Polyester Polyol-Based Adhesives on the Basis of Furandicarboxylic Acid Obtained from Renewable Raw Materials

Abstract

The present invention relates to adhesives which contain a polyester polyol on the basis of furandicarboxylic acid obtained from renewable raw materials, and to a method for bonding substrates, in particular film-like substrates, using said adhesive.

Claims

1. An adhesive for bonding plastics and/or metal substrates, the adhesive comprising at least one polyester polyol based on furandicarboxylic acid (FDCA) and at least one compound containing NCO groups, wherein the furandicarboxylic acid is obtained from renewable raw materials.

2. The adhesive according to claim 1, wherein the polyester polyol is a reaction product of furandicarboxylic acid with a polyol.

3. The adhesive according to claim 2, wherein the polyol is a diol.

4. The adhesive according to claim 3, wherein the polyester polyol is obtained entirely from renewable raw materials.

5. The adhesive according to claim 4, wherein the proportion of polyester polyol from renewable raw materials is at least 80 wt. %, based on the total weight of the polyester polyols in the adhesive.

6. The adhesive according to claim 1, wherein the compound containing NCO groups is a polyisocyanate having two or more isocyanate groups.

7. The adhesive according to claim 1, wherein the compound containing NCO groups is selected from the group consisting of 1,5-naphthylene diisocyanate (NDI), 2,4- or 4,4-diphenylmethane diisocyanate (MDI), isomers of toluene diisocyanate (TDI), methylene triphenyl triisocyanate (MIT), hydrogenated MDI (H12MDI), tetramethylxylylene diisocyanate (TMXDI), 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI), xylylene diisocyanate (XDI), hexane-1,6-diisocyanate (HDI), pentamethylene diisocyanate and dicyclohexylmethane diisocyanate, as well as oligomers and polymers thereof.

8. The adhesive according to claim 1, wherein the compound containing NCO groups is an NCO-terminated prepolymer.

9. The adhesive according to claim 1, wherein the adhesive contains solvents or is solvent-free or is present as a water-based dispersion.

10. A method for bonding at least two substrates, wherein an adhesive according to claim 1 is applied to at least one substrate and said substrate is then joined together with at least one further substrate.

11. The method according to claim 10, wherein at least one of the substrates has a metal surface or a printed surface.

12. The method according to claim 10, wherein the adhesive is applied to a first film-like substrate and said substrate is then bonded to a second film-like substrate.

13. The method according to claim 10, wherein the adhesive is applied in an amount of from 1 to 100 g/m.sup.2.

14. An article obtained using the method according to claim 10.

15. A food package obtained using the method according to claim 10.

Description

EXAMPLES

[0051] The present invention is explained in detail with reference to the following examples, said examples not being intended to be considered to limit the inventive concept.

a) Measurement Methods

[0052] The acid number was determined in accordance with DIN EN ISO 2114.
The number of OH groups was determined in accordance with DIN 53240-2.
The viscosity was determined using Brookfield (Thermosel), spindle 27 at 10 revolutions/minute.

b) Starting Materials Used

[0053] Adipic acid, available from BASF SE, Germany
2,5-furandicarboxylic acid from renewable raw materials, for example available from Synvina C.V, the Netherlands
Diethylene glycol from renewable raw materials, for example available from India-Glycols Ldt., India
Desmodur L 75 and Desmodur N 3300, available from Covestro AG, Germany
LOCTITE LIOFO L LA 7707 and LOCTITE LIOFOL LA 6707, available from Henkel AG & Co. KGaA, Germany

1. Synthesis of Polyester Polyol Based on Furandicarboxylic Acid (FDCA) Having a High FDCA Content

[0054] 119 g of adipic acid (17.05 mol. %), 195.72 g of 2,5-furandicarboxylic acid from renewable raw materials (26.35 mol. %) and 286 g of diethylene glycol (56.6 mol. %) were mixed in a 1 L four-necked flask having a nitrogen inlet, thermocouple, stirrer and distillation arm. The mixture was heated to 200 C. under a stream of nitrogen and stirred for approximately 8 hours. The reaction mixture was then cooled and 0.02 wt. % of titanium isopropoxide, based on the total weight of the raw material, was added and the pressure of the reaction mixture was gradually reduced to 30 mbar in order to achieve a complete reaction. As soon as an acid number of 2 or less was reached, the reaction mixture was cooled. The polyester polyol obtained had the following properties:

Acid number: 1.4 mg KOH/g
OH number: 121 mg KOH/g
Viscosity: 12,000 mPas (measured at 50 C.) [0055] 115,000 mPas (measured at room temperature)
Molecular weight (Mw): 2,946 g/mol
Molecular weight (Mn): 1,898 g/mol
Polydispersity: 1.6 (measured by GPC).

[0056] The content of cyclic esters in the polyester polyol according to Example 1 and a conventional ester were compared. A polyester polyol based on isophthalic acid was selected for comparison. The GC-MS method was used to determine the proportion of cyclic esters.

[0057] The polyester polyol obtained according to Example 1 and the comparative polyester polyol were each weighed out in headspace vials and mixed with 99.8% ethanol. The containers were then tightly sealed and the samples were extracted at 70 C. for 2 hours. 1 ml was then taken from each of the extracts, mixed with an internal standard (naphthalene-D8) and measured using GC-MS. Approximately 1 g of substance was extracted per sample. Identification was carried out with respect to naphthalene-D8 with a response factor 1 (RF=1). The results are summarized in Table 1.

TABLE-US-00001 TABLE 1 Sample Cycle type Cycle concentration Reference 2AA + 2DEG 2,000 ppm AA + DEG 3,500 ppm AA + IA + 2DEG 6,200 ppm 2IA + 2DEG 4,000 ppm Example 1 2AA + 2DEG 330-510 ppm AA + DEG 900 ppm AA + FDCA + 2DEG 820-940 ppm 2FDCA + 2DEG 410 ppm AA: adipic acid DEG: diethylene glycol IA: isophthalic acid FDCA: furandicarboxylic acid

[0058] As can be seen from Table 1, the proportion of cyclic esters in the polyester polyol according to Example 1 is significantly lower than that in the comparative sample. In the comparative sample, an amount of cyclic esters of 15,700 ppm was found, whereas the amount of cyclic esters was between 2,460 and 2,760 ppm in the polyester polyol according to Example 1.

2. Synthesis of Polyester Polyol Based on Furandicarboxylic Acid (FDCA) Having a Low FDCA Content

[0059] 205 g of adipic acid (41 mol. %), 16 g of 2,5-furandicarboxylic acid from renewable raw materials (2.92 mol. %), 53 g of 1,2-propylene glycol (20.35 mol. %) and 130 g of diethylene glycol (35.73 mol. %) were mixed in a 1 L four-necked flask having a nitrogen inlet, thermocouple, stirrer and distillation arm. The mixture was heated to 200 C. under a stream of nitrogen and stirred for approximately 8 hours. The reaction mixture was then cooled and 0.02 wt. % of titanium isopropoxide, based on the total weight of the raw material, was added and the pressure of the reaction mixture was gradually reduced to 30 mbar in order to achieve a complete reaction. As soon as an acid number of 2 or less was reached, the reaction mixture was cooled. The polyester polyol obtained had the following properties:

Acid number: 0.2 mg KOH/g
OH number: 124 mg KOH/g
Viscosity: 2,400 mPas (measured at room temperature)
Molecular weight (Mw): 3,094 g/mol
Molecular weight (Mn): 1,779 g/mol
Polydispersity: 1.7 (measured by GPC).

3. Laminating Adhesive I

Stage 1:

[0060] 79.33 g of ethyl acetate and 91.06 g of the polyester polyol from Example 1 were placed in a reactor and mixed. Once there was a homogeneous mixture, a sample was taken to determine the water content. The water content should be <300 ppm.

[0061] 4,4-MDI (addition ratio 4,4-MDI:polyester polyol=amount of substance NCO:OH=1.9:1; NCO content 4,4-MDI=33.5%) was added to the mixture and reacted for 2.75 hours at 78 C. After the theoretical NCO content (1.85% [+/0.1%]) had been reached, the temperature was lowered by switching on the cooling device and cooling to below 75 C.

Stage 2:

[0062] As soon as a temperature below 75 C. had been reached, 2.14 g of a silane adhesion promoter, 0.98 g of an aromatic trifunctional isocyanate (Desmodur L 75) and 4.02 g of an aliphatic trifunctional isocyanate (Desmodur N3300) were added and the mixture was cooled further.

[0063] The mixture was homogenized for 15 minutes and a sample was taken to determine the NCO content (NCO desired value stage 2: 2.35%). Then the mixture was cooled further to a temperature of from 50 C. to 40 C. and poured into prepared containers.

Film Lamination

[0064] Film samples of DIN A4 size were coated with the adhesive using a wire doctor blade, the solvent was evaporated in a drying cabinet and the films were laminated using a roll laminator. A PET/AI/cPP composite was produced, the adhesive being in the AI/cPP position. The plastics coating was 3.5 g/m.sup.2. The bond strength after curing (14 days at room temperature) was 3.6/3.7 N/15 mm.

[0065] The bond strength after sterilization (45 minutes at 134 C. after curing) was 4.6/4.7 N/15 mm, which meets the market requirements stipulating that the bond strength has to be more than 4 N/15 mm.

4. Laminating Adhesive II

[0066] The polyester polyol according to Example 2 was mixed with LA 7707 in the ratio specified above.

[0067] The laminating adhesive LOCTITE LIOFOL LA 7707/LA 6707 was selected as a reference.

LA 7707:

[0068] Basic component: NCO-terminated prepolymer based on PPG400, PPG1000, castor oil and 4,4-MDI.

[0069] NCO content: 12-12.6%

[0070] Viscosity: 3,000-5,000 mPas (measured at 40 C.)

LA 6707:

[0071] Hardener component: OH-functional, based on 100% polyester PES 218

[0072] OH number: 135+/6 mg KOH/g

[0073] Viscosity: 2,000-3,000 mPas (measured at 20 C.)

Mixing ratio LA7707/LA 6707 by weight: 100:75 (NC 0:0H1.6)

[0074] For the polyester comparison, the component LA 7707, which had been preheated to 40 C., was successively mixed once in each case with LA 6707 and the polyester polyol according to Example 2 and homogenized by hand for approximately 1 minute. For this purpose, 500 g LA 7707 was weighed and mixed with 375 g LA 6707 and 425 g polyester polyol according to Example 2 such that there was an NCO:OH ratio of approximately 1.6. The mixture was poured into the roll nip of a laminating machine (polytype, testing machine). A PET film on which 2 g of adhesive mixture was applied per 1 m.sup.2 was used as a carrier film. A PE film was then fed in and the resulting PET/PE laminate was wound up.

[0075] The composite was stored at room temperature and the bond strength of samples from the rolls was determined after certain periods of time.

[0076] Sealed seam adhesion was determined after 14 days. In addition, the samples were subject to what is referred to as a crease test, during which the samples were tightly bent after certain time intervals, fixed with a paper clip and stored in the oven at 80 C. for one hour.

[0077] DIN A4-sized samples were selected for testing the composite. Said samples were folded once in all directions (upward, to the right, downward, to the left) such that the edges were one on top of the other and a folded end piece of an area of approximately 5 cm7.5 cm was produced. The edges were pressed with light pressure using a ruler. The four-fold composite was fixed with a paper clip and stored in the oven at 80 C. for one hour. The samples were then removed from the oven, unfolded and visually inspected. If delaminations could be identified, the test had to be assessed as having failed. If the samples passed the crease test, the bond strength is so advanced that the laminate can withstand mechanical and thermal loads.

[0078] The results of the tests are summarized in Table 2:

TABLE-US-00002 TABLE 2 According to Comparison the invention Bond strength [N/15 mm] 1 day 2.5 2.2 2 days 2.8 3.0 3 days 3.0 3.2 4 days 3.4 3.4 7 days 3.3 3.3 14 days inseparable inseparable Sealed seam [N/15 mm] 14 days 38 41 Crease test 1 day inadequate inadequate 2 days OK OK

[0079] As can be seen from the table, the adhesive according to the invention exhibits satisfactory results which are comparable to, or partially exceed, those of a conventional adhesive.