Water-based adhesives for industrial applications
The invention relates to water-based adhesives for industrial applications obtained by mixing water-redispersible polymer powder and water-soluble polymer powder with water, wherein the weight ratio of the water-redispersible polymer powder to the water-soluble polymer powder is from about 0.001:1 to 100:1 and the water-based adhesive has a set speed of less than 300 sec, when measured with a 36 μm thick layer at 23° C. and 50% relative humidity and 385 μm thick carton boards with a weight of 275+/−3 g/m2 and Cobb values on one side of 43 g/min/m2 and 27 g/min/m2 on the other side, has a solids content of about 7.5 to 70 wt.-% and a Brookfield viscosity at 23° C. at 20 rpm, measured according to the ASTM D1084 standard, of about 500 to 10,000 mPas. The water-based industrial adhesive has the capability to bond a low surface tension substrate to a cellulosic substrate, in particular with a weight-ratio of water-redispersible polymer powder to water-soluble polymer powder from about 0.5:1 to 100:1 thus can replace conventional aqueous adhesives based on synthetic polymer dispersions. The benefits of the invention are manifold such as faster set speeds and increased machine speeds, logistical advantages due to handling powders instead of liquids, leading to e.g. prolonged shelf life, no water transportation and being an environmentally friendly, low VOC containing adhesive.
1. A water-based adhesive for industrial applications comprising an aqueous mixture of a water-redispersible polymer powder, a water-soluble polymer powder and optional components;
wherein the water-redispersible polymer powder is a water insoluble, film-forming polymer based on at least one monomer selected from the group consisting of vinyl esters of C1- to C20-carboxylic acids, ethylene, vinylchloride, C1- to C20-alkyl esters of acrylic acid and methacrylic acid, acrylonitrile, (meth) acrylamide, styrene, styrene derivatives and butadiene;
wherein the weight ratio of the water-redispersible polymer powder to the water-soluble polymer powder is from about 0.001:1 to 100:1; and
wherein the water-based adhesive (i) has a set speed of less than 300 sec, when measured with a 36 μm thick layer at 23° C. and 50% relative humidity and 385 μm thick carton boards with a weight of 275+/−3 g/m 2 ; (ii) has a Cobb values on one side of 43 g/min/m 2 and 27 g/min/m on the other side; (iii) has a solids content of about 7.5 to 70 wt.-% ; and (iv) has a Brookfield viscosity of about 500 to 10,000 mPas at 23° C. at 20 rpm, measured according to the ASTM D1084 standard.
2. The water-based adhesive according to claim 1 , wherein the water-soluble polymer powder is a synthetic polymer powder, or a modified or unmodified natural polymer powder.
3. The water-based adhesive according to claim 2 , wherein the water-based adhesive has a solids content of about 10 to 65 wt.-% , and a Brookfield viscosity of about 1000 to 7500 mPas at 23° C. and 20 rpm, measured according to the ASTM D1084 standard and
wherein the weight ratio of water-redispersible polymer powder to water-soluble polymer powder is about 0.01:1 to 50:1.
4. The water-based adhesive according to claim 2 , wherein the water-based adhesive has a set speed and open time at 23° C. and 50% relative humidity of less than 200 sec.
5. The water-based adhesive according to claim 2 , wherein the water-based adhesive has a level of grits, which have a mean particle size greater than 50 μm, lower than 10 ppm.
6. The water-based adhesive according to claim 2 , wherein the water-based adhesive is bonded to two substrates, wherein one substrate is a low surface tension substrate and the second substrate is a cellulosic substrate.
7. The water-based adhesive according to claim 6 , wherein the surface tension substrate has a surface tension of 42 dynes/cm or lower.
8. The water-based adhesive according to claim 2 , wherein the water-based adhesive has a VOC content, of below about 1000 ppm, is plasticizer free and/or has a biocide level of below about 0.1 wt %.
9. The water-based adhesive according to claim 2 , wherein the water-based adhesive contains a gas or gas mixture and the water-based adhesive has a density of about 0.010 to 1.20 g/cm 3 at 23° C.
10. The water-based adhesive according to claim 2 , wherein the optional components are selected from the group consisting of plasticizers, defoamers, wetting agents, adhesion promoters, foam generators, hardeners, waxes, surfactants, rheology modifiers, fragrances, dyes, pigments, preservatives, UV-indicators, coalescing agents, humectants, tackifiers, boric acid or their salts, pH-adjusters and/or buffers, water borne adhesives, organic fillers and inorganic fillers.