EA039581B1 - Greenhouse screen - Google Patents

Abstract

A greenhouse screen comprising strips (11) of film material that are interconnected by a yarn system of transverse threads (12, 14, 18) and longitudinal threads (13a, 13b; 15; 19) by means of knitting, warp-knitting or weaving process to form a continuous product is disclosed. At least some of the strips (11) comprise a film material in the form of a single- or multilayer polyethylene film having a thickness of 20-50 m. Said film comprises at least 2.0 to 4.0 wt.% SiO2 particles, based on the weight of the film, having a D50 of 5-7 m. The film is advantageously used as a screen providing light scattering properties particularly suited for greenhouse applications.

Description

The present invention relates to a greenhouse screen which comprises flexible strips of film which are interconnected by a thread frame by knitting, warp knitting or weaving to form a continuous product. More specifically, the invention relates to a shade screen that diffuses light to create a more uniform distribution of light within a greenhouse and a more moderate climate for plants.

Prerequisites for the creation of the invention

The goal of protected greenhouse cultivation is primarily to change the natural environment to increase yields, improve product quality, conserve resources and expand production areas and crop cycles. The greenhouse, depending on its location and the crop grown in it, must be shaded throughout the year or parts of the year to avoid harmful stress that leads to reduced yields.

Greenhouse screens are often used for energy saving, shading and temperature control. Screens must meet a number of requirements. On the one hand, the screen must let in some of the light necessary for the growth of plants, but on the other hand, it must prevent the passage of harmful light and an unnecessary part of the light, which can lead to excessive heating of the greenhouse.

One known type of greenhouse screen comprises flexible strips of film material running in parallel and interconnected by a knitting, warp knitting or weaving process to form a continuous product, the strips forming the majority of the surface area of the product. Such a greenhouse screen is known, for example, from EP 0109951. Other examples of screens of this type are shown in FR 2071064, EP 1342824 and WO 2008/091192.

The strips of film material can be made from selected materials that provide the desired properties in terms of reflection and transmission of light and heat.

The traditional way to provide shading is to apply chalk/whitewash to the greenhouse cover. This is a cheap and easy way to apply fixed shading to a greenhouse. The advantage of chalk is that it scatters the light that passes through it, which increases productivity as more light reaches the lower leaves of the plant, increasing photosynthesis. Diffused light also creates a more temperate climate in the greenhouse, and on days with strong sunlight, this results in lower temperatures at the top of the plants, preventing stress and production losses as well as quality problems. The main disadvantage of this method is that chalk or whitewash acts constantly both in the morning and in the afternoon, when a decrease in lighting is undesirable, as well as on cloudy days.

Some of the above problems are solved by installing a mobile shadow screen that can be removed when not needed. This has made it a standard item in most high end greenhouses, sometimes combined with whitewash. There are screens that give good light diffusion, but only at very high levels of shading.

ES 439227 describes films for use in greenhouses or conservatories as protection against cold at night and heat during the day. The films contain polyethylene or EVA copolymer (EVA) with less than 15% vinyl acetate and may contain 1 to 15% natural silica particles ranging in size from 0.1 to 10 microns. The films have a thickness of 150 µm and are reported to reduce the transmission of far infrared radiation (1450-730 cm ^-1 ), ie. radiation emitted by the soil at night. The infrared light is absorbed by the film as heat and re-radiated in and out of the greenhouse or cover, causing the temperature inside the greenhouse to rise at night. The films also have increased turbidity, which leads to an increase in the scattering of visible light inside the greenhouse, thereby reducing the shadows that form inside the greenhouse.

EP 1095964 describes a thermal polyolefin film for agricultural use, for example for greenhouses or ground covers. The foil is designed to reduce the risk of frost damage when there is no heating inside the greenhouse. The film contains low density polyethylene, borate compound or anhydrous borax together with silica, silicate, carbonate or sulfate compound as additives. The films are 200 µm thick and contain 1 to 15% silica with a particle size of 1 to 10 µm along with a zinc borate compound. Example 4 describes an LDPE film having a thickness of 200 µm containing 5.1% silica, giving a light transmission of 89.7%.

EP 2757869 describes a greenhouse screen containing strips of film material that are interconnected by a thread system of transverse threads and longitudinal threads through a knitting, warp knitting or weaving process to form a continuous product, where at least some of the strips contain a single or multilayer polyethylene film with a thickness of 10-70 microns.

US 2006/134382 describes a single or multilayer, biaxially oriented polyester film in which at least one layer comprises silica particles in an amount of from 0.2 to <1.0 wt.%, based on the total weight of the film, when In this case, the silica particles have a D ₅₀ of 2.5 to 4.5 µm. This film is suitable for use in greenhouse screens.

US 2011/0171424 describes a polyester film having a transparency of 70 to 99.5%,

- 1 039581 comprising particles of barium sulfate with an average size of 0.7 to 7 microns. Barium sulfate particles have an inorganic coating formed from oxides, mixed oxides or a mixture of Si oxides,

Al, Sn, Fe, In and/or Sb.

Thus, there is a need for a mobile shade screen that provides high transparency to visible light and at the same time provides good light diffusion to create a more uniform light distribution within the greenhouse.

The essence of the invention

The object of the present invention is to provide a greenhouse screen that diffuses light in order to create a more uniform distribution of light within the greenhouse and hence a more moderate climate for the plants. Another object of the invention is to provide a screen with low production costs (ie few ingredients and low cost), which, if necessary, can be produced in both small and large batches. Also, it is important that the screen has a lifespan of at least a couple of years before it needs to be replaced.

These tasks are solved using a greenhouse screen containing strips of film material, which are interconnected by a thread system of transverse and longitudinal threads through a knitting, warp knitting or weaving process to form a continuous product, in which at least some of the strips contain a film in the form single-layer or multi-layer polyethylene (PE) film with a thickness of 20 to 50 μm, and the specified film contains at least from 2.0 to 4.0 wt.% particles of SiO ₂ based on the total weight of the film, and these particles of SiO ₂ have D ₅₀ from 5 to 7 µm.

The greenhouse screen contains a plurality of narrow strips of film material held together by a filament frame. The strips of film material are preferably arranged close to each other so that they form a substantially continuous surface. The shield has a longitudinal direction y and a transverse direction x, with the strips of film material extending in the longitudinal direction. In some embodiments, the strips of film material may also extend in the transverse direction. The typical width of the strips is between 2 and 20 mm. The screen may include open areas that do not have strips to reduce heat buildup under the screen.

At least some of the strips of film material, preferably more than 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, but most preferably all of the strips in the screen contain film material in the form of a single or multilayer polyethylene (PE ) films as described in this document.

The polymer used in the single or multilayer film is polyethylene (PE), also called polyethene (IUPAC). There are several advantages to using polyethylene as the main component of a greenhouse screen, because it is cheaper than polyester, which is often used in greenhouse films, and because it can be easily produced in small batches. Polyethylene is classified by density and branching, with polyethylene usually being a mixture of the same type of ethylene polymers. The polyethylene described herein is a polyethylene or a polyethylene copolymer, said polyethylene copolymer being derived from ethane and at least one of the following olefins such as 1-butene, 1-hexene and 1-octene, etc. and their mixtures.

High density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE), or mixtures thereof, all of these polyethylenes can be used in the present invention in the production of films used for screens.

The main component of the film used for greenhouse screen is high density polyethylene (HDPE). HDPE is defined as having a density greater than or equal to 0.941 to about 0.970 g/cm ³ . HDPE has a low degree of branching. Mostly linear molecules are well packed together, so intermolecular forces are stronger than in highly branched polymers. Therefore, the film made from HDPE has high tear strength, high elongation at break, and low fibrillation tendency. HDPE is predominantly used to stretch the film or tape.

The film also contains a certain amount of low density polyethylene (LDPE) or linear low density polyethylene (LLDPE).

LDPE and LLDPE have unique rheological or melt flow properties, but one important use of LDPE or LLDPE is to use them as carriers for additives such as SiO ₂ particles, UV stabilizers or other additives.

The main purpose of a greenhouse screen as described herein is to diffuse incident sunlight to create a more uniform light distribution within the greenhouse and a more temperate climate for the plants. Light scattering does not necessarily remove light from the system, but instead redirects the light from the film into the greenhouse with its original color and intensity. Scattering of light occurs upon contact with pigment particles present in the screen.

Single-layer or multi-layer polyethylene (PE) film contains dioxide to scatter light

- 2 039581 silicon (light scattering particles). Single or multilayer polyethylene (PE) film contains at least 2.0 wt.% SiO ₂ and a maximum of 4.0 wt.% SiO ₂ . The multilayer film contains at least 2.0 wt.%, 2.1 wt.%, 2.2 wt.%, 2.3 wt.%, 2.4 wt.% and ideally at least 2.5 wt. .% SiO ₂ or more based on the total weight of the film, but preferably should not contain more than 4.0 wt.%, 3.9 wt.%, 3.8 wt.%, 3.7 wt.%, 3.6 wt.% and ideally 3.5 wt.% SiO ₂ or less. If the particle content is too low, the light scattering effect becomes too low. If the content is too high, the transparency is reduced.

As mentioned above, polyester is commonly used to make greenhouse screens. However, a screen made of polyethylene can have higher light transmission than a screen made of polyester with the same concentration of silica, which is a great advantage for screens with low shading requirements, since polyethylene allows a very high light transmittance to be combined with good distribution of light (light scattering).

The scattering of light depends very much on the size of the particles that provide the scattering effect. The SiO ₂ particles used for light scattering in the greenhouse screen described herein have a mass average diameter (D ₅₀ ) of 5 to 7 µm. Advantageously, the SiO ₂ particles used here have a D ₅₀ value of at least 5 µm or more, but advantageously, the D ₅₀ value of the SiO ₂ particles is less than 7 µm or less.

The term mass median diameter (MMD) as used herein is intended to refer to the median mass diameter of a lognormal distribution, with MMD being considered to be the median particle diameter by mass, i.e. the diameter of a spherical particle with the average mass of all particles in the sample.

Compared to the particles of the above size ranges, the use of particles with a D ₅₀ value of less than 5 μm results in a lower light scattering angle and a greater decrease in transparency than when the content of particles (in wt.%) corresponds to the content of SiO ₂ particles in the above range. The use of particles with a D ₅₀ value of more than 7 μm results in the same content of particles (in wt.%), but does not provide a further improvement in the light scattering effect compared to the case when the particle size falls within the required range. In addition, large voids (cavities) are formed around large particles, which reduce transparency.

Factors affected by the effect of light scattering.

Transparency combined with suitable scattering behavior is of particular importance when films are used in greenhouse screens. In general, in order to provide the plants with as much light as possible, a particularly high transparency is desirable. However, in regions with very warm climates, it may also be desirable to reduce the amount of light, in particular around two hours of solar peak. A film made in accordance with the invention, suitable for screens in these climatic zones, should have a transparency of 70 to 95%. For temperate climates (eg Europe, North America, Japan) the transparency of the film according to the invention is advantageously at least 80% and especially at least 83%. The greenhouse film described herein has a transparency of at least 70%, such as at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93% or higher.

In addition to transparency, three parameters: haze, optical clarity and diffusion factor (SF) are required to provide the film with adequate scattering properties. The first important parameter is turbidity. The haze should be 50-75%, eg 54-70%, eg 5767%. Preferably the turbidity is greater than 50%, 51%, 53%, 54%, 55%, 56% and preferably at least 57% or higher, but preferably the turbidity is lower than 75%, 74%, 73%, 72%, 71%, 70%, 69%, 68% and preferably 67% or below.

Transparency depends on the linearity of the passage of light rays through the material. Small deviations of light caused by scattering centers in the material lead to image degradation. These deviations are much smaller than those recorded in turbidity measurements. Whereas turbidity measurements depend on wide-angle scattering, optical purity is determined by small-angle scattering. The second parameter is therefore the optical purity of the film, which should be between 15% and 50%, preferably between 18% and 47%, for example between 21% and 45%, and ideally between 24% and 41%. Preferably the optical purity is greater than 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23% and preferably at least 24% or higher, but preferably the optical purity is less than 50%, 49%, 48%, 47%, 46%, 45% , 44, 43, 42% and preferably 41% or less.

Wide-angle and small-angle scattering are not directly related to each other, which means that turbidity measurements may not necessarily provide information about the optical purity of a sample, and vice versa. However, the following relationships are usually observed: if the haze is too high or the optical purity is too low, then the light becomes too diffuse. Due to the strong backscatter caused by the particles, high transparency values can no longer be achieved, and especially due to the large proportion of scattered light, too much light is lost in the greenhouse environment without reaching the plants. Then the ultimate goal with the use of light-diffusing films, namely illumination of the lower parts of the plants, cannot be achieved because the upper regions of the plants absorb the light and obscure the lower parts of neighboring plants. If the turbidity is too low, the light is not diversified enough and the upper areas of the plant receive too much light.

In addition to transparency, haze and optical clarity, the diffusion factor (SF) must also be taken into account. The diffusion factor is the ratio of the transparency measured in accordance with ASTM D 1003-61 (Method A) and the transparency measured using the Clarityport (see measurement methods for details):

SF = ASTM D 1003-61 (Method A) Clarity/Clarityport Clarity.

For optimal light scattering, the diffusion factor SF should be between 1 and 8, preferably between 1.5 and 7, such as between 1.8 and 6, such as between 1.9 and 5, and ideally between 2 and 4. Advantageously, the diffusion factor SF is greater than 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and preferably at least 2.0 or greater , but preferably the diffusion factor SF is below 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, and preferably 4 or below.

If the diffusion factor is set too low, then too much unscattered light passes through the film with the desired transparency. The light is not versatile enough, with the upper areas of the plant casting a shadow on the lower parts. Upper leaves receive too much light and photosynthetic activity is reduced by excessive heat, while lower leaves do not receive enough light for maximum photosynthetic activity. Therefore, for optimal illumination of plants, the average scattering angle must be optimally selected within the indicated limits.

If the diffusion factor is too high for a given transparency, then too much light is lost in the greenhouse environment due to the scattering effect. Then the ultimate goal with the use of diffuse films, namely illumination of the lower parts of the plants, cannot be achieved because the upper regions of the plants absorb the light and obscure the lower parts of neighboring plants.

The transparency of the film and its scattering behavior (possibly also the distribution of particles in layers) is achieved by careful selection of polymers, described in the preparation process below, and, additionally, by adding light scattering particles of an appropriate size, as well as their concentration.

Advantageously, the film has a total thickness of at least 20 µm and a maximum of 50 µm. Preferably the film thickness is at least 20 and not more than 50 µm, ideally at least 20 µm and at most 40 µm. Preferably the film thickness is more than 20 µm or more, but preferably the film thickness is less than 50, 45, 40 and preferably 35 µm or less. If the film thickness is less than 20 µm, then the risk of film damage with cracking during greenhouse application increases, and the mechanical strength of the film is no longer sufficient to withstand the tensile forces in the screens that occur during use. A film with a thickness above 50 µm becomes too stiff and difficult to handle. Also, the size of the assembled screen tends to increase with increasing film thickness, which is a disadvantage in handling and storage of the screen. Therefore, it is important to produce a film with a thickness within the above ranges.

In addition, the scattering process depends on the distance the light must travel through the film and on the likelihood that it will interact with the scattering particle along this path. Thus, for a given concentration of scattering particles in a film, the amount of light passing through the film decreases due to the increased probability of particle impact with increasing film thickness. As a result, light incident on the film at an angle of incidence other than 90° will scatter more than light incident on the film in a perpendicular direction due to its longer path through the film.

Single-layer films consist of only one layer of film, which is also called the substrate (B-layer). In a multilayer embodiment, the film comprises a substrate and at least one additional layer (for example, an A-layer and / or a C-layer), which, depending on its location in the film, is called an intermediate layer, when at least one additional layer is located on each of two surfaces, or the outer layer when it forms the top layer of the film.

Polyethylenes are theoretically UV stable due to their stable structure and the absence of chromophores. However, during production, their partial oxidation occurs, during which carbonyl and hydroxyl groups are formed. They also contain some impurities that can act as photoabsorbing chromophores. Therefore, it is necessary to protect the greenhouse film from solar radiation and especially from ultraviolet radiation. The retardation or protection against photodegradation can be carried out using additives such as UV stabilizers. UV stabilizers are often added to the polymer to provide resistance against photo-oxidation to protect the film from UV damage. The UV stabilizer is selected from the group consisting of UV absorbers, excited state quenchers, or hindered amine light stabilizers (HALS).

UV absorbers work by absorbing harmful ultraviolet radiation above 290nm and preventing it from reaching the chromophores present in the chemical structure of polyethylene.

Examples of UV absorbers are o-hydroxybenzophenone or benzotriazole derivatives. Nickel excited state quenchers act by deactivating the excited states of the chromophore groups responsible for photoinitiation by energy transfer. Nickel dibutyldithiocarbamates are examples of nickel quenchers.

Hindered amine light stabilizers (HALS) are based on bis-(2,2,6,6tetramethyl-4-piperidyl)sebact and are extremely effective stabilizers against light degradation of most polymers. HALS do not absorb ultraviolet radiation, but prevent polymer degradation. They slow down photochemically initiated degradation reactions, somewhat similar to antioxidants. The high efficiency and longevity of HALS is due to a cyclical process in which HALS is regenerated rather than consumed in the stabilization process. Due to the regenerative nature of this process, as well as the typically high molecular weights of the stabilizers, hindered amine stabilizers are able to provide extremely long-term temperature and light stability.

In addition, for greenhouse screen applications, the advantage is that the film's UV resistance is not compromised by pesticides that are often used in greenhouses. Pesticides are usually sulfur or halogen based compounds. In this situation, it may be necessary to combine HALS with an acid scavenger such as a metal oxide. Often, stearate is also added as an additional additive because it has a synergistic effect and improves the function of the metal oxide. If better performance is required, this is usually achieved with NOR-HALS, which is not deactivated by pesticides. The downside is that NOR-HALS is quite expensive. Examples of HALS that can be used as a UV stabilizer in film are Flamestab™ NOR 116 available from BASF Schweiz AG or Tinuvin™ NOR 371 from the same company.

Greenhouse screens can be a potential fire hazard, as a fire caused, for example, by damage to electrical equipment, can spread to the entire greenhouse and cause enormous economic damage. HALS Flamestab™ NOR 116 can be supplemented with a phosphorus based flame retardant (FR). Aflammit® PCO 700, Aflammit® PCO 800 and Aflammit® PCO 900, available from Thor Group Limited, England, are fire retardants that are synergistic with Flamestab™ NOR 116.

Preparation process.

The transparency of the film and its scattering behavior is achieved by the choice of polymers in the preparation process described below, by the addition of suitable particles of a certain size and concentration, and, in some cases, also by the distribution of particles in layers.

Film production includes the following steps: 1) polymer melt extrusion; 2) curing of the film upon cooling; 3) uniaxial tension at elevated temperature; 4) thermal relaxation or fixation; and 5) final laying of the film.

The extrusion of the polymer melt can be carried out by means of an annular or slotted die. If the melt is extruded with an annular die, then air is used to cool and solidify the film. When a slot die is used for extrusion, the polymer melt can be cooled and solidified either by water immersion or by chill roll processing. Stripping of the film is performed after the film has solidified, during the stretching operation, or later in the process before final laying.

The SiO ₂ particles and UV stabilizers are advantageously added to the HDPE polymer in the form of concentrated, particle or additive masterbatches in the form of granules prior to actual film extrusion. Masterbatch containing particles of SiO ₂ added to obtain a final concentration of 1.7 to 4.5 wt.% particles of SiO ₂ in the film.

It is also preferred that HALS (eg Flamestab™ NOR 116) is added to the extruder as a masterbatch to obtain a final concentration of 0.2 to 4.0 wt% UV stabilizer in the final melt.

Masterbatches containing additives are liquefied and mixed with HDPE polymer in a mixer and then transferred to an extruder. The melts are formed into flat films by blown or cast extrusion processes well known to those skilled in the art.

Blow molding processes include both high blow (high-stalk) and low blow (in-pocket) processes. At high blow-up, the extrudate exits the annular hole in the die in a mushroom shape, which is blown at some distance (usually the length of the mushroom) from the extrusion die. For the low blow process, the tube is inflated as it exits the die.

- 5 039581

Inflating the tube increases the dimensions of the film and ensures the orientation of the polymers. The tube passes through zones of chilled air which cures the polymer and controls crystallization.

After the tube is flattened and cooled, it can be cut to form a film.

The cast films are extruded through a very thin horizontal slot die (slit die). The polymer melt is then cooled and solidified by passing the film through a water bath or chill rolls. Rapid curing by cooling in water results in an increase in film tear strength compared to tubular blown film. The film can then be cut into strips before being stretched. Alternatively, the film is cut during or after stretching as described below.

The film strips can be produced in two different ways: a) the film can be stretched before the film is cut into strips, or b) the film strips can be stretched after the film is cut. In the first method (a), the film is stretched across its entire width by uniaxially orienting the film in the machine direction (MDO). During MDO, the film from the film blowing line or film casting process is heated to an orientation temperature approximately 5-7° C. below the melting temperature of the film. The heating is preferably performed using a plurality of heated rollers. The heated film is fed into a slow draw roller with a pressure roller whose rotation speed is equal to the speed of the heated rollers. The film then enters the quick draw roller. The speed of the fast pull roller is 2-10 times faster than the slow pull roller, which effectively orients the film on a continuous basis. The oriented film is thermally relaxed by keeping the film at an elevated temperature for some time to allow stress relaxation. The thermal relaxation temperature of the thermal rollers is preferably from about 100 to about 125° C. and the thermal relaxation time is from about 1 to about 2 seconds.

When the film is stretched after it has been cut into strips (method b), stretching on hot plates can be advantageous over stretching in hot air ovens because heat is transferred to the film by direct contact with the polished steel surface of the stretch plate. Heating of the stretching plate is carried out by circulation of hot oil. To obtain even film tapes, it is important that the temperature is evenly distributed over the stretch plate. At excessively high temperatures, film tapes can soften and stick to the metal surface. If the stretching temperature is too low, film tapes may break. Temperature profile with plate temperature rise in machine direction provides the best conditions for a smooth drawing process.

Tubular blown film can be stretched in any of three ways:

1) the tube is cut after the pressure roller is retracted and opened. The single layer film is cut into strips and then the strips are stretched as described above;

2) The tubular film is stretched as a double layer, and the flattened two-layer film is cut. The top film strips are stretched on the top side of the hot plate and the bottom film strips are stretched on the bottom side of the hot plate;

3) the film is both cut and stretched into two layers.

The coefficient of longitudinal (uniaxial) stretching has a value in the range from 1:3 to 1:10, preferably from 1:4 to 1:8, more preferably from 1:5 to 1:7. Preferably the stretch ratio is 1:3, 1:4 and preferably at least 1:5 or higher, but preferably the stretch ratio is 1:10, 1:9, 1:8 and preferably 1:7 or lower. This means that the film is stretched in the longitudinal direction so that the stretched film has a final thickness that is 3 to 10 times less after stretching than before. A stretch ratio in the longitudinal direction above 9 or 10 tends to reduce the effect of light scattering and should therefore be avoided. Stretch ratios above 10 result in a significant reduction in workability (tears). A stretch ratio below 1:3 may result in a matte film.

Then the film is wound in the usual way.

Preferably, one or more of said strips of film material has a width that is less than the distance between the longitudinal threads.

Advantageously, a gap is formed between said one or more strips of film material and adjacent strips, said gap allowing ventilation through said screen.

Preferably at least 10%, preferably at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least at least 70%, more preferably at least 80%, more preferably at least 90% of the strips of film material in the greenhouse screen contain the specified single or multilayer polyethylene film.

- 6 039581

Preferably all strips of film material in the greenhouse screen are made from said single-layer or multi-layer polyethylene film.

Brief description of the drawings

The invention is described below with reference to some of the embodiments shown in the drawings.

Fig. 1 is an enlarged view of a warp screen made according to the first embodiment;

fig. 2 - part of the warp-knitted screen, made in accordance with the second embodiment;

fig. 3 is an enlarged view of a part of a woven screen;

fig. 4 is a part of a woven screen made in accordance with another embodiment.

Detailed description

Films made in accordance with the invention are excellently suited as light-diffusing films, in particular for the production of greenhouse screens.

The greenhouse screen 10, made in accordance with the present invention, contains a plurality of narrow strips of film material 11, fastened together by a thread frame 12, 13a, 13b, 14, 15, 18, 19. The strips of film material 11 are preferably located close to each other, so that they form an essentially continuous surface. In all embodiments, the spacing between the strips 11 has been exaggerated for clarity in order to make the thread frame visible. The screen has a longitudinal direction y and a transverse direction x, with the strips of film material 11 extending in the longitudinal direction. In some embodiments, the strips of film material 11 can also extend in the transverse direction. Typical strip widths are 2 to 10 mm.

In FIG. 1 strips of film material 11 are interconnected by means of a warp knitting process as described in EP 0109951. The thread frame comprises warp threads 12 forming loops or stitches and predominantly extending in the longitudinal direction y. The warp threads 12 are connected to each other by weft threads 13a and 13b, which run across the film strips.

In FIG. 1 shows an example of a mesh pattern for a fabric made in a warp knitting process using four guide pins, one for the strips of film material 11, two for weft connecting threads 13a and 13b running across the strip of film, and one for longitudinal warp threads 12.

The spaces between the strips of film material 11 are greatly exaggerated in the drawing in order to make the grid pattern clear. Usually the strips of film material 11 are located close to each other: edge to edge. The longitudinal warp threads 12 are located on one side of the screen, namely the underside, while the transverse weft connecting threads 13a and 13b are located on both sides of the fabric, the top and bottom sides. The term transverse in this respect is not limited to a direction perpendicular to the longitudinal direction, but means that the weft connecting threads 13a and 13b run across the film material strips 11 as shown in the drawings. The connection between the warp MD yarns 12 and the weft CD yarns 13a and 13b is preferably made on the underside of the fabric. Thus, the strips of film material 11 can be arranged close to each other: edge to edge, without being limited by the longitudinal warp threads 12.

The longitudinal warp threads 12 shown in FIG. 1 extend continuously in an unbroken manner along opposite edges of adjacent strips of film material 11 in the form of a series of knitted loops in a so-called open loop chain.

The transverse weft threads 13a and 13b extend above and below the strips of the film material 11 in the same place, i.e. opposite each other to fix the capture of strips of film material. Each knitted loop in the longitudinal warp threads 12 has two such transverse weft threads 13a and 13b that engage with it.

In FIG. 2 shows another example of a fabric mesh pattern similar to that shown in FIG. 1. The difference is that the weft transverse threads 13a and 13b run alternately over one and two strips of film material 11.

In FIG. 3 shows a woven screen in which strips of film material 11 are interconnected by 5 warp threads 14 running in the longitudinal direction y and intertwined with weft threads 15 passing through the strips of film material 11 mainly in the transverse direction x.

In FIG. 4 shows another embodiment of a woven screen as described in US Pat. The weft strips 11' in the transverse direction can, as shown in FIG. 4 always be on the same side of the warp strips 11 in the longitudinal direction, or may alternate on the upper and lower sides of the longitudinal warp strips 11. The warp and weft strips 11 and 11' are held together by a thread carcass containing longitudinal and transverse threads 18 and 19.

- 7 039581 from strips.

Strips (11) of the film made in accordance with the present invention can be combined with strips of other films. Such strips can be made from materials providing the desired heat transfer and shading properties and can be made from plastic, metal foil or plastic/metal laminates. It is also possible to make the screen with open areas free of stripes allowing ventilation through said screen.

To provide the desired light scattering properties, at least 10%, preferably at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60% , more preferably at least 70%, more preferably at least 80%, more preferably at least 90% of the screen surface area should be strips (11) of a single or multilayer film made in accordance with the invention. According to one embodiment, all of the strips (11) in the screen are made of the single or multilayer polyethylene film described herein, with the strips (11) adjacent to each other so that they form a substantially continuous surface. Alternatively, the film itself is installed in the greenhouse.

In some embodiments, the strips of film may be connected by a threaded scaffold having the ability to transfer liquid due to capillary action. Preferably, the thread frame is thermally bonded to at least one side of the strips of film material, while also those parts of the thread frame that are thermally bonded to the strips have the ability to transfer liquid by capillary action. The designs described above result in a reduction in the amount of light reaching the plants and therefore in cooling during the day. At the same time, they evenly distribute the remaining amount of light, due to the high light scattering in space, thus ensuring good illumination of all plants and plant parts. At night, these structures lead to a reduction in heat loss from the greenhouse to the street.

Polyethylenes.

Suitable high density polyethylenes (HDPEs) for use in the film material as described herein comprise ethylene homopolymer and ethylene-α-olefin copolymers (from about 0.1 to about 10% by weight). Suitable α-olefins include 1-butene, 1-hexene, 1-octene, the like, and mixtures thereof. Advantageously HDPE has a melt flow rate of 1.6 to 2.0 g/10 min at 190°C/5.0 kg and 19 to 26 g/10 min at 190°C/21.6 kg, preferably a melt flow rate is 1.7 to 1.9 g/10 min at 190°C/5.0 kg and 20 to 25 g/10 min at 190°C/21.6 kg, more preferably the melt flow rate is 1.8 g/10 min at 190°C/5.0 kg and 21 to 23 g/10 min at 190°C/21.6 kg (as determined according to ISO 1133-1).

Preferably HDPE has a density of 0.940 to 0.955 g/cm ³ , preferably a density of 0.943 to 0.950 g/cm ³ and more preferably a density of 0.946 to 0.948 g/cm ³ (ISO 1183-1). Examples of HDPE to be used are Hostalen ACP 7740 F2 from Lyondellbasell Industries Holdings, BV (melt flow rate is 1.8 g/10 min at 190°C/5.0 kg and 23 g/10 min at 190°C /21.6 kg (as determined according to ISO 1133-1), density 0.948 g/cm3 (ISO ^1183-1 )), or HDPE Hostalen GF 9045 F from LyondellBasell Industries Holdings, BV (melt flow rate is 1, 8 g/10 min at 190°C/5.0 kg and 21 g/10 min at 190°C/21.6 kg (as determined in accordance with ISO 1133-1), density 0.946 g/cm3 ⁽ ISO 1183 -one)).

The film also contains a certain amount of low density polyethylene (LDPE) or linear low density polyethylene (LLDPE). LDPE is defined by a density range of 0.910 to 0.940 g/cm ³ . LDPE has a high degree of short and long chain branching, which means that the chains also do not pack into a crystal structure. Therefore, it has weaker intermolecular forces than HDPE because the instantaneous dipole induced dipole attraction is smaller. By including a certain amount of LDPE in a single or multilayer film, the plasticity of the film is improved.

LLDPE is a substantially linear polymer (polyethylene) with a significant amount of short branching, usually obtained by copolymerizing ethylene with longer chain olefins. Linear low density polyethylene is structurally different from conventional low density polyethylene (LDPE) due to the absence of long chain branching. LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and higher α-olefins such as butene, hexene or octene (about 5 to about 15 wt %). The copolymerization process results in an LLDPE polymer which has a narrower molecular weight distribution than conventional LDPE and, in combination with a linear structure, has significantly different rheological properties. The density of LLDPE has a value in the range from about 0.865 to about 0.925 g/cm ³ .

Examples 1-6.

Examples 1-6 use the following polymers and masterbatches:

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HDPE1:

HDPE Hostalen ACP 7740 F2 (LyondellBasell Industries Holdings, BV) having a melt flow rate of 1.8 g/10 min at 190°C/5.0 kg and 23 g/10 min at 190°C/21.6 kg (as defined in accordance with ISO 1133-1); density 0.948 g/cm3 (ISO ^1183-1 ).

MB3.2: 90 wt.% LDPE + 10 wt.% SiO ₂ (D ₅₀ = 3.2 µm). Plastron ANT PO 10B, Plastron SAS, 15 Rue des Marguerites, 68920 Wintzenheim, France. SiO ₂ was injected into the LDPE through a twin screw extruder.

MB5.8: 80 wt.% LDPE + 20 wt.% SiO ₂ (D ₅₀ = 5.8 µm). ARGU BLOCK AB 212 LD, ARGUS Additive Plastics GmbH, Oberer Westring 3-7, 33142 Buren, Germany. SiO ₂ was injected into the LDPE through a twin screw extruder.

MB16: 90 wt.% LDPE + 10 wt.% SiO ₂ (D ₅₀ = 16 μm). Plastron ANT PO 10E, Plastron SAS, 15 20 Rue des Marguerites, 68920 Wintzenheim, France. SiO ₂ was injected into the LDPE through a twin screw extruder.

In table. 1 shows the compositions, manufacturing conditions, and obtained film properties.

Table 1

Extrud. Film 1 Extrud. Film 2 Extrud. Film 3 Extrud. Film 4 Extrud. Film 5 Extrud. Film 6 Film thickness, µm thirty thirty thirty thirty thirty thirty HDPE1 (%) 90 86 90 86 90 86 MW3.2 (%) ten fourteen MW5.8(%) ten fourteen МВ16(%) ten fourteen Stretch ratio 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 SiCB concentration (wt%) 2.0 2.8 1.0 1.4 1.0 1.4 Size D50 (µm) of SiO ₂ particles 5.8 5.8 sixteen sixteen 3.2 3.2 Transparency (%) 93.4 86.0 93.6 93.6 95.0 95.0 Turbidity (%) 52 58 29 33 22 25 diffusion factor 1.8 3.0 1.4 1.4 1.2 1.3

Results.

Films containing SiO ₂ particles with a D ₅₀ of 5.8 µm gave even and smooth films with good light scattering properties. The particles were not visible in the film and the polymer mixture was easily extruded.

Films containing SiO ₂ particles with a D ₅₀ of 16 μm gave films with high transparency, but the particles were visible in the film and the films could not scatter light well.

Films containing SiO ₂ particles with a D ₅₀ of 3.2 μm or more gave films with high transparency but poor light diffusion properties. The particles were not visible.

Examples 7-18.

The following polymers and masterbatches are used in the tests below:

HDPE2:

HDPE Hostalen GF 9045 F (LyondellBasell Industries Holdings, BV) having a melt flow rate of 1.8 g/10 min at 190°C/5.0 kg and 21 g/10 min at 190°C/21.6 kg (as defined in accordance with ISO 1133-1); density 0.946 g/cm3 (ISO ^1183-1 ).

MBARX F85LD:

Masterbatch containing 70 wt.% + LLDPE + 30 wt.% Flamestab™ NOR 116 (Argus Additive Plastics GmbH).

MB WPT 1181N:

Masterbatch containing 80 wt.% LLDPE + 20 wt.% CaCO ₃ (Walter Kunstoffe GmbH).

ARX 601 AB02LD: 80 wt% carrier polymer + 20 wt% SiO ₂ , silica particles have a D _{50 of} approximately 10 µm (Argus Additive Plastics GmbH). SiO ₂ was injected into the LDPE through a twin screw extruder.

ARXV17/848: 80 wt% carrier polymer + 20 wt% SiO ₂ , silica particles have a D _{50 of} approximately 5.8 µm (Argus Additive Plastics GmbH). SiO ₂ was injected into the LDPE through a twin screw extruder.

ARXV17/885: 90 wt% carrier polymer +10 wt% SiO ₂ , silica particles have a D _{50 of} approximately 2.8 µm (Argus Additive Plastics GmbH). SiO ₂ was injected into the LDPE through a twin screw extruder.

For test films 7-18, the extruded melts were formed into flat films by blown processes and stretched in the machine direction with

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table 2

Machine settings for film production

Extruder temperature T1 190 °C T2 200 °C TK 210 °C T4 210 °C T5 210 °C Line speed 3.3 m/min MDO temperature during MD stretching T1 120 °C T2 122 °C TK 124 °C T4 124 °C T5 123 °C Tb 70 °C Linear speed of the winder 17.9 m/min

In table. 3 shows the compositions and obtained properties of the film.

Table 3

Film Compositions and Obtained Film Properties

Test film 7 Test film 8 Test film 9 Test film 10 Test film 11 Test film 12 Test film 13 Test film 14 Test film 15 Test film 16 Test film 17 Test film 18 Thickness thirty thirty thirty thirty thirty thirty thirty thirty thirty thirty thirty thirty HDPE2 92 87 82 77 92 87 82 77 92 87 82 77 ARX 601 5 ten fifteen 20 ARX VI 7/848 5 ten fifteen 20 ARX VI7/885 ten 20 thirty 40 MBARX 2 2 2 2 2 2 2 2 2 2 2 2 MB WPT one one one one one one one one one one one one Copceptration one 2 3 4 one 2 3 4 one 2 3 4 The size ten ten ten ten 5.8 5.8 5.8 5.8 2.8 2.8 2.8 2.8 Stretch ratio 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 1:5.8 Transparency 94.3 93.2 92.7 93.0 94.5 94.2 93.8 94.0 94.8 94.7 94.7 94.7 Transparency at the exit hole 61.5 51.2 43.6 21.7 65.4 55.0 46.3 40.9 72.0 65.0 60.4 56.3 Factor 1.5 1.8 2.1 4.3 1.4 1.7 2.0 2.3 1.3 1.5 1.6 1.7 Optical purity(%) 66.5 49.4 39.5 18.7 69.5 49.4 35.2 26.6 89.3 83.2 76.0 68.7 Turbidity 39.2 50.6 60.5 84.3 36.0 48.6 60.8 65.2 26.9 35.4 42.2 47.7

The results presented in table. 3 are the average of five measurements.

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Results.

Test film results Test film 7 The film is diffuse and grainy with visible particles. The film resembles the feel of paper. Test film 8 The film is slightly diffuse and grainy with visible particles. The film feels like paper. Test film 9 The film is inhomogeneous with short visible veins due to improper mixing and stretching of the film. The film feels like paper. Test film 10 Seals form in the film and the film cannot be stretched correctly. Test film 11 The film is diffuse, but homogeneous. Test film 12 The film is slightly diffuse, but uniform. Test film 13 The film is transparent and uniform. Test film 14 The film is transparent with several visible veins. Test film 15 The film is transparent but diffuse. The film is not completely homogeneous. Test film 16 The film is transparent but diffuse. The film is not completely homogeneous. Test film 17 The film is transparent, cloudy, but scattering. The film is not completely homogeneous. Test film 18 The film is transparent, cloudy, but scattering. The film is not completely homogeneous.

Analytical methods.

The following analytical methods were used to determine the parameters used.

Measuring the average particle diameter D50.

Determination of the average particle size D50 was carried out using a Malvern Mastersizer 2000. To do this, the particles were dispersed in water and transferred to a cuvette, which was analyzed in a meter in which the particle size was determined using laser diffraction. Typically, when the detector captures the image intensity of the diffracted laser light from the angle dependent light intensity using a mathematical correlation function, the particle size distribution is calculated. The particle size distribution is characterized by two parameters, the median value D50 (= location measure for the mean) and the degree of spread SPAN98 (= measure of the spread in particle diameter). The test procedure was carried out automatically and included the mathematical determination of the value of D ₅₀ .

Transparency.

Transparency was measured according to ASTM-D 1003-61 method A) from HAZE-GARD PLUS from BYK-Gardner GmbH, Germany.

Optical purity.

Determination of optical purity is carried out in accordance with ASTM-D-1003 and using HAZE-GARD PLUS from BYK-Gardner GmbH (BYK-Gardner GmbH, Lausitzer Strasse 8, 82538, Geretsried, Germany). The light is deflected within a small solid angle so that the amount of scattered light is concentrated in a narrow fraction. Optical purity is measured in an angular range of less than 2.5°. To measure the optical purity, the film is placed close to the light exit when the measurement is taken (image sharpness).

Evaluation of the light-scattering property (measurement of the diffusion factor SF).

Light scattering properties are of particular importance for a film made in accordance with the invention. The measurement was carried out using a transparency/opacity meter HAZE-GARD PLUS from BYK Gardner (BYK-Gardner GmbH, Lausitzer Strasse 8, 82538 Geretsried, Germany). For the SF measurement, the transparency of the film is measured as it is held under tension in the clamping ring, holding the film flush with the measurement hole used to measure haze and clarity, as described in ASTM D-1003-61 (Method A). The clamped film is then held flush with the light outlet (as in optical purity measurements) and transparency is measured again. The light diffusion factor SF corresponds to the ratio of these two readings.

Diffusion Factor (SF) = Clarity (measured in accordance with ASTM D-1003-61 Method A)/

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CLAIM

Claims (12)

CLAIM 1. Greenhouse screen containing strips (11) of film material, which are interconnected by a thread system of transverse threads (12, 14, 18) and longitudinal threads (13a, 13b; 15; 19) through the process of knitting, warp knitting or weaving with the formation of a continuous products, characterized in that at least some of the strips (11) contain a single-layer or multilayer film with a thickness of 20 to 50 μm, and the specified film contains polyethylene and at least 2.0 to 4.0 wt.% particles SiO ₂ based on the total weight of the film, and these particles of SiO ₂ have a D ₅₀ from 5 to 7 μm. 2. Greenhouse screen according to claim 1, characterized in that said polyethylene is high density polyethylene (HDPE). 3. Greenhouse screen according to claim 2, characterized in that said HDPE has a melt flow rate from 1.6 to 2.0 g/10 min at 190°C/5.0 kg and from 19 to 26 g/10 min at 190°C/21.6 kg (ISO 1133-1) and density from 0.940 to 0.955 g/cm ³ (ISO 1183-1). 4. Greenhouse screen according to any of the preceding claims, characterized in that said film has a transparency of at least 70%, such as at least 75, 80, 85, 86, 87, 88, 90, 91, 92, 93 % or greater, measured in accordance with ASTM-D 1003-61 Method A. 5. Greenhouse screen according to any one of the preceding claims, characterized in that said film has a haze of 50 to 75%, preferably 54 to 70%, more preferably 57 to 67%, measured according to ASTM-D 1003- 61 method A using HAZE-GARD PLUS from BYK-Gardner GmbH (BYK-Gardner GmbH, Lausitzer Strasse 8, 82538, Geretsried, Germany). 6. Greenhouse screen according to any of the preceding claims, characterized in that said film has a diffusion factor (SF) of 1.5 to 7, preferably 1.8 to 6, more preferably 1.9 to 5, or most preferably 2 up to 4 (measured as ASTM D 100361 (Method A) Clarity/Clarityport Clarity). 7. Greenhouse screen according to any one of the preceding claims, characterized in that said film has a total thickness of 20 to 40 µm, preferably 20 to 35 µm. 8. Greenhouse screen according to any of the preceding claims, characterized in that said film contains UV stabilizers in an amount of from 0.2 to 4 wt.% based on the weight of the film, where said UV stabilizers are selected from the group consisting of ultraviolet absorbers , excited state quenchers or hindered amine light stabilizers (HALS). 9. Greenhouse screen according to any one of the preceding claims, characterized in that the film is uniaxially stretched to a ratio of 1:3 to 1:10, eg 1:4 to 1:8, eg 1:5 to 1:7. 10. Greenhouse screen according to any one of claims 1 to 9, characterized in that one or more strips of film material (11) have a width smaller than the distance between the longitudinal threads (13a, 13b, 15, 19). 11. Greenhouse screen according to claim 10, characterized in that a gap is formed between said one or more strips of film material (11) and adjacent strip(s) of film (11), said gap providing ventilation through said screen. 12. Greenhouse screen according to any one of claims 1 to 11, characterized in that at least 10%, preferably at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90% and most preferably all strips of film material (11) in the greenhouse screen contain the specified single-layer or multilayer polyethylene film.