JPH0443933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an agricultural and horticultural film that has excellent anti-fogging properties. More specifically, after corona discharge treatment is applied to the surface of a polyolefin film, radically polymerizable monomers are surface graft-copolymerized using a redox polymerization reaction, and hydrophilic groups are introduced onto the film surface, resulting in antifogging properties. This invention relates to an agricultural and horticultural film that has improved sustainability. Because polyolefin has good moldability, it can be easily made into a film, and this film also has excellent characteristics in terms of transparency, water resistance, flexibility, and mechanical strength, and its uses are extremely wide. It covers a wide range of fields. It is also widely used in the agricultural and horticultural field as a covering film for greenhouses, tunnels, greenhouses, etc. However, since this polyolefin film is completely hydrophobic due to its chemical structure, this may appear as a drawback. For example, condensation of water droplets on the film surface is apt to occur, which reduces the light transmittance and prevents the crops from growing sufficiently, or the attached water droplets fall and damage or damage the crops. It is well known that this is the cause. In order to improve such drawbacks, there is generally a method of kneading a hydrophilic substance such as a surfactant into molding.
Alternatively, a method has been adopted in which a hydrophilic surfactant or water-soluble polymer is applied to the surface of the molded article. However, all of these modification methods achieve an antifogging effect by forming a film of a hydrophilic substance on the film surface, and the film of a hydrophilic substance that is easily soluble in water is washed away by water and disappears in a short period of time. There is a problem that the anti-fogging property is reduced. On the other hand, attempts have been made to improve the durability of anti-fogging by using lipophilic surfactants, adsorbing ionic electrolytes, etc.; It is a coating of a hydrophilic substance that does not have any properties, and its durability is limited, so it cannot be said to be a satisfactory method. The present inventors have arrived at the present invention as a result of extensive research into a method of imparting semi-permanent sustainability by graft polymerizing a hydrophilic substance onto the surface of a polyolefin film in order to improve the anti-fog durability. That is, in the present invention, 1 millijoule/millijoule/millijoule is applied to a polyolefin film by corona discharge in the atmosphere.
After applying energy of cm ³ to 10 joules/cm ³ , a hydrophilic and radically polymerizable monomer solution containing a reducing agent that forms a redox catalyst is applied in a nitrogen gas atmosphere to proceed with graft polymerization. The present invention provides an agricultural and horticultural film which has excellent anti-fogging properties and has a hydrophilic group introduced onto the surface of the film. The polyolefin film used in the present invention is one that can generate peroxide capable of initiating graft polymerization by corona treatment.
Examples include films of polyethylene, ethylene-vinyl acetate copolymer, and polypropylene, and films containing additives may also be used as long as graft polymerization is possible. For the corona discharge treatment of the present invention, a continuous treatment device consisting of an electrode and a treatment roller, which is normally used industrially to impart printability, is used.
The optimum processing conditions for corona discharge vary depending on the type of material, thickness and processing speed, but the energy supplied is approximately in the range of 1 millijoule to 10 joules per cm ³ of film surface area. The radically polymerizable monomer used in the present invention is not particularly limited as long as it imparts hydrophilicity after graft polymerization. For example, acrylamide, acrylamide compounds such as 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid compounds such as acrylic acid and methyl acrylate, sodium parastyrenesulfonate, diallylamine, allyl alcohol, etc. are used. Graft polymerization in the present invention is initiated by a corona discharge treatment in which peroxide generated on the film surface is decomposed by a reducing agent to generate radicals. The reducing agent used is a redox initiator.
There is no particular limitation as long as it is used, but if the process is carried out under conditions that are easily affected by impurities, such as when applying a small amount of monomer solution to the film surface, use a somewhat excessive amount of highly effective reducing agent. It is desirable to use it for For example, when using a reducing agent that combines sodium metaacid sulfite/ferrous sulfate, the monomer solution
0.5 to 20 mmol per g/2×10 ^-4 to 8×
It is desirable to add 10 ^-3 mmol. The method and apparatus for surface graft polymerization in the present invention are not particularly limited, but when applying a monomer solution onto the surface of a film treated with corona discharge, uneven adhesion of the monomer solution may occur due to the hydrophobicity of the film surface. In order to prevent this and achieve uniform surface treatment, cover the monomer-coated surface with a protective material.
A method of proceeding with a graft polymerization reaction is preferred.
An example of this method is shown in FIG. This consists of a corona treatment step [], a graft polymerization step [], a washing step [], a drying step [], and a winder []. The raw material film a is subjected to a corona discharge treatment on one side or both sides in a corona discharge treatment step [] which is equipped with a corona discharge electrode 1 and a corona discharge treatment roll 2, and then fed into a graft polymerization chamber 3 sealed with nitrogen. Here, a monomer solution to which a reducing agent has been added is applied from the monomer supply port 4, a net-like protective material 5 is inserted, and the material is wound up using a winding machine 6. Thereby, the monomer solution can be brought into uniform contact with the film surface. The reaction is completed by leaving it as it is for the required time, and then washing, drying, and winding are performed in this order to complete the surface treatment. As mentioned above, the agricultural and horticultural film with excellent anti-fog durability of the present invention has hydrophilic groups chemically bonded to the film surface, and the result is semi-permanent.
Compared to the conventional method of kneading or coating an antifogging agent, its durability is outstanding. EXAMPLES Hereinafter, the present invention will be explained in detail with reference to examples, but the present invention is not limited to the examples. The antifogging property was evaluated using the following method. The evaluation film was placed on a water tank kept at a water temperature of 60°C so as to maintain an inclination angle of 30 degrees with respect to the water surface, and the state of condensation of water droplets on the film surface was observed with the naked eye. In this way, initial antifogging properties and sustained antifogging properties were evaluated. Initial anti-fogging properties here are expressed as the time from when the film surface begins to become cloudy after the test starts, until this clouding turns into water droplets and begins to run off.The shorter the time, the better the initial anti-fogging properties are judged to be. Did. In addition, the continuous antifogging property was evaluated by the period during which the film surface remained transparent due to the droplet phenomenon, and the longer this state was maintained, the better. Further, the contact angle was measured using a goniometer type contact angle measuring device manufactured by Elma Optical Co., Ltd., and the measured value for water was obtained. Example 1 A low-density polyethylene film (density 0.923, thickness 100 μm, width 25 cm) was surface-treated using the processing apparatus shown in FIG. 1 at a processing speed of 2 m/min. The corona discharge treatment device is manufactured by Kasuga Electric Co., Ltd. (oscillator:
HFSS−101, frequency: 30KHz, output voltage: 34KV
(maximum output voltage 1KW, electrode shape: knife shape, length 30cm) was used. The corona discharge treatment conditions are as follows:
0.9mm, atmosphere is air, collector current 3A,
Continuous processing was performed under the condition of an output voltage of 250W. The energy applied by the corona discharge treatment is 2.5 joules/cm ³ . The corona discharge-treated film was sent into a nitrogen-sealed graft polymerization chamber and coated with a monomer solution. As a monomer solution, sodium metaacid sulfite (Na ₂ S ₂ O ₅ )/ferrous sulfate (FeSO ₄ .7H ₂ O) was added as a reducing agent to a 20% aqueous solution of acrylamide per 100 g of the aqueous solution. mmol/1.4×10 ^-3 mmol was used. At the same time as applying the monomer solution, the mesh protective material (thickness
50μm, distance 1.5mm, polyvinyl chloride resin mesh)
The mixture was sandwiched and rolled up, and left to react at room temperature for 2 hours. The protective material was then peeled off from the low-density polyethylene film, taken out in water, washed with water, and dried to obtain a surface-treated film. The antifogging properties of this surface-treated film were evaluated, and the observation results of the antifogging properties over time are shown in the table. Example 2 In Example 1, a 20% aqueous solution of sodium p-styrene sulfonate was used as the monomer solution, and sodium metaacid sulfite (Na ₂ S ₂ O ₅ )/ferrous sulfate (FeSO Example 1 was followed except that 5.3 mmol/3.6× ^{10 -3} mmol of _{4.7H 2} O) was added to 100 g of aqueous solution. The results of antifogging evaluation using this surface treated film are shown in the table. Example 3 The same procedures as in Example 1 were carried out except that a 20% aqueous solution of acrylic acid was used as the monomer solution. The results of antifogging evaluation using this surface treated film are shown in the table. Comparative Examples 1 to 2 The results of antifogging evaluation using the raw material low density polyethylene films used in Examples 1 to 3 above and films subjected only to corona discharge treatment are shown in the table. Example 4 In Example 1, an ethylene-vinyl acetate copolymer film (vinyl acetate content 15% by weight, width 25 cm, thickness 100 μm) was used as the raw material film, and a 20% aqueous solution of acrylamide was used as the monomer solution. , and meta-acid sodium sulfite (Na ₂ S ₂ O ₅ )/ferrous sulfate (FeSO ₄ 7H _{2 )} as a reducing agent.
O) per 100g of aqueous solution, 0.65 mmol/4.5
All procedures were carried out according to Example 1, except that x10 ^-4 mmol was used. The results of antifogging evaluation using this surface-treated film are shown in the table. Example 5 In Example 1, an ethylene-vinyl acetate copolymer film (vinyl acetate content:
_{15 wt .} )/ferrous sulfate (FeSO ₄ .7H ₂ O) in an amount of 1.3 mmol/9×10 ⁻⁴ mmol per 100 g of aqueous solution was used. The results of antifogging evaluation using this surface-treated film are shown in the table. Comparative Examples 3 to 4 The results of antifogging evaluation using the raw material ethylene-vinyl acetate copolymer film used in Examples 4 and 5 above and a film obtained by performing only corona discharge treatment on this film are shown in the table. . Comparative Examples 5 to 7 In order to compare the antifogging properties with currently commonly used agricultural films, commercially available agricultural films and ethylene-vinyl acetate copolymer films were also tested for their antifogging properties. Antifogging properties of ethylene-vinyl acetate copolymer films specially formulated to the target were evaluated in the same manner as in the Examples. The results are shown in the table.

[Table] △ Water droplets appear in some areas × No anti-fog property

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the process for carrying out the surface treatment of the polyolefin film of the present invention. DESCRIPTION OF SYMBOLS 1... Corona discharge electrode, 2... Corona discharge treatment roll, 3... Graft polymerization chamber, 4... Monomer supply port, 5... Net-like protective material, 6... Reaction winder,
7...Cleaning tank, 8...Drying room, 9...Product winding machine.

Claims (1)

[Claims] 1 After applying energy of 1 millijoule/cm ³ to 10 joules/cm ³ to a polyolefin film by corona discharge in the atmosphere, a radically polymerizable hydrophilic film is added with a reducing agent that forms a redox catalyst in a nitrogen gas atmosphere. This agricultural and horticultural film has excellent antifogging properties and is made by coating a monomer solution with good properties, allowing graft polymerization to proceed, and introducing hydrophilic groups onto the film surface.