Single-layer coated paperboard

Abstract

There is provided a coated paperboard comprising a paperboard substrate and a coating layer applied directly to a surface of a first side of the paperboard substrate wherein:-the coating layer comprises a polymeric binder and a calcium carbonate pigment in a dry weight ratio of between 10: 100 and 17: 100; -the polymeric binder and the calcium carbonate pigment comprise at least 85% of the dry weight of the coating layer; -the particle size distribution of the calcium carbonate pigment (% lt; 2 [mu] m) is between 50 and 70; and-the coating layer is the only pigment-based coating applied to the first side of the coated paperboard.

Description

Technical Field

[0001] The present disclosure relates to the field of pigment-coated paperboard. Background Art

[0002] Pigment-coated paperboard is typically provided with at least two coating layers, including a base coating and a top coating, to create certain surface characteristics. The base coating primes the surface, while the top coating adapts the surface characteristics to the specific application. A barrier coating may also be added.

[0003] For certain applications, such as liquid packaging board (LPB), a pigmented paperboard is covered with a layer of polyethylene (PE) to form a laminate. The purpose of the PE layer is generally to provide a barrier and / or facilitate heat sealing when the laminate is formed into a package. When using a laminate, it is important that the PE layer is firmly attached to the pigmented portion, i.e., to avoid delamination. Summary of the Invention

[0004] The present inventors have recognised a need to reduce the cost of paperboard manufacture whilst maintaining other properties such as PE adhesion and surface roughness at acceptable levels.

[0005] Thus, the present disclosure provides a coated paperboard comprising a paperboard substrate and a coating layer applied directly to a surface of a first side portion of the paperboard substrate, wherein:

[0006] - the coating layer comprises a polymer binder and a calcium carbonate pigment in a dry weight ratio between 10:100 and 17:100;

[0007] - the polymer binder and calcium carbonate pigment constitute at least 85% by dry weight of the coating layer;

[0008] - the particle size distribution of the calcium carbonate pigment (% <2 μm, percentage less than 2 μm) is between 50 and 70; and

[0009] The coating layer is the only pigment-based coating applied to the first side of the coated paperboard.

[0010] "Pigment-based coating" refers to a coating comprising at least 75% by dry weight of pigment.

[0011] The coating layer is located on one side of the paperboard substrate and is provided as a single layer with no other pigment-based coating layer on said side. The paperboard according to the present disclosure has improved PE adhesion, which is advantageous because delamination during forming of packages from the paperboard can be prevented.

[0012] The calcium carbonate pigments of the present disclosure are relatively large and result in coated paperboard having a lower surface roughness than would be achieved using a single coating layer containing finer calcium carbonate pigments.

[0013] In one embodiment, the coating layer is the only pigment-based coating applied to either side of the coated paperboard.

[0014] In an embodiment, the coating layer is applied by dispersion coating and the coated paperboard does not include other coating layers applied by dispersion coating on the same side of the paperboard as the coating layer.

[0015] In an embodiment, the polymer binder is a styrene-based copolymer, such as a styrene-butadiene copolymer or a styrene-acrylate copolymer.

[0016] In an embodiment, the calcium carbonate pigment is ground calcium carbonate (GCC).

[0017] In another embodiment, the coating layer has a coating weight of at least 10 g / m 2 , preferably at least 12 g / m 2 The upper limit of coating weight is 18g / m 2 or 20g / m 2 In one embodiment, the coating weight of the coating layer is 12 g / m 2 Up to 16g / m 2 The single coating layer can be applied at a similar coating weight to the base coating layer in conventional coated paperboard comprising at least two coating layers. Thus, since the coating layer is in the form of a single pigment-based coating layer, the total amount of coating material used can be reduced compared to conventional coating materials comprising at least two coating layers, thereby reducing costs. Furthermore, since a single coating machine is required to produce a single-coated product, the cost is lower from an investment and operating perspective.

[0018] The grammage of the paperboard substrate according to ISO 536:2019 may be, for example, between 100 g / m 2 With 400g / m 2 between, for example, between 120g / m 2 With 300g / m 2 Between, for example, between 125g / m 2 With 260g / m 2 between.

[0019] In an embodiment, the coated paperboard is liquid packaging board.

[0020] In another embodiment, the paperboard substrate of the liquid packaging board includes at least two layers, for example at least three layers, each layer comprising a hydrophobic slurry. The hydrophobic slurry may be alkenyl succinic anhydride (ASA), alkyl ketene dimer (AKD), and / or rosin slurry. Each layer of the paperboard substrate may include at least 1.5 kg of hydrophobic slurry per ton of fiber. Preferably, each layer comprises at least one of AKD and ASA.

[0021] The hydrophobic slurry is preferably added as an internal slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown are the surface characteristics of samples of coated paperboard produced in pilot trials.

[0023] Figure 2 Shown are the surface properties of samples of coated paperboard produced in a (full-scale) machine trial.

[0024] Figure 3 Shown are the PE adhesion values ​​for samples of coated paperboard produced in (full-scale) machine trials. DETAILED DESCRIPTION

[0025] The present disclosure relates to a coated paperboard comprising a paperboard substrate and a coating layer applied directly to a first surface of the paperboard substrate.

[0026] In one embodiment, the paperboard substrate comprises at least two layers, for example, at least three layers, wherein the top layer of the paperboard substrate is provided with a pigment coating. The top layer of the paperboard substrate is typically bleached. Each layer of the paperboard substrate may include a hydrophobic slurry, such as ASA, AKD, and / or rosin slurry. The amount of hydrophobic slurry added may be 1.5 kg per ton of fiber.

[0027] The paperboard substrate may contain other conventional additives such as fillers and colorants, but this is not required.

[0028] The coating layer includes a polymer binder and calcium carbonate pigment.

[0029] The polymer binder can be a synthetic binder and / or a bio-based binder. The polymer binder is preferably a styrene-based copolymer, such as a styrene-butadiene copolymer or a styrene-acrylate copolymer. For example, from an environmental perspective, a styrene-acrylate copolymer is preferred.

[0030] The particle size distribution (% < 2 μm) of the calcium carbonate pigment is between 50 and 70. Here, "%" means percentage by weight. In one embodiment, the weight median particle size d of the calcium carbonate pigment is 50The particle size distribution value can be determined using a SediGraph 5100 or 5120 device manufactured by Micromeritics, Inc., USA.

[0031] Thus, a person skilled in the art understands that "particle size distribution (% < 2 μm) between 50 and 70" means that between 50% and 70% by weight of the particles have an equivalent spherical diameter of less than 2 μm.

[0032] "% <2 μm" is a cut-off value commonly used in the art to define the particle size of pigment products. As an example, in the product name "Hydrocarb 60" (a calcium carbonate pigment quality from Omya), "60" represents the weight percentage of particles with a diameter less than 2 μm. Similarly, in the product "Hydrocarb 90" (Omya), "90" represents the weight percentage of particles with a diameter less than 2 μm.

[0033] Preferably, the calcium carbonate pigment is ground calcium carbonate (GCC).

[0034] The coating layer comprises a polymer binder and a calcium carbonate pigment in a dry weight ratio between 10:100 and 17:100, preferably 12:100 to 17:100.

[0035] The polymer binder and calcium carbonate pigment together constitute at least 85% of the dry weight of the coating layer, preferably at least 90% of the dry weight of the coating layer, more preferably at least 95% of the dry weight of the coating layer.

[0036] In one embodiment, the coating layer comprises only the binder, the calcium carbonate pigment, and the optional rheology modifier in dry form.

[0037] The coating layer is applied directly to the first surface of the paperboard substrate. This surface is preferably the printed side of the paperboard substrate. No additional pigment-based coating layer is present between the paperboard substrate and the coating layer, and thus no "base coating" layer is applied. The coating layer of the present disclosure is a single coating layer that serves as both a "base coating" layer and a "top coating" layer.

[0038] In one embodiment, the coating layer is the only pigment-based coating layer applied to either side of the coated paperboard.

[0039] It has surprisingly been discovered that PE adhesion can be improved by applying the coating disclosed herein as a single coating layer to a paperboard substrate.

[0040] Furthermore, it has been surprisingly found that when the coating layer is used as a single coating layer as claimed in the present disclosure, calcium carbonate pigments having a larger average particle size (50% to 70% < 2 μm) result in a coated paperboard having a lower Parker Print Surface (PPS) roughness and Bendtsen roughness than those obtained when using coatings containing finer calcium carbonate pigments.

[0041] The surface roughness of the coated paperboard can be further reduced by calendering the paperboard substrate or the coated paperboard. This calendering step can be performed, for example, using a pre-calender or a long-nip calender. The pre-calender is located upstream of the coating section (but downstream of the drying section), while the long-nip calender is located downstream of the coating section. Furthermore, the surface can be moistened by spraying it with a water mist before calendering.

[0042] The PPS roughness of the coated paperboard may be less than 3.8 μm, for example, 0.5 μm to 3.7 μm.

[0043] The coating layer may also include a rheology modifier (RM), such as an acrylic copolymer emulsion, which can facilitate application of the coating layer to the paperboard substrate. The amount of rheology modifier is typically 0.05% to 2% of the dry weight of the coating, for example, 0.1% to 1% of the dry weight of the coating.

[0044] In another embodiment, the coating layer has a coating weight of at least 10 g / m 2 (For example, 10g / m 2 Up to 20g / m 2 , for example 10g / m 2 Up to 18g / m 2 ), preferably at least 12 g / m 2 (For example, 12g / m 2 Up to 20g / m 2 , for example 12g / m 2 Up to 18g / m 2 The single coating layer can be applied at a similar coating weight to the base coating layer in conventional coated paperboards comprising at least two coating layers. Thus, because the coating layer is a single pigment-based coating layer, the total amount of coating material used can be reduced compared to conventional coating materials comprising at least two coating layers, thereby reducing costs. Furthermore, the production of single-coated products requires a single coating machine, resulting in lower costs from both an investment and operational perspective.

[0045] The coating layer may be applied to the first surface of the paperboard substrate by a dispersion coating comprising a latex binder and calcium carbonate pigment in an aqueous medium. The coating layer is preferably the only coating layer applied to the first surface by the dispersion coating.

[0046] In an embodiment, the coated paperboard is liquid packaging board.

[0047] Example

[0048] Example 1

[0049] Pilot tests were conducted by coating an uncoated paperboard (LPB) substrate having a grammage of approximately 220 g / m 2 It is composed of three layers, of which the top layer is bleached. All layers include hydrophobic pulp (AKD + ​​rosin pulp).

[0050] Six different coating concepts were evaluated, as shown in Table 1. The coatings were applied using a knife coater and an air dryer. Three concepts had a dual-coater structure (Concepts 1 to 3), and three concepts had a single-coater structure (Concepts 4 to 6). All tested coatings included a polymer binder and a pigment.

[0051] A reference paperboard was prepared by coating a paperboard substrate with a base coat and a top coat. The reference paperboard had a 20 g / m 2 of the total coating weight.

[0052] Table 1. Coating concepts used in pilot trials.

[0053]

[0054] Calcium carbonate and clay pigments are used. Calcium carbonate pigment is d 50 Hydrocarb 90 ("HC 90") with a particle size of 0.7 μm, d 50 Covercarb 75 ("CC 75") with a particle size of 0.63 μm, and d 50 The pigments used were Hydrocarb 60 ("HC 60") having a particle size of 1.4 μm and a particle size distribution (% < 2 μm) of 60. The calcium carbonate pigments were all from Omya. The clay pigments were flaky kaolin pigments. The polymer binder was a styrene-acrylate binder used as a latex (SA latex). The formulations for the various concepts are given in parts, which are parts by weight.

[0055] Parker Printed Surface (PPS) roughness and Bendtsen roughness were measured according to ISO 8791-4 and ISO 8791-2, respectively, and the results are shown in Figure 2. Figure 1 shown.

[0056] An increase in PPS roughness and Bendtsen roughness was observed between the reference and Concept 1. The difference between these concepts was that the top coating in Concept 1 had no clay and instead had a higher amount of HC 90, indicating that the addition of clay to the coating composition used in the two-coat structure reduced the PPS roughness and Bendtsen roughness of the surface of the coating formed from the composition.

[0057] The top coat weight was increased from 11.5 g / m 2 Reduced to 7g / m 2 (Concept 1 vs. Concept 2) There is no effect on the Bendtsen roughness, but it leads to a slight increase in PPS.

[0058] Changing the composition of the base coat by increasing the amount of rough particles and removing the clay (Concept 3) did not significantly change the PPS roughness and Bendtsen roughness.

[0059] As expected, the concepts with a single coating structure (Concept 4 to Concept 6) all had higher PPS roughness and Bendtsen roughness than the concepts with a double coating structure (Concept 1 to Concept 3 and the reference). This is likely because Concept 4 to Concept 6 only had one coating layer compared to the reference and Concept 1 to Concept 3 with double coating layers. In addition, compared to the single coating concept (14 g / m 2 ) compared to the double coating concept with a higher coating weight (20g / m 2 and 15.5g / m 2 ).

[0060] Interestingly, when comparing the single-coat concepts, Concept 6 has a significantly lower surface roughness than Concepts 4 and 5. The smaller average particle size of the calcium carbonate pigments in Concepts 4 and 5 should theoretically produce a smoother surface. However, in contrast, Concept 6, with its coarser particles, has lower PPS roughness and Bendtsen roughness.

[0061] Furthermore, in the case of the single-coat structure, the addition of clay appears to result in an increase in PPS roughness and Bendtsen roughness (Bendtsen and PPS values ​​for Concept 5 are slightly higher compared to Concept 4, while Bendtsen and PPS values ​​for Concept 6 are significantly lower compared to Concept 5).

[0062] Therefore, the single-coat structure in this experiment appears to behave differently than the two-coat structure in the experiment; different composition changes, such as changing the particle size of the pigment or adding clay, can produce different effects.

[0063] Example 2

[0064] The machine tests were carried out by coating an uncoated paperboard (LPB) substrate having a grammage of about 220 g / m 2 It is composed of three layers, of which the top layer is bleached. All layers include hydrophobic pulp (AKD + ​​rosin pulp).

[0065] Two different coating concepts (Concept 3 and Concept 6) were evaluated in Pilot Test / Example 1 and compared to the reference coating concept in Pilot Test / Example 1. The coatings were applied using a knife coater and an air dryer. As shown in Table 1, the reference and Concept 3 had a dual-coater structure, while Concept 6 had a single-coater structure.

[0066] The coating was applied using a knife coater and an air dryer.

[0067] Parker Printed Surface (PPS) roughness and Bendtsen roughness were measured according to ISO 8791-4 and ISO 8791-2 respectively. Figure 2 shown.

[0068] As expected, the PPS roughness and Bendtsen roughness of Concept 6 are higher than those of the reference and Concept 3. As mentioned above, this may be because Concept 6 has only a single coating layer and a lower coating weight.

[0069] The paperboard in the machine test was laminated with a layer of polyethylene (PE) on the coated side and the PE adhesion was tested according to ISO 6133. The PE adhesion was tested on 5 cm long strips of 15 mm wide PE laminated paperboard. The delamination of the PE film from the paperboard was tested using a tensile testing machine and the results are the average of 8 samples. The results of the PE adhesion can be found in Figure 3 Seen in.

[0070] The PE adhesion test showed that Concept 3 and Concept 6 had significantly higher values ​​compared to the reference.

[0071] It was surprisingly found that Concept 6 with a single coating and a coarser pigment had superior PE adhesion compared to the reference and Concept 3. It appears that the single coating combined with the use of calcium carbonate pigments with a larger average particle size improved PE adhesion.

Claims

1. A coated paperboard, comprising a paperboard substrate and a coating layer, wherein the coating layer is directly applied to a surface of a first side portion of the paperboard substrate, wherein: - the coating layer comprises a polymer binder and a calcium carbonate pigment in a dry weight ratio between 10:100 and 17:100; - the polymer binder and the calcium carbonate pigment constitute at least 85% by dry weight of the coating layer; - the particle size distribution of the calcium carbonate pigment (% < 2 μm) is between 50 and 70; as well as - The coating layer is the only pigment-based coating applied to the first side portion of the coated paperboard.

2. The coated paperboard according to claim 1, wherein The coating layer is applied by dispersion coating, and the coating layer is the only coating layer applied to the first side of the coated paperboard by dispersion coating.

3. A coated paperboard according to any one of the preceding claims, wherein The polymer binder is a styrene-based copolymer.

4. The coated paperboard according to claim 3, wherein: The styrene-based copolymer is a styrene-butadiene copolymer or a styrene-acrylate copolymer.

5. A coated paperboard according to any one of the preceding claims, wherein The calcium carbonate pigment is ground calcium carbonate.

6. A coated paperboard according to any one of the preceding claims, wherein The coating weight of the coating layer is at least 10 g / m 2 Preferably, the coating weight of the coating layer is at least 12 g / m 2 .

7. The coated paperboard according to claim 6, wherein: The coating weight of the coating layer is 10 g / m 2 Up to 20g / m 2 For example, the coating weight of the coating layer is 10 g / m 2 Up to 18g / m 2 .

8. The coated paperboard according to claim 6, wherein: The coating weight of the coating layer is 12 g / m 2 Up to 20g / m 2 For example, the coating weight of the coating layer is 12 g / m 2 Up to 18g / m 2 For example, the coating weight of the coating layer is 12 g / m 2 Up to 16g / m 2 .

9. The coated paperboard according to any one of the preceding claims, which is a liquid packaging board (LPB).

10. The coated paperboard according to claim 9, wherein The paperboard substrate includes at least two layers, for example, the paperboard substrate includes at least three layers, and each layer includes a hydrophobic pulp.

11. The coated paperboard according to claim 10, wherein Each layer of the paperboard substrate includes at least 1.5 kg of hydrophobic pulp per ton of fiber.

12. The coated paperboard according to claim 11, wherein The hydrophobic slurry is ASA, AKD and / or rosin slurry.

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