Starch-based highly dilutable adhesives for tissue paper lamination

Abstract

The present invention relates to an adhesive for a paper laminate, more particularly an adhesive for a tissue paper laminate comprising at least one tissue paper layer, where the tissue paper layer is adhered to itself (e.g., folded onto itself) or to another surface (e.g., folded onto itself) by means of the adhesive. ), the binder being an aqueous starch-based highly dilutable binder comprising at least one modified starch and having a viscosity as defined herein. Uses and methods of use of such adhesives as well as products, in particular laminates obtained by these methods and uses, are also encompassed.

Description

Technical Field

[0001] The present invention relates to an adhesive for paper laminates, more particularly an adhesive for tissue laminates comprising at least one tissue layer, wherein the tissue layer is bonded to itself (e.g. it is folded onto itself) or to another surface (e.g. another tissue layer or a nonwoven, woven substrate, etc.) by an adhesive, the adhesive being an aqueous, starch-based, highly dilutable adhesive comprising at least one modified starch and having a viscosity as defined herein. Background Art

[0002] Tissue paper products are used almost constantly in daily life. Toilet paper, facial tissue, wipes and paper towels are examples of tissue paper products commonly used in homes and industries. Tissue paper products can be made of a single layer (lamina or ply), or can be a laminate (or multilayer, or laminated) formed by two or more layers. As used herein, "layer" refers to a single sheet of tissue paper, and the term "laminate", or "multilayer", or "laminated" is used to characterize the paper prepared by joining several single layers or several layers together or joining several single layers or several layers to another woven or nonwoven substrate to produce a combined material. As used herein, the phrase "tissue paper laminate" refers to a laminate comprising at least one layer of tissue paper joined to another substrate or layer, and these are well known and recognized by those skilled in the art. "Tissue paper (tissue paper or tissue)" used herein refers to such a woven or nonwoven substrate, which is a relatively lightweight sheet used as a sanitary product (e.g., facial tissue and toilet paper or paper towel). These can also be manufactured in condenser, carbonized, packaging and cleaning grades. General properties can include one or more of softness, adequate strength and absorbency, clean appearance, and freedom from coarse and abrasive particles. In typical embodiments, the tissue paper can have a basis weight of no more than about 50 grams per square meter, more typically about 11 to about 30 grams per square meter.

[0003] Single-ply tissue products have several disadvantages. For example, single-ply tissue products are stiffer than dual-ply tissue products of the same total basis weight. This increased stiffness causes consumers to perceive single-ply tissue products as less soft than multi-ply tissue products and, therefore, may not be as preferred as multi-ply tissue products. Laminated tissue having the same total basis weight as a single-ply tissue product can be prepared to have a greater caliper. This increased caliper causes consumers to perceive the product as having thickness (loft) and high quality. Furthermore, in order to provide consumers with the convenience of using a predetermined length of material, the tissue laminate can be perforated at a pre-selected length.

[0004] However, tissue laminates are susceptible to skinning. Skinning occurs when the layers separate from each other and no longer remain intact to form an integral laminate. For example, skinning may occur when attempting to reduce tissue product packaging and shipping costs (e.g., compression of the tissue product, which may impart shear forces to the layers and cause skinning). Skinning may also occur during tissue converting production operations when the top sheet of a roll breaks due to friction between the surface in the production line and the roll in the contact area. It may also occur during consumer handling. In the case of perforated toilet paper, skinning can result in layer misalignment along the perforation lines when a portion of the top sheet of the roll is torn or lost.

[0005] Several attempts have been made in the art to connect tissue layers in a manner that reduces or minimizes peeling. One method involves applying mechanical forces (friction and compression) to interlock the sheets and prevent them from separating from each other. These forces are generated by piercing pinholes in the laminate with embossed edges in steel rolls to connect the sheets, or by pressing wavy lines in the tissue paper during embossing. Another method uses an adhesive to bond the layers together. For example, such methods have been described in International Patent Publications WO 2005 / 021623 and WO 2010 / 015280.

[0006] Tissue paper laminates prepared with water-soluble adhesives are susceptible to rupture when wetted, such as may occur when toilet paper or facial tissue is disposed of in a sewer system. Therefore, the adhesive used to bond the tissue paper layers together is desirably aqueous-based (solution, dispersion, emulsion, latex, etc.) and at least to some extent water-soluble (solution) or water-dispersible. For economic reasons, it is also desirable to use an aqueous-based adhesive.

[0007] Although various aqueous adhesives for the purpose are known in the art, such as known from WO 2005 / 021623, these aqueous adhesives are typically based on any one of polyvinyl alcohol (PVOH), polyvinyl acetate, cellulose ethers, acrylics and polyurethanes. Among these aqueous adhesives, PVOH-based adhesives are the main technology on the current tissue and paper towel lamination market. A wide variety of products with different viscosities, solid contents and properties are available on the market. However, the main disadvantage of these adhesives is that they rely on fossil-based raw material sources, and are therefore not optimal in terms of sustainability and environmental issues. Therefore, it is desirable to replace these materials with materials from renewable sources. In addition, PVOH-based adhesives are susceptible to bacterial and fungal contamination, and therefore preservatives are required to provide extended storage stability. The use of such preservatives, although very common, always brings such a risk: due to toxicity and allergic reasons, the availability of any other application for food applications and cosmetic applications or where tissue paper is in contact with the user's skin is limited. In addition, there is a general trend that in many fields where those adhesives are available, consumers increasingly prefer products without preservatives.

[0008] US 6,379,447 B1 relates to selected polysaccharide laminating or bonding adhesives having high bond strength and low bleed characteristics and which can be used in multi-layer, lightweight paper products. The patent discloses a lightweight, paper laminating, aqueous, high solids, polysaccharide adhesive composition comprising about 15 to 50 weight percent starch or dextrin or a blend of starch and dextrin as a continuous aqueous phase, these dispersed starches and dextrins having: a) a low viscosity at about 26% (+ / - 1%) solids, 120°F (49°C) and 0.1s -1 The adhesive composition has a zero-shear viscosity of 0.07 Pa.s at a shear rate of about 1.5 %, a) a shear thinning index of about 0.9 to 1.1, and a oozing time of the adhesive composition of greater than 15 seconds, both measured at 26% solids (+ / - 1%) and 49°C.

[0009] WO 2014 / 003556 A1 relates to the field of paper coating, more particularly to a tool and method for providing paper with at least one layer of pigment by using thin film coating to obtain a good printable surface. The invention also relates to a coated paper comprising paper and a certain amount of the paper coating composition of the invention on the paper, wherein water in the paper coating composition has been reduced or removed. The patent application discloses a method for preparing coated paper, the method comprising the following steps:

[0010] a) providing a pigmented wet coating formulation comprising water, 2 to 20 parts of a binder and 100 parts of a pigment, wherein at least 50% of the binder is a highly branched starch (HBS) characterized by a molecular weight of 0.5*10 5 Up to 1*10 6 Daltons and having a molecular branching degree of at least 6%, and the starch is obtained by treating gelatinized starch or a starch derivative with a glycogen branching enzyme (EC 2.4.1.18); and wherein at least 70% of the pigment is calcium carbonate; and

[0011] b) Applying the pigmented wet coating formulation to paper by film coating and drying the coated paper.

[0012] WO 2010 / 003054 A1 generally relates to compositions comprising protein and starch and methods for preparing and using the compositions. In one aspect of the invention, the compositions are used in adhesives or coatings. In another aspect of the invention, the compositions are used in adhesives to increase at least one of the viscosity or bonding strength of the adhesive or coating. The patent application discloses an adhesive composition comprising about 1% to about 99% of plant protein and about 1% to about 99% of starch.

[0013] US2007 / 240823 A1 relates to the field of adhesives. More specifically, the invention relates to adhesives that are particularly well suited for use in bottle labeling applications. The patent application discloses a water-based adhesive suitable for industrial bottle labeling applications comprising a starch component and a protein component, wherein the starch component does not contain legume starch having an amylose content of 25% or more and the protein component does not contain casein or gelatin, and wherein the adhesive does not contain synthetic polymers.

[0014] WO 2014 / 200344 A1 relates to an aqueous adhesive composition comprising starch. This patent application discloses an aqueous adhesive composition comprising highly branched starch (HBS), wherein the starch is obtained by treating starch or a starch derivative with a glycogen branching enzyme (EC 2.4.1.18), and the composition further comprises a carboxymethyl polysaccharide derivative.

[0015] WO 95 / 35202A1 relates to an adhesive bonding system for laminates (e.g. corrugated paperboard products or other types of composite boards) and to boards prepared by said method. The patent application discloses a method for bonding two substantially continuous material layers by an adhesive, the method comprising:

[0016] providing an application apparatus adapted to continuously extrude a plurality of juxtaposed, spaced-apart continuous beads of adhesive material, wherein the adhesive material comprises substantially gelatinized starch with a composition; gelatinizing the composition in the application apparatus to a viscosity as determined by the Stein-Hall cup method of greater than 200 seconds;

[0017] extruding the substantially gelatinized starch with the adhesive composition between the material layers; and

[0018] The layers are combined by bonding them from one to another by adhesive.

[0019] Therefore, there is a need for alternative adhesives for tissue paper bonding that are more sustainable and have a reduced content of fossil-based ingredients. In addition, it is particularly desirable that the adhesives can be provided without the need for preservatives. Therefore, there is a need for new adhesives that are bio-based and sustainable, preservation free, highly dilutable, and exhibit excellent performance in applications. Summary of the invention

[0020] The present invention is based on the surprising discovery of the inventors that the above objects can be achieved by using an aqueous and highly dilutable adhesive composition based on starch, wherein the adhesive composition preferably has an alkaline pH to eliminate the need for preservatives.

[0021] In a first aspect, the present invention therefore relates to a liquid aqueous adhesive composition comprising at least one modified starch in an amount of 2 to 60 wt.-%, preferably 5 to 50 wt.-%, relative to the total weight of the composition, wherein the adhesive composition has a dynamic viscosity at 23°C of 10,000 to 40,000 mPa*s, preferably 15,000 to 30,000 mPa*s (the dynamic viscosity is measured according to Brookfield with a Brookfield viscometer RVT, spindle 6 at 20 rpm).

[0022] In another aspect, the invention features the use of a liquid aqueous adhesive composition according to the invention as an adhesive for ply bonding, preferably for paper ply bonding, more preferably for tissue paper ply bonding.

[0023] In yet another aspect, the present invention relates to a method for producing a product comprising at least two plies, preferably 2 to 5 tissue paper plies, more preferably tissue paper plies, the method comprising:

[0024] (a) applying a liquid aqueous binder composition according to the invention or a dilution thereof in water to the first of the at least two layers, wherein the mass ratio of binder:water in the dilution is from 1:1 to 1:15 or from 1:1 to 1:11, preferably from 1:4 to 1:8; and

[0025] (b) Bonding the first layer with the adhesive obtained in (a) to the second layer and optionally other layers.

[0026] The present invention also encompasses a product obtainable by the process according to the present invention, wherein the product is preferably a paper laminate, more preferably a tissue paper laminate.

[0027] These and other aspects, features and advantages of the present invention will become apparent to those skilled in the art in the following detailed description and claims. Each feature in one aspect of the present invention may be used in any other aspect of the present invention. In addition, the examples included herein are intended to describe and illustrate the present invention, but not to limit it, and in particular, the present invention is not limited to these examples.

[0028] As used herein, "at least one (species)" refers to one (species) or more (species), i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or more (species) mentioned. With respect to a given species, the term does not relate to the total amount of molecules, but to the type of compound. "At least one modified starch" therefore means, for example, that only one type or several different types of modified starch may be contained, without specifying the amount of each compound.

[0029] Unless otherwise expressly stated, all percentages given herein in connection with a composition or formulation refer to the weight % relative to the total weight of the corresponding composition or formulation. Numerical ranges specifically specified in the format "from x to y" include the specifically specified values. If multiple preferred numerical ranges are specifically specified in this format, it is understood that all ranges generated by combining different endpoints are also included.

[0030] Numerical ranges specifically specified in the format "from x to y" include the specifically specified values. If several preferred numerical ranges are specifically specified in this format, then, of course, all ranges resulting from combinations of the different endpoints are also included.

[0031] Numerical values ​​herein without decimal places being specifically designated refer to the entire value with a decimal place being specifically designated, ie, for example, 99% refers to 99.0% unless otherwise specified.

[0032] The term "about" or "approximately" in relation to numerical values ​​means that the variance relative to the given numerical value is ±10%, preferably ±5% or ±1%.

[0033] Unless explicitly stated otherwise, when referring to molar masses in this text, this information always refers to the number-average molar mass M n The number-average molar mass can be determined, for example, by gel permeation chromatography (GPC) in accordance with DIN 55672-1:2007-08 with THF as eluent. w It can also be done by GPC such as targeting M n Described ok. DETAILED DESCRIPTION

[0034] The present invention relates to a liquid aqueous adhesive composition comprising at least one modified starch, the amount of the modified starch being 2 to 60 wt.-%, preferably 5 to 50 wt.-%, relative to the total weight of the composition, wherein the dynamic viscosity of the adhesive composition at 23° C. is 10,000 to 40,000 mPa*s, preferably 15,000 to 30,000 mPa*s (the dynamic viscosity is measured according to Brookfield with a Brookfield viscometer RVT, spindle 6 at 20 rpm).

[0035] "Liquid" as used in this context relates to the property of the composition being liquid under standard conditions (ie 20°C and 1013 mbar). However, this term does include pasty and gel-like compositions and liquids with non-Newtonian behavior, such as those having a pour point.

[0036] "Aqueous" as used in this context means that the composition contains water, i.e. as a solvent, typically as the main or only solvent. In various embodiments, this means that the water content is at least 50% by weight, preferably 60, 70, 80 or 90% by weight relative to the total content of solvent.

[0037] In some embodiments, it may be preferred that when water is the main solvent, the composition also comprises a small amount of an organic solvent, in particular an alcohol, more particularly a polyol, such as 1,2- or 1,3-propylene glycol, ethylene glycol or glycerol, in particular glycerol. Relative to the gross weight of the composition, the amount of such organic solvent is preferably not higher than 10% by weight, more preferably 5% by weight or less. In a preferred embodiment, the composition comprises an organic solvent (e.g. glycerol) that can also be obtained from a renewable source (e.g., a plant), in an amount of about 0.1 to 5% by weight, preferably about 0.5 to 5% by weight. It may be preferred that this organic solvent is the only additional solvent other than the water present.

[0038] The water content of the adhesive of the invention is preferably at least 40% by weight, typically 45 to 90% by weight, preferably 50 to 80% by weight or 55 to 80% by weight or 60 to 80% by weight.

[0039] The adhesives of the invention are preferably highly dilutable, i.e. they can be diluted with water to produce a ready-to-use formulation in a mass ratio of adhesive:water of at least 1:1, preferably at least 1:2. Typical dilution ratios are not higher than 1:15, preferably not higher than 1:11 or 1:10 or 1:9, with preferred ranges being in the range of 1:3 to 1:11, preferably in the range of 1:4 to 1:9 or 1:4 or 1:8, for example 1:4, 1:5, 1:6, 1:7 or 1:8. In various embodiments, it may be preferred that the adhesive is a concentrate, i.e. to be diluted with water before use. Thus, in various embodiments, the liquid aqueous adhesive composition according to the invention is designed and intended to be diluted with water in a mass ratio of adhesive:water of 1:1 to 1:11, preferably 1:4 to 1:8, before use. Due to these properties, the adhesives of the invention are particularly suitable for use on converting lines.

[0040] As described herein, the dilution medium or diluent is preferably water or at least a water-based solvent, wherein the solvent comprises water as a major component; i.e., the dilution medium preferably comprises at least 80 wt % or more, typically 90 wt % or more, for example 95 wt % to 100 wt % of water. The water used for dilution may be deionized water to avoid contamination by any unwanted salts, solutes or ions.

[0041] Adhesive of the present invention is based on starch, because they comprise at least one modified starch.The amount of starch present is usually in the range of 2 to 60 % by weight.The lower limit can be 2 % by weight, 3 % by weight, 4 % by weight, 5 % by weight, 6 % by weight or 7 % by weight, and the upper limit thereto is 60 % by weight, 55 % by weight, 50 % by weight, 45 % by weight, 40 % by weight or 35 % by weight.Depending on the type of starch used, relative to the gross weight of adhesive composition, the scope of typical amount is about 5 to about 50 % by weight or to about 40 % by weight.In the sense of the present invention, these amounts are intended to include any polysaccharide based on α-D-glucose with straight-chain starch and amylopectin components.Therefore, as long as it is present in the polysaccharide, it just covers enzymatic and chemically modified and degraded and gelatinized starch.

[0042] In various embodiments, starch used may not be completely soluble in water. In the described embodiment, adhesive composition of the present invention has the form of dispersion, wherein the water-based solvent is continuous and at least the modified starch is the dispersed phase. Therefore, in various embodiments, adhesive composition can have a solid content of 2 to 60 % by weight, preferably 5 to 50 % by weight.

[0043] In various embodiments, modified starch is a starch modified by (acid) hydrolysis, enzymatic or chemical modification or degradation, oxidation or ultrasonic treatment. Suitable methods for starch degradation are well known and widely practiced in the art, and such starches are commercially available. In some cases, modified starch is a starch obtained by acid hydrolysis or enzymatic modification / degradation. These starches can be obtained by natural starches by subjecting them to hydrolysis conditions or treating them with enzymes, wherein the natural starches are, for example, those obtained from vegetables and plants, in particular: cereal starch, preferably corn, barley, wheat or rice starch; tuber or root starch, preferably potato, sweet potato, cassava (cassava) or cassava (tapioca) starch; legume starch, preferably pea or bean starch; and sago or amaranth starch, including starch (waxy starch) with a high amylopectin content. Starch can be straight chain starch, and can be degraded by acid hydrolysis to produce shorter chain polysaccharides, which are fragments of the original long polysaccharide molecules. Similarly, such fragments may be produced by enzymatic activity, for example by an amylase (eg alpha-amylase).The modified starch of the present invention is not a cellulose or a modified cellulose.

[0044] Starches of natural origin usually have an amylose content of 20 to 40% by weight, depending on the plant species from which they are obtained. This amylose content is also preferred in the sense of the present invention. However, in certain plant cultivars there are also starches rich in amylopectin (waxy starches), which can also be used according to the present invention. Since these are already highly branched, the method described herein can even increase the branching.

[0045] Methods for degrading starch are well known in the art. Oxidants for oxidative decomposition include, but are not limited to, chromic acid, permanganate, hydrogen peroxide, nitrogen dioxide, hypochlorite, periodate, and peracids (e.g., peracetic acid). Hydrochloric acid, sulfuric acid, or phosphoric acid can be used as acids for acid hydrolysis decomposition, but other acids, such as acetic acid, oxalic acid, sulfurous acid, perchloric acid, or trichloroacetic acid, can also be used. Enzymes that can be used to decompose starch are alpha-amylase and beta-amylase, as well as glucoamylase and debranching enzymes.

[0046] The modified starch used according to the present invention can be a starch that is digested, degraded or dissolved. This starch can be obtained by gelatinization of native starch granules to obtain water-soluble starch. During this gelatinization process, the intermolecular bonds or starch molecules decompose in the presence of water and heat, so that the hydrogen bonding sites can absorb more water. This can more or less irreversibly dissolve the starch granules in water (wherein water acts as a plasticizer), thereby producing a polymer solution or dispersion. Then, this gelatinized starch can be chemically or enzymatically modified or degraded or rearranged.

[0047] In the context of the present invention, starch is considered to be fully gelatinized if it has a dynamic viscosity as a 40 wt% solution in deionized water at 20°C of less than 500000 mPa*s, wherein the viscosity is measured according to Brookfield (Brookfield RVT, spindle 7 and 20 rpm).

[0048] In various embodiments, the modified starch of the present invention is chemically or enzymatically modified by derivatizing starch or increasing its branching. Thus, in some embodiments, the modified starch is not a (unmodified) starch hydrolysate or starch fragment, although these materials can be used as starting products for further modification as described below herein. The modified starch of the present invention is preferably obtained by chemically or enzymatically modifying native starch, as described below.

[0049] In various embodiments, the modified starch is selected from: starch ethers, preferably alkyl ethers, alkenyl ethers, aryl ethers, aralkyl ethers, cycloalkyl ethers and cycloalkenyl ethers and corresponding hydroxy ethers. Corresponding hydroxy ethers include corresponding hydroxyalkyl ethers, hydroxyalkenyl ethers, etc. The alkyl and alkenyl groups in this type of starch ethers are typically short-chain alkyl and alkenyl groups, such as C1-C6 alkyl (alkenyl), particularly methyl, ethyl, propyl and butyl, including 1-propyl, 2-propyl, 1-butyl, 2-butyl, isobutyl and tert-butyl. Aryl is preferably C6 to C14 aryl, preferably monocyclic groups, such as phenyl. Preferred aralkyl includes benzyl. Cycloalkyl (cycloalkenyl) includes but is not limited to cyclohexyl and cyclohexenyl.

[0050] In various embodiments, suitable starch ethers are selected from allyl ethers, benzyl ethers, hydroxyethyl ethers, hydroxypropyl ethers, hydroxybutyl ethers and 2-hydroxy-3-butenyl-ethers, wherein hydroxypropyl ethers are particularly preferred. In various embodiments, modified starches comprise or consist of the following substances: starch ethers, such as hydroxypropyl starch (CAS 9049-76-7). Hydroxypropyl starch can be prepared, for example, by reacting starch (e.g. potato starch, which is typically provided in the form of an aqueous solution) with propylene oxide in the presence of an alkali (e.g. NaOH). As a by-product, 1,2-propylene glycol (CAS 57-55-6) is also produced in this reaction. Hydroxypropylated starch (e.g. hydroxypropylated extruded potato starch) can be obtained, for example, commercially available as Emcol HE (formerly Emsland Group).

[0051] In various embodiments, the modified starch is selected from: starch esters, preferably organic acid esters, such as esters of starch with C1 to C20 mono- and dicarboxylic acids, including but not limited to formates, acetates, propionates, butyrates, dodecanoates, octadecenoates, alkyl succinates and alkenyl succinates. For succinates, the same definitions of alkyl and alkenyl given above apply.

[0052] In further embodiments, modified starch includes amides, ketones, aldehydes, acetals and ketals, carboxylates, phosphates, sulfates, sulfonates, amines and starch derivatives containing ammonium groups. Amides can be obtained by reacting carboxylated or acid-modified starch with amides or ammonia to obtain corresponding amides. Ketones, aldehydes and carboxylates can be obtained by oxidizing the hydroxyl groups present in the starch. Carboxylates, phosphates, sulfates and sulfonates can be obtained by directly replacing hydroxyl groups with or carboxylates, phosphates, sulfates or sulfonate groups or organic moieties (e.g., alkyl, alkenyl, aryl, aralkyl or cycloalkyl (cycloalkenyl) groups) containing the carboxylates, phosphates, sulfates and sulfonate groups. Examples of the latter include, for example, carboxymethyl starch and carboxyethyl starch. Amines and starch containing ammonium groups can be obtained by replacing hydroxyl groups with amino or ammonium groups.

[0053] In various embodiments, the modified starch may be a carboxymethyl starch or a carboxyethyl starch, such as a carboxymethyl starch. Carboxymethyl starch obtained from corn starch is commercially available, for example, as Emprint CE (formerly Emsland Group).

[0054] It is understood that in all modified starches described herein, the starch generally retains hydroxyl groups, and the modification is therefore only partially modified. It is further contemplated that the modified starches described herein include any combination of the possible modifications discussed above. For example, the starch may therefore be hydroxypropyl-carboxymethyl starch. However, in some embodiments, the modified starch is not hydroxypropyl-carboxymethyl starch.

[0055] In various preferred embodiments, the modified starch is an enzymatically modified starch having a dynamic viscosity of less than 500000 mPa*s measured as a 40 wt% solution in deionized water at 20°C according to Brookfield (Brookfield RVT, rotor 7 at viscosities>50000 mPa*s and rotor 6 at viscosities≤50000 mPa*s, 20 rpm), and can be obtained by modification of natural starch with glycogen branching enzyme (EC 2.4.1.18). In a specific embodiment, the enzymatically modified starch has a dynamic viscosity of less than 200000 mPa*s, preferably less than 100000 mPa*s, more preferably less than 50000 mPa*s, but preferably at least 10000 mPa*s. Viscosities below 10000 mPa*s may result in undesirable extended processing times and color instability. In the preferred range of less than 200000 mPa*s, gelling and recrystallization can be inhibited, which is advantageous.

[0056] Such enzymatically modified starch may be selected from: cereal starches, preferably corn, barley, wheat or rice starch; tuber or root starches, preferably potato, sweet potato, cassava or tapioca starch; legume starches, preferably pea or bean starch; and sago and amaranth starches, including waxy starches derived from said plants; more preferably potato starch.

[0057] To obtain the enzymatically modified starch described above, the starch may be gelatinized, as described above, and then treated with a glycogen branching enzyme, particularly those of EC class 2.4.1.18.

[0058] Natural starch consists of two components (essentially linear amylose with α-1,4 glycosidic bonds and branched α-1,6 branched amylopectin). Branching enzymes are enzymes capable of converting α-1,4 glycosidic bonds into α-1,6 glycosidic bonds to produce additional branching points. During the incubation of this enzyme with starch, the linear structure is decomposed by cleaving 1,4-glycosidic bonds and transferring the linear molecular fragments thus obtained to new branching points by producing new α-1,6-glycosidic bonds. This shortens the average side chain length and significantly reduces the possibility of intermolecular interactions of the new branched molecules. The starch thus obtained combines many functional properties, such as low viscosity at high concentrations, less or no retrogradation, transparency of the solution and sufficiently high wet viscosity.

[0059] The present invention therefore also relates to the use of such (gelatinized and) enzymatically modified starch, wherein the starch has a dynamic viscosity of less than 500000 mPa*s measured at 20° C. as a 40% by weight solution in deionized water according to Brookfield (Brookfield RVT, rotor 7 at viscosities > 50000 mPa*s and rotor 6 at viscosities ≤ 50000 mPa*s, 20 rpm), and can be obtained from native starch by modification with a glycogen branching enzyme (EC 2.4.1.18). The level of branching can vary and depends on the desired application. Typically, the gelatinized and enzymatically modified starch has a molecular branching level of at least 4%. In a preferred embodiment, the gelatinized and enzymatically modified starch has a molecular branching level of at least 5.0%, more preferably at least 5.5% or in the range of 5.5 to 6.5%. The molecular branching level refers to the amount of α-1,6-glycosidic bonds relative to the total amount of α-1,4-glycosidic bonds and α-1,6-glycosidic bonds ((α-1,6 / (α-1,6+α-1,4)*100%), and can be determined according to methods known in the art. Typically, the upper limit of branching is about 8.0%, preferably 7.5% or less.

[0060] Prior to contact with the branching enzyme, the starch or its derivative is preferably gelatinized, as described above. The gelatinized starch can be adjusted to the desired pH by adding an acid or base. After reaching the desired pH and temperature, the branching enzyme is added and the starch solution is maintained at a predetermined temperature so that the enzymatic activity continues for a certain period of time required for branching. Alternatively, the enzyme can be added to a slurry of starch in water and then heated to the desired temperature under agitation (e.g., stirring).

[0061] The branching enzyme may be derived from any suitable microbial source. Preferably, it may be a thermostable glycogen branching enzyme obtained from a mesophil or thermophilic organism, such as an enzyme obtained from Aquifex aeolicus, Anaerobranca gottschalkii or Rhodothermus obamensis.

[0062] The enzymatically modified starch may comprise additional starch molecules, including those which have not been modified as described herein.In a preferred embodiment, the modified starch according to the invention comprises at least 65 wt%, preferably at least 80 wt%, more preferably at least 90 wt% of the total starch.

[0063] The liquid aqueous adhesive composition of the present invention preferably has a pH (measured at 20° C.) in the range of 9.0 to 12.0, preferably 10.0 to 11.5, most preferably 10.5 to 11.5. Such an alkaline pH eliminates the need for the addition of preservatives, since it prevents bacterial or fungal growth in the composition for a long period of time, for example during storage. It has further been found that such a pH value does not adversely affect the stability of the composition and its components.

[0064] In various embodiments, the adhesive compositions of the present invention, in particular those having the pH values ​​described above, are therefore free of preservatives, in particular free of preservatives that may be toxic and irritating upon skin contact, such as formaldehyde-releasing compounds, compounds of the isothiazolinone family (including chloro-, methyl- and benz-isothiazolinones), and nitro compounds such as bronopol (2-bromo-2-nitro-1,3-propanediol). In a preferred embodiment, all of these compounds are absent from the compositions of the present invention. As used in this context, "free of" means that these substances have not been purposefully added and that their amount in the composition is less than 1% by weight, preferably less than 0.5% by weight or less than 0.1% by weight or even less than 0.05% by weight (all relative to the total weight of the composition), or their amount is so low that it cannot be detected at all by conventional methods.

[0065] In addition to the modified starch and water, as disclosed herein above, the adhesive composition may further comprise additives such as any one or more of defoamers, humectants, pH adjusters, preservatives (although those are not particularly preferred), organic solvents (as detailed above), colorants, dyes, pigments and fragrances, preferably defoamers, humectants, pH adjusters and organic solvents.

[0066] According to a particularly preferred embodiment of the present invention, the adhesive composition comprises at least one defoamer.

[0067] Suitable humectants may include longer chain glycols such as heptanediol or octanediol. pH adjusters include hydroxides, particularly alkali metal hydroxides such as sodium hydroxide, potassium hydroxide; ammonia; organic acids such as acetic acid or citric acid; and inorganic acids such as sulfuric acid, nitric acid and phosphoric acid. Particularly preferred are hydroxides (particularly sodium hydroxide), citric acid and sulfuric acid.

[0068] If preservatives are used, these substances are preferably not listed herein as toxic or irritating. In various cases, it may be beneficial to use certain agents, such as citric acid, that have some bacteriostatic effect as a side effect and are primarily used for different purposes. In some embodiments, small amounts of hydrogen peroxide may be added, which may also favorably affect viscosity and act as a disinfectant.

[0069] In some embodiments, the adhesive composition comprises citric acid or a salt thereof, wherein the amount of citric acid or a salt thereof is preferably 0.5 to 3 wt %, such as 1.0 to 2.5 wt %. In such an embodiment, citric acid may be used.

[0070] Defoamers, if present, are typically used in an amount of no more than 1 wt%, such as no more than 0.7 wt% or no more than 0.5 wt%, such as at least 0.1 wt%. In various embodiments, the adhesive is not a foaming adhesive and is not used in the form of foam when applied. In order to ensure this non-foaming property, it may be preferred to include a defoamer.

[0071] Sodium hydroxide can be used in an amount of 0.01 to 5% by weight, depending on the amount required to obtain the desired pH. The same applies to the inorganic acids used, such as sulfuric acid.

[0072] Hydrogen peroxide may be used in absolute amounts of 0.01 to 0.1% by weight, typically as a solution in water (about 35%).

[0073] All amounts given above are relative to the total weight of the adhesive composition.

[0074] In various embodiments, the total amount of additives / further ingredients (such as those described above) does not exceed 15 wt%, preferably not more than 10 wt% or not more than 8 wt%, relative to the total weight of the composition.

[0075] The adhesive composition described herein is preferably used as an adhesive for layer bonding, preferably for paper layer bonding, more preferably for tissue paper layer bonding, wherein said use also forms part of the present invention. In such layer bonding processes, 2 to 5 layers, preferably 2, 3 or 4 layers can be bonded. The layers can be fibrous webs, including wovens and nonwovens; typically, they are tissue paper layers, preferably paper tissue paper layers. The tissue paper layers can be those typically used for toilet paper, kitchen paper, paper towels, facial tissue, cosmetic wipes, paper handkerchiefs, etc.

[0076] As described above with respect to the binder, also in the described uses, the binders described herein are typically used as dilutions in water, wherein the mass ratio of binder:water is 1:1 to 1:15 or 1:1 to 1:11, preferably 1:4 to 1:8.

[0077] The present invention also relates to a process for producing a product comprising at least two layers, preferably 2 to 5 layers of tissue paper, more preferably tissue paper layers, the process comprising:

[0078] (a) applying a liquid aqueous binder composition according to any one of claims 1 to 11 or a dilution thereof in water to a first layer of at least two layers, wherein the mass ratio of binder:water in the dilution is from 1:1 to 1:15 or from 1:1 to 1:11, preferably from 1:4 to 1:8; and

[0079] (b) Bonding the first layer with the adhesive obtained in (a) to the second layer and optionally other layers.

[0080] In such a process, the production line speed may be 5 to 600 m / min, for example 50 to 600 m / min, preferably at least 100 m / min, with a preferred range of 450 to 600 m / min. The "line speed" refers to the total length of the layers bonded in 1 minute. The layers are typically provided in very large rolls, and the bonded tissue laminate is typically rewound onto the roll.

[0081] In the method of the present invention, the method further comprises applying pressure in step (b) to bond the two layers. The step of contacting the two layers may also comprise the step of embossing the paper laminate, i.e. step (b) may comprise embossing at least two layers before, during and / or after bonding.

[0082] The adhesive is usually diluted and thus has a viscosity that enables it to penetrate the paper layers to bond multiple layers that may have been stacked in a single step. The application of the adhesive may be carried out by an embossing machine, wherein the adhesive is applied at least to the protrusions or raised portions of the embossing machine and thus to the layers during embossing by the embossing machine.

[0083] The present invention also relates to products obtainable according to the methods and uses described herein. Such products include but are not limited to paper laminates, preferably tissue paper laminates, such as multi-ply toilet paper, toilet paper, kitchen paper, paper towels, facial tissue, cosmetic wipes, paper handkerchiefs, etc.

[0084] All embodiments disclosed herein with respect to the adhesive composition are similarly applicable to the uses, methods and products, and vice versa. The present invention is further illustrated by the following examples, but is not limited thereto. The entire contents of all documents cited herein are incorporated by reference.

[0085] Example

[0086] The following formulation was prepared and successfully tested as a tissue layer adhesive. The listed ingredients were added in the order given:

[0087] Table 1: Adhesive compositions (all values ​​are in wt % relative to the total weight)

[0088]

[0089]

[0090] Comparative Examples CE1 and CE2 are not according to the claimed invention.

[0091] 3a, 3b and 3c and 3*a, 3*b and 3*c are added as a premix, if present. After each addition, the mixture is mixed as needed. After adding 3a, 3b and 3c, it is heated to 70°C and maintained at this temperature during the addition of 4. Before adding 8 and 9, the viscosity, pH and solid content are determined, and 8 and 9 are added as needed.

[0092] Adhesive Formulation 3 was successfully tested with a coater system (tissue laminator with DESL embossing unit) at a dilution ratio with water of not more than 1:8 for bonding 2 or 3 19 gsm plies (57 gsm in total) for making kitchen tissue at a line speed of not more than 500 m / min, and at a dilution ratio of not more than 1:11 for bonding 2 or 3 15 gsm plies for making toilet tissue at a line speed of not more than 600 m / min.

[0093] Table 2: Characteristics

[0094]

[0095]

[0096] 1 : As defined in the EU Biocidal Products Regulation ((EU) No. 528 / 2012 (BPR:: product type PT6 (preservatives for use in products during storage))).

[0097] The market standard comparative example CE1 shows acceptable performance on the machine when diluted with water in use at no higher than 1:6. The adhesion on the tissue layer in the final product is adequate and the machine runs at the same speeds as mentioned for the present invention without any serious problems. However, the biobased content is very low (<10%), as most PVOH is based on non-renewable sources; and preservatives are required. Therefore, comparative example CE1 does not meet the requirements for a biobased and sustainable, preservative-free adhesive, which are targeted in the present invention.

[0098] Comparative Example CE2 is based on the tapioca dextrin mentioned in patent US 6,379,447 B1, which can only be run at no more than 500 m / min. It has sufficient adhesion in the final product. However, in order to achieve this effect, a much higher solid content in use (26%) is required, which in turn has a negative impact on the sustainability evaluation. The solid content cannot be reduced because the adhesion will drop below a sufficient limit, which will cause the paper layer to delaminate, and the viscosity will be too low to transfer the adhesive well to the roller and ultimately to the paper substrate. Another disadvantage of Comparative Example CE2 is the need for a preservative system because the adhesive will be attacked by bacteria and fungi in a short period of time. This not only has a negative impact on the final performance of the consumer product (which may lead to contamination of the entire product), but also limits the use time of the adhesive to a very short time (< a few days) until it cannot be used and should be discarded.

[0099] On the other hand, Examples 1 and 1a according to the claimed invention are better sustainable products, since they can be diluted no higher than 1:5 (5% solids in use) and still show moderate adhesion and acceptable viscosity in use. They also have good stability, which allows use for up to 5 months until the thickening effect sets in, resulting in a too pasty structure for the concentrated adhesive. In contrast to Comparative Examples CE1 and CE2, these adhesives do not require a preservative system, but are still stable without possible contamination by fungi or bacteria.

[0100] Examples 2 and 2a according to the claimed invention show comparable performance to Examples 1 and 1a, but reduce the solids in use to only 2%. They show slightly lower adhesion, which may result in paper debonding, and a shorter use time until the concentrated adhesive may thicken to a pasty solution (1 month).

[0101] Example 3a* according to the claimed invention is the most concentrated adhesive with 43% solids, but it can also be diluted with water in a ratio not higher than 1:11, most preferably 1:8, still giving very strong adhesive properties. In addition, after dilution, the viscosity does not drop too low, so there are no problems on the machine. No preservatives need to be added, as also shown in Examples 1a and 2a. Thus, compared to the comparative example CE1 based on PVOH, this adhesive shows the same or similar performance at even higher possible dilutions, and at the same time this adhesive has an extremely high biobased content of more than 80%. Compared to the biobased solution of patent US 6379447 B1 (Comparative Example CE2), Example 3 shows better performance and allows a lower solid content in use and a much higher dilution with water. At the same time, the adhesive can be used without adding preservatives and still shows no problems with bacterial or fungal contamination in the challenge test, which shows that the safety standards of the product have been significantly improved.

Claims

1. A liquid aqueous adhesive composition comprising at least one modified starch in an amount of 2 to 60 wt.-%, preferably 5 to 50 wt.-%, relative to the total weight of the composition, wherein the dynamic viscosity of the adhesive composition at 23° C. is 10,000 to 40,000 mPa*s, preferably 15,000 to 30,000 mPa*s (the dynamic viscosity is measured according to Brookfield using a Brookfield viscometer RVT, spindle 6 at 20 rpm).

2. The liquid aqueous adhesive composition according to claim 1, wherein the pH (measured at 20°C) of the composition is in the range of 9.0 to 12.0, preferably 10.0 to 11.5, most preferably 10.5 to 11.

5.

3. The liquid aqueous adhesive composition according to any one of claims 1 to 2, wherein the adhesive composition is diluted with water before use, wherein the mass ratio of adhesive:water is 1:1 to 1:15 or 1:1 to 1:11, preferably 1:4 to 1:

8.

4. The liquid aqueous adhesive composition according to any one of claims 1 to 3, wherein the modified starch is a starch modified by (acid) hydrolysis, enzymatic or chemical modification or degradation, oxidation or ultrasound treatment, preferably a starch modified by enzymatic or chemical modification.

5. The liquid aqueous adhesive composition according to any one of claims 1 to 4, wherein the modified starch is selected from: starch ethers, preferably alkyl ethers, alkenyl ethers, aryl ethers, aralkyl ethers, cycloalkyl ethers and cycloalkenyl ethers or the corresponding hydroxy ethers; starch esters, preferably organic acid esters; amides, ketones, aldehydes, acetals and ketals; carboxylates, phosphates, sulfates, sulfonates, amines and starch derivatives containing ammonium groups; and combinations thereof.

6. The liquid aqueous adhesive composition according to claim 5, wherein the modified starch is selected from: starch ethers selected from allyl ether, benzyl ether, hydroxyethyl ether, hydroxypropyl ether, hydroxybutyl ether, 2-hydroxy-3-butenyl-ether, carboxymethyl ether, starch esters selected from formates, acetates, propionates, butyrates, dodecanoates, octadecenoates, alkyl succinates and alkenyl succinates, carboxylates, ketones and aldehydes; more preferably hydroxypropyl ether and carboxymethyl ether; most preferably hydroxypropyl ether.

7. The liquid aqueous binder composition according to any one of claims 1 to 4, wherein the modified starch is an enzymatically modified starch having a dynamic viscosity of less than 500000 mPa*s measured at 20° C. as a 40 wt% solution in deionized water according to Brookfield (Brookfield RVT, spindle 7 at viscosities >50000 mPa*s and spindle 6 at viscosities ≤50000 mPa*s, 20 rpm) and can be obtained from natural starch by modification with a glycogen branching enzyme (EC 2.4.1.18).

8. The liquid aqueous adhesive composition according to claim 7, wherein the enzymatically modified starch (1) having a dynamic viscosity of less than 200,000 mPa*s, preferably less than 100,000 mPa*s, more preferably less than 50,000 mPa*s, but preferably at least 10,000 mPa*s; and / or (2) selected from: cereal starch, preferably corn, barley, wheat or rice starch; tuber or root starch, preferably potato, sweet potato, cassava or tapioca starch; legume starch, preferably pea or bean starch; and sago and amaranth starch, including waxy starches derived from said plants; more preferably potato starch.

9. The liquid aqueous adhesive composition according to any one of claims 1 to 8, wherein the composition does not contain a preservative.

10. The liquid aqueous adhesive composition according to any one of claims 1 to 9, wherein the composition comprises one or more additives, the additives are preferably selected from defoamers, humectants, pH regulators, preservatives, organic solvents, colorants, pigments and fragrances, more preferably defoamers, humectants, pH regulators and organic solvents; wherein the total amount of the additives is preferably not more than 15% by weight.

11. Use of the liquid aqueous adhesive composition according to any one of claims 1 to 10 as an adhesive for layer bonding, preferably for paper layer bonding, more preferably for tissue paper layer bonding, wherein: Optionally, the paper has 2 to 5 tissue plies, preferably 2, 3 or 4 tissue plies.

12. Use according to claim 11, wherein the liquid aqueous binder composition according to any one of claims 1 to 10 is used as a dilution in water, wherein the mass ratio of binder:water is 1:1 to 1:11, preferably 1:4 to 1:

8.

13. A process for producing a product comprising at least two plies, preferably 2 to 5 plies of tissue paper, more preferably paper plies, the process comprising: (a) applying a liquid aqueous binder composition according to any one of claims 1 to 10 or a dilution thereof in water to a first layer of at least two layers, wherein the mass ratio of binder:water in the dilution is from 1:1 to 1:15 or from 1:1 to 1:11, preferably from 1:4 to 1:8; and (b) Bonding the first layer having the adhesive obtained in (a) to the second layer and optionally other layers.

14. The method according to claim 13, wherein (1) the production line speed is 5 to 600 m / min, preferably 450 to 600 m / min; and / or (2) The method further comprises applying pressure in step (b) to bond the two layers; and / or (3) Step (b) comprises embossing at least two layers before, during and / or after bonding.

15. A product obtainable according to the process according to any one of claims 13 to 14, wherein the product is preferably a paper laminate, more preferably a tissue paper laminate.

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