Glass paper with short fiber dosing and improved sustainability

Abstract

The present invention relates to a glass paper for stripping interleaving paper, wherein the majority of the fiber ingredients are non-regenerated bleached chemical pulp from hardwood such as birch or eucalyptus. A small amount of recycled pulp produced from release liner glass paper and / or pulp mill broke is used to adjust the characteristics of the fiber ingredients. The invention makes it possible to produce cellophane, wherein the fibrous ingredients do not contain non-recycled chemical pulp produced from cork.

Description

Technical Field

[0001] The present invention relates to a calendered glass paper suitable for release liner and a process for making such paper wherein the majority of the fiber furnish consists of non-recycled bleached chemical pulp (produced from hardwood, preferably birch and / or eucalyptus). Background Art

[0002] Release liners can be used to protect sensitive surfaces, such as the adhesive surface of self-adhesive labels, before use. Release liners are widely used in high-speed industrial labeling processes, where the number of products to be labeled can be very large. This requires large amounts of release liners as a carrier for the labels. High-speed processes require reliable die-cutting and separation of the self-adhesive labels from the release liners. Unexpected interruptions to the labeling process due to defects in the release liners are problematic. Therefore, release liners require strength and a uniform surface that exhibits stable release properties. Therefore, the expectation of high quality extends to the paper used as the release liner substrate, which should have sufficient properties to withstand the stresses applied at high-speed processes.

[0003] Cellophane is a unique type of paper that is used as a release liner substrate due to its outstanding properties. Cellophane is typically produced from highly refined bleached chemical pulp (hereinafter referred to as BCP). The production of cellophane is a complicated process that requires skill, a large amount of virgin wood material and energy. The BCP used to produce cellophane is typically a pulp mixture containing both BCP made from softwood and BCP made from hardwood. The original BCP made from softwood is preferred because the fibers in the BCP made from softwood are longer, which provides higher strength and rigidity. Such properties are useful for the paper intended to be used in release liner, where strength and durability are important.

[0004] Refining is a grinding operation performed on BCP before making glassine paper, in which the pulp fibers are subjected to high shear forces. This physically modifies the pulp fibers, for example by fibrillating them, resulting in a looser fiber structure. The degree of pulp refining can be determined using the Schopper-Riegler test, which measures the water drainage of a pulp suspension in water based on the Schopper-Riegler number (known as the SR number or °SR). Refining further reduces the average fiber length of the pulp fibers. Consequently, the specific volume of the resulting glassine paper is also reduced because the shorter fibers can be packed more tightly together. This also enables the production of glassine paper with higher surface smoothness and density. When producing release liner, a smooth and dense paper surface helps reduce the subsequent consumption of release coatings. However, refining also increases the water absorption of the BCP, expressed as swelling, because the loose fiber structure of the refined BCP is more accessible to water molecules. Therefore, when making glassine paper on a paper machine, refining increases the amount of water removed from the resulting paper web. When drying the paper web on the paper machine, excess water removed from the fibers can cause shrinkage, which changes the dimensions of the paper and also negatively impacts paper quality, such as strength. Thus, pulp refining has multiple downstream effects on the papermaking process. While some of the effects of refining are positive and improve the quality of the paper, others are not.

[0005] To balance the effects of extensive refining and to achieve final paper quality properties such as smoothness, thickness, density and clarity, glassine paper is typically surface sized and intensively calendered with the aid of a multi-nip calender or super calender.

[0006] In the past, considerable technical challenges have also been disclosed when attempting to reuse release liner materials without ensuring the quality of the repulped material. Pulps obtained from such materials have shown reduced quality and are used in products where quality is less important.

[0007] A large percentage of industrial paper grades, such as those used for printing and writing, use different types of furnishes than those typically used when making glassine paper for release liners. Many paper types primarily intended to convey information to consumers also contain relatively large amounts of various printing inks. This is a concern because dye-based inks and pigment-based inks have different de-inking properties.

[0008] Label waste poses another type of challenge, as the material to be recycled can often contain plastic and adhesive label residues. Release liners, on the other hand, contain cured silicone polymers that have adhered to the paper surface.

[0009] As an example, US Pat. No. 5,316,621 discloses that glassine paper, used as a release liner, is extremely difficult to defibrate because it is supercalendered, made from highly beaten pulp fibers, and contains release agents such as organosilicon compounds. This publication proposes an accelerated method involving the addition of acid and elevated temperature, followed by kneading, fine screening, and mechanical stirring of the thickened pulp at a temperature below 12°C. It is anticipated that mineral pigments will be added during the process to achieve even better results.

[0010] Furthermore, sustainability has become a prominent aspect that needs to be considered in the production of specialty papers. Sustainability encompasses both environmental aspects related to preserving biodiversity and aspects related to the circular economy through increased recycling of materials. Sustainability can also include the responsible sourcing of raw materials used in industrial production processes. Due to the large production volumes, the nature and origin of wood-based raw materials have a significant impact on the sustainability of industrially produced paper products. As an example, the current annual production of softwood kraft pulp in Finland is in the range of 4 million tons, while the annual production of hardwood kraft pulp is in the range of 2.5 million tons. Recently, sourcing wood for the pulping process from certain regions has become a challenge due to environmental and geopolitical reasons.

[0011] Due to the factors discussed above, the availability of bleached chemical pulp has become a hot topic. Growing sustainability demands have led to the production of significant quantities of release liners for the labeling industry, where paper is used as the release liner substrate. Shortages of certain types of wood fiber have been observed in the industry. Paper mills are no longer able to secure a stable supply of the specific types of pulp material traditionally used in the fiber furnish to produce high-quality glassine suitable for release liners. This has an impact on the production of high-quality release liners and is driving the development of new paper products and manufacturing methods for such applications. Summary of the Invention

[0012] The invention disclosed herein provides a solution to the challenges disclosed above by proposing a calendered glass paper suitable for use as a substrate for release liner and a process for producing such paper, wherein the majority of the fiber furnish consists of non-recycled BCP (produced from hardwoods such as eucalyptus, birch or a combination of these) and wherein the properties of the fiber furnish have been adjusted by a small amount of fibers coming from recycled pulp obtained from release liner glass paper, pulp mill broke or a combination of these.

[0013] Traditionally, the strength properties of glassine, such as tear strength, have been primarily achieved by adding large amounts of non-recycled BCP produced from softwood to the fiber furnish. However, experimental studies have shown that calendered glassine can maintain sufficient strength capabilities for use as a substrate for release liners when non-recycled BCP produced from hardwood is substituted for non-recycled BCP produced from softwood.

[0014] Replacing a BCP softwood component with a BCP hardwood component is possible because chemical pulps exhibit a two-way dependence between fiber properties and the manufacturing process. Thus, while the fibers of chemical pulps have an impact on the properties of the quality of the manufactured paper product, the paper manufacturing process also has an impact on the morphology of the fibers. For example, while reversible fiber deformations can be removed by refining the fiber, mechanical action at higher consistencies may cause irreversible damage to the fiber, such as permanently increasing fiber kinks in BCP produced from hardwood. In this context, fiber kinks refer to sudden changes in fiber curvature. Exploiting this two-way dependence is particularly relevant when considering that the fiber furnish can be arranged to include recycled fibers and non-recycled fibers. Recycled fibers and non-recycled fibers are distinguished because they have different processing histories and morphologies.

[0015] An important aspect is also understanding how to exploit the fiber properties of specific hardwood species in the production of calendered glass paper, where the fiber furnish consists mainly of non-recycled BCP (produced from hardwood).

[0016] The availability and growth rates of deciduous wood species are of particular interest because increasing the utilization of bleached chemical pulp produced from eucalyptus can provide a means of regenerating plantations more quickly while improving the conservation of boreal forests. Eucalyptus (Eucalyptus spp.) is a deciduous tree native to Australia but can be grown in temperate and / or tropical forest areas elsewhere and can reach harvestable size for pulpwood very quickly, such as in less than 10 years, optimally in 6 to 8 years. Eucalyptus plantations can produce over 40m3 of pulpwood annually. 3 / ha of wood suitable for chemical pulping processes. Therefore, eucalyptus plantations provide an excellent opportunity to improve the conservation of temperate forest wood species, which generally have slower growth rates. This also enables optimal harvesting of northern hemisphere boreal forest softwood species, such as spruce (Picea spp.) and pine (Pinus spp.), which are widely used in the production of chemical pulps, such as kraft pulp.

[0017] Different wood species contain different amounts of chemical components, such as cellulose, lignin, extractives and resins. In addition, physical properties, such as average fiber length, are also different between wood species. Typically, hardwood species contain more cellulose and hemicellulose and less lignin than softwood species. Compared with softwood species, hardwood species generally have shorter, less wide fibers. Therefore, when the amount of non-regenerated BCP produced by hardwood in the fiber furnish increases, better paper forming properties and cross-machine evaporation distribution can be obtained on the paper machine. The shorter fibers of hardwood species can also be more closely packed together, which can be limited by the amount of fiber present in every gram of pulp. Therefore, when the amount of non-regenerated BCP produced by hardwood in the fiber furnish increases, higher paper density can be obtained. Table 1 (hereinafter) illustrates some typical fiber properties between softwood species and hardwood species that can be used for chemical pulp production.

[0018] Table 1. Comparison of typical fiber properties in bleached chemical pulps produced from softwood (spruce) and hardwood (birch and eucalyptus).

[0019] Fiber properties spruce birch eucalyptus Average length (mm) 1.9-2.5 0.9-1.1 0.7-0.8 Average width (μm) 28-32 24-26 15-17 Average wall thickness (μm) 2.5-3.0 3.5 4.0-4.5 Roughness (μg / m) 140-200 90-100 70-80 Fiber count per gram (millions / g) 3 12 20

[0020] Based on Table 1, it is obvious that the non-regeneration BCP produced by birch and eucalyptus has different morphologies and characteristics, which is also different from the non-regeneration BCP produced by softwood. Fiber length and roughness have a great impact on paper properties, such as tear index, tensile index, folding resistance and formability. Higher roughness and fiber length are relevant to higher strength properties. It has been shown that fiber curling and kinking also can affect paper properties, such as tensile index, tensile stiffness, tear index, porosity, bulk, absorbency and fracturability. As mentioned above, the difference in fiber morphology has been illustrated how to consider the characteristics of specific wood species when changing the composition of fiber furnish. Eucalyptus fibers are short (average length), with thick walls (average thickness) but thin (average width), and have a roughness less than birch. Therefore, the BCP produced by eucalyptus can provide paper with higher bulk than the BCP produced by birch.

[0021] Information gathered from experimental studies has revealed how to modify the quality of glassine paper using non-recycled bleached chemical pulp from deciduous species, particularly birch (Betula spp.) and eucalyptus (Eucalyptus spp.), in an unconventional manner during the manufacturing process. A fiber furnish mixture, consisting primarily of non-recycled bleached chemical pulp produced from birch and / or eucalyptus, can be combined with glassine paper manufacturing operations, such as refining, mixing, forming, dewatering, and coal drying, to produce calendered glassine paper in which quality properties are sufficiently preserved for use as a substrate for release liners. This can be achieved through optimization of the fiber furnish mixture, which can also be detected in the produced paper product. For example, experimental studies on pulps used for calendered glassine paper have shown that BCP produced from eucalyptus has similar tear index and bond strength capabilities as BCP produced from birch. However, surprising differences have also been observed. When refined to the same tensile index value of 80 Nm / g, BCP produced from eucalyptus has higher opacity, higher °SR, higher water retention values, and requires approximately 60% more energy during refining than BCP produced from birch. The higher specific energy consumption during refining of BCP produced from eucalyptus also indicates that the fibers surprisingly well retain their initial strength properties during the refining process. On the other hand, the lower specific energy consumption during refining of BCP produced from birch indicates that birch fiber is easier to refine, thereby making it better able to provide internal bonding and strength.

[0022] Thus, as disclosed above, the behavior of chemical pulp during the glass paper manufacturing process can be used to provide calendered glass paper that is essentially free of non-recycled BCP produced from softwood, wherein the quality properties still meet the specifications for substrates used as release liners, particularly in terms of grammage, density and transparency.

[0023] Quality data is regularly collected at paper mills and laboratories. Therefore, the effects of different fiber furnish mixtures can be simulated with the aid of computational modeling. Predictive algorithms can analyze historical quality data from glass paper production to capture the relationships between multiple input and output variables. The input variables can be, for example, the composition of the fiber furnish, while the output variables can be paper quality parameters such as paper strength or clarity. Based on these relationships, a user can, for example, provide several input variable values that differ from a given reference case, and execute an algorithm to generate predictions about the endpoint quality parameter values that will occur when the pulp or paper composition changes by a certain amount relative to the given reference case. These can be used as a guide for laboratory experiments or when planning paper machine manufacturing trials. Thus, the effects of unconventional fiber furnish mixtures can be tested using simulated data and also combined with laboratory experiments, which enables the development of new, enhanced products for glass paper.

[0024] In addition to non-recycled BCP produced from hardwood, the fiber furnish for glassine paper can contain a small amount of recycled pulp, hereinafter referred to as optimized pulp. Optimized pulp can be used to further adjust the properties of glassine paper production. Recycled pulp obtained from release liner glassine paper and pulp mill broke differs from non-recycled BCP, which can also be referred to as virgin BCP. The fibers in both recycled pulp and pulp mill broke have, at least to some extent, been subjected to the papermaking process, which has an impact on the properties of the fibers therein, as will be explained below. Therefore, recycled pulp obtained from release liner glassine paper and / or pulp mill broke can be used to adjust the properties of glassine paper production.

[0025] Recycled pulp obtained from release liners made of cellophane is an especially excellent material from the perspective of fiber properties. The extensive industrial use of such release liners enables the targeted collection and sorting of used release liners for recycling. Of particular interest is the collection and sorting of release liners where the substrate is cellophane. Release liners where the substrate is cellophane will hereinafter be referred to as release liners and abbreviated as RGP.

[0026] The fibers of RGP have been subjected to very harsh conditions at the paper machine and have been subjected to repeated drying and wetting cycles in the presence of chemicals, relatively high temperatures and high pressures. These treatments lead to irreversible changes in the fiber structure, in particular the pores formed between the cellulose fibrils. This results in a reduction in the swelling capacity of the fibers. Therefore, when compared with other types of fibers (such as, for example, from non-regenerated BCP or pulp mill broke), the morphology of the fibers and their swelling capacity are different. Fiber furnish analysis according to ISO 9184-4 in combination with ISO 9184-1 can be used to identify the fibers and determine the fiber properties of a given pulp. Furthermore, the use of recycled pulp obtained from release liner glass paper in a method for manufacturing calendered glass paper suitable as a substrate for release liner improves the circular economy.

[0027] RGP recycling offers a more sustainable means of producing glasspaper while addressing the aforementioned challenges. Due to extensive keratinization, RGP fibers show signs of damage and no longer possess the same properties as fibers from virgin BCP made from softwood. However, separating RGP from other wastepaper provides a specific and highly homogeneous material for recycling, which enables better adjustment of the material's properties during the recycling process. This is advantageous because the compatibility of the recycled pulp can be tailored and optimized for glasspaper production. For example, over-refining of the recycled pulp can be avoided. In particular, pulp produced from RGP can be used to replace non-recycled BCP in the composition of glasspaper. Consequently, recycled pulp obtained from RGP can be recycled back into the manufacturing process, resulting in a more closed loop for papermaking fibers.

[0028] Recycled pulp obtained from release liner glassine paper refines very quickly compared to non-recycled pulp components. Recycled pulp obtained from RGP also has a relatively high SR number compared to unrefined non-recycled bleached chemical pulp. Therefore, recycled pulp obtained from RGP can be used in glassine paper production without further refining. When the fibrillation and drainage properties of the recycled pulp obtained from RGP have been pre-adjusted to appropriate levels, the recycled pulp obtained from RGP can be directly mixed with other non-recycled pulp components in the process for manufacturing glassine paper.

[0029] Experimental studies have shown that calendered glass paper suitable for use as a substrate for release liner can be manufactured such that it comprises a fiber furnish consisting essentially of non-recycled BCP from hardwoods such as eucalyptus, birch, or combinations thereof. To optimize the papermaking process, advantageously, a small amount of fiber in the fiber furnish, equal to or greater than 5% by weight, comes from recycled pulp obtained from release liner glass paper, pulp mill broke, or combinations thereof.

[0030] According to a first aspect, there is provided a calendered glass paper suitable for use as a substrate for a release liner, the calendered glass paper comprising a fiber furnish wherein

[0031] - an amount equal to or higher than 5% by weight of fibers from

[0032] ○ Recycled pulp obtained from release liner glassine paper,

[0033] ○Pulp mill broke and / or

[0034] ○ A combination of these,

[0035] And among them

[0036] the remainder of the fibres forming up to 100% by weight of the fibre furnish, the remainder being, in an amount equal to or higher than 60% by weight, non-recycled bleached chemical pulp produced from hardwood,

[0037] This amount can be determined as dry matter content according to SCAN-P 39:80, and the fiber content can be determined according to ISO 9184-4 in combination with ISO 9184-1;

[0038] The calendered glass paper has

[0039] - can be measured according to ISO 536 at 40g / m 2 Up to 120g / m 2 Within the range of gram weight,

[0040] - Equal to or higher than 1.050 g / cm3, measurable according to ISO 534 3 The density and

[0041] - A transparency equal to or higher than 40%, measurable according to ISO 2469.

[0042] According to a second aspect, there is provided a method for producing a calendered glass paper suitable for use as a substrate for a release liner, the method comprising

[0043] - mixing the pulp so as to obtain a raw material comprising a fiber furnish, wherein

[0044] ○ Fibers in an amount equal to or greater than 5% by weight are derived from

[0045] ■ Recycled pulp obtained from release liner glassine,

[0046] ■Pulp mill broke and / or

[0047] ■A combination of these,

[0048] o the remainder of the fibers forming the fiber furnish, the remainder being an amount equal to or higher than 60% by weight, coming from non-recycled bleached chemical pulp produced from hardwood,

[0049] This amount can be determined as dry matter content according to SCAN-P 39:80, and the fiber content can be determined according to ISO 9184-4 in combination with ISO 9184-1;

[0050] - forming a paper web of raw material on a paper machine;

[0051] - reducing the moisture content of the paper web in the pressing section;

[0052] - drying the coal web in the coal drying section to form paper; and

[0053] - calendering the paper so as to form calendered glassine paper,

[0054] The calendered glass paper has

[0055] - can be measured according to ISO 536 at 40g / m 2 Up to 120g / m 2 Within the range of gram weight,

[0056] - Equal to or higher than 1.050 g / cm3, measurable according to ISO 534 3 The density and

[0057] - A transparency equal to or higher than 40%, measurable according to ISO 2469.

[0058] According to a third aspect, there is provided a release liner comprising the calendered glass paper as disclosed above, further comprising a release coating.

[0059] Advantageously, the fiber furnish does not contain non-regenerated BCP produced from softwood. Further, the non-regenerated bleached chemical pulp produced from hardwood is advantageously birch (Betula spp.), eucalyptus (Eucalyptus spp.), or a combination thereof. The non-regenerated BCP produced from birch may advantageously comprise an average fiber length in the range of 0.9 mm to 1.0 mm and an average number of kinks in the range of 2100 to 3200 per meter. The non-regenerated BCP produced from eucalyptus may advantageously comprise an average fiber length in the range of 0.8 mm to 0.9 mm and an average number of kinks in the range of 2800 to 3500 per meter. A greater number of kinks per meter can be used as an indicator of a higher wet strength of the pulp.

[0060] Experimental studies have further shown that the amount of recycled pulp obtained from release liner glassine can be equal to or higher than 5% by weight of the fiber furnish, preferably in the range of 5% to 40% by weight of the fiber furnish, while maintaining the amount of non-recycled BCP produced from hardwood in the fiber furnish equal to or higher than 60% by weight, so that the total amount of fibers in the fiber furnish comprising non-recycled BCP produced from hardwood and recycled pulp obtained from release liner glassine is 100% by weight.

[0061] Typically, calendered glass paper has a thickness equal to or less than 120 g / m 2 , such as at 40g / m 2 Up to 120g / m 2 When producing substrates for use as release liners, lower grammages may be preferred, such as 40 g / m 2 Up to 90g / m 2 In the range of 45g / m 2 Up to 80g / m 2 In the range of 50g / m 2 Up to 60g / m 2 The range can be determined according to ISO 536. Glass paper with a lower grammage can be calendered to a smaller thickness and higher transparency. The thickness of glass paper can be controlled by calendering and is therefore related to the grammage and density.

[0062] In this context, sufficient quality properties are defined as calendered glass paper having a 3 Up to 1.200g / cm 3 Advantageously, the density is 1.060 g / cm 3 to 1.190g / cm 3 In the range of 1.060 g / cm 3 to 1.180g / cm 3The transparency is advantageously in the range of 42% to 53%, most preferably in the range of 44% to 52%, as determined by standard ISO 2469. The combination of density and transparency is relevant because it can be used as an indicator of the compressibility level of the calendered glass paper. Calendered glass paper intended for use as a release liner substrate has a thickness S parallel to the surface normal of the paper. z Appropriately low compressibility is required because release liner is typically used as a backing material for a surface material including an adhesive layer. The surface material is formed into a label using a cutting die, which is pressed against the surface material with a predefined pressure. When the release liner substrate exhibits appropriately low compressibility, the blade cuts through the surface material to a predefined depth, allowing the surface material including the adhesive layer to be peeled off around the cut area without damaging the substrate. Therefore, the combination of density and transparency indicates the suitability of calendered glass paper as a release liner substrate for self-adhesive labels.

[0063] Objects and embodiments of the invention are described in the independent and dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] As used herein, the symbol S x 、S z and S y Refers to coordinate directions that are orthogonal to each other.

[0065] Figure 1 By way of example, a cross-dimensional structure of a release liner is shown, which includes a surface-sized paper substrate and a release coating.

[0066] Figure 2 By way of example, a method for producing calendered glass paper is described, wherein the paper is formed from a raw material containing non-recycled bleached chemical pulp and recycled pulp obtained from release liner glass paper. The calendered glass paper can be used as a substrate for release liner paper. The release liner glass paper can be recycled and reused in the method for producing calendered glass paper.

[0067] Figure 3 By way of example, a method for producing recycled pulp from release liner glassine is described. The method comprises a sorting stage, a caustic circuit, and a cleaning circuit for disintegrating the fibers and for separating and removing non-fibrous material from the fibers. In addition to its primary function, the method is designed to improve the fiber properties so that the recycled pulp can be used as raw material for glassine production without further refining.

[0068] Figure 4Shown are data comparing the average length (mm) of fibers in recycled pulp obtained from RGP and non-recycled pulp types measured using a Valmet Fiber Image Analyzer (Valmet FS5).

[0069] Figure 5 Shown are data comparing the average fiber width (micrometers) of fibers in recycled pulp obtained from RGP and non-recycled pulp types measured using a Valmet Fiber Image Analyzer (Valmet FS5).

[0070] Figure 6 Comparative data are shown for the average amount of hydrophobic particles in different pulp types when measured by means of flow cytometry.The particles have been further sorted based on the average diameter.

[0071] Figure 7 is when using McNett sieve as F according to SCAN-CM 6:05 <200 During fraction determination, the fines content at the machine chest of a paper machine is plotted as a function of the amount of recycled pulp obtained from RGP in the feedstock.

[0072] Figure 8 This graph shows the trend of water retention at the machine chest of a paper machine as a function of pulp content. The amount of recycled pulp obtained from RGP is negatively correlated with the water retention value. As the amount of recycled pulp obtained from RGP increases, the water retention value decreases.

[0073] Figure 9 The graph shows the trend of water discharge as a function of pulp content when measured as the main steam group pressure level on the paper machine. Adding recycled pulp obtained from RGP reduces the steam demand in the pre-dryer.

[0074] Figure 10 Comparative data on the development of paper width (cm) at the reel of a paper machine when measured using the ABB Web Imaging System (WIS) are shown. y The paper shrinkage above is negatively correlated with the amount of recycled pulp obtained from RGP in the paper.

[0075] Figure 11 Shows that when in horizontal S y Comparative data on the induced curl of calendered glassine paper when measured from test pieces. The results show that the magnitude of the curl is negatively correlated with the amount of recycled pulp obtained from RGP in the furnish. Test pieces containing a higher amount of recycled pulp obtained from RGP showed less curl.

[0076] Figure 12Comparative data of experimental studies performed with computational modelling are shown, where bleached chemical pulp from softwood in the fibre furnish was gradually replaced by BCP from hardwood and / or recycled pulp obtained from RGP, and where the BCP from hardwood had been produced from birch, eucalyptus or a combination of these. DETAILED DESCRIPTION

[0077] Release liner cellophane

[0078] Release liner glass paper, abbreviated as RGP, is used to describe release liners in which the substrate is calendered glass paper. Several aspects distinguish RGP from other paper types collected for recycling.

[0079] Glass paper refers to a specific type of paper suitable for use as a substrate for release liners. Glass paper is typically made from highly refined bleached chemical pulp that has been intensively calendered, resulting in a special combination of high density, strength, and clarity—beneficial properties for a release liner substrate.

[0080] Typical properties of defined calendered glass paper are

[0081] - a smoothness of at least 900 seconds per minute (ISO 5627),

[0082] -Equal to or less than 120g / m 2 Gram weight (ISO 536),

[0083] -Equal to or higher than 1.050g / cm 3 density (ISO 534), where density is the weight per grammage (ISO 536) per thickness (ISO 534:2011),

[0084] - a porosity equal to or less than 15,000 pm / Pas (ISO 11004) and

[0085] - a transparency equal to or higher than 40% (ISO 2469),

[0086] Parameter values correspond to the ISO standards cited in brackets.

[0087] Calendered glassine papers suitable for release liners typically have

[0088] - at 40g / m 2 Up to 120g / m 2 Gram weight within the range (ISO 536),

[0089] -at 1.050g / cm 3 to 1.190g / cm 3 Density within the range (ISO 534) and

[0090] - Transparency in the range of 40% to 60% (ISO 2469),

[0091] High transparency is preferred, such as in the range of 42% to 56%, most preferably in the range of 44% to 53% (ISO 2469).

[0092] The thickness of calendered glass paper indicates the thickness in micrometers after the calendering treatment before the release coating is applied. Unless otherwise stated, the thickness refers to the apparent thickness, measured as a single sheet thickness (ISO 534:2011). The glass paper is calendered with a multi-nip calender or a super calender before or after the primer coating is applied. Calendering enables the production of glass paper with a high density surface and high transparency, but may result in a moderate reduction in the bursting strength, tensile strength and tear strength of the glass paper. Calendering also reduces the thickness of the glass paper to a predefined target thickness. Glass paper is typically surface sized with a primer coating that is chemically compatible with the silicone polymer release coating. The primer coating can be applied on one or both sides, typically at 1 g / m 2 Up to 5g / m 2 Within the range, preferably 1g / m 2 Up to 2g / m 2 Primer coatings for cellophane typically contain water-soluble binders such as starch, polyvinyl alcohol and / or carboxymethyl cellulose.

[0093] refer to Figure 1 , which discloses, by way of example, a cross-sectional view of the structure of a release liner REL1, wherein the substrate GLA1 is glassine paper. Herein, release liner REL1 refers to an industrially manufactured paper product comprising a release coating on at least one side of a calendered paper substrate GLA1. The release coating is often referred to as a release coating SIL1. The release coating can be used as a protective layer for self-adhesive labels comprising a surface material and an adhesive layer.

[0094] A method for producing a release liner REL1 comprises applying a release coating SIL1 to a paper substrate GLA1. The detackifying properties of the release coating SIL1 are typically obtained with the aid of an addition-curing silicone system in the presence of a suitable metal catalyst, such as platinum. The addition-curing silicone system comprises a reactive silicone polymer and a silane hydride crosslinker comprising functional vinyl groups, which are provided in fluid form and can be applied at a rate of about 1 g / m 2The reactive silicone polymer is typically spread on the paper substrate GLA1. When the release coating on the paper is exposed to a crosslinking temperature (typically in the range of 65°C to 150°C), a chemical reaction is initiated that cures the release coating and anchors it to the substrate GLA1. This method makes it possible to obtain a release liner REL1 comprising a debonding and hydrophobic surface coating based on a cured silicone polymer.

[0095] When used as substrate GLA1 in a release liner REL1, calendered glass paper typically comprises paper PAP1 as a support layer and a primer coating POL1. The paper PAP1 is formed on a paper machine in the machine direction S x The machine direction refers to the direction in which the paper web and paper travel on the paper machine. The properties of paper can be determined in the machine direction as well as in the direction perpendicular to the machine direction S along the surface of the paper. x direction (called transverse S y ) is different. The paper is parallel to the surface normal of the paper in the direction S z Unlike many other paper types, the surface of glassine paper is typically not coated with mineral pigments, at least not in significant amounts. However, glassine paper often includes a primer coating POL1, such as a surface sizing applied to at least one side of the paper. The surface sizing improves the surface properties of the glassine paper, such as barrier properties. An advantageous primer coating POL1 is a water-soluble polyvinyl alcohol containing hydroxyl groups. Some of the hydroxyl groups of the polyvinyl alcohol may have been modified to contain reactive groups, such as vinyl groups. This enables the polymer to participate in the crosslinking reaction of the addition-curing silicone system. The primer coating POL1 thus improves the anchoring of the debonding surface coating to the paper substrate GLA1.

[0096] Due to the high-quality hydrophobic silicone polymers used in release coatings for glassine today, RGP typically has stable release values. Consequently, very little adhesive residue remains on the release liner surface after the self-adhesive label has been removed. Consequently, RGP used as a carrier for self-adhesive labels contains very little adhesive residue.

[0097] A method for producing glass paper for release liner

[0098] refer to Figure 2 , which shows by way of example a method for producing calendered glass paper, the method comprising

[0099] - Refining 11 non-recycled bleached chemical pulp BCP1 produced from hardwood;

[0100] - mixing 12 together, if necessary, non-recycled bleached chemical pulp produced from hardwood BCP1 with recycled pulp obtained from release liner glassine REP1 and / or crushed BRK1 and white water WHT1 to obtain raw material MIX1;

[0101] - forming 13 a paper web at the headbox of a paper machine; and

[0102] - Forming 14 calendered glassine paper on a paper machine.

[0103] Calendered glass paper is suitable for use as substrate GLA1 in method 15 for producing release liner REL1.

[0104] In the method for producing calendered glass paper, stock MIX 1 is obtained after two or more pulps are mixed 12 together during stock preparation. Mixing can be performed, for example, by homogenizing stock MIX 1 in a mixer. Stock refers to the pulp mixture from which paper is made on a paper machine. Stock can also be referred to as furnish. During papermaking, stock is fed to the forming section of the paper machine. When the paper web 13 is formed in the headbox of the paper machine, a pulp suspension is required to adjust the loading during stock preparation and control fiber bonding. Therefore, the stock is typically first fed to a machine chest. The machine chest is a consistency leveling unit that provides holding time to smooth out any variations in consistency before the stock is pumped to the headbox, where the stock is evenly distributed onto the moving wire in the forming section of the paper machine. Consistency is expressed as the percentage of oven dry mass to total mass. Oven dry mass consistency is 100%. The machine chest contains a valve system unit arranged to receive feedback from an online scanner measuring basis weight, which enables adjustment of the basis weight of the paper to be formed.

[0105] Stock preparation may include loading and refining 11 one or more pulp fractions BCP1, REP1 to provide a pulp mixture with desired properties. The pulp fractions BCP1, REP1 may be refined individually. Depending on the paper to be manufactured, the stock MIX1 may further contain non-fiber additives, such as sizing agents.

[0106] In the present context, when making glassine paper, the raw material contains a fiber furnish in which

[0107] - an amount of at least equal to or higher than 60% by weight of the fiber furnish is non-recycled bleached chemical pulp produced from hardwood BCP1, and

[0108] the remainder of the fiber furnish, which remainder is an amount at least equal to or higher than 5% by weight, being recycled pulp obtained from release liner glassine REP1, pulp mill broke BRK1 or a combination thereof,

[0109] The combined amount of pulp components BCP1, REP1, BRK1 forms up to 100 wt.-% of the fiber furnish, which can be determined according to ISO 9184-4 in combination with ISO 9184-1, as dry matter content according to SCAN-P 39:80.

[0110] In this document, non-recycled pulp refers to virgin pulp material introduced into the papermaking process for the first time. Non-recycled pulp is bleached chemical pulp produced from hardwood in the Kraft process. Raw material MIX1 may contain pulp mill broke BRK1, which refers to off-specification material produced on the papermaking machine, such as paper trimmings. Pulp mill broke can be recycled back into the papermaking process. Pulp mill broke may be refined before mixing 12. However, the broke has already undergone at least a portion of the papermaking process on the papermaking machine and is therefore not considered virgin pulp material when reintroduced into the papermaking process. Broke is also not obtained from release liner REL1.

[0111] When preparing the stock MIX1, white water WHT1 can also be used. White water is used to describe the slurry formed in the forming section of the paper machine when the fine particles present in the stock are discharged from the formed paper web WEB1 into a pit below the paper machine. The white water contains fine particles suspended in the stock. Fine particles are particles with a width in the range of 10 microns to 75 microns and a length of less than 0.2 mm. The white water can be recycled back to the stock preparation by means of a short circuit of the paper machine, or it can be processed and used elsewhere in the papermaking process. The amount of recycled fine particles defines the retention level, which describes the ability of the formed paper web to retain fine particles and therefore describes the balance between drainage and formability 13 of the paper web.

[0112] In the forming section of a paper machine, after a paper web WEB1 is formed 13 from a pulp suspension and dewatered, the web moves to a pressing section to further reduce its moisture content. The pressing section of a paper machine typically includes a plurality of rollers for guiding and / or pressing the paper web. The web then moves from the pressing section to the drying section of the paper machine. In the drying section, the web is heated to evaporate most of the remaining moisture in the web. After the drying section, the web can have a dry matter content level equal to or greater than 90% by weight, for example, in the range of 90% to 95% by weight, as measured according to SCAN-P 39:80. Thus, paper forming 14 includes steps for reducing the moisture content of the web in the pressing section and drying the web in the drying section, thereby forming paper from a raw material MIX1 comprising non-recycled bleached chemical pulp BCP1 from hardwood and recycled pulp REP1 obtained from release liner glassine.

[0113] Weight percent, abbreviated as wt%, is used to describe the weight fraction of a component in a composition. Weight percent of pulp is used to describe the weight fraction of pulp in a material. The weight percent of pulp in paper, when determined according to the SCANP-39:80 test method for dry matter content, represents the dry weight of the pulp in the dry paper. The dry weight of the sample is determined by weighing 20 grams of the sample on a weighing dish before and after oven drying at 105°C and eliminating the mass of the empty weighing dish from the measurement. The oven dried pulp has been oven dried at 105°C until its mass is constant and then cooled in a cooler to an ambient temperature of 25°C before weighing.

[0114] As mentioned above, the raw material used to make glassine paper in this context is different because it mainly contains bleached chemical pulp made from softwood and hardwood. Recycled pulp obtained from RGP, due to its origin, also contains bleached chemical pulp made mainly from softwood and hardwood. The surface of glassine paper is typically coated with a water-soluble polymer (such as polyvinyl alcohol) at 1 g / m 2 Up to 5g / m 2 When compared to other paper types (such as printing and writing papers), RGP typically does not contain significant amounts of mineral fillers or coatings, such as kaolin (i.e., aluminosilicate dihydrate), clay pigments, or calcium carbonate. Therefore, the ash content of RGP, which can be determined according to standard Tappi T 413 om-17, is usually very low, such as less than 3% by weight, and typically ranges from 1% to 3% by weight of the weight of the paper.

[0115] The properties of glassine paper are typically achieved through the use of highly refined BCP, supercalendering, and surface sizing agents. Supercalendering of glassine paper is typically carried out at temperatures ranging from 120°C to 200°C. The line pressure used to supercalender glassine paper is typically in the range of 300 kN / m to 500 kN / m. Glassine paper is usually moistened before calendering to enhance the effect. This increases the transparency of calendered glassine paper. The transparency of calendered glassine paper is significantly higher than the typical transparency of other paper types with similar grammage. Calendering increases the surface density and transparency of the paper. Calendering also reduces the specific volume and thickness of the paper. Calendered glassine paper is very strong, with a very smooth and dense surface and excellent barrier properties. A smooth and dense surface that resists penetration by many fluids is beneficial when applying a release coating to the paper surface.

[0116] As is evident from the properties disclosed above, calendered glass paper is not designed for printing or writing. Instead, calendered glass paper is typically used as a substrate GLA1 to form 15 a release liner REL1, such as Figure 2As indicated. Consequently, RGP rarely contains significant amounts of printing ink. Typically, RGP is essentially unprinted, compared to other paper types, which facilitates its recycling 16 into pulp REP1 in the process for making calendered glass paper. Consequently, RGP possesses a combination of desirable properties not available to the same degree in other paper types.

[0117] When considered from the perspective of the circular economy, RGP is a special material. When glassine paper is produced from non-recycled BCP, the fibers are subjected to very harsh conditions. At the papermaking machine, delignified hardwood and / or softwood fibers in bleached chemical pulp undergo repeated drying and wetting cycles in the presence of chemicals, relatively high temperatures and high pressures. These treatments lead to irreversible changes in the fiber structure, in particular the pores formed between the cellulose fibrils. This results in a reduction in the swelling capacity of the fiber. When compared with other types of fibers (such as, for example, from non-recycled bleached chemical pulp or broke), the morphology and swelling capacity of the fibers are different. This phenomenon is unique to chemical pulping fibers. Due to this phenomenon, which is called keratinization, fibers derived from glassine paper show lower bonding ability. When producing release liner, the fibers are coated with a hydrophobic silicone polymer and heated, which exposes the fibers to further modification.

[0118] A method for producing recycled pulp from release liner glassine

[0119] In the following, a method for producing recycled pulp from release liner glassine is disclosed, the method comprising: - sorting the release liner glassine for recycling;

[0120] - disintegration of the sorted release liner glassine and separation of non-fibrous material from the fibers in a first process stage known as the caustic circuit; and

[0121] - the removal of non-fibrous material from the fibers in a second process stage known as the cleaning circuit,

[0122] wherein the process, the caustic circuit and the cleaning circuit are configured to regulate the fibrillation of the pulp suspension so that the recycled pulp obtained from the release liner glassine paper has a pulp fibrillation and drainage within a range that enables the use of the recycled pulp obtained from RGP in the process for manufacturing glassine paper. Advantageously, the caustic circuit and the cleaning circuit are configured to regulate the fibrillation of the pulp so that the recycled pulp obtained from RGP can be used in the process for manufacturing glassine paper without further refining.

[0123] Recycled pulp obtained from RGP has a pH in the alkaline range, as measured from aqueous pulp extracts. An alkaline pH during the regeneration process softens the pulp, requiring less energy for refining. However, an alkaline pH can inhibit subsequent drying of the pulp. Therefore, the pulp pH can be adjusted as needed before mixing with other pulp components. Advantageously, when the recycled pulp obtained from RGP is used in a process for making calendered glass paper suitable as a substrate for release liner, the recycled pulp obtained from release liner glass paper has a pH in the range of 6.0 to 9.1. Preferably, the pH is in the range of 7.0 to 8.5, as a high alkaline pH can inhibit the operation of cationic UV-curable silicone systems. Preferably, the pH is in the range of 7.5 to 8.2, thereby optimizing the drying and compatibility of the recycled pulp for use in glass paper production.

[0124] The recycled pulp obtained from RGP is refined very quickly compared to non-recycled pulp components. The recycled pulp obtained from RGP also has a relatively high SR number compared to non-recycled bleached chemical pulp that has not been refined. Therefore, the recycled pulp obtained from RGP can be used in glass paper production without further refining. When the fibrillation and drainage properties of the recycled pulp obtained from RGP have been pre-adjusted to suitable levels, the recycled pulp obtained from RGP can be directly mixed with other non-recycled pulp components in the process for making glass paper. Advantageously, the recycled pulp obtained from RGP has an SR number equal to or higher than 25, such as in the range of 25 to 65, preferably in the range of 30 to 60, and most preferably in the range of 40 to 55, when measured according to ISO 5267-1.

[0125] Recycled pulp obtained from RGP contains average fiber lengths in the same range as non-recycled BCP made from hardwood. However, the average fiber length of recycled pulp obtained from RGP is significantly less than the average fiber length of non-recycled BCP made from softwood or pulp mill broke used for glassine production. The amount of virgin fiber in pulp obtained from RGP also differs from that in non-recycled BCP. When measured by automated optical analysis using unpolarized light according to ISO 16065-2:2014, recycled pulp obtained from RGP contains fibers derived from recycled pulp having a length of less than 200 microns in an amount equal to or greater than 10%, such as in the range of 10% to 30%, preferably in the range of 12% to 20%, and most preferably in the range of 15% to 17%. Fibers of recycled pulp obtained from RGP typically have an average fiber width of less than 25 microns, preferably in the range of 19 to 25 microns, most preferably in the range of 19 to 21 microns, when determined by automated optical analysis using unpolarized light according to ISO 16065-2:2014.

[0126] Fiber furnish analysis according to ISO 9184-4 in conjunction with ISO 9184-1 can be used for fiber identification and to determine the fiber properties of a given pulp. Combined with pulp drainage analysis, such as the measurement of the pulp water retention value and / or SR number, these analyses distinguish between recycled pulp obtained from release liner glassine.

[0127] Empirical studies have shown that recycled pulp obtained from RGP has very favorable properties for glassine paper production throughout the entire manufacturing process at the paper machine. The fibers of recycled pulp obtained from RGP are less accessible to water molecules. Consequently, recycled pulp obtained from RGP inhibits moisture absorption by the raw material. Recycled pulp obtained from RGP has a low water retention value, typically lower than that of non-recycled BCP. Therefore, the amount of recycled pulp obtained from RGP can be used to control the dry matter content of the raw material when forming the paper web. The reduced ability of recycled pulp obtained from RGP to absorb moisture has also led to enhanced dewatering of the paper web in the press section of the paper machine. Consequently, upon entering the coal drying section, the paper web contains less moisture that needs to be evaporated. Consequently, less steam pressure is required, which improves the energy efficiency of the coal drying section during paper production.

[0128] The combined effects of reduced refining, improved dewatering, and more efficient coal drying can be observed by measuring the water retention and drying behavior of the paper web. For example, as the amount of recycled pulp obtained from RGP in the raw material increases, the water retention value decreases. This indicates that less water needs to be removed in the press section during glass paper production. Pulp analysis from the paper mill further shows that when using a McNett sieve as a F according to SCAN-CM 6:05 <200 When fractions were measured, replacing non-recycled BCP with recycled pulp derived from RGP in the pulp mixture resulted in an increase in the fines content of the pulp mixture. This suggests that recycled pulp derived from RGP can be used to adjust the quality of the paper web formed on the paper machine. Experimental results indicate that this has a positive impact downstream in the glassine paper production process. Drainage is related to the surface condition and swelling of the fibers and is an indicator of the amount of mechanical processing the pulp has undergone. Paper webs containing recycled pulp derived from RGP exhibit improved drainage on the paper machine. A higher amount of recycled pulp derived from RGP in the feedstock correlates with improved drainage, resulting in lower steam pressure required for drying. Surprisingly, when drying glassine paper, a 0.1 bar reduction in steam pressure was achieved at a composition of 5% by weight of recycled pulp derived from RGP. At a composition of 15% by weight of recycled pulp derived from RGP, steam pressures of less than 0.3 bar could be used for drying glassine paper. Consequently, significant energy savings can be achieved.

[0129] Furthermore, off-line analysis at the paper machine indicated that the produced paper exhibited less shrinkage and less variability in grammage in the cross-machine direction at the paper machine, which correlated with the amount of recycled pulp obtained from RGP. The amount of shrinkage is an indicator of dimensional stability. Less variability in grammage in the cross-machine direction at the paper machine is an indicator of a more uniform product. Therefore, calendered glass paper containing recycled pulp obtained from RGP exhibited improved quality characteristics. Experimental results also demonstrated reduced curl in paper samples containing recycled pulp obtained from RGP. The improved properties of calendered glass paper are important when considering the use of glass paper as a substrate onto which the release coating is subsequently applied and cured.

[0130] Recycled pulp obtained from RGP can be used to replace non-recycled BCP. Non-recycled BCP may also be referred to herein as virgin BCP. When recycled pulp obtained from RGP is used in place of non-recycled BCP, the refining of non-recycled BCP during the glass paper manufacturing process can be reduced. Reducing the refining of non-recycled BCP preserves fiber quality. In particular, non-recycled BCP can improve internal bond strength during web formation. This is particularly advantageous in the production of calendered glass paper, where the fiber furnish includes BCP from eucalyptus, where a milder refining process helps preserve the fiber structure.

[0131] When manufacturing glass paper on a paper machine, the retained quality of BCP fibers can be used to compensate for the negative impact that damaged fibers in recycled pulp obtained from RGP may have on paper formation. Advantageously, the retained quality of fibers in non-recycled BCP is used to increase the proportion of recycled pulp obtained from RGP in the glass paper composition. Thus, when recycled pulp obtained from RGP is used together with non-recycled BCP in a process for manufacturing glass paper, a synergistic effect is felt. The composition of the calendered glass paper advantageously contains recycled pulp obtained from RGP in an amount equal to or higher than 5% by weight, more preferably equal to or higher than 10% by weight, most preferably equal to or higher than 15% by weight, or equal to or higher than 30% by weight, as measured as dry matter content according to SCAN-P 39:80, such as in the range of 5% to 40% by weight, preferably in the range of 10% to 35% by weight, and most preferably in the range of 15% to 30% by weight.

[0132] When manufacturing white glass paper, the recycled pulp obtained from RGP can be produced without bleaching. Therefore, calendered glass paper suitable for use as a substrate for release liner can contain fibers from non-recycled bleached chemical pulp produced from hardwood, as well as recycled pulp obtained from release liner glass paper, which recycled pulp has not been bleached. Advantageously, the recycled pulp obtained from RGP is produced using white RGP grades. White RGP does not contain colorants. White RGP grades can be used to produce white calendered glass paper. In this context, paper whiteness and whiteness refer to the CIE L*, a*, b* color space coordinate values, where

[0133] -L* is in the range of 92 to 98,

[0134] -a* is in the range of -4 to +2, and

[0135] -b* is in the range of +3 to +9,

[0136] The values are measured according to ISO 5631:2022 using standard illuminant D65 and a 10° standard observer by means of the diffuse reflectance method with specular gloss eliminated.

[0137] Thus, the recycled pulp obtained from white release liner glass paper can be used in a process for making white calendered glass paper suitable for use as a substrate for release liner.

[0138] refer to Figure 3 . Release liner glassine has a common processing history. This enables the use of RGP as raw material in a regeneration process, which can be arranged to produce a pulp with excellent properties. In order to obtain a recycled pulp of sufficient quality for the method for manufacturing glassine, the raw material for the regeneration process should contain at least 75% by weight, more preferably at least 85% by weight, most preferably at least 90% by weight of release liner glassine. Advantageously, the raw material for the regeneration process consists essentially of release liner glassine. Therefore, a method for manufacturing recycled pulp from release liner glassine comprises a step for sorting RGP for regeneration.

[0139] A method for producing recycled pulp from release liner glassine includes a sorting stage 20 for separating RGP from other papers; a first process stage, designated as a caustic circuit CL1, which has the primary function of disintegrating the RGP into pulp and separating non-fibrous material from the fibers; and a second process stage, designated as a cleaning circuit NL1, which has the primary function of separating pulp fibers from non-fibrous material, particularly silicone particles derived from the release coating. The caustic circuit CL1 provides conditions under which the pulp fibers can swell and fibrillate. Cured silicon-based organic polymers, particularly polydimethylsiloxane, are generally water-resistant and relatively chemically inert. Consequently, under RGP regeneration conditions, as disclosed herein, the release coating typically breaks down into fragments, hereinafter designated as silicone-based particles. In addition to their primary function, the caustic circuit CL1 and the cleaning circuit NL1 are configured to regulate the fibrillation of the pulp suspension so that the recycled pulp obtained from the release liner glassine paper REP1 has a pulp drainage within a range that enables the recycled pulp obtained from RGP to be used in a process for manufacturing glassine paper without further refining. The caustic circuit CL1 and the cleaning circuit NL1 provide a means of controlling the chemical load and temperature of the regeneration process, as well as a means of regulating the consistency of the suspension.

[0140] Due to its industrial use in high-speed labeling processes, RGP can be collected in large quantities directly from industrial users. Therefore, advantageously, sorting of the RGP occurs at the location where, for example, the release liners REL1 and REL2 are used during the labeling process and converted into recyclable release liner waste. For example, polyethylene-coated kraft paper can be separated and excluded from recycling at this point. Unlike water-soluble polymers or mineral coatings, polyethylene film does not dissolve into a suspension and is therefore challenging to recycle. Alternatively, sorting can be performed later at a sorting unit, for example by using visual inspection, so that the release liner REL1 is separated from the other paper components REL2 and non-paper components. To the extent possible, non-paper components are rejected before entering the RGP recycling process. Non-paper components refer to objects that typically become part of the paper recycling process unintentionally due to material handling. Non-paper components do not adhere to the paper and are rejected during the recycling process. Examples of non-paper components are plastic and film components, as well as fragments of metal, glass or sand.

[0141] The sorted RGP can be further separated based on the hue of the paper. For example, light RGP hues (such as white and yellow hues) can be separated from dark RGP hues (such as blue and brown RGP hues). Advantageously, white RGP grades where the paper furnish does not contain colorants are separated from non-white RGP grades (such as yellow, blue and brown RGP grades). The CIELAB color space can be used to measure the color of the RGP and to reject non-light grades or non-white RGP grades. In this context, white glassine paper refers to the CIE L*, a*, b* color space coordinate values of the paper, where

[0142] -L* is in the range of 92 to 98,

[0143] -a* is in the range of -4 to +2, and

[0144] - b* is in the range of +3 to +9, preferably in the range of +5 to +7,

[0145] Values are measured from paper samples using the diffuse reflectance method with specular gloss eliminated, according to ISO 5631:2022, using standard illuminant D65 and a 10° standard observer. Sorting RGP based on its hue offers the advantage of allowing the production of recycled pulp from RGP without bleaching. Therefore, calendered glassine paper suitable as a substrate for release liner can contain fibers from non-recycled bleached chemical pulp produced from hardwood and softwood, as well as recycled pulp from release liner glassine paper, which has not been bleached.

[0146] Alternatively or in addition, sorting can be performed mechanically, for example, using automated image analysis. The automated image analysis system may include, for example, a detection unit, a control unit, and a sorting unit configured to detect RGPs based on particle shape, size, and contrast, and to separate them from other paper products and non-paper products. The detection unit may include optical instruments capable of detecting wavelengths in the visible spectrum for detecting and identifying the color of the paper. This may be supplemented by instruments capable of detecting near-infrared light, which can provide further information about the material properties in the paper. Automated image analysis can be configured to assess paper quality based on multiple parameters, such as paper whiteness, brightness, color shading, transparency, or contrast. Compressed air and nozzles operating on a conveyor belt can be used to separate rejected and accepted material. Advantageously, after sorting, the material contains RGPs in the range of 75% to 100% by weight, preferably 85% to 100% by weight, and most preferably 90% to 100% by weight, based on the weight of the recycled paper component. Ideally, the material sorted for recycling consists essentially of RGPs.

[0147] The caustic circuit CL1 comprises a high-consistency pulping unit 21, a screening unit 22, a cleaning unit 23, and a dewatering unit 24. The high-consistency pulping unit 21 is arranged to operate in batch mode, which facilitates adjustment of pulping conditions. When RGP and clean water F1 are fed to the high-consistency pulper, a pulp suspension is formed. The consistency of the pulp suspension can be adjusted by the amount of clean water F1, which can be obtained from another process. Clean water F1 can be fresh water. If desired, the consistency of the pulp suspension can be further adjusted by reusing process waters F2, F3, and F4 downstream in the regeneration process. The process water circulating within the circuits CL1 and NL1 can be further used to improve fiber recovery within the circuits CL1 and NL1. To effectively disintegrate the RGP, the consistency of the material during pulping should be above 15% by weight, preferably above 18% by weight, such as in the range of 20% to 30% by weight, and advantageously in the range of 20% to 25% by weight.

[0148] RGP pulping is carried out under alkaline conditions to promote the disintegration of cellulose fibers from the RGP, as RGP includes a dense surface, a polymer primer coating, and a release coating. Advantageously, the pH is maintained in the range of 8.5 to 10 during pulping. The pH can be adjusted by adding NaOH (known as caustic soda). Caustic soda reacts with the hydrogen groups of the fibers and promotes fiber swelling (known as alkali swelling), which relaxes the fiber network of the RGP. Caustic soda also acts as an activator for hydrogen peroxide, which can be used to promote oxidative bleaching when the pulp suspension contains colorants (e.g., blue colorants from non-white grades of RGP). Hydrogen peroxide is also used to prevent yellowing during pulping. Typically, hydrogen peroxide is added in a range of 0.5% to 2% by weight. Sodium silicate is typically added to buffer the pH of the pulp suspension and prevent the pH of the suspension from rising excessively at the beginning of pulping. Therefore, sodium silicate contributes to the alkalinity of the pulp suspension, making conditions suitable for caustic swelling. Sodium silicate can also be used as a stabilizer for hydrogen peroxide. Sodium silicate can further improve the release of the release liner from the fibers. Typically, sodium silicate is added in an amount ranging from 1% to 6% by weight. In addition to sodium silicate, a saponifying agent (typically a fatty acid such as palmitic acid or stearic acid) is used to promote the release of silicone-based particles and other hydrophobic impurities from the fibers. The fatty acid first reacts with the caustic soda and then with the calcium ions present in the pulp suspension to form calcium soap, which is insoluble in water and finely dispersed in the aqueous phase. The highly hydrophobic soap particles help keep the pulping fibers in the pulp suspension and the detached hydrophobic particles (such as silicone-based particles) separated from each other. Typically, the fatty acid is used in an amount ranging from 0.1% to 1.5% by weight of the RGP. The fatty acid dosage is advantageously matched to the water hardness so that the amount of fatty acid is substantially equal to the amount of calcium ions present in the suspension.

[0149] Depending on the HC pulper type, the pulping operation time can be adjusted. The total operation time (called pulping or residence time) is generally in the range of 30 minutes to 60 minutes, preferably at least 40 minutes, to ensure sufficient disintegration of the cellulose fibers. Typically, the temperature of the pulp suspension during pulping is at least 60°C, preferably at least 75°C, such as in the range of 60°C to 85°C. The primer coating of the RGP typically contains water-soluble polymers, such as partially or fully hydrolyzed polyvinyl alcohol, carboxymethyl cellulose and / or starch, which have a tendency to agglomerate at elevated temperatures. Although at least some of the water-soluble polymers can be dissolved during pulping and thus filtered out in a subsequent dewatering operation, the higher pulp suspension temperature, preferably at least 75°C, promotes agglomeration of any undissolved water-soluble polymer that has been detached from the fibers. Agglomerated polymer particles from the sizing agent or release coating are more easily removed in subsequent screening and cleaning operations.

[0150] Therefore, high consistency suspension, sufficient time, temperature and chemical additives such as hydrogen peroxide, sodium silicate (water glass) and caustic soda (NaOH) can be used to disintegrate and detach the fibers of RGP and induce caustic swelling despite fiber keratinization.

[0151] A coarse screening unit 22, such as a disc screen having a hole size equal to or less than 4 mm, such as in the range of 2 mm to 4 mm, preferably in the range of 2.0 mm to 3.0 mm, and most preferably in the range of 2.2 mm to 2.5 mm, is used to separate the particles from the pulper based on their size, form, and shape. The screen operates under pressure, and particles that pass through the holes are accepted, while other particles are rejected. This enables the removal of solid contaminants and non-paper components, such as sand and metal objects, as well as larger particle agglomerates, from the pulp suspension.

[0152] A high consistency cleaning unit 23 (such as a cleaner using a centrifugal field) is used to supplement the coarse screening to separate the pulp fibers from the contaminants based on specific gravity. A centrifugal cleaner can remove particles as small as 10 microns. In addition to heavy particles such as sand and metals, a centrifugal cleaner can also separate light particles present in the RGP, such as polymer particles, peel coating agglomerates, or residual adhesive stickies, when their density differs sufficiently from that of water. For example, PVA has a typical density of 1.19 g / cm at 25°C. 3 Up to 1.35g / cm 3 The density of the metal is in the range of 1.00 g / cm, which is significantly different from the density of water. 3The separation of high-density particles can be improved by increasing the pulp suspension temperature, which reduces the water density. The pulp suspension temperature during high-consistency cleaning is typically in the range of 30°C to 85°C, preferably in the range of 50°C to 85°C, to facilitate the cleaning of PVA. When using high-consistency detergents, pulp consistencies of 2% to 6% by weight are typically used. The consistency of the pulp suspension during cleaning can be adjusted by adjusting the pulping and screening conditions. If necessary, the consistency of the pulp suspension can be further adjusted by reusing process water F4 downstream in the regeneration process.

[0153] A dewatering unit 24, based on pressing or filtration, serves to mechanically remove process water F4 from the pulp suspension and increase the pulp consistency. Dewatering thus separates solids from the suspension. Preferably, a disc filter, a screw press, or a twin-wire press is used for effective circuit separation between the caustic circuit CL1 and the cleaning circuit NL1. High consistency enables effective dispersion in the cleaning circuit NL1, which can be used to adjust pulp fibrillation and drainability. Effective solids removal further enables the removal of dissolved sizing agents that have not been screened or removed from the pulp suspension. Pressing the pulp suspension at the dewatering unit 24 results in a thickened pulp suspension containing the fibers to be retained. Advantageously, at the end of the caustic circuit CL1, the pulp suspension is thickened to a consistency equal to or greater than 20% by weight, such as in the range of 20% to 50% by weight, preferably in the range of 25% to 40% by weight.

[0154] Cleaning circuit NL1 comprises a dispersion unit 25, a flotation unit 26, a second screening unit 27, a washing unit 28, and a dewatering unit 29. The dispersion unit is used to generate shear forces sufficient to detach remaining contaminants (such as silicone-based polymers) from the fibers and adjust the average size of the contaminant particles to below 100 microns, making them suitable for removal by flotation. The dispersion unit can be operated with a thickened pulp suspension received directly from the dewatering unit. The method may further include a dilution tank upstream of the dispersion unit for adjusting the consistency and / or temperature of the dewatered pulp suspension. Fresh water F1 and / or process waters F2 and F3 downstream of the regeneration process can be used to adjust the consistency of the dewatered pulp suspension. The process waters F2 and F3 downstream of the regeneration process can further be used to adjust the pH of the dewatered pulp suspension. The consistency of the dewatered pulp suspension provides a means for adjusting the amount of dispersing energy applied to the pulp suspension. Advantageously, a cone or disk disperser is used for dispersion instead of a kneader. Unlike kneaders, conical and disc dispersers operate under refining-like conditions. This enables efficient and simultaneous adjustment of pulp fiber properties, allowing at least some of the fiber properties of RGP fibers lost due to keratinization to be compensated during the RGP regeneration process. Consequently, recycled pulp properties, such as drainage and bulk, can be optimized for the process used to manufacture glassine paper. Conical and disc-type dispersers operate in such a way that there is a negative correlation between pulp fibrillation and temperature: a lower pulp suspension temperature at the inlet is associated with a higher reduction in fibrillation. Typically, when using a pulp suspension with a consistency in the range of 25% to 40% by weight, the temperature of the pulp suspension at the disperser inlet is in the range of 50°C to 130°C, preferably in the range of 50°C to 85°C. Therefore, in addition to the amount of specific energy consumed (SEC), pulp fibrillation and drainage can also be adjusted during dispersion by controlling pulp consistency and temperature. Typically, a SEC in the range of 30 kWh / t to 150 kWh / t, preferably in the range of 40 kWh / t to 100 kWh / t, most preferably in the range of 45 kWh / t to 90 kWh / t may be used during dispersion to obtain a pulp having an SR number equal to or higher than 25, such as in the range of 30 to 55, when measured according to ISO 5267-1.

[0155] The flotation cell 26 is used to remove hydrophobic particles from the pulp suspension using air bubbles, which collide and adhere to the particles. Fresh water F1 and / or process waters F2, F3 downstream of the regeneration process are used to adjust the consistency of the pulp suspension for flotation. Typically, a pulp suspension with a consistency of less than 2% by weight, such as in the range of 0.5% to 1.5% by weight, is used for flotation. The temperature of the pulp suspension during flotation is typically in the range of 40°C to 70°C. Advantageously, during flotation, the pH is maintained alkaline, in the range of 7 to 10, preferably equal to or above 8.5, such as in the range of 8.5 to 10. The pH can be adjusted and buffered by adding suitable alkaline agents, such as caustic soda and sodium silicate. Soaps, such as sodium soaps, or other surfactants containing hydrophilic and hydrophobic moieties are added to act as collectors. Collectors are used to promote agglomeration of the organosilicon particles and facilitate their loading and flotation. During flotation, a low water hardness in the range of 10 dH to 20 dH is preferred to further promote agglomeration.The flotation unit 26 may comprise several flotation cells arranged in a series.

[0156] The second screening unit 27 is used for fine screening to separate debris from the fibers from the flotation, in particular silicone particles from the release coating. The fine screening can use a slotted screen with a mesh size equal to or less than 0.25 mm, such as in the range of 0.10 mm to 0.25 mm, preferably in the range of 0.10 mm to 0.20 mm. The screening is operated under pressure, and the pulp suspension that passes through the mesh is acceptable.

[0157] A washing unit 28, such as a belt filter type machine, is used to separate particles from the pulp suspension by size. Washing is typically performed using a set of two or more rollers under wire pressure, with the wire having a mesh size ranging from 36 to 60 microns, so that particles with a maximum size of less than 30 microns are removed. Typically, a pulp suspension with a consistency equal to or less than 2% by weight, such as in the range of 0.5% to 2% by weight, is used at the inlet of the washing unit. Clean water F1 is used to wash the filtered fiber mat and adjust the consistency of the suspension during washing. The filtrate is used to remove dissolved contaminants. The filtrate can be used as process water F3 upstream of the regeneration process.

[0158] After washing, a second dewatering unit 29, based on pressing or filtration, is used to mechanically remove process water F2 from the washed pulp suspension. Due to the relatively low consistency of the pulp after the washing unit, a twin-wire press is preferred, allowing the pulp consistency to be efficiently increased for transport or storage. Advantageously, at the end of cleaning loop NL1, the pulp suspension is thickened to a consistency equal to or higher than 30% by weight, preferably equal to or higher than 40% by weight, such as in the range of 30% to 50% by weight. Thus, the recycled pulp obtained from release liner glass paper REP1 can then be used in a process for producing calendered glass paper.

[0159] As a transition to the above disclosure, and with reference to Figure 2 and Figure 3 The regeneration process 16 is arranged to include operations and conditions that optimize the separation of fibers from non-fiber components in the pulp suspension. At the same time, the caustic circuit and the cleaning circuit are configured to adjust the fibrillation of the pulp suspension so as to obtain a pulp drainage property that is within a range that allows the recycled pulp obtained from the RGP to be used in a process for making glass paper, preferably without further refining.

[0160] Thus, the regeneration process 16 is arranged to improve the fiber properties so that the recycled pulp REP1 can be used to prepare raw material for glass paper manufacturing without further refining. These operations and conditions homogenize the pulp and develop properties such as pulp fibrillation, drainage and pH, which improve the quality of the pulp used in the process for manufacturing glass paper.

[0161] A pulp consistency in the range of 30% to 50% by weight is advantageous because the pulp fibers are not exposed to further drying treatments that could lead to further keratinization. A pulp consistency in the range of 30% to 50% by weight is also advantageous when the recycled pulp REP1 is mixed with different pulps during raw material preparation. However, when preparing recycled pulp for storage, the dewatering unit 29 can be supplemented with a drying system (such as a fluffer) to increase the dryness of the pulp so that a pulp consistency equal to or higher than 80, such as in the range of 80% to 90% by weight, is obtained.

[0162] Properties of recycled pulp obtained from release liner glassine

[0163] As mentioned above, recycled pulp obtained from RGP typically has a neutral or alkaline pH, as measured from an aqueous pulp extract. An alkaline pH during regeneration is preferred because a higher pH softens the pulp and promotes flotation. Pulp alkalinity also facilitates changes in pulp fibrillation and drainage. Recycled pulp obtained from RGP requires less energy for refining when it has an alkaline pH. However, if desired, the pH can be adjusted before using the recycled pulp.

[0164] Recycled pulp obtained from RGP differs from non-recycled BCP due to the degree of fiber keratinization. This can be measured, for example, by the water retention value (abbreviated as WRV) according to ISO 23714:2014 (en). WRV is an empirical measure of the ability of a pulp sample to retain water. Typically, the WRV of recycled pulp obtained from RGP is low, such as in the range of 1.3 g / g to 1.6 g / g.

[0165] Recycled pulp obtained from RGP is also distinguished by its drainage resistance, which is a measure of the fibrillation of the pulp and can be determined by the Schopper-Riegler test. The SR number is a measure of the degree of fibrillation in the recycled pulp REP1. Recycled pulp obtained from RGP can have an SR number equal to or higher than 25, such as in the range of 25 to 65, when measured according to ISO 5267-1. Typically, recycled pulp obtained from RGP has an SR number equal to or higher than 30 if the aqueous extract in which the measurement is made is process water containing electrolytes. When the drainage resistance of dry pulp is measured with standard water according to ISO 5267-1 in combination with ISO 14487, the SR number can be higher, such as equal to or higher than 40, because the concentration of electrolytes (salts) in the pulp suspension affects the drainage. Regardless of the initial SR number, the SR number of recycled pulp obtained from RGP develops very quickly during refining. This is a characteristic of recycled pulp obtained from RGP that can be used to distinguish recycled pulp obtained from RGP from other non-recycled pulp components used in glassine paper. Table 2 (below) shows, by way of example, the development of the SR number (°SR) in recycled pulp obtained from RGP as a function of the specific energy consumption (SEC) in kWh / t. In this example, a specific edge load (SEL) of 0.3 J / m was applied using a Voith-Sulzer laboratory refiner with 40D hardwood boards. Before refining, the recycled pulp obtained from RGP exhibited an SR number of 32.

[0166] Table 2. Development of SR in recycled pulp obtained from RGP according to SEC (kWh / t).

[0167] SEC (kWh / t) °SR 0 32 10 37 20 43 30 48 40 54 50 58 60 63 70 67

[0168] Advantageously, the recycled pulp obtained from the release liner glassine paper has a °SR equal to or higher than 25, such as in the range of 25 to 65, preferably in the range of 30 to 60, most preferably in the range of 40 to 55, when measured according to ISO 5267-1, before mixing in the process for making calendered glassine paper.

[0169] Advantageously, when the recycled pulp obtained from RGP is used in a process for manufacturing calendered glass paper suitable for use as a substrate for release liner, the recycled pulp obtained from the release liner glass paper has a pH in the range of 6.0 to 9.1. Preferably, the pH is slightly alkaline, such as in the range of 7.0 to 8.5. Recycled pulp obtained from release liner glass paper with an alkaline pH requires less energy to refine the fibers. A high alkaline pH can inhibit the operation of cationic UV-curable silicone systems. Preferably, the pH is in the range of 7.5 to 8.2, thereby optimizing the drying and compatibility of the recycled pulp for glass paper production. When determining the pH of a dried pulp sample, standard ISO 6588-2 (2020) can be used. When determining the pH of a pulp suspension sample from a paper machine, the pH can be measured directly from the pulp sample (when the consistency is 5% by weight or less) or from the filtrate (when the consistency is higher than 5% by weight). As used herein, filtrate refers to an aqueous extract. When measuring the pH of dry pulp, 2 grams of dry pulp are cut into pieces so that each piece has a maximum dimension of 1 cm. The cut pieces are mixed with 100 ml of deionized water to disperse the pulp, resulting in a suspension having a pulp concentration of 2% by weight. The sample thus obtained is heated to boiling point and boiled for 60 minutes. After boiling, the sample is cooled so that the sample temperature is within the range of 20°C to 25°C and filtered through a filter with a 200-mesh mesh, for example, using a Büchner funnel, to obtain a filtrate separated from the pulp. The pH is measured from the filtrate thus obtained.

[0170] The pulp pH is measured from an aqueous extract having a temperature in the range of 20° C. to 25° C. with the aid of a pH meter using two buffer solutions having respectively pH 4 and pH 7. Suitable pH meters are, for example, pH meter CG840 with electrode N 1042A, Knick pH meter 766 Calimatic with electrode SE 103 or Mettler-Toledo MP 120, which are used according to the manufacturer's instructions.

[0171] When recycled pulp is produced from release liner glassine as disclosed above, the removal of silicone-based particles is incomplete. The recycled pulp obtained from RGP still contains traces of the cured release coating in the form of very small, chemically quite inert particles. The maximum particle size of the silicone-based particles is typically in the range of 100 to 150 microns and is limited by the mesh size of the fine screening used in the cleaning circuit NL1. Although detectable, the amount of silicone-based particles in recycled pulp obtained from RGP has not been observed to cause problems when producing calendered glassine on a paper machine. The amount of silicone-based particles can be measured using energy-dispersive X-ray spectroscopy from test samples burned at 900°C, according to Tappi Standard T 413 for the detection of silicon oxides. Typically, calendered glassine paper comprising recycled pulp from RGP contains silicon in an amount equal to or less than 0.3 wt.-%, preferably equal to or less than 0.28 wt.-%, most preferably equal to or greater than 0.25 wt.-%, such as in an amount ranging from 0.01 wt.-% to 0.3 wt.-%, as can be determined as dry matter content from a paper sample burned at 900° C. using energy dispersive X-ray spectroscopy according to Tappi standard T 413.

[0172] Experimental studies

[0173] refer to Figures 4 to 11 An experimental study was prepared to evaluate the properties of recycled pulp obtained from RGP and to determine its effect in a process for manufacturing calendered glass paper.

[0174] Experimental Study 1 - Properties of Recycled Pulp Obtained from RGP

[0175] In the first experimental study, the pulp properties of recycled pulp obtained from RGP were measured and compared with the properties of non-recycled bleached chemical pulp used for glassine production at the paper mill and pulp mill broke. The pulp types and their abbreviations used in the experimental study are listed below:

[0176] BCP SW Northern Bleached Softwood Kraft Pulp (Coniferous Tree)

[0177] BCP HW bleached hardwood kraft pulp (eucalyptus)

[0178] BCP SW rf. Paper mill refined BCP SW (SEC 240kWh / t)

[0179] BCP HW rf. Paper mill refined BCP HW (SEC 135kWh / t)

[0180] Millbroke pulp mill broke from glassine production

[0181] REP1 Recycled pulp obtained from RGP

[0182] The consistency of the pulp in the study was 4 wt%. The properties of non-recycled bleached chemical pulp were measured before and after refining in order to compare the properties of recycled RGP and non-recycled bleached chemical pulp.

[0183] Pulp analysis

[0184] The pH of the pulps disclosed above was measured from an aqueous pulp extract according to ISO 6588-2 (2020). The results are shown in Table 3 (below).

[0185] Table 3. pH measured for pulp samples.

[0186] sample pH BCP SW 5.3 BCP HW 5.1 REP1 6.8 Paper mill broke 5.3

[0187] The results represent the average value of measurements, during which the pH of recycled pulp obtained from RGP varied within the range of 6.8 to 7.3. The pH measured in recycled pulp obtained from RGP was significantly higher than that measured in non-recycled chemical pulp made from softwood or hardwood. The pH measured in recycled pulp obtained from RGP was also significantly higher than that in pulp mill broke.

[0188] The pulp as disclosed above is further analyzed by means of a fiber furnish analysis according to ISO standards ISO 9184-1 and 9184-4:1990. Fiber furnish analysis enables the identification of papermaking fibers from a sample. The analysis can further be used to quantify the average size of different fiber types detected in a sample. Wood species used in pulp can be distinguished by a comparative method, in which sample fibers are compared with known reference fibers. The Valmet fiber image analyzer (Valmet FS5) is an example of an apparatus that can be used to perform fiber furnish analysis according to the manufacturer's instructions. For example, automated optical analysis (such as an ultra-high resolution (UHD) camera system equipped with image analysis software) can be used to acquire a grayscale image of the sample, from which the properties of the fibers in the sample can be determined. According to the ISO 16505-2 standard, a grayscale image can be acquired from a sample placed in a transparent sample holder (such as a cuvette) using a focal depth of 0.5 mm. The Valmet Fiber Image Analyzer (Valmet FS5) can further be used to determine fiber dimensions such as fiber length and fiber width, and length-weighted distribution of pulp fibers by means of automated optical analysis using unpolarized light according to ISO 16065-2:2014.

[0189] refer to Figure 4, which shows the average length (in millimeters) of fibers in recycled pulp obtained from RGP and other pulp types, measured as length-weighted average fiber length using a Valmet fiber image analyzer (Valmet FS5). The recycled pulp obtained from RGP contained an average fiber length of 0.94 mm. Non-recycled BCP made from hardwood contained an average fiber length of 0.86 mm, which was reduced to 0.84 mm during refining. Therefore, the average fiber length of the recycled pulp obtained from RGP was higher than the average fiber length of the non-recycled BCP made from hardwood. Non-recycled BCP made from softwood contained an average fiber length of 2.10 mm, which was reduced to 2.00 mm during refining. Therefore, the average fiber length of the recycled pulp obtained from RGP was significantly smaller than the average fiber length of the non-recycled BCP made from softwood. Pulp mill broke had an average fiber length of 1.04 mm.

[0190] Further references Figure 5 , which shows comparative data of the average fiber width (micrometers) of fibers in recycled pulp obtained from RGP and other pulp types measured using a Valmet fiber image analyzer (Valmet FS5). The recycled pulp obtained from RGP comprises an average fiber width of 20 micrometers. Non-recycled BCP made from hardwood comprises an average fiber width of 18 micrometers, which increases to 19 micrometers during refining. Therefore, the average fiber width of the recycled pulp obtained from RGP is greater than the average fiber width of the non-recycled BCP made from hardwood. Non-recycled BCP made from softwood comprises an average fiber width of 28 micrometers, which increases to 29 micrometers during refining. Therefore, the average fiber width of the recycled pulp obtained from RGP is significantly less than the average fiber width of the non-recycled BCP made from softwood. Pulp mill broke has an average fiber width of 20 micrometers.

[0191] Therefore, the average fiber length and width of recycled pulp obtained from RGP are closer to the average fiber length of non-recycled BCP made from hardwood or broke, but are significantly different from the average fiber length of non-recycled BCP made from softwood.

[0192] According to the manufacturer's instructions, the length-weighted distribution of pulp fibers was further analyzed using a Valmet fiber image analyzer (Valmet FS5). In the analysis, fibers were defined as the pulp fraction comprising particles having a width in the range of 10 microns to 75 microns and a length in the range of 0.2 mm to 7.0 mm. Fines were defined as the pulp fraction comprising particles having a width in the range of 10 microns to 75 microns and a length less than 0.2 mm. Fibrils were defined as the pulp fraction comprising particles having a width less than 10 microns and a length longer than 0.2 mm. Flakes were defined as the pulp fraction comprising particles having a width less than 200 microns and a length less than 0.2 mm. Fibrils are typically particles generated from the secondary walls of the wood cell layer structure, which can improve the adhesive properties of the pulp due to their elongated shape. Flakes are typically particles generated from the middle glue layer and primary walls of the wood cell layer structure, which tend to reduce the adhesive properties of the pulp. The flakes scatter light and can therefore affect the optical properties of the pulp by increasing opacity and reducing transparency.

[0193] The fines content in bleached chemical pulps, such as bleached kraft pulp, naturally varies depending on the wood species used. The fines content in pulp also changes due to pulp processing, such as refining and recycling, as disclosed above. The length-weighted distribution of fines is a fundamental property of pulp that, among other things, influences the formability of the paper web during manufacturing. Pulp properties also have an impact on the tensile strength, bursting strength, folding endurance, and tear resistance of the paper.

[0194] The analysis results show that the amount of fines in the recycled pulp obtained from RGP, as measured as length-weighted average fiber length by automated optical analysis using unpolarized light in accordance with ISO 16065-2:2014, was 16.3% of the total amount of fibers in the recycled pulp. The amount of fines in the recycled pulp obtained from RGP is comparable to that in non-recycled bleached chemical pulp refined from paper mills made from hardwood. Surprisingly, the amount of virgin fiber in the recycled pulp obtained from RGP was much higher than that in non-recycled bleached chemical pulp refined from paper mills made from hardwood, but lower than that in non-recycled bleached chemical pulp refined from paper mills made from softwood. The results indicate that recycled pulp obtained from release liner glassine contains particles of recycled pulp originating from recycled pulp having a length of less than 200 microns in an amount equal to or greater than 10%, such as in the range of 10% to 30%, preferably in the range of 12% to 20%, and most preferably in the range of 15% to 17%.

[0195] The Valmet Fiber Image Analyzer also provides results on the amount of fiber deformation in the pulp, such as fiber kinks and fiber curl. Fiber kinks and curl tend to reduce the tensile strength of the resulting paper due to a reduction in the bonding ability of the fibers in the fiber network. It is noteworthy that the number of kinks in the recycled pulp obtained from RGP is 32,500 1 / m, which is significantly higher than the number of kinks in non-recycled bleached chemical pulp after refining or in pulp mill broke. The number of kinks in non-recycled bleached chemical pulp made from hardwood is 28,800 1 / m before refining and 2,310 1 / m after refining. The number of kinks in non-recycled bleached chemical pulp made from softwood is 3,410 1 / m before refining and 27,300 1 / m after refining.

[0196] In the experimental study, the results of measured fiber analyses of recycled pulp obtained from RGP, non-recycled bleached chemical pulp (before and after refining at the paper mill), and pulp mill broke used for glassine production at the paper mill are presented in Table 4 (below). Comparison of the samples shows that the fiber properties and the relative amounts of fiber fractions are different in the recycled pulp obtained from RGP.

[0197] Table 4. Fiber analysis results and properties of recycled pulp (REP1) obtained from RGP, non-recycled bleached chemical pulp (before and after refining at the paper mill), and pulp mill broke used for glassine production at the paper mill.

[0198]

[0199]

[0200] refer to Figure 6. The pulp as disclosed above was further analyzed based on the hydrophobic properties of the pulp. The hydrophobicity of the particles in the pulp was measured by means of flow cytometry, which is a well-known analytical method for counting, identifying and sorting particles based on selected properties. The analysis was performed using a Sysmex CyFlow Cube 6 (V2m) benchtop flow cytometer. A 20 ml representative sample was collected from the paper machine and diluted 5 times with ultrapure water, and the diluted and well-mixed sample was then filtered through a 200 mesh sieve. A 50 ml aliquot of the filtrate was collected for further dilution. A series of dilutions (in the range of 10 to 1000 times) was prepared with ultrapure water so that a suitable dilution was obtained that contained particles in an amount that produced 700 to 1000 events per second when analyzed by flow cytometry. A certain volume of 20 ml of the dilution to be analyzed was mixed with 1 ml of Nile red stain, which was used as a fluorescent marker to selectively stain the hydrophobic parts of the sample. Before analyzing the samples, the flow cytometer was calibrated to a size standard using 3 μm commercially available polystyrene beads. Relative hydrophobicity (>10) was used to gate the particles. The particles in each sample were further sorted based on their size, so that hydrophobic particles with a diameter of 1 μm or less were denoted as small, while hydrophobic particles with a diameter of more than 1 μm were denoted as large. The results showed that the recycled pulp obtained from RGP contained 2 to 3 times more large and small hydrophobic particles than non-recycled BCP made from hardwood. The recycled pulp obtained from RGP contained nearly 10 times more large and small hydrophobic particles than non-recycled BCP made from softwood. The difference from pulp mill broke was also obvious. Although the majority of the hydrophobic particles in all analyzed samples belonged to the large particle group, i.e. with a diameter of more than 1 μm, the highest relative difference between recycled pulp obtained from RGP and other pulp types was measured in the small particle group. The amount of hydrophobic particles in the samples (in pieces per milliliter (pcs / ml)) and the total amount of particles measured in the samples (pcs) are shown in Table 5 (below).

[0201] Table 5. Amount of hydrophobic particles and total particles in samples measured by flow cytometry.

[0202]

[0203] The increase in hydrophobic particles, especially small hydrophobic particles, observed in recycled pulp obtained from RGP was expected to be due to silicone polymer residues forming the release coating. However, despite the presence of hydrophobic particles in recycled pulp obtained from RGP, no detectable problems with runnability or paper quality were observed in the experimental glass paper production.

[0204] Experimental Study 2 - Effect of Recycled Pulp Obtained from RGP on Glass Paper Production

[0205] In the second experimental study, a 53 g / m 2 Calendered glass paper with a grammage of 100 μm and a thickness of 48 μm was used, resulting in varying amounts of recycled pulp derived from RGP in the raw material. The amount of recycled pulp derived from RGP varied between 0% and 30% by weight, based on the dry matter content of the produced glass paper, according to SCAN-P 39:80. The ratio of non-recycled bleached chemical pulp produced from hardwood to non-recycled bleached chemical pulp produced from softwood remained constant. Thus, the non-recycled BCP contained 35% by weight of non-recycled BCP produced from softwood and 65% by weight of non-recycled BCP produced from hardwood. Thus, as the amount of recycled pulp derived from RGP in the raw material increased, the amount of BCP decreased, maintaining the same proportion of non-recycled BCP from hardwood to softwood. The amount of broke remained constant at 12% by weight in all experiments.

[0206] The samples were measured at various test points. The composition containing only non-recycled bleached chemical pulp and broke, but no recycled pulp obtained from RGP, was Figures 7 to 11 The reference point is marked in FIG and abbreviated as REF. The composition containing 15 wt.% recycled pulp obtained from RGP is Figures 7 to 11 The composition containing 30 wt.% of recycled pulp obtained from RGP was Figures 7 to 11 The raw material compositions for the reference point and test points 1 and 2 are described in Table 6 (below).

[0207] Table 6. Composition of the feedstock for the reference site and test sites 1 and 2 in the experimental study. The abbreviation "BCP total." refers to the total amount of non-recycled bleached chemical pulp in the feedstock, expressed in weight percent. Broke refers to the amount of paper mill-derived pulp in the feedstock, expressed in weight percent. REP1 refers to the amount of recycled pulp obtained from RGP in the feedstock, expressed in weight percent. The last column on the right indicates the contribution of each component (BCP SW, BCP HW, broke, REP1) to the feedstock, totaling 100 weight percent.

[0208]

[0209] Fines content at the pulp chest (BMN method)

[0210] refer to Figure 7The effect of recycled pulp obtained from RGP on the production of glass paper was evaluated by measuring the development of the fines content at the machine chest of the paper machine as a function of the amount of recycled pulp obtained from RGP in the raw material. In this context, the fines content refers to the fibrous material in the pulp, which was classified according to SCAN-CM 6:05 using a 20-minute classification time, a set of 16-mesh, 28-mesh, 48-mesh and 200-mesh screens and a weighed filter paper (Macherey-Nagel MN616, 125 mm diameter) for collecting the fiber fraction with a McNett sieve as F <200 Fraction determination. This method describes a fiber fractionation procedure in which the fibers in a pulp suspension are grouped into fractions of different average fiber sizes. The mass of fiber retained in the fractions is expressed as a percentage of the dry mass of the original sample. When the relative ratio of BCP SW and BCP SW remains constant, the retained F <200 The fractions were used as an indicator of how much the fines content in glassine paper production changes due to increasing amounts of pulp derived from RGP, while the amount of pulp mill broke remains the same. The results demonstrate that when the amount of recycled pulp derived from RGP in the glassine paper ranges from 0% to 10% by weight, the fines content remains relatively stable, ranging from 10.2% to 10.5% by weight. However, unexpectedly, when the amount of recycled pulp derived from RGP in the glassine paper is equal to or greater than 10% by weight, the fines content begins to increase more rapidly. In particular, when the amount of recycled pulp derived from RGP in the glassine paper is equal to or greater than 15% by weight, such as in the range of 15% to 30% by weight, the fines content in the fiber furnish of the glassine paper increases very rapidly. During the experiment, the fines content increased from 10.2% to 13.8% by weight when the amount of recycled pulp derived from RGP in the glassine paper ranged from 0% to 30% by weight. The fines content has an impact on paper properties. This effect can already be detected when forming a paper web. The results show that the amount of recycled pulp obtained from RGP in the stock can be used to adjust the retention level, which describes the ability of the formed paper web to retain fine particles on the paper web and therefore describes the balance between drainage and formability of the paper web.

[0211] Water retention value in the pulping tank

[0212] refer to Figure 8 The impact of recycled pulp obtained from RGP on glass paper production was further evaluated by measuring the water retention value (abbreviated as WRV) at the machine chest according to ISO 23714:2014 (en). WRV was determined as the average of two replicate samples, each consisting of 1 g of dry pulp diluted in 500 ml of water and having a temperature of 23 ± 3 °C. The following materials and methods were used:

[0213] Beckman Coulter Avanti J-30I Laboratory Centrifuge

[0214] Centrifugal force 3000g±50g, 30 minutes

[0215] JS 7,5 rotor (speed 5350; RPM 5289)

[0216] After centrifugation, the sample was weighed for the first time. The sample was then dried overnight (12 h) at 105 ± 2 °C and cooled in a dryer to room temperature (23 ± 3 °C). The sample was then weighed a second time using a laboratory balance (0,0001 g precision).

[0217] Calculate the water retention value according to the following equation 1:

[0218] Equation 1:

[0219] in

[0220] m1 = mass of the sample after centrifugation, in grams

[0221] m2 = mass of the sample after drying the coal, in grams.

[0222] The results demonstrate that replacing non-recycled BCP with recycled pulp from RGP leads to a steady decrease in water retention, which is inversely proportional to the amount of recycled pulp from RGP in the glassine paper. Each 10% by weight replacement of non-recycled BCP with recycled pulp from RGP resulted in a decrease in the WRV of the glassine paper over a range of 0.1 g / g. The WRV reduction was evident across the entire range. At the reference point, the WRV was 1.98 g / g. At test point 1, the WRV was 1.83 g / g. At test point 2, the WRV was 1.72 g / g. The results of the water retention level analysis support and validate the observations from the fines content analysis disclosed above. The correlation of WRV with the amount of recycled pulp from RGP in the feedstock indicates that recycled pulp from RGP in the feedstock can be used to adjust the water retention level. The lower WRV of fibers from recycled pulp from RGP, compared to fibers from non-recycled BCP, is beneficial during coal drying. The reduced amount of water absorbed into the fiber network at the machine chest indicates that the glassine paper has better dimensional stability during coal drying. Therefore, taking into account the fines content and drainage trends discussed below, the calendered glassine advantageously contains equal to or less than 50% by weight, such as in the range of 5% to 50% by weight, preferably in the range of 10% to 45% by weight, and most preferably in the range of 15% to 40% by weight, of recycled pulp obtained from release liner glassine, when measured as dry matter content according to SCAN-P 39:80. In addition, the stock at the machine chest of the paper machine has a water retention value in the range of 1.5 g / g to 1.9 g / g, preferably in the range of 1.55 to 1.85, and most preferably in the range of 1.6 to 1.8, which can be determined according to ISO 23714:2014 from a sample having a dry matter content of 1 gram.

[0223] Main steam group pressure in paper drainage-drying section

[0224] refer to Figure 9 . The effect of recycled pulp obtained from RGP on the production of glass paper was next evaluated by measuring the main steam group pressure at the paper machine during the production of glass paper. The main steam group pressure is an indication of drainage and is also direct evidence of the amount of energy consumed when drying coal paper. The results demonstrate that drainage improves when the amount of recycled pulp obtained from RGP in the glass paper increases. The formed glass paper has a higher dry matter content. Furthermore, glass paper comprising a higher amount of recycled pulp obtained from RGP requires less steam pressure for drying coal. Surprisingly, drainage appears to be most effective when the amount of recycled pulp obtained from RGP in the glass paper is equal to or less than 15 wt%, such as in the range of 5 wt% to 15 wt%, as measured by means of the main steam group pressure. As Figure 9As shown, an amount of 5 wt% recycled pulp obtained from RGP in the composition already requires a steam pressure of less than 0.1 bar to dry the cellophane. An amount of 15 wt% recycled pulp obtained from RGP in the composition already requires a steam pressure of less than 0.3 bar to dry the cellophane.

[0225] Transverse paper profiling at the winder

[0226] The effect of recycled pulp obtained from RGP on the production of glass paper was further evaluated in the dry coal section. The density of the calendered glass paper samples was 1100 g / m 3 ±11g / m 3 The results show that the properties of the samples produced according to the reference point and test point compositions are presented in Table 7 (below). For all compositions (REF, TP1, TP2), the test point was run at the same speed and settings, making it possible to evaluate the effect of recycled pulp obtained from RGP on calendered glass paper.

[0227] Table 7. Properties of calendered glassine paper samples.

[0228]

[0229] The results show that recycled pulp obtained from RGP makes it possible to maintain the quality properties of calendered glass paper, such as density and transparency, at a sufficient level. The combination of retained density and transparency serves as an indirect indicator of this.

[0230] refer to Figure 10 The paper width was measured from the calendered glass paper samples at the reference point, test point 1, and test point 2. The paper width (in centimeters) at the reel was measured with the aid of a Web Imaging System (WIS), an automated image analysis system supplied by ABB. The system was used according to the manufacturer's instructions. Figure 10 The width of the paper shown is perpendicular to the machine direction S x Horizontal S yThe WIS results are the average of 8 measurements taken along the surface of the paper. The results demonstrate that replacing non-recycled BCP with recycled pulp obtained from RGP leads to a reduction in the shrinkage of glassine paper, which is proportional to the amount of recycled pulp obtained from RGP in the glassine paper. Replacing 15 wt.% of the non-recycled BCP with recycled pulp obtained from RGP resulted in glassine paper that exhibited 3 cm less shrinkage than the reference value. Replacing 30 wt.% of the non-recycled BCP with recycled pulp obtained from RGP resulted in glassine paper that exhibited 4 cm less shrinkage than the reference value. The WIS results were verified in an independent test run, in which the paper was profiled off-line at the winder from 30 calendered and uncalendered paper samples with the aid of Tapio PMA (automated paper quality control system provided by Tapiotechnologies). The system was used according to the manufacturer's instructions. The results of the latter independent test run with Tapio PMA verified the paper width results of the first test run. In the samples without recycled pulp obtained from RGP (REF), in the transverse direction S y The shrinkage measured along the surface of the paper was 3.6%. In the sample (TP1) containing 15 wt.% of recycled pulp obtained from RGP, the shrinkage in the transverse direction S y The shrinkage measured along the surface of the paper was 3.0%. In the sample (TP2) containing 30 wt.% of recycled pulp obtained from RGP, the shrinkage in the transverse direction S y During a subsequent test run, the shrinkage of the uncalendered paper along the paper surface in the transverse direction S was also determined simultaneously from 30 paper samples according to the manufacturer's instructions using the Tapio PMA. y The variability analysis of grammage showed that the standard deviation of the samples at test points 1 and 2 containing recycled pulp obtained from RGP was 0.5 g / m 2 This is at the same level as the standard deviation of the samples at the reference point, which does not contain recycled pulp obtained from RGP (REF). In all the measured sample compositions (REF, TP1, TP2), the variability in grammage (maximum - minimum) is within 3.1 g / m 2 Up to 3.6g / m 2within the range of . The thickness variability analysis showed that the standard deviation of the samples containing recycled pulp obtained from RGP at test points 1 and 2 (TP1, TP2) was 0.4 μm, which was at the same level as the standard deviation of the samples at the reference point, which did not contain recycled pulp obtained from RGP (REF). However, when the amount of recycled pulp obtained from RGP was larger, the thickness variability (maximum-minimum) showed a reduced variability. In the reference sample (REF), the thickness variability (maximum-minimum) was 2.4 μm, while the thickness variability (maximum-minimum) of test points 1 and 2 (TP1, TP2) was 1.9 μm and 2.1 μm, respectively. In addition to the reduction in shrinkage, replacing non-recycled BCP with recycled pulp obtained from RGP resulted in a reduction in thickness variability, which correlated with the shrinkage results, while maintaining the grammage variability. Therefore, both shrinkage and thickness variability at the paper machine are related to the amount of recycled pulp obtained from RGP. Reduced shrinkage and stable grammage variability are indicators of improved dimensional stability.

[0231] Induced curl test of calendered paper

[0232] refer to Figure 11 The calendered glass paper samples produced in the industrial scale pilot run were subjected to the S y The induced curl of the paper was further evaluated and expressed as paper curl (CD). Curl was induced at 150°C (laboratory oven) for 1 minute and then measured immediately. The induced curl method was chosen because it provides an indication of the processability of calendered glass paper when used as a substrate for release coatings. Release coatings are typically cured under conditions similar to those used in this case.

[0233] Induced curl is measured using a modified version of test method ISO 11556:2005 (en). A sheet with a length of 10 cm (lateral S of the paper) is cut from the middle of the paper which has been allowed to stabilize under NTP conditions (25°C, 1 bar) for 24 hours after production. y ) and has a width of 5 cm (machine direction S of paper x). The specimen was placed on a cylindrical holder with a diameter of 10 mm and a slot extending over 5 cm along the length of the cylindrical holder. When placed in the slot, the specimen was suspended from the center by the slot across its entire width, allowing each half of the specimen's length to extend freely for a distance of 4.5 cm in opposite directions. The cylindrical holder was attached to a curling template to measure the magnitude of the induced curl. Before induced curling, the test specimen was aligned parallel to a reference position. The reference plane was given a value of zero. Because the induced curl on the suspended specimen approximates a circular arc, a mark indicating the angle of curvature from the reference plane was imprinted on the template. Therefore, the magnitude of the curl was imprinted in the template as the curvature angle of the curled specimen relative to the reference plane, in degrees. The curl of the specimen was compared with the curvature angle imprinted on the curling template; the curvature on both sides was recorded. Two specimens were measured, and the four recorded values were averaged. The curl test result is therefore the average of the four values recorded. If the curl is recorded towards the wire side, the curl value is positive. If the curl is recorded towards the top side, the curl value is negative. In this context, the wire side refers to the side of the paper that has come into contact with the forming wire of the paper machine when forming the paper web. In this context, the top side refers to the back side of the paper.

[0234] The results demonstrate that replacing non-recycled BCP with recycled pulp obtained from RGP results in a steady reduction in curl values, which is proportional to the amount of recycled pulp obtained from RGP in the glassine paper. In the sample without recycled pulp obtained from RGP (REF), the measured curl was 61 mm. In the sample containing 15 wt.% recycled pulp obtained from RGP (TP1), the measured curl was 47 mm. In the sample containing 30 wt.% recycled pulp obtained from RGP (TP2), the measured curl was 32 mm. Thus, replacing 15 wt.% of non-recycled BCP with recycled pulp obtained from RGP results in a 23% reduction in curl of calendered glassine paper. Furthermore, replacing 30 wt.% of non-recycled BCP with recycled pulp obtained from RGP results in a 48% reduction in curl of calendered glassine paper. The reduction in curl was demonstrated in all measured samples. The induced curl results support and verify the observations disclosed above. Therefore, when taking into account the improved dimensional stability and drainage discussed above, the calendered glassine advantageously contains equal to or less than 50 wt. %, such as in the range of 5 wt. % to 50 wt. %, preferably in the range of 10 wt. % to 45 wt. %, most preferably in the range of 15 wt. % to 30 wt. % of recycled pulp obtained from release liner glassine, when measured as dry matter content according to SCAN-P 39:80.

[0235] Paper strength properties

[0236] The strength properties of calendered glass paper samples produced in industrial scale pilot runs were further evaluated. Machine direction (MD) S was measured according to ISO 1924-3 x and crosswise (CD)S y tensile strength in MD, strain at break in MD, and tensile energy absorption in MD.

[0237] When calendered glass paper is used as a substrate for release liners in labeling operations, tensile strength can be used as an indicator of the calendered glass paper's potential resistance to web breakage. Break strain can be used as an indicator of how well the paper will conform to irregular shapes and, along with tensile energy absorption, as an indicator of the paper's performance under dynamic strain and stress. Tensile energy absorption is a measure of the paper's ability to absorb energy. Thus, tensile energy absorption is an indication of the toughness of the paper sheet. Consequently, these parameters predict the performance of the paper, especially when the paper is subjected to uneven or dynamic stresses. Table 8 (below) indicates the results measured from a calendered glass paper sample containing no recycled pulp obtained from RGP (REF), a calendered glass paper sample containing 15% by weight of recycled pulp obtained from RGP (TP1), and a calendered glass paper sample containing 30% by weight of recycled pulp obtained from RGP (TP2).

[0238] Table 8. Comparative results from calendered glassine paper samples (MD and CD).

[0239]

[0240] The results show that despite the replacement of non-recycled BCP with recycled pulp obtained from RGP, the paper strength in the samples, as measured by tensile strength, strain at break and tensile energy absorption, remained at a sufficiently high level. During the test period, no significant changes in paper strength or orientation properties were observed.

[0241] In summary, the compatibility of recycled pulp produced from release liner glassine for glassine production is excellent. Several different methods have been used to better measure the positive effects of the glassine manufacturing process, such as improved dewatering during web formation and in the press section, and improved drainage in the coal drying section, while maintaining the properties of the calendered glassine at a level sufficient for use as a release liner substrate. The improved manufacturing process is also noticeable in the produced glassine, which exhibits reduced shrinkage, better dimensional stability, and reduced curl.

[0242] Experimental Study 3 - Comparing Fiber Properties with Computational Modeling

[0243] In further experimental studies, the effect of replacing non-recycled BCP from softwood with non-recycled BCP from hardwood and / or recycled pulp obtained from RGP in glassine production was investigated with the aid of computational modeling.

[0244] Computational modeling was performed using SoftaCell, a mathematical modeling software for multivariable optimization and simulation developed by a commercial vendor (GloCell Oy). The software is designed to simulate the changes that would occur if pulp or paper quality parameters (such as fiber furnish mixture and degree of refining) were changed by a certain amount from a given reference condition. Historical data on the main factors affecting paper quality—that is, previously measured quality characteristics of specific pulp samples and fiber furnish mixtures from paper machines and / or laboratory experiments—are used to create a comprehensive database model for the software, which then uses the existing data to simulate the effects of changing parameters on the process and / or product.

[0245] The following parameters were used for modeling the pulp in the fiber furnish recipe:

[0246] -bleached chemical pulp from eucalyptus

[0247] ○°SR=52

[0248] SEC = 162 kWh / t

[0249] -bleached chemical pulp from birch

[0250] ○°SR=35

[0251] SEC = 124 kWh / t

[0252] - Recycled pulp obtained from RGP

[0253] ○°SR=51

[0254] ○Unrefined

[0255] In the case of 60g / m 2 The simulation was carried out on calendered glass paper with a grammage of 1000 grammage.

[0256] In the simulation, the reference case is a sample where the fiber furnish contains

[0257] - bleached chemical pulp from softwood (pine) in an amount of 20% by weight and

[0258] - bleached chemical pulp from hardwood (birch) in an amount of 80% by weight,

[0259] The pulp forms up to 100% by weight of the fiber furnish.

[0260] The quality characteristics of the reference case are known from previous measurements on samples of calendered glassine paper originating from a paper machine.

[0261] The simulations performed were compared with an experimental research program in which bleached chemical pulp from softwood in the fiber furnish was gradually replaced by bleached chemical pulp from hardwood, which could be produced from birch, eucalyptus or a combination of these, and / or recycled pulp obtained from release liner glassine.

[0262] Simulation 1 - Cellophane from birch

[0263] The first simulation aimed to determine the effect of replacing a non-recycled BCP softwood component in the fiber furnish with a non-recycled BCP hardwood component from birch, in the presence or absence of a recycled pulp component.

[0264] Ten test points were created, in which the amount of bleached chemical pulp from birch was varied from 65% to 100% by weight of the fiber furnish, while the amount of bleached chemical pulp from pine was reduced from 20% to 0% by weight of the fiber furnish. The first test point, STP1, was the reference case. In the next four test points, STP2 to STP5, the amount of bleached chemical pulp from pine was reduced by 5% by weight per test point, while the amount of bleached chemical pulp from birch was increased by 5% by weight per test point, from 80% to 100% by weight of the fiber furnish.

[0265] Test site STP6 simulates a situation where the fiber furnish contains

[0266] - bleached chemical pulp from softwood (pine) in an amount of 20% by weight,

[0267] - bleached chemical pulp from hardwood (birch) in an amount of 65% by weight and

[0268] - recycled pulp obtained from release liner glassine paper in an amount of 15% by weight,

[0269] Pulp forms up to 100% by weight of the fiber furnish

[0270] The next four test points STP7 to STP10 differed from STP6 in that the amount of bleached chemical pulp from pine was reduced by 5 wt% per test point, while the amount of recycled pulp obtained from release liner glassine was kept at 15 wt%, and at the same time the amount of bleached chemical pulp from birch was increased by 5 wt% per test point of the fiber furnish from 65 wt% to 85 wt%.

[0271] Simulation 2 - Cellophane from Eucalyptus

[0272] The second simulation aimed to determine the effect of replacing a non-recycled BCP softwood component in the fiber furnish with a non-recycled BCP hardwood component from eucalyptus, in the presence or absence of a recycled pulp component.

[0273] In the second simulation, ten new test points (STP10 to STP20) were created. Reference case STP11 was identical to reference case STP1 from the first simulation, but in test points STP11 to STP20, all the bleached chemical pulp from hardwood was from eucalyptus. The amount of bleached chemical pulp from eucalyptus varied from 65% to 100% by weight of the fiber furnish, while the amount of bleached chemical pulp from pine was reduced from 20% to 0% by weight of the fiber furnish. In test points STP12 to STP15, the amount of bleached chemical pulp from pine was reduced by 5% by weight per test point, while the amount of bleached chemical pulp from eucalyptus was increased by 5% by weight per test point, from 80% to 100% by weight of the fiber furnish.

[0274] Test point STP16 simulates a situation where the fiber furnish contains

[0275] - bleached chemical pulp from softwood (pine) in an amount of 20% by weight,

[0276] - bleached chemical pulp from hardwood (eucalyptus) in an amount of 65% by weight and

[0277] - recycled pulp obtained from release liner glassine paper in an amount of 15% by weight,

[0278] Pulp forms up to 100% by weight of the fiber furnish

[0279] The next four test points STP17 to STP20 differed from STP16 in that the amount of bleached chemical pulp from pine was reduced by 5 wt% per test point, while the amount of recycled pulp obtained from release liner glassine was kept at 15 wt%, and at the same time the amount of bleached chemical pulp from eucalyptus was increased by 5 wt% per test point from 65 wt% to 85 wt% of the fiber furnish.

[0280] Simulation 3 - Cellophane from birch and eucalyptus

[0281] The third simulation aimed to determine the effect of providing glassine paper without a non-recycled BCP softwood component, such that the fiber furnish contained only non-recycled BCP hardwood components from birch, eucalyptus, or a mixture of these two components, with no recycled pulp component present.

[0282] In the third simulation, 11 additional test points, STP21 to STP31, were created, using the same reference case STP1 as in the first simulation. In test point STP21, all hardwood-derived bleached chemical pulps were derived from eucalyptus. The amount of bleached chemical pulp from eucalyptus was varied from 100% to 0% by weight of the fiber furnish, while the amount of bleached chemical pulp from birch was varied from 0% to 100% by weight of the fiber furnish. In test points STP21 to STP31, the amount of bleached chemical pulp from eucalyptus was decreased by 10% by weight per test point, while the amount of bleached chemical pulp from birch was increased by 10% by weight per test point, so that the total amount of BCP from eucalyptus and birch was 100% by weight of the fiber furnish.

[0283] Simulation 4 - Cellophane from birch and recycled pulp from RGP

[0284] The fourth simulation was designed to determine the effect of providing glassine paper without a non-recycled BCP softwood component, so that the fiber furnish contained only a non-recycled BCP hardwood component from birch and a recycled pulp component from RGP.

[0285] In the fourth simulation, 10 additional test points (STP32 to STP41) were created, using the same reference case (STP1) as in the first simulation. In test point STP32, all birch-derived bleached chemical pulp was derived from eucalyptus. The amount of birch-derived bleached chemical pulp varied from 100% to 55% by weight of the fiber furnish, while the amount of recycled pulp from RGP varied from 0% to 45% by weight of the fiber furnish. In test points STP32 to STP41, the amount of birch-derived bleached chemical pulp decreased by 5% by weight per test point, while the amount of recycled pulp from RGP increased by 5% by weight per test point, resulting in a total of 100% by weight of the fiber furnish for BCP from birch and recycled pulp from RGP.

[0286] Simulation 5 - Cellophane from Eucalyptus and Recycled Pulp from RGP

[0287] The fifth simulation was designed to determine the effect of providing glassine paper without a non-recycled BCP softwood component, so that the fiber furnish contained only a non-recycled BCP hardwood component from eucalyptus and a recycled pulp component from RGP.

[0288] In the fifth simulation, 10 additional test points (STP42 to STP51) were created, using the same reference case (STP1) as in the first simulation. In test point STP42, all hardwood-derived bleached chemical pulp was derived from eucalyptus. The amount of bleached chemical pulp derived from eucalyptus was varied from 100% to 55% by weight of the fiber furnish, while the amount of recycled pulp derived from RGP was varied from 0% to 45% by weight of the fiber furnish. In test points STP42 to STP51, the amount of bleached chemical pulp derived from eucalyptus was decreased by 5% by weight per test point, while the amount of recycled pulp derived from RGP was increased by 5% by weight per test point, so that the total amount of BCP derived from eucalyptus and recycled pulp derived from RGP was 100% by weight of the fiber furnish.

[0289] Simulation 6 - Cellophane from birch, eucalyptus and recycled pulp from RGP

[0290] The sixth simulation was designed to determine the effect of providing glassine paper without a non-recycled BCP softwood component, wherein the relative proportions of a non-recycled BCP hardwood component from birch, a non-recycled BCP hardwood component from eucalyptus, and a recycled pulp component from RGP in the fiber furnish were varied.

[0291] In the sixth simulation, 12 additional test points, STP52 to STP63, were created, using the same reference case STP1 as in the first simulation. In test point STP52, 60% by weight of the fiber furnish was bleached chemical pulp from birch, 30% by weight of the fiber furnish was bleached chemical pulp from eucalyptus, and 10% by weight of the fiber furnish was recycled pulp from RGP. The amount of bleached chemical pulp from birch ranged from 60% to 40% by weight of the fiber furnish, the amount of bleached chemical pulp from eucalyptus varied from 0% to 50% by weight of the fiber furnish, and the amount of recycled pulp from RGP varied from 10% to 40% by weight of the fiber furnish.

[0292] In test points STP52 to STP54, respectively, the amount of recycled pulp from RGP was maintained at 10 wt% of the fiber furnish, while the amount of bleached chemical pulp from birch was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from eucalyptus was increased by 10 wt% units per test point from 30 wt% to 50 wt% of the fiber furnish.

[0293] In test points STP55 to STP57, respectively, the amount of recycled pulp from RGP was maintained at 20 wt% of the fiber furnish, while the amount of bleached chemical pulp from birch was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from eucalyptus was increased by 10 wt% units per test point from 20 wt% to 40 wt% of the fiber furnish.

[0294] In test points STP58 to STP60, respectively, the amount of recycled pulp from RGP was maintained at 30 wt% of the fiber furnish, while the amount of bleached chemical pulp from birch was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from eucalyptus was increased by 10 wt% units per test point from 10 wt% to 30 wt% of the fiber furnish.

[0295] In test points STP61 to STP63, respectively, the amount of recycled pulp from RGP was maintained at 40 wt% of the fiber furnish, while the amount of bleached chemical pulp from birch was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from eucalyptus was increased by 10 wt% units per test point from 00 wt% to 20 wt% of the fiber furnish.

[0296] Simulation 7 - Cellophane from Eucalyptus, Birch and Recycled Pulp from RGP

[0297] The seventh simulation was designed to determine the effect of providing glassine paper without a non-recycled BCP softwood component, wherein the relative proportions of a non-recycled BCP hardwood component from eucalyptus, a non-recycled BCP hardwood component from birch, and a recycled pulp component from RGP in the fiber furnish were varied.

[0298] In the seventh simulation, 12 additional test points, STP64 to STP75, were created, using the same reference case STP1 as in the first simulation. In test point STP64, 60% by weight of the fiber furnish was bleached chemical pulp from eucalyptus, 30% by weight of the fiber furnish was bleached chemical pulp from birch, and 10% by weight of the fiber furnish was recycled pulp from RGP. The amount of bleached chemical pulp from eucalyptus ranged from 60% to 40% by weight of the fiber furnish, the amount of bleached chemical pulp from birch varied from 0% to 50% by weight of the fiber furnish, and the amount of recycled pulp from RGP varied from 10% to 40% by weight of the fiber furnish.

[0299] In test points STP64 to STP66, respectively, the amount of recycled pulp from RGP was maintained at 10 wt% of the fiber furnish, while the amount of bleached chemical pulp from eucalyptus was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from birch was increased by 10 wt% units per test point from 30 wt% to 50 wt% of the fiber furnish.

[0300] In test points STP67 to STP69, respectively, the amount of recycled pulp from RGP was maintained at 20 weight % of the fiber furnish, while the amount of bleached chemical pulp from eucalyptus was reduced by 10 weight % unit per test point from 60 weight % to 40 weight % of the fiber furnish, and the amount of bleached chemical pulp from birch was increased by 10 weight % unit per test point from 20 weight % to 40 weight % of the fiber furnish.

[0301] In test points STP70 to STP72, respectively, the amount of recycled pulp from RGP was maintained at 30 wt% of the fiber furnish, while the amount of bleached chemical pulp from eucalyptus was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from birch was increased by 10 wt% units per test point from 10 wt% to 30 wt% of the fiber furnish.

[0302] In test points STP73 to STP75, respectively, the amount of recycled pulp from RGP was maintained at 40 wt% of the fiber furnish, while the amount of bleached chemical pulp from eucalyptus was reduced by 10 wt% units per test point from 60 wt% to 40 wt% of the fiber furnish, and the amount of bleached chemical pulp from birch was increased by 10 wt% units per test point from 0 wt% to 20 wt% of the fiber furnish.

[0303] Results of experimental studies

[0304] The results of computational modeling are as follows Figure 12 In the accompanying drawings, the following abbreviations have been used for the cellophane:

[0305] Fiber ingredients:

[0306] - BCP SW Pine (wt%) = non-recycled bleached chemical pulp from pine softwood, expressed as a percentage by weight of the fiber furnish

[0307] - BCP HW Birch = non-recycled bleached chemical pulp from birch hardwood, expressed as a percentage by weight of the fiber furnish

[0308] - BCP HW Eucalyptus = Non-recycled bleached chemical pulp from eucalyptus hardwood, the value refers to the weight percentage of the fiber furnish

[0309] - REP1 = recycled pulp from release liner glassine paper, as a percentage by weight of the fiber furnish

[0310] Quality parameters:

[0311] -CSF = Canadian Standard Freeness, in milliliters (ml)

[0312] -WRV = Water Retention Value, in grams of water per gram of pulp (g / g)

[0313] -FL = length-weighted average fiber length, in millimeters (mm)

[0314] - Bulk = the reciprocal of density, in cubic centimeters per gram (cm 3 / g)

[0315] -Bendsen air permeability, in milliliters per minute (ml / min)

[0316] -Bendsen roughness, in milliliters per minute (ml / min)

[0317] - tensile index, in Newton meters per gram (Nm / g)

[0318] -TEA = Tensile Energy Absorption, in Joules / gram

[0319] - Tear index = tear strength / gram, in millinewtons times square meters per gram (mNm 2 / g)

[0320] -Scott bond test, unit is joules / square meter (J / m 2 )

[0321] -Paper brightness, in percentage

[0322] - Paper opacity in percentage

[0323] Comparisons show that non-recycled BCP from eucalyptus has lower freeness, lower fiber length, and lower roughness than birch, but higher elongation, tear strength, brightness, and opacity. The absence of non-recycled BCP from softwood reduces tear strength levels. When all non-recycled BCP in the glasspaper fiber furnish is from hardwood birch, bulk and air permeability increase, while tear strength decreases. When all non-recycled BCP in the glasspaper fiber furnish is from hardwood eucalyptus, tensile strength decreases, but elongation and opacity increase.

[0324] The comparison results further show that when the amount of recycled pulp from release liner glassine paper is small and less than 15% by weight of the fiber furnish, the water retention value, tensile strength and brightness of the glassine paper decrease, but the bulk and opacity increase. No significant effect on tear strength is observed within this range.

[0325] Interestingly, when the amount of recycled pulp from release liner glassine is high, such as in the range of 10% to 40% by weight, preferably in the range of 20% to 40% by weight, the recycled pulp from release liner glassine produces different effects depending on whether the recycled pulp from release liner glassine is used in combination with a non-recycled BCP from eucalyptus or a non-recycled BCP from birch. It is also apparent that the recycled pulp from release liner glassine has a greater effect on tensile strength than on tear strength.

[0326] When the amount of recycled pulp from release liner glassine is in the range of 10% to 40% by weight, freeness and roughness are reduced in the case where 60% by weight or more of the fiber furnish is non-recycled BCP from eucalyptus. In addition, the elongation is reduced less than in the case where 60% by weight or more of the fiber furnish is non-recycled BCP from birch.

[0327] When the amount of recycled pulp from release liner glassine paper ranges from 10% to 40% by weight, in cases where 60% by weight or more of the fiber furnish is non-recycled BCP derived from birch, the internal strength, tensile strength, and tensile stiffness, as represented by the Scott Bond value, decrease less than in cases where 60% by weight or more of the fiber furnish is non-recycled BCP derived from eucalyptus. Furthermore, the increase in opacity is less, and there is essentially no observed effect on light scattering.

[0328] When the amount of recycled pulp from release liner glassine is in the range of 10% to 40% by weight, the non-recycled BCP from eucalyptus better promotes the tear strength of the glassine than the non-recycled BCP from birch. On the other hand, the non-recycled BCP from birch better promotes the tensile strength of the glassine than the non-recycled BCP from eucalyptus.

[0329] Test points STP1 to STP5 show that for calendered glass paper containing a fiber furnish without non-recycled BCP from softwood and in which the non-recycled BCP from hardwood is birch, the average fiber length decreases and the paper becomes smoother. Replacing softwood with birch does not significantly affect the tensile strength or optical properties of the paper, but the tear strength does decrease.

[0330] Test sites STP11 to STP15 showed that calendered glassine paper containing a fiber furnish without non-recycled BCP from softwood and in which the non-recycled BCP from hardwood was eucalyptus, showed a decrease in average fiber length and a smoother paper. Unlike the substitution with birch, substituting eucalyptus for softwood also affected the tensile strength and optical properties of the paper. Tear and tensile strength decreased, while bulk and opacity increased. Freeness (CSF) decreased.

[0331] Test points STP6 to STP10 further demonstrate that when recycled pulp from RGP is added to a fiber furnish where the non-recycled BCP from hardwood is birch, the tensile strength and opacity of the paper can be adjusted to some extent.

[0332] The results thus show the difference between calendered glass paper whose fiber furnish is non-recycled BCP from birch and calendered glass paper whose fiber furnish is non-recycled BCP from eucalyptus. The results further show that recycled pulp from RGP can be used as an optimized pulp to adjust the properties of calendered glass paper, where the fiber furnish does not contain non-recycled BCP produced from softwood.

[0333] Test points STP21 to STP31 further demonstrate that calendered glass paper wherein the fiber furnish does not contain non-recycled BCP from softwood and wherein the amount of non-recycled BCP from birch and the amount of non-recycled BCP from eucalyptus are substantially equal comprises properties similar to the reference case. Test points STP32 to STP41 further demonstrate that, in a fiber furnish containing no non-recycled BCP from softwood and wherein the non-recycled BCP from hardwood is birch, higher amounts of recycled pulp from RGP can be used to increase the bulk of the paper and adjust the transparency of the paper.

[0334] Test points STP42 to STP51 also show that in a fiber furnish containing no non-recycled BCP from softwood and in which the non-recycled BCP from hardwood is eucalyptus, a higher amount of recycled pulp from RGP reduces the bond strength, tear strength, and tensile strength of the paper while increasing opacity, thereby reducing the clarity of the paper. Thus, test points STP42 to STP51 move further away from the reference case.

[0335] Test points STP52 to STP75 show that glassine paper containing no non-recycled BCP softwood component and wherein the relative proportions of non-recycled BCP hardwood components from eucalyptus and birch are essentially equal, preferably in the range of 40 wt% to 50 wt% of the fiber furnish, and wherein the amount of recycled pulp component from RGP is equal to or higher than 5 wt% of the fiber furnish, preferably in the range of 5 wt% to 40 wt%, preferably in the range of 10 wt% to 40 wt%, presents properties similar to those determined from the reference case.

[0336] Thus, the results of experimental studies indicate that preferably calendered glass paper contains a fiber furnish in which the majority of the fibers are derived from non-recycled bleached chemical pulp produced from birch (Betula spp.) and eucalyptus (Eucalyptus spp.), and in which the properties of the glass paper have been adjusted by a small amount of fibers derived from recycled pulp obtained from release liner glass paper. Advantageously, the amount of recycled pulp from RGP in such a fiber furnish is in the range of 5% to 40% by weight of the fiber furnish, preferably in the range of 10% to 40% by weight, and most preferably in the range of 20% to 40% by weight.

[0337] Experimental Study 4 - Comparison of the Effects of Non-Regenerated BCP from Eucalyptus and Birch in Calendered Glass Paper Production

[0338] Further experimental studies were carried out on an industrial paper machine, where BCP produced from eucalyptus and birch were compared in two pilot production runs for 60 g / m 2 The impact of calendering on the quality of glass paper was investigated. First, a pilot run, TP101, was conducted, in which glass paper was produced containing a fiber furnish of 63% by weight of birch-derived BCP. Subsequently, a second pilot run, TP102, was conducted, in which glass paper was produced containing a fiber furnish of 63% by weight of eucalyptus-derived BCP. Thus, the difference between the glass paper produced in the two pilot runs was the type of hardwood BCP used. By switching the feed from a first pulp storage tank containing birch-derived BCP to a second pulp storage tank containing eucalyptus-derived BCP, the switch from birch to eucalyptus was achieved on the same production line.

[0339] The following production parameters shown in Table 9 (below) were used at the beginning of the two test sites.

[0340] Table 9. Pilot production parameters for cellophane manufacturing.

[0341] Paper machine speed 1300m / min Steam pressure before sizing 163 bar Steam pressure after sizing 175 bar Paper width 652mm Hardwood Refining 100kWh / t Combined Refining 155kWh / t Cork Refining 305kWh / t Cut and polish 35kWh / t

[0342] Eucalyptus fiber has a higher bonding area than birch fiber conventionally. In addition, the result that obtains from the above disclosed computational modeling and previous experience from laboratory refining result show that the quality from the BCP of eucalyptus can benefit from the refining of higher degree to obtain the quality of expectation. The edge cutting sample that gathers after the web section shows that the dry matter content of the paper web that comprises the BCP of eucalyptus is 16 % by weight, and this is significantly lower than the dry matter content (18 % by weight) of the paper web that comprises the BCP of birch. The reduction of dry matter content shows that the runnability of the paper web that comprises the BCP of eucalyptus may have difficulty after the pressing section.

[0343] During the two pilot runs, paper machine speeds were gradually increased. In the first run, in which calendered glass paper containing birch-derived BCP was produced, a paper machine speed of 1,397 m / min was achieved without runnability issues. However, in the second run, in which calendered glass paper containing eucalyptus-derived BCP was produced, web shrinkage on the paper machine was observed when the speed was increased. When the degree of refining was reduced from 100 kWh / t to 85 kWh / t, a paper machine speed of 1,309 m / min could be maintained stably without runnability challenges. Surprisingly, the steam group pressure in the dry coal section was lower for the glass paper containing eucalyptus-derived BCP.

[0344] The quality characteristics were determined on two glass papers produced after calendering in a pilot production. The quality parameters are presented in Table 10 below.

[0345] Table 10. Comparative quality parameters of calendered glass papers with paper furnishes comprising 63 wt% BCP from birch or 63 wt% BCP from eucalyptus.

[0346]

[0347] When producing calendered glassine paper in which a major portion of the fiber furnish is BCP from eucalyptus, runnability can be improved by reducing the production speed of the paper machine.

[0348] In the case of calendered glass paper where the majority of the fiber furnish was BCP from eucalyptus, the clarity of the paper was also significantly reduced. This could be compensated to some extent by increasing the moisture content of the paper before supercalendering. However, even a 0.5 wt% higher moisture content at the supercalender still resulted in a 2% difference in clarity, with the calendered glass paper from birch containing a higher clarity. Both trials achieved the quality parameters, with the produced paper having

[0349] - at 40g / m 2 Up to 90g / m 2 Within the range of gram weight,

[0350] -at 1.050g / cm 3 Up to 1.200g / cm 3 The density within the range and

[0351] - Transparency in the range of 40% to 53%.

[0352] Furthermore, the tensile strength values for the calendered glass paper from eucalyptus were lower. However, the tensile strength was still high enough to be used as a release liner substrate. The biggest differences between the papers from the two pilot runs were in the adhesive strength values and Bekk smoothness. In particular, the smoothness values for the calendered glass paper from eucalyptus were better, which appears to produce a paper with better smoothness than birch for release liner purposes.

[0353] The results demonstrate that calendered glass paper can be manufactured in an unconventional manner, where the majority of the fiber furnish is birch or eucalyptus BCP. However, to maintain the quality of the resulting glass paper during the manufacturing process, the characteristics of the fibers in the furnish need to be considered. This was demonstrated by comparing quality parameters, as both manufactured papers exhibited quality characteristics within the defined specifications for glass paper used as a substrate for release liners.

[0354] Experimental Study 5 - Calendered Glass Paper Made from Non-Recycled BCP from Eucalyptus

[0355] Further experimental studies were carried out on an industrial paper machine, where three pilot products, TP201, TP202, and REF200, were produced, each with a cellophane volume ranging from 350 to 1500 tonnes. The target grammage of the cellophane in all products was 55 g / m 2 In both test sites TP201 and TP202, the glassine papers contained a fiber furnish of which 96% by weight was made from non-recycled bleached chemical pulp produced from hardwood (eucalyptus). The non-recycled bleached chemical pulp produced from hardwoods SF1 and SF2 came from two suppliers. In both paper groups, a small amount of 4% by weight of the fiber furnish was made from non-recycled bleached chemical pulp produced from softwood LF. In the reference glassine paper REF200, 17% by weight of the fiber furnish was made from non-recycled bleached chemical pulp produced from softwood. The production parameters for the pilot production are presented in Table 11 (below).

[0356] Table 11. Production parameters of pilot products TP201, TP202, and REF.

[0357] parameter unit REF200 TP201 TP202 speed m / min 1339 1341 1364 Paper loss weight% 11.5 20.7 17.5 SF1 SEC kWh / t 153 154 164 SF2 SEC kWh / t 154 159 169 LF SEC kWh / t 255 222 135 SF1 Refined °SR 44.2 42.5 41.3 SF2 Refining °SR 42.4 42.6 42.7 LF Refining °SR 36 41.7 29.2

[0358] The quality parameters of the calendered glass paper produced in the pilot production are presented in Table 12 below.

[0359] Table 12. Quality parameters of calendered glass paper produced in the pilot production. These values are average values calculated based on the pilot production.

[0360] Quality parameters unit REF200 TP201 TP202 Paper thickness μm 50.0 49.7 49.7 Weight <![CDATA[g / m 2 ]]> 54.7 55.3 55.0 density <![CDATA[g / cm 3 ]]> 1.094 1.113 1.106 Water content ％ 6.62 6.53 6.50 Gurley breathability s 2076 1974 1881 Bekk porosity s 113 140 134 Bekk minimum porosity s 79 93 85 Bekk changes s 61 72 80 Oil absorption, top <![CDATA[g / m 2 ]]> 0.64 0.59 0.61 PPS, top μm 1.78 1.69 1.77 PPS, bottom μm 2.42 2.29 2.33 transparency ％ 50.7 50.4 49.4 Formability Index 25.3 23.6 26.2 Tensile strength MD kN / m 6.31 6.36 5.83 Tensile strength CD kN / m 3.27 3.42 3.12 Stretch ratio 1.95 1.87 1.89 Tear strength MD mN 287 280 284 Tear strength CD mN 308 298 300 I-bond 401 <![CDATA[J / m 2 ]]> 2000 2000 2000 Curl / MD middle Spend 26 27 27

[0361] The results show that, in the whole pilot production process, even if the paper density is higher, the paper thickness (paper thickness) can also be maintained. When the amount of the non-regenerated BCP produced by hardwood in the fiber furnish increases, an excellent forming index can be maintained on the paper machine. In calendered glass paper TP201, TP202, a higher paper density may also be arranged, wherein the fiber furnish is mainly the non-regenerated BCP produced by hardwood. The shorter fiber length and the roughness of the BCP produced by eucalyptus seem to have some influence on calendered paper properties, such as tensile strength and formability. However, the fiber furnish mixture (wherein most of the fibers come from the non-regenerated bleached chemical pulp produced by eucalyptus) can be used in the industrial glass paper manufacturing process, thereby obtaining calendered glass paper, wherein quality characteristics have been fully retained to be used as the base material of release liner.

[0362] The pilot production results thus further reinforce the insights already gained from the computational modeling disclosed above. In particular, the quality parameters of the calendered glass paper produced in the pilot production demonstrate that it is possible to produce calendered glass paper suitable for use as a substrate for release liners, where the fiber furnish consists primarily of non-recycled BCP produced from hardwood, particularly eucalyptus. The fiber furnish's properties can be further modified by adding small amounts of recycled pulp, such as pulp mill broke. Furthermore, non-recycled BCP produced from softwood can be replaced by non-recycled bleached chemical pulp produced from hardwood or recycled pulp.

Claims

1. A calendered glass paper suitable for use as a substrate (GLA1) for a release liner, the calendered glass paper comprising a fiber furnish wherein - an amount equal to or higher than 5% by weight of fibers from o Recycled pulp (REP1) obtained from release liner glassine, o Pulp mill broke (BRK1) or o any combination of these, And among them the remainder of said fibers forming up to 100% by weight of said fiber furnish is non-recycled bleached chemical pulp (BCP1) produced from hardwood, wherein said remainder is an amount equal to or higher than 60% by weight, The amount can be determined as dry matter content according to SCAN-P 39:80, the fiber furnish can be determined according to ISO 9184-4 in combination with ISO 9184-1, The calendered glass paper has - can be measured according to ISO 536 at 40g / m 2 Up to 120g / m 2 Within the range of gram weight, - Equal to or higher than 1.050 g / cm3, measurable according to ISO 534 3 The density and - A transparency equal to or higher than 40%, measurable according to ISO 2469.

2. A method for producing a calendered glass paper suitable for use as a substrate (GLA1) for release liner, the method comprising - mixing the pulp so as to obtain a raw material (MIX1) comprising a fiber furnish, wherein o Fibers in an amount equal to or greater than 5% by weight are derived from ■ Recycled pulp (REP1) obtained from release liner glassine paper, ■Pulp mill broke (BRK1) or ■Any combination of these, and o the remainder of said fibers forming said fiber furnish comes from non-recycled bleached chemical pulp (BCP1) produced from hardwood, wherein said remainder is an amount equal to or higher than 60% by weight, The amount can be determined as dry matter content according to SCAN-P 39:80, the fiber furnish can be determined according to ISO 9184-4 in combination with ISO 9184-1, - forming a paper web (WEB1) of said stock (MIX1) on a paper machine; - reducing the moisture content of the paper web (WEB1) in the pressing section; - drying the paper web (WEB1) in a drying section, thereby forming paper; and - calendering the paper so as to form calendered glassine paper, The calendered glass paper has - can be measured according to ISO 536 at 40g / m 2 Up to 120g / m 2 Within the range of gram weight, - Equal to or higher than 1.050 g / cm3, measurable according to ISO 534 3 The density and - A transparency equal to or higher than 40%, measurable according to ISO 2469.

3. The method according to claim 2, wherein said method, before said mixing, - said non-recycled bleached chemical pulp (BCP1) produced from hardwood has a Schopper-Riegler number equal to or less than 50, such as in the range of 25 to 50, preferably in the range of 25 to 45, most preferably in the range of 25 to 40, and - said recycled pulp (REP1) obtained from release liner glassine has a Schopper-Riegler number equal to or higher than 25, such as in the range of 25 to 65, preferably in the range of 30 to 60, most preferably in the range of 40 to 55, said Schopper-Riegler number being determinable according to ISO 5267-1.

4. The method according to claim 2 or 3, wherein the non-recycled bleached chemical pulp (BCP1) produced from hardwood - from birch (Betula spp.), - an average fiber length comprised in the range of 0.9 mm to 1.0 mm, and - Contains an average number of kinks in the range of 2100 to 3200 per meter.

5. The method according to claim 2 or 3, wherein the non-recycled bleached chemical pulp (BCP1) produced from hardwood - from the eucalyptus tree (Eucalyptus spp.), - an average fiber length comprised in the range of 0.8 mm to 0.9 mm, and - Contains an average number of kinks in the range of 2800 to 3500 per meter.

6. Paper according to claim 1 or method according to claim 2 or 3, wherein the non-recycled bleached chemical pulp (BCP1) produced from hardwood is birch (Betula spp.), eucalyptus (Eucalyptus spp.) or a combination of these.

7. Paper or method according to any of the preceding claims, wherein the recycled pulp (REP1) obtained from release liner glassine paper contains particles having a length of less than 200 microns originating from the recycled pulp in an amount equal to or higher than 10% of the total amount of fibers in the recycled pulp, when measured as length-weighted average fiber length by automated optical analysis using unpolarized light according to ISO 16065-2:2014.

8. Paper or process according to any of the preceding claims, wherein the fibers of the recycled pulp (REP1) obtained from release liner glassine paper have an average fiber width of less than 25 μm, preferably in the range of 19 to 25 μm, most preferably in the range of 19 to 21 μm, when determined by automated optical analysis using unpolarized light according to ISO 16065-2:2014.

9. The paper or method according to any one of the preceding claims, wherein the calendered glass paper has - can be measured according to ISO 536 at 40g / m 2 Up to 90g / m 2 In the range of 45g / m 2 Up to 80g / m 2 In the range of 50g / m 2 Up to 60g / m 2 Within the range of gram weight, - can be measured according to ISO 534 at 1.050 g / cm 3 Up to 1.200g / cm 3 In the range of 1.060 g / cm 3 to 1.190g / cm 3 range, most preferably 1.060 g / cm 3 to 1.180g / cm 3 Density within the range and / or - a transparency, measurable according to ISO 2469, in the range of 40% to 60%, preferably in the range of 42% to 53%, most preferably in the range of 44% to 52%.

10. Paper or method according to any of the preceding claims, wherein the fibers are derived from recycled pulp (REP1) obtained from release liner glassine paper in an amount in the range of 5 to 40 wt. %, preferably in the range of 10 to 40 wt. %, most preferably in the range of 20 to 40 wt. %, so that the total amount of fibers in the fiber furnish is 100 wt. %, said amount being measurable as dry matter content according to SCAN-P 39:80, said fiber furnish being measurable according to ISO 9184-4 in combination with ISO 9184-1.

11. Paper or method according to any one of the preceding claims, wherein the fiber furnish does not comprise non-recycled chemical pulp produced from softwood.

12. A release liner (REL1) comprising the calendered glass paper according to any one of claims 1 or 4 to 11 and a release coating.

13. Use of fibers from non-recycled bleached chemical pulp (BCP1) produced from hardwood in combination with fibers from recycled pulp (REP1) obtained from release liner glassine or pulp mill broke (BRK1) and without fibers from non-recycled chemical pulp produced from softwood for the manufacture of calendered glassine paper suitable for use as a substrate for release liner paper, wherein - the amount of non-recycled bleached chemical pulp (BCP1) produced from hardwood is equal to or higher than 60% by weight, and - the amount of recycled pulp (REP1) obtained from release liner glassine or pulp mill broke (BRK1) is equal to or higher than 5% by weight of the fiber furnish, so that the total amount of fibers in the fiber furnish is 100% by weight.

14. Use according to claim 13, wherein the amount of recycled pulp (REP1) obtained from release liner glassine paper is in the range of 5 wt.-% to 40 wt.-%, preferably in the range of 10 wt.-% to 40 wt.-%, most preferably in the range of 20 wt.-% to 40 wt.-%, so that the total amount of said fibers in the fiber furnish is 100 wt.-%, said amount being determinable as dry matter content according to SCAN-P 39:80, said fiber furnish being determinable according to ISO 9184-4 in combination with ISO 9184-1.

15. Use according to claim 13, wherein the non-recycled bleached chemical pulp produced from hardwood is birch (Betula spp.), eucalyptus (Eucalyptus spp.) or a combination of these.

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