The invention relates to an adhesive product defined in the preamble of claim 1. Further, the in ^¬ vention relates to a method defined in the preamble of claim 12 for making an adhesive product. Further, the invention relates to use of an adhesive product de ^¬ fined in the preamble of claim 18. Further, the inven ^¬ tion relates to a layered product defined in the pre ^¬ amble of claim 20. BACKGROUND OF THE INVENTION

In patent publication WO 2009/103848 it is said that a polyolefin film contains maleated polyole- fin which contains maleic anhydride reactive groups. OBJECTIVE OF THE INVENTION

The objective of the invention is to disclose a new adhesive product and method for making an adhe ^¬ sive product. Further, another objective of the inven ^¬ tion is to produce a new type of a layered product with good quality.

SUMMARY OF THE INVENTION

The adhesive product according to the present invention is characterized by what is presented in claim 1.

The method for making adhesive product ac ^¬ cording to the present invention is characterized by what is presented in claim 12. The use of the adhesive product according to the present invention is characterized by what is pre ^¬ sented in claim 18.

The layered product according to the present invention is characterized by what is presented in claim 20.

BRIEF DESCRIPTION OF THE FIGURES The accompanying figures, which are included to provide a further understanding of the invention and constitutes a part of this specification, illus ^¬ trate some embodiments of the invention and together with the description help to explain the principles of the invention. In the figures:

Fig. 1 is a flow chart illustration of a method according to one embodiment of the present in ^¬ vention,

Fig 2 is a flow chart illustration of a blow film process, and

Fig 3 is a structural picture of the film.

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on an adhesive product. According to the present invention the adhe ^¬ sive product is in the form of a film (8) which con ^¬ tains at least one adhesive layer (20) including ther ^¬ moplastic polymer and thermoplastic polymer with anhy- dride moieties and at least one inert surface layer (22) containing thermoplastic polymer, and the inert surface layer is formed on at least one surface of the adhesive layer by reconstructing the surface of the adhesive layer, preferably toward lower surface free energy, so that the thin inert surface layer consist ^¬ ing of mainly pure non-polar thermoplastic polymer is formed on the surface of the adhesive layer, and a thickness of the thin inert surface layer is below 100 nm on the surface of the adhesive layer.

Further, the present invention is based on a method for making an adhesive product (8) . According to the present invention thermoplastic polymer (2) and thermoplastic polymer with anhydride moieties (3) are mixed (1), e.g. in an extruder or other device, to form an adhesive composition (4) , the film (8) which contains at least one adhesive layer including the adhesive composition (4) is formed (7) by means of heat and with pressure or without pressure, and the film (8) is cooled (9) to provide sufficient time for a surface reconstruc ^¬ tion in order to form at least one inert surface layer containing thermoplastic polymer on at least one sur ^¬ face of the adhesive layer by reconstructing the surface of the adhesive layer, preferably toward lower surface free, energy so that the thin inert surface layer consisting of mainly pure non-polar thermo- plastic polymer is formed on the surface of the adhe ^¬ sive layer, and a thickness of the thin inert surface layer is below 100 nm on the surface of the adhesive layer. Preferably the film (8) is cooled (9) slowly to provide sufficient time for a surface reconstruction. In one embodiment the anhydrides of the adhesive composi ^¬ tion (4) hydrolyzed to acids are activated (5) back to anhydrides during the forming of the adhesive composi ^¬ tion .

An embodiment of the method of the present invention is shown in figure 1.

The invention is specifically based on a re ^¬ construction of the film surface so that long non- modified thermoplastic polymer is arranged on the sur ^¬ face. During the reconstruction polar anhydride moie- ties, e.g. anhydride groups, turn inside in air while non-polar and pure thermoplastic polymer segments point out. Pure non-polar thermoplastic polymer mole ^¬ cules forms protective layer on the surface. By means of the reconstruction lower surface free energy is achieved. For example, in the reconstruction small mo- lecular weight polymers, free moieties and impurities are preferably evaporated. In one embodiment the re ^¬ construction rate can be raised by increasing temperature or reducing molecular weight and crystallinity of film components. The reconstruction is energy and en- tropy driven phenomena and hence spontaneous. Reactive anhydride moieties groups may be protected with thin surface layer of thermoplastic polymer molecules. The thin inert surface layer contains mainly only thermo ^¬ plastic polymer substantially without the anhydride moieties, preferably without free anhydride and corre ^¬ sponding acid and their residue. Preferably, when the film is cooled by air then sufficient time for a surface reconstruction can be achieved.

In this specification the expression "thermo- plastic polymer" should be understood as any thermo ^¬ plastic polymer suitable to be used in the present in ^¬ vention including also its derivatives and modifica ^¬ tions. Different thermoplastic polymers may have dif ^¬ ferent properties, e.g. molecular composition, molecu- lar weight and molar mass. In this invention thermo ^¬ plastic polymer can include at least one polymer com ^¬ ponent or combination of different polymer components. In one preferred embodiment the thermoplastic polymer is grafted.

In one embodiment the thermoplastic polymer is polyolefin. In one embodiment of the present inven ^¬ tion polyolefin is selected from a group consisting of polyethylene, polypropylene, other polyolefin and their co-polymers and combinations. In this specifica- tion the expression "polyolefin" should be understood as any polyolefin suitable to be used in the present invention including also its derivatives and modifica ^¬ tions. Different polyolefin may have different proper ^¬ ties, e.g. molecular weight and molar mass. In this invention polyolefin can include at least one polyole- fin component or combination of different polyolefin components .

Alternatively, thermoplastic polymer can be other suitable thermoplastic polymer, e.g. EVA (eth ^¬ ylene vinyl acetate copolymer) or PUR (polyurethane) or the like, or their combination or mixture.

In one embodiment thermoplastic polymer and thermoplastic polymer with anhydride moieties can com ^¬ prise same polymer, e.g. polyolefin, or polymer composition, e.g. polyolefin composition. In one embodiment thermoplastic polymer and thermoplastic polymer with anhydride moieties contain different polymer, e.g. polyolefin, or comprise different polymer composi ^¬ tions .

In this specification the expression "inert surface" should be understood as any inert or stable surface of the film.

In one embodiment the adhesive layer contains less than 1.1 % anhydride moieties, free anhydride and corresponding acid and their residue in relation to quantity of thermoplastic polymer in the adhesive lay ^¬ er. In one embodiment the film contains less than 1.07 mol-%, preferably less than 0.6 mol-% and more prefer ^¬ ably less than 0.3 mol-%, free anhydride moieties, such as unbounded anhydride and corresponding acid, in relation to total amount of anhydride moieties, such as anhydride and corresponding acid.

In a preferred embodiment anhydride moieties act as adhesion promoters.

In the reconstruction the polar and reactive anhydride moieties turn inside in the film (8) and non-polar and pure thermoplastic polymer segments point out. Pure non-polar thermoplastic polymer mole ^¬ cules form an inert surface layer on the surface of the film. Then the formed inert surface layer protects reactive anhydride moieties groups in the film.

After the re-reconstruction the anhydride moieties point out. Then the anhydride moieties set on the surface of the film (8) in order to make the film reactive .

In a preferable embodiment a migration of the anhydride moieties into the inside of the film happens during the reconstruction of the film. In the migration the anhydride moieties go inside in the film.

In a preferable embodiment a re-migration of the anhydride moieties onto the surface of the film hap- pens during the re-reconstruction of the film. In the re-migration the anhydride moieties go from the inside the film toward onto the surface of the film. Prefera ^¬ bly the anhydride moieties set on the surface of the film and new anhydride moieties groups go from the in- side of the film toward onto the surface.

Preferably, the surface free energy of the material can be determined by means of contact angle measurements .

In one embodiment the inert surface layer has contact angle with distilled water which contact angle is substantially same than the contact angle of said pure non-polar thermoplastic polymer in the surface layer. Preferably, the contact angle is measured to ensure the forming of the inert surface layer.

In one embodiment the contact angle of the inert surface is 0.9 - 1.1 times the contact angle of the pure same thermoplastic polymer, in one embodiment 0.95 - 1.05 times the contact angle of the pure same thermoplastic polymer. Then gloss of the surface is preferably similar. In contrast to similar film mate ^¬ rial without moieties the contact angle of the film is between 90 - 110 %, when measured with distilled wa ^¬ ter .

Preferably, wettability of the modified ther ^¬ moplastic polymer film is directly related to the chemical composition of its surface. The wettability is measured by contact angle. In the present invention the contact angle of the film must be substantially in the level of pure thermoplastic polymer when the film is in the stable form. To get good adhesiveness the contact angle of the film must be low at melted state against polar other material, e.g. wood based veneer.

In a preferred embodiment the film is re ^¬ activated by means of re-reconstruction of the surface before the use of the film. Then the inert surface changes from inert to reactive, preferably to adhe ^¬ sive. The film can be made chemically reactive by re- reconstructing the surface layer so that anhydride moieties are pointing toward surface to be adhered by exposing it to polar matter. Preferably, the film is stable before the re-activation of the film. In one embodiment the film is re-activated by heat and polar substrate .

A technical effect of the invention is that a stable adhesive film is achieved but film can be easi- ly re-activated by re-heating. An additional technical effect is forming adhesive product which is moisture resistant and heat resistant under normal surrounding conditions. One additional technical effect is that long term stability against moist air is achieved.

In one embodiment of the present invention the thickness of the inert surface layer is arranged below 70 nm, preferably 50 nm and more preferably below 30 nm. In one embodiment of the present invention the thickness of the inert surface layer is arranged between 0.1 - 100 nm, in one embodiment between 5 - 100 nm. In one embodi ^¬ ment the thickness of the inert surface layer is between 5 - 70 nm, in one embodiment between 5 - 50 nm, in one embodiment between 5 - 30 nm and in one embodiment be ^¬ tween 10 - 50 nm. It is important for the thickness of the inert surface that the inert surface protects the film and its reactive anhydride moieties groups, and wa ^¬ ter is not absorbed on the surface of the film. For ex ^¬ ample water does not go through the inert surface under conditions in which relative humidity is less than 65 % and temperature is about 25 °C. Preferably, free surface energy is determined as a function of temperature. On the other hand, it is important for the thickness of the inert surface that the film can be easily re-activated, e.g. by heating quickly. Preferably, the inert surface is hydrophobic.

In one embodiment the film (8) is formed (7) by means of an extrusion process. In one embodiment the film (8) is formed (7) by means of a blown film process. In one embodiment the film is formed by a blown film ex ^¬ trusion and especially by a blown film co-extrusion. In one embodiment the film is formed by means of a cast film extrusion or similar film making extrusion process. The film can be formed any suitable film making process but always the cooling (9) is carried out slowly, for example against non-polar substrate such as air, to en ^¬ sure inert outer layers on the surface of the film (8) . In one embodiment the blown film production is carried out after an extruder.

Blown film extrusion can be used to make thermoplastic films, tubes or bags. The cross-section of the film can be uniform or multilayered . The film extrusion can be carried out by blowing the film upward, downward or horizontal depending on the machine construction used. The thermoplastic polymer material starts in a pellet form, which are successively com ^¬ pacted and melted in extruder and molten thermoplastic material is then forced, or extruded, through an annu- lar die. The extruder temperature is typically around 190 - 200°C and temperature can be different in dif ^¬ ferent zones of the extruder heating unit. There can be one or more extruders forcing one or more thermo- plastic materials in the die unit and the orifices in the die are arranged such that the different material layers merge together before cooling. This method is called blown film co-extrusion producing multilayered films. The thermoplastic used to make the film can be homogeneous or mixture of different thermoplastic pol ^¬ ymers with or without additives. Measured at the annu ^¬ lar die opening, the temperature of blown film can be as less as about 125 - 135°C or higher. Additionally, higher die temperatures or heated extrusion die lips can be used if needed. Typically production rates are usually in the level of 100 m/min, but can be up to 300 m/min with special machines. Air or other gaseous substance is blown through a hole in the center of the die. The pressure inside the film bubble causes the extruded melt to stretch and expand into a bubble. The gas entering the bubble replaces gas leaving it, so that even and constant pressure is maintained to en ^¬ sure uniform thickness of the film. During the pro ^¬ cess, the bubble is pulled continually forwards from the die and a cooling ring blows air or other gaseous substance onto the film. The film can also be cooled from the inside using internal bubble cooling. This reduces the temperature inside the bubble, while main ^¬ taining the blown film diameter at the same time. Af- ter solidification at the frost line, the film moves into a set of nip rollers which collapse the bubble and flatten it into two flat film layers. Blown film has a less effective cooling process than flat film keeping the film surface at melted state for longer time. Flat film cooling is done by means of chill rolls or water, which have significantly higher spe- cific heat capacities than the air or other gaseous substance used in the blown film cooling process. The film is then pulled by puller rolls onto windup roll ^¬ ers. Typically the film passes through idler rolls during this process to ensure that there is uniform tension in the film. The film may pass through a treatment zone also. During this zone or stage, the film may be slit to form one or two films, or surface treated with flame, corona or plasma for example.

In one embodiment the adhesive product is a blown-formed product which has been arranged in the form of the film.

In one embodiment the film (8) is cooled (9) by air. A technical effect is that then sufficient slow time for a surface reconstruction is achieved. An addi ^¬ tional technical effect is that the surface stays warm sufficient long time against non-polar substrate. Then a sufficient surface reconstruction is achieved on the surface before the thermoplastic surface reaches glass transition temperature. In one embodiment air is cold or warm. In one embodiment air is dried. In one embodiment air is typical room air.

In one preferred embodiment air is used dur ^¬ ing the film making (7) to ensure the coming of the pure thermoplastic polymer onto the surface of the film (8) and the going of the anhydride moieties into the inside of the film (8) . The air used can be dry air or moisture content in the air can be even 80 %. The re-migration of the anhydride moieties towards the surface can happen when the air is completely removed and the film is pressed against a solid surface, pref ^¬ erably polar surface.

In one embodiment process agents and small mo ^¬ lecular thermoplastic polymers can be removed during the film making. Then the chemical bonding in the film can be improved. In one embodiment of the present invention the adhesive product is in the form of a film (8) which contains two adhesive layers including thermoplastic polymer (2) and thermoplastic polymer with anhydride moieties (3) and at least one intermediary thermo ^¬ plastic polymer layer, e.g. polyolefin layer, and the intermediary thermoplastic polymer layer is arranged between two adhesive layers and the inert surface lay ^¬ er is arranged on the outer surface of the film (8) .

In one embodiment the thickness of the inter ^¬ mediary thermoplastic polymer layer is between 100 - 300 ym. In one embodiment the thickness of the adhe ^¬ sive layer is between 30 - 100 ym. Preferably, by means of the thinner adhesive layer can be achieved more effective process in the film manufacturing and in the final product manufacturing. Then the manufac ^¬ turing can be performed at lower temperatures and/or at higher running speed.

In one embodiment of the present invention the inert surface layers containing thermoplastic pol ^¬ ymer, e.g. polyolefin, are formed on the both surfaces of the film (8) . In alternative embodiment the inert surface layer is formed only on one surface of the film.

In one embodiment of the present invention the adhesive product has been activated (5) before the form ^¬ ing of the inert surface. Preferably, at the same pro ^¬ cess stage any free anhydride moieties or pre-compound of the anhydride moieties, e.g. carboxylic acid of the same, is removed or decreased. In one embodiment the ac ^¬ tivation (5) is carried out at temperatures over about 150 °C. In one embodiment the activation process (5) is started at temperature over 150 °C. The activation pro ^¬ cess (5) can be accelerated by increasing temperature and/or by catalyst. In a preferred embodiment all water generated during the activation (5) must be evaporated out .

In one embodiment of the present invention thermoplastic polymer (2) and thermoplastic polymer with anhydride moieties (3) are mixed (1) and heated to temperature over 180 °C during the activation (5) .

The thickness of the anhydride moieties con ^¬ taining layer in the film (8) must be small enough to make stable end products. Thin film (8) releases inter ^¬ nal moisture produced in the activation (5) more easily. The internal moisture ruins the stability. Moisture, as well as hazardous impurities, needs to be removed before and/or during the film manufacturing (7) . In one embodiment the anhydride moieties containing layer includes less than 500 ppm, preferably less than 200 ppm and more preferably 150 ppm, free anhydride and corresponding ac ^¬ id. In one embodiment the film includes less than 70 %, preferably less than 50 % and more preferably less than 30 %, water in relation to total amount of the anhydride moieties .

In one embodiment maleic anhydride is used as the anhydride moieties. In one embodiment the anhy ^¬ dride moieties are activated (5) so that free and/or grafted maleic acid in the adhesive composition is con ^¬ verted to reactive maleic anhydride during less than 2 minutes, preferably during about 1 minute, at tempera ^¬ ture over 180 °C. In one embodiment the anhydride moie ^¬ ties are activated (5) so that free and/or grafted male ^¬ ic acid in the adhesive composition is converted to re ^¬ active maleic anhydride during 2 - 4 minutes at tempera ^¬ ture over 180 °C. In one embodiment free and/or grafted maleic acid is converted at temperature 180 - 190 ^° C. In one embodiment the adhesive composition includes maleic anhydride and maleic acid before the converting maleic acid to maleic anhydride. Preferably, the anhydride moi ^¬ eties are activated so that free maleic acid is removed. Free and residual maleic acid and free anhydrides can be removed or decreased during this process and/or after an extrusion, e.g. in a cooling stage. Further, moisture and contaminants can be removed. In one embodiment con ^¬ version with over about 80 % anhydride and below about 20 % acid is provided by the activation. When free male ^¬ ic acid and maleic anhydride is removed from the film it increases stability of the film. Preferably, the inert surface layer is formed so that there is no free maleic anhydride on the surface of the film. The free maleic anhydride or corresponding carboxylic acid can be any monomer, oligomer or polymer containing these moieties and able to evaporate or surface segregate below the melting point of the base thermoplastic polymer of the adhesive layer.

In this invention any suitable agent, com ^¬ pound or composition containing anhydride or derivate of anhydride can be used as anhydride moieties. The anhydride moieties can include one or more than one anhydride moieties component. In one embodiment the anhydride moieties contain functional groups which may be activated into reactive form and which are capable of forming bonding with the other material.

In one embodiment the thermoplastic polymer with anhydride moieties is anhydride grafted thermo ^¬ plastic polymer or anhydride grafted thermoplastic polyolefin .

In one embodiment thermoplastic polymer has similar or lower molecular weight than molecular weight of the thermoplastic polymer with anhydride moieties .

In one embodiment of the present invention the adhesive layer contains less than 10 % by weight, preferably 1 - 4 %, in one embodiment 2 - 7 %, maleic anhydride grafted thermoplastic polymer. In one embodiment the adhesive product in ^¬ cludes suitable additives which can be selected from the group: reinforcement fiber, filler, stabilizer agent, fire retardant agent, coloring agent and other suitable additive and their combinations. In one em ^¬ bodiment the intermediary layer includes at least one said additive.

In one embodiment of the present invention the adhesive product is capable of forming covalent bonding with the other material, e.g. wood, metal, pa ^¬ per, plastic or other suitable material.

Further, the invention relates to use of the present adhesive product (8) as glue so that the adhe ^¬ sive product (8) is heated (10) at least over the melting point of the thermoplastic polymer in the in ^¬ ert surface for activating the adhesive product and the adhesive product (8) is used in the gluing. In one embodiment the adhesive product is heated over the melt ^¬ ing point of the thermoplastic polymer in the inert sur- face. In one embodiment the adhesive product is heated over the melting points of the thermoplastic polymers in the inert surface and in the adhesive layer.

In one embodiment of the present invention the adhesive product (8) is used in the manufacturing (12) of a layered product (11) in which layers of the layered product are glued together by means of the adhesive product ( 8 ) .

In one embodiment the adhesive product (8) is used directly as the glue. In one embodiment the glue includes the adhesive product of the present invention which can be treated in a desired way.

Preferably, when the film (8) of the present invention is pressed against polar other material at elevated temperature, the protective inert surface layer disappears while polar anhydride moieties groups turn pointing toward interface. Temporarily anhydride moieties free zone under interface anhydride moieties will be fulfilled with bulk anhydride moieties by mo ^¬ lecular diffusion. Diffusion/migration is energy and entropy driven and hence spontaneous. After this reac- tive anhydride moieties are able to make covalent bonds with the other material. Re-reconstruction and diffusion rate are higher at elevated temperatures.

Further, the invention relates to a layered product (11) formed of two or more layers, such as ve- neers, being arranged the one above the other and com ^¬ bined by means of gluing with glue including said ad ^¬ hesive product (8) of the present invention.

In one embodiment, a layered product (11) can be selected from a group consisting of a veneer product, wood board, panel product, plywood, fiber board, film product, composite board, block board, strand board, moulding product or their combinations.

In one embodiment a layered product (11) is formed of two or more veneers being arranged the one above the other and combined by means of glue.

A layer of the layered product can be formed any suitable material. In one embodiment the layer of the layered product is formed wood, metal, paper, glass, plastic, other suitable material or their com- binations.

In one embodiment a layered product (11) is formed of two or more wood based veneers being ar ^¬ ranged the one above the other and combined by means of glue of the present invention.

The method of the present invention offers a possibility to prepare stable adhesive products which are moisture and temperature resistant and are capable of forming covalent bonding with the other material, e.g. with wood, metal, paper, plastic or other suita- ble material. The adhesive product is easy to process, and it gives good protection to the final product. Further, the layered product with good dimension sta ^¬ bility can be achieved. The layered product is post- and re-formable after re-heating, and it has good im ^¬ pact strength, moisture resistance and fatigue re- sistance. The adhesive product and final product, e.g. the layered product, can be formed cost-effectively.

EXAMPLES

In the following, the invention is described in more detail by means of detailed exemplary embodi ^¬ ment with reference to the accompanying figures.

Example 1

In this example 3-layer film 8 is formed. The film comprises two adhesive layers 20 and one polyole- fin layer 21 between the adhesive layers.

The adhesive layers of the film 8 are formed from the adhesive composition 4 containing maleic anhydride grafted polyethylene 3 in polyethylene 2. Pure polyethylene 2 is mixed 1 with maleic anhydride graft ^¬ ed polyethylene 3 at temperature over 180 °C. The re ^¬ sidual and hydrolysed maleic acid in the adhesive com ^¬ position 4 is converted to reactive maleic anhydride during 2 - 4 minutes at temperature 180 - 190 ^° C in the activation step 5. Then maleic acid content de ^¬ creases significantly and reactive maleic anhydride content increases. The adhesive composition 4 contain ^¬ ing 2 to 10 % by weight maleic anhydride grafted poly ^¬ ethylene 3 in polyethylene 2. Maleic anhydride grafted polyethylene 3 includes 0.2 to 5 mol-% maleic anhy ^¬ dride. Then total molecular anhydride concentration is 0.004 to 0.25 mol-%.

The film 8 is formed 7 by a blow film co- extrusion which is shown in figure 2. In one example, production rate is about 6 m/min and temperature of the extruder is between 180 - 200 °C in the blown film co-extrusion. The extrusion step 7 in which the anhydride moieties are activated takes about 1 minute. The length of the film bubble is about 17 m, and the temper ^¬ ature of the film is about 40 °C before nip rollers. Preferably, the activation step 5 is a part of the ex ^¬ trusion step 7.

The thickness of the polyolefin layer is about 200 - 300 ym, and the thickness of the adhesive layer is about 50 ym. After the film making 7 the film 8 is cooled 9 slowly to provide sufficient time for re-crystallization of the polyethylene and surface re ^¬ construction and/or to provide sufficient time for so ^¬ lidification of the polyethylene and surface recon ^¬ struction. In this embodiment, the cooling is made at a rate of about 1 degree per second. In one embodi ^¬ ment, the cooling happens so that the film cools about 50 degrees per meter from about 200 °C to 100 °C dur ^¬ ing the first two meters, i.e. about 5 degrees per se ^¬ cond. Thin inert surface layers 22 are formed on the both outer surfaces of the film 8, on the surfaces of the adhesive layers. The inert surface layer is formed by means of reconstruction of the surface. In the re ^¬ construction the polar anhydride groups turn inside the film and non-polar polyethylene segments points out, toward the surface of the film. The inert surface layer contains polyethylene but not reactive maleic anhydride grafted polyethylene. During forming inert surface layers residual moisture can be removed. The thickness of the inert surface layer is arranged be- tween 5 - 50 nm. The reactive maleic anhydride is pro ^¬ tected with the inert surface layers.

The formed polyethylene film 8 does not ex ^¬ hibit any moisture adsorption. The stable structure in humid air is achieved.

The formed adhesive film 8 is used as glue in plywood application 12 to glue veneers together. In the gluing the adhesive film 8 is heated 20 - 50 ^° C over the melting temperature of polyethylene in the heating step 10. Then the re-reconstruction of the surface happens and the active maleic anhydride groups go from inside of the film toward onto the contacting surface of the film. The veneers and the adhesive film are brought into contact in the heating step 10.

With low anhydride level in the adhesive lay ^¬ ers there is always excess of substrate groups present in gluing process. This leads to surface anhydride en- richment by re-reconstruction assisted migration on polar groups of the substrate. Higher coverage can be achieved if more time and temperature are used.

It was discovered that the adhesive film of the present invention acts very good in the gluing ap- plication.

Example 2

In this example the stability of the film was tested with field tests. The 3-layer film is formed in accordance with example 1.

In the tests the stability, especially against external moisture, of anhydride groups was tested during two years. Conditions in the tests were following: humidity about 65 % and temperature about 23 °C. The humidity test results for the film with 0 - 2 year are shown in table 1.

Table 1

Humidity test results

Aging time Glue line shear Wood breakage, % strength, N/mm2

0 3.22 97

3 months 3.14 90

6 months 3.52 88

24 months 3.84 87 Further, the films (0 - 6 months) were ana ^¬ lyzed by Intertek. Intertek cut away the top 30 ym of the coating of the film. The results indicated that the anhydride level in the maleinised layers were un ^¬ affected by aging for 6 months at 65 % RH.

It was discovered in the tests that the sta ^¬ bility of the film against external moisture was good. Further, it was shown that the film is stable against moist air in typical warehouse conditions. The film was stable over at least one year stored at normal conditions at typical warehouse without special cover ^¬ ings. The protective layer remained on the top of the film surface; no hydrolysis was happened.

Example 3

In this example an amount of maleic anhydride was examined in the film, especially in the adhesive layer by Intertek.

An ethylene-butene LLDPE (later LLDPE) which was grafted with about 0.17 mol% of maleic anhydride was used to form pendant succinic acid/anhydride groups. The level of maleinisation in LDPE (later LDPE) co-polymerized with maleic anhydride was about 1.1 mol%, much higher than in the LLDPE. In the 2 % LLDPE laminate, the combined level of anhydride and acid was only about 0.0034 mol%, i.e. about 34 ppm.

The adhesive product according to the present invention is suitable in different embodiments to be used for gluing. The method according to the present invention is suitable in different embodiments to be used for making the most different kinds of adhesive products. The adhesive product according to the pre- sent invention is suitable in different embodiments to be used in different final products, e.g. adhesive compositions and layered products.

The invention is not limited merely to the example referred to above; instead many variations are possible within the scope of the inventive idea de ^¬ fined by the claims.