EP3931281A1

EP3931281A1 - Hmpsa incorporating a plasticiser made from a renewable raw material

Info

Publication number: EP3931281A1
Application number: EP20710221.1A
Authority: EP
Inventors: Christophe Robert; Amandine RAFAITIN; Lahoucine IDTTALBE
Original assignee: Bostik SA
Current assignee: Bostik SA
Priority date: 2019-02-28
Filing date: 2020-02-13
Publication date: 2022-01-05
Also published as: CN113454177A; FR3093301B1; WO2020174154A1; CN113454177B; US20220135850A1; JP7460647B2; JP2022522360A; FR3093301A1

Abstract

The invention relates to: 1) an HMPSA composition containing from 20 to 50% styrenic block copolymer composition; from 35 to 65% tackifying resin; and from 7 to 25% vegetable oil as a plasticiser, selected from sunflower oil, rapeseed oil, linseed oil and soybean oil; 2) a multilayer system comprising: - an adhesive layer (A) consisting of composition 1); - a support layer (B) adjacent to the adhesive layer (A); and - a non-stick protective layer (C) adjacent to the adhesive layer (A); and 3) the use of said system for manufacturing self-adhesive articles.

Description

HMPSA INCORPORATING A PLASTICIZER IN RAW MATERIAL

RENEWABLE

The present invention relates to a hot-melt pressure sensitive adhesive composition (or HMPSA) as well as a multilayer system comprising an adhesive layer constituted by said composition and which is suitable for the manufacture of self-adhesive articles, in particular of self-adhesive labels.

Pressure sensitive adhesives (also called self-adhesive glues or, in English, "Pressure Sensitive Adhesives" or PSA) are substances which give the support layer which is coated therewith an immediate tackiness at room temperature. Often referred to as by the English term of "tack" or even sometimes by the term of "tack", this immediate tackiness allows the instantaneous adhesion of said self-adhesive support to all kinds of substrates, under the effect of a light and brief pressure PSAs are widely used for the manufacture of self-adhesive labels which are affixed to articles (eg packaging) for the purpose of presenting information (such as barcode, denomination, price) and / or at decorative purposes. PSA are also used for the manufacture of self-adhesive tapes of various uses. One can quote for example in addition to the transparent adhesive tape widely used in the daily life: the setting for me and the assembly of cardboard packaging; protection of surfaces for painting work, in construction; the maintenance of electric cables in the transport industry; the gluing of the carpets with double-sided adhesive tapes.

PSAs are generally applied, by continuous coating processes implemented by manufacturers called "coaters", over the entire surface of a support layer, if applicable printable, of large dimensions, at a rate of 'an amount

(generally expressed in g / m ² ) and hereinafter designated by the term "basis weight". The support layer generally consists of paper or film of a polymeric material with one or more layers. The layer of adhesive composition which covers the support layer is itself covered with a protective non-stick layer (often referred to by the English name of “release liner”), which often consists of a silicone film. The multilayer system obtained is generally packaged by winding in the form of large coils (or rolls) up to 2 m in width and 1 m in diameter, which can be stored and transported, such packaging often being referred to as "roll stock".

This multilayer system can be subsequently converted into self-adhesive labels applicable by a label manufacturer called "transformer" (or sometimes by the English name of "converter"). The transformation processes implemented include printing the desired informative and / or decorative elements on the printable side of the support layer, then cutting to the desired shape and dimensions.

The protective release layer can be easily removed without modifying the adhesive layer which remains attached to the printable backing layer. After separation of its protective non-stick layer, the label is generally applied at a temperature close to ambient temperature on the article (for example the packaging) to be coated either manually or using labelers on automated packaging lines.

This multilayer system can also be transformed into self-adhesive tapes by cutting and packaging in rolls of determined width and length.

PSAs advantageously allow, because of their high tack at room temperature, a rapid setting or adhesion of the label and / or of the self-adhesive tape on the substrate (or article) to be coated (for example, in the case of labels, on packaging or, in the case of ribbons, on packaging boxes to be shaped), suitable for obtaining high industrial production rates.

Hot melt adhesives (often referred to as "Hot Melt adhesives" or HM) are substances that are solid at room temperature and do not contain water or solvents. They are applied in the molten state and solidify on cooling, thus forming a seal which, due to its adhesive power, secures the substrates to be assembled. Some Hot Melts are formulated in such a way as to impart a relatively hard and tack free character to the substrate coated therewith. Other Hot Melts give the support a relatively soft character and high tack: these are PSAs which are widely used for the manufacture of self-adhesive articles (for example self-adhesive labels). The corresponding adhesives are designated by the designation of "hot melt pressure sensitive adhesives" or, in English, by that of "Hot Melt Pressure Sensitive Adhesive" (or "HMPSA"). They therefore also make it possible, by virtue of their adhesive power, to firmly fix the label or the tape on the desired substrate, whether it is for example the packaging to be labeled or the cardboard to be assembled. HMPSAs generally comprise a thermoplastic polymer (particularly a styrenic block copolymer) in combination with tackifying resins and plasticizers.

Such HMPSA compositions and multilayer systems are known, for example from international applications WO 2008/077509 and WO 2008/110685, which comprise an adhesive layer consisting of said composition, as well as a printable support layer and an adjacent protective layer.

The plasticizers which are used in these HMPSA compositions, and in particular those disclosed by these last 2 applications, are generally hydrocarbon oils which are derived from crude oil and which are of paraffinic, aromatic and / or naphthenic nature. Such plasticizers are for example marketed under the name Primol ^® 352 by ExxonMobil, Nyflex ^® 222B or Nyflex ^® 223 by the company Nynas.

However, within the current framework of the development of a "green" chemistry, one seeks more and more to free oneself, or at least to decrease the share, of non-renewable raw materials, of petroleum or fossil origin, in profit from renewable raw materials, particularly of plant origin.

There is therefore a need to replace the plasticizers of petroleum origin used in the HMPSA compositions by plasticizers obtained from renewable raw materials.

International application WO 99/13016 describes heat-fusible compositions which contain, as plasticizer, a natural hydrogenated or non-hydrogenated oil comprising fatty acids containing from 6 to 22 carbon atoms. Preferred fatty acids are mixtures of C 10-04 carbon atoms, such as coconut oil, and mixtures of C 8 such as soybean and sunflower oils. These thermo-fusible compositions are used in a process for bonding a substrate based on fabric or nonwoven on other substrates, with a view to the manufacture of a disposable absorbent product, such as, for example, disposable diapers. . However, this document in no way teaches the application of such a method for the manufacture of self-adhesive articles, nor a multilayer system suitable for such manufacture.

An aim of the present invention is to provide an HMPSA composition, the plasticizer of which is made from renewable raw materials, as well as a multilayer system which is suitable for the manufacture of self-adhesive articles, in particular self-adhesive labels. , and which comprises an adhesive layer made of said composition. Another aim of the present invention is to provide such a multilayer system, the adhesive layer of which also has an appropriate adhesive power on various substrates.

Another aim of the present invention is to provide such a multilayer system, the adhesive layer of which also has an appropriate tack on different substrates.

It has now been found that these aims can be achieved in whole or in part by means of the HMPSA composition and the multilayer system comprising a layer made of said composition, as described below.

A subject of the present invention is therefore firstly an HMPSA composition (a) comprising, on the basis of the total weight of said composition:

- From 20 to 50% by weight of a composition (a1) of styrene block copolymers which comprise at least one elastomer block;

- from 35 to 65% by weight of one or more tackifying resins (a2); and

- from 7 to 25% by weight of a plasticizer (a3);

characterized in that the plasticizer (a3) is a vegetable oil which is chosen from sunflower, colza, linseed and soybean oil, and of which the derived fatty acids comprise a proportion of at least 75% of acids fatty including from 16 to 22 carbon atoms, said percentage being a percentage by weight expressed on the basis of the total weight of fatty acids derived from vegetable oil.

It has been found that said HMPSA composition (a), in addition to its reduced content of non-renewable raw materials due to the use of a vegetable oil as a plasticizer, is quite suitable, due to its adhesive power and its tack, to constitute the adhesive layer of a multilayer system intended to be used for the manufacture of self-adhesive articles, and more particularly for the manufacture of self-adhesive labels. In fact, this latter composition makes it possible to obtain an adhesive power (also called "peel" or "peel"), measured according to the FINAT test method no. 1, which is advantageously greater than 5 N / 2.54 cm for metallic or polymeric substrates, and greater than 3 N / 2.54 cm for cardboard substrates. The HMPSA composition (a) also makes it possible to obtain a tack, measured according to the instantaneous adhesion test known as the loop described in the FINAT test method No. 9, which is advantageously greater than 10 N / 2.54 cm on glass substrates, greater than 8 N / 2.54 cm on polymeric substrates and greater than 3 N / 2.54 cm on cardboard substrates. Composition (a1) of styrene block copolymers):

The HMPSA composition (a) comprises from 20 to 50% by weight of a composition (a1) of styrene block copolymers which comprise at least one elastomer block.

Said styrenic block copolymers have an average molar mass Mw generally of between 50 kDa and 500 kDa. They consist of blocks of different polymerized monomers including at least one polystyrene (or styrene) block, and are prepared by radical polymerization techniques.

In the absence of any indication to the contrary, the weight-average molar masses M _w which are given in the present text are expressed in dalton (Da) and are determined by gel permeation chromatography, the column being calibrated with polystyrene standards. .

According to a preferred embodiment, said composition (a1) consists, on the basis of its total weight:

- from 30 to 90% by weight of at least one diblock copolymer chosen from the group comprising SI, SIB, SB, SEB, and SEP, and

- From 10 to 70% by weight of at least one triblock copolymer chosen from the group comprising SIS, SIBS, SBS, SEBS and SEPS;

the content of total styrenic units of said composition (a1) varying from 10 to 40% by weight based on the total weight of (a1).

The triblock copolymers include 2 polystyrene blocks and an elastomer block. They can take on various structures: linear, star (also called radial), branched or even comb. Diblock copolymers include 1 polystyrene block and 1 elastomer block.

The tri-block copolymers have the general formula:

ABA (I)

in which :

- A represents a non-styrenic elastomeric block (or polystyrene), and

- B represents an elastomeric block which can be:

- polyisoprene. The block copolymer then has the structure:

polystyrene-polyisoprene-polystyrene, and for denomination: SIS;

- polyisoprene followed by a polybutadiene block. The block copolymer then has the structure: polystyrene -polyisoprene -polybutadiene -polystyrene, and the name: SIBS - polybutadiene. The block copolymer then has the structure:

polystyrene-polybutadiene-polystyrene, and for name: SBS;

- totally or partially hydrogenated polybutadiene. The block copolymer then has the structure: polystyrene-poly (ethylenebutylene) - polystyrene and the name: SEBS;

- totally or partially hydrogenated polyisoprene. The block copolymer then has the structure: polystyrene-poly (ethylenepropylene) - polystyrene and the name: SEPS.

The di-block copolymers have the general formula:

A-B (II)

in which A and B are as defined above.

When composition (a1) comprises several triblock styrenic copolymers, the latter being chosen from the group comprising SIS, SBS, SEPS, SIBS, SEBS, it is understood that said triblock may belong to one or more of these 5 families of copolymers. The same is true, mutatis mutandis, for the diblock copolymers.

It is preferred to use a composition (a1) comprising a triblock copolymer and a diblock copolymer having the same elastomeric block, in particular because of the fact that such mixtures are commercially available.

According to a preferred embodiment, the content of diblock copolymer in composition (a1) ranges from 70 to 90% by weight.

The styrenic block copolymers containing an elastomeric block, in particular of the SI and SIS type, which can be used in composition (a1) are available commercially, often in the form of triblock / diblock mixtures.

Europrène ^® Sol T 166, available from Polimeri Europa (Italy) is a mixture consisting, respectively, of 90% and 10% of triblock SBS (M _w approximately 121 kDa) and diblock SB (M _w approximately 64 kDa), each of these copolymers having about 30% styrene.

Solprene ^® 1205, available from the company Dynasol, is an SB diblock copolymer (Mw approximately 100 kDa) having approximately 30% styrene.

Kraton ^® DI 183 PT, available from the company Kraton, is a mixture consisting, respectively, of 62% and 38% of triblock SIS and diblock SI, having about 16% of styrene. Kraton ^® DI 118, available from the company Kraton, is a mixture consisting, respectively, of 22% and 78% of SBS triblock and SB diblock, having approximately 33% styrene.

According to a preferred variant, the HMPSA composition (a) comprises from 25 to 45% by weight of the composition (a1) of styrene block copolymers, and even more

preferably from 31 to 40% by weight.

Tackifying resins:

The HMPSA composition (a) comprises 35 to 65% by weight of one or more tackifying resins (a2).

The tackifying resin (s) (a2) which can be used have average molar masses M _w generally of between 300 and 7000 Da and are chosen in particular from:

- (i) rosins of natural or modified origin, such as for example rosin extracted from pine gum, wood rosin extracted from tree roots and their hydrogenated, dehydrogenated, dimerized, polymerized or esterified by monoalcohols or polyols such as glycerol;

- (ii) resins obtained by hydrogenation, polymerization or copolymerization (with an aromatic hydrocarbon) of mixtures of unsaturated hydrocarbons having approximately 5, 9 or 10 carbon atoms obtained from petroleum fractions;

- (iii) terpene resins resulting from the polymerization of terpene hydrocarbons such as, for example, mono-terpene (or pinene) in the presence of Friedel-Crafts catalysts, optionally modified by the action of phenols;

- (iv) copolymers based on natural terpenes, for example styrene / terpene, alpha-methyl styrene / terpene and vinyl toluene / terpene.

The tackifying resin (s) (a2) have a softening temperature

generally between 5 and 150 ° C.

The softening temperature is determined in accordance with the standardized test ASTM E 28, the principle of which is as follows. A brass ring with a diameter of about 2 cm is filled with the resin to be tested in the molten state. After cooling to room temperature, the ring and the solid resin are placed horizontally in a thermostatically controlled glycerin bath, the temperature of which can vary by 5 ° C. per minute. A steel ball with a diameter of approximately 9.5 mm is centered on the solid resin disc. The softening temperature is - during the temperature rise phase of the bath at a rate of 5 ° C. per minute - the temperature at which the resin disc creeps from a height of 25.4 mm under the weight of the ball. According to a preferred embodiment, the tackifying resin (s) used have a softening temperature of between 80 and 120 ° C, even more

preferably between 90 and 110 ° C.

The tackifying resins are commercially available, and the following products may be mentioned, for example, in the above families:

Family (i): Sylvalite® ^® RE 100S from Arizona Chemical (rosin ester and pcntaérythritol having a softening temperature of about 100 ° C);

family (ii): Escorez ^® 2203LC from the company ExxonMobil Chemical, having a softening temperature of about 93 ° C.

According to a preferred variant, the HMPSA composition (a) comprises from 40 to 60% of tackifying resins (a2), even more preferably from 40 to 55% by weight.

Plasticizer (a3):

The HMPSA composition (a) comprises, as plasticizer (a3), a vegetable oil selected from sunflower, rapeseed, linseed and soybean oil, in an amount ranging from 7 to 25% by weight. The fatty acids derived from said vegetable oil comprise a proportion of at least 75% fatty acid including from 16 to 22 carbon atoms, said proportion being expressed as a percentage by weight based on the total weight of fatty acids derived from said oil.

The aforementioned vegetable oils are compositions of triple esters of fatty acids and glycerol (also called "triglycerides"). They are obtained from the seeds of plants and are of course widely available commercially.

The expression "fatty acids derived from vegetable oil" is thus intended to denote fatty acids present in the molecular structure of these triglycerides. Said fatty acids can be obtained, in the form of isolated compounds, by saponification, hydrolysis or methanolysis of said triglycerides.

The proportion of fatty acids including from 16 to 22 carbon atoms is preferably at least 80% by weight, and even more preferably at least 85% by weight, based on the total weight of the fatty acids derived from 'vegetable oil.

It has been found that the aforementioned oils are suitable, unlike castor oil, for obtaining homogeneous HMPSA compositions. The fatty acids derived from triglycerides, for castor oil, comprise approximately 90% by weight, on the basis of their total weight, of a C 8 fatty acid, monounsaturated and hydroxylated: ricinoleic acid. According to a preferred variant, the HMPSA composition (a) comprises from 7 to 20% by weight of plasticizer (a3), and even more preferably from 10 to 19%.

Stabilizers (a4):

According to a preferred embodiment, the HMPSA composition (a) further comprises from 0.1 to 2% of one or more stabilizers (or anti-oxidant) (a4).

These compounds are introduced to protect said composition from degradation resulting from a reaction with oxygen which is liable to form by the action of heat, light or residual catalysts on certain raw materials such as tackifying resins. . These compounds can include primary anti-oxidants which scavenge free radicals and are generally substituted phenols such as IRganox ^® 1010 from BASF. The primary antioxidants can be used alone or in combination with other antioxidants such as phosphites such as Irgafos ^® 168 also from BASF, or alternatively with UV stabilizers such as amines.

Wax:

The HMPSA composition (a) can also include a wax (a5) of a polyethylene homopolymer (such as ^AC® 617 from Honeywell) or of a copolymer of polyethylene and vinyl acetate. The corresponding amount can be up to 5%.

Finally, it can optionally include pigments, dyes or fillers.

According to a preferred variant, the HMPSA composition (a) comprises, and preferably consists essentially of:

- From 25 to 45% by weight of the composition (a1) of styrene block copolymers;

- from 40 to 60% by weight of the tackifying resin (s) (a2); and

- from 7 to 20% by weight of the plasticizer (a3).

According to an even more preferred variant, the HMPSA composition (a) comprises, and preferably consists essentially:

- From 31 to 40% by weight of the composition (a1) of styrene block copolymers;

- from 40 to 55% by weight of the tackifying resin (s) (a2); and

- 10 to 19% by weight of the plasticizer (a3).

The viscosity of the HMPSA composition (a), measured by a viscometer

Brookfield ^® RYT to 163 ° C, is between 4 and 50 Pa.s, preferably between 8 and 30 Pa.s. Such a viscosity is particularly well suited to nozzles used in industrial units of coaters for its coating on a printable support layer.

The self-adhesive hot-melt composition according to the invention is prepared by simply mixing its components at a temperature between 130 and 200 ° C, until a homogeneous mixture is obtained. The required mixing techniques are well known to those skilled in the art.

The present invention also relates to a multilayer system comprising:

- an adhesive layer (A) consisting of the HMPSA composition (a) as defined above;

- a support layer (B) adjacent to the adhesive layer (A); and

- a non-stick protective layer (C), adjacent to the adhesive layer (A).

Adhesive layer (A):

According to a preferred variant of the multilayer system according to the invention, the thickness of the adhesive layer (A) is strictly greater than 10 μm, preferably within a range ranging from 11 to 100 μm, more preferably from 12 to 35 μm.

Support layer (B):

The support layer (B) included in the multilayer system according to the invention is adjacent to the adhesive layer (A).

According to a more preferred variant of the invention, said layer (B) consists of paper or of a film comprising one or more homogeneous layers of a polymer.

Among the suitable polymers, mention may be made of polyolefins, such as polyethylene, including high density polyethylene, low density polyethylene,

linear low density polyethylene and ultra low linear density polyethylene, polypropylene and polybutylenes; polystyrene; natural or synthetic rubber; vinyl copolymers, such as polyvinyl chloride, plasticized or unplasticized, and poly (vinyl acetate); olefinic copolymers, such as copolymers

ethylene / methacrylate, ethylene / vinyl acetate copolymers, acrylonitrile / butadiene / styrene copolymers, and ethylene / propylene copolymers; acrylic polymers and copolymers; polyurethanes; polyethers; polyesters; and mixtures thereof. Preferably, the support layer (B) is based on acrylic polymers, polyethylene (PE), oriented, non-oriented or bi-oriented polypropylene (PP), polyimide, polyurethane, polyester such as polyethylene terephthalate (PET).

According to yet another variant, the support layer (B) is a printable support layer.

Non-stick protective layer (C):

The protective non-stick layer (C) can be easily removed without modifying the layer (A) which remains attached to the support layer (B).

According to a preferred variant, said layer (C) comprises a silicone-based material, said material being either constituting said layer (C), or present in the form of a surface coating of said layer (C), said coating being intended to be in contact with the adhesive layer (A).

According to a preferred variant of the multilayer system according to the invention, said system is packaged in the form of a winding around a coil (or roll), the dimensions of which can vary over a wide range. Thus, the diameter of such a roll can range from 0.25 to 1 m, and its width from 0.25 to 2 m.

According to this preferred variant, the protective non-stick layer (C) consists of the support layer (B) included in the multilayer system, in which the face which is opposite to the face in contact with the adhesive layer (A) is coated with silicone material. Such a multilayer system in which the protective non-stick layer (C) is not distinct from the layer (B) is sometimes referred to under the English name of “linerless”. Said packaging is particularly advantageous, due to its simplicity and the resulting economy, for processors who convert these roll stocks into final self-adhesive items, such as labels or self-adhesive tapes.

The HMPSA composition (a) is applied in the molten state at a temperature greater than 130 ° C. on the support layer (B), in an amount which is strictly greater than 10 g / m ² and which generally ranges from 11 to 100 g / m ² , preferably 11 to 35 g / m ² , to constitute the adhesive layer (A).

The application is carried out by known coating techniques such as for example lip nozzle type (at a temperature of about 160 to 180 ° C) or curtain type (at a temperature of about 120 to 180 ° C) . The application of HMPSA by lip nozzle is generally carried out on the non-stick protective layer (C), the assembly then being laminated on the support layer (B) (transfer coating). The application of HMPSA by curtain type coating can be carried out directly on the support layer (B), depending on the coating temperature.

The present invention also relates to the use of the multilayer system as defined above for the manufacture of self-adhesive articles, such as self-adhesive labels and adhesive tapes.

The subject of the invention is also a self-adhesive label capable of being obtained by transformation of the multilayer system described above. In this case, a printable support layer (B) is preferred.

The transformation process implemented generally includes:

- a printing step on the printable support layer (B), then

- a step of cutting the multilayer system so as to reduce its width, and therefore to repackage it on a reel of reduced width, then

- a step (called weeding) of obtaining a multilayer system, conditioned on the reel of the previous step, in which the non-stick protective layer (C), unchanged, is linked only to the part of the layer printed media that matches the shape and dimensions of the self-adhesive label suitable for its end use. This step therefore consists in selective cutting, then in the elimination of the undesirable part of the printable support layer (B) and of the adhesive layer (A), said part often being called “label backbone”.

The latter multilayer system is implemented on the packaging lines of the articles to be labeled, such as for example packaging, by means of automated systems which separate the self-adhesive labels from the protective layer, and attach them to the articles to be labeled. The labeled article is preferably a package or container consisting of:

- of glass ;

- a usual plastic material chosen from PolyEthylene Terephthalate (PET), Polyvinyl Chloride (PVC), PolyEthylene (PE), in particular High Density PolyEthylene (HDPE), or even PolyPropylene (PP); or

- of cardboard, such as for example the cardboard known under the name of FIPAGO cardboard (from the International Federation of Manufacturers of GOmmé PApiers) of Kraftliner grade and grammage 200 g / m ² .

The following examples are given purely by way of illustration of the invention and should not be interpreted in such a way as to limit its scope. Examples A (reference) and Examples 1 to 3 (according to the invention):

The compositions appearing in Table 1 below are prepared by simple hot mixing at 180 ° C. of the ingredients indicated.

The Brookfield viscosity of these compositions was measured at a temperature of 163 ° C. The result is shown in Table 2 in mPa.s.

These compositions were also tested according to the tests described below.

Adhesive power: peel test

The adhesive power of the compositions is evaluated by the peel test (or peel) at 180 ° C on a plate of a certain substrate, as described in the FINAT test method n ° 1, published in the FINAT Technical Manual 6 ^th edition, 2001. FINAT is the international federation of manufacturers and converters of self-adhesive labels.

The principle of this test is as follows. The HMPSA is coated beforehand at a rate of 20 g / m ² on a support layer consisting of a 50 μm thick PET film.

A test piece in the form of a rectangular strip (25.4 mm × 175 mm) is cut from the self-adhesive support thus obtained. This test piece is fixed on a plate made of a certain substrate. The assembly obtained is left for 20 minutes at room temperature. It is then introduced into a traction device capable of peeling or unsticking the strip at an angle of 180 ° and with a separation speed of 300 mm per minute. The apparatus measures the force required to take off the tape under these conditions.

The result is expressed in N / 2.54 cm and is indicated, as well as the nature of the substrate of the plate, in Table 2.

Immediate tackiness: loop tack test

The immediate tackiness or tack of the compositions is evaluated by the instantaneous adhesion test known as the loop (also called "loop tack"), described in the FINAT test method No. 9.

The HMPSA is coated beforehand at a rate of 20 g / m ² on a support layer consisting of a 50 μm thick PET film, so as to obtain a rectangular strip 25.4 mm by 175 mm. The 2 ends of this strip are joined so as to form a loop, the adhesive layer of which faces outwards. The 2 joined ends are placed in the movable jaw of a traction device capable of imposing a displacement speed of 300 mm / minute along a vertical axis with the possibility of going and returning. The The lower part of the loop placed in a vertical position is first brought into contact with a horizontal plate of a certain 25 mm by 30 mm substrate over a square area of about 25 mm square. From this contact, the direction of movement of the jaw is reversed. Immediate tack is the maximum amount of force required for the loop to completely peel off the substrate plate.

The peel and tack results obtained for Examples 1 to 3 based on a plasticizer consisting of vegetable oil are generally lower than those of Example A, the plasticizer of which is of petroleum origin. However, these results are perfectly acceptable, with regard to the expected values for self-adhesive articles, and more particularly for self-adhesive labels, as indicated in the description of the present application. Example B (comparative):

The same ingredients as those of Example 1 are mixed hot at 180 ° C and in the same proportions, with the exception of replacing the sunflower oil with castor oil.

The composition obtained is cloudy and inhomogeneous, with the presence of solid deposits.

Such a composition is not suitable as an HMPSA composition.

Table 1

Table 2

Claims

1. HMPSA composition (a) comprising, on the basis of the total weight of said composition:

- from 35 to 65% by weight of one or more tackifying resins (a2); and

- from 7 to 25% by weight of a plasticizer (a3);

2. HMPSA composition (a) according to claim 1, characterized in that the composition (a1) of styrene block copolymers consists, on the basis of its total weight:

3. HMPSA composition (a) according to one of claims 1 to 2, characterized in that the tackifying resin (a2) is chosen from:

- (i) rosins of natural or modified origin and their hydrogenated, dehydrogenated, dimerized, polymerized or esterified by monoalcohols or polyols;

- (ii) resins obtained by hydrogenation, polymerization or copolymerization (with an aromatic hydrocarbon) of mixtures of unsaturated hydrocarbons having approximately 5, 9 or 10 carbon atoms obtained from petroleum fractions; - (iii) terpene resins resulting from the polymerization of terpene hydrocarbons in the presence of Friedel-Crafts catalysts, optionally modified by the action of phenols;

- (iv) copolymers based on natural terpenes.

4. HMPSA composition (a) according to one of claims 1 to 3, characterized in that the tackifying resin (a2) has a softening temperature of between 80 and 120 ° C.

5. HMPSA composition (a) according to one of claims 1 to 4, characterized in that it comprises 7 to 20% by weight of vegetable oil (a3).

6. A HMPSA composition (a) according to one of claims 1 to 5, characterized in that its viscosity measured with a Brookfield ^® viscometer RYT to 163 ° C, is between 4 and 50

Not.

7. Multilayer system comprising:

- an adhesive layer (A) consisting of the HMPSA composition (a) as defined in one of claims 1 to 6;

- a support layer (B) adjacent to the adhesive layer (A); and

- a non-stick protective layer (C), adjacent to the adhesive layer (A).

8. Multilayer system according to claim 7, characterized in that the thickness of the adhesive layer (A) is strictly greater than 10 µm, and preferably within a range of 11 to 100 µm.

9. Multilayer system according to one of claims 7 or 8, characterized in that the support layer (B) consists of paper or a film comprising one or more homogeneous layers of a polymer.

10. Multilayer system according to one of claims 7 to 9, characterized in that the printable support layer (B) is based on acrylic polymers, polyethylene (PE), Oriented, unoriented or bi-oriented polypropylene (PP), polyimide, polyurethane, polyester such as Polyethylene terephthalate (PET).

11. Multilayer system according to one of claims 7 to 10, characterized in that the protective non-stick layer (C) comprises a silicone-based material.

12. Multilayer system according to one of claims 7 to 11, characterized in that it is packaged in the form of a winding around a coil.

13. Multilayer system according to claim 12, characterized in that the protective non-stick layer (C) consists of the support layer (B) in which the face which is opposite to the face in contact with the adhesive layer (A) is coated with a silicone material.

14. Use of the multilayer system as defined in one of claims 7 to 13, for the manufacture of self-adhesive articles.

15. Self-adhesive label obtainable by processing the multilayer system as defined in one of claims 7 to 13.