JPS6011050B2 - Agricultural mulching film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an agricultural mulching film, in which a black colored polyethylene film is used as a mulching film and has improved heat shrinkage when exposed to sunlight and the temperature rises. related to things.

Mulching film is becoming one of the main uses for agricultural films, and in so-called mulch cultivation, which uses this mulching film, for example, the entire ridge in which strawberries are planted can be planted with one strawberry plant. The neck of each plant is exposed and the board is covered with a film for heat retention effect.
It is designed to enhance the effect of preventing weed growth.

As this mulching film, there is a demand for a film that has sufficient strength even if it is thin, is inexpensive, and has a low heat shrinkage rate.

Low-density polyethylene is used as this mulching film, but conventional ones have a high heat shrinkage rate.
For example, if you cover the entire enemy with a length of 50, if
% heat shrinkage is accompanied by a 50-arc contraction, which can break the necks of crops such as strawberries, remove leaves, and sometimes cause the film to get caught in the necks of crops and tear or tear.
In particular, when a black polyethylene film is used as a mulching film, the film itself becomes extremely hot due to direct sunlight in the summer, and the temperature of the film easily rises to 8-0 or higher, making it even more likely to undergo thermal shrinkage. As a mulching film, an example of using low density polyethylene as described in Japanese Patent Publication No. 55-45762 is known.

However, what is described in this publication is aimed at improving the eroding resistance of low-density polyethylene films used as covering films and mulching films for agricultural greenhouses, tunnel houses, etc. Not only is there no mention of reducing heat shrinkage, there is also no mention of using the film as a mulching film in a state where heat shrinkage is likely to occur, that is, using the film by coloring it black. I don't need it.
In order to prevent heat shrinkage of the mulching film as described above, 10% of high density polyethylene is added to low density polyethylene.
There is also a method of blending ~30% and forming it into a film, but in this case, the heat shrinkability decreases, but the film tends to tear vertically, and if a notch is created for some reason, it will tear and break from there. , it is useless as a mulching film. As described above, the present invention has been developed to improve the heat shrinkability of conventional mulching films, especially black mulching films that tend to heat up when exposed to direct sunlight. To provide a mulching film made of a black polyethylene film using low-density polyethylene, which has an extremely small measured value of heat shrinkage when the temperature changes from 6 x 0 to 8 x 0.

In the present invention, low density polyethylene that falls within a certain range has a melt flow ratio of 35 or less and a melt index of 4.
The number of unsaturated groups per 100 carbon atoms contained in the molecular chain is 0.3 or less.

Further, the mulching film in the present invention is a black colored polyethylene film. When this low-density polyethylene is molded into a film together with a black colorant, a film with a heat shrinkage rate of 4.0 cm can be formed. At this time, even if the thickness of the film is made as thin as 0.025 or less, the film remains weather resistant, and this thin film can be used for agricultural purposes as is. Such a black mulching film has a low thermal shrinkage rate, so even if it has good heat absorption from direct sunlight, it can not only reduce the shrinkage, but also have a good weed prevention effect as described above. When the melt flow ratio of low-density polyethylene exceeds 35, the heat shrinkage rate of the formed film increases and the weather resistance also decreases.

Furthermore, if the number of unsaturated groups is 0.3 or more per 100 carbon atoms and the melt index is 4 or more, the film resistance of the formed film will decrease. It is particularly effective to use low-density polyethylene alone within the above certain range, but it can also be increased to 40% or more, with a melt flow ratio of 35 or more, a melt index of 4 or less, and a density of 0.9.
18 to 0.925 general purpose low density polyethylene
Even if a film is prepared by mixing less than 20% by weight with a black colorant, the heat shrinkage rate is small, and it is possible to form a tear-resistant mulching film that improves the drawbacks of general-use low-density polyethylene film.

Next, examples of the present invention will be explained in comparison with comparative examples.

Commercially available agricultural or packaging low-density polyethylene was used as the low-density polyethylene in the Examples and Comparative Examples.

In the examples, the melt flow ratio, melt index, and number of unsaturated groups were measured, and a low density polyethylene having the characteristic values shown in the table below was selected from commercially available low density polyethylenes and used alone. , and other general-purpose low-density polyethylenes are used, which are mixed with carbon black in the following formulation and formed into a film. In addition, the above fractionation method involves dissolving 50 ml of each commercially available low density polyethylene in 500 cc of orthodichlorobenzene, injecting this solution into a gel permeation chromatograph for fractionation, and dissolving 8 ml of the above solution.
It was separated into two fractions, and the fourth to seventh fractions were combined and purified.

Then, the above operation was repeated several times to obtain the required sample amount. Low density polyethylene 10 Ikarito carbon black 2.5 parts Sunnox (product name) 0.1 part 102.6
Here, Sunnox is an antioxidant manufactured by American Cynamide.

Furthermore, a film was formed using a mixture of the above-mentioned carbon black-mixed low-density polyethylene and a commercially available general-purpose low-density polyethylene, and its heat shrinkage rate was measured.

In addition, as comparative examples, general-use low-density polyethylene was measured for the above items such as melt flow ratio, and those having the characteristics shown in the table below and those in which carbon black was mixed therewith were used as comparative examples.

A heat shrinkage test was conducted on these Examples and Comparative Examples.

Here, the film forming conditions are as follows.

Extruder (inflation molding machine manufactured by Madan Maminary)
4 broadside die diameter 10mm, blow ratio 2.0, thickness 0.0
2nd side/Molding resin temperature 160~180o○, take-up speed 2
0/min.

In the heat shrinkage test, the film was first examined to see how much the film would rise in temperature upon irradiation with sunlight, and then the heat shrinkage rate was measured at a temperature within a certain range.

In the temperature increase test, the film was used as a multi-sog film and exposed to sunlight for 7 hours (9:30 a.m. to 4:30 p.m.) during the summer to determine the maximum temperature it reached. At this time, the outside air temperature and wind speed were also measured. The temperature of the mulching film was measured by sandwiching the sensor part of the thermistor between the same type of film as the mulching film on the ridge side of the back side of the mulching film, and securing this with a cello tape. In addition, the method for measuring the heat shrinkage rate is to make a test piece of film with 6 lengths and 20 ribs in the middle, and hang the test piece with a load of 5 cm across the lower part of the test piece. In this state, increase the temperature at a rate of 1°C per minute from 6 pi○ to measure the distance between the above gauges.

*Temperature and shrinkage rate were measured (Yano Cha: Applied Physics 27274, 1958). Here, the shrinkage rate (%) is L
Obtained from EE5×10 skin.

However, L spots and J teeth are the lengths between gauge points at a temperature of 60qo and a temperature of 85°C. In addition, as a measure of the ease with which the film can be torn vertically, the tearing strength of the film both vertically and vertically was determined using an Elmendorf tear tester.

It is known that materials with a large warp/horizontal tear strength ratio and a low warp tear strength are very likely to tear in the warp direction. In the above table, Comparative Examples 6 and 7 are high-density polyethylene, i.e., Stafrene E505, which is manufactured by the trade name Shorex N50.

In addition, the melt flow ratio is the value of the flow rate nomel index under a load of 21.6k9, and the number of unsaturated groups is 10.35μ, 1 by the baseline method using an infrared spectrometer.
The absorbance of 1.0 mm and 11.25 mm was calculated (R,
J. decock: J,poIMmersci,Par
tB2 339 (19 mice).

From the above results, even if an uncolored film is exposed to direct sunlight, the temperature rise is as low as 60°, and thermal shrinkage of the film is not much of a problem at this stage, but a black colored film The temperature reaches 83 to 90°C, so if the low density polyethylene used in the comparative example is used for general purpose, the heat shrinkage rate will be high, but the example used low density polyethylene within a certain range. This shows that the thermal shrinkage rate can also be reduced.

In addition, a blend of the low-density polyethylene used in the above example and the low-density polyethylene used in the comparative example, which was made black in the same machine as the above, was the same as the comparative example in terms of heat shrinkage rate and tear strength. The results, which show a more significant improvement, are shown below.

In addition, general-purpose low-density polyethylene has a melt flow ratio of 35 or more, a melt index of 4 or less, and a density of 0.91.
8 to 0.925 polyethylene. From these results, as can be seen from Comparative Examples 12 to 16, the heat shrinkage rate of the film formed by blending general low-density polyethylene and high-density polyethylene with carbon black is proportional to the increase in the blending ratio of high-density polyethylene. However, the tear strength in the longitudinal direction decreases rapidly, making it unsuitable as a mulching film. On the other hand, the black films made of low-density polyethylene with a low heat shrinkage rate of Examples 6 and 7 and general-use low-density polyethylene have a low heat shrinkage rate, and the tear strength in both vertical and horizontal directions does not change much. Recognize. According to the present invention, a black polyethylene film made of low-density polyethylene that falls within a certain range is created, so its heat shrinkage rate can be kept low even when the film temperature reaches 86 to 90 degrees Celsius due to exposure to sunlight. .

Therefore, on the one hand, by heating the film to a large extent, it is possible to particularly improve the effect of preventing the growth of weeds, and at the same time, it is possible to reduce adverse effects on crops such as crop neck breakage and tearing of the film due to thermal deformation.
In this way, it is possible to provide an agricultural mulching film that is optimal as a polyethylene film. In addition, if a black film is created by mixing low-density polyethylene that falls within this certain range with general-purpose low-density polyethylene, the heat shrinkage rate and tear strength of polyethylene made from general-purpose polyethylene can be improved, and its versatility can be improved. can be increased.

Claims (1)

[Claims] 1. In agricultural polyethylene films mainly composed of low density polyethylene, 40 to 10
0% by weight has a melt flow ratio of 35 or less, a melt index of 4 or less, and 1000 carbon atoms contained in the molecular chain.
The polyethylene film is made of low-density polyethylene with a number of unsaturated groups of 0.3 or less per piece, and the polyethylene film is colored black, and the temperature of the black polyethylene film reaches 60°C to 85°C when exposed to sunlight. An agricultural mulching film characterized by an extremely low measured heat shrinkage rate.