Starch as a primer for substrates

Abstract

The present invention provides a method of coating a substrate, comprising the steps of: (i) applying a primer to a substrate; (ii) applying the coating to the primed substrate; and (iii) drying and / or curing the applied coating; The primer is a water-based primer comprising one or more pregelatinized starches.

Description

Technical Field

[0001] Description The present invention relates to a method for coating an inorganic or non-inorganic substrate, wherein a primer containing alpha-starch is applied to the substrate before coating. The coating is preferably a plaster or a filler. The present invention further relates to a coated substrate obtained by the method, a primer composition, and the use of alpha-starch for primer coating.

[0002] Prior Art Aqueous polymer dispersions are widely used in the construction field as primers or undercoats for preparing porous or high-density substrates before coating or filler coating, plastering, adhesion, or wallpaper pasting operations. The requirements that a primer should meet are diverse, such as penetration into porous substrates, dust binding and consolidation of unstable surfaces, setting of defined absorbency, and improvement of adhesion between the substrate and the paint to be applied next.

[0003] Aqueous polymer dispersions contain base polymers such as acrylate copolymers, for example styrene acrylate, or ethylene vinyl acetate copolymers. The base polymers are usually mixed with suitable additives to adjust specific properties such as the minimum film formation temperature (MFT), film hardness, wetting behavior, defoaming, non-freezing property, and storage stability.

[0004] The primer is also called a deep (penetrating) primer or an undercoat. The primer is applied directly or diluted to substrates such as bricks or masonry, fillers (also called putties), gypsum boards, plasters, cement screeds, calcium sulfate screeds, etc. The primer is inexpensive and can be produced with simple equipment from readily available polymer dispersions. Craftsmen at construction sites apply the primer undiluted or diluted with water at a ratio specified by the manufacturer according to the work at hand.

[0005] International Publication No. 97 / 35818 describes the use of redispersible powders based on acrylate and vinyl ester copolymers for priming inorganic and non-inorganic substrates before coating, particularly before filler coating.

[0006] European Patent No. 1624122(A2) relates to an arrangement of sound-absorbing material to be installed on the inside of the exterior wall of a building, comprising a lower layer mainly composed of cellulose and a connected upper layer, wherein the lower layer is sprayed on the inside of the exterior wall of the building and the upper layer includes a plaster coating.

[0007] European Patent No. 0521920(B1) relates to a deep primer based on a particulate aqueous polymer dispersion containing a specific alcohol ethoxylate in an amount of 5 to 80% by weight based on solid content, and optionally containing additives.

[0008] Patent Publication No. 2008-201997(A) relates to a wall coating material comprising a mixture of 70-85% by weight of water-insoluble cellulose and 15-30% by weight of an adhesive, wherein the adhesive comprises one or more of starch paste, konjac paste, and cellulose ether, and an anchor coat may be applied to the wall substrate before the coating material is applied.

[0009] KR100653385(B1) relates to a soundproof and fireproof interior building material comprising a perforated base plate made from a magnesium oxide disc, a surface member layer consisting of starch, polyethylene oxide, sorbic acid, cellulose ethane, ammonium phosphate, and cotton yarn, chaff, straw, cork chips or powder, and a sound-absorbing material layer formed between the base plate and the surface member layer, consisting of starch, polyethylene oxide, sorbic acid, cellulose, ammonium phosphate, and cellulose paper.

[0010] A drawback of conventional primers based on aqueous polymer dispersions is that the polymers they contain are synthetic polymers that consume natural resources and produce microplastics that are difficult to decompose in the environment. This is an environmental concern.

[0011] Therefore, there is a need for alternative primers that are more environmentally friendly, free of microplastics, and at the same time possess properties at least comparable to those of conventional primers. [Modes for carrying out the invention]

[0012] In the research that forms the basis of this invention, it was unexpectedly discovered that these objectives could be achieved by using pregelatinized starch for the primer coating of the substrate.

[0013] Accordingly, the present invention relates to the method according to claim 1, as well as the coated substrate, corresponding primer composition, and use described in further independent claims. Preferred embodiments of the present invention are shown in the dependent claims.

[0014] Therefore, the present invention relates to a method for coating a substrate, (i) A step of applying a primer to the substrate, (ii) A step of applying a coating to a primer-coated substrate, and (iii) a step of drying and / or curing the applied coating, The present invention relates to a method in which the primer is an aqueous primer containing one or more types of pregelatinized starch.

[0015] The advantages of the present invention are that the pregelatinized starch used in the primer is based on renewable raw materials, and microplastics are avoided. Surprisingly, the primer according to the present invention has properties that are at least equivalent to, or in part, superior to, conventional primers. The adhesion-enhancing effect is comparable to, or even better than, conventional primers.

[0016] Aqueous primers containing one or more types of pregelatinized starch are used to primer-coat inorganic and non-inorganic surfaces or substrates. Primer coating primarily improves adhesion between the substrate and the subsequent coating by mainly binding dust and reducing the absorbency of the substrate.

[0017] A method for coating a substrate according to the present invention includes (i) a step of applying a primer to the substrate before the next coating. The substrate may be an absorbent substrate or a non-absorbent substrate. The substrate may be an inorganic substrate or a non-inorganic substrate. The substrate is preferably a building substrate.

[0018] According to a preferred embodiment, the inorganic substrate is selected from brick or masonry, concrete substrate, gypsum board, filler, plaster, stone, or tile. Brick or masonry is particularly absorbent brick or masonry, such as cellular concrete block, silica brick, or red brick. Gypsum board is also called drywall. Filler is also called leveling compound, joint compound, or putty. Examples of tiles are terrazzo tiles and ceramic tiles. Substrates such as stone or tile may also be used. Examples of non-inorganic substrates include wood-based substrates such as wood chip board.

[0019] According to the present invention, a primer, which is an aqueous primer containing one or more types of pregelatinized starch, is applied to a substrate.

[0020] Pregelatinized starch is a modified starch. Pregelatinized starch is starch that has been treated with hot water, typically by heating it in water and then drying it, usually in a drum dryer or extruder, to make the starch soluble or swollen in cold water, respectively. Pregelatinized starch is preferably well soluble in cold and hot water. Therefore, aqueous primers preferably contain an aqueous solution of pregelatinized starch. Therefore, aqueous primers are preferably aqueous solutions.

[0021] The gelatinized starch may be the gelatinized starch dried by a drum dryer or the gelatinized starch dried by an extruder.

[0022] The starch of one or more types of gelatinized starch is preferably selected from the starch of wheat, waxy wheat, potato, corn, waxy corn, rice seedlings or pea or a mixture of two or more of them.

[0023] The gelatinized starch may be based on unprocessed starch or starch subjected to further processing in other respects. Such processed starch may be selected from propoxylated starch, enzyme-treated starch, acid-treated starch, phosphate-crosslinked starch or coated starch. This processing may be carried out before, during or after the gelatinization of the starch.

[0024] In addition to the gelatinized starch, the primer may further contain one or more additives selected from, for example, preservatives, wetting agents, dispersants, defoaming agents, fillers including fibrous fillers, anti-blocking agents, and plasticizers such as glycols. The use of such additives is customary in the art. Such additives may be used to improve the processing characteristics or performance characteristics of the primer.

[0025] The total amount of the additives is preferably less than 5% by weight based on the dry weight of the primer. The dry weight is intended to mean the weight of the primer without moisture.

[0026] The primer is an aqueous primer and thus contains water. The aqueous primer is a liquid primer, preferably a paste-like primer, that is, a paste. The primer can be delivered in such a form, for example, in a suitable container, as an aqueous primer that can be used immediately or as a concentrate.

[0027] Of course, if necessary, it may be further diluted with water before use. Depending on the viscosity and usage amount of starch, high-concentration paste or liquid paste can be obtained for delivery. The primer can be easily adjusted to the required processing viscosity by the worker using water under the on-site construction conditions.

[0028] In a preferred embodiment, the solid form of the primer is sold as a dry mix, which may be soluble, emulsifiable or dispersible in water. By adding water and mixing, a usable primer can be obtained on-site. By varying the concentration, an appropriate primer can be produced according to the absorbency of the substrate.

[0029] Therefore, the method may further include the step of preparing an aqueous primer by adding water to a solid primer comprising or consisting of one or more types of pregelatinized starch. Of course, the solid primer may further contain one or more additives as described above. Therefore, the solid primer may consist of one or more types of pregelatinized starch, or may be obtained by adding and mixing one or more additives to one or more types of pregelatinized starch.

[0030] The solid primer is preferably a flowable solid. The solid primer is usually a dry mix or powder. The solid primer may also be in an aggregated form such as granular. The aqueous primer can be obtained from the solid primer by adding water. The terms solid and solid primer are used herein in the same meaning.

[0031] Storing and delivering primers in solid or powder form, which are mixed by the user, offers several advantages. First, customers do not need to "purchase" water as with previous primers, and solid primers are frost-resistant. Packaging is also simple, as cardboard boxes can be used for packaging solid or powder primers. Furthermore, solid primers do not require, or only require, preservatives such as biocides and fungicides. This is more difficult in liquid form because starch forms a good breeding ground for microorganisms.

[0032] In a preferred embodiment, the primer contains one or more pregelatinized starches in an amount of 80% to 100% by weight, preferably 90% to 100% by weight, and most preferably 97% to 100% by weight, based on the dry weight of the primer.

[0033] For application, the water content of the aqueous primer may be, for example, 80% to 99% by weight, preferably 85% to 95% by weight, and most preferably 89% to 91% by weight, based on the total weight of the aqueous primer.

[0034] The aqueous primer may be applied to the substrate by conventional means, such as brushing or spraying. The primer applied to the surface is preferably dried before applying the coating. The suitable drying time depends on the type of substrate, but is usually 1 to 24 hours, preferably 16 to 24 hours. Drying can be carried out under environmental conditions such as standard air.

[0035] The method of the present invention further includes the step of applying a coating to a primer-treated substrate.

[0036] The coating may be any coating suitable for the substrate, particularly the substrate of a building. The coating is preferably a plaster or filler, and more preferably selected from plasters or fillers based on clay, gypsum, lime, cement, cement lime, or synthetic resin. In a preferred embodiment, the coating is selected from clay plaster, gypsum plaster, lime plaster, cement plaster, cement lime plaster, synthetic resin plaster, gypsum filler, cement filler, or synthetic resin filler.

[0037] In a preferred embodiment, the coating is applied by filler coating or plaster coating. After application, the coating is dried and / or cured.

[0038] The present invention also relates to coated substrates obtained by the method of the present invention described above. All process steps, materials, features, and related descriptions of the method also apply to the coated substrates, so please refer to those descriptions.

[0039] The present invention also relates to a primer composition used on a substrate to enhance the adhesion of the following coating to the substrate, comprising or containing one or more pregelatinized starches, particularly the solid primer or aqueous primer described above. All process steps, materials, features and related descriptions of the method also apply to the primer composition, so please refer to those descriptions. The primer composition is usually a solid, preferably a fluid solid, and is an aqueous primer composition such as an aqueous primer or aqueous concentrate to which water is added before use in priming, or which is ready to use.

[0040] The present invention also relates to the use of a composition comprising or containing one or more pregelatinized starches for priming a substrate to be coated with a coating agent. The composition comprising or containing one or more pregelatinized starches is, in particular, the solid primer or aqueous primer described above.

[0041] In preferred embodiments, the composition is a solid, preferably a fluid solid, to which water is added before use in primer coating, or the composition is a ready-to-use aqueous primer or a concentrate that can be diluted with water before use as needed. A concentrate refers to an aqueous primer concentrate.

[0042] All process steps, materials, features, and related descriptions of the method also apply to the use of the present invention; therefore, please refer to those descriptions.

[0043] The present invention will be further illustrated below by examples, but these examples should not be construed as limiting the scope of this application in any way. [Examples]

[0044] Adhesion test The red bricks used as the base material were pre-treated with the following primers.

[0045] [Table 1]

[0046] CWS 30 10% and Lightec 10% are used according to the present invention, and Aufbrennsperre 1:4 is a conventional primer.

[0047] A primer was applied to the red brick substrate, and after the primer had dried, one of the following coatings was applied to the primer-coated substrate according to the manufacturer's instructions.

[0048] [Table 2]

[0049] The adhesion of gypsum plaster was tested according to DIN EN 13279-2 (published March 2014). The results are shown in the table below.

[0050] HR stands for adhesion crack ("Haftriss"), and PR stands for plaster crack ("Putzriss"). Adhesion crack means that the plaster adhesion eventually cracks, i.e., the adhesion is not good. When plaster cracks, the adhesion of the plaster to the substrate is clearly superior to the internal strength of the plaster itself. Therefore, if adhesion cracks are absent and only plaster cracks (100%) are present, the plaster can be seen as very promising because, practically speaking, it does not crack on its own under real-world conditions.

[0051] [Table 3]

[0052] [Table 4]

[0053] [Table 5]

[0054] [Table 6]

[0055] [Table 7]

[0056] [Table 8]

[0057] Crack pattern and N / mm 2 By using the results of the tensile strength of adhesion per unit as a basis, we can draw conclusions regarding improved adhesion.

[0058] As the results show, primers made from pregelatinized starch perform at least as well as, and sometimes even better than, conventional primers, but are in all cases significantly cheaper than primers made from synthetic polymers.

[0059] In particular, using the starch solution of the present invention as a primer reduces the percentage of adhesion cracks, resulting in equivalent or superior adhesion.

[0060] Effect of primer on processing time The treatment and handling of plastering on different substrates (red brick, cellular concrete, limestone sandstone) were tested, taking into account different primers and plasters. Limestone sandstone is highly absorbent, cellular concrete is less absorbent, and brick is the least absorbent.

[0061] The table below shows the processing times for Plaster MP 75 L Neuherberg on different substrates with no primer and with different primers (Lightec 10%, CWS40 10%, Aufbrennsperre 1:4).

[0062] To determine the processing time, the following procedure was performed: First, the primer was applied to the substrate (except for the "no primer" experiment), followed by a 24-hour waiting period, and then the plaster was applied (defined as 0 minutes). In this embodiment, several (standard) steps were performed during the plaster curing process. These steps (leveling, scratching, felting / roughening, first smoothing, second smoothing) were performed according to the times listed in the table (i.e., fairly short timeframes, e.g., + / - 10 minutes), depending on the properties of the components (e.g., viscosity) in a particular experiment at a particular time. Those skilled in the art can know when to proceed to the next step, for example, by testing the plaster with their finger, according to their experience. Standard tools known to those skilled in the art, e.g., trapezoidal slats, H-slats, smoothing discs, smoothing trowels, or (surface) smoothers, were used in each step. In the felting / roughening step, a sponge disc (or sponge washer) containing (a small amount of) water was used. The results (in minutes) are shown in the table below.

[0063] [Table 9]

[0064] The results for Lightec 10% were very uniform across all substrates, and the effect was similar to that of Aufbrennsperre. The results for CWS40 10% were also very uniform across all substrates, and the effect was similar to that of Aufbrennsperre.

[0065] The table below shows the processing times for Rotband Embsen plaster on different substrates with no primer and with different primers (Lightec 10%, CWS30 10%, Aufbrennsperre 1:4).

[0066] The same procedure as above was used to determine the processing time. The results are shown in the table below.

[0067] [Table 10]

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

[0069] The results indicate that the pregelatinized starch solution achieves an effect similar to that of a primer (Aufbrennsperre). These results suggest that pregelatinized starch reduces the absorbency of the substrate through film formation, but is redissolved by the applied plaster, partially migrates into the plaster, and improves adhesion during film reformation.

Claims

1. A method for coating a substrate, (i) A step of applying a primer to the substrate, (ii) A step of applying a coating to the primer-coated substrate, and (iii) a step of drying and / or curing the applied coating, The primer is an aqueous primer containing one or more types of pregelatinized starch. A method wherein the primer contains 80% to 100% by weight of one or more types of pregelatinized starch based on the dry weight of the primer.

2. The method according to claim 1, wherein the substrate is an inorganic substrate or a non-inorganic substrate, and / or the substrate is an absorbent substrate or a non-absorbent substrate.

3. The method according to claim 1 or 2, wherein the substrate is selected from brick, masonry, concrete substrate, gypsum board, filler, plaster, stone, tile, or wood substrate.

4. The method according to any one of claims 1 to 3, wherein the starch of the one or more types of pregelatinized starch is starch from wheat, glutinous wheat, potato, corn, waxy corn, rice, or pea, or a mixture of two or more of these.

5. The pregelatinized starch is drum-dried pregelatinized starch or extruded pregelatinized starch, and / or The method according to any one of claims 1 to 4, wherein the one or more pregelatinized starches are based on unprocessed starch, or processed starch selected from propoxylated starch, enzyme-treated starch, acid-treated starch, phosphate-crosslinked starch, or coated starch.

6. The method according to any one of claims 1 to 5, wherein the primer further comprises one or more additives selected from preservatives, wetting agents, dispersants, defoaming agents, fillers, fibrous fillers, antiblocking agents, and plasticizers.

7. The method according to claim 6, wherein the total amount of the additive is less than 5% by weight based on the dry weight of the primer.

8. The method according to any one of claims 1 to 7, further comprising the step of preparing an aqueous primer by adding water to a solid primer containing one or more types of pregelatinized starch, or consisting of one or more types of pregelatinized starch.

9. The method according to any one of claims 1 to 8, wherein the primer contains 90% to 97% by weight of one or more types of pregelatinized starch based on the dry weight of the primer.

10. The method according to any one of claims 1 to 9, wherein the water content of the aqueous primer is 85% to 95% by weight based on the total weight of the aqueous primer.

11. The method according to any one of claims 1 to 10, wherein the primer applied to the surface is dried before the coating is applied.

12. The method according to claim 11, wherein the drying time is 1 to 24 hours.

13. The method according to any one of claims 1 to 12, wherein the coating is a plaster or a filler.

14. The method according to any one of claims 1 to 13, wherein the coating is applied by filler coating or plaster coating.

15. A primer composition used on a substrate to improve the adhesion of the next coating to the substrate, The primer is an aqueous primer containing one or more types of pregelatinized starch. The primer composition wherein the primer contains 80% to 100% by weight of one or more types of pregelatinized starch based on the dry weight of the primer.

16. The use of a primer composition for applying a primer coating to a substrate to be coated with a coating agent, The primer is an aqueous primer containing one or more types of pregelatinized starch. The use wherein the primer contains 80% to 100% by weight of one or more types of pregelatinized starch based on the dry weight of the primer.

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