Water-based adhesive for the bonding of cellulose based substrates

Abstract

Water-based adhesive composition comprising: from 30% to 60% by weight (expressed as dry content) of a chloroprene modified acrylic emulsion (A); and from 0.05% to 0.45% by weight (expressed as dry content) of a water soluble polymer (B) selected among xanthan gum and konjac gum; said composition being obtainable by a process (P) comprising a first step (i) of dissolving into water polymer (B) in the form of a powdered solid. Use of said composition, for the bonding of at least one cellulose based substrate.

Claims

1. A water-based adhesive composition comprising, on the basis of its total weight: from 30% to 60% by weight (expressed as dry content) of a chloroprene modified acrylic emulsion (A); and from 0.05% to 0.45% by weight (expressed as dry content) of a water soluble polymer (B) that is xanthan gum or konjac gum; said composition being obtained by a process (P) comprising a first (i) dissolving into water polymer (B) in the form of a powdered solid, so as to obtain a composition (S) consisting essentially of a water solution of polymer (B).

2. The water-based adhesive composition according to claim 1, having a viscosity at room temperature of 150 to 5000 mPas.Math.s.

3. The water-based adhesive composition according to claim 1, having a viscosity at room temperature of 200 to 4000 mPa.Math.s.

4. The water-based adhesive composition according to claim 1, wherein the chloroprene modified acrylic emulsion (A) is an aqueous dispersion comprising polychloroprene and at least one polymer (C) obtained starting from one or more monomers that are meth(acrylic) acid, meth(acrylate)esters, styrene or acrylonitrile.

5. The water-based adhesive composition according to claim 4, wherein the chloroprene modified acrylic emulsion (A) is an aqueous dispersion of polychloroprene and polymer (C), both forming an interpenetrating polymer network.

6. The water-based adhesive composition according to claim 1, having a content of chloroprene modified acrylic emulsion (A) of 35% to 55%.

7. The water-based adhesive composition according to claim 1, wherein the water soluble polymer (B) is xanthan gum.

8. The water-based adhesive composition according to claim 1, wherein the water soluble polymer (B) is Konjac gum.

9. A method for bonding of at least one cellulose based substrate, comprising bonding said cellulose based substrate to an additional substrate using the water-based adhesive composition of claim 1.

10. The method according to claim 9, wherein the cellulose based substrate is cardboard, paper or cellulose based nonwoven fabrics.

11. The method according to claim 9, wherein the cellulose based substrate is a glossy paper having one face coated with a UV primer.

12. The method according to claim 9, wherein the cellulose based substrate is bonded to a non cellulose based substrate.

13. A method according to claim 9, wherein the substrate is part of an assembly of cardboards in the rigid packing industry or in the bookbinding and/or graphic arts industry.

14. The method according to claim 11, wherein the UV primer is an acrylic primer.

15. The method according to claim 12, wherein the cellulose based substrate is bonded to a PolyVinylChloride (PVC) film, PolyEthyleneTerephtalate (PET) film or a low surface tension plastic film.

Description

EXAMPLE A (REFERENCE)

(1) Water solutions of xanthan gum were prepared by dissolving (at room temperature) xanthan gum powder into water, in order to obtain the concentrations pointed out here-below:

(2) TABLE-US-00001 TABLE 1 Water solution (S) of xanthan gum xanthan gum concentration 2.5 3 5 (% by weight expressed as dry content)

Example 1: Water-based Adhesive Dispersion Comprising LOTER 990 and Xanthan Gum, Prepared Starting from the Xanthan Gum Water Solution (S) at 2.5%

(3) 100 g of LOTER 990 were added to a plastic cup and stirred at a speed of 600 rpm with an appropriate mixer.

(4) An appropriate amount of the water solution (S) with 2.5% xanthan gum (prepared according to example A) was then gradually introduced into the plastic cup, so as to obtain a concentration in xanthan gum in the final adhesive dispersion (expressed in dry content) of 0.12% by weight. During the introduction of (S), an increase of the viscosity was visually observed.

(5) After complete introduction of (S), a homogeneous adhesive dispersion was obtained in which the concentration of LOTER 990, expressed as dry content, was 47.6% by weight.

(6) Its viscosity at room temperature was measured (with a Brookfield RVT viscometer equipped with a n 3 spindle rotating at 20 rotations per minute) and found to be 250 mPa.Math.s.

(7) Wet Tack Test:

(8) The wet tack property was assessed by the following test.

(9) The substrate to be used for this test was a rectangular strip (15 cm5 cm) of a glossy printing paper with a weight of about 355 g/m.sup.2 which was coated on its glossy face by a layer of an acrylic UV primer with a thickness corresponding to 5 g/m.sup.2.

(10) The water-based adhesive dispersion was coated by means of a brush on a rectangular area (1 cm5 cm) located at one end of the UV primer coated surface of the strip. The coating weight of the water-based adhesive which was so applied was about 20 g/m.sup.2 (expressed in wet).

(11) Immediately after the application, the rectangular strip of 15 cm5 cm was shaped into an open cylinder of 5 cm height, by adhering the 1 cm5 cm coated area with the non UV primer coated surface, in such a way as to create an overlapping area (or bonding area) of 5 cm1 cm.

(12) Adhering was made by hand-pressing said overlapping area, corresponding to a pressure of about 0.5 MPa which was maintained during 5 seconds. Then, the pressure was released.

(13) One could observe that the bonding area remained stable, despite the shear stress exerted by the tension of the paper cylinder.

(14) This observation pointed to a good wet tack property.

(15) Bonding Test:

(16) The wet tack test was repeated until the assembly of the two 5 cm1 cm areas of UV primer coated surface and non coated surface and formation of the paper cylinder.

(17) Then, said paper cylinder was allowed to stay 1 day at room temperature, for drying.

(18) After one day, manual peeling of the bonding area was done and resulted in the destruction of the substrate, which was an evidence of the high strength of the adhesive joint.

(19) Bonding Test after Accelerated Storage:

(20) The wet tack test was repeated until the assembly of the two 5 cm1 cm areas of UV primer coated surface and non coated surface and formation of the paper cylinder.

(21) Then, said paper cylinder was subjected to the following low-high temperature cycle: 60 minutes to switch from 23 C. and 50% Relative Humidity (RH) to 80 C. and 80% RH, then 240 minutes to stay at 80 C. and 80% RH, then 120 minutes to switch from 80 C. and 80% RH to 40 C., then 240 minutes to stay at 40 C., then 60 minutes to switch from 40 C. to 23 C. and 50% RH.

(22) After that, this cycle was repeated 7 times.

(23) It was then found that the bonding area remained stable and no delamination was observed.

Examples 2-5: Water-based Adhesive Dispersions Comprising LOTER 990 and Xanthan Gum

(24) Example 1 was repeated, using the water solution (S) of xanthan gum pointed out in Table 2 and adjusting the amount of said solution (S) introduced into the plastic cup in order to obtain the concentrations in LOTER 990 and xanthan gum (both by weight expressed as dry content) which are shown in Table 2.

(25) A homogeneous adhesive dispersion was also obtained with the Brookfield viscosity pointed out in Table 2.

(26) The wet tack test, bonding test, and bonding test after accelerated storage gave the same results.

Example 6 (Comparative)

(27) Example 1 was repeated, except that xanthan gum was introduced directly as a powder in LOTER 990 in such an amount as to target a concentration (based on the total weight of the composition) of 0.12% by weight, without implementation of the water solution (S).

(28) Immediate formation of a gel was observed and no homogeneous adhesive dispersion could be obtained.

Example 7 (Comparative)

(29) Example 1 was repeated, using the water solution (S) with 3% xanthan gum and introducing gradually, into the plastic cup, an amount of it corresponding to a targeted concentration in LOTER 990 and xanthan gum (both by weight expressed as dry content) which are shown in Table 2.

(30) However, during the introduction, the formation of a gel was observed.

(31) After the introduction, no homogeneous adhesive dispersion was obtained.

(32) TABLE-US-00002 TABLE 2 Content in % by weight Ex. 7 Ex. 8 Ingredient Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 (comp.) (comp.) LOTER 990 47.6 45.5 47.6 45.5 43.5 41.7 47.6 (% by weight expressed as dry content) Xanthan gum 0.12 0.23 0.14 0.27 0.39 0.50 0.24 Xanthan gum 2.5 2.5 3 3 3 3 5 content in water solution (S) (% by weight expressed as dry content) Brookfield 250 1350 450 1750 2750 viscosity of the adhesive dispersion (mPa .Math. s)

Example 8 (Comparative)

(33) Example 7 was repeated, using the water solution (S) with 5% xanthan gum and introducing gradually, into the plastic cup, an amount of it corresponding to a targeted concentration in LOTER 990 and xanthan gum (both by weight expressed as dry content) which are shown in Table 2.

(34) The same observations were made.

Example 9 (Comparative): Water-based Adhesive Dispersion Comprising LOTER 990 and an Alkali Swellable Acrylic Thickener

(35) Alkali swellable acrylic thickener Viscoatex 730 (from Coatex) was used, which is a water-based dispersion with a pH of 3 and 30% by weight in dry content.

(36) 100 g of LOTER 990 were added to a plastic cup and stirred at a speed of 600 rpm with an appropriate mixer. The pH was adjusted to 6-7 by adding suitable amount of ammonia water.

(37) After the introduction of 0.1 g of Viscoatex 730, a homogeneous adhesive dispersion was obtained, with a Brookfield viscosity of about 1000 mPa.Math.s.

(38) The wet tack performance was assessed by repeating the wet tack test described in Example 1, with the result that the bonding area of the cylinder opened, releasing the corresponding ends of the paper strip. This observation pointed to a lack of the wet tack property.

EXAMPLE B (REFERENCE)

(39) Water solutions of Konjac gum were prepared by dissolving (at room temperature) Konjac gum powder into water, in order to obtain the concentrations pointed out here-below:

(40) TABLE-US-00003 TABLE 3 Water solution (S) of Konjac gum Konjac gum concentration 2 3 (% by weight expressed as dry content)

Example 10: Water-based Adhesive Dispersions Comprising LOTER 990 and Konjac Gum, Prepared Starting from the Konjac Gum Water Solution (S) at 2%

(41) Example 1 was repeated, except that the water solution (S) with 2.5% xanthan gum was replaced by the Konjac gum water solution (S) at 2%, which was introduced into the plastic cup, so as to obtain a concentration in Konjac gum in the final adhesive dispersion (expressed in dry content) of 0.10% by weight.

(42) A homogeneous adhesive dispersion was also obtained with the Brookfield viscosity pointed out in Table 4.

(43) The wet tack test, bonding test, and bonding test after accelerated storage gave the same results.

Examples 11-13: Water-based Adhesive Dispersion Comprising LOTER 990 and Konjac Gum

(44) Example 10 was repeated, using the water solution (S) of Konjac gum pointed out in Table 4 and adjusting the amount of said solution (S) introduced into the plastic cup in order to obtain the concentrations in LOTER 990 and Konjac gum (both by weight expressed as dry content) which are shown in Table 4.

(45) A homogeneous adhesive dispersion was also obtained with the Brookfield viscosity pointed out in Table 4.

(46) The wet tack test, bonding test, and bonding test after accelerated storage gave the same results.

Example 14 (Comparative)

(47) Example 10 was repeated, except that Konjac gum was introduced directly as a powder in LOTER 990 in such an amount as to target a concentration (based on the total weight of the composition) of 0.10% by weight, without implementation of the water solution (S).

(48) Immediate formation of a gel was observed and no homogeneous adhesive dispersion could be obtained.

Example 15 (Comparative)

(49) Example 10 was repeated, using the water solution (S) with 3% Konjac gum and introducing gradually, into the plastic cup, an amount of it corresponding to a targeted concentration in LOTER 990 and Konjac gum (both by weight expressed as dry content) which are shown in Table 4.

(50) However, during the introduction, the formation of a gel was observed.

(51) After the introduction, no homogeneous adhesive dispersion was obtained.

(52) TABLE-US-00004 TABLE 4 Content in % by weight Ex. 15 Ingredient Ex. 10 Ex. 11 Ex. 12 Ex. 13 (comp.) LOTER 990 47.6 45.5 43.5 41.7 47.6 (% by weight expressed as dry content) Konjac gum 0.10 0.20 0.30 0.40 0.15 Konjac gum 2 2 2 2 3 content in water solution (S) (% by weight expressed as dry content) Brookfield 500 1000 2000 3000 viscosity of the adhesive dispersion (mPa .Math. s)

(53) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(54) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.