JPS606968B2 - Agricultural laminated film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to agricultural laminate films, and more particularly to agricultural laminates that are substantially transparent to visible light and substantially opaque to infrared radiation. It's about film.

Conventionally, glass, polyvinyl chloride film, and polyethylene film have been mainly used as greenhouse covering materials for greenhouse cultivation of agricultural products. Glass has excellent durability, transparency, and heat retention properties, making it ideal as a greenhouse covering material.
Unfortunately, glass has the drawbacks of being brittle, easily broken, and having poor workability. Furthermore, since it is not possible to reduce the thickness, the weight per unit area covered becomes large and the facility cost becomes high. PVC film has light transmittance,
It has excellent durability, toughness, workability, and economy, and although it is not as good as glass in terms of heat retention, it is superior to polyethylene film, which will be described later, so it can be used as a covering material for agricultural greenhouses and tunnels. Most commonly used these days.

Agricultural polyvinyl chloride film is commonly called "agricultural vinyl," and most of it is made of so-called semi-rigid or soft polychloride film containing low-molecular plasticizers for its strength, workability, and economic efficiency. It's vinyl film. However, although polyvinyl chloride films containing these plasticizers have excellent initial light transmittance, after long-term use, the plasticizer itself or other components such as additives and auxiliaries are degraded by the effects of sunlight, repeated cold and hot temperatures, etc. transfers to the film surface, and as a result, the film surface becomes sticky, attracts dust and the like in the air, becomes dirty, and has the disadvantage that light transmittance is significantly reduced. Although polyethylene film is slightly inferior to polyvinyl chloride film in terms of initial light transmittance, it does not contain elusive substances such as low-molecular plasticizers, so it is not as good as the above-mentioned polyvinyl chloride film. No damage occurs and the light transmittance of the film continues to a considerable extent, but on the contrary, the light transmittance decreases due to adsorption of dust due to charging.

Furthermore, a serious drawback of polyethylene film as an agricultural film is that it has poorer heat retention properties than glass or polychloride-based films. This drawback is clearly recognized from experience at the farmer level, and although polyethylene film has the aforementioned advantages of long-lasting light transmittance and is advantageous in terms of cost, This is the main reason why it has not been used as a film for covering greenhouses. As described above, heat retention is an extremely important property for agricultural films.
In general, the heat retention property of a greenhouse covering material refers to the magnitude of the greenhouse effect (greenhouse effect), and in the daytime, the heat retention property of a greenhouse covering material refers to the magnitude of the greenhouse effect, which is effective against visible light, which accounts for the main part of the energy radiated by the sun during the day. is transparent, so it supplies and absorbs as much energy as possible to the plants and the earth in the greenhouse, and conversely, the infrared rays emitted by the plants and the earth (which can almost be regarded as black body radiation, so at around room temperature the wavelength It can be considered to follow Planck's law of blackbody radiation, which has a peak around 1-kite.

), and the greater the ability to prevent infrared radiant energy from dissipating to the outside, the greater the greenhouse effect. Generally, it is common knowledge that the visible light transmittance of materials used as greenhouse covering materials is in the range of 30 to 100%, and in the case of transparent films, it is usually 50% or more. .

Therefore, ``Among the contents of the greenhouse effect mentioned above, regarding the transmitted energy of visible light, the difference depending on the type of covering material is at most 2.
~3 times as much. On the other hand, regarding the transmittance of radiant infrared rays,
There is an extremely large difference depending on the type of coating material; for example, the transmittance of ordinary glass and polyethylene film differ by more than 100 times. In particular, at night, there is no inflow of solar energy, and only infrared radiation from plants and the earth occurs. (Of course, heat transfer to the air inside the greenhouse, heat transfer by air convection, heat transfer by water evaporation, heat transfer to the outside through covering materials and other materials, etc. occur in parallel, but (Heat transfer by infrared radiation is most important.) Therefore, the degree of cooling in a greenhouse at night is determined primarily by the ability of the coating to block infrared radiation.Based on this logic, greenhouse coatings The heat retention ability of a material can be considered in relation to the infrared transmittance of nearby wavelengths.In order to completely block infrared radiation at night, it is necessary to use a mirrored metal plate to completely reflect infrared rays. is the most effective, but it is not used because it loses visible light transparency during the day.

As the next best method, it has been proposed to form a metal vapor-deposited thin film on the surface of a transparent resin film to impart infrared opacity while maintaining visible light transmittance to some extent. However, with this method, the transmittance of visible light is inevitably 5.
There are problems such as a decrease to 0% or less and difficulty in performing vacuum deposition uniformly over a wide area. Furthermore, there is a proposal to improve heat retention by dispersing fine powder of an inorganic compound with high infrared absorption ability in a resin film such as polyethylene or polypynyl chloride.

However, this method requires the addition of a fairly large amount of inorganic powder in order to increase heat retention to the required level.
Therefore, visible light transmittance decreases. In addition, even if an attempt is made to improve transparency by making the powder ultra-fine, the L inorganic fine powder tends to aggregate and coarsen in the hydrophobic resin, making it difficult to transmit visible light and infrared rays at the same time. I can't satisfy you. As explained in detail above, ``Conventionally known greenhouse covering materials have advantages and disadvantages, and in particular, resin films that have optical properties such as glass that are transparent to visible light and opaque to infrared rays are not known. It was strongly requested.

The present invention provides a resin film that can meet this demand.

That is, the present invention has a hydrophobic resin layer on the surface of a polyvinyl alcohol film made of a polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units, and is substantially transparent to visible light, The invention relates to an agricultural laminated film that is substantially opaque to infrared rays, and the laminated film has the visible light transmittance and heat retention properties of glass and the toughness, workability, and workability of conventional resin films. It can be said to be ideal as a greenhouse covering material because it is also economical. The present inventors have discovered that a polyvinyl alcohol film made of a polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units, which has a high infrared absorption ability by itself, is extremely resistant to visible light. Although it is transparent, it is extremely opaque to infrared rays and has excellent heat insulation and heat retention properties against heat radiation, and we have found the beginnings of solving the various problems of conventional greenhouse covering materials mentioned above. Open.

In other words, polyvinyl alcohol resin containing 30 mol% or more of pinyl alcohol units has a large number of alcoholic hydroxyl groups in its molecules, so it has 8 to 1 It has a mode of molecular motion with strong absorption in the wavelength region.

In addition, polyvinyl alcohol resin containing 30 mol% or more of pinyl alcohol units has a remarkable ability to emit infrared rays from the resin itself at the same temperature, and although it is transparent, it has a radiation system number close to that of a perfect black body. . Therefore, it has a great ability to radiate the infrared energy once absorbed into the greenhouse as infrared rays, and therefore has high heat retention properties. Furthermore, since polypynyl alcohol resin is aggregated by strong intermolecular forces including hydrogen bonds between hydroxyl groups in the molecules, its film also has excellent mechanical properties. These characteristics of polyvinyl alcohol resins make them ideal as agricultural film materials. However, polypynyl alcohol resin alone cannot be said to have excellent water resistance.
Since it swells and stretches when exposed to water, it is suitable for applications such as greenhouse linings that are directly exposed to wind and rain, and has a hydrophobic resin layer on the surface of the polyvinyl alcohol film, which is virtually resistant to visible light. Agricultural laminated film that is transparent and substantially opaque to infrared rays has extremely good water resistance, and can be used as a greenhouse covering material.
The present invention was completed after discovering that the present invention is extremely practical and suitable. Contains 30 mol% of vinyl alcohol units, which are one component of the agricultural laminated film in the present invention.
A polyvinyl alcohol film made of the polyvinyl alcohol resin containing the above can be easily obtained by a conventionally known method using the polyvinyl alcohol resin.

30 mol% of vinyl alcohol units used in the present invention
The polyvinyl alcohol resins containing the above include polyvinyl alcohol, polyvinyl acetal derived from polyvinyl alcohol, polyvinyl formal, polyvinyl butyral, polyvinyl benzal, and polyvinyl alcohol in which a part of the hydroxyl group is chemically modified or reacted. Examples include so-called modified polyvinyl alcohols containing 30 mol% or more of vinyl alcohol units.

Polyvinyl alcohol is usually produced by saponifying pinyl acetate obtained by polymerizing vinyl acetate, but it can also be obtained by saponifying polyvinyl trifluoroacetate, polypinyl formate, polypinyl benzoate, etc. .

Furthermore, by saponifying a copolymer of vinyl acetate and another vinyl monomer, a copolymer containing vinyl alcohol polymerized units, that is, a polyvinyl alcohol copolymer can be obtained.

These polyvinyl alcohol copolymers and their acetalized products, modified products, which contain 3 vinyl alcohol units.
Those containing 0 mol% or more can also be used in the present invention. Vinyl monomers that can be copolymerized with vinyl acetate and can therefore be used as constituents of polyvinyl alcohol copolymers include ethylene, vinyl fluoride, vinyl chloride, styrene, methyl methacrylate, vinyl versatate, and lauryl vinyl ether. , olefin sulfonic acid (salt), etc.

A polyvinyl alcohol resin containing all of the above-mentioned polymer compounds is useful for the purpose of the present invention, but in order to obtain a film with sufficient infrared opacity, it is necessary to rate is 30%
It is necessary that it is at least 50%, and more preferably 50%.
The above is desirable.

In addition, when molding the polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units into a film, small proportions of ultraviolet absorbers, coloring pigments, fillers, deterioration inhibitors, plasticizers, and other resins are added. Additives such as ingredients can be added.

Furthermore, in the case of a resin component that can be mixed with the polypynyl alcohol-based resin, it is also possible to form a blend film depending on the purpose. The hydrophobic resin layer, which is another component of the agricultural laminated film of the present invention, is made of a hydrophobic resin such as polyethylene, polypropylene, or polyvinyl chloride.

There are no particular restrictions on the method of laminating the agricultural laminated film of the present invention, but for example, a polyvinyl alcohol film made from a polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units and a polyvinyl alcohol film prepared separately from it are used. Alternatively, a hydrophobic film formed from a hydrophobic resin may be laminated by a conventionally known method, or a solution or melt of the hydrophobic resin may be applied on the surface of the polyvinyl alcohol film. A laminated film may be formed by coating and providing a hydrophobic resin layer.

Alternatively, on the contrary, 30 vinyl alcohol units may be added to the surface of a hydrophobic film previously formed from a hydrophobic resin.
A film may be formed by coating a solution or melt of a polyvinyl alcohol resin containing mol% or more to form a laminated film. In the agricultural laminated film of the present invention, in order to obtain a greenhouse coating material with good water resistance, it is often preferable that hydrophobic resin layers be provided on both surfaces of the polyvinyl alcohol film.
Of course, a laminated film having a hydrophobic resin layer on one surface may also be used.

In the present invention, a laminated film that is substantially transparent to visible light means a laminated film having a visible light transmittance of at least 30% or more, preferably 50% or more. In addition to the above-mentioned laminated films, the above-mentioned laminated films can also be bonded to loose fabrics, cheesecloth, fabrics, non-woven fabrics, paper, etc. that are woven into a rough texture that allows light to pass through. These include composite laminated films made of laminates, fiber-reinforced laminate films made of short fibers or long fibers inside the laminate films, and the like.

The mode of presence of the polyvinyl alcohol film in the agricultural laminated film of the present invention is arbitrary, and the purpose is as long as it exists substantially over the entire surface of the laminated film and can effectively absorb and re-radiate infrared rays. can be achieved.

Therefore, the film itself made of a polyvinyl alcohol resin containing 30 mol % or more of vinyl alcohol units does not need to be a completely continuous film, and may be discontinuous. It may also have holes here and there. The agricultural laminated film of the present invention, which is substantially transparent to visible light and substantially opaque to infrared rays, is usually a sheet-like product with a thickness of several tens of mm to several hundred mm. A reasonable thickness should be determined based on common sense depending on the purpose of use.
For example, as a covering material for tunnel cultivation, a thickness of 20 to 5 mm is sufficient, and for medium and large greenhouse cultivation, a thickness of 10 to 5 mm is sufficient.
The thickness of the desk is 200 mm. These thicknesses are mainly determined by the required level of mechanical properties (strength), and will be different values in the case of composite laminated films and fiber-reinforced laminated films. In the agricultural laminated film of the present invention, the basic idea of the present invention is as follows.
Utilizing the high infrared absorption ability and infrared re-radiation ability of a polyvinyl alcohol film made of a polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units, it is substantially transparent to visible light and infrared rays. Various embodiments may be adopted as long as they do not violate the principle of producing an agricultural film with good heat retention that is substantially impermeable to water.

The principles, embodiments, and effects of the present invention will be explained in more detail by the following examples, which are given merely as examples, and modifications of these embodiments and operations will be apparent to those skilled in the art. This is not intended to limit the present invention in any way, since it would be easy to make an analogy.

Parts and percentages used in the following examples are by weight unless otherwise specified.

Example 1 A three-layer sandwich film was prepared by using a polyvinyl alcohol film made of a single polyvinyl alcohol resin as an intermediate layer and laminating hydrophobic resin films on both sides.

In lamination, films coated with an epoxy or isocyanate adhesive are stacked together and passed through a heated roll. This was done by a so-called dry lamination method.
As a control sample, a film was also created in which three identical hydrophobic resin films were laminated. The polyvinyl alcohol film used was ■Polyvinyl alcohol resin [■Kuraray Poval HC manufactured by Kuraray (Saponification degree: 9)
9.9 mol %)] polyvinyl alcohol film (Kuraray Vinylon Film), ■ Ethylene-vinyl alcohol copolymer resin [■ Kuraray Eval Resin (
Ethylene-vinyl alcohol copolymer film made of ethylene unit content: 33 mol%) (Eval Film, manufactured by Kuraray); Alcohol copolymer film, ■ Styrene-vinyl alcohol comb-shaped copolymer resin [■ Manufactured by Kuraray,
Styrene-vinyl alcohol comb-shaped copolymer film made of styrene unit content: 10 mol%] ・■ Butyralized polyvinyl alcohol resin made of butyralized polyvinyl alcohol resin (butyralization degree 60 mol%, vinyl alcohol unit content: 40 mol%) Five types of alcohol films were used.

Two types of hydrophobic resin films were used: a polyethylene film and a polypropylene film whose adhesion was improved by corona discharge treatment.

Each layer has a thickness of 5 layers. The three-layer sandwich films obtained by laminating hydrophobic films on both sides were transparent and had good water resistance.

Water resistance was evaluated by visually observing the smoothness of the film after repeating the drying cycle five times with a water immersion rating of 5,000, and good results were marked with a mark of ◯. The results are shown in Table 1. Table 1 also shows the measurement results of visible light transmittance and infrared transmittance of various laminated films prepared by the above-mentioned method.

The visible light transmittance is determined from the ultraviolet-visible light absorption spectrum chart of the laminated film (measured with a self-recording spectrophotometer E-Rainbow type manufactured by Hitachi). Degree value (%)
It was expressed as The value of infrared transmittance (%) is determined from the infrared absorption spectrum chart of the laminated film measured by Hitachi's self-recording infrared spectrophotometer EPI-○2 model', near the peak of the infrared radiation energy spectrum of a blackbody near room temperature. The average value is calculated by integrating the infrared transmittance in the range of 8 to 1 wavelength. The abbreviations of resin material names in the table each have the following meanings.

PVA: Polyvinyl alcohol resin [Kuraray Boval HC manufactured by Kuraray (saponification degree: 99.9 mol%)] EVA-
1: Ethylene-vinyl alcohol copolymer resin [■ EVAL resin manufactured by Kuraray (ethylene unit content: 33 mol%)]
EVA-2: Ethylene-vinyl alcohol copolymer resin (ethylene unit content: 60 mol%) SVA: Styrene-vinyl alcohol comb-shaped copolymer resin [■ manufactured by Kuraray, styrene unit content: 10 mol%] B-PVA : Butyralized polyvinyl alcohol resin (butyralization degree 60 mol%, vinyl alcohol unit amount: 40 mol%) PE: High pressure polyethylene (Sumikasen manufactured by Sumitomo Chemical) PP: Polypropylene (Chisso Polyp manufactured by Chisso.

) Table 1 From the results in Table 1, a three-layer sandwich film in which a polyvinyl alcohol film made of a polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units is used as an intermediate layer and hydrophobic films are laminated on both sides has water resistance. It is easily understood that it has excellent visible light transmittance and infrared ray opacity.

Example 2 In order to test the heat retention properties against night radiation when various films are used as greenhouse covering materials, a model greenhouse made of expanded polystyrene was created, various covering materials were attached to the closed part of the top surface, and the greenhouse was exposed to sunlight on an outdoor day. The maximum temperature inside the box was measured within two short periods of time.

A maximum/minimum thermometer was used for temperature measurement. Inside the model greenhouse, a mixture of kaolin clay and black iron oxide powder was placed on the bottom to create a black body absorber/radiator. As a control, the temperature of a model greenhouse without any covering material attached to the top opening was measured. Since the absolute values of the maximum and minimum temperatures vary significantly depending on weather conditions, the temperature difference (ΔT) from the control was used as a measure of heat retention. The experiment was conducted on a sunny day between late July and mid-September.

Seven types of films shown in Table 2 were used as the covering materials.

Sample numbers 1, 2, 3, and 4 are multilayer laminated films, and samples numbers 5 to 7 are single-layer resin films. Table 2 *The meanings of the abbreviations are as follows.

PVA: Polyvinyl alcohol resin [■ Kuraray Poval HC manufactured by Kuraray (saponification degree: 99.9 mol%)] EVA-
13 ethylene-vinyl alcohol copolymer resin [■Eval resin manufactured by Kuraray (ethylene unit content: 33 mol%)]
EVA-2: Ethylene-vinyl alcohol copolymer resin (ethylene unit content: 60 mol%) B-PVA: Butyralized polyvinyl alcohol resin (butyralization degree 60
mol%, vinyl alcohol unit content: 40 mol%)]P
E: High pressure polyethylene (Sumikasen manufactured by Sumitomo Chemical) PP
: Polypropylene (Chisso Polypro) PVC:
Consists of European polyvinyl chloride, 10 parts of polyvinyl chloride resin, and 50 parts of a plasticizer (dioctyl phthalate).

The values of △T (max) and △T (min) in the table are the maximum daytime temperature T (max) and the minimum night temperature T (min) of the model greenhouse covered with the film, respectively.
) and those without coating (To(max) and To(min)).

That is, △T (max) = T (max) - To (max) △T (
min)=T(min)−To(min).

Claims (1)

[Claims] 1. A polyvinyl alcohol film made of a polyvinyl alcohol resin containing 30 mol% or more of vinyl alcohol units has a hydrophobic resin layer on the surface, and is substantially transparent to visible light and infrared rays. is a laminated agricultural film that is substantially opaque.