Non-reactive hot-melt adhesive with specific resin

Abstract

The invention pertains to a non-reactive hot-melt adhesive comprising 10-90 wt. %, calculated on the weight of the adhesive, of amorphous thermoplastic resin which is compatible with polylactic acid, wherein the amorphous thermoplastic resin is a random copolymer of lactic acid and further reactive monomer, 10-90 wt. %, calculated on the weight of the adhesive, of a polylactic acid polymer unit (PLAU) selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the unit having a number average molecular weight of at least 0.75 kg/mol.

Claims

1. A non-reactive hot-melt adhesive comprising 10-90 wt. %, calculated on the weight of the adhesive, of an amorphous thermoplastic resin that is compatible with polylactic acid, wherein the amorphous thermoplastic resin is a random copolymer of lactic acid and further reactive monomer, 10-90 wt. %, calculated on the weight of the adhesive, of a first polylactic acid polymer unit (PLAU) selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the unit having a number average molecular weight (Mn) of from 0.75 to 10 kg/mol; and 0-20 wt. %, calculated on the weight of the first PLAU, of a second polylactic acid polymer unit (PLAU) selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the optional second PLAU having a number average molecular weight of from 0.75 to 10 kg/mol, wherein when the first PLAU is PLLAU, the second PLAU is PDLAU and when the first PLAU is PDLAU, the second PLAU is PLLAU, wherein the phrase “number average molecular weight (Mn)” is defined as being determined by Gel Permeation Chromatography (GPC) with chloroform as a solvent and running phase and polystyrene standard, with detection via Refractive Index, and wherein the phrase “amorphous thermoplastic resin” is defined as a thermoplastic resin that has an enthalpy of melting of at most 2.0 J/gram as determined by Differential Scanning calorimetry.

2. The non-reactive hot-melt adhesive according to claim 1, which further comprises 0.5-20 wt. %, calculated on the weight of the first PLAU, of the second polylactic acid polymer unit (PLAU) selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the unit having a number average molecular weight of from 0.75 to 10 kg/mol, wherein when the first PLAU is PLLAU, the second PLAU is PDLAU and when the first PLAU is PDLAU, the second PLAU is PLLAU.

3. The non-reactive hot-melt adhesive according to claim 1, wherein the first PLAU is PLLAU and wherein the second PLAU, if present, is PDLAU.

4. The non-reactive hot-melt adhesive according to claim 1, wherein the first PLAU and/or the second PLAU, if present, have a number average molecular weight in the range of 1.5 to 7.5 kg/mol.

5. The non-reactive hot-melt adhesive according to claim 1, wherein the amorphous thermoplastic resin has a number average molecular weight (Mn) in the range of 10 to 100 kg/mol.

6. The non-reactive hot-melt adhesive according to claim 1, which comprises 20-80 wt. %, calculated on the weight of the adhesive, of amorphous thermoplastic resin and 20-80 wt. %, calculated on the weight of the adhesive, of the total of the first polylactic acid polymer unit (PLAU) and, if present, the second polylactic acid polymer unit (PLAU).

7. The non-reactive hot-melt adhesive according to claim 6, which comprises 40-60 wt. %, calculated on the weight of the adhesive, of amorphous thermoplastic resin and 40-60 wt. %, calculated on the weight of the adhesive, of the total of the first polylactic acid polymer unit (PLAU) and, if present, the second polylactic acid polymer unit (PLAU).

8. The non-reactive hot-melt adhesive according to claim 1, wherein the random copolymer of lactic acid and further reactive monomer comprises 10-90 wt. % of lactic acid monomer and 90-10 wt. % of further reactive monomers.

9. The non-reactive hot-melt adhesive according to claim 1, wherein the further reactive monomer comprises caprolactone.

10. The non-reactive hot-melt adhesive according to claim 9, wherein the copolymer of lactic acid monomer and caprolactone has a number average molecular weight (Mn) in the range of 10 to 50 kg/mol, and/or the non-reactive hot-melt adhesive comprises 40-60 wt. %, calculated on the weight of the adhesive, of amorphous thermoplastic resin and 40-60 wt. %, calculated on the weight of the adhesive, of the total of the first and, if present, second PLA units.

11. The non-reactive hot-melt adhesive according to claim 1, wherein the thermoplastic resin and the polylactic acid polymer units together make up at least 50 wt. % of the adhesive.

12. A method for manufacturing a non-reactive hot-melt adhesive according to claim 1, comprising combining and mixing, to form a liquid composition, 10-90 wt. %, calculated on the weight of the adhesive, of amorphous thermoplastic resin which is compatible with polylactic acid, wherein the amorphous thermoplastic resin is a random copolymer of lactic acid and further reactive monomer; 10-90 wt. %, calculated on the weight of the adhesive, of a first polylactic acid polymer unit (PLAU) selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the unit having a number average molecular weight (Mn) of from 0.75 to 10 kg/mol; and, 0-20 wt. %, calculated on the weight of the first PLAU, of a second polylactic acid polymer unit (PLAU) selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the optional second PLAU having a number average molecular weight of from 0.75 to 10 kg/mol, wherein when the first PLAU is PLLAU, the second PLAU is PDLAU and when the first PLAU is PDLAU, the second PLAU is PLLAU, wherein the phrase “number average molecular weight (Mn)” is defined as being determined by Gel Permeation Chromatography (GPC) with chloroform as a solvent and running phase and polystyrene standard, with detection via Refractive Index, and wherein the phrase “amorphous thermoplastic resin” is defined as a thermoplastic resin that has an enthalpy of melting of at most 2.0 J/gram as determined by Differential Scanning calorimetry.

13. The method according to claim 12 comprising combining and mixing in an amount of from 0.5-20 wt. %, calculated on the weight of the first PLAU, the second polylactic acid polymer unit (PLAU) to form the liquid composition, wherein the second polylactic acid is selected from poly-L-lactic acid (PLLAU) and poly-D-lactic acid (PDLAU), the unit having a number average molecular weight of from 0.75 to 10 kg/mol, wherein when the first PLAU is PLLAU, the second PLAU is PDLAU and when the first PLAU is PDLAU, the second PLAU is PLLAU.

14. The method according to claim 13, wherein in a first step the thermoplastic resin and one of the first or second PLAU are combined to obtain a liquid mixture, and in a second step the other of the first or second PLAU is added to form a homogeneous mixture.

15. The method for arranging substrates in a fixed position with respect to each other, comprising the steps of applying an amount of a non-reactive hot-melt adhesive according to claim 1 in liquid form onto a surface of a first substrate, applying a surface of a second substrate onto the amount of non-reactive hot-melt adhesive, and cooling the assembly of substrates and non-reactive hot-melt adhesive to a temperature below the melting point of the non-reactive hot-melt adhesive.

Description

EXAMPLE 1

(1) Formulations where made from the following starting materials:

(2) As thermoplastic resin a random copolymer of caprolactone and lactic acid was used, comprising 30 wt. % of caprolactone and 70 wt. % lactic acid. The copolymer had a molecular weight Mn of 15 kg/mol. The copolymer was manufactured by ring-opening polymerization of caprolactone and lactide.

(3) As first PLAU a PLLA (initiated with cetyl alcohol) was used with a Mn of 2.5 kg/mol.

(4) As second PLAU a PDLA (initiated with cetyl alcohol) was used with a Mn of 3.5 kg/mol.

(5) Three compositions were prepared, namely composition A, which contained the first PLAU but not the second PLAU and compositions B and C, both of which contain the first PLAU and different amounts of second PLAU. All compositions were prepared by mixing the thermoplastic resin with the first PLAU in the liquid phase until a homogeneous mixture was obtained, followed, for compositions B and C, by the addition of the second PLAU under stirring.

(6) The compositions were tested in an adhesive test unit as follows: A line with a length of 140 mm of the adhesive to be tested was applied at 165° C. onto a cardboard substrate. After a fixed open time of 0.5 seconds, five 25 mm sections of a second cardboard substrate were applied onto the adhesive with a contact speed of 0.5 m/s and kept at a pressure of 0.5 kg/25 mm.

(7) After an initial assessment, the five bonds were sequentially ruptured at 1 m/s. The set time was defined as the time the bond required under pressure to ensure that upon rupture fibre tear of the cardboard substrate was obtained, while the set adhesive remained intact. Three replicate tests were made for each adhesive.

(8) TABLE-US-00001 TABLE 1 Thermoplastic First PLA Second PLA Set time resin (wt. %) (wt. %) (wt. %) (s) A 50 50 — 7.6 B 49.5 49.5 1 6.7 C 48.5 48.5 3 4.3

(9) As can be seen from Table 1, all compositions show a manageable set time. Compositions B and C, which contain both the first PLAU and the second PLAU show a lower set time than Composition A. Composition C, which has a slightly higher content of second PLAU than Composition B has a set time which is even lower.

EXAMPLE 2

(10) Formulations where made from the following starting materials:

(11) As thermoplastic resin a random copolymer of adipic acid (40.02 wt. %), neopentyl glycol (40.02 wt. %) and lactide (29.81 wt. %) was used. The weight percentages are calculated on the amounts of monomer before synthesis. The total of the weight percentages is above 100% due to the water removal during the esterification/polymerization reaction. The copolymer had a molecular weight Mn of 8.0 kg/mol.

(12) As first PLAU a PLLA (initiated with cetyl alcohol) was used with a Mn of 2.5 kg/mol.

(13) As second PLAU a PDLA (initiated with cetyl alcohol) was used with a Mn of 3.5 kg/mol.

(14) Two compositions were prepared, namely composition D, which contained the first PLAU but not the second PLAU and composition E which contained the first PLAU and the second PLAU. The compositions were prepared and tested as described in Example 1, except that an application temperature of 160° C. was used. The results are presented in Table 2 below.

(15) TABLE-US-00002 TABLE 2 Thermoplastic First PLA Second PLA Set time resin (wt. %) (wt. %) (wt. %) (s) D 50 50 — 8 E 48.5 48.5 3 6

(16) As can be seen from Table 2, both compositions showed an acceptable set time, with the set time being reduced if the second PLA was added.