IT8922596A1 - POLYVINYL ALCOHOL-STARCH FILM - Google Patents

Description

Description of the industrial invention entitled: "POLVINYLALLCOL-STARCH FILM"

SUMMARY

There is disclosed a polyvinyl alcohol-starch film prepared from a composition comprising a polyvinyl alcohol having a degree of hydrolysis of at least 93 mol% and a starch, the film being monoaxially stretched halithene. The film of the present invention exhibits excellent water resistance and degradability.

DESCRIPTION OF THE INVENTION

The present invention relates to a film prepared from a couplet composition of a polyvinyl alcohol and a starch or a crosslinking agent in addition to the two previous components, and more. particularly a polyvinyl alcohol-starch film having excellent water resistance and easily degradable by mechanical actions or microorganisms living in the soil.

Compositions comprising a polyvinyl alcohol and a starch have been anxiously used in various fields. For example, the composition is used for adhesives, sizing materials for fibers or fabrics, yet formed into molded articles such as films or sheets, and the like. Regarding such conventional uses, in many cases the capacity is used. of dissolution in water, what? a feature of polyvinyl alcohol and starch. In other words, the characteristic of solubility? in water is actually used in cases such as desizing after warp sizing, when the conposition is used as material for sizing, the possibility? removing the film through the water closet when the film composition is used as a film for sanitary napkins, and the like.

However, when the polyvinyl alcohol-starch film mentioned above (the film prepared by the composition comprising the polyvinyl alcohol and the starch) is used as a suitable material for agricultural purposes, for example as a root protection film suitable for protecting a root during transport or transplanting of plants, films (multi-films) for the removal of weeds, suitable for the prevention of the propagation of weeds, used by covering the surface of cultivated fields with film to intercept the sunlight, tapes for nesters, suitable for binding in sheaves rice, barley or wheat plants after harvesting, and the like, the poor water resistance of the polyvinyl alcohol-starch film limits its widespread use.

On the other hand, the polyvinyl alcohol-starch film is reported to be decomposed by microorganisms in the soil. Consequently, if the polyvinyl alcohol-starch film can? be used as a useful material for uses in agriculture, as mentioned above, it does not cause any pollution of the environment, and in other words you can? say that such a film? remarkably useful from an industrial point of view.

When the polyvinyl alcohol-starch film is used in an area that requires water resistance, for example in the case of materials suitable for agricultural purposes, an attempt is made to impart water resistance to the film by using a hydrophobic resin, for example a vinylidene chloride polymer solution is coated on the surface of the film or another film, such as a polyethylene film, is laminated onto the first film, and so on. Street.

An object of the present invention? to provide a polyvinyl alcohol-starch film having excellent water resistance and easily degradable by mechanical action or by microorganisms in the soil.

Another object of the present invention? supply and use the aforementioned film as a suitable material for use in agriculture.

These other objects of the present invention will appear from the following description.

SUMMARY OF THE INVENTION

Yup ? It has now been found that a polyvinyl alcohol-starch film, prepared from a composition comprising a polyvinyl alcohol having a degree of hydrolysis of at least 93 mol% and a starch, or containing a crosslinking agent in addition to the two aforementioned components, and which is at least monoaxially stretch, can? achieve the objectives mentioned above.

According to the present invention, a polyvinyl alcohol-starch film is provided, prepared from a composition comprising a polyvinyl alcohol having a degree of hydrolysis of at least 93 mol% and a starch, the film being at least monoaxially stretched.

Further, according to the present invention, the use of the aforementioned film is provided as a suitable material for agricultural purposes.

DETAILED DESCRIPTION

The present invention provides films having improved water resistance and the desired capacity. of degradation, according to the purposes, which can? be easily controlled, by the use of polyvinyl alcohol having the degree of hydrolysis within the range indicated above and by the simple operation of stretching the film at least monoaxially.

For example, when the film is used as a suitable material for agricultural uses, the properties? of the film can be kept at the desired level for a long period of time, without being damaged by rainwater or ground water. On the other hand, the film naturally degrades after it? after a certain period of time, or following mechanical operations, for example using a tractor, and moreover, if the broken film is left on a field as such, it does not cause environmental pollution, since? the decomposition of the film progresses thanks to the microorganisms present in the soil.

In the present invention the polyvinyl alcohol must have a degree of hydrolysis of at least 93 mol%, and preferably a degree of hydrolysis of at least 95 mol%. When is the degree of hydrolysis? water resistance less than 93% by moles? scarce.

The degree of polymerization of polyvinyl alcohol? 300 to 10,000, preferably about 1,000 to about 6,000.

Polyvinyl alcohol in the present invention it is possible to use not only the polyvinyl alcohols obtained by hydrolyzing the polyvinyl acetate, but also hydrolyzed copolymers of vinyl acetate or with another mononer which can be copolymerized with it (for example an olefin of ethylene, propylene, butene, -dodecene or -octadecene, a unsaturated carboxylic acid such as acrylic acid, crotonic acid, maleic acid or itaconic acid, or its allylesters, salts, arimides or nitriles, an unsaturated sulfonic acid, and the like) and modified polyvinyl alcohols, for example acetalized polyvinyl alcohol or polyvinyl alcohol copolymers.

Examples of the starches used in the present invention are as follows: (1) crude starch: wheat starch, potato starch, sweet potato starch, wheat starch, cassava starch, metroxyl starch, tapioca starch, sorghum starch, rice starch, legume starch, kudzu starch, fern starch, Euphrates lotus starch, water chestnut starch, and the like.

(2) Modified starch:

(i) physically modified starch: -amicto (pregelatinised starch), fractionated amylose, moist heat treated starch and the like (ii) starch modified with an enzyme: dextrin (produced by hydrolysis or enzymolysis of starch), amylose and the like

(iii) starch modified by chemical decanposition: starch treated with an acid, oxidized starch such as an oxidized starch with hypochlorous acid, dialdehyde starch and the like

(iv) chemically modified starch derivatives:

(a) esterified starch: starch esterified with acetic acid (starch acetate), starch succinate, starch nitrate, starch phosphate, starch urea-phosphate, starch xanthate, starch acetoacetate, and the like

(b) etherified starch: allylether starch, methylether starch, carboxymethylene starch, carboxyethyl ether starch, hydroxyethyl ether starch, hydroxypropyl ether starch, and the like (c) cationic starch: reaction product of a starch with 2-diethylaminoethyl chloride (a tertiary antnine), reaction product of a starch with 2,3-epoxypropyltrimethylaninonium chloride (a quaternary ammonium salt), and the like (d) cross-linked starch: cross-linked starch with formaldehyde, cross-linked starch with epichlorohydrin, cross-linked starch with phosphoric acid, cross-linked starch with acrolein, and similar.

The starches used in the present invention are not limited to those mentioned above.

Among the above mentioned methods, modified starches are preferably used, such as physically modified starches, starches modified with enzymes, starches modified by chemical decomposition and chemically modified starch derivatives as a component capable of giving the film a high resistance to water. In particular, the chemically modified starch derivatives are used advantageously.

The quantities polyvinyl alcohol and starch are not particularly limited and they can be used in any quantity. From the point of view of the balance between water resistance and property? of degradability?,? it is preferable that the weight ratio between polyvinyl alcohol and starch is from 75/25 to 1/99, plus? preferably from 70/30 to 5/95, even more? preferably from 70/30 to 10/90.

In the present invention, in order to further improve the water resistance of the film,? It is possible to mix a crosslinking agent with the two components mentioned above. In the present invention it is possible to use as a cross-linking agent any compound, as long as? it can react with any reactive groups in the polyvinyl alcohol and in the starch to form an intermolecularly cross-linked structure. In general, compounds having a polyfunctional group capable of reacting with the hydroxyl group in the polyvinyl alcohol and in the starch are used.

Examples of crosslinking agents used in the present invention are as follows:

(1) Compounds of polyisocyanates: tolylene diisocyanate, hydrogenated tolylene diisocyanate, an adduct of trimethylolpropane and tolylene diisocyanate, triphenyl methylenedisocyanate, methylene bis (4-phenylmethane) triisocyanate, isophorone diisocyanate or the like reaction products thereof.

(2) Polyaldehydes: glyoxal, succinolialdehyde, malonaldehyde, maleic dialdehyde, phthalic dialdehyde, glutaric aldehyde, adipaldehyde, and the like. (3) Polyepoxy compounds: ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1-6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diglycidylamnine, and the like.

(4) Polyamino compounds: urea, melamine, methylolurea, methylolmelamine, hexaraethylenediartrain, triethanolamine, and the like.

(5) Compounds capable of producing a radical: hydrogen peroxide, potassium peroxodisulfate, amnonium persulfate, benzoyl peroxide, succinic acid peroxide, t-butylperoxymaleate, benzoin alkyl ethers such as t-butyl-hydroperoxydobenzoinmethyl ether, benzoin-ethopylether and benzoyl ether , organic sulfur compounds such as dibutyl sulfide, benzyl sulfide and decylphenyl sulfide, diazonium salt and triazonium salts, their double salt with zinc chloride or its condensation product, azobisisobutyronitrile, 2,2'-azobis (2-airmidinopropane) dihydrochloride , dyes such as methylene blue or a combination of p-toluenesulfonate ion with it, a pyrilium scyl, a thiapyrilium salt, ammonium dichromate, acetophenone, benzophenone, benzyl, phenanthrene, thioxanthene, dichloropropylphenylketone, anthraquinone, 2-chloroantraquinone, 2-bromoanthraquinone, anthraquinon-? -sol phonate sodium, 1, 5-dinitroantraehinone, 1, 2-benzanthraquinone, phenanthrenchinone, 5-benzoylacethenaphthene, 5-nitroacetonaphthene, 1,4-naphthoquinone, 1,8-phthaloylnaffalene, 2-nitrofluorene, p-nitroaniline and s? mili.

(6) oxidizing agents: potassium dichramate, annonium dicranate, calcium perchlorate, and the like.

(7) Polymerizable monomers: 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-vinylpyrrolidone, 2-hydroxyethylacryloyl phosphate, acrylamri.de, methacrylateimu.de, N- methylideolacrylate-methacrylate. methoxymethylacrylamide, N- ethoxymethylacrylamide, ethylene glycol monoacrylate, diprpyleneglycol monoacrylate, N, N-dimethylarmri.noethylacrylate, styrene, vinyltoluene, monochlorostyrene, dialiylphthalate, vinyl acetate, glycidyl methacrylate and the like.

(8) Salts of polyvalent metals: a chloride, bromide, nitrate, sulfate or acetate of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium or zirconium, particularly copper chloride , aluminum chloride, ferric chloride, stannic chloride, zinc chloride, nickel (II) chloride, magnesium chloride, aluminum sulfate, cupric acetate, chromium acetate, and the like. Crosslinking agents are not limited to them.

The quantity of crosslinking agent? preferably from 0.1 to 50 parts by weight, plus preferably from 0.5 to 30 parts by weight, with respect to 100 parts by weight of polyvinyl alcohol and starch. When the quantity? of crosslinking agent? pi? of 0.1 parts by weight out of 100 parts by weight of polyvinyl alcohol and starch, the property? to improve the water resistance of the film can? be greatly influenced. On the other hand, if the quantity? of crosslinking agent? pi? of 50 parts by weight, the film becomes brittle.

The composition mentioned above can? if necessary, take plasticizers such as glycerol, ethylene glycol, propylene glycol, trimethylolpropane and polyethylene glycol, an inorganic fine powder such as silica, calcium carbonate and clay (kaolin), additives usually added to molded articles such as coloring agents, surfactants, antioxidants, water repellent agents, enzymes, fertilizers, pesticides and germicides, and the like. Furthermore, other water-soluble resins can be suitably added to the composition.

When preparing the film of the invention, can you? apply any method such as casting molding, for example the extrusion or tubular film forming process, and melting the film. Generally the film is prepared by casting. In this case, known methods can be applied, such as a method using a rotating drum and a method using an endless belt.

For example, in the invention, an aqueous solution containing the composition comprising polyvinyl alcohol and starch or the composition comprising polyvinyl alcohol, starch and cross-linking agent, aqueous solution usually having a concentration of polyvinyl alcohol and starch of about 10 to 40% by weight, is subjected to melting with formation of a film. Generally said melting is carried out by maintaining the aqueous solution at a temperature of about 60 ° C. at 95? C, and then the formed film is dried at a temperature of about 60? at 100? C.

When casting stalling, the composition comprising polyvinyl alcohol and starch, or the composition comprising the two preceding components and crosslinking agent, is melted at a temperature of 150 "to 250 DEG C..

In the present invention? It is essential that the film is stretched at least monoaxially. Stretching is performed during or after drying of the unstretched film. The water content of the film during stretching is controlled according to the stretch ratio of the film. any method of stretching, such as the method using a cylinder and the method using a drying rack, can be applied.

The film is stretched at least monoaxially in a stretch ratio of not less than 1.2, preferably 1.2 to 6. When is the stretch ratio? less than 1.2, the film is not given water resistance. When is the film stretched biaxially,? useful that the stretching ratio is from 1.2 to 3 in the direction of the machine and from 1.2 to 3 in the transverse direction. also be stretched temporarily in the direction of the machine and in the transverse direction. also be stretched in one direction and then in another.

The stretched film is subjected to a post-treatment, such as a heat treatment or water content control in the usual way. It is desirable that the heat treatment be conducted at a temperature of about 130? at 250? C, for a few seconds to a few minutes, while stretching the film. After the heat treatment, usually, the water content of the film is suitably adjusted in order to improve the stability. dimension of the film itself.

The stretched film like this? obtained can? be used in practice as such. If necessary, can it? any post-treatment may be carried out, such as for example a treatment in which the film is acetalized or a treatment in which the film is coated or laminated with a hydrophobic resin.

The thickness of the film of the invention is not? particularly limited.Generally the thickness? from about 10 to 80? m. Furthermore, in the invention one can? adopt a thickness from about 100 to 200? m. The film of the invention comprises not only the so-called films (generally having a thickness of about 10 to 80? M) but also the so-called sheets (usually having a thickness of about 100 to 200? M) and furthermore the processed goods coming from films or from sheets, such as tapes, containers or vessels.

The film of the invention not only? suitable for the aforementioned uses in agriculture, for example in the case of films to protect the roots, films to remove weeds, tapes for binding and films for sowing, but the films are also used meat films, bags, containers or containers for packaging or packaging food or fabrics.

The stretched film of the invention, prepared from the composition comprising the polyvinyl alcohol and the starch, as well as the crosslinking agent, can be used. be greatly improved in water resistance by the stretching operation, and further by the use of crosslinking. ; The present invention? described and explained more? precisely by means of the following examples, in which all percentages and parts are by weight unless otherwise indicated. It is understood that the present invention does not? limited to examples, and that various changes and modifications can be made to the invention without departing from its spirit and purpose. Examples 1-9 and Comparative Examples 1 and 2 A polyethylene terephthalate film was attached to a hot plate with a temperature of 50? at 60 ° C, an aqueous solution (concentration: 10%) of a composition of a polyvinyl alcohol and a starch illustrated in Table 1 was coated on them, using an applicator, and the film was dried at 90 ° C for 5 minutes, at give a film with a thickness of 50? m. After peeling of the polyethylene terephthalate film, the obtained film was stretched monoaxially at 160 ° C, under conditions such that the water content was 10% .During the biaxial stretching of the film, it was stretched in one direction and then in the other, under the same conditions as above. The stretched film was subjected to heat treatment at 160 ° C for one minute to give a film having a thickness of 40? m. ; The strength, swelling ratio in water and the wet strength of the film (sample) were measured using the following methods. The results are shown in table 1. Resistance: after the sample is adjusted to 65% humidity? relative to 20 ° C, the tensile strength at break is measured using an autograph (speed of traction: 40 nm / minute, length of the sample: 20 mn) Swelling ratio with water: after immersing the sample in water at a temperature of 20 ° C for 5 minutes, the length and width of the immersed sample are measured. The relationship between the measured and original dimensions? shown in table 1.; Resistance to imido: after the sample is immersed in water at a temperature of 20eC for 5 minutes, the tensile strength at break is measured using an autograph (speed of traction: 40 iim / minute, length of sample: 20 mm). After subjecting the film to the break test, the condition of the film is observed and resistance is measured in the same way as above. The results are shown in table 1.; State of the film:; [evaluation] A: yes pu? confirm with the naked eye that the film is? route. ; B: the shape of the film is maintained, but it is easily broken by crumpling it. The break test was conducted using a sunlight veterometer manufactured by Suga Shikenki Kabushiki Kaisha. ; Test conditions: temperature: 50? C; one cycle: water is sprayed for 12 minutes and the light is irradiated for 48 minutes. In the rupture test 110 cycles are repeated. ; ; ; ; ; ; Examples 10-18; The procedure of Example 1 was repeated, except that a composition of polyvinyl alcohol, starch and a crosslinking agent illustrated in Table 2 was used instead the composition illustrated in Table 1, to give a stretched film. ; As regards the film, the resistance, the swelling ratio to water and the wet resistance were measured, in the same node as in Example 1. The results are shown in Table 2.; After having subjected the film to the breaking in the same way as in Example 1, the state of the film was observed and its resistance was measured in the same way as in Example 1. The results are shown in Table 2.; ; ; ; ; The stretched film of the present invention has excellent water resistance and properties. of degradation and d? useful for materials suitable for use in agriculture. In addition to the ingredients used in the examples, other ingredients may be used in the examples as indicated in the description, to achieve substantially the same results. *

Claims (8)

CLAIMS 1. Polyvinyl alcohol-starch film, prepared from a composition comprising a polyvinyl alcohol having a degree of hydrolysis of at least 93 mol% and a starch, said film being stretched at least monoaxially. 2. The film of claim 1, wherein said composition further comprises a crosslinking agent. 3. The film of claim 1, wherein said starch? a modified starch. 4. The film of claim 1, wherein said film? uniaxially stretched in a stretch ratio of not less than 1.2. The film of claim 1, wherein the polyvinyl alcohol / starch weight ratio? from 75/25 to 1/99. 6. Film of claim 2, wherein the quantity? of said crosslinking agent? from 0.1 to 50 parts by weight with respect to 100 parts by weight of said polyvinyl alcohol and said starch. 7. Film of claim 1, which? a multi-film. 8. Use of the film of claim 1 as a suitable material for agricultural uses.