Water-Soluble Film or Sheet

The present invention relates to a water-soluble film or sheet, and more particularly to a water-soluble film or sheet of a special polyoxyalkylene compound.

Hitherto. films of polyvinyl alcohol (hereinafter referred to as "PVA"), methyl cellulose, polyethylene oxide, starch and hydroxypropyl cellulose are known as water-soluble films, and PVA sheets are also known as water-soluble sheets. In particular, water-soluble PVA films and sheets are widely employed at the present time. The water-soluble PVA films have been employed. for instance, as unit packaging films of various materials such as germicide, insecticide and dyestuff, laundry bags for hospital use or the like, backing films for wall papers with adhesives, and wrapping films for a sanitary napkin. Also, the water-soluble PVA films and sheets have been employed, for instance, as water-soluble tapes. The water-soluble PVA films and sheets are colorless, transparent, excellent in physical properties such as tear strength and insoluble in most of organic solvents, and have an adequate moisture absorbing property and an oil resistance.

It is known that polyethylene oxide having a high molecular weight provides a water-soluble film. However, polyethylene oxide having a film-forming property must have a very high molecular weight, e.g. more than 200,000, and such a polyethylene oxide is expensive as compared with PVA.

Hithereto, polyoxyalkylene high molecular weight compounds having an average molecular weight of not less than 20,000 have been prepared by, for instance, as represented by polyethylene oxide, polymerizing an alkylene oxide such as ethylene oxide in the presence of a special catalyst such as diethylzinc, strontium carbonate or triethyaluminum under a special polymerization condition (e.g. in a solvent such as n-hexane, 1.4-dioxane or n-heptane). However, in such a conventional process, the solvent is indispensable for promoting the polymerization, and a step for removing the solvent such as distillation is required for taking out the product after the completion of the polymerization. Also, since a metal ion such as Zn.sup.2+ or Al.sup.3+ of the metal compound used as a catalyst remains in the so obtained product. it causes a problem upon using the product in various purposes such as a binder for granular agricultural chemicals and a binder for use in inorganic industry.

On the other hand, it is known to prepare water-soluble high molecular weight compounds (polyester resins) by esterifying a relatively low molecular weight polyalkylene glycol used as a glycol component with a dicarboxylic acid such as maleic acid or succinic acid or its derivative. However, in this process, it is necessary to control the content of the polyalkylene glycol low for producing the high molecular weight compounds. For this reason, the product has been merely employed in limited purposes e.g. modification of polyester fibers.

It is an object of the present invention to provide novel polyoxyalkylene high molecular weight compounds which are soluble in organic solvents and/or water, moldable, and usable in many purposes.

A further object of the invention is to provide a process for preparing polyoxyalkylene high molecular weight compounds which are soluble in organic solvents and/or water moldable and usable in many purposes.

Another object of the invention is to provide a novel, inexpensive water-soluble film or sheet of a polyoxyalkylene compound having physical properties comparable or superior to those of a water-soluble PVA film or sheet and being also soluble in organic solvents.

These and other objects of the present invention will become apparent from the description hereinafter.

It has been found that a polyoxyalkylene high molecular weight compound having a solubility in water and/or organic solvents and a film-formability is easily and inexpensively prepared by a process which comprises addition-polymerizing an alkylene oxide containing ethylene oxide to an active hydrogen compound having at least 2 active hydrogens to produce a polyhydroxyl compund having an average molecular weight of not less than 1,000, and reacting the polyhydroxyl compound with an esterifying agent selected from the group consisting of a polycarboxylic acid, an anhydride thereof and a lower alkyl ester thereof by means of esterification or interesterification reaction under a reduced pressure of 0.001 to 20 mmHg, thereby chemically linking the molecules of the polyhydroxyl compound with each other through ester linkages. The polyoxyalkylene compounds, especially polyoxyalkylene compounds having an average molecular weight of at least 50,000 obtained from the polyhydroxyl compounds having an oxyethylene unit content of at least 70% by weight, are particularly excellent in water-solubility and form water-soluble films and sheets having excellent physical properties and being also soluble in organic solvents.

In accordance with the present invention, there is provided a water-soluble film or sheet comprising a polyoxyalkylene compound having an average molecular weight of at least 50,000 and being prepared by chemically linking molecules of a polyhydroxyl compound with each other through an esterifying agent selected from the group consisting of a polycarboxylic acid, an anhydride thereof and a lower alkyl ester thereof, said polyhydroxyl compound having an average molecular weight of at least 3.000 and a content of oxyethylene units of at least 70% by weight.

The polyhydroxyl compound used for preparing the polyoxyalkylene high molecular weight compounds of the present invention can be prepared by known processes. For instance, it is prepared by addition-polymerizing an alkylene oxide to an active hydrogen compound having at least 2 active hydrogens. Organic compounds having alcoholic hydroxyl groups, amino groups or phenolic hydroxyl groups are employed as the active hydrogen compounds. Water and ammonia may also be employed as the active hydrogen compounds. Typical examples of the organic compound having at least 2 active hydrogens are, for instance, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, aniline, butylamine, octylamine, laurylamine, cyclohexylamine, glycerin, trimethylolpropane, pentaerythritol, diglycerin tris(2-hydroxyethyl)isocyanurate, dipentaerythritol, sorbitol, sucrose, monoethanolamine, diethanolamine, triethanolamine, isopropanolamine. ethylenediamine, diethylenetriamine triethylenetetramine, tetraethylenepentamine, polyethyleneimine, tolylenediamine, diaminodiphenylmethane, novolak resin, aniline resen, and the like.

The addition polymerization is carried out, preferably in the presence of an alkali metal hydroxide as a catalyst such as sodium hydroxide or potassium hydroxide, at a temperature of about 90.degree. to about 200.degree. C. for about 2 to about 30 hours. This reaction does not particularly require the use of a solvent and, therefore, according to the process of the invention a step for removing a solvent can be omitted.

The alkylene oxide to be subjected to the polymerization is ethylene oxide alone or a mixture of alkylene oxides containing ethylene oxide as an essential component. The alkylene oxides other than ethylene oxide include, for instance, propylene oxide, butylene oxide and styrene oxide. The content of ethylene oxide in the mixture of alkylene oxides is usually not less than 30% by weight, preferably not less than 50% by weight. The active hydrogen compound is employed in an amount of about 0.1 to about 20 parts by weight per 100 parts by weight of the alkylene oxides. The amount of the catalyst is selected from 0.01 to 1 part by weight per 100 parts by weight of the whole reactants, namely 100 parts by weight of the total of the alkylene oxides and the active hydrogen compound.

Since the reaction mixture obtained by the polymerization does not contain a solvent and since the alkali metal hydroxide used as a catalyst also serves as a catalyst for the esterification in the next step, the reaction mixture can be used for the next step as it is without being treated.

The polyhydroxyl compound having an average molecular weight of at least 1,000, especially at least 2,000, is subjected to esterification or interesterification reaction with polycarboxylic acids, anhydrides thereof or lower alkyl esters thereof as an esterifying agent, whereby the molecules of the polyhydroxyl compound are linked with each other through ester linkages to produce a polyoxyalkylene high molecular weight compound having an average molecular weight of more than 20,000, preferably not less than 30,000, more preferably not less than 50,000, and being soluble in water and/or organic solvents and moldable.

The esterification or interesterification reaction to chemically bond the polyether chains to each other is carried out by adding an esterifying agent such as polycarboxylic acid, its anhydride or its lower alkyl ester to the polyhydroxyl compound elevating the temperature, and conducting dehydration or dealcoholization reaction at a temperature of 80.degree. to 250.degree. C. under a reduced pressure of 0.001 to 20 mmHg, usually for 30 minutes to 10 hours. The amount of the esterifying agent is from 0.5 to 5.0 moles per mole of the polyhydroxyl compound. Preferably, the esterifying agent is employed in such an amount that the ratio of carboxyl group to hydroxyl group is from about 0.7 to about 1.5 by mole.

The interesterification is preferred, since the polymer chains are hard to be severed. Also, in case of preparing the polyhydroxyl compound in a non-solvent system using an alkali metal hydroxide as a catalyst, the alkali metal hydroxide can also be utilized as a catalyst in the interesterification and, therefore, the reaction mixture can be subjected to the interesterification as it is without being treated.

Examples of the esterifying agent used in the present invention are, for instance, polycarboxylic acids such as malonic acid succinic acid, maleic acid, fumaric acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, itaconic acid, trimellitic acid, pyromellitic acid and dimer acid, lower alkyl esters of the above-mentioned polycarboxylic acids such as the monomethyl esters, dimethyl esters, monoethyl esters, diethyl esters, monopropyl esters, dipropyl esters, monobutyl esters and dibutyl esters, and anhydrides of the above-mentioned polycarboxylic acids.

The process of the present invention has the following features as compared with conventional processes for preparing a polyoxyalkylene high molecular weight compound having an average molecular weight of at least 20,000.

(1) A conventional process for preparing a polyoxyalkylene high molecular weight compound in one stage requires a long time in preparing the high molecular weight compound having a molecular weight of not less than 20,000. On the other hand, according to the process of the present invention, since a polyhydroxyl compound having a relatively low molecular weight is prepared in the first step and then esterified in the second step and these both reactions are relatively promptly completed, the product having a molecular weight of more than 20,000 can be obtained in a shortened period of time.

(2) The process of the invention does not require the use of a solvent in both of the first and second steps, and accordingly a step for removing a solvent as required in a conventional process can be omitted.

(3) The high molecular weight compounds obtained by the process of the invention are easily soluble in organic solvents such as tetrahydrofuran, dioxane, dichloroethane, ethyl alcohol and isopropyl alcohol. If the content of ethylene oxide is adjusted. the products become soluble in water. Also, the products of invention have excellent adhesion property and film-forming property.

(4) The process of the invention does not require the use of a special metallic compound as a catalyst, and the polymerization in the first step and the esterification in the second step can be carried out by employing a usual catalyst such as alkali metal hydroxides.

(5) In a conventional process for preparing a polyoxyalkylene high molecular weight compound using a special catalyst as mentioned before, there are cases where the metal ions remaining in the product produce undesirable precipitates such as ZnCO.sub.3 and SrSO.sub.4 upon use in various fields if carbonate ion or sulfate ion is present and the precipitates cause problems. On the other hand, the products of the invention can be used in a wider range, because of not producing such precipitates.

As mentioned above, since the high molecular weight compounds of the present invention have excellent solubility in water and/or organic solvents and film-forming property and moreover do not contain a metal ion such as Zn.sup.2+ or Al.sup.3+, they can be used for various purposes, e.g. water-soluble film or sheet, agent for paper making, water-soluble binder, binder for ceramics, agent for fibers, agent for agricultural use, agent for mining use, thickener and modifier for resins.

The polyoxyalkylene compound having an average molecular weight of at least 50.000 prepared from the polyhydroxyl compound containing at least 70% by weight of oxyethylene units is particularly suited for providing water-soluble films or sheets. When the molecular weight is less than 50,000, water-soluble films or sheets are not formed or the film strength is insufficient. When the content of the oxyethylene units in the polyhydroxyl compound is less than 70% by weight, there is a case where the end product obtained by linking the polyhydroxyl compound molecules with each other through ester linkages becomes insoluble in water depending on the molecular weight thereof. Also, the rate of the condensation reaction for the linking becomes slow, thus a long time is required in the linking. Further, there is a case where the end product does not solidify at ordinary temperature due to lowering of the melting point.

Preferably, the polyhydroxyl compound having an average molecular weight of at least 3.000, preferably at least 8,000, is employed in the reaction with the esterifying agent, since it is relatively easy to produce a water-soluble polyoxyalkylene compound having an average molecular weight of at least 50,000.

The polyoxyalkylene compound can be formed into films or sheets by known methods, e.g. solution casting method, calendering and melt-extrusion method such as T-die method or inflatioh method. The films or sheets of the invention may contain usual additives such as an antioxidant or ultraviolet absorber.

The films or sheets of the present invention have excellent physical properties and are soluble in water and specific organic solvents such as toluene, methylene chloride, methyl ethyl ketone, ethanol and tetrahydrofuran. The films of the invention have a good gas permeability, and also the heat sealing is possible. Further, the films of the inventioh have the advantages that the moisture absorption is low and accordingly they do not cause blocking and are easy to handle, and that the rate of dissolution in water is higher than that of PVA. It is also possible to uniaxially or biaxially stretch the films of the invention.

The water-soluble films and sheets of the present invention are applicable to various purposes to which known water-soluble films and sheets have been conventionally applied, e.g. unit packaging for germicide and insecticide, a sheet for a heat seal pack of seeds and a water-soluble tape. Also, the films and sheets of the present invention have good solubility in various organic solvents and good physical properties as well as the water-solubility and accordingly can be used in a wider range of uses.

The present invention is more specifically described and explained by means of the following Examples. in which all parts and % are by weight unless otherwise noted. It is to be understood that the present invention is not limited to the Examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

An autoclave was charged with 106 parts of diethylene glycol and 20 parts of potassium.hydroxide flakes. The polymerization of ethylene oxide was carried out at 130.degree. C. and 2 kg./cm..sup.2 G, while gradually adding 12,000 parts of ethylene oxide to the autoclave. The polyhydroxyl compound obtained as an intermediate had a weight average molecular weight of about 10,000 which was calculated on the basis of the hydroxyl value and the base number.

To 100 parts of the intermediate was added 1.85 parts of dimethyl terephthalate. and after elevating the temperature to 120.degree. C., methanol was removed under a reduced pressure of 5 mmHg to produce a polyoxyalkylene high molecular weight compound. The weight average molecular weight of the product measured by a high performance liquid chromatography was about 200,000. The solubility of the product was examined by dissolving 5 parts of the product in 95 parts of water, and it was confirmed that the product was completely dissolved in water.

The film-forming property of the product was examined as follows: The product was dissolved in water to give a 10% aqueous solution, 100 g. of the aqueous solution was placed in a laboratory dish having a diameter of 20 cm. and water was evaporated at ordinary temperature to give a film. The properties of the obtained film was measured according to JIS K 6301 with respect to elongation (%), tensile strength (kg./cm..sup.2) and tear strength (kg./cm.).

The results are shown in Table 1.

Polyoxyalkylene high molecular weight compounds were prepared in the same manner as in Example 1 except that the active hydrogen compound having at least 2 active hydrogens, the alkylene oxide, the amount of potassium hydroxide and the esterifying agent were changed as shown in Table 1. The molecular weight of the intermediates, the molecular weight and presence of the film-forming property of the high molecular weight compounds and the properties of the films prepared from the high molecular weight compounds are shown in Table 1.

The high molecular weight compounds obtained in Examples 2, 8, 14 and 15 were water-swellable, and were not completely soluble in water. However, since they were soluble in tetrahydrofuran, the film formation was conducted by employing tetrahydrofuran as a solvent.

Also, in Table 1, polyproyplene glycol used in Example 8 was that having a molecular weight of 1,000, polyethylene glycol used in Example 9 was that having a mclecular weight of 2,000, and polytetramethylene glycol used in Example 14 was that having a molecular weight of 700.

A high molecular weight compound was prepared in the same manner as in Example 9 except that 323 parts of bisphenol A diglycidyl ether (commercially available under the commercial name "Epikote 828" made by Shell Kagaku Kabushiki Kaisha) was employed as a coupling agent for combining the intermediary polyhydroxyl compounds instead of the esterifying agent.

The obtained high molecular weight compound was insoluble in water and tetrahydrofuran (THF), and it was impossible to form a film.

High molecular weight compounds were prepared in the same manner as in Comparative Example 1 except that the active hydrogen compound, the alkylene oxide, the amount of potassium hydroxide and the coupling agent were changed as shown in Table 2. The molecular weight of the intermediates, and the molecular weight, solubility in solvents and presence of the film-forming property of the high molecular weight compounds are shown in Table 2.

In Table 2, the high molecular weight compounds obtained in Comparative Examples 1 to 3 were insoluble in water and THF, and accordingly the measurement of the average molecular weight by high performance liquid chromatography was impossible. Also, since the high molecular weight compounds were not possible to form films (Comparative Examples 1 to 3) or have no film-forming property (Comparative Examples 5 to 7), the properties of the films were not measured.

Also, in Table 2, polyethylene glycol used in Comparative Example 1 was that having a molecular weight of 2,000.

In an autoclave, 6.5 parts of a 50% aqueous solution of potassium hydroxide was added to 134 parts of trimethylolpropane. The dehydration was conducted at 120.degree. C. under reduced pressure, and after gradually introducing 1.600 parts of propylene oxide at a pressure of not more than 5 kg./cm..sup.2 G, the reaction was conducted. To the obtained reaction mixture was added 43 parts of a 50% aqueous solution of potassium hydroxide, and after conducting the dehydration at 120.degree. C. under reduced pressure, the polymerization of ethylene oxide was conducted, while gradually introducing 30,300 parts of ethylene oxide to the autoclave at a pressure of not more than 5 kg./cm..sup.2 G. The polyhydroxyl compound obtained as an intermediate had a weight average molecular weight of about 30,000 which was calculated on the basis of the hydroxyl value and the base number.

To 100 parts of the thus obtained reaction mixture was added 0.46 part of dimethyl maleate, and after elevating the temperature to 120.degree. C., methanol was removed under a reduced pressure of 1 mmHg to produce a high molecular weight compound. The average molecular weight of the product measured by gel permeation chromatography was about 600,000. The solubility of the product was examined by dissolving 5 parts of the product in 95 parts of water, and it was confirmed that the product was completely dissolved in water.

The results are shown in Table 3.

Polyoxyalkylene high molecular weight compounds were prepared in the same manner as in Example 16 except that the active hydrogen compound, the alkylene oxide, the amount of potassium hydroxide and the esterifying agent were changed as shown in Table 3.

The results are shown in Table 3.

The high molecular weight compounds obtained in Examples 31 to 37 were water-swellable and were not completely dissolved in water, but were soluble in tetrahydrofuran. Therefore, the film formation was conducted by employing tetrahydrofuran as a solvent.

In Table 3, the novolak resin used in Example 26 was that having 6 phenol nuclei.

A high molecular weight compound was prepared in the same manner as in Example 29 except that 210 parts of bisphenol A diglycidyl ether (commercially available under the commercial name "Epikote 828" made by Shell Kagaku Kabushiki Kaisha) was employed as a coupling agent instead of the esterifying agent.

The obtained high molecular weight compound was insoluble in water and tetrahydrofuran (THF), and it was impossible to form a film.

High molecular weight compounds were prepared in the same manner as in Comparative Example 7 except that the active hydrogen compound, the alkylene oxide, the amount of the catalyst and the coupling agent were changed as shown in Table 4. The molecular weight of the intermediates, and the molecular weight, solubility in water and THF and presence of the film-forming property of the high molecular weight compounds are shown in Table 4.

In Table 4, the high molecular weight compounds obtained in Comparative Examples 7 to 10 were insoluble in water and THF, and accordingly the measurement of the average molecular weight by gel permeation chromatography was impossible. For the same reason, they were not subjected to the test for examining the film-forming property. Also, with respect to the products (Comparative Examples 7 to 10) which could not subjected to the test for examining the film-forming property and the products (Comparative Examples 11 to 13) which had no film-forming property, it was of course impossible to measure the properties of films.

An autoclave was charged with 106 parts of diethylene glycol as an active hydrogen compound and 20 parts of potassium hydroxide flakes. The polymerization of ethylene oxide was carried out at 130.degree. C. and 2 kg.cm..sup.2 G, while gradually adding 12,000 parts of ethylene oxide to the autoclave. The polyoxyethylene glycol obtained as an intermediate had a weight average molecular weight of about 10,000 which was calculated on the basis of the hydroxyl value and the base number.

To 100 parts of the intermediate was added 1.94 parts of dimethyl terephthalate as a condensing agent. After elevating the temperature to 190.degree. C., the reaction was carried out at that temperature, while removing methanol under a reduced pressure of 0.1 mmHg, to produce a polyoxyalkylene compound. The weight average molecular weight of the product measured by a high performance liquid chromatography was about 200,000. The solubility of the product was examined by dissolving 5 parts of the product in 95 parts of water, and it was confirmed that the product was completely dissolved in water.

The above procedure was repeated to produce polyoxyalkylene compounds except that the ingredients shown in Table 5 were employed.

Also, the sheets of the obtained polyoxyalkylene compounds were prepared by heat press, and the mechanical properties of the films were measured according to JIS K 6760 and JIS K 6301.

The results are shown in Table 5.

The solubility in organic solvents of polyoxyalkylene compounds obtained in Run Nos. 1 to 6 of Example 38 was observed by dissolving 5 parts of each polyoxyalkylene compound in 95 parts of the organic solvents shown in Table 6.

The results are shown in Table 6.

The solubility in organic solvents and mechanical properties of commercially available water-soluble PVA films were measured in the same manner as in Examples 38 and 39.

The results are shown in Table 7.

In addition to the ingredients used in the Examples, other ingredients can be used in the Examples as set forth in the specification to obtain substantially the same results.