CA1121083A - Agricultural covering film or sheet and method for thermal insulation - Google Patents
Agricultural covering film or sheet and method for thermal insulationInfo
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- CA1121083A CA1121083A CA000304543A CA304543A CA1121083A CA 1121083 A CA1121083 A CA 1121083A CA 000304543 A CA000304543 A CA 000304543A CA 304543 A CA304543 A CA 304543A CA 1121083 A CA1121083 A CA 1121083A
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Abstract
ABSTRACT OF THE DISCLOSURE
A resin composition in the form of a covering film or sheet comprising (A) 100 parts by weight of a thermoplastic olefinic resin and (B) about 1 to about 20 parts by weight of an acetal resin; and a method for maintaining an agricultural locus at temperatures suitable for the growth of plants, using above covering film or sheet.
A resin composition in the form of a covering film or sheet comprising (A) 100 parts by weight of a thermoplastic olefinic resin and (B) about 1 to about 20 parts by weight of an acetal resin; and a method for maintaining an agricultural locus at temperatures suitable for the growth of plants, using above covering film or sheet.
Description
~ 2. -Thi~ invention relates to an agricul~ural co~er-ing film or sheet for maintaining a particular ag~i-cultural locus at ten~eratures suitable for th~ growth of plants, especially crops; and to a method for ther mally insulating the agrlcul~ural locus u5ing such a ~heet or film.
Various synthetic resin ~ilms or sheets (in-cludlng fo~ned ones) have been utilized heretofore a~
agricultural covering films or sheets, for exa~ple, in agricultural tthe term is meant to inelude "horticul-tural") housas and tunnel houses, or in ~nulching~ Ex-amples are vinyl chloride resin films such as polyvinyl chloride films and olefinic resin films such as ~ilms of polyethylene or an ethylene~vinyl acetate copolymer.
The vinyl chloride resin film or sheet most frequently used amonS them has the defect that the plastic~~er oon-tained in it collects dust on the surface of the film or sheet during use, and consequently, its light transmis-~ion i3 reduced to prevent the increa~e of the tempera-ture within the hou~e. ~oreover, burning of the usedvinyl chloride resin film or sheet causes a pollution by evulution o~ chlorine gas, hydrogen chloride gas, etc.
The ~hermoplast~c olefi~ic re~in film or ~heet is superior to the vinyl chloride re~in film or sheet :Ln that it is che~lically more stable, ~carcely changes in light tran3mlsgion *uring a long-term use~ and does not generate no~ious ga~es upon burning. However, it has the defect ~f h~ving an inferior thermal insulating '~
.
property to the vinyl chloride resin film or sheet.
The thermal insulating property of a converting film or sheet deno~es its property of preventing a decrease in the inside temperature of a large-sized agricultur~l house, tunnel house or the like covered with the covering film or sheet, especially at night. The heat from the sunlight which has been absorbed in the soil within the house during the daytime is irradiated at night as radiant rays from the ground surface, thereby to maintain the in side of the house at a higher temperature than the tem-perature of the outer atmosphere. If the covering film or sheet has a high transmittance o~ radiant rays from the surface of the ground within the house, the radiant rays dissipate out of the house, and the gro~md temperature within the house decr0ases. Consequently, the inside tem-perature of the house cannot be maintained at a higher temperature than the outer atmosphere. Accordingly, the ~hermally insulating property of the covering film or sheet is better when it reflects or absorbs radiant rays to a higher degree from the ground surface at night.
Japanese Patent Publication No. 13853/72 dis-closes a covering film composed of an olefinic resin con-taining 1 to 10~ by weight of silicon oxide, which has an improved thermally insulating property. However, when naturally occurring silicon oxide is used as the additive~
even a small amount of it markedly impairs the transparency of the resulting olefinic resin film because it has a large particle size and contains grea~ quantities of .''~`~i impurities. In ord~r that the addition of l~o by ~ight or more of silicon oxide to an olefinic resin may not impair the trans~arenGy of the resulting film, it is necessary to use synthetic silico~l oxide having a fine particle size of about ~everal tens of millimicronsO ~owr ever~ fine silicon oxide is very bulky ~ith an apparent densi~y o~ 60 to 80 g~liter, and its mixing with the ole-finic resin is difficult. It is more difficult to mix such silicon oxide in an amou~t of at least 12% by volume (w~en the amount is l~o by weight)~ c~nd film ~ormation cannot be performed with a good efficiency, Another dis advantag~ is t~at the high cost of synthetic silicon oxide adds to the cost of the resultirlg covering film or sheet~
The present inventors undertook investigations in order to pro~ide an improved covering film or sheet of an olefinic thermoplast~c resin which retains the afore-said advantages of the olefinic resin film or sheet and eliminates the defect of its poor thermal insulation and espscially c~n preven~ the dissipation of radiant heat at nig~t. These in~estigations led to the discovery that a resir~ cotnposit~ or in ~e form of a covering film or sheet comprising (A) a thermoplastic olefinic resin and ~B) A certain minor amount of an acetal resin ha~ the aforesaid advantages and prevents the dissipation of radiant heat, and is very useful as an agricultural cover-ing film or sheetO
It is an object of this invention therefore to provide a resin composition in the form of a covering film or sheet suitable for use in agriculture and horticulture.
Another object of this invention is to provide a method for maintaining a particular agricultural locus at temperatures sui.table for the growth of plants, especially crops, by utilizing the aforesaid covering film or sheet.
In one aspect the present invention provides a resin composition in the form of a covering film or sheet consisting essentially of (A) 100 parts by weight of a thermoplastic olefinic resin selected from the group consisting of polyethylene, an ethylene/vinyl acetate copolymer, and mixtures of these and (B) about 1 to about 20 parts by weight of an acetal resin hav-ing a degree of polymerization of about 500 to about 3,500 and selected from the group consisting of polyoxymethylene polymer and polyoxymethylene copoly-mer containing up to about 3% by weight of comonomer.
In another aspect the invention provides a method for maintaining an agricultural locus at temperatures sui.table for the growth of plants, which comprises covering the locus with a covering film or sheet of a resin composition compriSing (A) 100 parts by weight of a thermoplastic olefinic resin se].ected from the group consisting of polyethylene, an ethylene/vinyl acetate copolymer, and mixtures of these and ~B) about 1 to about 20 parts by weight of an acetal resin having a degree of polymerization of about 500 to about 3,500 and selected from the group consisting of polyoxymethylene polymer and polyoxymethylene copolymer containing up to about 3% by weight of a comonomer.
The thermoplastic olefinic resin ~A) includes, for example, homo-polymers or copolymers of ~-olefins, and copolymers of ~-olefins with other comonomers copolymerizable with the ~-olefins. Specific examples are low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, an ethylene/propylene copolymer, an ethylene/butylene copoly-mer, and an ethylene/vinyl acetate copolymer. Chlorinated polyethylene, chlorinated polypropylene, an ethylene/acrylic acid copolymer an ethylene/
~gL%~q~83 methacrylic acid copolymer, and blends of these and aforesaid resins can also be used. Among these, ethylene resins, especially low-density polyethylene and an ethylene/vinyl acetate copolymer, are preferred because they can afford films or sheets having better transparency - 5a -~.
~L~2~ 3 and suppleness than the other thermoplastic olefinic resins at lower costs. lhe ethylene/vinyl acetate copolymer is especially preferred be-cause it has superior thermal insulation and does not easily permit the ad-hesion of water droplets. Conveniently, the copolymer has a vinyl acetate content of about 5 to about 20% by weight.
Suitable acetal resins (B) are polyoxymethylene polymers or co-polymers having polyoxymethylene units of the formula -[HCHO]-. Examples are polyformaldehyde (termed an acetal homopolymer) which is regarded as a polymer of formaldehyde and an acetal copolymer resulting from the copoly-merization of ethylene oxide or dioxane with polyoxymethylene. The copoly-mers may be block or graft copolymers which have a polyoxymethylene chain as the main chain or side chain of the molecules and the remainder of the molecule comprising ethylene, ethylene/vinyl aceta~e, ethylene/vinyl chlor-ide, ethylene/vinyl chloride/vinyl acetate, ethylene/acrylic acid, ethylene/
acrylate ester, acrylate ester, ethylene oxide, propylene oxide, propylene, butadiene or vinyl chloride.
Preferred acetal resins have a degree of polymerization of about 500 to about 3,500, espccially about 2,000 to about 3,500. Especially pre-ferred are those in which up to about 3% by weight, for example 1 to 3% by weight, of a comonomer such as ethyle~e oxide is copolymerized in the poly-ox~ethylene molecules. If the degree of polymerization of the acetal resin is below about 2,000, especially below about 500, its viscosity becomes low, and uniform mixing of i~ with the olefinic resin (A) is difficult. On the other hand, if the degree of polymerization is above 3,500, the melting point of the acetal resin ~B) becomes too high. Hence, the resulting resin composition is difficult to shape, and the olefinic resin ~A) is likely to decompose during film or sheet formation. Inclusion of a comonomer such as ethylene oxide is preferred because the acetal resin ~B) becomes chemically and thermally stable. Especially preferred acetal resins are those having terminal carboxyl groups.
~ - 6 -According to a preferred embodiment of the present invention, there is provided a resin composition in the form of a covering film or sheet which comprises ~A) 100 parts by weight or a thermoplastic olefinic resin selected from the group consisting of ethylene resins, especially low-density polyethylene, and an ethylene/vinyl acetate copolymer, and mixtures of these, and (B) about 1 to about 20 parts by weight of a polyoxymethylene polymer or copolymer preferably con~aining up to about 3% by weight of a comonomer.
The resin composition of this invention in the form of a covering film or sheet useful for agricultural application can be produced by forming the composition composed of the resins (A) and (B) into a film or sheet.
Known means for film or sheet formation can be used to shape the resin com-position. For examp]e, resins (A) and (B) are mixed and directly fed into an extruder where they are melt-kneaded. Or the resins (A) and (B) are melt-mixed and pelletized, and then fed into an extruder where the pellets are melt-kneaded. In either case, the molten mixture is then extruded into a film or sheet by such means as an inflation molding method or T-die molding method. A method is also available which comprises melt-kneading resin (A) with a heat-decomposable blowing agent such as an azo-type chemical blowing agent at a temperature at which the blowing agent does not decompose, ex-truding the mixture to form pellets, feeding the pellets and resin (B) into an extruder, and mel~-extruding the mixture at a temperature at which the blowing agent decomposes, thereby to form a foamed film or sheet. Another method for preparing a ~oamed film or sheet comprises mixing resins (A) and (B), feeding the mixture into an extruder, continuously forcing a liquefied gas such as butane at a fixed rate into the extruder through an opening in it during the melt-extruding step, and further kneading and extruding the mixture.
The film or sheet so obtained may be oriented or heat-treated by stretching, heat-treatment, etc. For example, when the film or sheet as ,~, biaxially stretched by a tenter stretching method while being heated with hot air, its strength increases. The film has a uniform streng~h and is free from stress when heat-treated, or first stretched and then heat-treated.
The covering film or sheet o~ this invention may contain various additives. ~xamples of the additives are surface-active agents for impart-ing the property of flowing down the dew formed on the inside surface of an agricultural house, such as pentaerythritol fatty acid esters; ultraviolet absorbers for increasing weatherability, such as 2-~2'-hydroxy-5'-methyl-phenyl)benzotriazole; and antioxidants for inhibiting thermal degradation byou~door exposure, such as butylated hydroxytoluene.
The amounts of these additives are optionally determined, but gen-erally are about 0.2 to about 2.0% by weight for the surface-active agents;
about 0.05 to about 0.5~ by weight for the ultraviolet absorbers; and about 0.01 to about 0.1% by weight for the antioxidants, all based on the weight of the resin tA).
In the resin composition of this in~rention, the proportion of the acetal resin (B) based on the thermoplastic olefinic resin (A) is determined optionally according to a particular end use as an agricultural covering ma-terial. Usually, the amount of the acetal resin (B) is at leas~ about 1part by weight per 100 parts by weight of the thermoplastic olefinic resin.
If it is less than about 1 part by weight, the thermal insulating e~fect of the covering material is insufficient. When the proportion of the acetal resin (B) is increased, the thermal insulating property of the resulting composition increases, but the resulting co~ering material becomes hard and brittle and is susceptible to breakage (the strength is lost). Hence, for use as an outer covering of an agricultural house, the amount of the acetal resin (B) is preferably about 1 to about 20 parts by weight per 100 parts by weight of olefinic resin. For uses which require thermal insulation but do not strictly require strength and transparency, for e~ample, in the case of a covering material for a tunnel house within an agricultural house, a thermally insulating covering material for additionally covering the inner surface of an agricultural house or a tunnel house only during nightl or a mulching material or covering material for growing rice seedlings, the pre~
ferred amount of the acetal resin (B) is at least about 12 parts by weight.
According to another aspect of this inventionJ there is provided a method for maintaining an agricultural locus at temperatures suitable for the growth of plants, especially crops, which comprising covering the said locus with a covering film or sheet of a resin composition comprising (A) 100 parts by weight of a thermoplastic olefinic resin and (B) about 1 to about 20 parts by weight of an acetal resin.
The particular agricultural locus, as referred to in the present application, is a locus where plants are being grown or will be grown. It should be understood that this locus includes the one where the terrestrial portion of a plant does not appear but its bulbs, roots or seeds are presenti The following Pxamples illustrate ~he present invention.
Example l A mixture of 100 parts by weight of low-density polyethylene (YuXalon YF-30, a trademark for a product of ~itsubishi Petrochemical Co.
Ltd.; ~I-l.0), 12 parts by weight o~ polyacetal (Duracon M-25-lOr a trade-mark for a product o~ Polyplastics Co., Ltd.; MI-2.5) and 0.5 part by weight of a 1:1 mixture of pentaerythritol monostearate and pentaerythritol monobiphenate as a surface-active agent (in the form o a mixture with the low-density polyethylene) was fed into an extruder and kneaded at 200 to 220C., and extruded from T-die to obtain a film having a thickness of 0.1 mm. The film was found to have much the same transparency, strength and suppleness as a film of ~he low-density polyethylene alone.
Example 2 The p~rocedure o Example 1 was rPpeated exc~pt ~hat medium-density polyethylene (Showlex 5008, a trademark for a product of Showa Yuka Kabushiki Kaisha; MI=0.8) was used ins~ead of the low-density polyethylene.
A transparent film with a thickness of 0.1 mm was obtained.
Example 3 The procedure o~ Example 1 was repeated except that an ethylene/
vinyl acetate copolymer (Evaflex V~501, a trademark for a product of Mitsui Polychemical Co., Ltd.; a vinyl acetate content of 14.5% by weight and MI of 1.3) was used instead of the low-density polyethylene, and the amount of the polyacetal was changed to 7 parts by weight. A tTansparent film with a thickness of 0.1 mm was obtained.
Example ~
The procedure of Example 1 was repeated except that polypropylene (Mitsubishi Noblene, a trademark for a produc~ of Mitsubishi Petrochemical Co. Ltd.; MI=8.0) was used instead of the low-density polyethylene, and 0.2 part by weight of a light stabilizer (Tinuvin 1~0, a trademark for a product of Ciba-Geigy) was added together with the surface-active agent. A trans-parent film with a thickness of 0.1 mm was obtained.
Agricultural houses were built by using the films obtained in Ex-amples 1 to 4 as covering materials. The air tempera~ure and the tempera-ture of the ground (measured at a position 5 cm below the ground surface) within each house were measured. The results are shown in Table 1.
For comparison, similar agricultural houses were built by using a 0.1 mm-thick polyethylene film (Comparative Example 1), an ethylene/vinyl acetate copolymer film (Comparative Example 2), and a polyvinyl chloride film ~Comparative Example 3) which were conventional covering films, and the air temperatures and the ground temperatures within the houses were measured in the same way. The results are also shown in Table 1.
3~
Table 1 _ ____ _ , . ___~._ .~.~.~,~,.
Temperature of the inside of the house (,,C? , Transmit- 1:00 a.m. 6:00 a.m.
tance of ~ ~ _ _ infrared Ground Ground rays Air tem- tempera- Air tem- ~empera-Run (%) perature ture perature ture . . ______ __ Example 1 9 -2.9 4.8 -3.0 4.2 Example 2 9 -2.9 4.8 -2.9 4.2 Example 3 5.5 -2.7 5.0 -2.7 4.3 Example 4 8 -2.9 4.9 -2.8 4.2 Comparative Example 1 80 -3.8 4.1 -4.0 3.0 Comparative Example 2 35 -3.0 4.8 -3.0 4.2 Comparative Example 3 . -2.S 5.2 -2.8 _ _ The above temperatures were measured at Uji City, Kyoto, Japan in January 1976. At 6:00 a.m. on the day of measurement, the atmospheric tem-perature was -4.0C. and the ground temperature outside the houses was -1 .0C .
The transmittance ~%~ of infrared rays is that of infrared rays having a wavelength of 9 to 11 micTons. The mechanism of thermal insulation of the agricultural houses at night is that the covering film reflects and absorbs radiant rays from the soil within the house and thus prevents radi-ant rays from dissipating out of the house. The radiant rays from theground surface have a waveleng~h in th~ range of 5 to 20 microns, and their radiant energy becomes maximum at a wavelength of 9 to 11 microns. Hence, the thermal insulation of the covering film is better when the transmittance of radiant rays within this wavelength region is lower.
The results in Table 1 show that when the covering material of this invention is used, ~he air temperature and ground temperature within ~jr ~ 11 --3~33 the house are higher than in the case of using the conventional olefinic resin films (Comparative Examples 1 and 2). In particular, a composition of it with the low-density polyethylene film ~Comparative Example 1) shows that the air temperature within the house covered by the present invention was 0.9-1.3C higher between 1:00 a.m. and 6:00 A.m. This indicates the superior thermal insulation of the covering film or sheet of the present in-vention. When the temperature at dawn is higher even slightly, the tempera-ture within the house during the daytime is far higher than the outer atmos-pheric temperatureJ and thus, the average air temperature in a given day in-creases greatly. Thus, ~he difference becomes great in the integrated tem-perature ~the average temperature of one day multiplied by the number of days) in the course of growth of crops, and greatly affects the amount and time of harvest of crops.
.
The procedure of Example 3 was repeated except that the amount of the polyacetal was inc~eased to 20 parts by weight. A film having a thick-ness o~ 0.1 mm was obtained. The film was somewhat cloudy, but was a cover-ing material having superior thermal insulation for a tunnel house of crops which did not strictly require light transmission.
Example 6 ~ mixture of 100 parts by weight of the same low-density poly-ethylene as used in Example 1 and 6 parts by weight of the same polyacetal as used in Example 1 was fed into an extruder, and melt-kneaded at 190 to 210C. Liquid butane (13 parts by weight) was poured as a blowing agent into the mixture through an opening in the extruder and kneaded. The mixture was extruded through a T-die to make a foamed sheet having a thickness of 2 mm and an expansion factor o~ 30.
Example 7 The procedure of Example 6 was repeated except that high-density polyethylene (Novatec ET-008, a trademark for a product of Mitsubishi ~' .~ .~
,. :
Chemical Co., Ltd.; MI=0.8) was used instead of the low-density polyethyl-ene, and the amount of the blowing agent was changed to 15 parts by weight.
A foamed sheet having a thickness of 2 mm and an expansion factor of 30 was obtained.
Example 8 The procedure of Example 6 was repeated except that polypropylene (the same one as used in Example 4) was used instead of the low-density polyethylene, and the amount of the blowing agent was changed to 15 parts by weight. Thus, a 2 mm-thic~ foamed sheet having an expansion factor of 30 was obtained.
The foamed sheets obtained in Examples 6 to 8 were used as cover-ing materials for tunnel houses, and the air temperature within the houses at night was measured. The results are shown in Table 2. The foamed sheets were removed durin~ the daytime, and placed in position in the evening to confirm the thermally insulating effect of the foamed sheets.
For comparison, the same test was performed using a con~entional low-density polyethylene foamed sheet with a ~hickness of 2 mm and an ex-planation factor of 30 (Comparative Example 4~.
Table 2 _ _ _ _ _ Air temperature (C) within the tunnel house 1.00 a m. 6.00 a.m.
_ ... ..... ~ .
Foamed sheet 0.4 -1.1 of Ex~ple ~
Foamed sheet 0.4 -1.0 of Example 7 Foamed sheet 0.5 -1.0 of Example ~
Foamed sheet -0.7 -2.7 of Compara-tive Example 4 , . . _ ~. .. __ __ _ _ The temperature meas`urement was made at Uji City, ~yoto, Japan in '.~
~l~2~
January 1976. At 6:00 a.m. on the day of measurement, the atmospheric tem-perature was -3.4C.
It is seen from Table 2 that with the foamed sheets of this in-vention, the air temperature inside the house was l.l - 1.6C higher than with the conventional foamed sheet between l:00 a.m. and 6:00 a.m. This in-dicates the superior thermal insulating property of the foamed sheet pre-pared from the composition of this invention.
The films or sheets ~including foamed sheets) prepared from the resin composition of this invention can be used with good thermal insulating properties as mulching materials in addition to covering materials for agri-cultural houses or tunnel houses.
The agricultural covering material in accordance with this inven-tion is made by forming the composition of a thermoplastic olefinic resin and an acetal resin into films, and has superior thermal insulating proper-ties to conventional olefinic resin films used heretofore as agricultural covering materials. The film or sheet of the invention has thermal insulat-ing properties comparable to vinyl chloride resin films without substantial-ly impairing the transparency and strength of the olefinic resin, and is free from the defects of the vinyl chloride resin films.
Since the acetal resin is an organic polymer, it can be easily mixed with the olefinic resin or vinyl chloride resin unlike the conventional silicon oxide additive. Thus, the films or sheets (including foamed ones) can be easily prepared by conventional molding apparatuses.
`~
Various synthetic resin ~ilms or sheets (in-cludlng fo~ned ones) have been utilized heretofore a~
agricultural covering films or sheets, for exa~ple, in agricultural tthe term is meant to inelude "horticul-tural") housas and tunnel houses, or in ~nulching~ Ex-amples are vinyl chloride resin films such as polyvinyl chloride films and olefinic resin films such as ~ilms of polyethylene or an ethylene~vinyl acetate copolymer.
The vinyl chloride resin film or sheet most frequently used amonS them has the defect that the plastic~~er oon-tained in it collects dust on the surface of the film or sheet during use, and consequently, its light transmis-~ion i3 reduced to prevent the increa~e of the tempera-ture within the hou~e. ~oreover, burning of the usedvinyl chloride resin film or sheet causes a pollution by evulution o~ chlorine gas, hydrogen chloride gas, etc.
The ~hermoplast~c olefi~ic re~in film or ~heet is superior to the vinyl chloride re~in film or sheet :Ln that it is che~lically more stable, ~carcely changes in light tran3mlsgion *uring a long-term use~ and does not generate no~ious ga~es upon burning. However, it has the defect ~f h~ving an inferior thermal insulating '~
.
property to the vinyl chloride resin film or sheet.
The thermal insulating property of a converting film or sheet deno~es its property of preventing a decrease in the inside temperature of a large-sized agricultur~l house, tunnel house or the like covered with the covering film or sheet, especially at night. The heat from the sunlight which has been absorbed in the soil within the house during the daytime is irradiated at night as radiant rays from the ground surface, thereby to maintain the in side of the house at a higher temperature than the tem-perature of the outer atmosphere. If the covering film or sheet has a high transmittance o~ radiant rays from the surface of the ground within the house, the radiant rays dissipate out of the house, and the gro~md temperature within the house decr0ases. Consequently, the inside tem-perature of the house cannot be maintained at a higher temperature than the outer atmosphere. Accordingly, the ~hermally insulating property of the covering film or sheet is better when it reflects or absorbs radiant rays to a higher degree from the ground surface at night.
Japanese Patent Publication No. 13853/72 dis-closes a covering film composed of an olefinic resin con-taining 1 to 10~ by weight of silicon oxide, which has an improved thermally insulating property. However, when naturally occurring silicon oxide is used as the additive~
even a small amount of it markedly impairs the transparency of the resulting olefinic resin film because it has a large particle size and contains grea~ quantities of .''~`~i impurities. In ord~r that the addition of l~o by ~ight or more of silicon oxide to an olefinic resin may not impair the trans~arenGy of the resulting film, it is necessary to use synthetic silico~l oxide having a fine particle size of about ~everal tens of millimicronsO ~owr ever~ fine silicon oxide is very bulky ~ith an apparent densi~y o~ 60 to 80 g~liter, and its mixing with the ole-finic resin is difficult. It is more difficult to mix such silicon oxide in an amou~t of at least 12% by volume (w~en the amount is l~o by weight)~ c~nd film ~ormation cannot be performed with a good efficiency, Another dis advantag~ is t~at the high cost of synthetic silicon oxide adds to the cost of the resultirlg covering film or sheet~
The present inventors undertook investigations in order to pro~ide an improved covering film or sheet of an olefinic thermoplast~c resin which retains the afore-said advantages of the olefinic resin film or sheet and eliminates the defect of its poor thermal insulation and espscially c~n preven~ the dissipation of radiant heat at nig~t. These in~estigations led to the discovery that a resir~ cotnposit~ or in ~e form of a covering film or sheet comprising (A) a thermoplastic olefinic resin and ~B) A certain minor amount of an acetal resin ha~ the aforesaid advantages and prevents the dissipation of radiant heat, and is very useful as an agricultural cover-ing film or sheetO
It is an object of this invention therefore to provide a resin composition in the form of a covering film or sheet suitable for use in agriculture and horticulture.
Another object of this invention is to provide a method for maintaining a particular agricultural locus at temperatures sui.table for the growth of plants, especially crops, by utilizing the aforesaid covering film or sheet.
In one aspect the present invention provides a resin composition in the form of a covering film or sheet consisting essentially of (A) 100 parts by weight of a thermoplastic olefinic resin selected from the group consisting of polyethylene, an ethylene/vinyl acetate copolymer, and mixtures of these and (B) about 1 to about 20 parts by weight of an acetal resin hav-ing a degree of polymerization of about 500 to about 3,500 and selected from the group consisting of polyoxymethylene polymer and polyoxymethylene copoly-mer containing up to about 3% by weight of comonomer.
In another aspect the invention provides a method for maintaining an agricultural locus at temperatures sui.table for the growth of plants, which comprises covering the locus with a covering film or sheet of a resin composition compriSing (A) 100 parts by weight of a thermoplastic olefinic resin se].ected from the group consisting of polyethylene, an ethylene/vinyl acetate copolymer, and mixtures of these and ~B) about 1 to about 20 parts by weight of an acetal resin having a degree of polymerization of about 500 to about 3,500 and selected from the group consisting of polyoxymethylene polymer and polyoxymethylene copolymer containing up to about 3% by weight of a comonomer.
The thermoplastic olefinic resin ~A) includes, for example, homo-polymers or copolymers of ~-olefins, and copolymers of ~-olefins with other comonomers copolymerizable with the ~-olefins. Specific examples are low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, an ethylene/propylene copolymer, an ethylene/butylene copoly-mer, and an ethylene/vinyl acetate copolymer. Chlorinated polyethylene, chlorinated polypropylene, an ethylene/acrylic acid copolymer an ethylene/
~gL%~q~83 methacrylic acid copolymer, and blends of these and aforesaid resins can also be used. Among these, ethylene resins, especially low-density polyethylene and an ethylene/vinyl acetate copolymer, are preferred because they can afford films or sheets having better transparency - 5a -~.
~L~2~ 3 and suppleness than the other thermoplastic olefinic resins at lower costs. lhe ethylene/vinyl acetate copolymer is especially preferred be-cause it has superior thermal insulation and does not easily permit the ad-hesion of water droplets. Conveniently, the copolymer has a vinyl acetate content of about 5 to about 20% by weight.
Suitable acetal resins (B) are polyoxymethylene polymers or co-polymers having polyoxymethylene units of the formula -[HCHO]-. Examples are polyformaldehyde (termed an acetal homopolymer) which is regarded as a polymer of formaldehyde and an acetal copolymer resulting from the copoly-merization of ethylene oxide or dioxane with polyoxymethylene. The copoly-mers may be block or graft copolymers which have a polyoxymethylene chain as the main chain or side chain of the molecules and the remainder of the molecule comprising ethylene, ethylene/vinyl aceta~e, ethylene/vinyl chlor-ide, ethylene/vinyl chloride/vinyl acetate, ethylene/acrylic acid, ethylene/
acrylate ester, acrylate ester, ethylene oxide, propylene oxide, propylene, butadiene or vinyl chloride.
Preferred acetal resins have a degree of polymerization of about 500 to about 3,500, espccially about 2,000 to about 3,500. Especially pre-ferred are those in which up to about 3% by weight, for example 1 to 3% by weight, of a comonomer such as ethyle~e oxide is copolymerized in the poly-ox~ethylene molecules. If the degree of polymerization of the acetal resin is below about 2,000, especially below about 500, its viscosity becomes low, and uniform mixing of i~ with the olefinic resin (A) is difficult. On the other hand, if the degree of polymerization is above 3,500, the melting point of the acetal resin ~B) becomes too high. Hence, the resulting resin composition is difficult to shape, and the olefinic resin ~A) is likely to decompose during film or sheet formation. Inclusion of a comonomer such as ethylene oxide is preferred because the acetal resin ~B) becomes chemically and thermally stable. Especially preferred acetal resins are those having terminal carboxyl groups.
~ - 6 -According to a preferred embodiment of the present invention, there is provided a resin composition in the form of a covering film or sheet which comprises ~A) 100 parts by weight or a thermoplastic olefinic resin selected from the group consisting of ethylene resins, especially low-density polyethylene, and an ethylene/vinyl acetate copolymer, and mixtures of these, and (B) about 1 to about 20 parts by weight of a polyoxymethylene polymer or copolymer preferably con~aining up to about 3% by weight of a comonomer.
The resin composition of this invention in the form of a covering film or sheet useful for agricultural application can be produced by forming the composition composed of the resins (A) and (B) into a film or sheet.
Known means for film or sheet formation can be used to shape the resin com-position. For examp]e, resins (A) and (B) are mixed and directly fed into an extruder where they are melt-kneaded. Or the resins (A) and (B) are melt-mixed and pelletized, and then fed into an extruder where the pellets are melt-kneaded. In either case, the molten mixture is then extruded into a film or sheet by such means as an inflation molding method or T-die molding method. A method is also available which comprises melt-kneading resin (A) with a heat-decomposable blowing agent such as an azo-type chemical blowing agent at a temperature at which the blowing agent does not decompose, ex-truding the mixture to form pellets, feeding the pellets and resin (B) into an extruder, and mel~-extruding the mixture at a temperature at which the blowing agent decomposes, thereby to form a foamed film or sheet. Another method for preparing a ~oamed film or sheet comprises mixing resins (A) and (B), feeding the mixture into an extruder, continuously forcing a liquefied gas such as butane at a fixed rate into the extruder through an opening in it during the melt-extruding step, and further kneading and extruding the mixture.
The film or sheet so obtained may be oriented or heat-treated by stretching, heat-treatment, etc. For example, when the film or sheet as ,~, biaxially stretched by a tenter stretching method while being heated with hot air, its strength increases. The film has a uniform streng~h and is free from stress when heat-treated, or first stretched and then heat-treated.
The covering film or sheet o~ this invention may contain various additives. ~xamples of the additives are surface-active agents for impart-ing the property of flowing down the dew formed on the inside surface of an agricultural house, such as pentaerythritol fatty acid esters; ultraviolet absorbers for increasing weatherability, such as 2-~2'-hydroxy-5'-methyl-phenyl)benzotriazole; and antioxidants for inhibiting thermal degradation byou~door exposure, such as butylated hydroxytoluene.
The amounts of these additives are optionally determined, but gen-erally are about 0.2 to about 2.0% by weight for the surface-active agents;
about 0.05 to about 0.5~ by weight for the ultraviolet absorbers; and about 0.01 to about 0.1% by weight for the antioxidants, all based on the weight of the resin tA).
In the resin composition of this in~rention, the proportion of the acetal resin (B) based on the thermoplastic olefinic resin (A) is determined optionally according to a particular end use as an agricultural covering ma-terial. Usually, the amount of the acetal resin (B) is at leas~ about 1part by weight per 100 parts by weight of the thermoplastic olefinic resin.
If it is less than about 1 part by weight, the thermal insulating e~fect of the covering material is insufficient. When the proportion of the acetal resin (B) is increased, the thermal insulating property of the resulting composition increases, but the resulting co~ering material becomes hard and brittle and is susceptible to breakage (the strength is lost). Hence, for use as an outer covering of an agricultural house, the amount of the acetal resin (B) is preferably about 1 to about 20 parts by weight per 100 parts by weight of olefinic resin. For uses which require thermal insulation but do not strictly require strength and transparency, for e~ample, in the case of a covering material for a tunnel house within an agricultural house, a thermally insulating covering material for additionally covering the inner surface of an agricultural house or a tunnel house only during nightl or a mulching material or covering material for growing rice seedlings, the pre~
ferred amount of the acetal resin (B) is at least about 12 parts by weight.
According to another aspect of this inventionJ there is provided a method for maintaining an agricultural locus at temperatures suitable for the growth of plants, especially crops, which comprising covering the said locus with a covering film or sheet of a resin composition comprising (A) 100 parts by weight of a thermoplastic olefinic resin and (B) about 1 to about 20 parts by weight of an acetal resin.
The particular agricultural locus, as referred to in the present application, is a locus where plants are being grown or will be grown. It should be understood that this locus includes the one where the terrestrial portion of a plant does not appear but its bulbs, roots or seeds are presenti The following Pxamples illustrate ~he present invention.
Example l A mixture of 100 parts by weight of low-density polyethylene (YuXalon YF-30, a trademark for a product of ~itsubishi Petrochemical Co.
Ltd.; ~I-l.0), 12 parts by weight o~ polyacetal (Duracon M-25-lOr a trade-mark for a product o~ Polyplastics Co., Ltd.; MI-2.5) and 0.5 part by weight of a 1:1 mixture of pentaerythritol monostearate and pentaerythritol monobiphenate as a surface-active agent (in the form o a mixture with the low-density polyethylene) was fed into an extruder and kneaded at 200 to 220C., and extruded from T-die to obtain a film having a thickness of 0.1 mm. The film was found to have much the same transparency, strength and suppleness as a film of ~he low-density polyethylene alone.
Example 2 The p~rocedure o Example 1 was rPpeated exc~pt ~hat medium-density polyethylene (Showlex 5008, a trademark for a product of Showa Yuka Kabushiki Kaisha; MI=0.8) was used ins~ead of the low-density polyethylene.
A transparent film with a thickness of 0.1 mm was obtained.
Example 3 The procedure o~ Example 1 was repeated except that an ethylene/
vinyl acetate copolymer (Evaflex V~501, a trademark for a product of Mitsui Polychemical Co., Ltd.; a vinyl acetate content of 14.5% by weight and MI of 1.3) was used instead of the low-density polyethylene, and the amount of the polyacetal was changed to 7 parts by weight. A tTansparent film with a thickness of 0.1 mm was obtained.
Example ~
The procedure of Example 1 was repeated except that polypropylene (Mitsubishi Noblene, a trademark for a produc~ of Mitsubishi Petrochemical Co. Ltd.; MI=8.0) was used instead of the low-density polyethylene, and 0.2 part by weight of a light stabilizer (Tinuvin 1~0, a trademark for a product of Ciba-Geigy) was added together with the surface-active agent. A trans-parent film with a thickness of 0.1 mm was obtained.
Agricultural houses were built by using the films obtained in Ex-amples 1 to 4 as covering materials. The air tempera~ure and the tempera-ture of the ground (measured at a position 5 cm below the ground surface) within each house were measured. The results are shown in Table 1.
For comparison, similar agricultural houses were built by using a 0.1 mm-thick polyethylene film (Comparative Example 1), an ethylene/vinyl acetate copolymer film (Comparative Example 2), and a polyvinyl chloride film ~Comparative Example 3) which were conventional covering films, and the air temperatures and the ground temperatures within the houses were measured in the same way. The results are also shown in Table 1.
3~
Table 1 _ ____ _ , . ___~._ .~.~.~,~,.
Temperature of the inside of the house (,,C? , Transmit- 1:00 a.m. 6:00 a.m.
tance of ~ ~ _ _ infrared Ground Ground rays Air tem- tempera- Air tem- ~empera-Run (%) perature ture perature ture . . ______ __ Example 1 9 -2.9 4.8 -3.0 4.2 Example 2 9 -2.9 4.8 -2.9 4.2 Example 3 5.5 -2.7 5.0 -2.7 4.3 Example 4 8 -2.9 4.9 -2.8 4.2 Comparative Example 1 80 -3.8 4.1 -4.0 3.0 Comparative Example 2 35 -3.0 4.8 -3.0 4.2 Comparative Example 3 . -2.S 5.2 -2.8 _ _ The above temperatures were measured at Uji City, Kyoto, Japan in January 1976. At 6:00 a.m. on the day of measurement, the atmospheric tem-perature was -4.0C. and the ground temperature outside the houses was -1 .0C .
The transmittance ~%~ of infrared rays is that of infrared rays having a wavelength of 9 to 11 micTons. The mechanism of thermal insulation of the agricultural houses at night is that the covering film reflects and absorbs radiant rays from the soil within the house and thus prevents radi-ant rays from dissipating out of the house. The radiant rays from theground surface have a waveleng~h in th~ range of 5 to 20 microns, and their radiant energy becomes maximum at a wavelength of 9 to 11 microns. Hence, the thermal insulation of the covering film is better when the transmittance of radiant rays within this wavelength region is lower.
The results in Table 1 show that when the covering material of this invention is used, ~he air temperature and ground temperature within ~jr ~ 11 --3~33 the house are higher than in the case of using the conventional olefinic resin films (Comparative Examples 1 and 2). In particular, a composition of it with the low-density polyethylene film ~Comparative Example 1) shows that the air temperature within the house covered by the present invention was 0.9-1.3C higher between 1:00 a.m. and 6:00 A.m. This indicates the superior thermal insulation of the covering film or sheet of the present in-vention. When the temperature at dawn is higher even slightly, the tempera-ture within the house during the daytime is far higher than the outer atmos-pheric temperatureJ and thus, the average air temperature in a given day in-creases greatly. Thus, ~he difference becomes great in the integrated tem-perature ~the average temperature of one day multiplied by the number of days) in the course of growth of crops, and greatly affects the amount and time of harvest of crops.
.
The procedure of Example 3 was repeated except that the amount of the polyacetal was inc~eased to 20 parts by weight. A film having a thick-ness o~ 0.1 mm was obtained. The film was somewhat cloudy, but was a cover-ing material having superior thermal insulation for a tunnel house of crops which did not strictly require light transmission.
Example 6 ~ mixture of 100 parts by weight of the same low-density poly-ethylene as used in Example 1 and 6 parts by weight of the same polyacetal as used in Example 1 was fed into an extruder, and melt-kneaded at 190 to 210C. Liquid butane (13 parts by weight) was poured as a blowing agent into the mixture through an opening in the extruder and kneaded. The mixture was extruded through a T-die to make a foamed sheet having a thickness of 2 mm and an expansion factor o~ 30.
Example 7 The procedure of Example 6 was repeated except that high-density polyethylene (Novatec ET-008, a trademark for a product of Mitsubishi ~' .~ .~
,. :
Chemical Co., Ltd.; MI=0.8) was used instead of the low-density polyethyl-ene, and the amount of the blowing agent was changed to 15 parts by weight.
A foamed sheet having a thickness of 2 mm and an expansion factor of 30 was obtained.
Example 8 The procedure of Example 6 was repeated except that polypropylene (the same one as used in Example 4) was used instead of the low-density polyethylene, and the amount of the blowing agent was changed to 15 parts by weight. Thus, a 2 mm-thic~ foamed sheet having an expansion factor of 30 was obtained.
The foamed sheets obtained in Examples 6 to 8 were used as cover-ing materials for tunnel houses, and the air temperature within the houses at night was measured. The results are shown in Table 2. The foamed sheets were removed durin~ the daytime, and placed in position in the evening to confirm the thermally insulating effect of the foamed sheets.
For comparison, the same test was performed using a con~entional low-density polyethylene foamed sheet with a ~hickness of 2 mm and an ex-planation factor of 30 (Comparative Example 4~.
Table 2 _ _ _ _ _ Air temperature (C) within the tunnel house 1.00 a m. 6.00 a.m.
_ ... ..... ~ .
Foamed sheet 0.4 -1.1 of Ex~ple ~
Foamed sheet 0.4 -1.0 of Example 7 Foamed sheet 0.5 -1.0 of Example ~
Foamed sheet -0.7 -2.7 of Compara-tive Example 4 , . . _ ~. .. __ __ _ _ The temperature meas`urement was made at Uji City, ~yoto, Japan in '.~
~l~2~
January 1976. At 6:00 a.m. on the day of measurement, the atmospheric tem-perature was -3.4C.
It is seen from Table 2 that with the foamed sheets of this in-vention, the air temperature inside the house was l.l - 1.6C higher than with the conventional foamed sheet between l:00 a.m. and 6:00 a.m. This in-dicates the superior thermal insulating property of the foamed sheet pre-pared from the composition of this invention.
The films or sheets ~including foamed sheets) prepared from the resin composition of this invention can be used with good thermal insulating properties as mulching materials in addition to covering materials for agri-cultural houses or tunnel houses.
The agricultural covering material in accordance with this inven-tion is made by forming the composition of a thermoplastic olefinic resin and an acetal resin into films, and has superior thermal insulating proper-ties to conventional olefinic resin films used heretofore as agricultural covering materials. The film or sheet of the invention has thermal insulat-ing properties comparable to vinyl chloride resin films without substantial-ly impairing the transparency and strength of the olefinic resin, and is free from the defects of the vinyl chloride resin films.
Since the acetal resin is an organic polymer, it can be easily mixed with the olefinic resin or vinyl chloride resin unlike the conventional silicon oxide additive. Thus, the films or sheets (including foamed ones) can be easily prepared by conventional molding apparatuses.
`~
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A resin composition in the form of a covering film or sheet consisting essentially of (A) 100 parts by weight of a thermoplastic olefinic resin selected from the group consisting of polyethylene, an ethylene/vinyl acetate copolymer, and mixtures of these and (s) about 1 to about 20 parts by weight of an acetal resin having a degree of polymerization of about 500 to about 3,500 and selected from the group consisting of polyoxymethylene polymer and polyoxymethylene copolymer containing up to about 3% by weight of comonomer.
2. The composition according to claim 1 wherein the olefinic resin is low density polyethylene.
3. The composition according to claim 1 wherein the olefinic resin is an ethylene/vinyl acetate copolymer having a vinyl acetate content of about 5 to about 20%.
4. The covering sheet or film of claim which is in the foamed state.
5. A method for maintaining an agricultural locus at temperatures suitable for the growth of plants, which comprises covering the locus with a covering film or sheet of a resin composition comprising (A) 100 parts by weight of a thermoplastic olefinic resin selected from the group consisting of polyethylene, an ethylene/vinyl acetate copolymer, and mixtures of these and (B) about 1 to about 20 parts by weight of an acetal resin having a degree of polymerization of about 500 to about 3,500 and selected from the group consisting of polycxymethylene polymer and polyoxymethylene copolymer containing up to about 3% by weight of a comonomer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000304543A CA1121083A (en) | 1978-05-31 | 1978-05-31 | Agricultural covering film or sheet and method for thermal insulation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000304543A CA1121083A (en) | 1978-05-31 | 1978-05-31 | Agricultural covering film or sheet and method for thermal insulation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121083A true CA1121083A (en) | 1982-03-30 |
Family
ID=4111592
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000304543A Expired CA1121083A (en) | 1978-05-31 | 1978-05-31 | Agricultural covering film or sheet and method for thermal insulation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1121083A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019115783A1 (en) * | 2017-12-15 | 2019-06-20 | Abu Dhabi Polymers Company Limited (Borouge) L.L.C. | Foamed polyethylene film |
| CN114752134A (en) * | 2022-06-15 | 2022-07-15 | 河北上东包装科技有限公司 | Polyethylene easily-torn film |
-
1978
- 1978-05-31 CA CA000304543A patent/CA1121083A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019115783A1 (en) * | 2017-12-15 | 2019-06-20 | Abu Dhabi Polymers Company Limited (Borouge) L.L.C. | Foamed polyethylene film |
| CN114752134A (en) * | 2022-06-15 | 2022-07-15 | 河北上东包装科技有限公司 | Polyethylene easily-torn film |
| CN114752134B (en) * | 2022-06-15 | 2022-09-09 | 河北上东包装科技有限公司 | Polyethylene easily-torn film |
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