Two-component polyurethane adhesive for lamination

Abstract

1) Two-component polyurethane-based adhesive composition comprising an —NCO component and an —OH component, such that: the —NCO component is obtained by polyaddition between MDI and a composition of polyols comprising a polyether diol and a polyether triol, in an —NCO/—OH molar equivalent ratio of between 2.5 and 6.5; the —OH component is obtained by polyaddition between MDI and a composition of polyols with a functionality of 2 comprising an aliphatic polyester diol, a partially aromatic polyester diol and an aliphatic polyether diol, in an —NCO/—OH molar equivalent ratio of between 0.05 0.50; the amounts of the —NCO and —OH components being such that the —NCO/—OH molar equivalent ratio is within a range extending from 1.5 to 1.7. 2) Multilayer film comprising 2 thin layers of material linked to one another by a continuous layer constituted by said crosslinked adhesive composition. 3) Process for preparing said film and use thereof in the manufacture of flexible packagings.

Claims

1. Two-component polyurethane-based adhesive composition comprising an —NCO component and an —OH component, such that: the —NCO component is a composition A comprising polyurethane prepolymers A1 comprising at least two —NCO end groups, A1 being obtained by polyaddition reaction between: a composition A1.C1 of diphenylmethanediisocyanate (MDI) comprising at least 35% by weight of the 4,4′ elastomer, said percentage being expressed on the basis of the total weight of said composition, and a composition A1.C2 of polyols comprising a polyether diol PE.sub.A.sup.1 with a molar mass Mn of between 800 and 1200 g/mol and a polyether triol PE.sub.A.sup.2 with a molar mass Mn of between 350 and 550 g/mol, in an amount corresponding to a PE.sub.A.sup.2/(PE.sub.A.sup.1+PE.sub.A.sup.2) weight/weight ratio of between 15 and 30%, the amounts of A1.C1 and A1.C2 used being such that the —NCO/—OH molar equivalent ratio is between 2.5 and 6.5; the —OH component is a composition B comprising polyurethane prepolymers B1 comprising at least two —OH end groups, B1 being obtained by polyaddition reaction between: a composition B1.C1 of diphenylmethanediisocyanate (MDI) comprising at least 35% by weight of the 4,4′ elastomer, said percentage being expressed on the basis of the total weight of said composition, and a composition B1.C2 of polyols with a functionality of 2 comprising, on the basis of the total weight of said composition: from 38 to 42% by weight of a composition B1.C2.D comprising an aliphatic polyester diol PES.sub.B.sup.1 with a molar mass Mn of between 800 and 1200 g/mol and a partially aromatic polyester diol PES.sub.B.sup.2 with a molar mass Mn of between 1000 and 1400 g/mol, in an amount corresponding to a PES.sub.B.sup.1/PES.sub.B.sup.2 weight/weight ratio of between 0.35 and 0.45; and from 58 to 62% by weight of an aliphatic polyether diol PE.sub.B with a molar mass Mn of between 350 and 550 g/mol; the amounts of B1C1 and B1C2 used being such that the —NCO/—OH molar equivalent ratio is between 0.05 and 0.50; it also being specified that the amounts of the —NCO and —OH components of said two-component adhesive composition are such that the —NCO/—OH molar equivalent ratio is within a range extending from 1.5 to 1.7.

2. Two-component adhesive composition according to claim 1, characterized in that the 2,2′ isomer content of the MDI composition A1.C1 used in the preparation of A1 is less than 1% by weight, on the basis of the total weight thereof.

3. Two-component adhesive composition according to claim 1, characterized in that the MDI composition A1.C1 comprises at least 49% by weight of the 4,4′ isomer.

4. Two-component adhesive composition according to claim 1, characterized in that the polyether diol PE.sub.A.sup.1 and the polyether triol PE.sub.A.sup.2 used in the polyol composition A1.C2 are propylene glycols with the respective functionalities 2 and 3.

5. Two-component adhesive composition according to claim 1, characterized in that the —NCO end group weight content of the polyurethane prepolymers A1 varies in a range extending from 9 to 18%.

6. Two-component adhesive composition according to claim 1, characterized in that the composition A, as —NCO component, consists essentially of the polyurethane prepolymers A1.

7. Two-component adhesive composition according to claim 1, characterized in that the composition A, as —NCO component, also comprises an aliphatic polyisocyanate A2, the —NCO end group functionality of which is within a range extending from 2 to 3.5 and the —NCO content of which, expressed by weight on the basis of the weight of A2, is between 17 and 27%.

8. Two-component adhesive composition according to claim 7, characterized in that the aliphatic polyisocyanate A2 bears an allophanate.

9. Two-component adhesive composition according to claim 1, characterized in that the total —NCO group content, expressed as % by weight on the basis of the total weight of the composition A, is within a range extending from 13 to 18%.

10. Two-component adhesive composition according to claim 1, characterized in that the —OH group content, expressed as % by weight on the basis of the total weight of the composition B, is within a range extending from 3 to 5%.

11. Two-component adhesive composition according to claim 1, characterized in that the viscosity, measured at 23° C., of each of the two —NCO and —OH components is less than or equal to 25 Pa.Math.s.

12. Two-component adhesive composition according to claim 1, characterized in that the viscosity thereof, measured at 50° C., at the time of mixing its 2 components, is within a range extending from 500 to 2 000 Pa.Math.s.

13. Multilayer film comprising 2 thin layers of material linked to one another by a continuous layer, characterized in that said layer is constituted by the two-component adhesive composition as defined in claim 1, in the crosslinked state, in an amount of less than 10 g/m.sup.2.

14. Process for continuously preparing the multilayer film as defined in claim 13, comprising the sequential steps of: (i) combining the —NCO and —OH components in the form of an adhesive mixture made flowable by heating at a suitable temperature, (ii) coating, with said adhesive mixture, a first thin layer of material in the form of a substantially continuous layer, (iii) laminating a second thin layer, on the first thin layer coated in accordance with step (i), then (iv) crosslinking the adhesive mixture.

15. Flexible packaging comprising the multiplayer film according to claim 1.

Description

EXAMPLE 1 (REFERENCE): —NCO COMPONENT—PREPARATION OF A COMPOSITION A CONSISTING OF POLYURETHANE PREPOLYMERS A1

(1) The following are placed, under a nitrogen stream and at ambient temperature, in a closed 1 litre reactor equipped with a stirrer, heating means and a temperature probe, and connected to a vacuum pump: 519.12 g of LUPRANAT® MIPI, 220.74 g of Voranol® 1010L, 60.08 g of Voranol® CP450 and 0.08 g of phosphoric acid (solution at 85%).

(2) These amounts of reagents correspond to an —NCO/—OH molar equivalent ratio equal to 4.94.

(3) The mixture is then heated to 80° C. with mechanical stirring and maintained at this temperature for 4 hours, which reaction time makes it possible to achieve a weight content of NCO functions (monitored by potentiometric titration) of 17.5% (weight/weight).

(4) Particular attention is paid to the monitoring of the temperature which must not exceed 80° C. For that, the polyols are added portionwise (exothermia checked between each addition of polyol).

(5) Once the reaction is complete, the reaction medium is then cooled to 40° C. and maintained at a reduced pressure of 20 mbar in order to degas the mixture.

(6) The weight of reagents/ingredients introduced is related back to the total weight of the composition A and indicated as a percentage in Table 1.

(7) The Brookfield viscosity at 23° C. is measured and the value obtained is shown in Table 1.

EXAMPLE 2 (REFERENCE): —NCO COMPONENT—PREPARATION OF A COMPOSITION A CONSISTING OF POLYURETHANE PREPOLYMERS A1

(8) Example 1 is repeated while modifying the reagent weights so as to obtain an —NCO/—OH molar equivalent ratio of 3.67 (cf Table 1).

(9) The —NCO function content of the polyurethane prepolymers A1 obtained and the Brookfield viscosity at 23° C. are also indicated in Table 1.

EXAMPLE 3 (REFERENCE): —NCO COMPONENT—PREPARATION OF A COMPOSITION A CONSISTING OF POLYURETHANE PREPOLYMERS A1 AND OF AN ALIPHATIC POLYISOCYANATE A2

(10) Example 1 is repeated while replacing the LUPRANAT® MIPI with ISONATE® M125 and modifying the reagent weights so as to obtain the —NCO/—OH molar equivalent ratio indicated in the table.

(11) The —NCO function content of the polyurethane prepolymers A1 obtained is 13.9% (indicated in Table 1).

(12) Once the level of —NCO functions of A1 has reached the indicated value, 80.00 g of DESMODUR® XP 2860 are introduced. The mixture is kept stirring at a temperature of between 70 and 80° C. for 1 hour. The reaction medium is then cooled to 40° C. and maintained at a reduced pressure of 20 mbar in order to degas the mixture.

(13) The weight content of —NCO functions of the composition A is 14.5% (weight/weight).

EXAMPLE 4 (REFERENCE): —OH COMPONENT—PREPARATION OF A COMPOSITION B CONSISTING OF POLYURETHANE PREPOLYMERS B1

(14) The following are placed, under a nitrogen stream and at ambient temperature, in a closed 1 litre reactor equipped with a stirrer, heating means and a temperature probe, and connected to a vacuum pump: 80.00 g of DEKATOL® 3008, 208.00 g of DEKATOL® 1105 and 432.00 g of VORANOL® P400. The mixture is then heated to 80° C. with mechanical stirring and maintained at a reduced pressure of 20 mbar for one hour in order to dehydrate the polyols.

(15) 80.00 g of ISONATE® M125 are then introduced.

(16) These amounts of reagents correspond to an —NCO/—OH molar equivalent ratio equal to 0.25.

(17) The mixture is maintained at 80° C. for 4 hours, which reaction time makes it possible to achieve total consumption of the NCO functions, monitored by potentiometric titration.

(18) Once the reaction is complete, the reaction medium is then cooled to 40° C. and maintained at a reduced pressure of 20 mbar in order to degas the mixture.

(19) The amounts of reagents/ingredients introduced are related back to the total weight of the composition B and indicated as a percentage in Table 2.

(20) The Brookfield viscosity at 23° C. is measured and the value obtained is indicated in Table 2.

(21) The —OH function content of the polyurethane prepolymers B1 obtained and constituting the composition B, and also the Brookfield viscosity at 23° C. measured for the composition B, are also indicated in Table 2.

EXAMPLE 5 (ACCORDING TO THE INVENTION): TWO-COMPONENT ADHESIVE COMPOSITION OBTAINED BY MIXING THE —NCO COMPONENT OF EXAMPLE 1 AND THE —OH COMPONENT OF EXAMPLE 4

(22) The —NCO component of Example 1 is mixed with the —OH component of Example 4 in an —NCO/—OH molar equivalent ratio equal to 1.65, which corresponds to an —NCO component/—OH component weight ratio equal to 100 g of —NCO component for 110 g of —OH component.

(23) The mixing is carried out at a temperature of 50° C. in the lamination machine feed tank and the Brookfield viscosity is measured at this same temperature as soon as the mixing is performed.

(24) The corresponding data are indicated in Table 3.

EXAMPLES 6 AND 7 (ACCORDING TO THE INVENTION): TWO-COMPONENT ADHESIVE COMPOSITION OBTAINED BY MIXING THE —NCO COMPONENT OF EXAMPLE 2 (RESPECTIVELY OF EXAMPLE 3) AND THE —OH COMPONENT OF EXAMPLE 4

(25) Example 5 is repeated with the —NCO component of example 1 being replaced with the —NCO component of Example 2 (respectively of Example 3).

(26) The values of the —NCO/—OH molar equivalent ratio and of the —NCO component/—OH component weight ratio are indicated in Table 3 with the Brookfield viscosity measured at 50° C.

EXAMPLE 8 (ACCORDING TO THE INVENTION): THREE-LAYER FILM OF WHICH THE ADHESIVE LAYER BONDS AN OPA LAYER AND A PE LAYER

(27) A biaxially-oriented-polyamide film 15 μm thick is used for the PA layer and a polyethylene film 50 μm thick is used for the PE layer.

(28) This three-layer film is obtained by feeding the tank of a lamination machine of Nordmeccanica type with the two-component adhesive composition of Example 5.

(29) Said lamination machine is provided with a coating device of role type with an open tank operating at a temperature of 50° C. and at a rate of forward progression of 50 m/minute; the adhesive layer bonding the PA and PE layers has a thickness ranging from 2 g/m.sup.2.

(30) Immediately after its production, this three-layer film is stored at a temperature of 23° C. and under an atmosphere at 50% relative humidity (RH).

(31) This three-layer film is subjected to the following tests:

(32) A. Determination of the Crosslinking Time:

(33) A.1. Principle of the Test:

(34) The objective of this test is to measure the time (expressed in days) required for the crosslinking of the constituent two-compound adhesive of the adhesive layer of the three-layer film, starting from the production of said film by lamination.

(35) This time is evaluated by the number of days required for the film to be sufficiently cohesive, and more specifically for the cohesion of said film, measured by means of the 180° peel test (described below), to be greater than a reference value equal to 3 N/15 mm.

(36) A.2. Sampling of the Film:

(37) A sample is taken each day from the three-layer film which is kept under the storage conditions at 23° C. and 50% RH specified above. This sample is subjected to a 180° peel test.

(38) A.3. Description of the 180° Peel Test:

(39) The 180° peel test is as described in the French standard NF T 54-122. The principle of this test consists in determining the force necessary to separate (or peel) 2 individual layers of films bonded by the two-component adhesive.

(40) A test specimen of rectangular shape 15 mm wide and approximately 10 cm long is cut out from the two-layer film. The two individual layers of the film included in this strip are manually detached from the end of this test specimen, and over approximately 2 cm, and the 2 free ends thus obtained are attached to two holding devices respectively connected to a stationary part and a movable part of a tensile testing device which are located on a vertical axis.

(41) While a drive mechanism imparts a uniform rate of 100 mm/minute to the movable part, resulting in the detachment of the 2 layers, the detached ends of which gradually move along a vertical axis with the formation of an angle of 180°, the stationary part—connected to a dynamometer—measures the force withstood by the test specimen thus held, which force is measured in N/15 mm.

(42) A.4. Result:

(43) The crosslinking time is 2 days.

(44) B. Determination of the Cohesion:

(45) A sample is taken from the three-layer film, which is maintained under the storage conditions at 23° C. and 50% RH specified above, after 30 days of storage.

(46) This sample is subjected to the 1800 peel test described in A.3.

(47) The cohesion is 6.55 N/15 mm.

(48) C. Determination of the Amount of Primary Aromatic Amines (PAAs):

(49) A sample is taken from the three-layer film, which is maintained under the storage conditions at 23° C. and 50% RH specified above, after 1 day of storage, then after 2 days of storage.

(50) The three-layer film thus sampled is shaped into 20 cm-sided square-shaped bags by heat-sealing on 3 sites, one side remaining open The bags are filled with 200 ml of an aqueous acetic acid solution (3% by weight).

(51) The bags are then heat-sealed and placed in an oven for 2 h at 70° C.

(52) The bags are then opened, in order to extract therefrom the aqueous solution and to analyse it.

(53) The PAAs are quantitatively determined by UV spectrometry at 550 nm, after diazotation and reaction with N-naphthyl-1-ethylenediamine hydrochloride, then concentration of the colour on a solid-phase column.

(54) The result is expressed in mg of aniline per kg of the aqueous acetic acid solution packaged in the bags, and presented in ppb.

(55) The following is obtained after 1 day of storage of the three-layer film: 18 ppb.

(56) The following is obtained after 2 days of storage of the three-layer film: 3 ppb.

EXAMPLES 9 AND 10 (ACCORDING TO THE INVENTION): THREE-LAYER FILM OF WHICH THE ADHESIVE LAYER BONDS AN OPA LAYER AND A PE LAYER

(57) Example 8 is repeated, with the two-component adhesive composition of Example 5 being replaced with that, respectively, of Example 6 and Example 7.

(58) The crosslinking time, the cohesion and the amount of PAA of the corresponding three-layer films are indicated in Table 3.

EXAMPLE 11 (ACCORDING TO THE INVENTION): THREE-LAYER FILM OF WHICH THE ADHESIVE LAYER BONDS A METALLIZED-PET LAYER AND A PE LAYER

(59) A three-layer film is first of all produced by repeating Example 8, except that the biaxially-oriented-polyamide layer 15 μm thick is replaced with a layer 9 μm thick consisting of PET surface-metallized by an aluminium layer.

(60) The cohesion of the three-layer film thus obtained is determined by repeating the protocol of section B of Example 8.

(61) The cohesion is 1.74 N/15 mm.

EXAMPLES 12 AND 13 (ACCORDING TO THE INVENTION): THREE-LAYER FILM OF WHICH THE ADHESIVE LAYER BONDS A METALLIZED-PET LAYER AND A PE LAYER

(62) Example 11 is repeated, with the two-component adhesive composition of Example 5 being replaced with that, respectively, of Example 6 and Example 7.

(63) The cohesion of the three-layer film thus obtained is indicated in Table 3.

(64) TABLE-US-00001 TABLE 1 Compositions A (—NCO component) Content (as % by weight/weight) Ingredients Ex. 1 Ex. 2 Ex. 3 Polyurethane LUPRANAT ® MIPI 64.89 57.80 — prepolymers ISONATE ® M125 — — 52.00 A1 VORANOL ® 1010L 27.59 33.20 29.90 VORANOL ® CP450 7.51  9.00 8.10 —NCO/—OH 4.94  3.67 3.66 equivalent ratio —NCO weight 17.5 13.8  13.9 content (as %) A2 DESMODUR ® XP — — 10.00 2860 composition A —NCO weight 17.5 13.8  14.5 content (as %) Brookfield viscosity at 2750 17 100      9100 23° C. (mPa .Math. s)

(65) TABLE-US-00002 TABLE 2 composition B (—OH component) Content (as % by weight/weight) Ingredients Example 4 Polyurethane ISONATE ® M125 10 prepolymers B1 DEKATOL ® 3008 10 DEKATOL ® 1105 26 VORANOL ® P400 54 —NCO/—OH    0.25 equivalent ratio composition B —OH weight   3.9 content (as %) Brookfield viscosity at 13 600    23° C. (mPa .Math. s)

(66) TABLE-US-00003 TABLE 3 Two-component adhesive compositions Example 5 Example 6 Example 7 —NCO Component Example 1 Example 2 Example 3 —OH Component Example 4 Example 4 Example 4 —NCO/—OH molar equivalent ratio 1.65 1.59 1.50 —NCO component/ 100/110 100/90 100/100 —OH component weight ratio Brookfield viscosity at 50° C. (mPa .Math. s) 984 1,260 1,030 Trilayer with PA/PE Crosslinking time (in days) 2 1 1 Cohesion (in N/15 mm) 6.55 5.04 6.1 PAA after 1 day of storage (in ppb) 18 18 13 PAA after 2 days of sotrage (in ppb) 3 <2 3 Trilayer with metPET/PE Cohesion (in N/15 mm) 1.74 1.43 1.4