by dry weight. All base papers used in the examples section are formed from pulps in which all cellulose fibres are virgin softwood fibres.
• a bleached sack kraft paper having a grammage of 70 g/ m 2 , a Cobb 60s value of 30 g/m 2 , a Gurley value of 16 s and an MD stretchability of about 2.3 % was used as the base paper.
• the top side of the base paper was blade coated with a pre-coating composition
• a pre-coating composition comprising 100 parts of Hydrocarb 60 (a relatively coarse calcium carbonate pigment commercialized by OMYA), 13.5 parts of Ligos P 1217 (an SBR binder commercialized by TRINSEO), 0.62 parts of Finnfix 10 (a CMC rheology modifier commercialized by Nouryon), 0.01 parts of an anti-foaming agent, 0.001 parts of colour and 0.07 parts of NaOH.
• the (dry) coat weight of the pre-coating was 8 g/m 2 .
• the precoated side was blade coated with a coating composition
• the (dry) coat weight of this coating was 7 g/m 2 .
• the double-coated base paper was calendered in a soft nip calender at a temperature of 14O°C using a line load of 160 kN/m.
• a coated paper was produced on several occasions over a production period of about one year.
• a bleached sack kraft paper having a grammage of 80 g/m 2 , a Cobb 60s value of about 80 g/m 2 and an MD stretchability of 6% was used as the base paper.
• the wire side of the base paper was blade coated with a pre-coating composition
• a pre-coating composition comprising 100 parts of Hydrocarb 60 (a relatively coarse calcium carbonate pigment commercialized by OMYA), 13.5 parts of Litex P6115 (an SBR binder commercialized by Eka Synthomer), 0.62 parts of Finnfix 10 (a CMC rheology modifier commercialized by Nouryon), 0.024 parts of an anti-foaming agent and 0.097 parts of NaOH.
• the (dry) coat weight of the pre-coating was 8 g/m 2 .
• the precoated side was blade coated with a barrier coating composition
• the (dry) coat weight of the barrier coating was 7 g/m 2 .
• the double-coated base paper was calendered in a soft nip calender at a temperature of 80 °C using a line load of 70 kN/m.
• the precoated side was blade coated with a barrier coating composition comprising 100 parts of Hydragloss 90, 50 parts of Litex P6115, 0.16 parts of Rheocoat 27 and 0.13 parts of NaOH.
• the (dry) coat weight of the barrier coating was 7 g/m 2 .
• the double-coated base paper was calendered in a soft nip calender at a temperature of 8o°C using a line load of 70 kN/m.
• a coated paper was produced on several occasions over a period of about nine months. The same base paper as in reference trial 2 and was used.
• the wire side of the base paper was blade coated with a pre-coating composition comprising 100 parts of Hydrocarb 60 (a relatively coarse calcium carbonate pigment commercialized by OMYA), 9 parts of Ligos P1217, 0.16 parts of Rheocoat 27 and 0.13 parts of NaOH.
• the (dry) coat weight of the pre-coating was 8 g/m 2 .
• the precoated side was blade coated with a barrier coating composition comprising 100 parts of Hydragloss 90, 50 parts of Ligos P 1217, 0.16 parts of Rheocoat 27 and 0.13 parts of NaOH.
• the (dry) coat weight of the barrier coating was 7 g/m 2 .
• the double-coated base paper was calendered in a soft nip calender at a temperature of 80 °C using a line load of 70 kN/m.
• Barrisurf LX (used in reference trial 2) is an expensive hyper-platy clay pigment specifically designed to improve the water vapour barrier properties of coatings of fibre-based substrates.
• table 2 shows that the relatively inexpensive clay pigment Hydragloss 90 that was used in inventive trials 1 and 2 provided WVTR values on par with that for Barrisurf when used together with a SBR binder on top of a pre-coating.
• a comparison to the data in table 1 shows that the WVTR values at 38°C/ 90% RH for inventive trials 1 and 2 are much lower than that for reference trial 1.
• Base papers (hi) and (iv) comprised wet strength agent. Further, these base papers comprised more AKD than (i) and (ii), which is reflected by lower Cobb values.
• each of the base papers (i)-(iv) was blade coated with a pre-coating composition comprising 100 parts of Hydrocarb 60, 13.5 parts of Ligos P1217, 0.62 parts of Finnfix 10 and 0.07 parts of NaOH.
• the (dry) coat weight of the pre-coating was 8 g/m 2 .
• the precoated side was blade coated with a barrier coating composition comprising 100 parts of HG90, 50 parts of Ligos P1217, 0.16 parts of Rheocoat 27 and 0.13 parts of NaOH.
• the (dry) coat weight of the barrier coating was 7 g/m 2 .
• the double-coated base paper was calendered in a soft nip calender at a temperature of 80 °C using a line load of 70 kN/m.
• the coated papers of inventive trial 3 exhibit much better water vapour barrier properties than those of the coated paper of reference trial 1. Further, the WVTR values at 38°C/ 90% RH are lower in inventive trial 3 than in reference trial 2.
• HG90 i.e. a clay pigment having particle size distribution (% ⁇ 2 pm) of 96-100 and a shape factor below 20
• HG90 was uncomplicated to handle in full-scale operation and did not cause any particular runnability problems.
• Friction is needed in most processes of conversion of the paper to a sack.

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Citations (4)

• 2021
  • 2021-12-14 ES ES21214389T patent/ES2977361T3/es active Active
  • 2021-12-14 FI FIEP21214389.5T patent/FI4198199T3/fi active
  • 2021-12-14 EP EP21214389.5A patent/EP4198199B1/de active Active
• 2022
  • 2022-12-14 CA CA3240543A patent/CA3240543A1/en active Pending
  • 2022-12-14 WO PCT/EP2022/085973 patent/WO2023111088A1/en active Application Filing
  • 2022-12-14 MX MX2024006937A patent/MX2024006937A/es unknown

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