WO2014125172A1

WO2014125172A1 - Pressure-sensitive laminates and method of producing the same

Info

Publication number: WO2014125172A1
Application number: PCT/FI2014/050112
Authority: WO
Inventors: Riku Talja; Jarmo Ropponen; Kristiina Poppius-Levlin; Ali Harlin
Original assignee: Teknologian Tutkimuskeskus Vtt
Priority date: 2013-02-13
Filing date: 2014-02-13
Publication date: 2014-08-21
Also published as: FI20135133L

Abstract

A pressure-sensitive laminate and a method of producing the same. The laminate comprises a first sheet of material having a front side and an opposite back side, a pressure-sensitive adhesive layer provided on the back side of said first sheet of material, and a release material having a front side and an opposite back side. The front side of the release material is releasably superimposed on said adhesive layer and it comprises a coating of a polysaccharide fatty acid ester which contacts with the pressure-sensitive adhesive layer. By the present invention envelope and packaging closing strip, address and decoration labels and packaging tapes can be provided from biodegradable materials.

Description

Pressure-sensitive laminates and method of producing the same

Technical Field The present invention relates to pressure-sensitive adhesive products and the production thereof. In particular, the present invention concerns pressure-sensitive laminates typically comprising a first sheet of material having a front side and an opposite back side, a pressure-sensitive adhesive layer provided on the back side of said first sheet of material, and a release material having a front side and an opposite back side, said front side of said release material being releasably superimposed on said adhesive layer.

Background Art

Pressure-sensitive adhesives are adhesives that are typically applied as thin solid layers and the degree of the bond (i.e. how strongly it adheres to the any superimposed surface) is dependent on how much pressure is applied to the surface(s).

Pressure-sensitive adhesives can be used to produce bonds that are permanent, but not creep resistant. Importantly, they can also be employed for giving rise to temporary or semi-temporary bonds.

PSAs are frequently used supported on flexible substrates. Thus, pressure-sensitive adhesives are widely used in, for example, labels, stickers and note pads, tapes (e.g.

packaging tapes), and for sealing various packages, such as envelope closing stripes.

The PSAs are typically capable of being applied as dispersions, solutions or hot melts and that are converted to give rise to a rubbery, tacky film of relatively low adhesive strength and rather higher cohesive strength at service temperature. With regard to pressure-sensitive adhesives, reference is further made to Cope B. C. (2005) Adhesive classification. In many of the above applications, such as labels and stickers, packaging tapes, envelope closing stripes, there is a need for covering and protecting the adhesive surface before use. Typically, protection is provided by releasing sheets, films, foils or strips or other materials, which at least roughly have the same area and shape as the application area of the PSA on the substrate. The release surface provides temporary adherence of the protecting material to the PSA to allow for peeling off of the label, sticker, tape etc. at will without damaging of the adhesive or of the protecting material. For that purpose, the release surface typically comprises a coating which provides non-stick properties, for example high smoothness and low surface energy.

Typically non-stick properties are attained by release layers formed from soft elastomeric coatings, for example, poly(dimethylsiloxane), urethanes, acrylic and fluorocarbons. Such coatings are frequently used on release papers for labels and stickers. The conventional coating materials are based on petrochemicals and therefore neither derived from renewable source nor biodegradable. In addition to this, the impact of any fluorocarbons on the environment has to be taken into account.

Further known technology is represented by JP2000008094 A (Nitto Denko Corp) which discloses a releasant, separator and adhesive member. The document relates to

modification of PVOH with long alkyl chains to provide a releasing compound. This releasing compound is mixed with cellulose ester to give a releasant.

Summary of Invention

Technical Problem

There is a need for alternative release coatings produced by materials which are based on renewable sources. Solution to Problem

Hemicellulose and cellulose derivatives, such as fatty acid esters, and their uses, are disclosed in our co-pending patent applications; we refer in particular to our co-pending patent application titled "A coating and a method for preparing thereof as well as to published patent application, WO2008145828 which discloses dispersions formed by hemicellulose esters and a method of producing the same thereof. Talja et al., "Cellulose esters from birch kraft pulp - new biomaterials for barrier coatings", ISWFPC 2011, discusses barrier films produced by dissolving a cellulose ester in an organic solvent for coating of cardboard.

It has now been found that polysaccharide derivatives of the indicated kind are capable of functioning as surface layers for release substrates in a pressure-sensitive adhesive laminates.

Thus, in pressure-sensitive laminates of the present kind, the front side of the release material comprises a coating of a polysaccharide fatty acid ester which contacts with the pressure-sensitive adhesive layer and allows for release of the adherent material.

In addition to controlled release of the PSA, good adhesion between the substrate and the coating is achieved. The coating layer is intact when the PSA is peeled off.

Using the derivatives, coatings can be formed on substrates, such as fibrous webs and sheets of, for example, paper and cardboard materials. The coatings have advantageous properties, such as good adhesion on low weight paper substrate, flexibility, high smoothness and low surface energy.

More specifically, the present laminate is mainly characterized by what is stated in the characterizing part of claim 1.

The method according to the present invention is characterized by what is stated in the characterized part of claim 12. The uses according to the present invention are characterized by what is stated in claims 18 and 19.

Advantageous Effects of Invention

The coating has advantageous properties for the release paper application, such as good adhesion on low weight paper substrate, flexibility, high smoothness and low surface energy. Thus, pressure and heat activated xylan fatty acid ester coatings gives coatings that have advantageous properties for the bio-based release paper applications, such as good adhesion on low weight paper substrate, flexibility, high smoothness and low surface energy. The coating flexibility increases handling properties. The coating smoothness minimized the surface area being in contact with PSA. The peeling force of the PSA label can decreased due to the smoothness in conjuction with low surface energy.

The coating material in this invention is based on renewable resources and biorefmery as an alternative choice for petrochemical based products

Brief Description of Drawing

Figure 1 is a photograph showing two papers after peeling off of a tape with a pressure- sensitive adhesive which has been pressed against the surfaces of the papers; the paper with xylan ester coating (left) and the paper without the coating (right) attached on tape (PSA) followed by peeling of them

Description of Embodiments

As discussed above, controlled release of pressure-sensitive adhesive (PSA) from a solid thin layer is needed for example in sticker/label applications. In addition, environmentally friendly materials are required. To achieve controlled release, a solid thin layer is applied to a substrate to form a release surface on which the label or sticker can be applied. The release material protects the PSA until just prior to use. In the present technology it has been found that suitable coatings can be produced from polysaccharide derivatives, in particular hemicelluloses or cellulose fatty acid esters.

Thus, the present technology relies, for example, on the finding that polysaccharide ester coatings prepared by dispersion coating followed by pressure and heat activation can be used as a thin solid layer with release properties. This technology is therefore based on renewable resource and biorefmery replacing petrochemistry derived chemicals.

US 2,353,717 describes generally the coating of a substrate with a thermoplastic polymer by using regenerated cellulose and cellulose esters. There is no particular teaching with regard to the use of materials of the present kind for providing releasing layers.

Generally, in the present method of producing a laminate, such as a label or sticker deposited on a release substrate, comprises the steps of

- providing a first sheet of material having a front side and an opposite back side, exhibiting a pressure-sensitive adhesive layer provided on the back side of said first sheet of material, and

- superimposing a release material, having a front side and an opposite back side, on said adhesive layer, such that said front side of said release material contacts with the pressure-sensitive adhesive layer,

wherein the front side of the release material is provided with a coating of a polysaccharide fatty acid ester.

In one particular embodiment, the release material is provided with a thermoplastic coating from a hemicellulose polymer or a cellulose polymer by a method comprising at least the following steps:

- providing a cellulose polymer or a hemicellulose polymer having at least one

hydroxyl group which can be used for forming cellulose or hemicellulose ester, - reacting hemicellulose polymer or cellulose polymer with a residue originating to hydrophobic fatty acid with an aliphatic carbon tail of 4 to 28 carbons, preferably of 6 to 22 carbons or ester thereof for obtaining hemicellulose fatty acid ester or cellulose fatty acid ester,

- dispersing the hemicellulose fatty acid ester or cellulose fatty acid ester into

aqueous solution to form a dispersion, and

- coating the dispersion on a substrate, such as a fibrous sheet or web, to produce a coated substrate.

On the coated surface, heat and pressure is preferably applied to fix the coating to the surface of the substrate.

As a result of the novel technology, the present pressure-sensitive laminates comprise generally

- a first sheet of material having a front side and an opposite back side,

- a pressure-sensitive adhesive layer provided on the back side of said first sheet of material, and

- a release material having a front side and an opposite back side, said front side of said release material being releasably superimposed on said adhesive layer, wherein the front side of the release material comprises a coating of a polysaccharide fatty acid ester which contacts with the pressure-sensitive adhesive layer.

Typically, the coating comprises a layer of cellulose or hemicelluloses fatty acid ester, or a mixture thereof, applied on the front side of the release material such that it covers the part of the front side superimposed on the adhesive layer.

The pressure-sensitive laminate can be split by removing the first sheet of material (below "sticker or label") without damage to the release material.

The polysaccharide esters that are of particular interest are esters of cellulose or hemicelluloses. For the purpose of the present invention, "cellulose" stands for a polysaccharide comprising a linear chain of several hundred to over ten thousand [beta(l - 4) linked D- glucose units. Cellulose is the structural component of the primary cell wall of green plants and can be also produced by many micro-organisms. For industrial use, cellulose is mainly obtained from wood pulp for making paper or paper board.

Herein "hemicellulose" means xylans, mannans or arabinogalactans. Depending on the source, their structure varies.

Hemicelluloses are polysaccharides, macromolecular carbohydrates consisting of large number of monosaccharides connected to each other by glycosidic bonds. Hemicelluloses are one of the most abundant renewable biopolymers in the world. Especially wood hemicelluloses, depending on their origin, can be divided into two main components glucuronoxylan and glucomannan. The hemicellulose content in dry wood is between 20 to 35 wt-%.

Mannans have a backbone of mannose units. Glucomannan comprises also glucose units and galactoglucomannan comprises also galactose units. Mannans are the second main components of hemicelluloses found from wood. Gluco mannans are mainly found from softwood.

Arabinogalactan is a component of the heartwood of larches, also found in coffee beans. Backbone of arabinogalactans forms from galactose units which are highly branched containing also arabinose and galacturonic acid units.

As to xylans, there exist four main forms, viz. glucoronoxylan, arabinoglucuronoxylan, neutral arabinoxylan and heteroxylan, which differ from each other in regard to how the xylose backbone is substituted.

One particularly preferred embodiment of the invention relates to the use in release coatings of starting materials wherein free hydroxyl groups of the polysaccharide polymer are esterified. Such esters are obtained by reacting a hemicellulose polymer or cellulose polymer with a hydrophobic fatty acid with an aliphatic carbon tail of 4 to 28 carbons, or a reactive derivative thereof (e.g. acid chloride or ester or anhydride), for obtaining the corresponding hemicellulose fatty acid ester or cellulose fatty acid ester.

The fatty acid reactant is either saturated or unsaturated. Preferably the fatty acid residue of the ester is the residue of a short, medium or long chain fatty acid with a carbon backbone of 4 to 28 carbons, in particular 6 to 22 carbons, more preferably 12 to 18 carbons. In one preferred embodiment, the polysaccharide is hemicellulose which contains xylose backbone, which has been esterified with a fatty acid originating to a short, medium or long chain fatty acid with a carbon backbone of 4 to 28 carbons.

In another even more preferred embodiment, the polysaccharide is hemicellulose which contains xylose backbone, which has been esterified with a fatty acid originating to a short, medium or long chain fatty acid with a carbon backbone of 6 to 22 carbons, more preferably 12 to 18 carbons.

The fatty acid can be, for example, palmitic acid, laurc acid, linoleic acid or oleic acid. In one preferred embodiment, the polysaccharide ester contains hydrophobic fatty acid residues which are residues of palmitic acid (palmitoyl).

Preferably the hemicellulose polymer is a xylan polymer, and the xylose units of the prepared xylan ester polymer have an average degree of substitution (DS) of over 0.6. Palmitoyl esters of xylan are particularly preferred.

The present polysaccharide esters can be formulated into dispersions, in particular aqueous dispersions. Typically, the polysaccharide esters are added to water by the aid of a dispersion auxiliary (e.g. a colloidal protecting agent), whereby the ester compound can be dispersed in water in sufficiently fine particles in order to form a stable dispersion. Examples of dispersion auxiliaries include polyvinyl alcohol (PVA), particularly PVA having a weight-average molar mass of approximately 10,000 to 115,000. Other dispersion auxiliaries (protective colloids) include cationic starch and hydroxyalkyl starch which may be used separately or together with PVA. Furthermore, as additives or auxiliaries, the dispersions may contain alkylketene dimer (AKD) wax and beeswax.

For producing release coatings on substrates, such as paper or cardboard or similar fibrous substrate which will be discussed below in more detail, in one embodiment additives are incorporated into the dispersion. Examples of such additives include pigments, sizes, fillers and plasticizers. Fillers are exemplified by talc, CaC0₃, starch, kaolin, bentonite, surfactants, and pigments by titanium dioxide.

The content of the additives are generally in the range of 0.1 to 100 % by weight, typically about 1 to 50 % by weight, for example 1 to 30 % by weight, of the polysaccharide polymer.

In one particularly preferred embodiment, bentonite is used as an additive. Bentonite is a montmorillonite type mineral, sometimes called as nano clay. Bentonite is dispersible into aqueous solutions without additives and is therefore suitable for use in combination with the polysaccharide ester (hemicellulose fatty acid ester or cellulose fatty acid ester) dispersed into an aqueous solution. It would appear that bentonite will improve the surface properties of the formed coating or film. After the application, heat and pressure are, in one embodiment, applied on the coated surface of the substrate, such as fibre web or sheet, for preparing a substrate with a coating fixed onto its surface. The temperature can vary freely. Typically it is in the range of 30 to 300 °C, for example 40 to 250 °C. In one embodiment, the upper limit is defined by the glass transition point of the polysaccharide polymer.

In a particular embodiment, the coating is heat-sealed to produce a heat sealed coating on a fibrous web. The coating of the release surface, obtained as explained above, exhibits at least one of the following properties: flexibility, high smoothness and low surface energy, preferably a combination of two or more of these parameters. The thickness of the coating is typically in the range of 1 to 500 um, for example about 5 to 200 um, in particular about 10 to 150 um, for example about 10 to 100 um.

The amount of coating, in terms of dried solids content, is generally in the range of 0.1 to 100 g/m², typically 1 to 50 g/m², advantageously 5 to 30 g/m².

Pressure-sensitive adhesive for the label or sticker (cf. below), which can be used in the present technology include conventional compositions, such as polyisobutylene rubber, butyl rubber, rubber adhesive which comprises mixtures of polyisobutylene rubber and butyl rubber, for example dissolved in organic solvents (examples of which include benzene, toluene, xylene and hexane), an adhesive obtained by mixing such an adhesive with a tackifier (examples of which include abietic acid rosin ester, terpene-phenol copolymers and terpene-indene copolymers, and acrylic adhesives which can be produced by dissolving acrylic copolymers having glass transition points of up to -20 °C in an organic solvent such as toluene and xylene. Examples of the latter kind of copolymers include 2-ethylhexyl acrylate-n-butyl acrylate copolymers and 2-ethylhexyl acrylate-ethyl acrylate-methyl methacrylate copolymers. The foregoing lists are by no means exhaustive.

A novel group of pressure-sensitive adhesives disclosed in a co-pending patent application, titled "Novel uses of hemicellulose derivatives", comprises hemicellulose derivatives.

Such adhesive compositions are formulated so that it consists essentially of the

hemicellulose derivative as such or preferably the derivative is present in mixture with at least one second component. The at least one second components is typically selected from the group of cohesive compounds, in particular components having a higher molecular weight than the hemicellulose derivative, and softeners.

The cohesive compound is present in a concentration of up to 50 % by weight. The hemicellulose derivative forms about 1 to 99 % of the total weight of the composition, typically it forms about 10 to 85, preferably about 20 to 75 % of the total weight of the composition. In a preferred embodiment it is used with cohesive components having higher molecular weight, forming jointly up to 75 % of the total weight, in particular about 25 to 70 % of the total weight of the composition.

The hemicellulose derivative is a derivative, in particular chemical derivative, of xylan or galactoglucomannan or glucomannan. Preferred derivatives include ethers, esters and combinations thereof. Hydroxyalkylated derivatives (hemicellulose ethers) are particularly preferred wherein the alkyl chain comprises 1 to 6 carbon atoms, propyl and butyl being particularly preferred. The ester groups can be derived from Ci to C₂o carboxylic acids and combinations thereof, in particular Ci to C₆ or Ci₆ to C₂o or combinations thereof.

The derivatization, in particular chemical derivatization will confer properties of thermoplasticity.In all of the above mentioned derivatives, the degree of substitution is 0.1 to 3, in particular 0.15 to 1.5.

For the pressure-sensitive adhesive application, the average molecular weight M_w of the hemicellulose is, preferably also after derivatization, 3 000 to 200 000, for example 5 000 to 100 000, in particular 7 000 to 40 000 Da. Molecular weights in the range of about 20 000 to 35 000 are particularly interesting since they combine good mechanical properties with softness of the material.

Specific examples include the following: hydroxyalkylated xylan or galactoglucomannan, in particular hydroxypropylated xylan or galactoglucomannan, esters of hydroxyalkylated xylan or galactoglucomannan, in particular a C₂ to C₂o, preferably a C₂ to C₆ ester thereof.

The coated amount of the pressure-sensitive adhesive is preferably from 1 to 50 g/m², typically 3 to 40 g/m², advantageously 10 to 30 g/m², calculated in terms of dried solid content.

The thickness of the pressure-sensitive adhesive which has been applied and dried is normally from 10 to 300 um, for example about 10 to 50 um, if it is an acrylic adhesive, 80 to 150 um, if it is a rubber adhesive, and 50 to 300 um for hemicelluloses derivatives of the above kind.

The product to be adhered to a substrate (in the following also exemplified by "labels" or "sticker" or equivalent) can be of any suitable material, but preferably comprises a laminar material, such as a sheet or web or parts thereof. Particularly interesting materials are fibrous materials and other porous materials, which allow for proper attachment of the pressure-sensitive adhesive. Typically, the material (first layer) is selected from paper and cardboard sheets and webs. These can have generally a grammage of 1 to 500 g/m², often about 10 to 350 g/m² although these are no absolute ranges. The paper or cardboard sheets or webs can be coated or uncoated or they can have a laminated coating. Other equally suitable materials are films and foils and strips of polymer materials, such as thermoplastic materials, and metals, e.g. aluminium foils.

The product (such as "labels" or "stickers") is frequently provided with a printed front side. The front side can also be modified in other fashions to incorporate, e.g., pigments, holograms and other security markings, as well as fields of conductivity.

The substrate of the release material can be of any suitable material, preferably it comprises a laminar material, such as a sheet or web. The substrate may be comprised of one layer or it can be a laminate comprising 2 to 50 layers, for example 2 to 10 layers.

Particularly interesting materials are fibrous materials (and other porous materials), which allow for proper adherence of the release coating. Another group of materials are porous materials which also allow for good adherence.

Typically, the substrate is selected from paper and cardboard sheets and webs. These can have generally a grammage of 10 to 500 g/m². The paper or cardboard sheets or webs can be coated or uncoated. Other potential materials are films and foils and strips of regenerated natural fibres or polysaccharides, such as cellofan, polymer materials, such as thermoplastic materials, or metals. A particularly interesting application for the present technology is in the fields of envelope and packaging closing strip, address and decoration labels and packaging tapes.

The following non-limiting examples illustrate the present technology.

Examples

Example 1 Xylan from the bleached birch kraft pulp was used as a starting material in an esterification reaction with a fatty acid chloride (palmitoyl chloride). Palmitoyl chloride was made as follows: palmitic acid (50 g) was dissolved into dichloromethane (CH₂CI₂) (150 ml). To this solution dimethylformamide (DMF) (cat.) and thionyl chloride (SOCl₂, 46.4 g) were added at room temperature and the mixture was refluxed for 2 h. Excess of SOCl₂ was evaporated and the residue was stripped with CHCI₃ (3x30ml) and dried in vacuum overnight. Product, palmitoyl chloride, was obtained as brownish oil. Xylan was modified by esterification with this obtained palmitoyl chloride to increase its hydrophobicity and thermoplasticity. Palmitoyl chloride (25 g) was added dropwise at a room temperature to the solution of xylan (5g) in pyridine. After addition, temperature was raised to 105 °C for 4 hours. Solid was filtered and washed several times with hot ethanol. The white solid product was dried in vacuum overnight.

The degree of substitution (DS) of palmitoyl xylan and starting material (xylan) were analysed by the 1H and ¹³C NMR techniques.

The glass transition temperature (Tg) was measured for xylan and palmitoylated xylan as follows: a differential scanning calorimeter (DSC, DSC20, Metttler-Toledo) was used at a heating rate of 10 °C/min and a dynamic heating tempature range from -50 to 200 °C to determine the glass transition temperature (taken from a midpoint) of the xylans before and after esterification. The samples (about 10 mg) were sealed in 40 ul aluminum pans with a pinhole on the lid. Tg was determined from the midpoint of the endothermic transition obtained from the second heating cycle. A polydispersity value (PD) gives information about molar mass distribution of a sample. A polymer with homogeneous molar mass distribution has the PD value of 1. The PD of the xylan and its derivatives varied from 1.5 to 2 indicating heterogeneous molar mass distribution. Table 1 indicates the polydispersity for the xylan.

The soluble matter: The xylan and esterified xylan powder was weighed into a breaker followed by water addition to form a 1 % suspension. The suspension was mixed at room temperature for min by Ultra-Turrax (IKA T18 Basic) mounted with the cutter (S18N- 19G). For the first minute the cutter speed of 3500 rpm was used and then raised up to 10000 rpm for the last 4 min. The solution was centrifuged to separate the insoluble matter from the solution at 8800 rpm for 15 min. The soluble matter was determined by weighing approximately 20 g of the solution into evaporation dish followed by drying at 105 °C overnight. A fraction of the soluble matter was calculated. Table 1. A fraction of the water soluble fraction, the molar mass (Mw), the polydispersity (PD), the degree of substitution (DS) and the glass transition temperature (Tg) determined for the xylan and its derivatives.

Mw Soluble

Sample Abbr. (Dalton) PD DS Tg (°C) matter (%)

Xylan X 20 000 1.7 0 171 10.0

Palmitoylated xylan pX N/A N/A > 0.6 N/A 1.5 The obtained xylan fatty acid ester was dispersed into aqueous solution without additives. The xylan fatty acid ester (/2.0 g or 2.7 g) was weighed in a vial (25 x 85 mm) followed by water addition (6.3 g) to form a suspension, whose concentration was respectively 23 % and 30 %. The suspension was dispersed at room temperature for 5 min by Ultra-Turrax (IKA T 18 Basic) mounted with the blender (S18N-10G). For the first minute the cutter speed of 3500 rpm (set value 1) was used and then raised up to 15 000 rpm (set value 4) for the last 4 min.

The dispersion obtained was coated on a base paper. Single coating layer was applied by a laboratory coater (Erichsen) mounted with spiral resulting wet thickness of 60 um. A rough xylan fatty acid ester layer on the base paper was obtained after an oven drying at 105 °C for 5 min.

The coated base paper was pressed by thermo press using pre-heating at 180 °C for 2 min followed by pressing at 180 °C for 3 min under pressure of 1000 psi. As a result a smooth intact coating layer was obtained.

The coating prepared by afore-mentioned procedures from palmitoyl xylan has enhanced barrier properties against water vapour, WVTR being 85 g^~2 d^"1 at 23 °C at relative humidity of 50 %. This value is as good as that of a commercial PLA coated board (84 g m^"2 d^"1).

For the coating prepared from lauroyl xylan or xylan esterified with tall oil (contains mainly palmitic acid, linoleic acid and oleic acid) on a base paper, with similar method as presented above for palmitoyl xylan. WTR- values were correspondingly 302 g^"2 d^"1 and 302 g^"2 d^"1 283 at 23 °C at relative humidity of 50 %.

As a result of the above, a coating was produced with a non-stick surface suitable for pressure-sensitive adhesives. The products are also heat sealable and can emit water and oxygen after a mild heat-sealing-process.

Example 2

Tests are carried out for the release paper.

The release papers to be tested comprised palmitoylated xylan (cf. Table 1) reinforced with nano clay (bentonite, 10 % of the xylan derivative).

Determination of peeling force in each combinations of the release paper and conventional PSA.

As shown in Figure 1 , the coated paper can be peeled easily from the pressure-sensitive adhesive (PSA) without causing damage either of them Further, suitability of the xylan ester coating has been tested successfully by hand with three different PSAs (envelope closing strip, address label and packaging tape). All the PSAs tested were visually intact after they were peeled from the xylan ester coating. Also the xylan ester coating was intact. The PSAs were peeled easily from the coating.

The barrier coating has a brownish colour but is not a disadvantage due to the fact that the release paper is covered by a sticker. Additionally, the release paper has secondary role to protect adhesive in the sticker application prior to use. The release paper is discarded after peeling off.

Biodegradability and repulping or recycling properties are good.

Industrial Applicability

Primarily the present pressure and heat activated polysaccharide, in particular xylan, ester coatings have advantageous properties for bio-based release paper applications.

Citation List

Patent Literature

JP 2000008094 A

US 2,353,717 A

WO 2008145828 Al

Non-Patent Literature

Talja et al., Cellulose esters from birch kraft pulp - new biomaterials for barrier coatings. ISWFPC 2011

Claims

Claims:

1. A pressure-sensitive laminate comprising

- a first sheet of material having a front side and an opposite back side,

- a release material having a front side and an opposite back side, said front side of said release material being releasably superimposed on said adhesive layer, wherein

- the front side of the release material comprises a coating of a polysaccharide fatty acid ester which contacts with the pressure-sensitive adhesive layer.

2. The laminate according to claim 1, wherein the coating comprises a layer of cellulose or hemicelluloses fatty acid ester, or a mixture thereof, applied on the front side of the release material such that it covers the part of the front side superimposed on the adhesive layer.

3. The laminate according to claim 1 or 2, wherein the cellulose or hemicelluloses fatty acid esters are selected from the group of hydrophobic fatty acids with an aliphatic carbon tail of 4 to 28 carbons, preferably of 6 to 22 carbons.

4. The laminate according to any of claims 1 to 3, wherein the fatty acids are selected from the group of palmitic acid, lauric acid, linoleic acid and oleic acid and combinations thereof, in particular the polysaccharide ester contains hydrophobic fatty acid palmitoyl or lauroyl residues.

5. The laminate according to any of the preceding claims, wherein the polysaccharide fatty acid ester is a xylan polymer, and the xylose units of the xylan ester polymer have an average degree of substitution (DS) of over 0.6.

6. The laminate according to any of the preceding claims, wherein the thickness of the coating is in the range of 1 to 500 um, for example about 5 to 200 um, in particular about 10 to 150 um, for example about 10 to 100 um.

7. The laminate according to any of the preceding claims, wherein the pressure-sensitive adhesive is an acrylic adhesive, a rubber adhesive, or a hemicellulose derivatives.

8. The laminate according to any of the preceding claims, wherein the first material layer is selected from laminar materials, such as sheets or webs or parts thereof, in particular the first material layer is a fibrous material, or porous material or an similar material which allows for proper attachment of the pressure-sensitive adhesive, advantageously a paper or cardboard sheet or web or a film or foils or strips of regenerated natural fibres or polysaccharides, or a polymer material or a metal, which optionally is surface treated.

9. The laminate according to any of the preceding claims, wherein the substrate of the release material is a laminar material comprised of one layer or of a laminate with 2 to 50 layers.

10. The laminate according to claim 9, wherein the substrate is a fibrous material, in particular a paper and cardboard sheet or web, or a film or foils or strips of regenerated natural fibres or polysaccharides, or a polymer material or a metal.

11. The laminate according to any of the preceding claims, wherein the release material comprises a envelope and packaging closing strip, the release sheet for address and decoration labels or packaging tapes.

12. A method of producing a laminate, comprising the steps of

- providing a first sheet of material having a front side and an opposite back side, with a pressure-sensitive adhesive layer provided on the back side of said first sheet of material, and

13. The method according to claim 12, wherein the coating is produced by dispersion coating of a dispersion of a polysaccharide derivative, such as a hemicellulose or cellulose fatty acid ester, on said front side.

14. The method according to claim 12 or 13, wherein the dispersion is an aqueous dispersion.

15. The method according to any of claims 12 to 14, comprising applying, in terms of dried solids content, 0.1 to 100 g/m², typically 1 to 50 g/m², advantageously 5 to 30 g/m², of polysaccharide derivative on the front side.

16. The method according to any of claims 12 to 15, comprising preparing the release material from a hemicellulose polymer or a cellulose polymer by

- providing a cellulose polymer or a hemicellulose polymer having at least one

hydroxyl group which can be used for forming cellulose or hemicellulose ester,

- reacting hemicellulose polymer or cellulose polymer with a residue originating to hydrophobic fatty acid with an aliphatic carbon tail of 4 - 28 carbons, preferably of 6 - 22 carbons or ester thereof for obtaining hemicellulose fatty acid ester or cellulose fatty acid ester,

aqueous solution to form a dispersion, and

17. The method according to claim 16, comprising applying on the coated surface, heat and preferably pressure, in order to fix the coating to the surface of the substrate.

18. Use of polysaccharide fatty acid esters in release surfaces of release substrates for pressure-sensitive adhesive layers.

19. Use of a method according to any of claims 12 to 17 for providing envelope and packaging closing strip, address and decoration labels and packaging tapes.