Low opacity paper packaging material

Abstract

A low grammage, low opacity, and heat sealable paper is disclosed. The low opacity and heat sealable paper is manufactured from a web containing highly refined cellulosic fibers. The web may first be coated with a bio-based wax (e.g., coconut-based wax). The web is also coated with a coating composition that forms a heat sealable coating on the outer surface of the coated paper. The product may have excellent transparent or translucent properties. The product also has excellent heat sealability, so that the product is very suitable for producing packaging.

Description

Background Technology

[0001] Transparent or translucent materials are used in all types of applications. For example, transparency is a highly desirable quality for packaging materials. While packaging materials are necessary to protect products from damage during transportation and sales, consumers prefer to be able to see the product through the packaging.

[0002] In the past, most transparent or translucent materials, including packaging materials, were made from plastics such as polyester polymers and polyolefin polymers. However, these plastics are derived from non-renewable fossil resources, including petroleum-based resources. These resources are unsustainable, non-renewable, and produce polymer products that are not easily degraded. Therefore, efforts have been made in the past to produce transparent or translucent materials from renewable resources such as cellulose materials.

[0003] For example, low-opacity or transparent paper has been developed and produced in the past. Transparent paper products have been used, for instance, as transparent windows in tracing paper or envelopes. However, these materials have had limited success in producing packaging materials because they lack sufficient heat-sealing properties.

[0004] Furthermore, to produce transparent or translucent paper, non-renewable resources or components that are not easily biodegradable are combined with paper. For example, one type of paper produced in the past was made from wood pulp fibers, which may have been combined with enzymes such as xylanase. These substrates typically have a relatively high basis weight to provide sufficient strength or other mechanical properties. To reduce the thickness of cellulose paper, densify the paper, and produce transparent properties, the paper is combined with petroleum-based chemicals or synthetic resins and then fed through a supercalendering process. As used herein, in supercalendering, the paper is first calendered by pressing it between metal cylinders or rollers. The paper is then fed into another set of calenders to produce an even smoother and more glossy paper, referred to as supercalendered paper. A supercalender consists of multiple cylinders alternating between a polished metal surface and a soft, elastic surface. The supercalender applies pressure, heat, and friction to smooth both surfaces of the paper, resulting in a smooth and / or glossy paper.

[0005] As mentioned above, transparent or translucent papers manufactured in the past have various drawbacks and limitations. For example, although the fibers used to produce the paper are derived from renewable resources and are biodegradable and compostable, the paper is often combined with petroleum-based chemicals or other synthetic resins, which can hinder the goal of producing biodegradable materials. Furthermore, while supercalendering can very effectively alter the properties of paper, the process is extremely energy-intensive. Additionally, none of the aforementioned papers include heat-sealable properties.

[0006] For packaging materials, barrier properties against water, water vapor, and grease are very important. These properties are typically only achievable using petroleum-derived materials.

[0007] In light of the above, there is a current need for low-opacity paper with a bio-source of 90% or more, and which is biodegradable and / or compostable. There is also a need for low-opacity paper that can be produced without supercalendering and potentially using less material, such as fewer cellulose fibers. Furthermore, there is a need for low-opacity paper that is free of petroleum-based raw materials and possesses good barrier properties. Additionally, there is a need for low-opacity paper with heat-sealable properties, allowing the paper itself to be thermally bonded together to form transparent packaging. Summary of the Invention

[0008] The object of this invention is to provide an alternative to plastic films currently on the market. More specifically, this disclosure relates to low-opacity paper that can be manufactured at a relatively low basis weight, contains no petroleum-based resources, and requires no supercalendering, thereby reducing the energy requirements for manufacturing the product. The low-opacity paper of this disclosure can also be formulated to be fully biodegradable and compostable. Furthermore, low-opacity paper can have an excellent balance of properties, including high transparency and low permeability providing high barrier properties, good mechanical properties for conversion and handling, and excellent heat-sealable properties.

[0009] In one aspect, this disclosure relates to paper articles having low opacity characteristics. The paper article comprises a fiber web containing cellulose fibers. The cellulose fibers contained in the web can be refined to a relatively high degree, which can be measured by a freeness value. The freeness value (°SR) is typically a measure of the filtration rate of a diluted suspension of refined fibers. The freeness is measured by the Schopper Riegler method for filtration. As used herein, the freeness can be measured according to DIN EN ISO 5267-1:2000. The refining degree of the cellulose fibers contained in the web can be greater than or equal to about 60°SR, for example, greater than or equal to about 70°SR. The freeness value of the fibers is typically less than or equal to about 100°SR, for example, less than or equal to about 90°SR. In another aspect, the fiber web can also have a relatively low basis weight, thereby increasing transparency. For example, the basis weight of the web can be less than or equal to about 38 g / m³. 2 For example, less than or equal to approximately 35 g / m 2 For example, less than or equal to approximately 33 g / m 2 For example, less than or equal to approximately 30 g / m 2 For example, less than or equal to approximately 28 g / m 2 For example, less than or equal to approximately 25 g / m 2 For example, less than or equal to approximately 23 g / m 2 And usually greater than or equal to about 10 g / m 2 For example, greater than or equal to approximately 12 g / m2 In a preferred embodiment, the basis weight of the fiber web is between 10 and 24 g / m². 2 Within the range, and preferably between 10 and 18 g / m 2 Within the range. The fiber web defines a first surface and a second surface. As will be readily understood by those skilled in the art, the first surface and the second surface are the principal surfaces of the fiber web, and they may also be referred to as the "upper" surface and the "lower" surface and are positioned opposite each other.

[0010] According to this disclosure, at least two different coating compositions can be applied to the surface of a fiber web. The first coating comprises a clarifying agent, such as a bio-based wax or oil, for reducing opacity. In another aspect, the second coating composition can form a heat-sealable coating that can be applied over the clarifying agent coating on the first and / or second surfaces of the fiber web (and preferably only on one of the first and second surfaces). This is the subject of feature (i) of claim 2. In a variation, the first and second coating compositions can be applied to opposite surfaces of the fiber web, i.e., its first and second surfaces, as described in feature (ii) of claim 2. According to another aspect of this disclosure, the second coating composition can be combined with the clarifying agent coating composition and applied as a single coating to the web. This is the subject of claim 1.

[0011] When combined with a transparent coating composition, the heat-sealable coating composition can also form the outer surface of a paper article. The heat-sealable coating can contain a polymer, such as a thermoplastic polymer, or a protein. The polymer can be a polyester, protein, polysaccharide, polysaccharide ester, polysaccharide ether, or polysaccharide ether ester. The protein can be casein, whey protein, etc. Paper articles manufactured according to this disclosure can exhibit an opacity of less than or equal to about 45% when tested according to ISO 2471:2008. For example, the opacity can be less than or equal to about 40%, such as less than or equal to about 35%.

[0012] The amount of clearing agent incorporated into a product depends on a variety of factors. The basis weight (dry weight) of the clearing agent coating can be approximately 0.5 g / m³. 2 Approximately 18 g / m 2 Including all 0.5 g / m 2 The increment. For example, the basis weight of a clearing agent coating can be greater than or equal to about 2 g / m³. 2 For example, greater than or equal to approximately 4 g / m 2 For example, greater than or equal to about 5 g / m 2 For example, greater than or equal to approximately 6 g / m 2 For example, greater than or equal to approximately 7 g / m 2 For example, greater than or equal to approximately 8 g / m 2The basis weight of the transparent coating can be less than or equal to approximately 20 g / m³. 2 For example, less than or equal to about 15 g / m 2 For example, less than or equal to about 12 g / m 2 For example, less than or equal to about 10 g / m 2 For example, less than or equal to about 8 g / m 2 .

[0013] In one embodiment, the transparent agent can be miscible with water and applied to the fiber web as an aqueous composition.

[0014] As described above, in one aspect, the heat-sealable coating may comprise a polymer. In another aspect, the polymer may be a thermoplastic starch or a protein. The heat-sealable coating may be applied to a cellulose layer such that its dry basis weight is greater than or equal to about 1 g / m³. 2 For example, greater than or equal to approximately 3 g / m 2 For example, greater than or equal to approximately 4 g / m 2 For example, greater than or equal to about 5 g / m 2 And typically less than or equal to about 20 g / m 2 For example, less than or equal to about 15 g / m 2 For example, less than or equal to about 10 g / m 2 For example, less than or equal to about 8 g / m 2 When combined with a clearing agent, the basis weight of the coating can be greater than or equal to approximately 3 g / m³. 2 For example, greater than or equal to approximately 5g / m 2 For example, greater than or equal to approximately 8 g / m 2 For example, greater than or equal to approximately 12 g / m 2 And typically less than or equal to about 35 g / m 2 For example, less than or equal to approximately 30 g / m 2 For example, less than or equal to approximately 25 g / m 2 For example, less than or equal to approximately 20 g / m 2 .

[0015] On one hand, the fiber web can comprise a wet-laid web. The fiber web can contain individual wood pulp fibers or wood pulp fibers combined with bast fibers. Bast fibers are plant fibers collected from the phloem or phloem tissue surrounding the stem of a dicotyledonous plant. For example, bast fibers can be obtained from flax, hemp, ramie, nettle, linden, willow, oak, wisteria, and mulberry. From an economic perspective, bast fibers are preferably obtained from flax, hemp, or ramie. For example, the wood pulp fibers can be softwood fibers, hardwood fibers, or combinations thereof. This paper product can be produced without any paraffin, mineral oil, or hydrocarbon oil. Therefore, on one hand, this paper product can be recycled into pulp and composted.

[0016] The fiber web (before any coating is applied) typically contains cellulose fibers in an amount greater than or equal to about 65% by weight, for example greater than or equal to about 75% by weight, for example greater than or equal to about 80% by weight, for example greater than or equal to about 85% by weight, for example greater than or equal to about 90% by weight, for example greater than or equal to about 95% by weight. Cellulose fibers are typically present in the fiber web in an amount of 100% by weight, or in an amount less than or equal to about 99% by weight, for example less than or equal to about 98% by weight.

[0017] In one specific embodiment, the fiber web may contain a first cellulose fiber blended with a second cellulose fiber. The average fiber length of the first cellulose fiber may be shorter than the average fiber length of the second cellulose product. For example, based on the total weight of the fibers contained in the web, the fiber web may contain approximately 30% to 70% by weight of the first cellulose fiber, and the second cellulose fiber may be present in the fiber web in an amount of approximately 70% to 30% by weight. For example, the average fiber length of the first cellulose fiber may be approximately 2.5 mm to 5 mm.

[0018] The paper articles disclosed herein can have a combination of various beneficial properties. For example, according to EN ISO 534:2011, the paper articles can be relatively thin, with a thickness of less than or equal to about 80 µm, for example less than or equal to about 70 µm, for example less than or equal to about 60 µm, and generally greater than or equal to about 30 µm. According to ISO 5636:2003, the Gurley permeability of the paper articles can be less than or equal to about 45,200 seconds, for example less than or equal to about 20,000 seconds, for example less than or equal to about 10,000 seconds, for example less than or equal to about 1000 seconds, and generally greater than or equal to about 600 seconds. According to TAPPI T 432 cm-09 (tested using 2 µL of water), the water droplet resistance of the paper articles can also be greater than or equal to 5 min. According to ASTM E96 / E96M – 15:2014, the water vapor barrier properties of the paper articles at 23°C and 50% HR can be less than or equal to 80 g / m³. 2 / day, for example, less than or equal to 50 g / m 2 / day, and greater than or equal to approximately 0.1 g / m 2 / day (coated side up, measurements taken within 3 days).

[0019] The present invention also relates to packaging formed from coated paper. In one embodiment, the packaging may be defined as a hollow, closed space or internal space formed between two layers of coated paper. The coated paper may be heat-sealed together along the edges of the product. In one aspect, the paper can be used as packaging material for food, tobacco, cosmetics, pharmaceuticals, and other products.

[0020] In another aspect, this disclosure also relates to a method for producing low-opacity paper articles as described above. The method includes coating a fiber web with an aqueous composition containing bio-based waxes or oils (e.g., coconut-based waxes or oils, rice-based waxes, palm-based waxes or oils, and / or soybean-based waxes or oils). According to this disclosure, a second coating is then applied to the fiber web, thereby forming a heat-sealable coating on the web. The heat-sealable coating may be applied over the first coating.

[0021] On the other hand, the heat-sealable composition can be combined with a transparent agent composition to form a single coating with heat-sealable properties on the web.

[0022] The method may further include calendering the coated fiber web. Calendering can be performed after the first coating has been applied and / or after the heat-sealable coating has been applied. In this document, a coating containing a heat-sealable composition is sometimes referred to as a "heat-sealable coating." On one hand, an aqueous composition containing a clearing agent is applied to the fiber web using a sizing machine. On the other hand, the heat-sealable coating can also be applied using a sizing machine or through an offline process, such as using a doctor blade coating technique.

[0023] Other features and aspects of this disclosure are discussed in more detail below. Attached Figure Description

[0024] The remainder of this specification sets forth in more detail the complete and authorized disclosure of this disclosure, including with reference to the accompanying drawings, wherein: Figure 1 This is a schematic cross-sectional view of one embodiment of a low-opacity paper manufactured according to the present disclosure.

[0025] The repeated use of reference numerals in this specification and accompanying drawings is intended to indicate the same or similar features or elements of the invention.

[0026] definition As understood herein, a coating agent, typically liquid, can be applied to one or more surfaces of a fiber web using any suitable coating, impregnation, or saturation technique, such as air knife coating, roll-to-roll coating, doctor blade coating, spraying, Mayer bar coating, direct gravure printing, offset gravure printing, reverse gravure printing, smooth roll coating, curtain coating, bead coating, slot coating, filler press coating, or impregnation via a sizing machine, thereby obtaining (providing) a “coating” on the surface of the fiber web. The coating can be a continuous coating or a discontinuous coating. Thus, the coating can be present in a portion of the fiber web or throughout the entire fiber web along its transverse dimension. When the coating composition is applied to the fiber web, it penetrates into some of the internal spaces and pores between the fibers of the fiber web, resulting in the fiber web being saturated and / or impregnated by the coating (composition). That is, in this invention, the coating penetrates into the fiber web, particularly into its internal spaces and pores, and furthermore, it can cover, and preferably in the form of a surface coating, at least a portion of the first and / or second surfaces of the fiber web. In other words, as understood in this article, the “coating” on the fiber web encompasses the saturation and impregnation of the fiber web.

[0027] As used herein, the term "low opacity" means transparent or translucent. A product is considered to have low opacity when tested according to ISO 2471:2008 and exhibits, for example, an opacity of less than or equal to about 45%. Low opacity characteristics refer to properties that provide transparency or translucency to paper products, such as the presence of a transparent agent.

[0028] As used herein, the term "clearing agent" refers to an agent that reduces the opacity of a fiber web when applied to the interior or web itself. Examples include waxes or oils of plant or animal origin, such as coconut-based waxes, palm-based waxes, and / or soybean-based waxes. As understood herein, plant or animal-derived components may be derived from biomass. Clearing agents may be bio-based waxes or oils.

[0029] As used herein, the term "biomass" is broadly understood to encompass all kinds of plant and animal material and materials derived therefrom. Biomass does not include petroleum or petroleum-derived products.

[0030] Biomass used in this invention may comprise macromolecular compounds, examples of which are lignin and polysaccharides, such as starch, protein, cellulose, and hemicellulose.

[0031] As will be understood, certain types of biomass may include materials of plant and animal origin. For example, manure, night soil, and sewage sludge may be mentioned. While the biomass used in this invention is preferably plant biomass, i.e., biomass from plants or derived from plants, it may contain a certain amount of animal biomass (i.e., biomass from animals or derived from animals). For example, the biomass may contain up to 30% animal biomass. According to a preferred embodiment, the biomass used in this disclosure (preferably plant biomass) contains, based on the solids content, greater than or equal to 70 wt%, most preferably greater than or equal to 90 wt% of polysaccharides and lignin.

[0032] For example, plant biomass can be agricultural plant materials (such as agricultural waste) or various wood materials.

[0033] Examples of biomass include, but are not limited to, crops, agricultural food and waste, feed crop residues, wood (e.g., wood flour, wood waste, scrap wood, sawdust, wood chips, and waste), straw (including rice straw), grass, leaves, rice husks, and bagasse. Additionally, industrial and municipal waste, including waste paper, can also be cited as examples. Biomass also encompasses oils and waxes obtained or derived from plant or animal materials.

[0034] As used herein, a “biodegradable” component is a component that can be broken down by living organisms (e.g., bacteria or fungi). Therefore, a biodegradable component can be decomposed by microorganisms (e.g., bacteria or fungi) under aerobic or anaerobic conditions. In one respect, a biodegradable component meets the requirements of at least one of the international industrial standards ISO 14855:2018, ISO 14853:2017, and ASTM D5338:2015.

[0035] As used herein, the term "compostable" refers to a component that can decompose into non-toxic natural elements. For example, compostable components can degrade at a rate consistent with similar organic materials. Compostable components degrade upon exposure to microorganisms, moisture, and / or heat, thereby producing the final compost product. Coated paper manufactured according to this disclosure can be formulated to conform to international industrial standards ISO 17088:2021, DIN EN 13432:2007, DIN EN 14995:2007, and / or ASTM 6400:2021, which define the requirements for industrial compostable components.

[0036] As used herein, the term "pulp" refers to fibers derived from natural sources, such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, rice straw, jute, hemp, and bagasse. Pulp fibers can include hardwood fibers, softwood fibers, and mixtures thereof.

[0037] As used in this article, opacity is measured according to ISO 2471:2008. Opacity is an indicator of a paper product's ability to block light from passing through. The lower the level of opacity, the higher the level of translucency / transparency.

[0038] As used in this article, the term "fiber web" refers to an uncoated sheet made from pulp by a wet web-forming process.

[0039] As used herein, the term "bio-based wax or oil" refers to a wax or oil with a bio-based content of 90% or more. Examples include coconut-based wax, palm-based wax, and / or soybean-based wax. According to the implementation scheme, bio-based waxes or oils are obtained by processing plant materials.

[0040] As used in this article, the term "re-pulping" refers to the decomposition of paper during the pulping process in water. Detailed Implementation

[0041] Those skilled in the art will understand that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this disclosure.

[0042] In general, this disclosure relates to low-opacity paper with heat-sealable properties. In one aspect, the paper can be transparent. Optionally, the paper can be formulated to be translucent. The low-opacity paper of this disclosure can be formed entirely from sustainable resources, meeting all requirements for post-use paper recycling processes. In the past, for example, transparent paper typically contained components derived from fossil-based resources, such as petroleum-derived products. However, the low-opacity paper of this disclosure can be produced without any mineral oils or hydrocarbons (including mineral oil-saturated hydrocarbons and mineral oil aromatic hydrocarbons). Furthermore, in one aspect, the low-opacity paper can be formulated to be paraffin-free. Therefore, low-opacity paper can be constructed to meet all requirements for food contact and food handling.

[0043] Furthermore, the low-opacity paper of this disclosure can possess excellent barrier and heat-sealing properties. For example, a heat-sealing coating can be formed on the outer surface of paper articles. The heat-sealing coating not only promotes the formation of thermal bonds between the coated paper and adjacent surfaces (e.g., another layer of coated paper), but can also be manufactured entirely from sustainable, biodegradable, and compostable materials.

[0044] Another advantage is that the low-opacity paper of this disclosure can be developed to minimize material usage while still possessing sufficient mechanical properties for handling, processing, and end-use applications. For example, the low-opacity paper of this disclosure can be produced with relatively low basis weight and relatively low thickness.

[0045] In one aspect, the low-opacity paper of this disclosure is formed from a fiber web containing cellulose fibers refined to a relatively high degree. According to this disclosure, the fiber web is combined with a clearing agent, which may be a bio-based wax or oil. The clearing agent not only improves the barrier properties of the paper but also reduces its opacity. Ultimately, paper with an opacity of less than or equal to about 45% can be produced. For example, the opacity of paper articles can be less than or equal to about 40%, such as less than or equal to about 38%, such as less than or equal to about 35%. The actual opacity depends on various factors and is generally greater than or equal to 5%, such as greater than or equal to 10%.

[0046] refer to Figure 1 This illustrates one embodiment of a low-opacity paper or paper article 10 manufactured according to this disclosure. Figure 1 This is a schematic cross-sectional view of article 10. As shown, in this embodiment, the low-opacity paper 10 comprises a paper base sheet 12, which is a fiber web formed from cellulose fibers. For example, the fiber web 12 may be a wet-laid paper web. However, in other embodiments, the fiber web 12 may be manufactured using any suitable papermaking technology. The fiber web 12 includes a first surface and an opposing second surface. Applied to the first surface of the fiber web 12 are a first coating 14 and a second coating 16. The first coating 14 contains a transparent agent that reduces the opacity of the paper article 10. Figure 1 The first coating 14 is shown as a separate layer, but as described above, it is also embedded in the fiber web 12. As will be described in more detail below, the first coating 14 may be made of bio-based oils or waxes. In one specific aspect, for example, the first coating 14 is formed of coconut-based wax, soybean-based wax, rice-based wax, and / or palm-based wax.

[0047] exist Figure 1 In the illustrated embodiment, on the other hand, a second coating or heat-sealable coating 16 is applied over the first coating 14. The heat-sealable coating 16 further enhances the barrier properties of the entire product. The heat-sealable coating 16 is also heat-sealable, and therefore can be used to bond coated paper to adjacent coated paper for producing packaging or other articles requiring a hollow shell.

[0048] For example, the heat-sealable coating 16 may contain plant- or animal-derived waxes, alone or in combination with other components, such as polymers. For example, the polymers combined with plant- or animal-derived waxes may be polyester polymers, proteins (such as casein), polysaccharides, polysaccharide esters, polysaccharide ethers, polysaccharide ether esters, or combinations thereof.

[0049] In one embodiment (i.e., the subject matter of claim 2), the transparent coating 14 and the heat-sealable coating 16 may be applied to one side or different sides of the cellulose layer. In another embodiment (i.e., the subject matter of claim 1), the composition for forming the first coating may be combined with the composition for forming the second coating and applied as a single coating to the mesh, thereby reducing opacity and providing heat-sealable properties.

[0050] like Figure 1 As shown, the low-opacity paper 10 can be manufactured entirely from a single layer of fiber web combined with a first coating 14 and a second coating 16 (or a single coating that combines the first coating component and the second coating component).

[0051] like Figure 1 As shown, the coated paper 10 defines an outer surface 18, which is a heat-sealable surface. For example, surface 18 can be formulated to be non-sticky at room temperature. Surface 18 or the heat-sealable coating 16 can be heat-sealable at temperatures greater than or equal to about 100°C, for example greater than or equal to about 110°C, for example greater than or equal to about 120°C, for example greater than or equal to about 130°C, for example greater than or equal to about 140°C, for example greater than or equal to about 150°C, for example greater than or equal to about 160°C, for example greater than or equal to about 170°C, for example greater than or equal to about 180°C, and less than or equal to about 250°C, for example less than or equal to about 230°C, for example less than or equal to about 220°C, for example less than or equal to about 210°C, for example less than or equal to about 200°C, for example less than or equal to about 190°C, for example less than or equal to about 180°C. A particular advantage is that the coating exhibits excellent heat-sealable properties even at relatively low basis weights.

[0052] like Figure 1 As shown, coated paper 10 can be used to form various different packages using different technologies and processes.

[0053] As described above, in one embodiment, the fiber web 12 can be a wet-laid paper web formed from cellulose fibers. For example, the fiber web can be formed from an aqueous suspension of fibers. The cellulose fibers contained in the fiber web can be pulp fibers (including wood pulp fibers), plant waste fibers, or other plant fibers. During the formation of the fiber web, an aqueous suspension of fibers can be deposited onto a porous forming surface, allowing water to drain out, thereby forming the fiber web. After the web is formed and dried, the paper can be calendered.

[0054] On one hand, the fiber web is primarily made of plant-derived fibers or natural fibers. Natural (plant-derived) fibers can be selected from chemical pulps, such as sulfate pulp and sulfite pulp, organic solvent pulp, recycled fibers, and / or mechanical pulps, including, for example, refined mechanical pulp (RMP), pressure refined mechanical pulp (PRMP), and pretreated refined chemical alkaline peroxide mechanical pulp (P-RC). APMP, Thermomechanical Pulp (TMP), Thermomechanical Chemical Pulp (TMCP), High Temperature Thermomechanical Pulp (HT-TMP), RTS-TMP, Basic Peroxide Pulp (APP), Basic Peroxide Mechanical Pulp (APMP), Basic Peroxide Thermomechanical Pulp (APTMP), Thermal Pulp, Groundwood Pulp (GW), Stone-ground Wood Pulp (SGW), Pressure Groundwood Pulp (PGW), Ultra-High Pressure Groundwood Pulp (PGW-S), Thermal Groundwood Pulp (TGW), Thermal Stone-ground Wood Pulp (TSGW), Chemimechanical Pulp (CMP), Chemically Refined Mechanical Pulp (CRMP), Chemimechanical Thermomechanical Pulp (CTMP), High Temperature CTMP (HT-CT) Pulps containing various types of wood include: sulfite-modified thermomechanical pulp (SMTMP), waste CTMP (CTMPR), groundwood CTMP (G-CTMP), semi-chemical pulp (SC), neutral sulfite semi-chemical pulp (NSSC), high-yield sulfite pulp (HYS), biomechanical pulp (BRMP), pulps produced according to OPCO, explosion pulping, Bi-Vis, dilution water sulfonation (DWS), sulfonated long fiber (SLF), chemically treated long fiber (CTLF), long fiber CMP (LFCMP), Kraft wood pulp, medium-density fiberboard (MDF) fibers, nanocellulose, and their modifications and combinations. Pulps can be bleached or unbleached. Pulp can be derived from hardwoods or softwoods, including birch, beech, poplar (e.g., European poplar), alder, eucalyptus, maple, acacia, mixed tropical hardwoods, pine (e.g., spruce), fir, hemlock, larch, spruce (e.g., black spruce or Norway spruce) and mixtures thereof.

[0055] Non-woody plant fibers, such as seed hair fibers, leaf fibers, and bast fibers, can also be used. Plant fibers can be provided from, for example, the straw of cereal crops, wheat straw, reeds, flax, hemp, kenaf, jute, ramie, seeds, sisal, abaca, coconut fiber, bamboo, bagasse, cotton-kapok blends, milkweed, pineapple, cotton, rice straw, reeds, esparto grass, Phalaris arundinacea, or combinations thereof.

[0056] The fiber web can be formed primarily of cellulose fibers without being combined with other components, such as fillers. For example, the fiber web (before coating) may contain more than or equal to about 90% by weight, for example, more than or equal to about 95% by weight, of cellulose fibers. Specific cellulose fibers well suited for producing the fiber web include cork fibers, hardwood fibers, birch fibers, hemp fibers, or mixtures thereof. For example, in one embodiment, the fiber web may be made entirely of cork fibers or a combination of cork and hardwood fibers. Alternatively, the fiber web may be made from a blend of wood pulp fibers (e.g., cork fibers) and bast fibers (e.g., hemp or flax fibers). For example, cellulose fibers can be selected to produce a web that can be effectively filtered from aqueous fluids during the forming process and can produce relatively low opacity paper at a lower basis weight while still retaining the mechanical properties required for processing and handling.

[0057] Once a suitable fiber feedstock is selected to produce a fiber web, the fibers used to form the web can optionally be fed through a refining process to increase their degree of freedom, as measured by the water-retaining Schopper-Riegler method (ISO 5267-1:2000). As used herein, refining cellulose fibers differs from producing pulp fibers. In the pulping process, lignin is removed from the cellulose fibers. On the other hand, in the refining process, the fibers of the individual protofibrils that constitute the outer surface or fiber wall of the fibers stand up; this is sometimes referred to as defibering. Refining is the mechanical and / or chemical action that causes defibering.

[0058] On the one hand, in preparing the fibers used to generate the fiber web, the fibers can first undergo appropriate pretreatment, such as washing, and especially if bast fibers are used, they can be shredded. Furthermore, the fibers can be fed through a hammer mill or subjected to various different chemical treatments.

[0059] Cellulose fibers can be mixed with aqueous solutions or solvents, and this mixing can be carried out in a refining machine (such as a twin-screw extruder). If desired, wetting agents, acids, or alkalis can be added to soften the cellulose fibers. Furthermore, one or more alcohols, including methanol, ethanol, or mixtures thereof, can be added to the fibers.

[0060] An aqueous suspension can be fed into or formed within a refining machine and undergo mechanical refining. The consistency of the fibers in the refining machine can range from approximately 1% to 30% solids content. In a refining machine (e.g., a twin-screw refining machine), the pulp suspension undergoes mechanical action, thereby forming larger fibrils within each fiber.

[0061] It should be understood that any suitable refining apparatus can be used to increase the degree of fiber freeness, and the twin-screw refining machine represents only one instrument, process, or technology that can be used.

[0062] According to this disclosure, after leaving one or more refining machines, the degree of freeness of cellulose fibers is greater than or equal to about 60° SR, for example, greater than or equal to about 65° SR, for example, greater than or equal to about 70° SR. On one hand, the cellulose fibers have been refined to a degree of freeness greater than or equal to about 73° SR, for example, greater than or equal to about 75° SR, for example, greater than or equal to about 78° SR, for example, greater than or equal to about 80° SR, for example, greater than or equal to about 82° SR. The degree of freeness of the fibers is less than or equal to about 95° SR, for example, less than or equal to about 90° SR, for example, less than or equal to about 85° SR, for example, less than or equal to about 80° SR. It has been found that refining the fibers to the above degree not only improves the drainage of the web during production but also reduces the opacity properties of the paper. Refining cellulose fibers can also reduce the thickness of the sheet while still providing good mechanical properties. For example, it has been found that for a given basis weight, the reduction in thickness unexpectedly increases transparency while still maintaining a good balance with mechanical properties. Adjusting the refining level of cellulose fibers can also regulate the barrier properties of low-opacity paper. For example, refined fibers can be used to adjust air permeability and develop air barrier properties, water barrier properties, oil barrier properties, etc.

[0063] Once the cellulose fibers are refined, they are formed into a web. On the one hand, the basis weight of the web is relatively low. For example, the basis weight of a fiber web can be less than or equal to about 38 g / m². 2 For example, less than or equal to approximately 36 g / m 2 For example, less than or equal to approximately 34 g / m 2 For example, less than or equal to approximately 32 g / m 2 For example, less than or equal to approximately 30 g / m 2 For example, less than or equal to approximately 28 g / m 2 For example, less than or equal to approximately 25 g / m 2 For example, less than or equal to approximately 23 g / m 2 The basis weight is typically greater than or equal to approximately 10 g / m³. 2 For example, greater than or equal to approximately 12 g / m 2 In one specific aspect, the basis weight of the fiber web is approximately 10 g / m². 2 Approximately 24 g / m 2 Preferably about 10 g / m 2 Approximately 18 g / m 2 Including all 1 g / m 2 The increment.

[0064] According to this disclosure, two coating compositions or a combination of coating compositions are applied to a fiber web. A first coating is applied to the fiber web to reduce the opacity of the final product. Alternatively, the second coating may be a heat-sealable coating to provide heat-sealable properties to the paper article. Furthermore, the two coatings can work synergistically to provide excellent barrier properties. The paper article can possess excellent aesthetics and functionality, making it ideal for packaging applications. In one aspect, the first coating may form a layer on one side of the fiber web and may also implicitly penetrate into the web. The second coating may form a surface layer located beneath the first coating.

[0065] According to this disclosure, the first coating comprises a clarifying agent. The clarifying agent may comprise a bio-based wax or oil. For example, the bio-based wax or oil may be derived from animal or plant biomass. In one aspect, the clarifying agent may be a bio-based wax derived from at least 80% by weight of vegetable oil, such as at least about 90% by weight of vegetable oil, such as up to 100% by weight of vegetable oil. This bio-based wax or oil may be paraffin-free and may be free of mineral oil saturated hydrocarbons and mineral oil aromatic hydrocarbons. A particular advantage is that the clarifying agent can meet all government requirements for food contact and food handling. The coating composition can meet all requirements of FDA 21 CFR § 176.180 for components of paper and paperboard in contact with dried foods. Similarly, the clarifying agent and low-opacity paper can also meet all requirements of European Commission Regulation 1935 / 2004 regarding materials and articles in contact with food.

[0066] In one embodiment, the melting point of the bio-based wax can be from about 25°C to about 75°C, including all 1°C increments therebetween. The melting point of the bio-based wax can be less than or equal to about 70°C, for example, less than or equal to about 65°C, for example, less than or equal to about 60°C, for example, less than or equal to about 55°C, for example, less than or equal to about 50°C, for example, less than or equal to about 45°C, for example, less than or equal to about 40°C. The melting point of the bio-based wax can be greater than or equal to about 25°C, for example, greater than or equal to about 30°C, for example, greater than or equal to about 35°C, for example, greater than or equal to about 40°C, for example, greater than or equal to about 45°C, for example, greater than or equal to about 50°C. Bio-based waxes with specific melting points well-suited to particular applications can be selected.

[0067] In one specific embodiment, the transparent agent comprises a bio-based wax, which is a coconut-based wax, a rice-based wax, a palm-based wax, a soybean-based wax, or a mixture thereof.

[0068] On one hand, for example, the clarifying agent is coconut-based wax or oil. The melting point of coconut-based wax can be from about 25 degrees Celsius to about 45 degrees Celsius, for example from about 30 degrees Celsius to about 40 degrees Celsius. Coconut-based wax can be applied to the fiber web in the form of anionic aqueous dispersion.

[0069] On the other hand, the clarifying agent can be palm-based wax or oil. Palm-based waxes have a melting point of about 50 degrees Celsius to about 70 degrees Celsius, for example, about 55 degrees Celsius to about 65 degrees Celsius. Palm-based waxes can be applied to the fiber web in the form of anionic aqueous dispersions.

[0070] Alternatively, the clarifying agent may be a soybean-based wax and may be applied in the form of an aqueous cationic emulsion having a melting point of about 55 degrees Celsius to about 80 degrees Celsius, for example, about 63 degrees Celsius to about 72 degrees Celsius.

[0071] On the one hand, bio-based waxes can be water-dispersible or water-miscible. Therefore, transparent agents can be incorporated into aqueous compositions for application to the fiber web during the production of low-opacity paper.

[0072] The amount of clearing agent incorporated into a product depends on a variety of factors. The basis weight (dry weight) of the clearing agent coating can be approximately 0.5 g / m³. 2 Approximately 18 g / m 2 Including all 0.5 g / m 2 The increment. For example, the basis weight of a clearing agent coating can be greater than or equal to about 2 g / m³. 2 For example, greater than or equal to approximately 4 g / m 2 For example, greater than or equal to about 5 g / m 2 For example, greater than or equal to approximately 6 g / m 2 For example, greater than or equal to approximately 7 g / m 2 For example, greater than or equal to approximately 8 g / m 2 The basis weight of the transparent coating can be less than or equal to approximately 20 g / m³. 2 For example, less than or equal to about 15 g / m 2 For example, less than or equal to about 12 g / m 2 For example, less than or equal to about 10 g / m 2 For example, less than or equal to about 8 g / m 2 .

[0073] On the one hand, the clarifying agent may be present in paper articles in an amount greater than or equal to about 2% by weight, for example, in an amount greater than or equal to about 3% by weight, for example, in an amount greater than or equal to about 4% by weight, for example, in an amount greater than or equal to about 5% by weight, for example, in an amount greater than or equal to about 10% by weight, for example, in an amount greater than or equal to about 13% by weight. The clarifying agent is typically present in paper articles in an amount less than or equal to about 35% by weight, for example, in an amount less than or equal to about 25% by weight, for example, in an amount less than or equal to about 20% by weight, for example, in an amount less than or equal to about 15% by weight, for example, in an amount less than or equal to about 10% by weight, for example, in an amount less than or equal to about 8% by weight, for example, in an amount less than or equal to about 6% by weight.

[0074] Clearing agents can improve various properties and characteristics of coated paper. For example, clearing agents can increase the transparency of the final product and / or reduce its opacity. Clearing agents can also reduce the permeability of low-opacity paper and improve the paper's barrier properties.

[0075] As described above, the first coating applied to the fiber web can cover a second coating or a heat-sealable coating, or can be combined with a heat-sealable coating composition. The heat-sealable coating can be applied directly to the clearing agent coating and can be applied to the coated paper without any type of adhesive or bonding layer between the clearing agent coating and the heat-sealable coating. In fact, the coated paper of this disclosure can be manufactured without any adhesive layer between any coatings or between the fiber web and the coating.

[0076] Alternatively, the first coating containing a transparent agent can be combined with a heat-sealable coating composition and applied as a single coating to the mesh.

[0077] On the other hand, a heat-sealable (second) coating can be applied to the side of the fiber web opposite to the side coated with the first coating containing a transparent agent, thereby providing the first coating on the first surface of the fiber web and the second coating on the second surface.

[0078] Heat-sealable coatings can contain polymers and various other components. The polymer can be selected from the group consisting of proteins, polysaccharides, polysaccharide ethers, polysaccharide esters, and polysaccharide ether esters. These polymers can completely replace petroleum-derived heat-sealable polymers used in the past. For example, these polymers can be produced from biomass. Therefore, these polymers can be as sustainable and environmentally friendly as plant- or animal-derived waxes or oils, and exhibit excellent heat-sealable properties.

[0079] The polymer is preferably a protein and / or thermoplastic polymer that improves heat-sealing properties.

[0080] The polymer can be a thermoplastic polymer with a melting point in the range of 60 to 200°C, more preferably in the range of 100 to 180°C, and most preferably in the range of 110 to 180°C. When the heat-sealable coating of the coated paper (paper article) of this disclosure comprises a thermoplastic polymer with a melting point in the range of 60 to 200°C, the heat-sealable properties of the coated paper are improved.

[0081] In addition, the polymer is preferably a biomass-based polymer, which makes the coated paper more sustainable and environmentally friendly.

[0082] For example, the polymer can be a polyester polymer, which can be selected from the group consisting of polyhydroxyalkanoates, polylactic acid, polyglycolic acid, polybutylene succinate, polycaprolactone, polybutylene adipate, and polylactic acid-polyethylene glycol.

[0083] Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates. PHAs are thermoplastic. They can be homopolymers or copolymers, and their properties vary depending on their chemical composition (i.e., the hydroxyalkanoates they contain).

[0084] PHA can be one or more polyesters selected from the group consisting of: poly(3-hydroxypropionate), poly(3-hydroxybutyrate), poly(4-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxyundecanoate), poly(3-hydroxydodecanate), poly(3-hydroxytetradecanoate), poly(3-hydroxypentadecanate), and poly(3-hydroxyhexadecanoate). PHA can also be one or more copolyesters obtained by copolymerization of two or more hydroxyalkyl acids. More specifically, the PHA copolyester can be one or more selected from the group consisting of: poly(3-hydroxypropionate-co-3-hydroxybutyrate), poly(3-hydroxypropionate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate).

[0085] PHA is preferably one or more polyesters selected from the group consisting of poly(3-hydroxypropionate), poly(3-hydroxybutyrate), poly(4-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate). PHA is most preferably poly(3-hydroxybutyrate).

[0086] Polybutylene adipate terephthalate is preferably a block copolymer. Polylactic acid-polyethylene glycol is preferably a block copolymer.

[0087] Polysaccharides can be one or more polymers selected from the group consisting of starch, cellulose, arabinoxylan, chitin, and pectin. Preferred polysaccharides are starch or cellulose, such as cellulose derivatives.

[0088] Plasticizers can be added to polysaccharides to improve their thermoplasticity. Thus, thermoplastic polysaccharides containing both polysaccharides and plasticizers are obtained.

[0089] Plasticizers can be one or more compounds selected from the group consisting of polyols, glycols, polyol esters, and aliphatic esters of monocarboxylic acids, dicarboxylic acids, or polycarboxylic acids. Plasticizers are preferably polyols or glycols, and most preferably one or more compounds selected from glycerol, ethylene glycol, and sorbitol. Glycerol can be vegetable glycerol (VG). Vegetable glycerol is glycerol obtained from vegetable oils (e.g., soybean oil, coconut oil, or palm oil).

[0090] Thermoplastic polysaccharides preferably comprise at least one of starch and cellulose. In other words, the thermoplastic polysaccharide is preferably thermoplastic starch, thermoplastic cellulose, or a combination thereof, and more preferably thermoplastic starch. Thermoplastic starch preferably comprises one or more plasticizers selected from the group consisting of glycerol, ethylene glycol, and sorbitol.

[0091] On the one hand, thermoplastic polysaccharides are derived from agricultural waste from corn.

[0092] The polymers used in this disclosure may also be polysaccharide ethers, polysaccharide esters, or polysaccharide ether esters.

[0093] The polysaccharide ether is preferably a cellulose ether. More preferably, it is carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, ethyl methyl cellulose, and hydroxypropyl methyl cellulose. Most preferably, it is carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose.

[0094] Polysaccharide esters can be cellulose esters, such as cellulose acetate.

[0095] Polysaccharide ether esters can be cellulose ether esters, such as hydroxypropyl methylcellulose acetate succinate and carboxymethylcellulose acetate butyrate.

[0096] The polymer is preferably selected from one or more of the group consisting of poly(3-hydroxybutyrate), poly(4-hydroxybutyrate), polylactic acid, polylactic acid-polyethylene glycol block copolymer, polybutylene adipate terephthalate and thermoplastic starch.

[0097] Polymers can also be proteins, especially plant-derived proteins. These proteins include soy protein isolate, whey protein isolate, or casein.

[0098] The heat-sealable coating used in this disclosure may contain one or more additives. Each additive may be present in the coating in an amount from about 0.01% by weight to about 7% by weight, for example from about 0.1% by weight to about 3% by weight. The additive may be at least one compound selected from the group consisting of rheology modifiers and softeners.

[0099] Rheology modifiers can be one or more compounds selected from the group consisting of cellulose, starch, or their derivatives. For example, rheology modifiers can be microcrystalline cellulose and / or nanocellulose. Rheology modifiers preferably have water solubility or water dispersibility. Most preferably, rheology modifiers are biomass-based and / or biodegradable. Rheology modifiers can thicken emulsions and improve emulsion stability, thus preventing dripping during coating application.

[0100] The heat-sealable coating disclosed herein may also contain a softener. The softener may be one or more compounds selected from the group consisting of polyols, glycols, polyol esters, and aliphatic esters of monocarboxylic acids, dicarboxylic acids, or polycarboxylic acids. The softener is preferably a polyol or glycol, and most preferably one or more compounds selected from bio-based glycerol or glycerol, ethylene glycol, and sorbitol.

[0101] In one exemplary embodiment, the coating comprises up to 90 wt.% polymer, 0 to 3 wt.% rheology modifier, and 0 to 7 wt.% thickener, based on the total weight of the coating.

[0102] Based on the total weight of the coating mixture, the heat-sealable coating used in this invention can be mixed with a clearing agent at a ratio of about 10 to 90 wt.-% wax and about 10 to 90 wt.-% polymer, and more preferably, it can contain 10 to 40 wt.-% wax and 60 to 90 wt.-% polymer. Furthermore, based on the total weight of the coating, paper coated with a coating containing 10 to 90 wt.-% wax and 10 to 90 wt.-% polymer possesses both paper-like appearance and feel, as well as processability and heat-sealability comparable to plastic films. When the coating contains 10 to 40 wt.-% wax and 60 to 90 wt.-% polymer based on the total weight of the coating, the heat-sealability of the coated paper can be improved. Furthermore, based on the total weight of the coating, coated paper having a coating containing 10 to 40 wt.-% wax and 60 to 90 wt.-% polymer exhibits improved water vapor barrier properties. In a particularly preferred embodiment, the coating comprises 20 to 40 wt.% wax and 60 to 80 wt.% polymer, based on the total weight of the coating. This coating achieves an optimal balance between water vapor barrier properties and heat-sealing properties.

[0103] The basis weight of a heat-sealable coating can vary depending on the specific application and the end use of the coated paper. Typically, the basis weight of a heat-sealable coating can be approximately 1 g / m². 2 Approximately 20 g / m 2 Including all 1 g / m 2 The increment. For example, the basis weight of a heat-sealable coating can be greater than or equal to about 1 g / m³. 2 For example, greater than or equal to approximately 3 g / m2 The basis weight of the heat-sealable coating can be less than or equal to approximately 20 g / m³. 2 For example, less than or equal to approximately 18 g / m 2 For example, less than or equal to about 15 g / m 2 For example, less than or equal to about 13 g / m 2 For example, less than or equal to about 10 g / m 2 For example, less than or equal to about 8 g / m 2 .

[0104] If the transparent coating composition is mixed with the heat-sealable coating composition and applied as a single coating, the resulting coating may have a basis weight of approximately 3 g / m³. 2 Approximately 35 g / m 2 Including all 1 g / m 2 The increment. For example, the basis weight of the combined coating can be greater than or equal to about 5 g / m³. 2 For example, greater than or equal to approximately 8 g / m 2 The basis weight of the combined coating can be less than or equal to approximately 30 g / m³. 2 For example, less than or equal to approximately 25 g / m 2 For example, less than or equal to approximately 20 g / m 2 For example, less than or equal to approximately 18 g / m 2 For example, less than or equal to about 15 g / m 2 .

[0105] The clarifying agent can be applied to the fiber web using any suitable method or technique. For example, in one embodiment, an aqueous composition containing the clarifying agent can be applied to the fiber web using a sizing machine at the wet end of the paper machine or after the web has dried. Alternatively, the fiber web can be formed and then coated with the composition containing the clarifying agent. Coating can be performed using any suitable method, including air knife coating, roll-to-roll coating, doctor blade coating, spraying, Mayer bar coating, direct gravure printing, offset gravure printing, reverse gravure printing, smooth roll coating, curtain coating, bead coating, slot coating, filler press coating, etc.

[0106] The coating composition can be applied over a clear coat by spraying, brushing, or rolling to form a heat-sealable coating. After application to the surface, the surface coating composition undergoes film formation.

[0107] A heat-sealable coating can be formed by a coalescence-based film-forming method. Coalescence-based film formation utilizes polymer particles dispersed in a liquid phase, preferably latex polymers, and most preferably a combination of an aqueously dispersed polymer selected from the group consisting of polyesters, polysaccharides, polysaccharide esters, polysaccharide ethers, and polysaccharide ether esters with a wax of plant or animal origin.

[0108] The heat-sealable coating composition may be an aqueous dispersion or emulsion comprising wax and / or polymer. The wax is preferably the wax defined in the first aspect of the invention. In other words, the wax is preferably a plant wax or an animal wax, and more preferably a plant wax. The wax contained in the heat-sealable coating composition is most preferably one or more selected from the group consisting of coconut wax, soybean wax, palm wax, rice bran wax, and mixtures thereof. The dropping point of the wax is preferably in the range of 60°C to 120°C.

[0109] After applying the first and second coating compositions, the coatings are dried to form coated paper. On one hand, the first coating composition may be applied and dried, followed by the application of the second coating composition and then drying. Alternatively, the first and second coating compositions may be combined and then applied to a fiber web, followed by drying.

[0110] Drying can be achieved by blowing hot, dry air onto the coating, thereby raising the coating temperature to a point where moisture evaporates from the coated paper, leaving the coated paper relatively dry. During the drying process, the web temperature, i.e., the temperature of the fiber web, must be below the dropping point of the wax. Therefore, the web temperature during the drying process is preferably less than or equal to 120°C. The web temperature of the paper can be determined by non-contact temperature measurement using an infrared non-contact thermometer.

[0111] Coated fiber webs can be calendered without supercalendering. On one hand, a plain weave filament press can be used to create a smooth effect on the product surface. For example, the calendering rollers may include hard rollers opposite soft rollers. The pressure applied to the coated paper can be greater than or equal to about 200 kPa (2 bar), for example greater than or equal to about 400 kPa (4 bar), for example greater than or equal to about 500 kPa (5 bar), and typically less than or equal to about 1200 kPa (12 bar), for example less than or equal to about 1000 kPa (10 bar), for example less than or equal to about 800 kPa (8 bar), for example less than or equal to about 700 kPa (7 bar). Calendering can be performed at ambient temperature, or alternatively, one or both calendering rollers can be heated.

[0112] In one embodiment, a transparent agent can be applied to the fiber web, and the fiber web can be calendered. After calendering, a heat-sealable coating can be applied to the web. Optionally, the coated fiber web can be calendered after both coatings have been applied to the web, i.e., after the heat-sealable coating has been applied and formed on the web. In another embodiment, the coated fiber web can be calendered multiple times. For example, in one embodiment, a transparent agent can be applied to the fiber web, and the fiber web can be subjected to a first calendering process. Next, a heat-sealable coating can be applied and formed on the fiber web, and then the coated web can be calendered again.

[0113] In addition to having relatively low opacity, the coated paper of this disclosure can also have relatively low thickness. For example, the thickness of the paper can be less than or equal to about 80 µm, for example less than or equal to about 70 µm, for example less than or equal to about 60 µm. The thickness of the paper is typically greater than or equal to about 20 µm, for example greater than or equal to about 25 µm, for example greater than or equal to about 30 µm.

[0114] The low-opacity paper manufactured according to this disclosure not only exhibits low opacity and heat-sealing properties, but also a beneficial combination of other properties. For example, the Gurley permeability of the low-opacity paper can be less than or equal to about 45,200 seconds, for example less than or equal to about 20,000 seconds, for example less than or equal to about 10,000 seconds, for example less than or equal to about 1,000 seconds, and typically greater than or equal to about 600 seconds.

[0115] According to TAPPI T 432 cm-09 (using 2µL of water in the test), the water droplet resistance of low-opacity, heat-sealable paper can also be greater than or equal to 10 min. According to ASTM E96 / E96M – 15:2014, the water vapor barrier properties of paper products at 23°C and 50% HR can be less than or equal to 80 g / m³. 2 / day, for example, less than or equal to 50 g / m 2 / day. The low-opacity and heat-sealable paper disclosed herein has a variety of uses and applications. For example, the low-opacity and heat-sealable paper can be used as a packaging material. For example, the low-opacity and heat-sealable paper can be manufactured in a flexible or semi-rigid form, making the product ideal for constructing packaging.

[0116] In addition to relating to low-opacity, heat-sealable paper and products made from such paper, this disclosure also relates to a method for producing low-opacity, heat-sealable paper. The method includes forming a fiber web from a fibrous raw material. For example, the fiber web may be a wet-laid web. The fiber web is then coated with an aqueous composition containing the aforementioned clarifying agent. Any suitable coating technique can be used to coat the fiber web. For example, in one aspect, a sizing machine can be used to coat the fiber web.

[0117] The coating applied to the fiber web can be dried, and then optionally calendered. Next, a second coating containing a heat-sealable component can be applied to the fiber web. The coating is dried to form a heat-sealable coating, and the coated and dried web can optionally be calendered.

[0118] Alternatively, a heat-sealable composition or component can be combined with a transparent composition or component, and the resulting heat-sealable transparent composition can be applied to a mesh to form a single, heat-sealable coating with reduced opacity. The coating can be dried and then optionally calendered.

[0119] According to an embodiment of the present invention, the paper article comprises: i) Paper-based sheet, which is a fiber web containing cellulose fibers, wherein the fibers are refined cork fibers, and the basis weight of the fiber web is 10 g / m². 2 25 g / m or more and less than or equal to 25 g / m 2 And preferably at 10 g / m 2 Up to 24 g / m 2 Within the range; and ii) A coating comprising a transparent agent composition (containing soybean-based wax) and a heat-sealable coating composition (containing polysaccharides). The opacity of the paper product is less than or equal to 35%.

[0120] According to an embodiment of the present invention, the paper article comprises: i) Paper-based sheet, which is a fiber web containing cellulose fibers, wherein the fibers are refined cork fibers, and the basis weight of the fiber web is 10 g / m². 2 25 g / m or more and less than or equal to 25 g / m 2 And preferably at 10 g / m 2 Up to 24 g / m 2 Within the range; and ii) A first coating of a transparent agent composition (containing coconut-based wax); and iii) A second coating of a heat-sealable coating composition (containing / comprises casein); The opacity of the paper product is less than or equal to 35%, preferably less than or equal to 20%.

[0121] The following examples can be used to better understand this disclosure.

[0122] Example According to this disclosure, a low-opacity, heat-sealable paper was manufactured, and various properties were tested. Three different samples were produced.

[0123] Each sample included a fiber web, also known as the base web. The basis weight of the fiber web in sample 1 was 14 g / m². 2 Its Schopper-Riegler freeness value was 86° SR. The basis weight of the fiber web in samples 2 and 3 was 22 g / m. 2Its Schopper-Riegler freeness value is 82° SR. Each fiber web is made of pulp fibers (especially refined cork fibers).

[0124] Samples 1 and 2 were coated with a mixture of a clearing agent composition containing soybean-based wax and a heat-sealable coating composition containing polysaccharides derived from agricultural corn waste. In samples 1 and 2, the basis weight of the heat-sealable clearing agent coating was 11 g / m³. 2 .

[0125] Sample No. 3 was first coated with a clearing agent composition containing coconut-based wax, and then coated with a heat-sealable coating composition containing casein, with a sealing temperature of 130 to 220°C. The weight of the two coating layers was 11 g / m². 2 .

[0126] Then, various performance tests were performed on the coated paper samples, and the following results were obtained. For each performance, the coated paper was tested twice, and the results were averaged. Heat-sealing performance was tested at 160°C using a heat-sealing laminator (e.g., YOSAN LM-260). All coated papers demonstrated heat-sealing properties. As shown above, the coated paper sample exhibits very low opacity while also possessing excellent mechanical strength and barrier properties. The sample demonstrates sealability at 150°C.

[0127] These and other modifications and variations of the invention can be practiced by those skilled in the art. Embodiments of the invention are set forth in the appended claims. Furthermore, it should be understood that aspects of the various embodiments may be interchanged, in whole or in part.

Claims

1. A paper product comprising: A fibrous web comprising cellulose fibers, wherein the cellulose fibers have a Schopper-Riegler freeness value in the range of 60° SR to 95° SR as measured according to ISO 5267-1 :2000, the fibrous web having a basis weight of less than or equal to 38 g / m 2 and defines a first surface and a second surface; and a coating on the first surface and / or the second surface of the fibrous web, preferably on one of the first surface and the second surface, wherein the coating comprises a transparency agent, the transparency agent comprising a bio-based wax or oil, and a heat-sealable composition, the heat-sealable composition comprising a polymer, the polymer comprising a polyester, a protein, a polysaccharide, a polysaccharide ester, a polysaccharide ether, or a polysaccharide ether ester; wherein the coating defines an outer surface (18) of the paper product; and wherein the paper product exhibits an opacity of less than or equal to about 45%.

2. A paper product comprising: A fibrous web comprising cellulose fibers, wherein the cellulose fibers have a Schopper-Riegler freeness value in the range of 60° SR to 95° SR as measured according to ISO 5267-1 :2000, the fibrous web having a basis weight of less than or equal to 38 g / m 2 and defines a first surface and a second surface; and a first coating comprising a transparency agent, the transparency agent comprising a bio-based wax or oil, and a second coating comprising a heat-sealable composition, the heat-sealable composition comprising a polymer, the polymer comprising a polyester, a protein, a polysaccharide, a polysaccharide ester, a polysaccharide ether, or a polysaccharide ether ester; wherein the paper product exhibits an opacity of less than or equal to about 45%; and wherein one of the following features (i) or (ii) is met: (i) the first coating and the second coating are provided sequentially on the same surface, i.e. on the first surface and / or the second surface of the fibrous web; (ii) the first coating is provided on the first surface of the fibrous web and the second coating is provided on the second surface of the fibrous web.

3. The paper product as defined in claim 2, wherein the first coating is provided on the first surface of the fibrous web and the second coating is provided on the second surface of the fibrous web.

4. The paper product as defined in any one of the preceding claims, wherein the cellulose fibers have a Schopper-Riegler freeness value in the range of 70° SR to 90° SR.

5. The paper product as defined in any of the preceding claims, wherein the fiber web has a basis weight of less than or equal to 24 g / m 2 , preferably less than or equal to 22 g / m 2 , more preferably less than or equal to 20 g / m 2 , and greater than or equal to 10 g / m 2 .

6. The paper product as defined in any one of the preceding claims, wherein the paper product is calendered but not super-calendered.

7. The paper product as defined in any one of the preceding claims, wherein the bio-based wax or oil is a plant-based wax or oil, preferably having a melting point of 25°C to 75°C.

8. The paper product as defined in any one of the preceding claims, wherein the bio-based wax or oil is a coconut-based wax, a palm-based wax, a soy-based wax, a rice-based wax, or a mixture thereof.

9. The paper product as defined in any one of the preceding claims, wherein the paper product has an opacity of less than or equal to 42%, preferably less than or equal to 32%.

10. The paper product as defined in any one of the preceding claims, wherein the polymer contained in the heat-sealable composition comprises a thermoplastic starch.

11. The paper product as defined in any one of the preceding claims, wherein the polymer contained in the heat-sealable composition comprises a protein, preferably whey protein, soy protein, casein protein, or a mixture thereof.

12. The paper product as defined in any of the preceding claims, wherein the basis weight of the coating comprising the heat-sealable composition is from about 1 g / m 2 to about 35 g / m 2 , preferably from about 3 g / m 2 to about 25 g / m 2 , and more preferably from about 4 g / m 2 to about 20 g / m 2 .

13. The paper product as defined in any one of the preceding claims, wherein the paper product is free of paraffin wax, mineral oil, or hydrocarbon oil.

14. The paper product as defined in any one of the preceding claims, wherein the fibrous web comprises wood pulp fibers alone or in combination with bast fibers.

15. The paper product as defined in any of the preceding claims, wherein the paper product has a thickness of less than or equal to 80 pm, preferably less than or equal to 70 pm, more preferably less than or equal to 60 pm, and greater than or equal to 30 pm.

16. The paper product as defined in any of the preceding claims, wherein the transparency agent is present in the paper product in an amount of greater than or equal to 2 wt%, preferably in an amount of greater than or equal to 4 wt%, more preferably in an amount of greater than or equal to 6 wt%, even more preferably in an amount of greater than or equal to 8 wt%, and in an amount of less than or equal to 25 wt%, preferably in an amount of less than or equal to 20 wt%, more preferably in an amount of less than or equal to 15 wt%.

17. The paper product as defined in any of the preceding claims, wherein the paper product has an air permeability of less than or equal to 45,200 seconds, preferably less than or equal to 20,000 seconds, more preferably less than or equal to 10,000 seconds, even more preferably less than or equal to 1000 seconds, and greater than or equal to 600 seconds, according to ISO 5636-5:2003.

18. The paper product as defined in any of the preceding claims, wherein the paper product has a water vapor transmission rate of less than or equal to 80 g / m 2 / day, preferably less than or equal to 50 g / m 2 / day, at 23 °C and 50% HR according to ASTM E96 / E96M - 15:2014.

18. The paper product as defined in any of the preceding claims, wherein the paper product has a water vapor transmission rate of less than or equal to 80 g / m 2 / day, preferably less than or equal to 50 g / m 2 / day, at 23 °C and 50% HR according to ASTM E96 / E96M - 15:2014.

19. The paper product as defined in any of the preceding claims, wherein the paper product is a packaging material.

20. The paper product as defined in any of the preceding claims, wherein the bio-based wax or oil is obtained by processing a plant material.

21. Use of the paper product as defined in any of the preceding claims as a wrapping paper for food, cosmetics or pharmaceuticals, or as a wrapping for cigarette packets, cigarette paper boxes, cigar packets, heat-not-burn packets and heat-not-burn boxes.

22. A method for producing a paper product as defined in claim 1, the method comprising: coating a fibrous web with a mixture of a transparency agent and a heat sealable composition; and optionally calendering the coated fibrous web.

23. A method for producing a paper product as defined in claim 2, the method comprising: coating a fibrous web with an aqueous composition containing a transparency agent; then coating the fibrous web with a heat sealable composition; and optionally calendering the coated fibrous web.

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