Dry bonding acrylate adhesive layers

Abstract

A radiation curable adhesive comprising (i) (meth)acrylic monomer(s) and/or oligomer(s), wherein said (meth)acrylic monomers or oligomers comprise 5 to 50 wt % of esters of (meth)acrylic acid with polyetherpolyols having the formula HO—((CH.sub.2).sub.m—O).sub.n—X wherein m=2, 3 or 4; n=2 to 50; X=H, linear, branched or aromatic C1 to C12-alkyl, the ester having a molecular weight from 150 to 2000 g/mol; (ii) non-reactive (co)polymer(s) based on unsaturated monomers, wherein said unsaturated monomers are selected from vinyl esters, (meth)acrylate esters and C2 to C8 unsaturated olefins, the (co)polymer having a molecular weight from 5000 g/mol to 500000 g/mol, such adhesive can form a solid adhesive layer after being cross-linked by radiation, the layer, has a non tacky surface but can be adhesively bonded under pressure to a second layer of the adhesive.

Claims

1. A radiation curable adhesive comprising: (i) (meth)acrylic monomer(s) and/or oligomer(s), wherein said (meth)acrylic monomers or oligomers comprise 5 to 50 wt % of esters of (meth)acrylic acid with polyetherpolyols having the formula
HO—((CH.sub.2).sub.m—O).sub.n—X wherein: m=2,3 or 4; n=2 to 50; X=H, linear, branched or aromatic C1 to C12-alkyl, the ester having a molecular weight from 150 to 2000 g/mol; and (ii) non-reactive (co)polymer(s) based on unsaturated monomers, wherein said unsaturated monomers are selected from vinyl esters, (meth)acrylate esters, and C2 to C8 unsaturated olefins, the (co)polymer having a molecular weight from 5000 g/mol to 500000g/mol; wherein the adhesive after radiation curing is in a solid form, the solid adhesive being bondable to a second layer of the adhesive but having a non tacky surface that is non-adherent to substrates other than a second layer of the adhesive.

2. A radiation curable adhesive according to claim 1, wherein the adhesive has a viscosity from 2000 to 200000 mPas at 50° C. or from 2000 to 200000 mPas at 30° C.

3. A radiation curable adhesive according to claim 1, wherein the (meth)acrylic acid esters are selected from esters having 3 to 20 repeating units of ethylene oxide and/or propylene oxide.

4. A radiation curable adhesive according to claim 1, wherein the adhesive comprises from 2 to 35 wt-% of said non-reactive (co)polymer(s).

5. A radiation curable adhesive according to claim 1, wherein the adhesive comprises at least one additive selected from photoinitiators, adhesion promoters, fillers or stabilisers.

6. A radiation curable adhesive according to claim 1, wherein the adhesive comprises from 10 to 35 wt-% of caprolactone (meth)acrylate ester.

7. A layer of a radiation curable adhesive according to claim 1, wherein said layer is applied to a substrate selected from cellulose or polymeric material.

8. A layer of a radiation curable adhesive according to claim 1, wherein said layer is applied to a flexible film or sheet selected from cellulose or polymeric material.

9. A layer of a radiation curable adhesive according to claim 1, wherein the layer is about 5 to 500 μm thick.

10. A process for bonding substrates, wherein at least part of surfaces of said substrates are coated with a cured adhesive layer manufactured from an adhesive according to claim 1, and both layers are bonded together by pressure.

11. A process for bonding substrates according to claim 10, wherein the bonded layers can be separated by adhesive failure to one substrate or fiber tear.

12. A process for bonding substrates according to claim 10, wherein the bonded layers can be separated from another by mutual adhesive failure of the adhesive layers.

13. A process for bonding substrates according to claim 12, wherein the adhesive layers form reclosable surfaces.

14. A radiation curable adhesive according to claim 1, wherein the adhesive comprises from 2 to 35 wt-% of ethylene vinyl acetate copolymers.

15. A radiation curable adhesive according to claim 1, further comprising 10 to 60 wt % of acrylate substituted urethane.

16. A radiation curable adhesive according to claim 1, comprising: 5 to 50 wt-% monomers of mono or poly (meth)acrylic esters, 10 to 60 wt-% (meth) acrylate substituted polymers based on polyester, polyurethane or polyacrylate, 5 to 50 wt-% of a polyether-based acrylic esters, 2 to 35 wt-% of a non-reactive polymer, and 0 to 20 wt-% of additives, wherein the sum of all components is 100%.

Description

EXAMPLE PROCEDURE

(1) A reaction vessel is used comprising a mixing device and a heating bath. To this vessel the acrylate components and the inert copolymer, as described in Table 1 below, are added. This composition was mixed, stirred and heated for about 6 hours at 80° C. The copolymer was thereafter dissolved. The photoinitiators are added and mixed, then the adhesive is cooled and can be applied.

(2) TABLE-US-00001 TABLE 1 Molecular Adhesive 1 Adhesive 2 Adhesive 3 Adhesive 4 weight Component (g) (g) (g) (g) (about) THF-acrylate 4.8 4.8 4.9 4.6 170 Acrylic acid 0 0 4.6 Trimethylolpropantriacrylate 9.6 0 0 0 Caproactone 12.2 25 17.1 23.9 350 acrylate PEG dimethacrylate 9.6 6.7 9.6 6.4 730 Polyethyleneglycol- 20.1 0 24.7 0 400 acrylate Polyester- 19.2 27 19.2 27.5 5000 acrylate Urethan- 0 21.2 0 22.8 3000 diacrylate EVA 20.7 9.6 20.7 4.6 Irgacure 819 1.9 1.9 1.9 1.9 Irgacure 2959 1.9 1.9 1.9 1.9 SiO.sub.2 0 1.9 0 1.8 Reversible

(3) The adhesive mixture is homogenous and liquid at room temperature.

(4) A layer of about 30 μm was applied by a doctor blade to a paper substrate. Curing takes place after 3 to 5 seconds under a mercury lamp (1000 W) at about 365 nm (UVALOC).

(5) The adhesive layers showed a clear surface and were not tacky. They could be stored adjacent to another non coated substrate without sticking together.

(6) For bonding test two substrate layers (15×80 mm) were pressed together by rolling a 1 kg roll twice across the bonded substrates. The substrates were allowed to rest for about 10 min. Then the peel values were measured by an Instron Tensile machine (speed 250 mm/min). The test results are given in Table 2 below.

(7) TABLE-US-00002 TABLE 2 Adhesive -1- -2- -3- -4- Substrate Paper Paper Paper PET film Tear test 3.2 4.6 6 8 N/15 mm fiber tear fiber tear fiber tear first tear. reversible 7-5.5 2nd to 8th tear

(8) The test results show that a one time closure is achieved and in Example 4 a reversible closure with mutual adhesive failure.