Use of a single-component laminating adhesive for composite film lamination

Abstract

A description is given of the use of a one-component laminating adhesive for composite film lamination, and also of a method for composite film lamination. The laminating adhesive comprises an aqueous polymer dispersion preparable by radical emulsion polymerization of monomers comprising (a) at least 60 wt %, based on the total amount of monomers, of at least one monomer selected from the group consisting of C1 to C20 alkyl acrylates, C1 to C20 alkyl methacrylates, vinyl esters of carboxylic acids comprising up to 20 carbon atoms, vinylaromatics having up to 20 carbon atoms, vinyl halides, vinyl ethers of alcohols comprising 1 to 10 carbon atoms, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds, and mixtures of these monomers, and (b) at least 0.1 wt %, based on the total amount of monomers, of at least one monomer having at least one acid group, and (c) 0.1 to 5 wt %, based on the total amount of monomers, of at least one ethylenically unsaturated compound having at least one functional group selected from keto groups and aldehyde groups; where the aqueous polymer dispersion comprises at least one compound A which has at least two functional groups that are able to enter into a crosslinking reaction with keto groups or with aldehyde groups; where the molar ratio of the groups of the compound A that are reactive with keto groups or with aldehyde groups to the keto and aldehyde groups of the monomer (b) is from 1:10 to 2:1; and where, in the composite film lamination, at least two films are bonded to one another with the laminating adhesive so firmly that the peel strength is 2.5 N/15 mm or more or that the films bonded to one another are partable only with destruction of at least one of the films. The composite films can be used for the packing of foods.

Claims

1. A method for producing a composite film, comprising: bonding, without UV cross-linking, at least two films together with a one-component laminating adhesive that comprises no UV-crosslinkable components; wherein the laminating adhesive being present in the form of an aqueous polymer dispersion, and the aqueous polymer dispersion comprising polymer particles in dispersion in water that are obtained by radical emulsion polymerization of monomers comprising a) 90 to 99.4 wt %, based on the total amount of monomers, of a mixture of C1 to C8 alkyl acrylates and styrene, b) 0.1 to 5 wt %, based on the total amount of monomers, of at least one monomer having at least one acid group, and c) 0.1 to 5 wt %, based on the total amount of monomers, of at least one ethylenically unsaturated compound having at least one functional group selected from the group consisting of keto groups and aldehyde groups; where the aqueous polymer dispersion comprises at least one compound A which has at least two functional groups that are able to enter into a crosslinking reaction with the keto groups or with the aldehyde groups, and is present in an amount of up to 1.6 wt % based on the total amount of the monomers; where the molar ratio of the groups of the compound A that are reactive with keto groups or with aldehyde groups to the keto and aldehyde groups of the monomer c) is in a range from 1:1.3 to 1.3:1; where, in the composite film, the at least two films are bonded to one another with the laminating adhesive so firmly that the peel strength, measured 24 h after laminate production and at 23° C., is 2.5 N/15 mm or more or that the films bonded to one another are partable only with destruction of at least one of the films.

2. The method according to claim 1, wherein the laminating adhesive has a tack of less than 1.7 N/25 mm, measured as loop tack in an applied thickness of 20 μm, applied to a polyester film 12 μm thick, and measured on steel at room temperature (20° C.) with a removal velocity of 300 mm/min.

3. The method according to claim 1, wherein the polymer particles are produced from monomers further comprising d) 0 to 10 wt %, based on the total amount of monomers, of other monomers, different from the monomers a) to c).

4. The method according to claim 3, wherein the other monomers d) are present, and are selected from the group consisting of acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, phenyloxyethyl glycol mono(meth)acrylate, monomers comprising hydroxyl groups, monomers comprising amino groups, nitriles of alpha,beta-monoethylenically unsaturated C3-C8 carboxylic acids, bifunctional monomers which as well as an ethylenically unsaturated double bond have at least one glycidyl group, oxazoline group, ureido group or ureido-analogous group, and crosslinking monomers which have more than one radically polymerizable group.

5. The method according to claim 3, wherein the monomers b) are selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, and the other monomers d) are present, and are selected from the group consisting of hydroxyalkyl (meth)acrylates having 1 to 10 carbon atoms in the alkyl group.

6. The method according to claim 1, wherein the monomers c) are selected from the group consisting of acrolein, methacrolein, vinyl alkyl ketones having 1 to 20 carbon atoms in the alkyl radical, formylstyrene, alkyl (meth)acrylates having one or two keto or aldehyde groups or having one aldehyde and one keto group in the alkyl radical, N-oxoalkyl(meth)acrylamides, acetoacetyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, and diacetoneacrylamide.

7. The method according to claim 1, wherein the compound A comprises a compound having hydrazide, hydroxylamine, oxime ether, or amino groups.

8. The method according to claim 1, wherein compound A is a dicarboxylic dihydrazide having 2 to 10 carbon atoms, and monomer c) is selected from the group consisting of acetoacetyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, and diacetoneacrylamide.

9. The method according to claim 1, wherein compound A is adipic dihydrazide and monomer c) is diacetoneacrylamide.

10. The method according to claim 1, wherein the polymer particles are produced from monomers comprising b) 0.5 to 3 wt %, based on the total amount of monomers, of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, c) 0.1 to 5 wt %, based on the total amount of monomers, of at least one ethylenically unsaturated compound having at least one keto group, selected from the group consisting of acetoacetyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, and diacetoneacrylamide, and d) 0 to 5 wt %, based on the total amount of monomers, of other monomers, different from the monomers a) to c), selected from the group consisting of acrylamide, methacrylamide, N-methylolacrylamide and N-methylolmethacrylamide, phenyloxyethyl glycol mono(meth)acrylate, monomers comprising hydroxyl groups, monomers comprising amino groups, nitriles of alpha,beta-monoethylenically unsaturated C3-C8 carboxylic acids, bifunctional monomers which as well as an ethylenically unsaturated double bond have at least one glycidyl group, oxazoline group, ureido group or ureido-analogous group, and crosslinking monomers which have more than one radically polymerizable group, and where compound A is a dicarboxylic dihydrazide having 2 to 10 carbon atoms.

11. The method according to claim 1, wherein the material of the films to be bonded is selected from the group consisting of polyethylene, oriented polypropylene, undrawn polypropylene, polyamide, polyethylene terephthalate, polyacetate, cellophane, metalized films, and metal foils.

12. The method according to claim 1, wherein the polymer particles have a glass transition temperature of −40 to +15° C.

13. The method according to claim 1, wherein less than 1 part by weight of emulsifier is used per 100 parts by weight of monomers in the emulsion polymerization.

14. The method according to claim 1, wherein the monomers comprise: b) 0.5 to 3 wt %, based on the total amount of monomers, of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, c) 0.1 to 5 wt %, based on the total amount of monomers, of at least one ethylenically unsaturated compound selected from the group consisting of acetoacetyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, and diacetoneacrylamide, and d) 0.1 to 5 wt % of a hydroxyalkyl (meth)acrylate having 1 to 10 carbon atoms in the alkyl group or 0.1 to 4 wt % of a chain transfer agent having a thiol group; and where compound A is a dicarboxylic dihydrazide having 2 to 10 carbon atoms and the films are polyester films.

15. The method according to claim 14, wherein compound A is adipic dihydrazide and monomer c) is diacetoneacrylamide.

16. The method according to claim 1, wherein the monomers comprise: b) 1.0 to 3 wt %, based on the total amount of monomers, of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, c) 1.0 to 5 wt %, based on the total amount of monomers, of at least one ethylenically unsaturated compound selected from the group consisting of acetoacetyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, and diacetoneacrylamide, and d) 1.0 to 5 wt % of a hydroxyalkyl (meth)acrylate having 1 to 10 carbon atoms in the alkyl group or 1.0 to 4 wt % of a chain transfer agent having a thiol group; and where compound A is adipic dihydrazide.

17. The method according to claim 16, wherein compound A is present in an amount of up to 1 wt % based on the total amount of the monomers.

18. The method according to claim 16, wherein compound A is present in an amount of up to 0.5 wt % based on the total amount of the monomers.

19. The method according to claim 1, wherein the monomers are free of isocyanate crosslinkers.

Description

EXAMPLES

Abbreviations

(1) IA itaconic acid AA acrylic acid S styrene MA methyl acrylate nBA n-butyl acrylate HPA hydroxypropyl acrylate DAAM diacetoneacrylamide ADDH adipic dihydrazide Basonat® LR 9056 water-dispersible polyisocyanate based on isocyanuratized hexamethylene diisocyanate EHTG 2-ethylhexyl thioglycolate (chain transfer agent) pphm parts per hundred monomers (parts by weight per 100 parts by weight of monomers) SC solids content LT light transmissibility; parameter for determining differences in particle size. In this case the polymer dispersion is diluted to a solids content of 0.01% and the light transmissibility is measured in comparison to pure water. Tg (calc.) glass transition temperature as calculated by the Fox equation from the glass transition temperature of the homopolymers of the monomers present in the copolymer and their weight fraction:
1/Tg=xA/TgA+xB/TgB+xC/TgC+ . . . . Tg: calculated glass transition temperature of the copolymer TgA: glass transition temperature of the homopolymer of monomer A TgB, TgC: Tg correspondingly for monomers B, C, etc. xA: mass of monomer A/total mass of copolymer, xB, xC correspondingly for monomers B, C etc.

Examples 1 and 2

(2) TABLE-US-00001 Example 1 Example 2 Monomers (parts by weight) (parts by weight) MA 65.1 63.1 nBA 29.8 29.8 HPA 2 2 IA 1 1 AA 0.1 0.1 DAAM 2 4

(3) The monomers listed are polymerized in the presence of 0.1 pphm polystyrene seed and 0.1 pphm emulsifier (Disponil® FES 27) in water at a temperature of 85° C. The initiator used is sodium peroxodisulfate. For further stabilization of the polymer particles, a total of 0.35 pphm base (ammonia) is added in the course of polymerization. To bring about a reduction in monomers in the polymer dispersion, a chemical deodorization by means of Rongalite C and tert-butyl hydroperoxide is employed after the polymerization. Following cooling to room temperature, the polymer dispersion is admixed with ADDH.

Example 3 (Comparative Example)

(4) TABLE-US-00002 Example 3 (parts by weight) MA 67.1 nBA 29.8 HPA 2 IA 1 AA 0.1 DAAM —

(5) The monomers listed are polymerized in the presence of 0.3 pphm polystyrene seed and 0.25 pphm emulsifier (Disponil® FES 27) in water at a temperature of 80° C. The initiator used is sodium peroxodisulfate. For further stabilization of the polymer particles, a total of 0.3 pphm base (ammonia) is added in the course of polymerization. To bring about a reduction in monomers in the polymer dispersion, a chemical deodorization by means of acetone bisulfite and tert-butyl hydroperoxide is employed after the polymerization.

Examples 4 and 5

(6) TABLE-US-00003 Example 4 Example 5 (parts by weight) (parts by weight) n-BA 62 72.3 S 35.5 23.7 AA 1.5 2 DAAM 1 2 EHTG 1 0.1

(7) The monomers listed are polymerized in the presence of 0.1 (example 4) or 0.3 (example 5) pphm polystyrene seed and 0.1 (example 4) or 0.5 (example 5) pphm emulsifier in water at a temperature of 85° C. The initiator used is sodium peroxodisulfate. For further stabilization of the polymer particles, a total of 0.35 pphm base (ammonia) is added in the course of polymerization. To bring about a reduction in monomers in the polymer dispersion, a chemical deodorization by means of acetone bisulfite and tert-butyl hydroperoxide is employed after the polymerization. Following cooling to room temperature, the polymer dispersion is admixed with ADDH.

Example 6 (Comparative Example)

(8) TABLE-US-00004 Example 6 (parts by weight) n-BA 63 S 35.5 AA 1.5 EHTG 1 DAAM —

(9) The monomers listed are polymerized in the presence of 0.1 pphm polystyrene seed and 0.1 pphm emulsifier (Disponil® LDBS 20) in water at a temperature of 85° C. The initiator used is sodium peroxodisulfate. For further stabilization of the polymer particles, a total of 0.35 pphm base (ammonia) is added in the course of polymerization. To bring about a reduction in monomers in the polymer dispersion, a chemical deodorization by means of acetone bisulfite and tert-butyl hydroperoxide is employed after the polymerization.

Example 7 (Comparative)

(10) Acronal® A 245 aqueous pressure-sensitive adhesive dispersion of an acrylate copolymer

(11) TABLE-US-00005 TABLE 1 Wet specimen values of examples 1-7 Tg Polymer composition (calc.) SC LT Example [parts by weight] Emulsifier [° C.] [%] [%] pH Example 1 65 MA, 30 nBA, 2 HPA, 1 0.1% Disponil ® −9 45.2 56 7.9 IA, 2 DAAM; 1.6 ADDH LDBS 20 Example 2 63 MA, 30 nBA, 2 HPA, 1 0.1% Disponil ® −8 45.2 57 7.3 IA, 4 DAAM; 3.2 ADDH LDBS 20 Example 3 63 MA, 34 nBA, 2 HPA, 1 0.25% Disponil ® −14 51.5 71 6.8 comparative IA FES 27 Example 4 62 nBA, 35.5 S, 1.5 AA, 1 0.1% Disponil ® −5 45 34 6.9 DAAM; 0.5 ADDH; 1 EHTG LDBS 20 Example 5 72 nBA, 24 S, 2 AA, 2 0.5% Disponil ® −16 46 50 6.0 DAAM; 1 ADDH; 0.1 EHTG LDBS 20 Example 5a 72 nBA, 24 S, 2 AA, 2 2% Disponil ® −16 47 50 6.0 DAAM; 1 ADDH; 0.1 EHTG LDBS 20 Example 6 63 nBA, 35.5 S, 1.5 AA; 1 0.1% Disponil ® −6 45.5 34 7.6 comparative EHTG LDBS 20 Example 7 63 nBA, 27 2-EHA, 5 MA, 3 1.4% Lumiten ® I- −45 52 75 7.5 S, 1 AA, 0.7 DAAM; 0.3 SC/1% ADDH Disponil ® FES77
Applications-Related Tests
Substrates, Laminating Films:
Polyester film, 12 μm thick, corona pretreated, surface tension>38 mN/m;
PE film 60 μm thick, corona pretreated, surface tension>38 mN/m
Adhesive Application:

(12) Directly to the corona-pretreated side of the base film, with an application weight of 2.5-3.0 g/m.sup.2 dry.

(13) Loop Tack:

(14) The adhesive is applied in an application thickness of 20 μm (dry) to a polyester film 12 μm thick, and drying is carried out at 90° C. for 3 minutes. A strip 25 mm wide and 200 mm long is cut from the coated polyester film, and this strip is formed into a loop. This loop, with the adhesive outward, is clamped at the two ends into the jaws of a tensile testing machine. The loop is moved at a velocity of 300 mm/min onto a polished stainless steel surface in such a way as to produce a contact area of 40×25 mm. The loop is then pulled off from the steel surface at a velocity of 300 mm/min, in the course of which the loop tack is determined as the maximum force in N/25 mm (at room temperature; 20° C.).

(15) Dynamic Peel Resistance at 23° C.:

(16) The base film is fixed on the laboratory coating unit with the pretreated side upward and the adhesive under test is knife-coated directly onto the film. The adhesive is dried for 2 minutes with a hot air blower and then the laminating film is placed on with a manual roller and pressed in the roller laminating station at 70° C. with a roll speed of 5 m/minute and a laminating pressure of 6.5 bar. After that, using a cutting stencil, the laminate is cut into strips 15 millimeters wide and subjected to various storage cycles. Following storage, the laminate strip is pulled apart on a tensile testing machine, and the force required to achieve this is recorded. The test takes place on a tensile testing machine at an angle of 90 degrees and a removal velocity of 100 mm/min. The test strip is opened up on one side, with one of the resultant ends being clamped into the upper jaw and the other into the lower jaw of the tensile testing machine, and the test is commenced. The result reported is the average of the force from 3 individual measurements, in N/15 mm.

(17) The specimens can be tested after different storage conditions: 1. immediately after laminating (<3 min) 2. after 24 h (at 23° C./50% rel. humidity) 3. after 24 h (at 23° C./50% rel. humidity)+7 d at 50° C. in ketchup
Dynamic Peel Resistance at 90° C.:

(18) The base film is fixed on the laboratory coating unit with the pretreated side upward and the adhesive under test is knife-coated directly onto the film. The adhesive is dried for 2 minutes with a hot air blower and then the laminating film is placed on with a manual roller and pressed in the roller laminating station at 70° C. with a roll speed of 5 m/minute and a laminating pressure of 6.5 bar. The laminate is then cut into strips 15 millimeters wide using the cutting stencil, and stored for a minimum of 24 hours at 23° C./50% relative humidity. Following storage, the laminate strip is pulled apart on a tensile testing machine with climate chamber at a temperature of 90° C., and the force required to achieve this is recorded. The test takes place on a tensile testing machine with climate chamber, at a removal velocity of 100 mm/min. The test strip is opened up on one side, with one of the resultant ends being clamped into the upper jaw and the other into the lower jaw of the tensile testing machine, and the test is commenced. The measurement starts after a waiting time of 1 minute, for conditioning of the test strip. Evaluation: The result reported is the average of the force from three individual measurements, in N/15 millimeters.

(19) Assessment of the Fracture Mode:

(20) A=adhesive layer remains completely on the base film (adhesive fracture)

(21) K=separation in the adhesive layer without detachment from a material (cohesive fracture)

(22) MB=partial or complete fracture of a film

(23) TABLE-US-00006 TABLE 2 Adhesive values of the adhesive dispersions Addition Peel Peel strength of 6%, strength Peel after 24 h at solids after <3 strength 23° C. + 7 d Peel on min at after 24 h at 50° C. in strength solids, 23° C. at 23° C. ketchup at 90° C. of [N/15 mm]/ [N/15 mm]/ [N/15 mm]/ [N/15 mm]/ Basonat ® fracture fracture fracture fracture Ex. LR 9056 mode mode mode mode 1 no 2.2 A 4.0 MB 1.4 A 1.4 A 2 no 1.8 A 3.5 MB 1.8 A 1.1 A 3 no 0.5 A 0.7 A 0.1 K 0.4 K 3 yes 1.9 A 3.2 MB 1.9 A 0.6 K 4 no 2.6 A 4.4 MB 1.6 A 0.7 K 5 no 2.8 A 4.2 MB 3.4 A 0.5 K 5a no 1.3 4.0 MB 3.2 A 0.5 K 6 no 1.0 A 1.2 A 0.1 K 0.1 K 6 yes 2.5 A 4.1 MB 1.7 A 0.7 K 7 no 1.1 A 2.3 K 1.1 K 0.4 K

(24) This table shows that the examples according to the invention can be used very effectively as a one-component adhesive in composite film lamination, particularly if high thermal stability and resistance to migratable chemicals are required.

(25) The preferred emulsifier amount of <1 pphm produces a particularly high immediate strength of the laminates produced using the dispersions of the invention (example 5 vs. example 5a).