WO2005071020A1

WO2005071020A1 - Screening agent

Info

Publication number: WO2005071020A1
Application number: PCT/NL2005/000045
Authority: WO
Inventors: Stéphan Henrick Dick HULLEMAN; Marc Oswald Houweling
Original assignee: HOUWELING INTERNATIONAL BV
Current assignee: HOUWELING INTERNATIONAL BV
Priority date: 2004-01-23
Filing date: 2005-01-21
Publication date: 2005-08-04
Anticipated expiration: 2006-07-23

Abstract

The invention relates to a screening agent comprising (a) a pigment, (b) a binder and (c) an adhesion promoter, wherein the binder is a natural polymer with a weight-average molecular weight of 200,000 to 1,000,000,000 g/mol. The screening agent can be used to form a protective layer that can be removed using a removal agent that contains a base and optionally a complexing composent.

Description

Screening agent

Subject of the invention The present invention relates to a screening agent and a method for forming a protective layer of a screening agent.

Background to the invention In horticulture many plants are cultivated in greenhouses. In this way the plants can benefit from optimised conditions, such as temperature, light, humidity and the like. However, in sunny conditions the cultivated plants are exposed to too great an amount of light, which has an adverse effect on the growth and living conditions of the plants. This can even lead to scorching of the plants, hi horticulture it is therefore customary to provide the glass surfaces of greenhouses with a layer of a so-called screening agent during spring and summer (usually on the outside, that is to say on the side that is exposed to the effects of weather) in order to prevent the problems mentioned above. Of course, the layer of the screening agent used must offer adequate protection to the plants against the adverse influences of a large amount of light. The layer must also adhere sufficiently strongly to the glass surfaces of the greenhouse and be sufficiently resistant to weather effects, such as rain. On the other hand., since the layer has to be removed again after the summer and when changing the crop, when the amount of sunlight decreases appreciably, the layer must also not adhere so strongly that this can be removed only with difficulty and only using aggressive agents. In this context it is also important that when the layer of screening agent is removed a clean surface, that is to say a non-hazy surface, remains, so that optimum light yield in the greenhiouse is obtained. Screening agents based on chalk, polymers and chromium-containing compounds, where the polymer acted as binder and the chromium-containing compound as adhesive, have been used for a long time. A layer of such a screening agent could easily be removed using, for example, a solution of citric acid in water, although a film does remain on the glass surfaces of the greenhouse. On environmental grounds, the use of chromium- containing substances has recently been prohibited in Dutch horticulture. Other screening agents are, for example, disclosed in EP-A 428 937 and EP-A 478 067, which are discussed in EP-A 999 736. EP-A 999 736 relates to a screening agent that can be removed with the use of a removal agent that contains a strong base and a complexing component, the screening agent comprising a pigment and a binder. The binder is a polymer with a weight-average molecular weight of 10,000 to 100,000 and an acid number of 40 to 250, the polymer preferably being based on monomers such as acrylate compounds and styrene. The strong base is preferably a metal hydroxide, such as sodium hydroxide, and the complexing component the trisodium salt of nitrilotriacetic acid or the tetrasodium salt of ethylenediaminetetraacetic acid. The screening agent preferably also contains an adhesion promoter that is soluble in water, preferably a silane, which is used in an amount of 0.05 to 1 % (m/m), based on the weight of the screening agent. According to Example 1 of EP-A 999 736 even 0.12 % (m/m) silane is used. However, the screening agent according to EP-A 999 736 has disadvantages. The binder used is expensive and environmentally unfriendly since the binder used has poor biodegradability, in particular when this contains styrene. Another disadvantage is that the amount of silane that has to be used is relatively high, which also makes the screening agent expensive. Yet a further disadvantage is that the screening agent according to EP-A 999 736 has to be transported as an aqueous dispersion or as a solution which is further diluted with water on site to give the desired concentration. It will be clear to a person skilled in the art that transporting relatively large amounts of water is undesirable. Moreover, the removal agent also has to contain a complexing component in addition to the strong base. Yet a further disadvantage of the screening agent according to EP-A 999 736 is that this can contain environmentally unfriendly components such as benzyl alcohol. It has also been found that when it is raining a layer containing the screening agent according to EP-A 999 736 allows relatively little light through, so that the use of assimilation lighting is needed earlier. The aim of the present invention is to provide a screening agent that has good biodegradability and consequently is environmentally friendly in use and is not expensive. Yet a further aim of the present invention is to provide a screening agent that has to contain only a small amount of water-soluble adhesion promoter, which promotes the environmentally friendliness of the screening agent. Yet a further aim of the present invention is to provide a screening agent in powder form that can be diluted to the desired concentration on site, so that unnecessary transport of large amounts of water is not necessary. As will be clear to a person skilled in the art, this aspect of the invention also promotes the environmentally friendly nature of the screening agent according to the invention. A further aim of the present invention is to provide a layer containing a screening agent according to the invention where the layer transmits a relatively large amount of light when it is raining, so that the use of assimilation lighting is not necessary.

Yet a further aim of the present invention is to provide a layer containing the screening agent according to the present invention that can be removed easily and completely with simple agents after the summer or when changing the crop.

Summary of the invention

The present invention relates to a screening agent comprising (a) a pigment, (b) a binder and (c) an adhesion promoter, wherein the binder is a natural polymer with a weight-average molecular weight of 200,000 to 1,000,000,000 g/mol.

Detailed description of the invention

According to the invention the weight-average molecular weight is preferably 500,000 to 500,000,000 g/mol. Furthermore, it is preferable that the natural polymer is a polysaccharide. More preferentially the natural polymer is chosen from the group that consists of starch, amylose, amylopectin and combinations thereof and the natural polymer is in particular starch. Most preferentially the natural polymer is prestiffened starch or starch soluble in cold water, which usually has a lower molecular weight (approximately 10,000 to approximately 1,000,000,000 g/mol). The pigment (a) is such that this provides adequate protection against (sun)light.

Preferably the pigment is essentially white, so that an essentially white layer is formed when the screening agent is applied. On the other hand, it is also possible to use a coloured pigment. According to the invention the pigment is preferably chosen from the group that consists of calcium carbonate (i.e. chalk), titanium dioxide, a silicate, gypsum, barite and combinations thereof. In particular the pigment is calcium carbonate. According to the invention the adhesion promoter (c) is preferably an organic silicon compound, more preferentially a silane and even more preferentially an alkoxysilane or an aminoalkyltrialkoxysilane. The alkoxysilane has the formula S1R , where R represents H or Cι-C₆ alkoxy. The aminoalkyltrialkoxysilane has the formula:

R^!R²N - R³ - Si - (R⁴)_n(R⁵)_3-n where: 1

R and R independently of one another represent H or Cι-C₆ alkyl, R³ represents Cι-C₆ alkylene,

R⁴ and R⁵ independently of one another represent Cι-C₆ alkoxy and n is 0, 1 or 2. The alkyl group, the alkoxy group and the alkylene group can independently of one another be straight-chain, branched or cyclic. Examples of suitable alkyl groups are methyl, ethyl, n-propyl, n-butyl, n-pentyl and n-hexyl. Examples of suitable alkylene groups are methylene, ethylene, propylene and the like. Examples of suitable alkoxy groups are those which have been mentioned for alkyl groups but with the proviso that these are bound to an oxygen atom. The adhesion promoter is preferably an alkylsilane as described above and suitable silanes according to the invention are 3-aminopropyltriethoxysilane, 3-amino- propyltrimethoxysilane, 3 -(methylamino)propyltrimethoxysilane, 3 -aminopropylmethyl- diethoxysilane, N-methyl-3-aminopropyltrimethoxysilane, N-butyl-3-aminopropyl- trimethoxysilane, N-ethyl-3-aminoisobutyltrimethoxysilane and N-ethyl-3-aminoisobutyl- methyldimethoxysilane. A very suitable silane is Dynasylan® 1151 from Degussa. This is an aqueous solution of 3-aminopropyltriethoxysilane where the ethoxy groups have been hydrolysed (autocatalytically by the amino group). Thus, if the silane is used as an aqueous solution, one or more of the alkoxy groups can be in the hydrolysed form, that is to say in the form of hydroxyl groups, so that in this case R⁴ and/or R⁵ can be OH. According to the invention the screening agent preferably contains 0.01 to

0.04 % (m/m) of an adhesion promoter (c), based on the total weight of the screening agent, in particular 0.01 to 0.03 % (m m). Based on the total weight of the screening agent, the screening agent preferably contains 80.00 to 99.00 % (m/m) pigment (a), in particular 85.00 - 95.00 % (m/m). Based on the total weight of the screening agent, the screening agent preferably contains 0.99 to 19.96 % (m/m) binder (b), in particular 4.99 to 14.97 % (m/m). Advantages of the screening agent according to the invention are mainly that this is environmentally friendly, does not contain any expensive components, can be removed easily and after removal leaves no film on glass surfaces and still transmits a rela.tively large amount of light in bad weather. The screening agent can also be applied to greenhouses with polyethene sheeting. The invention also relates to the formation of a protective layer of a screening agent that can be removed with a removal agent, wherein the screening agent comprises (a) a pigment, (b) a binder and (c) an adhesion promoter, wherein the binder is a natural polymer with a weight-average molecular weight of 200,000 to 1,000,000,000 g/mol. The removal agent preferably contains a base, for example a metal hydroxide, such as sodium hydroxide. Preferably the removal agent is an aqueous solution with a pF3 that corresponds to a sodium hydroxide solution in water that contains 1.0 - 100.O g/1, preferably 2.5 - 75 g/1 NaOH. The removal agent preferably also contains a complexing component, that is to say a component that is able to form a metal complex with a metal ion, the complexing component being soluble in water. Suitable complexing components are those which are mentioned in EP-A 999 736, for example the alkali metal salts of EDTA. Another, very suitable group of removal agents comprises phosphonates. According to the invention the phosphonates have one of the following formulae:

A— CB₂- -A

where A represents a -CH₂P(O)(OH)₂ group, B represents a hydrogen atom, a C1-C₄. alkyl group (where the alkyl group is as defined above) or a hydroxyl group, n = 0 - 2 and m = 1 - 3. Preferably the phosphonate is chosen from the Dequest® phosphonates 2000, 2006, 2010, 2016, 2016D, 2060S, 2066A and 2066 and in particular from 2000 and 2010. These phosphonates are marketed by Solutia Europe S.A. According to the invention a layer of the screening agent is applied to a greenhouse surface that is essentially translucent, that is to say a window or polyethene sheeting, and preferably on the outside, that is to say that side of the surface that is exposed to the weather conditions such as rain and wind. The present invention also relates to a removal agent for removing a layer of a screening agent according to the invention, wherein the removal agent comprises a base. Preferably this removal agent also comprises a complexing component as has been described above.

Examples Example 1

For experiment 1 the chalk (CaCO ), the binder and sodium bichromate were mixed by hand. 1 kilogram of this mixture was suspended in 4 litres of water in approximately 2 minutes using a cordless drill with paint stirrer at high speed. In 1.1 and 1.2 the adhesion promoter was added after suspending the solids in water. Using a backpack sprayer, approximately 12 m² glass surface area at an angle of inclination of 30° was sprayed, per composition. The screening agents were dried in the air. No rain fell for 2 weeks and then it rained heavily for 1.5 days. Following the rainy period, the panes were assessed for adhesion after drying in the air.

Quello: prestiffened starch (AVEBE) Dynasylan® 1151: 40 % aqueous solution of hydrolysed 3-aminopropylsilane (DEGUSSA) CMC: Cekol 100,000, carboxymethylcellulose (NOVIANT; mol. wt = 100,000)

The adhesion after drying and the resistance of the screening agent after exposure to rain are good.

Example 2

The following compositions were mixed dry with the aid of a cordless drill (see Example 1). Dynasylan® 1151 was added after suspending the powder in water. Greenhouse panes (approximately 2 m² per composition) at an angle of inclination of 45° were sprayed with the screening agent.

* Some of the screening agent remains on the pane immediately after spraying with sodium hydroxide solution but after a few rain showers the greenhouse panes were completely clean.

It can be seen from Experiment 2 that if Dynasylan® 1151 is used as adhesion promoter the screening agents can easily be removed with 1 (40 g/1 = 4 %) and 0.5 M (20 g/1 = 2 %) NaOH. Either starch or CMC can be used as binder. The disadvantage of CMC, however, is the low adhesion under wet conditions.

Example 3

The following amounts of CaCO and binder were mixed for 10 minutes in a concrete mixer. Dynasylan® 1151 was then added to the powder in the course of 5 minutes using a plant sprayer, with continued mixing using the concrete mixer.

SP: stiffened potato starch (Rodenburg Biopolymers; mol. wt = approx. 10,000 - 50,000,000 g/mol; SP contains more than 98 % potato starch that has been subjected to thermomechanical degradation). After 20 hours the powders were suspended in 100 litres of water and sprayed on greenhouses (angle of inclination approximately 30°) by a professional whitewasher. Both compositions showed good coverage, good spraying characteristics and good initial adhesion to the pane. After 24 hours in water the compositions were also still readily sprayable after brief mixing. After 6 months on the greenhouse, the layers of both compositions showed slight wear. Both compositions can be removed easily with 40 g/1 NaOH solution.

Example 4

Preparation: see Example 3.

These compositions were applied by a professional whitewasher to greenhouses with an angle of inclination of 30°. All compositions could be sprayed easily and showed good coverage and adhesion and little wear. The chalking agents had a stability of > 4 months. The screening agents were easy to remove with 1 M NaOH solution that contained a thickener (Cekol 100,000). The thickener was added to prevent unnecessary blowing around of the mist to protect the labourer and the environment.

Example 5

In the following experiment an existing mixer for pulverulent chalking agents was filled with 50 kg CaCO₃ (Craie P5 or Romanian chalk) and 4.5 kg SP whilst rotating. After mixing for 1 minute, 25 or 75 ml Dynasylan® 1151 was then sprayed into the powder in 5 seconds with the aid of a nozzle under atmospheric pressure. The entire procedure was repeated once. After 2 fills, 2 x 25 kg of the material was packed into bags and the procedure was repeated until 250 kg chalking agent had been produced. The following compositions were made.

After storing for 5 days, 25 kg of each screening agent was suspended in 100 litres of water and sprayed on approximately 40 m² greenhouse panes (angle of inclination 30°) by a professional whitewasher. The screening agents showed very good adhesion under very severe conditions (6 days heavy rainfall and low temperatures of between -2 °C and 5 °C).

Claims

1. Screening agent comprising (a) a pigment, (b) a binder and (c) an adhesion promoter, wherein the binder is a natural polymer with a weight-average molecular weight of 200,000 to 1,000,000,000 g/mol.

2. Screening agent according to Claim 1, wherein the natural polymer is a polysaccharide.

3. Screening agent according to Claim 1 or Claim 2, wherein, the natural polymer is selected from the group consisting of starch, amylose, amylopectin and combinations thereof.

4. Screening agent according to Claim 3, wherein the natural polymer is starch, preferably prestiffened starch or starch soluble in cold water with a weight-average molecular weight of approximately 10,000 to approximately 1,000,000,000 g/mol.

5. Screening agent according to one of the preceding claims, wherein the pigment is a white pigment.

6. Screening agent according to Claim 5, wherein the white pigment is selected from the group consisting of calcium carbonate, titanium dioxide, a silicate, gypsum, barite and combinations thereof.

7. Screening agent according to Claim 6, wherein the white pigment is calcium carbonate.

8. Screening agent according to any one of the preceding claims, wherein the adhesion promoter is an organic silicon compound.

9. Screening agent according to Claim 8, wherein the organic silicon compound is a silane.

10. Screening agent according to any one of the preceding claims, wherein the screening agent contains 0.01 to 0.04 % (m m) adhesion promoter, based on the total weight of the screening agent.

11. Screening agent according to any one of the preceding claims, wherein the screening agent contains 80.00 to 99.00 % (m/m) pigment, based on the total weight of the screening agent.

12. Screening agent according to any one of the preceding claims, wherein the screening agent contains 0.99 to 19.96 % (m/m) binder, based on the total weight of the screening agent.

13. Method for forming a protective layer of a screening agent that can be removed with a removal agent, wherein the screening agent comprises (a) a pigment, (b) a binder and (c) an adhesion promoter, wherein the binder is a natural polymer with a weight- average molecular weight of 200,000 to 1,000,000,000 g/mol.

14. Method according to Claim 13, wherein the removal agent comprises a base.

15. Method according to Claim 13 or Claim 14, wherein the removal agent contains a complexing component.

16. Method according to one of Claims 13 - 15, wherein the protective layer is applied to a surface of a greenhouse that is essentially translucent.

17. Removal agent for removing a layer of a screening agent according to one of Claims 1 - 12, wherein the removal agent comprises a base.

18. Removal agent according to Claim 17, wherein the removal agent contains a complexing component.