WO2006088351A1

WO2006088351A1 - Protective agent

Info

Publication number: WO2006088351A1
Application number: PCT/NL2005/000125
Authority: WO
Inventors: Antonius Franciscus Maria Bertels; Marcellus Franciscus Johannes Schoondergang
Original assignee: Rsb Laboratorium B.V.
Priority date: 2005-02-21
Filing date: 2005-02-21
Publication date: 2006-08-24

Abstract

The invention relates to a protective agent, particularly a protective agent intended for use on horticultural greenhouses, to a method for applying a protective layer by using said protective agent and to the protective layer thus obtained. What is special about a protective agent according to the invention is that a protective layer is obtained therewith which transmits more light in wet conditions than in dry conditions.

Description

Title: Protective agent

The invention relates to a protective agent, particularly to a protective agent intended for use on horticultural greenhouses, to a method for applying a protective layer by using this protective agent and the protective layer thus obtained. In horticulture, many crops are cultivated in greenhouses. In this manner, they can benefit from optimized conditions, such as temperature, amount of light, moisture and the like. However, a problem is that, in warm, sunny weather conditions, the cultivated plants are exposed to a large amount of radiation so that the plants can be disturbed in their living conditions and growth, and can even burn. In order to obviate this problem, it is common practice in horticulture to protect the crops from the adverse effect of excess radiation during spring and summer by providing the transparent surfaces of the greenhouse with a protective layer.

One of the most important requirements imposed on such a protective layer is that sufficient screening of light and particularly heat is achieved. In order to fulfill this requirement, the protective layer needs to contain a pigment, such as chalk, aluminum silicate or titanium oxide. Further, an important requirement is that the protective agent, from which the protective layer is formed, adheres sufficiently to the surface of a greenhouse and has sufficient cohesion. When the adhesive power is too small, the layer will not be resistant to weather influences and it will be necessary to restore or replace the layer multiple times per season. When the adhesion and/or cohesion is too great, it takes a lot of effort to remove the layer at the end ojζthe season. European patent application 0 999 736 describes a protective layer based on a specific binder, which is sufficiently stable to offer protection from radiation and different weather influences for a prolonged period without needing to be restored. The protective layer according to this patent application can be removed in a simple manner which is not particularly labor-intensive or requires chemicals which unacceptably burden the environment and/or forms a risk to health.

A drawback of known protective layers is that they stop virtually just as much sunlight and heat in dry and sunny weather as in cloudy and wet weather. This is disadvantageous because, as a result, the crops cultivated in a greenhouse cannot receive sufficient light in cloudy weather. Although the use of some pigments, such as calcium carbonate, somewhat reduces the protective action when the protective layer becomes wet by rain or sprinkling, this decrease is insufficient.

According to the present invention, it has surprisingly been found that, through use of a pigment consisting of hollow spheres, a protective layer can be obtained which is virtually transparent in moist condition and has a very good protective action in dry condition. Accordingly, the invention relates to a protective agent comprising a pigment, a binder and water, while the pigment is a polymeric material consisting of hollow spheres. A great advantage of a protective layer obtained by applying a protective agent according to the invention is that the light transmission can be controlled. In cloudy weather or rain, when reduced protective action is desired or even necessary, the protective action can be reduced by moistening the protective layer. The moistening can take place spontaneously by rain or by sprinkling. When the weather is dry and sunny, the protective layer will dry and again offer an increased protective action.

A protective agent according to the invention can be applied to surfaces from different materials. Preferably, a substantially transparent surface is involved, such as an outer surface of a greenhouse, for instance a horticultural greenhouse. The surface will usually be from glass or plastic. Conventional plastics are, for instance, polycarbonates, polyolefins, polyethylene terephthalate and polyesters.

An important aspect of a protective agent according to the invention is the pigment present therein. According to the invention, as a pigment, a polymeric material is used which consists of hollow spheres. These spheres preferably have dimensions between 0.1 and 1.5 μm, more preferably between 0.3 and 0.8 μm.

Examples of polymeric materials which consist of hollow spheres and are suitable as a pigment in a protective agent according to the invention are described in inter alia US patents 4,427,836, 4,880,465 and

6,139,961, and European patent applications 1 344 803 and 1 344 804. The hollow spheres can be obtained by means of emulsion polymerization according to known methods, as described in inter alia

US patents 5,229,209, 4,594,363, 4,427,836 and 4,089,800 and in Journal of Polymer Science - Part A, vol. 39, pp. 1435-1449 (2001). Therein, it is described how the dimensions of the cavities in the spheres can be controlled.

The hollow spheres can be prepared from a great diversity of monomers, preferably vinyl monomers. These may be homopolymers or copolymers. Examples of suitable polymers include styrene, vinyl toluene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile,

(meth)acrylamide, alkyl (me th) aery late, where alkyl stands for an alkyl group with 1-20 carbon atoms, and alkenyl (meth)acrylate, where alkenyl stands for an alkenyl group with 3-20 carbon atoms. Preferred monomers are methyl methacrylate, ethyl acrylate, butyl acrylate and styrene.

The polymeric material from which the hollow spheres have been formed usually has a glass transition temperature of -50°C to 15O⁰C, preferably higher than 70⁰C. The glass transition temperature can be set in a known manner by means of a suitable choice of monomers and their relative amounts. Suitable examples of polymeric materials consisting of hollow spheres which can be used as a pigment in a protective agent according to the invention are commercially available under the name Ropaque™ from the firm of Rohm en Haas and under the names HS 3000NA Hollow Sphere Plastic Pigment, HS 3020NA Hollow Sphere Plastic Pigment and HS 3028NA Hollow Sphere Plastic Pigment from The Dow Chemical Company. Preferably, the product Ropaque™ Ultra from Rohm en Haas is used.

The pigment is preferably present in an amount of 10-30 wt.%, more preferably of 20-25 wt.%, based on the weight of the protective agent.

As a binder in a protective agent according to the invention, any conventional binder for such products can be used. Suitable examples comprise starch and starch derivates and vinyl polymers. Preferably, a vinyl polymer, such as a polyvinyl acetate, polyacrylate or polystyrene acrylate is used.

A binder which is particularly preferred is described in European patent application 0 999 736. This binder is a polymer which has a weight-average molecular weight, as determined with, for instance, gel permeation chromatography (GPC), of 10,000-100,000, preferably between 15,000 and 75,000, more preferably between 20,000 and 50,000. The acid value of this binder is preferably 40-250. The acid value is related to the average number of free acid groups per chain of the polymeric binder. This number is preferably 60-160. The acid value can be determined by titrating with potassium hydroxide, whereby the end point is determined potentiometrically. The acid value then corresponds to the number of milligrams of potassium hydroxide per gram of the polymeric binder used up in the titration. Further, this binder preferably has a polydispersity with a value of 2 to 6, preferably of 3 to 5. In this text, the term polydispersity is understood to mean the ratio of the weight-average molecular weight to the number-average molecular weight (M_w/M_n). Just like the weight-average molecular weight, the number-average molecular weight can be determined using GPC. This binder preferably has a glass transition temperature between 10 and 60°C, most preferably between 20 and 50°C.

The binder according to European patent application 0 999 736 may be either a homopolymer or a copolymer. The nature of the monomers in the binder is less important than the above-mentioned parameters. The binder is preferably a vinyl polymer. The use of a vinyl polymer as a binder yields an excellently suitable protective layer. Suitable monomers are, for instance, vinyl aromatic monomers, such as α-methylstyrene and styrene, acrylonitrile, methacrylonitrile , acrylamide, vinyl acetate, vinyl chloride, phenoxyethyl acrylate, multifunctional acrylates, such as hexanediol dimethyl acrylate, glycol dimethyl acrylate, divinylbenzene and esters of methacrylic acid or acrylic acid, or mixtures of these esters. Examples of suitable esters comprise alkyl esters, where the alkyl group can contain from 1 to 20 carbon atoms, alkoxyalkyl esters, such as butoxyethyl acrylate and butoxyalkyl methacrylate, and hydroxyalkyl esters. An acrylic acid or methacrylic acid ester can constitute up to 90% of the polymer. When acrylonitrile or acrylamide is present in the vinyl polymer, these monomers will usually be present in the polymer in amounts smaller than 10-15 wt.%. Styrene and vinyl acetate can constitute up to 30 and 50 wt.% of the polymer, respectively. Other suitable monomers are acid monomers such as acrylic acid, methacrylic acid, malic acid, fumaric acid, crotonic acid, itaconic acid, aconic acid and half -esters thereof, and malic acid anhydride and the like. These acid monomers can be present in amounts of up to 50 wt.%. Particularly suitable monomers are methyl methacrylate, butyl acrylate, 2-ethylhexyl-acrylate, ethyl acrylate, styrene, methacrylic acid and acrylic acid.

It is further possible that the polymer is wholly or partly cross-linked. As cross-linking monomers, methylol acrylamide, methylol methacrylamide and the like qualify. These cross-linking monomers will usually constitute no more than 5 wt.% of the polymer.

The binder is preferably present in an amount of 3-12 wt.%, more preferably of 5-10 wt.%, based on the weight of the protective agent. It has been found that a protective layer containing the above-mentioned components in the above-mentioned amounts has both an optimal protective action and an optimal adhesive power.

In addition to a pigment, a binder and water, a protective layer according to the invention may also contain a few other components. It is, for instance, advantageous to include an adhesion promoter in the protective agent. The adhesion of the protective agent to a surface will be improved by the presence of an adhesion promoter, while the ease with which the obtained protective layer can be removed is hardly or not affected. Depending on the material of the surface to which a protective layer is to be applied, a skilled person will be able to choose a suitable adhesion promoter. Preferably, the adhesion promoter needs to be soluble in water and contain an amino group. For the use on glass surfaces, the use of a silane, such as γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ- (methylamino)propyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-(2-aminoethyl-3-aminopropyl)triethoxysilane and γ-(2-aminoethyl-3- aminopropyl)methyldimethoxysilane, is recommended. An adhesion promoter will usually be present in the protective agent in an amount of 0.05 to 1 wt.%, preferably of 0.1 to 0.3 wt.%, based on the weight of the protective agent. Another component which is advantageous is a pigment dispersant.

The presence of such a substance prevents aggregation of pigment during the drying up of the protective agent, which has been applied in diluted form for forming the protective layer. A pigment dispersant can be present in amounts of 0.1 to 0.5 wt.%, based on the weight of the protective agent. The nature of the pigment dispersant depends on the nature of the pigment present in the protective layer. For instance, sodium hexametaphosphate is very suitable when calcium carbonate is used as a pigment. When titanium oxide is used as a pigment, for instance a polymeric multifunctional tenside, such as Ser-Ad FA 607^® (available from the firm of Hύls AG) can excellently be used as a pigment dispersant.

In order to optimize the viscosity of the protective agent for forming a protective layer according to the invention, a thickener can be included. The optimum viscosity of the protective agent depends on the method with which the layer is applied to a surface. If a surface is spread with a protective agent, a higher viscosity will be desired than when a surface is sprayed with a protective agent. Further, the viscosity needs to be sufficient to obtain a thick layer. On the basis of his normal professional knowledge, a skilled person will be able to determine what viscosity is most suitable in which case. Examples of thickeners comprise organic and inorganic thickeners, such as hydroxyethylcellulose, acrylates, magnesium aluminum silicate and combinations thereof. The amount of the thickener will be adjusted to the desired viscosity and will usually be between 0.5 and 3 wt.%, based on the weight of the protective agent.

Other possible additional components of the protective layer may be detergents, anti-foaming agents, preservatives and the like.

Preferably, further, a weak base is present in the protective agent according to the invention. This ensures neutralization of free acid groups present in one or more components of the agent. It has also been found that the presence of the weak base results in an improved film formation of the protective agent to be applied during drying, when a protective layer is formed. Preferably, the weak base is chosen from the group of ammonia, mono, di and trialkyl amines, with the alkyl group containing 1 to 8 carbon atoms. There is a particular preference for ammonia.

The weak base is preferably present in an amount of 0.2-5 wt.%, more preferably of 0.4-3 wt.%, based on the weight of the protective agent. As said, the application of the protective agent for forming a protective layer can take place in different manners. Possible manners comprise spraying, spreading and the like. The protective action of the layer will hardly or not be affected by the manner of application. It will be clear that the invention also relates to a protective layer formed with a protective agent as described hereinabove.

In due course, for instance at the end of the season, protective layers need to be removed, particularly when used on horticultural greenhouses. Depending on the composition of the protective agent, and particularly of the binder therein, a protective layer according to the invention can be removed in a suitable manner. In this context, suitable methods include brushing and chemical removal with an oxidizing agent, acid or fluoride solution.

A great advantage of the use of a binder as described in the above- mentioned European patent application 0 999 736 is that a protective layer obtained with a protective agent based thereon can easily be removed, while an excellent adhesion is achieved during the season. For removal of a protective layer based on that binder, this layer is treated with a remover comprising a strong base and a complex former. The remover causes the binder in the protective layer to become soluble in water.

The strong base is present in the remover in an amount of 2-10 wt.%, more preferably of 2-5 wt.%, based on the weight of the remover. Suitable strong bases are for instance alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide. In addition to the strong base, preferably an amount of 2-10 wt.%, based on the weight of the remover, of a complex former is present. It has been found that particularly the use of the trisodium salt of nitrilotriacetic acid or the tetrasodium salt of ethylenediaminetetraacetic acid strongly stimulates the protective layer to become soluble. The use of trisodium salt of nitrilotriacetic acid is preferred. This substance is well and quickly biologically degradable.

In addition to the above-mentioned components, the remover can contain a thickener such as xanthan gum. Xanthan gum makes the remover strongly pseudoplastic, so that it is thin during application and thick after application. This property prevents the remover from flowing from the surface too quickly. Further, the remover can also contain a substance which lowers the surface tension, or an emulsifier. Suitable is, for instance, the sodium salt of dodecylbenzenesulphonic acid. To remove the protective layer, this layer is treated with the above -de scribed remover. This treatment comprises applying the remover to the layer to be removed in a suitable manner, such as spraying or pouring.

Usually, the remover is used in a fivefold to tenfold dilution. After applying the remover, the surface can be rinsed with water. It is also possible to have all this wash off in the rain. Then, virtually all traces of the protective layer will have disappeared.

The invention will now be explained on the basis of the following examples.

EXAMPLE l

Specification of hollow-sphere polymeric pigment used

(Ropaque™ Ultra):

Polymer: Styrene acrylate Solid in weight %: 30%

Density of the dry polymer: 0.591 g/cm³ pH: 8-9

Average sphere size: 0.4 μm

Preparation of the protective agent:

In a reaction vessel, the following substances were added in the indicated order:

Water 10.4 %

Anti-foaming agent 0.3 % 30 % Solution

Sodium hexametaphosphate 1.0 %

Ammonia 25 % 1.0 %

Hydroxy ethylcellulose 0.5 %

Polymer dispersant^* 13.3 % Hollow Sphere Polymer 73.4 % (=22% solid)

Preservative 0.1 %

^* The polymer dispersant used is an acrylate type with a solid content of 45 % and acid value of 73, based on the content of solid EXAMPLE 2

Of the formulation of Example 1, a dilution with water was made of 1 part of protective agent with 2 parts of water. The diluted solution was applied to a glass plate and to a plastic film (Hyplast) used in horticulture. After drying, a dry, indelible and wear-resistant layer was obtained.

Artificial ageing with a high UV load and flowing water only cause d a slight wear.

A part of the layer had been sprayed with a remover based on sodium hydroxide and trisodium nitrilotriacetate as described in Example 2 of European patent application 0 999 736. After action of the remover and rinsing with water the protective layer has been removed.

EXAMPLE 3 With the plates obtained in Example 2 light measurements were carried out in a laboratory setting to determine the protective action in dry and in wet conditions. Here, the following results were obtained:

Dry Wet

Chalk product 1 to 3^* 77 % 60 % Product from Example 1 to 2 glass^** 64 % 24 %

Product from Example 1 to 2 film^** 69 % 27 %

Glass without protective agent 11 % 10 %

^* This product contained 1 weight part of chalk and 3 weight parts of water

^** This product contained 1 weight part of the product from Example 1 and 2 weight parts of water

Claims

1. A protective agent comprising a pigment, a binder and water, wherein the pigment is a polymeric material consisting of hollow spheres.

2. A protective agent according to claim 1, wherein the pigment has a sphere size of 0.1 to 1.5 μm.

3. A protective agent according to claim 1 or 2, wherein the pigment is a homopolymer or copolymer from one or more of the following monomers: styrene, vinyl toluene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, (meth)acrylamide, alkyl (meth)acrylate, wherein alkyl stands for an alkyl group with 1-20 carbon atoms, and alkenyl (meth) aery late, wherein alkenyl stands for an alkenyl group with 3-20 carbon atoms.

4. A protective agent according to any one of the preceding claims, wherein the binder is a polymer with a weight -average molecular weight of 10,000-100,000 and an acid value of 40-250.

5. A protective agent according to claim 4, wherein the binder has an acid value between 60 and 160, has a polydispersity of 2-6 and has a glass transition temperature between 10 and 60⁰C, preferably between 20 and 50⁰C.

6. A protective agent according to claim 4 or 5, wherein the binder is a vinyl polymer based on one or more monomers chosen from the group of methyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, styrene, methacrylic acid and acrylic acid.

7. A protective agent according to any one of the preceding claims, wherein the pigment is present in an amount of 10 to 30 wt.%, based on the weight of the protective agent.

8. A protective agent according to any one of the preceding claims, wherein the binder is present in an amount of 3 to 12 wt.%, based on the weight of the protective agent.

9. A method for applying a protective layer, wherein a protective agent according to any one of the preceding claims is applied to a substantially transparent surface, which protective agent forms the protective layer after drying.

10. A method according to claim 9, wherein the substantially transparent surface is an outer wall surface of a greenhouse.

11. A protective layer comprising a pigment and a binder, wherein the pigment is a polymeric material consisting of hollow spheres, obtained by applying a protective agent according to any one of claims 1-8 to a surface.

12. A substantially transparent surface provided with a protective layer according to claim 11.

13. A greenhouse provided with a protective layer according to claim 11.

14. Use of a polymeric material consisting of hollow spheres as a pigment in a protective agent.