Release liner base paper based on recycled fibers for release liner applications

Abstract

The present invention relates to a release liner base paper comprising at least 5 wt% of recycled fibers from recycled paperboard-based fibers, printing material-based fibers or both, and having a density of at least 1.00 g / cm3. Further aspects of the invention relate to a method for producing said release liner base paper, to the use of said release liner base paper in a method for producing a release liner, to a release liner comprising said release liner base paper and to a laminate comprising said release liner.

Description

TECHNICAL FIELD

[0001] The present invention relates to a high-quality release liner base paper, which comprises at least 5 wt% of fibers from recycled cardboard-based fibers, printed material-based fibers or recycled fibers from two different sources, and has a density of at least 1.00 g / cm 3 ³. In addition, the present invention relates to a method for producing the release liner base paper described herein.

[0002] A further aspect of the present invention relates to the use of the release liner base paper in a method for producing a release liner, a release liner comprising the release liner base paper, and a laminate comprising the release liner. BACKGROUND OF THE INVENTION

[0003] Release liners are effective carriers for self-adhesive labels and adhesive materials. The release liner is formed by applying a release coating composition on a base layer and curing the coating composition to provide a release coating, usually a silicone layer. Self-adhesive labels and self-adhesive materials are everywhere in daily necessities, as well as in complex applications and durable equipment.

[0004] The base layer to be silicified must have certain properties to ensure the two main functions of the release liner: protecting the self-adhesive product before use and perfectly transferring the adhesive upon removal. The key features required for manufacturing such a base layer include different mechanical properties and a perfect silicone anchorage rate. The base layer should also have a low air permeability to limit the penetration of silicone inside the base layer as much as possible, so as to achieve sufficient release properties and reduce the amount of silicone. The base layer should also have a high density to have mechanical properties, so as to be able to perform further die-cutting steps on the labels placed on the silicified base layer. In addition, the chemical structure of the base layer should not prevent the cross-linking of the silicone system.

[0005] Compared with release liners based on synthetic polymers, release liners based on natural fibers help reduce product waste because they contain a base paper made of cellulose fibers and are therefore suitable for recycling. In addition, cellulose fibers are derived from wood, which is a completely renewable resource. However, the global social goal of sustainability also extends to the release liner market. Given its numerous applications, there is an increasing need for more sustainable release liners to help protect the environment, save resources and reduce the carbon footprint of release liners.

[0006] Since paper has good recyclability, a common method for improving the manufacturing sustainability of paper-based products is to add recycled raw materials. However, those skilled in the art of release liner production are well aware that there are high-quality requirements for the fibers used to produce the release liner base paper, and the fibers are required to have desired mechanical properties, silicone anchorage and cross-linking.

[0007] When using fibers from recycled post-consumer waste (PCW), i.e., waste paper from various sources, the fibers also contain various impurities, including so-called silicone curing poisoning additives. It is expected that the desired base paper characteristics will deteriorate. Such poisoning additives are substances known to inhibit or poison the crosslinking reaction of silicone release coatings (see Table No. 30-1053-01 on consumer.dow.com). Without limitation, examples of such inhibitors or poisons are optical brighteners, colorants, deinking agents, and other compounds containing one or more groups selected from nitrogen, sulfur, and phosphorus groups.

[0008] For this reason, so far, if any, only a very small amount of PCW fibers have been added to release liners. For example, US2012 / 0121893 mentions the possibility of adding fibers from recycled sources, including PCW, but does not further specify the actual presence of detectable amounts of such fibers.

[0009] WO 2020 / 084188 describes an alternative method for increasing the amount of recycled fibers in release liners. Among them, very high-quality fibers from very narrow recycled sources are used. Specifically, only recycled release liner pulp is considered to meet the high standards for release liner production. EN 643 (European list of standard grades for recycled paper and board) assigns recycled release liners to a very specific grade 5.05.03 according to Group 5. However, providing such high-quality recycled fibers is associated with a relatively high pretreatment input under high energy demand.

[0010] Another problem that may prevent technicians from using recycled fibers from various sources is the possible presence of materials based on recycled cardboard. Such materials have a high ash content. In the field of release liners, the goal is to maintain a low ash content because an increase in ash content is generally associated with a decrease in the mechanical properties and transparency of the finished product. In addition, technicians will not consider using cardboard-based materials because the high ash content increases the likelihood of fouling of the paper machine circuit and wire scaling.

[0011] Technical Problem

[0012] In order to protect the environment, save resources, and reduce the carbon footprint of release liner base paper, it is necessary to further improve the sustainability of state-of-the-art release liners containing release liner base paper made of cellulose fibers. Generally, this can be achieved by adding recycled fibers. However, it is currently not possible to use a large amount of waste paper from various sources while maintaining the desired release liner base paper characteristics. So far, only a very limited amount of recycled fibers or a significantly narrowed source of recycled fibers has been used.

[0013] In view of the above, there is a need for a more sustainable release liner, that is, to provide a base paper for a release liner, the base paper for the release liner comprising a large amount of recycled PCW fibers from various sources while maintaining the desired characteristics. In addition, there is a need for a simple and low-energy-consuming method for producing a base paper containing a large amount of recycled fibers. Summary of the Invention

[0014] The present invention is based on the discovery that the above problems can be solved by preparing a base paper for a release liner having a density of at least 1.00 g / cm 3 using at least 5 wt% of recycled fibers from recycled cardboard-based fibers, printed material-based fibers, or both. That is, the present invention provides a more sustainable base paper for a release liner, which comprises a large amount of recycled fibers from various sources while maintaining the desired characteristics.

[0015] Accordingly, a first aspect of the present invention provides a base paper for a release liner, which comprises at least 5 wt% of recycled fibers from recycled cardboard-based fibers, printed material-based fibers, or both, and has a density of at least 1.00 g / cm 3 .

[0016] In a second aspect, the present invention provides a method for producing a base paper for a release liner. The method comprises the steps of: dispersing recycled fibers and optionally virgin fibers in a pulper, refining the fiber suspension, placing the refined fiber suspension on a forming wire and dewatering the refined fiber suspension, applying a base coat composition on at least one side of the dewatered paper web, and drying it.

[0017] In a third aspect, the present invention provides the use of the base paper for a release liner according to the first aspect as a base layer in a method for producing a release liner. The method comprises the steps of: applying a release coat composition on at least one side of the base paper for a release liner, and curing the composition to form a release coating.

[0018] In a fourth aspect, the present invention provides a release liner, which comprises the base paper for a release liner according to the first aspect and a release coating on at least one side of the base layer.

[0019] In a fifth aspect, the present invention provides a laminate, which comprises the release liner according to the fourth aspect, a facing material, and an adhesive layer disposed between the release liner and the facing material. Brief Description of the Drawings

[0020] Figure 1 Shows a comparison of the air permeability values of the base papers E1-A (expressed as 14.3 wt%) and E1-B (expressed as 21.4 wt%) of the present invention with the standard base paper CE1.

[0021] Figure 2 Shows the comparison of the Rizinus Cobb values of the base papers E1-A (represented by 14.3 wt%) and E1-B (represented by 21.4 wt%) of the present invention with the standard base paper CE1.

[0022] Figure 3 Shows the comparison of the air permeability values of the base paper E2 (represented by 14.3 wt%) of the present invention with the standard base paper CE2.

[0023] Figure 4 Shows the comparison of the Rizinus Cobb values of the base paper E2 (represented by 14.3 wt%) of the present invention with the standard base paper CE2.

[0024] Figure 5 Shows the comparison of the air permeability values of the base paper E3 (represented by 14.3 wt% + 50 wt%) of the present invention with the standard base paper CE3.

[0025] Figure 6 Shows the comparison of the Rizinus Cobb values of the base paper E3 (represented by 14.3 wt% + 50 wt%) of the present invention with the standard base paper CE3.

[0026] Figure 7 Shows the comparison of the release force and silicone coating weight of the base paper E3 of the present invention with the standard base paper CE3. Detailed Description

[0027] In a first aspect of the present invention, the present invention relates to a novel release liner base paper comprising recycled fibers and having a density of at least 1.00 g / cm 3 The recycled fibers are fibers based on recycled cardboard, fibers based on printed materials, or both, and based on the total weight of the fibers in the release liner base paper, the amount of the recycled fibers in the release liner base paper is at least 5 wt%.

[0028] The term "recycled fiber" refers to fibers obtained from recycled and reprocessed waste materials for use in new products. Recycling is a key aspect of the circular economy, thus saving resources in terms of raw materials. That is to say, recycled fibers are derived from products that were once made from virgin fibers. The term "virgin fiber" refers to fibers that have not been processed in the manufacture of a product.

[0029] The fibers contained in the base paper according to the present invention are preferably composed of cellulose fibers. The base paper may contain natural cellulose fibers, including pulp, artificial fibers, or mixtures thereof. Artificial fibers may be synthetic fibers or modified cellulose fibers, also known as regenerated cellulose fibers. There are two main types of regenerated cellulose: Lyocell and viscose fiber, also known as rayon. The diameter and length ranges of cellulose fibers depend on the type and source of the fibers. Generally, however, the length of recycled fibers is shorter than that of untreated virgin fibers of the same type and source.

[0030] The recycled fibers according to the present invention are not limited to a specific source, but are based on general post-consumer waste selected from fibers based on recycled cardboard, fibers based on recycled printed materials, or both. Recycled fibers are recycled fibers included in Group 1, Group 2, Group 3 (except grade numbers 3.18 and 3.20), Group 4, and Group 5 (except grade numbers 5.05.03 and 5.06) as defined in EN 643. Exemplary embodiments of printed materials and cardboard include product packaging materials, newspapers, printed office paper, printed writing paper, printed letters and envelopes, multi-ply boards, boxes, kraft paper bags, paper cups and tableware, books, and magazines. Thus, the recycled fibers according to the present invention include a wide variety of materials.

[0031] An amount of at least 5 wt% of recycled fibers means that, based on the total weight of the fibers in the release liner base paper, the amount of virgin fibers in the release liner base paper is 95 wt% or less. In the present disclosure, the total weight of the fibers in the release liner base paper refers to the dry weight of the fibers. In the case where the amount of recycled fibers is less than 5 wt%, the base paper is insufficient in terms of improving air permeability, energy conservation, and resource savings.

[0032] The virgin fibers commonly used to prepare the release liner base paper may be selected from bleached or unbleached softwood pulp, bleached or unbleached hardwood pulp, bleached or unbleached chemical pulp from hardwood or softwood, bleached or unbleached chemithermomechanical pulp from hardwood or softwood, or mixtures thereof. The ratio of unbleached pulp to bleached pulp in the virgin pulp may be from 0 (no unbleached pulp) to 3, preferably from 0.3 to 2.7, more preferably from 0.5 to 2.5.

[0033] Based on the total weight of the virgin fibers, the virgin fibers can comprise at least 10 wt%, or at least 25 wt%, or at least 45 wt%, or at least 70 wt% of bleached chemical pulp. The bleached chemical pulp can be composed of a blend of hardwood fibers and softwood fibers, and based on the total weight of the bleached chemical pulp, the hardwood fibers are present in this blend in an amount of at least 50 wt%, preferably at least 75 wt%, and based on the total weight of the bleached chemical pulp, the softwood fibers are present in an amount of at most 50 wt%, preferably at most 25 wt%. Based on the total weight of the virgin fibers, the virgin fibers can further comprise at least 2 wt% and less than 50 wt% of bleached chemithermomechanical pulp. According to some specific embodiments, based on the total weight of the virgin fibers, the bleached chemithermomechanical pulp can be present in the virgin fibers in an amount of 5 wt% to 45 wt% or 10 wt% to 35 wt%.

[0034] Based on the total weight of the virgin fibers, the virgin fibers can comprise 0 wt%, at least 10 wt%, or at least 20 wt%, or at most 75 wt%, or at most 60 wt% of unbleached virgin pulp. Preferably, based on the total weight of the virgin fibers, the virgin fibers can comprise 10 wt% to 75 wt% of unbleached virgin pulp, and more preferably 20 wt% to 60 wt%. In the following, when referring to "unbleached pulp" or "unbleached fibers", this refers to "virgin fibers comprising unbleached pulp".

[0035] The unbleached pulp can be composed of hardwood fibers, softwood fibers, or a blend of both. Based on the total weight of the unbleached pulp, the hardwood fibers can be present in an amount of at least 50 wt%, preferably at least 75 wt%. Based on the total weight of the unbleached pulp, the softwood fibers can be present in an amount of at most 50 wt%, preferably at most 25 wt%. Based on the total weight of the virgin fibers, the virgin fibers can further comprise at most 50 wt% of unbleached chemithermomechanical pulp or chemical pulp. Preferably, based on the total weight of the virgin fibers, at most 50 wt% of unbleached chemithermomechanical pulp, chemical pulp, or both are composed of a blend of hardwood and softwood.

[0036] Surprisingly, it has been found that the properties of a release liner base paper according to the invention comprising at least 5 wt% of recycled fibers are the same as or better than those of a release liner base paper without recycled fibers. Considering the very diverse sources of fibers based on recycled cardboard and printed materials and containing various impurities, the overall good properties are particularly unexpected. Without being bound by any theory, the heterogeneous fiber mixture (i.e., a mixture of virgin fibers and recycled fibers) seems to produce a specific structural design in which the recycled fibers according to the invention interact with the commonly used virgin fibers. In this way, a particularly beneficial base paper structure is formed, which is able to compensate for the negative effects caused by the presence of impurities.

[0037] In particular, considering the presence of the silicone curing poisoning additive as discussed above, the good silicone anchoring and crosslinking of the release liner base paper according to the invention is surprising, as will be discussed in more detail later.

[0038] It has also surprisingly been found that the high ash content of the material based on recycled cardboard does not have a negative impact on the mechanical properties and transparency of the finished product. As previously discussed, this is not what would be expected when using materials based on recycled cardboard. Without being bound by theory, it is clear that the specific structural design of the base paper according to the invention as described previously compensates for any negative effects that are usually associated with a high ash content.

[0039] Furthermore, it has been very surprisingly found that the release liner base paper according to the invention containing at least 5 wt% of recycled fibers is more closed than the base paper without recycled fibers. That is to say, the base paper according to the invention exhibits an improved (lower) air permeability as the amount of recycled fibers increases. Figure 1 The air permeability values of base papers containing 0 wt% (not shown), 14.3 wt% and 21.4 wt% of recycled fibers were compared. The measurement points were obtained by measuring jumbo reels of different base papers produced in a continuous process. Without being bound by any theory, in the specific structural design described previously, the recycled fibers according to the invention seem to be able to interact with the virgin fibers in a particularly beneficial and tight manner.

[0040] It has also surprisingly been found that introducing at least 5 wt% of recycled fibers into the composition of the release liner base paper can reduce the energy consumption during the manufacture of the release liner base paper, and in particular reduce the refining energy of the fibers before they are deposited on the forming wire of the paper machine.

[0041] In addition, it has been found that when the release liner base paper contains unbleached virgin fibers in addition to recycled fibers, the above-mentioned effects brought about by introducing recycled fibers can still be observed. This is not what would be expected, because unbleached pulp still contains a certain amount of lignin, which is usually removed by the bleaching process. Lignin keeps the fibers hydrophobic and rigid. Therefore, unbleached pulp requires higher refining energy to provide a base paper with high density, low porosity and a certain degree of transparency. Given these difficulties in processing unbleached pulp, unbleached pulp has not been successfully used so far in the preparation of high-end release liner base papers, especially when producing cellophane or SCK products by supercalendering. However, unexpectedly, it has been found that when unbleached pulp is added to the release liner base paper according to the invention, a dense release liner base paper with a very low porosity and high transparency can be obtained.

[0042] Furthermore, it has surprisingly been found that the properties of such base papers according to the preferred embodiments described in further detail below are not only good overall, but are even improved. That is to say, despite the presence of a large amount of unbleached pulp, this base paper according to the preferred embodiments of the present invention still exhibits an improved (lower) air permeability (see Figure 5 , described in further detail below) and an improved (reduced) Rizinus Cobb (see Figure 6 , described in further detail below) compared to a standard base paper without recycled fibers and unbleached pulp. The use of unbleached pulp also contributes to the production of a more sustainable release liner base paper, since, unlike bleached pulp, unbleached pulp does not undergo chemical treatment (i.e., bleaching) during production.

[0043] In another preferred embodiment of the first aspect, based on the total weight of the fibers in the release liner base paper, the amount of recycled fibers in the release liner base paper is at least 10 wt%, preferably 15 wt% to 80 wt%, more preferably 20 wt% to 50 wt%. This means that based on the total weight of the fibers in the release liner base paper, the amount of virgin fibers is 90 wt% or less, preferably 85 wt% to 20 wt%, more preferably 80 wt% to 50 wt%. When the amount of recycled fibers in the release liner base paper is at least within the above-mentioned preferred lower limit range, the air permeability, energy conservation and resource savings are further improved. In the case where the amount of recycled fibers is higher than the preferred upper limit range, the processability may be reduced. Furthermore, it has been found that the release liner base paper according to the present invention containing at least 20 wt% of recycled fibers is even more closed, thereby further improving the air permeability and also improving the Rizinus Cobb. Figure 2 The Rizinus Cobb values of base papers containing 0 wt% (not shown), 14.3 wt% and 21.4 wt% of recycled fibers were compared. The measurement points were obtained by measuring jumbo reels of different base papers produced in a continuous process.

[0044] In a preferred embodiment of the first aspect of the present invention, the release liner base paper has a basis weight of 1.05 g / cm 3 to 1.26 g / cm 3 , preferably 1.09 g / cm 3 to 1.24 g / cm 3 and more preferably 1.12 g / cm 3 to 1.22 g / cm 3The density. The density can be measured by methods well-known in the paper field. For example, the density can be calculated by dividing the basis weight of the release liner base paper (measured according to ISO 536 standard) by the thickness of the release liner base paper (measured according to ISO 534 standard). The density of the release liner base paper represents the technical characteristic properties of the high-quality base paper required to provide the desired properties for the release liner. That is, at least 1.00 g / cm 3 The high density ensures that the release liner base paper has mechanical properties, enabling further die-cutting steps on the label placed on the release liner without cutting the release liner.

[0045] Preferably, the quality of the release liner base paper and the suitability for coating with a silicone release coating composition can be further determined by the following technical characteristics. If one or more technical characteristics selected from the group consisting of air permeability, transparency, Bekk smoothness, Rizinus Cobb, tensile strength, and tear resistance can be further improved, the main functions of the release liner discussed previously can be further improved. When producing the release liner, the silicone release coating composition needs to be retained on the surface of the base paper to limit silicone consumption. Therefore, the release liner base paper should absorb as little silicone as possible.

[0046] That is, in a preferred embodiment of the first aspect, the base paper has an air permeability of 100 pm / Pa·s to 70000 pm / Pa·s. The term "air permeability" as mentioned herein is the rate at which air flows vertically through a known area under a specified air pressure difference between the two surfaces of the material. Preferably, the base paper has an air permeability in the range of 500 pm / Pa·s to 50000 pm / Pa·s measured according to the SCAN P26 standard. When the air permeability is within the range of the preferred embodiment, the silicone adhesiveness can be further improved. As previously mentioned and as Figure 1 shown, it has been found that the air permeability decreases as the amount of recycled fiber according to the present invention increases.

[0047] In another preferred embodiment of the first aspect, the release liner base paper has a transparency of 4% to 65%, preferably 25% to 60% measured according to the DIN 53147 standard, and has a basis weight of 30 g / m 2 to 140 g / m 2 , preferably 45 g / m 2 to 90 g / m 2Basis weight. Transparency may be particularly relevant for certain types of release liner base papers, such as the high-end product glassine paper described in further detail below. This is achieved by supercalendering the base paper (described in further detail below) until the desired transparency is reached. The term "basis weight" is synonymous with the term "grammage" and refers to the areal density of the paper product, expressed as weight per unit area (gsm = g / m 2 ). The basis weight of the release liner base paper includes the basis weight of an optionally applied undercoat formed on at least one side of the base paper, as defined in further detail below in the preferred embodiments.

[0048] In yet another preferred embodiment of the first aspect, the base paper has a Bekk smoothness of 15 seconds to 1500 seconds, preferably 25 seconds to 1200 seconds, as measured according to the TAPPI T479 standard, on the back side, and a Bekk smoothness of 400 seconds to 4000 seconds, preferably 500 seconds to 3500 seconds, on the front side. When the Bekk smoothness is below the said range, the formation of the release coating may be impaired.

[0049] In a further preferred embodiment of the first aspect, the base paper has a Rizinus Cobb value of 0.2 g / m 2 to 4 g / m 2 , preferably 0.3 g / m 2 to 3 g / m 2 , more preferably 0.6 g / m 2 to 1.4 g / m 2 . Rizinus Cobb refers to the oil permeability and is measured on the front side according to the ISO 535 standard. As mentioned above and as Figure 2 shown, it has been found that release liner base papers according to the invention containing at least 20 wt% recycled fibers can be even more closed, thus improving (reducing) the Rizinus Cobb. The Rizinus Cobb value measures the ability of silicone to penetrate into the release liner base paper. A release liner base paper with a lower Rizinus Cobb value allows less silicone to penetrate into the paper, thus reducing silicone consumption in the production of release liners.

[0050] In another preferred embodiment of the first aspect, the release liner base paper has a tensile strength of 2.0 kN / m to 18.0 kN / m, preferably 4.0 kN / m to 15.0 kN / m, in the longitudinal direction as measured according to the ISO 1924 standard and has a tensile strength of 1.0 kN / m to 15 kN / m, preferably 2.0 kN / m to 12.0 kN / m, in the cross direction. Tensile strength refers to the maximum tensile force per unit width that paper and paperboard can withstand before breaking, under the conditions defined in the ISO 1924 standard.

[0051] In yet another preferred embodiment of the first aspect, the base paper has a tear resistance of 100 mN to 1500 mN, preferably 150 mN to 1300 mN, in the longitudinal direction as measured according to ISO 1974 standard and has a tear resistance of 100 mN to 1500 mN, preferably 150 mN to 1300 mN, in the cross-longitudinal direction. Tear resistance refers to the maximum force required to tear a sample in a specific direction.

[0052] As used herein, the term "longitudinal direction" refers to the direction in which the paper moves through the paper machine and the term "cross-longitudinal direction", also known as "transverse direction", is the direction perpendicular to the longitudinal direction.

[0053] In another preferred embodiment of the first aspect, the present invention relates to a novel release liner base paper, which, in addition to at least 5 wt% of recycled fibers as described above, further comprises virgin fibers, and the virgin fibers comprise unbleached fibers. Based on the total weight of the fibers in the release liner base paper, the amount of unbleached fibers in the release liner base paper can be at least 10 wt%. Preferably, based on the total weight of the fibers in the release liner base paper, the amount of unbleached virgin fibers can be at least 10 wt% or at least 20 wt% or at most 70 wt% or at most 60 wt%. Specifically, the base paper according to a preferred embodiment of the present invention may comprise 10 wt% to 70 wt%, preferably 20 wt% to 60 wt% of unbleached virgin fibers; 10 wt% to 65 wt%, preferably 15 wt% to 50 wt% of recycled fibers; and 25 wt% to 50 wt%, preferably 30 wt% to 45 wt% of bleached virgin fibers. The unbleached virgin fibers, recycled fibers and bleached virgin fibers are as described above. More specifically, the ratio of unbleached pulp to bleached pulp in the virgin pulp can be at most 3, preferably 0.3 to 2.7, more preferably 0.5 to 2.5.

[0054] Preferably, the release liner base paper of the preferred embodiment, in addition to recycled fibers, further comprises unbleached fibers, which may have a transparency of at least 30%, preferably at least 37%, more preferably at least 43% as measured according to DIN 53147 standard, while having a basis weight of 40 g / m 2 to 80 g / m 2 as measured according to ISO 536. Achieving such a high transparency by adding unbleached fibers to the base paper of the present invention is absolutely unexpected to those skilled in the art, and the base paper already contains at least 5 wt% of recycled fibers from various sources and thus already has some inherent coloring. Transparency is achieved by refining the pulp and supercalendering the base paper. As discussed above, these are challenging processing steps when applied to unbleached fibers that have become hard due to residual lignin.

[0055] Although the release liner base paper of the preferred embodiment allows for sufficient transparency to be achieved for high - demand applications, such as in the pressure - sensitive adhesive or label markets, due to the use of recycled fibers and unbleached fibers, the base paper has a natural coloring. This natural coloring allows for the omission of the addition of dyes, which is common in the field of release liner base paper production. That is, the base paper of the preferred embodiment limits the use of chemicals and is thus more environmentally friendly.

[0056] The general considerations outlined above regarding the technical features indicating the quality of the release liner base paper according to the present invention and its suitability for silicone coating also apply to the preferred embodiment containing recycled fibers and unbleached fibers. That is, the base paper of the preferred embodiment containing recycled fibers and unbleached fibers can have a density, air permeability, transparency, Bekk smoothness, Rizinus Cobb, tensile strength, and tear resistance within the ranges described above, thereby further improving the main functions of the release liner made from such a base paper. Additionally, the following observations were made regarding air permeability and Rizinus Cobb.

[0057] Figure 5 The air permeability values of a standard base paper containing 0 wt% recycled fibers and 0 wt% unbleached fibers (not shown) were compared with those of a base paper according to the present invention containing 14.3 wt% recycled fibers, 50 wt% unbleached virgin pulp, and 35.7 wt% bleached virgin pulp. The measurement points were obtained by measuring jumbo reels of different base papers produced in a continuous process and supercalendered under the same conditions. As described above and as Figure 5 shown, it has been found that the release liner base paper containing recycled fibers and unbleached virgin pulp exhibits improved (lower) air permeability. That is, the recycled fibers according to the present invention even seem to be able to interact with the unbleached pulp in a particularly beneficial way to form a tight structure, thus compensating for their rigidity and producing a more closed structure than the base paper without recycled fibers and unbleached pulp. The reduction in air permeability can also reduce the silicone consumption in the silicification step during release liner production.

[0058] Figure 6 The Rizinus Cobb values of a standard base paper containing 0 wt% recycled fibers and 0 wt% unbleached pulp (not shown) were compared with those of a base paper according to the present invention containing 14.3 wt% recycled fibers, 50 wt% unbleached virgin pulp, and 35.7 wt% bleached virgin pulp. The measurement points were obtained by measuring jumbo reels of different base papers produced in a continuous process. As described above and as Figure 6As shown, it has been found that the release liner base paper containing a large amount of unbleached virgin pulp in addition to recycled fibers improves (decreases) the Rizinus Cobb value in the case of 14.3 wt% recycled fibers. That is to say, the release liner base paper containing recycled fibers and unbleached virgin pulp according to the preferred embodiment allows less silicone to penetrate into the paper, and thus reduces the silicone consumption in the production of release liners.

[0059] In addition, it has surprisingly been found that the carbon footprint is significantly reduced when producing the release liner base paper of the preferred embodiment compared to the standard release liner base paper that does not contain unbleached virgin pulp and recycled fibers. In 2021, the amount of supercalendered base paper used for label applications was approximately 1 million tons. Currently, the base paper required for this application is made using bleached virgin pulp. Bleached pulp is produced by treating unbleached pulp with chemicals in order to whiten the fibers by removing the lignin that is naturally present in these fibers. In the case of the preferred embodiment, which contains a large amount of unbleached virgin pulp, the degree of pretreatment of the pulp can be significantly reduced. When producing the release liner base paper of the preferred embodiment, the carbon footprint can be reduced by 3% to 50% as measured according to the ISO 14067 standard described in the experimental section.

[0060] The release liner base paper of the present invention The release liner base paper can preferably be selected from the group of release liners known in the field of paper release liners and consists of cellophane, clay-coated kraft (CCK) paper, and supercalendered kraft (SCK) paper.

[0061] According to a preferred embodiment of the first aspect, the release liner base paper of the present invention is cellophane. Cellophane is usually made from bleached chemical pulp and is widely used as a release liner for self-adhesive materials. Cellophane has a transparency of preferably 43% (basis weight 90 g / m 2 ) to 55% (basis weight 45 g / m 2 ). As previously mentioned, such a high transparency is achieved by supercalendering the base paper, as described in further detail below. Preferably, according to the ISO 3687 standard, the base paper has a Gurley value of 100 seconds to 2000 seconds when measured in the rewetted state immediately before the supercalendering step.

[0062] According to another preferred embodiment of the first aspect, the release liner base paper is clay-coated kraft (CCK) paper. CCK paper usually comprises a paper substrate with clay coated on the front side and is used for high-quality printing in cases where good dimensional stability is required. Usually, CCK paper has a basis weight of 1.00 g / cm 3 to 1.04 g / cm 3The density. Such paper has no requirement for transparency and is usually below 20%. The grammage of CCK paper is 60 g / m 2 to 140 g / m 2 , and such CCK paper has an air permeability rate in the range of 100 pm / Pa·s to 1000 pm / Pa·s.

[0063] In a further preferred embodiment of the first aspect, the release liner base paper comprises a base coat applied on at least one side. In a more preferred embodiment, when the release liner base paper of the present invention is cellophane, the base coat is compatible with the silicone release coating composition. The base coat may comprise at least one water-soluble binder selected from the group consisting of: polyvinyl alcohol, polyvinyl alcohol modified with an olefin group, a silanol group or a silane hydride group, starch, alginate or carboxymethyl cellulose. Preferably, the base coat comprises a modified polyvinyl alcohol as disclosed in EP 2 539 505. Preferably, the basis weight of the base coat formed by coating on at least one side of the cellophane is 0.1 g / m 2 to 10 g / m 2 , more preferably 1 g / m 2 to 3 g / m 2 .

[0064] In an alternative more preferred embodiment, when the release liner base paper of the present invention is CCK paper, the base coat is a coating comprising at least one pigment and a latex as a binder. The at least one pigment may be selected from clay, carbonate or talc. Preferably, the pigment is calcium carbonate and the binder is an emulsion comprising styrene butadiene and styrene acrylate. The binder may account for approximately 25 wt% of the dry weight of the base coat and the carbonate may account for approximately 75 wt% of the dry weight of the base coat. Preferably, the basis weight of the base coat formed by coating on at least one side of the CCK paper is 15 g / m 2 to 30 g / m 2 , more preferably 20 g / m 2 .

[0065] In a second aspect of the present invention, the present invention relates to a method for producing a release liner base paper according to the first aspect. The method comprises the following steps: dispersing recycled fibers and optionally virgin fibers in a pulper (step a), refining the fiber suspension (step b), placing the refined fiber suspension on a forming wire (step c) and dewatering the refined fiber suspension (step d), applying a base coat composition on at least one side of the dewatered paper web (step e), and drying it (step f). The recycled fibers are fibers based on recycled cardboard, fibers based on printed materials, or both, and based on the total weight of the fibers in the release liner base paper, the amount of the recycled fibers in the release liner base paper is at least 5 wt%.

[0066] The method for producing a release liner base paper according to the second aspect of the present invention can be carried out using equipment known in the art for paper production. The method can be carried out in a continuous process or can be interrupted when changing equipment.

[0067] The fibers based on recycled cardboard, fibers based on printed materials, or both according to the second aspect of the present invention are defined as above with respect to the first aspect. The amount of at least 5 wt% of recycled fibers means that based on the total weight of the fibers in the release liner base paper, the amount of virgin fibers in the release liner base paper is 95 wt% or less, which are dispersed together with the recycled fibers in the pulper in step a).

[0068] In the prior art, the step b) of refining the fibers usually requires high energy. This is used to increase the specific surface area of the fibers and thus improve the smoothness and density of the base paper. For example, when producing cellophane according to the first aspect, the pulp is usually refined to achieve a certain fiber fineness, thereby forming a dense and almost pore-free paper surface. This surface has strong resistance to air and liquids such as oil and water.

[0069] When using at least 5 wt% of recycled fibers from recycled cardboard, printed materials, or both according to the present invention, it has surprisingly been found that the refining energy in step b) can be reduced without causing any damage to the desired base paper characteristics. In Figure 3 and Figure 4 the air permeability and Rizinus Cobb value of another base paper according to the present invention containing 14.3 wt% of recycled fibers are compared with the performance of a comparative standard base paper (containing 0 wt% of recycled fibers, not shown). Compared with the standard base paper, the base paper according to the present invention is obtained, wherein the refining energy is reduced by 11%. Therefore, the method for producing a release liner base paper according to the second aspect of the present invention reduces the refining energy required for producing the release liner base paper while maintaining high quality requirements.

[0070] In step e) of the method according to the second aspect, the undercoat composition is placed on at least one side of the release liner base paper by any suitable method, and preferably by rod coating or knife coating.

[0071] In the case where the release liner base paper of the present invention is cellophane, the undercoat composition may comprise at least one water-soluble binder selected from the group consisting of polyvinyl alcohol, polyvinyl alcohol modified with olefin groups, silanol groups or silane hydride groups, starch, alginate or carboxymethyl cellulose, in order to achieve compatibility with the silicone release coating composition applied in the subsequent steps described below. A particularly preferred undercoat composition may comprise a modified polyvinyl alcohol as described in EP 2 539 505. Preferably, the basis weight of the undercoat formed by coating on at least one side of the cellophane is 0.1 g / m 2 to 10 g / m 2 , more preferably 1 g / m 2 to 3 g / m 2 .

[0072] When the release liner base paper of the present invention is CCK paper, the undercoat composition may comprise at least one pigment and a latex as a binder. The at least one pigment may be selected from clay, carbonate or talc. Preferably, the pigment is calcium carbonate and the binder is an emulsion comprising styrene butadiene and styrene acrylate. The binder may account for about 25 wt% and the carbonate may account for about 75 wt%, each based on the dry weight of the undercoat composition. Preferably, the basis weight of the undercoat formed by coating on at least one side of the CCK paper is 15 g / m 2 to 30 g / m 2 , more preferably 20 g / m 2 .

[0073] In a preferred embodiment of the second aspect, the method further comprises a step of calendering the dried, undercoat-coated paper web. In the case where the release liner base paper of the present invention is cellophane according to the first aspect, the undercoat-coated paper web is subjected to a series of wetting and multi-roll nip calendering or supercalendering steps to obtain a very dense paper having a smooth surface, high impact strength, high tear resistance and transparency. In contrast, in the case where the release liner base paper of the present invention is CCK paper according to the first aspect, calendering is carried out with only one nip.

[0074] In another preferred embodiment of the second aspect, based on the total weight of the fibers in the release liner base paper, the amount of recycled fibers in the release liner base paper is at least 10 wt%, preferably 15 wt% to 80 wt%, more preferably 20 wt% to 50 wt%. This means that based on the total weight of the fibers in the release liner base paper, the amount of non-recycled fibers is 90 wt% or less, preferably 85 wt% to 20 wt%, more preferably 80 wt% to 50 wt%.

[0075] In yet another preferred embodiment of the second aspect, the basis weight of the undercoat layer applied to at least one side of the paper, measured according to ISO 536, is 0.1 g / m 2 to 30 g / m 2 , preferably 1 g / m 2 to 20 g / m 2 . The basis weight of the undercoat layer refers to the undercoat layer in the dry state. In a more preferred embodiment, when the base paper is cellophane, the basis weight of the undercoat can be 0.1 g / m 2 to 10 g / m 2 , more preferably 1 g / m 2 to 3 g / m 2 . In a more preferred embodiment, when the base paper is CCK paper, the basis weight of the undercoat can be 15 g / m 2 to 30 g / m 2 , more preferably 20 g / m 2 .

[0076] In a further preferred embodiment of the second aspect, the recycled fibers used in step a) of the method have a dry content of greater than 50% as measured according to the TAPPI 210 standard. Using fibers with a dry content greater than 50% is more ecological in terms of transportation, storage, and processing due to the increased raw material rate per unit volume.

[0077] In another further preferred embodiment of the second aspect, the recycled fibers used in step a) of the method have a pulp freeness of 25°SR to 60°SR, preferably 30°SR to 50°SR, as measured according to a derived standard of the UNI 7621 standard. At a pulp freeness of 25°SR to 60°SR, the recycled fibers help reduce the refining energy applied in the pulp mixture to achieve the required air permeability level of the finished product.

[0078] In yet another further preferred embodiment of the second aspect, the recycled fibers used in step a) of the method have an ash content of from 0.1% to 8%, preferably from 0.5% to 7%, measured according to a derived standard of TAPPI 211 standard. When the ash content is in the range of 0.1% to 8%, the effects brought about by the specific structural design described previously are further enhanced without affecting the transparency and mechanical properties of the finished product.

[0079] In another further preferred embodiment of the second aspect, the recycled fibers used in step a) of the method have a pH value of from 5 to 12, preferably from 6 to 11, measured according to a derived standard of TAPPI 209 standard. A pH value of from 5 to 12 ensures good stability of the production process and avoids negative impacts on the properties of the finished product.

[0080] In an even more preferred embodiment of the second aspect, the recycled fibers have a dry content of greater than 50%, a pulp freeness of 25°SR to 60°SR, an ash content of from 0.1% to 8%, a pH value of from 5 to 12, and in the most preferred embodiment of the second aspect, the recycled fibers have a dry content of greater than 50%, a pulp freeness of 30°SR to 50°SR, an ash content of from 0.5% to 7%, a pH value of from 6 to 11, each measured according to the standards defined above.

[0081] In a third aspect of the present invention, the present invention relates to the use of a release liner base paper according to the first aspect as a base layer in a method for producing a release liner. The method comprises the following steps: applying a release coating composition on at least one side of the release liner base paper, and curing the composition to form a release coating.

[0082] In the context of the present invention, the term "curing" is synonymous with "crosslinking" and refers to the addition polymerization reaction between the vinyl functional groups of the silicone resin and the hydrosiloxane functional groups of the crosslinking agent.

[0083] Preferably, a silicone release coating composition according to the third aspect can be applied to one side of the release liner base paper, which release liner base paper comprises an undercoat as defined above, and the undercoat is compatible with the silicone release coating composition.

[0084] A silicone release coating composition known in the field of release liners (such as that disclosed in EP 2 539 505) can be applied to at least one side of the release liner base paper. Generally, such compositions comprise a polymer, a crosslinking agent, and a catalyst, preferably a platinum-based catalyst. Subsequently, crosslinking is carried out by curing the composition at a high temperature until curing is complete. Preferably, the crosslinking is carried out at a temperature in the range of 70°C to 160°C and under air flow, particularly preferably in a ventilation drying kiln for 10 seconds to 120 seconds.

[0085] In a fourth aspect of the present invention, the present invention relates to a release liner, which comprises a release liner base paper according to the first aspect as a base layer and a release coating on at least one side of the base layer.

[0086] In a preferred embodiment of the fourth aspect, the release coating is silicone. As previously mentioned, it has been found that the silicone anchoring and crosslinking of the release liner base paper according to the present invention containing at least 5 wt% recycled fibers meet the strict performance targets of release liner materials. This is particularly surprising considering the highly diverse sources of recycled cardboard-based and print material-based fibers in the base paper and the presence of various impurities, including the silicone curing poisoning additives described above. Without being bound by theory, apparently, the specific structural design of the base paper according to the present invention described previously compensates for any negative effects typically associated with a high ash content.

[0087] The crosslinking rate and the anchoring rate of the silicone layer are checked by the polymerization and "erasion" tests described subsequently. Silicone crosslinking is analyzed by the polymerization test, which measures the amount of silicone remaining on the silicated paper sample after immersing the sample in an organic solvent (toluene or methyl isobutyl ketone) of non-crosslinked silicone. The anchoring rate of silicone on the paper is analyzed by the erasure test. This test measures the silicone remaining on the textile after a wear test under a heavy weight. More specifically, the erasure test is carried out by applying a dynamic force of 225 g / cm 2 at a speed of 7 meters per minute on the silicone-coated paper substrate for 25 cm.

[0088] In another preferred embodiment of the fourth aspect, the release liner base paper has at least 95%, more preferably in the range of 96% to 100% silicone crosslinking, because a ratio higher than 96% indicates particularly satisfactory crosslinking.

[0089] In yet another preferred embodiment of the fourth aspect, the silicone anchoring rate on at least one side of the release liner base paper is at least 60%, preferably at least 80%, more preferably 95% to 100%. A ratio above 60% confirms that the anchoring rate is sufficient, and a ratio above 80% generally indicates good anchoring. If the polymerization test is above 95%, the value is significant.

[0090] The application fields of the release liner according to the fourth aspect are very wide. Without being limited thereto, the release liner can be used for high-speed marking applications, for consumer product branding, and also for its pricing, identification or weighing. Further, the release liner can be used for medical applications, such as release liner protecting plasters, transdermal drug delivery systems or ostomy products, to maintain hygiene, effective treatment and human health. Another exemplary application can be the assembly of components using double-sided tape.

[0091] In a fifth aspect of the present invention, the present invention relates to a laminate comprising a release liner according to the fourth aspect, a facing material, and an adhesive layer disposed between the release liner and the facing material.

[0092] Experimental Section

[0093] The present invention and the advantages it provides will be further explained in detail by the following examples with reference to the accompanying drawings.

[0094] Among various release liner base paper products, glassine paper, a high-end product, sets the highest standards for its mechanical properties and generally has very high quality requirements for the fibers used. Therefore, the following experiments will use this high-end product category to illustrate the effects of the present invention.

[0095] Preparation of Release Liner Base Paper

[0096] In the following experiments, virgin fibers and recycled fibers were used to prepare the release liner base paper. As the virgin fibers, a commercially available standard pulp used for manufacturing release liners as defined above and containing 100% virgin cellulose fibers was used.

[0097] As the recycled fibers, the recycled pulp provided by WEPA Greenfield SAS contains 100% fibers from a mixture of recycled cardboard and printing materials (see Groups 1, 2, 3 (except grade numbers 3.18 and 3.20), 4, and 5 (except grade numbers 5.05.03 and 5.06) as defined in EN 643). The recycled fibers have a pulp freeness of 34°SR, an ash content of 1.36%, and a pH value of 8.58, each measured according to the above standards.

[0098] Experiment 1

[0099] The following glassine release liner base paper was produced on a standard paper machine using a continuous process, and the effects of different amounts of recycled fibers were studied.

[0100] [Base Paper E1-A]

[0101] First, 2970 kg of bleached virgin fibers and 500 kg of recycled fibers were dispersed in a pulper equipped with 95 wt% water as the dispersion medium (based on the total weight of the fibers). To produce this first base paper E1, the refining energy applied to the fiber suspension was maintained at the standard production level for Comparative Example CE1 described below.

[0102] Next, the suspension of the refined fibers is placed on a flat forming wire and dewatered. Meanwhile, a base coat composition is prepared. According to this specific embodiment, the base coat composition corresponds to the polyvinyl alcohol modified composition disclosed in EP 2 539 505. The base coat composition is applied by a size press at 65 °C to the front side of the dewatered paper web, and a surface treatment agent (such as polyvinyl alcohol, starch, CMC, alginate) is applied to the back side to produce a base coat coated paper web. According to this specific embodiment, the total amount applied to the dewatered paper on a dry weight basis is 1.5 g / m 2 .

[0103] Subsequently, the base coat coated paper web is dried in an infrared oven. In the last step, the dried, base coat coated paper web is re-wetted to about 15 - 20% of the paper web solids content. The Gurley value of the re-wetted release liner base paper is 669 seconds. Thereafter, the re-wetted release liner base paper is off-line supercalendered to form a cellophane base paper.

[0104] [Base paper E1 - B]

[0105] The cellophane base paper E1 - B is manufactured, base coat coated and supercalendered under the same conditions as described for E1 - A, except that 2720 kg of bleached virgin fibers and 750 kg of recycled fibers are dispersed in the pulper. The Gurley value of the re-wetted release liner base paper measured immediately before the supercalendering step is 808 seconds.

[0106] [Comparative base paper CE1]

[0107] Comparative Example CE1 is a standard cellophane, which is manufactured, base coat coated and supercalendered under the same conditions as described for E1 - A and E1 - B, except that 3470 kg of bleached virgin fibers (a mixture of softwood, hardwood and BCTMP) are dispersed in the pulper. Thus, CE1 does not contain any recycled fibers. CE1 is manufactured during the same machine run as E1 - A and E1 - B. More specifically, CE1 is produced before and after E1 - A and E1 - B, as Figure 1 and Figure 2 shown. The Gurley value of the re-wetted release liner base paper measured immediately before the supercalendering step is 552 seconds.

[0108] [Characterization]

[0109] The cellophane base papers E1 - A, E1 - B and CE1 are produced in jumbo reels and the properties of these cellophanes summarized in Table 1 below are measured on each jumbo reel. The values of CE1 are averages.

[0110] Table 1: Characteristics of base papers E1-A, E1-B, and CE1.

[0111]

[0112]

[0113] As shown in Table 1, the characteristics of the high-sensitivity glassine release liner base paper according to the present invention are generally good.

[0114] In addition, base papers E1-A and E1-B containing 14.3 wt% or 21.4 wt% of recycled fibers, respectively, have a more closed structure than comparative example CE1. This is reflected in the lower air permeability and Rizinus Cobb, which means that samples E1-A and E1-B will absorb less silicone, and thus the silicone adhesion is improved compared to CE1.

[0115] In addition, it was surprisingly found that the high ash content of the material based on recycled cardboard does not have a negative impact on the mechanical properties and transparency of the finished product.

[0116] Experiment 2

[0117] The following glassine release liner base papers were produced on a standard paper machine using a continuous process, and the effect of changing the applied refining energy on the fiber suspension was studied. This required slightly different settings so that the values obtained in Experiments 1 and 2 are not directly comparable. However, the values obtained for comparative example CE2 can be directly compared with the values obtained for base paper E2 produced with 11% less refining energy.

[0118] [Base paper E2]

[0119] First, 2970 kg of bleached virgin fiber and 500 kg of recycled fiber were dispersed in a pulper equipped with 95 wt% water as the dispersion medium (based on the total weight of the fibers). To produce base paper E2, the refining energy applied to the fiber suspension was reduced by 11% compared to comparative example CE2 described below.

[0120] Subsequent manufacturing, undercoat coating, and supercalendering steps were carried out as described for base paper E1-A in Experiment 1 above. According to this specific embodiment, the total amount coated on the dewatered paper was also 1.5 g / m 2 . In addition, the Gurley value of the rewetted release liner base paper measured immediately before the supercalendering step was 747 seconds.

[0121] [Comparative base paper CE2]

[0122] Comparative Example CE2 is a standard cellophane paper, which is manufactured, undercoated, and supercalendered under the same conditions as described for E2, except that 3470 kg of bleached virgin fibers (a mixture of softwood, hardwood, and BCTMP) are dispersed in the pulper. Additionally, the fiber suspension has been refined with the energy typically used for producing this grade of paper. That is, the refining energy applied to the fiber suspension has been increased by 11%. Comparative Example CE2 does not contain any recycled fibers. CE2 and E2 were manufactured during the same machine run. More specifically, CE2 was manufactured before and after E2, as Figure 3 and Figure 4 shown. The Gurley value of the rewetted release liner base paper measured immediately before the supercalendering step was 718 seconds.

[0123] [Characterization]

[0124] The cellophane base papers E2 and CE2 were produced in jumbo reels and the properties of these papers summarized in Table 2 below were measured on each jumbo reel. The values for CE2 are the average values.

[0125] Table 2: Properties of the base papers E2 and CE2.

[0126]

[0127]

[0128] As shown in Table 2, compared with CE2, the introduction of recycled fibers in sample E2 can reduce the manufacturing energy consumption of this cellophane base paper without affecting the properties of this base paper.

[0129] Experiment 3

[0130] The following cellophane release liner base papers were produced on a standard paper machine using a continuous process, and the effects of unbleached virgin pulp and recycled fibers were studied.

[0131] [Base paper E3]

[0132] In the first step, 1250 kg of bleached virgin fibers, 1750 kg of unbleached virgin fibers, and 500 kg of recycled fibers were dispersed in a pulper equipped with 95 wt% water as the dispersion medium (based on the total weight of the fibers). According to this specific embodiment, the ratio of unbleached virgin fibers to bleached virgin fibers is 2 based on the total amount of virgin fibers. To produce base paper E3, the refining energy applied to the fiber suspension was maintained at the standard production level for Comparative Example CE3 described below.

[0133] Subsequent manufacturing, base coating application, and supercalendering steps were carried out as described for base paper E1-A in Experiment 1 above. According to this specific embodiment, the total amount applied to the dewatered paper, on a dry weight basis, was also 1.5 g / m 2 . Additionally, the Gurley value of the rewetted release liner base paper measured immediately before the supercalendering step was 701 seconds.

[0134] [Comparative base paper CE3]

[0135] Comparative Example CE3 was a standard cellophane that was manufactured, base coated, and supercalendered under the same conditions as described for E3, except that 3470 kg of bleached virgin fibers (a mixture of softwood, hardwood, and BCTMP) were dispersed in the pulper. Thus, CE3 did not contain any recycled or unbleached virgin fibers. CE3 and E3 were manufactured during the same machine run. More specifically, CE3 was produced before E3, as Figure 5 and Figure 6 shown. The Gurley value of the rewetted release liner base paper measured immediately before the supercalendering step was 621 seconds.

[0136] [Characterization]

[0137] The cellophane base papers E3 and CE3 were produced in jumbo reels and the properties of these papers summarized in Table 3 below were measured on each jumbo reel. The values for CE3 are averages.

[0138] Table 3: Properties of base papers E3 and CE3.

[0139]

[0140] As shown in Table 3, the properties of the high-sensitivity cellophane release liner base paper according to the preferred embodiment of the present invention are generally good. That is, despite the presence of recycled and unbleached virgin fibers, the density and transparency are high, and the Bekk smoothness, tensile strength, and tear resistance are comparable to those of the standard base paper CE3. Given that the E3 base paper can achieve a balance between sufficient transparency and desired coloring, there is no need to add dyes.

[0141] Furthermore, the base paper E3 containing 14.3 wt% recycled fibers and 50 wt% unbleached virgin fibers has a more closed structure than Comparative Example CE3. This is reflected in the lower air permeability and Rizinus Cobb, which means that sample E3 will absorb less silicone, and thus the silicone adhesion is improved compared to CE3. In other words, as Figure 7 shown and discussed in further detail below, in order to achieve the same release force, less silicone is applied to the base paper E3 compared to the base paper CE3.

[0142] Carbon footprint

[0143] In order to quantify the potential carbon footprint associated with the production of the release liner base paper, the following assumptions were made when using the ISO 14067 standard.

[0144] First, the quantification is based on a direct comparison of the raw materials used to produce a standard release liner base paper containing only bleached virgin pulp (hereinafter referred to as "bleached") under the same conditions with the base paper according to the present invention (hereinafter referred to as "recycled") and the base paper according to a preferred embodiment of the present invention (hereinafter referred to as "unbleached"). The "bleached" standard base paper contains 100 wt% bleached virgin fibers; the "recycled" base paper contains 14.3 wt% recycled fibers and 85.7 wt% bleached virgin fibers; and the "unbleached" base paper contains 14.3 wt% recycled fibers, 50 wt% unbleached virgin fibers and 35.7 wt% bleached virgin fibers; each based on the total weight of the fibers in the release liner base paper.

[0145] In the carbon footprint quantification, the situations to be considered are associated with the extraction and production of the raw materials.

[0146] The carbon footprint quantification can follow the EF3.0 methodology and calculate the potential carbon footprint of each grade using the climate change impact category.

[0147] Table 4: Carbon footprint quantification based on a direct comparison of the raw materials used to produce the release liner base paper according to the present invention ("recycled" and "unbleached") with the raw materials used to produce the above-mentioned standard release liner base paper ("bleached").

[0148] "Bleaching" "Recycling" "Unbleached" Influence of raw materials 0％ -12％ -46％

[0149] As shown in Table 4, the production of release liners containing recycled fibers can reduce the carbon footprint, and the production of base papers containing unbleached fibers in addition to recycled fibers can even significantly reduce the carbon footprint. Even in further production, the advantages related to carbon footprint reduction are maintained. That is, the present invention not only helps to protect the environment and save resources while maintaining the desired properties of the release liner base paper, but also reduces the carbon footprint.

[0150] Preparation of single-sided silicone-coated release liner

[0151] The above-mentioned Examples E1-A, E1-B, E2, E3, CE1, CE2 and CE3 were used as the base layer by applying 100 g of resin W920 (provided by ), 2.5 g of crosslinking agent V24 (provided by ), and 1 g of catalyst OL (platinum-based, provided by A silicone release coating composition prepared as provided) is applied to the front side of a release liner base paper to prepare a release liner. Subsequently, crosslinking is carried out by curing the composition at 140 °C for 30 seconds in a ventilated drying kiln.

[0152] Table 5: Characteristics of release liners obtained from E1-A, E1-B, E2, E3, CE1, CE2, and CE3.

[0153] Technical features E1-A E1-B CE1 E2 CE2 E3 CE3 Erasing anchorage rate [%] 96.5 97.4 97.3 97.4 97.8 96.9 97.5 Polymerization crosslinking [%] 97.9 98.8 98.2 98.8 98.2 97.9 96.8

[0154] As shown in Table 5, neither the introduction of recycled fibers with a very diverse origin and containing various impurities (including the silicone curing poisoning additives added to the cellophane as previously described) nor the addition of unbleached virgin fibers affects silicone anchoring and crosslinking. The results show that the polymerization test values and erasure test values of all cellophanes are higher than 95%, thus indicating good silicone anchoring and crosslinking even when using recycled fibers.

[0155] Siliconization test

[0156] The above-mentioned Examples E3 and CE3 were used as substrates to prepare release liners with different amounts of silicone release coating to measure the release force relative to the weight of the silicone coating. The release force corresponds to the force required to peel a label from the siliconized release liner.

[0157] As Figure 7 shown, as additional evidence, at a low silicone coating weight, the release force required for the cellophane prepared from the base paper E3 of the present invention is lower than the release force required for the standard cellophane prepared from CE3. For example, to achieve a release force of 20 cN / 25 mm using a standard base paper, approximately 0.75 g / m 2 of silicone deposition is required. Using the base paper E3 according to a preferred embodiment of the present invention, which contains unbleached fibers in addition to recycled fibers, only 0.7 g / m 2 of silicone deposition is sufficient to achieve the same release force.

[0158] The observations of the above siliconization test are consistent with the reduction of the Rizinus Cobb of the paper and the decrease in air permeability. That is, the present invention can reduce the amount of silicone to be coated, which is usually the most expensive part of the release liner material.

[0159] Summary

[0160] The characterization of the produced cellophane base paper confirms that the characteristics of the examples according to the present invention are the same as or better than those of cellophanes without recycled fibers.

[0161] This is absolutely unexpected by those skilled in the art and is also confirmed by the prior art. So far, when preparing the release liner base paper, only recycled fibers that are carefully selected and have a rather narrow source are used in a relatively high proportion. When using recycled fibers from waste paper mixtures of unknown origin, only uncertain and negligible amounts of these fibers have been used so far.

[0162] Considering the very diverse sources of recycled cardboard-based and printed material-based fibers and the various impurities they contain, including silicone-curing poisoning additives, the overall good properties of the release liner base paper according to the present invention are very surprising. In particular, the still good silicone anchoring and crosslinking measured for cellophane containing recycled fibers according to the present invention are surprising.

[0163] Furthermore, those skilled in the art would not expect that the base paper according to the present invention would have overall good properties when using recycled cardboard-based materials. It is known that such materials have a high ash content, which has a negative impact on the mechanical properties and transparency of the finished product.

[0164] In addition, it is very surprisingly found that when using at least 5 wt% of recycled fibers from recycled cardboard, printed materials or both according to the present invention, not only can the properties of the release liner base paper be maintained, but also the air permeability and Rizinus Cobb value are even improved compared to cellophane that does not contain any recycled fibers.

[0165] In the prior art, the step of refining the fibers usually requires high energy. It improves the smoothness and density of the base paper by reducing the average fiber length. When using at least 5 wt% of recycled fibers from recycled cardboard, printed materials or both according to the present invention, it is surprisingly found that the refining energy can be reduced without causing any damage to the desired base paper characteristics (see the results of base paper E2). Therefore, the method for producing the release liner base paper according to the second aspect of the present invention reduces the refining energy required for producing the release liner base paper while maintaining high-quality requirements.

[0166] In addition, it is found that the properties of the base paper containing unbleached virgin pulp in addition to recycled fibers according to the preferred embodiment are improved. That is, despite the presence of a large amount of unbleached virgin pulp, compared to the standard base paper without recycled fibers and unbleached virgin pulp, this base paper exhibits improved (lower) air permeability and improved (reduced) Rizinus Cobb. In addition, less silicone is required in the release coating, and the carbon footprint can be significantly reduced. Using unbleached pulp can also produce a release liner paper with a natural color and without adding dyes.

[0167] In addition, it is noted that the presence of recycled fibers or the presence of recycled fibers and unbleached virgin pulp can reduce the air permeability and Rizinus Cobb of the base paper. Therefore, the amount of silicone coated on these base papers can be reduced. Advantageously, the reduction in the silicone coating weight can improve the recyclability of the silicone-coated release liner material.

[0168] Embodiment

[0169] [Embodiment 1]

[0170] A release liner base paper comprising recycled fibers, wherein the release liner base paper has a density of at least 1.00 g / cm 3 of density,

[0171] wherein the recycled fibers are fibers based on recycled cardboard and / or fibers based on printed materials, and

[0172] wherein the amount of recycled fibers in the release liner base paper is at least 5 wt% based on the total weight of the fibers in the release liner base paper.

[0173] [Embodiment 2]

[0174] The release liner base paper according to Embodiment 1, wherein the amount of recycled fibers in the release liner base paper is at least 10 wt%, preferably 15 wt% to 80 wt%, more preferably 20 wt% to 50 wt% based on the total weight of the fibers in the release liner base paper.

[0175] [Embodiment 3]

[0176] The release liner base paper according to Embodiment 1 or 2, wherein the release liner base paper has an air permeability of 100 pm / Pa·s to 70000 pm / Pa·s, preferably 500 pm / Pa·s to 50000 pm / Pa·s, measured according to the SCAN P26 standard.

[0177] [Embodiment 4]

[0178] The release liner base paper according to any one of Embodiments 1 to 3, wherein the release liner base paper has a density of 1.05 g / cm 3 to 1.26 g / cm 3 , preferably 1.09 g / cm 3 to 1.24 g / cm 3 , more preferably 1.12 g / cm 3 to 1.22 g / cm 3 of density.

[0179] [Embodiment 5]

[0180] The release liner base paper according to any one of Embodiments 1 to 4, wherein the release liner base paper has a transparency of 4% to 65%, preferably 25% to 60%, measured according to the DIN 53147 standard, and has a basis weight of 30 g / m 2 to 140 g / m 2 , preferably 45 g / m 2 to 90 g / m 2 as measured according to ISO 536.

[0181] [Embodiment 6]

[0182] The release liner base paper according to any one of Embodiments 1 to 5, wherein the release liner base paper has a Bekk smoothness of 15 seconds to 1500 seconds, preferably 25 seconds to 1200 seconds, measured according to the TAPPI T479 standard on the back surface, and a Bekk smoothness of 400 seconds to 4000 seconds, preferably 500 seconds to 3500 seconds, on the front surface.

[0183] [Embodiment 7]

[0184] The release liner base paper according to any one of Embodiments 1 to 6, wherein the release liner base paper has a Rizinus Cobb value of 0.2 g / m 2 to 4 g / m 2 , preferably 0.3 g / m 2 to 3 g / m 2 , more preferably 0.6 g / m 2 to 1.4 g / m 2 as measured according to the ISO 535 standard on the front surface.

[0185] [Embodiment 8]

[0186] The release liner base paper according to any one of Embodiments 1 to 7, wherein the release liner base paper further comprises virgin fibers, and based on the total weight of the virgin fibers, the virgin fibers comprise at least 10 wt% or at least 25 wt% or at least 45 wt% or at least 70 wt% of bleached chemical pulp.

[0187] [Embodiment 9]

[0188] The release liner base paper according to Embodiment 8, wherein the bleached chemical pulp comprises hardwood fibers, softwood fibers or a blend of both.

[0189] [Embodiment 10]

[0190] The release liner base paper according to embodiment 8 or 9, wherein the bleached chemical pulp comprises hardwood fibers, and based on the total weight of the bleached chemical pulp, the hardwood fibers are present in this blend in an amount of at least 50 wt%, preferably at least 75 wt%.

[0191] [Embodiment 11]

[0192] The release liner base paper according to any one of embodiments 8 to 10, wherein the bleached chemical pulp comprises softwood fibers, and based on the total weight of the bleached chemical pulp, the softwood fibers are present in an amount of at most 50 wt%, preferably at most 25 wt%.

[0193] [Embodiment 12]

[0194] The release liner base paper according to any one of embodiments 8 to 11, wherein based on the total weight of the virgin fibers, the virgin fibers further comprise at least 2 wt% and less than 50 wt%, preferably 5 wt% to 45 wt%, more preferably 10 wt% to 35 wt% of bleached chemi-thermomechanical pulp.

[0195] [Embodiment 13]

[0196] The release liner base paper according to any one of embodiments 1 to 12, wherein the release liner base paper further comprises virgin fibers, and the virgin fibers comprise unbleached fibers,

[0197] wherein based on the total weight of the fibers in the release liner base paper, the amount of the unbleached fibers in the release liner base paper is at least 10 wt%.

[0198] [Embodiment 14]

[0199] The release liner base paper according to embodiment 13, wherein the release liner base paper has a transparency of 4% to 65%, preferably 25% to 60% as measured according to the DIN 53147 standard, and has a basis weight of 30 g / m 2 to 140 g / m 2 , preferably 45 g / m 2 to 90 g / m 2 as measured according to ISO 536.

[0200] [Embodiment 15]

[0201] The release liner base paper according to embodiment 13 or 14, wherein the release liner base paper does not contain dyes.

[0202] [Embodiment 16]

[0203] The release liner base paper according to any one of embodiments 13 to 15, wherein the carbon footprint of the release liner base paper is reduced compared to a standard release liner base paper that does not contain unbleached fibers and recycled fibers, preferably wherein the carbon footprint is reduced by 3% to 50% as measured according to the ISO 14067 standard.

[0204] [Embodiment 17]

[0205] A method for producing the release liner base paper according to any one of embodiments 1 to 16, the method comprising the following steps:

[0206] a) Disperse recycled fibers and optionally virgin fibers in a pulper to form a fiber suspension,

[0207] b) Refine the fiber suspension to form a refined fiber suspension,

[0208] c) Place the refined fiber suspension on a forming wire,

[0209] d) Dehydrate the refined fiber suspension to form a dewatered paper web,

[0210] e) Apply a base coat composition on at least one side of the dewatered paper web to form a dewatered, base coat-coated paper web, and

[0211] f) Dry the dewatered, base coat-coated paper web and the base coat composition to form a dried, base coat-coated paper web,

[0212] wherein the recycled fibers are fibers based on recycled cardboard and / or fibers based on printed materials, and

[0213] wherein based on the total weight of the fibers in the release liner base paper, the recycled fibers are added in an amount of at least 5 wt%.

[0214] [Embodiment 18]

[0215] The method for producing the release liner base paper according to embodiment 17, the method further comprising the step of calendering the dried, base coat-coated paper web.

[0216] [Embodiment 19]

[0217] The method according to embodiment 17 or 18, wherein based on the total weight of the fibers in the release liner base paper, the recycled fibers are added in an amount of at least 10 wt%, preferably 15 wt% to 80 wt%, more preferably 20 wt% to 50 wt%.

[0218] [Embodiment 20]

[0219] The method according to any one of embodiments 17 to 19, wherein the base weight of the primer coat layer applied on at least one side of the paper, measured according to ISO 536, is 0.1 g / m 2 to 30 g / m 2 , preferably 1 g / m 2 to 20 g / m 2 .

[0220] [Embodiment 21]

[0221] The method according to any one of embodiments 17 to 20, wherein the recycled fibers used in step a) satisfy one or more of the following:

[0222] i) The dry content measured according to the TAPPI 210 standard is greater than 50%;

[0223] ii) The pulp freeness measured according to the derivative standard of the UNI 7621 standard is 25°SR to 60°SR, preferably 30°SR to 50°SR;

[0224] iii) The ash content measured according to the derivative standard of the TAPPI 211 standard is 0.1% to 8%, preferably 0.5% to 7%; and

[0225] iv) The pH value measured according to the derivative standard of the TAPPI 209 standard is 5 to 12, preferably 6 to 11.

[0226] [Embodiment 22]

[0227] The method according to any one of embodiments 17 to 21, wherein based on the total weight of the virgin fibers, the virgin fibers comprise at least 10 wt% or at least 25 wt% or at least 45 wt% or at least 70 wt% of bleached chemical pulp.

[0228] [Embodiment 23]

[0229] The method according to any one of embodiments 17 to 22, wherein the bleached chemical pulp comprises hardwood fibers, softwood fibers or a blend of both.

[0230] [Embodiment 24]

[0231] The method according to any one of embodiments 17 to 23, wherein the bleached chemical pulp comprises hardwood fibers, and based on the total weight of the bleached chemical pulp, the hardwood fibers are present in this blend in an amount of at least 50 wt%, preferably at least 75 wt%.

[0232] [Embodiment 25]

[0233] The method according to any one of embodiments 17 to 24, wherein the bleached chemical pulp comprises softwood fibers, and the softwood fibers are present in an amount of at most 50 wt%, preferably at most 25 wt%, based on the total weight of the bleached chemical pulp.

[0234] [Embodiment 26]

[0235] The method according to any one of embodiments 17 to 25, wherein the virgin fibers further comprise at least 2 wt% and less than 50 wt%, preferably 5 wt% to 45 wt%, more preferably 10 wt% to 35 wt% of bleached chemi-thermomechanical pulp, based on the total weight of the virgin fibers.

[0236] [Embodiment 27]

[0237] Use of a release liner base paper according to any one of embodiments 1 to 16 as a base layer in a method for producing a release liner, the method comprising the steps of: applying a release coating composition on at least one side of the release liner base paper, and curing the composition to form a release coating.

[0238] [Embodiment 28]

[0239] A release liner comprising a release liner base paper according to any one of embodiments 1 to 16 as a base layer and a release coating on at least one side of the base layer.

[0240] [Embodiment 29]

[0241] The release liner according to embodiment 28, wherein the release coating is silicone, and the silicone anchorage rate of the release liner base paper on the at least one side, measured according to the friction test described in this specification, is at least 60%, preferably at least 80%, more preferably 95% to 100%.

[0242] [Embodiment 30]

[0243] A laminate comprising a release liner according to embodiment 28 or 29, a facing material, and an adhesive layer disposed between the release liner and the facing material.

Claims

1. A release liner base paper, the release liner base paper comprising recycled fibers, wherein the release liner base paper has a density of at least 1.00 g / cm 3 and, wherein the recycled fibers are fibers based on recycled cardboard and / or fibers based on printed materials, and wherein, based on the total weight of the fibers in the release liner base paper, the amount of the recycled fibers in the release liner base paper is at least 5 wt%.

2. The release liner base paper according to claim 1, wherein, based on the total weight of the fibers in the release liner base paper, the amount of the recycled fibers in the release liner base paper is at least 10 wt%, preferably 15 wt% to 80 wt%, more preferably 20 wt% to 50 wt%.

3. The release liner base paper according to claim 1 or 2, wherein the release liner base paper has an air permeability of 100 pm / Pa·s to 70000 pm / Pa·s, preferably 500 pm / Pa·s to 50000 pm / Pa·s, measured according to the SCAN P26 standard.

4. The release liner base paper according to any one of claims 1 to 3, wherein the release liner base paper has a density of 1.05 g / cm 3 to 1.26 g / cm 3 , preferably 1.09 g / cm 3 to 1.24 g / cm 3 , more preferably 1.12 g / cm 3 to 1.22 g / cm 3 .

5. The release liner base paper according to any one of claims 1 to 4, wherein the release liner base paper has a transparency of 4% to 65%, preferably 25% to 60%, measured according to the DIN 53147 standard, and has a basis weight of 30 g / m 2 to 140 g / m 2 , preferably 45 g / m 2 to 90 g / m 2 , measured according to the ISO 536 standard.

6. The release liner base paper according to any one of claims 1 to 5, wherein, measured according to the TAPPI T479 standard, the release liner base paper has a Bekk smoothness of 15 seconds to 1500 seconds, preferably 25 seconds to 1200 seconds, on the back side, and a Bekk smoothness of 400 seconds to 4000 seconds, preferably 500 seconds to 3500 seconds, on the front side.

7. The release liner base paper according to any one of claims 1 to 6, wherein the release liner base paper has a surface energy of 0.2 g / m2 to 4 g / m 2 and preferably 0.3 g / m 2 to 3 g / m 2 and more preferably 0.6 g / m 2 to 1.4 g / m 2 of the Rizinus Cobb value.

8. The base paper for release liner according to any one of claims 1 to 7, wherein the base paper for release liner further comprises virgin fibers, and the virgin fibers comprise unbleached fibers, wherein, based on the total weight of the fibers in the base paper for release liner, the amount of the unbleached fibers in the base paper for release liner is at least 10 wt%.

9. The base paper for release liner according to any one of claims 1 to 8, wherein the base paper for release liner has a transparency of 4% to 65%, preferably 25% to 60%, measured according to the DIN 53147 standard, and has a basis weight of 30 g / m 2 to 140 g / m 2 and preferably 45 g / m 2 to 90 g / m 2 as measured according to ISO 536.

10. A method for producing the base paper for release liner according to any one of claims 1 to 9, the method comprising the following steps: a) dispersing recycled fibers and optionally virgin fibers in a pulper to form a fiber suspension, b) refining the fiber suspension to form a refined fiber suspension, c) placing the refined fiber suspension on a forming wire, d) dewatering the refined fiber suspension to form a dewatered paper web, e) applying a base coat composition on at least one side of the dewatered paper web to form a dewatered, base coat-coated paper web, and f) drying the dewatered, base coat-coated paper web and the base coat composition to form a dried, base coat-coated paper web, wherein the recycled fibers are fibers based on recycled cardboard and / or fibers based on printed materials, and wherein, based on the total weight of the fibers in the base paper for release liner, the recycled fibers are added in an amount of at least 5 wt%.

11. The method for producing the base paper for release liner according to claim 10, the method further comprising the step of calendering the dried, base coat-coated paper web.

12. The method according to claim 10 or 11, wherein based on the total weight of the fibers in the release liner base paper, the recycled fibers are added in an amount of at least 10 wt%, preferably 15 wt% to 80 wt%, more preferably 20 wt% to 50 wt%.

13. The method according to any one of claims 10 to 12, wherein the basis weight of the primer coat layer applied to at least one side of the paper, measured according to ISO 536, is 0.1 g / m 2 to 30 g / m 2 Preferably 1 g / m 2 to 20 g / m 2 .

14. The method according to any one of claims 10 to 13, wherein the recycled fibers used in step a) satisfy one or more of the following: i) The dry content measured according to the TAPPI 210 standard is greater than 50%; ii) The pulp freeness measured according to a derivative standard of the UNI 7621 standard is 25°SR to 60°SR, preferably 30°SR to 50°SR; iii) The ash content measured according to a derivative standard of the TAPPI 211 standard is 0.1% to 8%, preferably 0.5% to 7%; and iv) The pH value measured according to a derivative standard of the TAPPI 209 standard is 5 to 12, preferably 6 to 11.

15. Use of a release liner base paper according to any one of claims 1 to 9 as a base layer in a method for producing a release liner, the method comprising the steps of: applying a release coating composition to at least one side of the release liner base paper, and curing the composition to form a release coating.

16. A release liner, the release liner comprising a release liner base paper according to any one of claims 1 to 9 as a base layer and a release coating on at least one side of the base layer.

17. The release liner according to claim 16, wherein the release coating is silicone, and the silicone anchorage rate of the release liner base paper on the at least one side, measured according to the friction test described in this specification, is at least 60%, preferably at least 80%, more preferably 95% to 100%.

18. A laminate, the laminate comprising a release liner according to claim 16 or 17, a facing material, and an adhesive layer disposed between the release liner and the facing material.

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