Starch as a Primer for Substrates

Abstract

The invention relates to a process for coating a substrate including the steps of (i) applying a primer on the substrate; (ii) applying a coating on the primed substrate; and (iii) drying and/or hardening the applied coating; wherein the primer is an aqueous primer comprising one or more pregelatinized starches.

Claims

1. A process for coating a substrate comprising the steps of: (i) applying a primer on the substrate; (ii) applying a coating on the primed substrate; and (iii) drying and/or hardening the applied coating; wherein the primer is an aqueous primer comprising one or more pregelatinized starches.

2. The process according to claim 1, wherein the substrate is a mineral substrate or a non-mineral substrate, and/or wherein the substrate is an absorbing substrate or a non-absorbing substrate.

3. The process according to claim 1, wherein the substrate is selected from a brick or masonry, in particular an absorbent brick, a concrete substrate, a plasterboard, a filler, a plaster, stone, a tile or a wood substrate.

4. The process according to claim 1, wherein the starch of the one or more pregelatinized starches is a starch of wheat, waxy wheat, potato, corn, waxy corn, rice or peas or a mixture of two or more thereof.

5. The process according to claim 1, wherein the pregelatinized starch is a drum-dried pregelatinized starch or an extruded pregelatinized starch; and/or the one or more pregelatinized starches are based on an unmodified starch or a modified starch selected from a propoxylated starch, an enzyme-treated starch, an acid-treated starch, a phosphate-crosslinked starch or a coated starch.

6. The process according to claim 1, wherein the primer further comprises one or more additives selected from preservatives, wetting agents, dispersing agents, defoamers, fillers, fibrous fillers, anti-blocking agents, and plasticizers, wherein the total amount of additives is preferably less than 5% by weight, based on the dry weight of the primer.

7. The process according to claim 1, wherein the process further comprises the step of preparing the aqueous primer by adding water to a solid primer comprising or consisting of one or more pregelatinized starches, wherein the solid is preferably a free-flowing solid.

8. The process according to claim 1, wherein the primer comprises 80% by weight to 100% by weight, preferably 90% by weight to 97% by weight, of the one or more pregelatinized starches, based on the dry weight of the primer.

9. The process according to claim 1, wherein the water content of the aqueous primer is 80% by weight to 99% by weight, preferably 85% by weight to 95% by weight, most preferably 89% by weight to 91% by weight, based on the total weight of the aqueous primer.

10. The process according to claim 1, wherein the primer applied on the surface is dried before the coating is applied, wherein the drying time is preferably from 1 to 24 hours.

11. The process according to claim 1, wherein the coating is a plaster or filler, preferably selected from a plaster or filler based on clay, gypsum, lime, cement, cement-lime or synthetic resin.

12. The process according to claim 1, wherein the coating is applied by filling or plastering.

13. A coated substrate, obtainable by a process according to claim 1.

14. A primer composition to be used on a substrate in order to enhance adhesion of a subsequent coating on the substrate, wherein the primer composition consists of or comprises one or more pregelatinized starches.

15. A method, comprising the steps of providing a composition consisting of or comprising one or more pregelatinized starches, priming a substrate, and coating the substrate with a coating.

16. The method according to claim 15, wherein the composition is a solid, preferably a free-flowing solid, to be supplemented with water before use for priming, or wherein the composition is a ready-to-use aqueous primer or concentrate, which can be diluted with water before use, if necessary.

Description

EXAMPLES

[0051] Adhesion Tests

[0052] Red bricks as a substrate were pre-treated with the following primers

TABLE-US-00001 Aufbrennsperre concentrated primer on a synthetic resin emulsion 1:4 basis, from Knauf Gips KG, dilution ratio (by volume) Aufbrennsperre : water = 1:4 Lightec 10% from Krner-Strke GmbH, pregelatinized wheat starch having excellent cold swelling properties, moisture content about 8%, used as a 10 % by weight solution in water CWS 30 10% Allstarch Swellster CWS 30 from Interstarch GmbH, pregelatinized native waxy corn starch, white/ yellowish powder, water content 3 to 10%, obtained by physical extraction from waxy corn, used as a 10 % by weight solution in water

[0053] CWS 30 10% and Lightec 10% are used according to the invention, Aufbrennsperre 1:4 is a prior art primer.

[0054] After application of the primer on the red brick substrate and drying of the primer, one of the following coatings was applied on the primed substrate according to the instructions of the manufacturer:

TABLE-US-00002 Rotband Embsen Gypsum plaster from Knauf Gips KG, manufactured in Embsen MP 75 L Gypsum plaster from Knauf Gips KG, manufactured Neuherberg in Neuherberg

[0055] The adhesion of the gypsum plasters is tested according to DIN EN 13279-2, issue date March 2014. The results are shown in the following tables.

[0056] HR means adhesive crack (Haftriss), PR means plaster crack (Putzriss). An adhesive crack means that the adhesion of the plaster will eventually crack, i.e. the adhesion is not as good. If the plaster cracks, the adhesion of the plaster to the substrate is obviously better than the internal strength of the plaster itself. So if there is no adhesive crack, but only a plaster crack (100%), this can be seen as very positive, because the plaster practically does not crack in itself under real conditions.

TABLE-US-00003 TABLE 1 Primer: Aufbrennsperre 1:4, Coating: Rotband Embsen measured values adhesive tensile average average crack scale crack pattern strength [N/mm.sup.2] [N/mm.sup.2] pattern 0 demolished 0.00 0.38 40% HR/ 60 50% HR/50% PR 0.31 60% PR 82.5 20% HR/80% PR 0.42 125 40% HR/60% PR 0.64 57.5 100% PR 0.29 47.5 100% PR 0.24

TABLE-US-00004 TABLE 2 Primer: Lightec 10%, Coating: Rotband Embsen measured values adhesive tensile average average crack scale crack pattern strength [N/mm.sup.2] [N/mm.sup.2] pattern 67.5 100% PR 0.34 0.35 100% PR 120 100% PR 0.61 75 100% PR 0.38 50 100% PR 0.25 50 100% PR 0.25 55 100% PR 0.28

TABLE-US-00005 TABLE 3 Primer: CWS 30 10%, Coating: Rotband Embsen measured values adhesive tensile average average crack scale crack pattern strength [N/mm.sup.2] [N/mm.sup.2] pattern 62.5 100% PR 0.32 0.41 100% PR 80 100% PR 0.41 87.5 100% PR 0.45 80 100% PR 0.41 82.5 100% PR 0.42 95 100% PR 0.48

TABLE-US-00006 TABLE 4 Primer: Aufbrennsperre 1:4, Coating: MP 75 L Neuherberg measured values adhesive tensile average average crack scale crack pattern strength [N/mm.sup.2] [N/mm.sup.2] pattern 50 10% HR/90% PR 0.25 0.29 39% HR/ 47.5 10% HR/90% PR 0.24 61% PR 50 80% HR/20% PR 0.25 55 30% HR/70% PR 0.28 57.5 85% HR/15% PR 0.29 80 20% HR/80% PR 0.41

TABLE-US-00007 TABLE 5 Primer: Lightec 10%, Coating: MP 75 L Neuherberg measured values adhesive tensile average average crack scale crack pattern strength [N/mm.sup.2] [N/mm.sup.2] pattern 55 10% HR/90% PR 0.28 0.32 8% HR/ 55 10% HR/90% PR 0.28 92% PR 65 0% HR/100% PR 0.33 75 20% HR/80% PR 0.38 65 0% HR/100% PR 0.33 60 10% HR/90% PR 0.31

TABLE-US-00008 TABLE 6 Primer: CWS 30 10%, Coating: MP 75 L Neuherberg measured values adhesive tensile average average crack scale crack pattern strength [N/mm.sup.2] [N/mm.sup.2] pattern 55 20% HR/80% PR 0.28 0.32 3% HR/ 85 0% HR/100% PR 0.43 97% PR 55 0% HR/100% PR 0.28 55 0% HR/100% PR 0.28 55 0% HR/100% PR 0.28 72.5 0% HR/100% PR 0.37

[0057] On the basis of the results of crack pattern and adhesive tensile strength in N/mm.sup.2, conclusions can be drawn about the adhesion promotion.

[0058] As can be seen from the results, a primer made of pregelatinized starch is at least as good and sometimes even better as the conventional primer, but in any case significantly cheaper than a primer made of synthetic polymers.

[0059] In particular, comparable or better adhesion is shown by using the inventive starch solution as a primer, as the percentage of adhesive crack is reduced.

[0060] Effect of Primer on Processing Time

[0061] Processing and handling for plastering different substrates (red brick, cellular concrete, lime sandstone) was tested in view of different primers and plasters.

[0062] Lime sandstone is highly absorbent, cellular concrete is less absorbent, and brick least absorbent.

[0063] The following table shows processing times for plaster MP 75 L Neuherberg for different substrates without primer and with different primers (Lightec 10%, CWS40 10%, Aufbrennsperre 1:4).

[0064] For the determination of the processing times, the following procedure was carried out: first, the primer was applied onto the substrate (apart from the no primer experiments) followed by 24 hours waiting, then the plaster was applied (defined as minute 0). During the hardening process of the plaster, several (standard) steps were conducted in this example. These steps (spreading (levelling), scratching, felting/roughening, 1.sup.st smoothing and 2.sup.nd smoothing) depend on the properties (e. g. the consistency) of the ingredients in the specific experiment at a specific time and are processed according to the times mentioned in the table (i. e. in a rather small time frame, e. g. +/10 min). The person skilled in the art knows according to his experience when to proceed with the next step, e. g. by testing the plaster with his fingers. Standard tools, which are known to the person skilled in the art, were used for the respective steps, e. g. a trapezoidal slat, an H-slat, a smoothing disc, a smoothing trowel, or a (surface) smoother. For the felting/roughening step a sponge disk (or sponge washer) with (some) water was used. The results (in minutes) are shown in the following table.

TABLE-US-00009 TABLE 7 Coating: MP 75 L Neuherberg Aufbrenn- no Lightec CWS40 sperre work step substrate primer 10% 10% 1:4 spreading cellular 45 80 80 75 concrete lime 65 sandstone red brick 40 scratching cellular 65 115 115 100 concrete lime 90 sandstone red brick 55 felting/roughening cellular 80 135 135 120 concrete lime 105 sandstone red brick 70 1.sup.st smoothing cellular 90 150 150 145 concrete lime 120 sandstone red brick 75 2.sup.nd smoothing cellular 160 220 220 210 concrete lime 180 sandstone red brick 125

[0065] The result for Lightec 10% is very uniform for all substrates, and the effect is similar to Aufbrennsperre. The result for CWS40 10% is very uniform for all substrates, and the effect is similar to Aufbrennsperre.

[0066] The following table shows processing times for plaster Rotband Embsen for different substrates without primer and with different primers (Lightec 10%, CWS30 10%, Aufbrennsperre 1:4).

[0067] For the determination of the processing times the same procedure as above was used. The results are shown in the following table.

TABLE-US-00010 TABLE 8 Coating: Rotband Embsen Aufbrenn- no Lightec CWS30 sperre work step substrate primer 10% 10% 1:4 spreading cellular 60 75 75 70 concrete lime 70 sandstone red brick 40 scratching cellular 75 100 100 95 concrete lime 90 sandstone red brick 60 Felting/roughening cellular 85 110 110 100 concrete lime 100 sandstone red brick 65 120 120 110 1.sup.st smoothing cellular 90 125 125 105 concrete lime 110 sandstone red brick 75 130 130 120 2.sup.nd smoothing cellular 125 135 135 125 concrete lime 130 sandstone red brick 100 140 140

[0068] The purpose of a primer is to improve adhesion by reducing the absorbency of the substrate and to achieve more uniform sucking on different substrates with different absorbencies.

[0069] The results show that the pregelatinized starch solution achieves similar effects to primer Aufbrennsperre. Based on the results, it is assumed that the pregelatinized starch reduces the absorbency of the substrate through film formation, but dissolves again through the applied plaster, partially migrates into the plaster and improves adhesion when re-filming.