Water-soluble film and package

Abstract

[Problem] To provide a water-soluble film that contains a small amount of a surfactant, has good release properties from a support, and has good transparency. [Solution] A water-soluble film comprising: a polyvinyl alcohol resin; and a surfactant, wherein the contained amount of the surfactant is 0.005-1 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin, and the ratio S(0) / S(32) of S(0) to S(32) is in the range of 100-500, where S(0) represents the amount of the surfactant present on at least one of the surfaces of the water-soluble film, and S(32) represents the amount of the surfactant present at a plane located at a depth of 32 nm from that surface of the water-soluble film, S(0) and S(32) being measured by the count of fragment ions derived from the surfactant detected by time-of-flight secondary ion mass spectrometry, on at least one of the surfaces of the water-soluble film.

Description

Technical Field

[0001] The present invention relates to a water-soluble film containing a polyvinyl alcohol resin suitably used for packaging various drugs and the like, and a package using the same.

Background Art

[0002] Water-soluble films are used in a wide range of fields, such as packaging various drugs such as liquid detergents and agricultural chemicals, and seed tapes containing seeds, by utilizing their excellent solubility in water.

[0003] For water-soluble films used for the above-mentioned applications, polyvinyl alcohol resins (hereinafter sometimes referred to as PVA) are mainly used. And, water-soluble films with enhanced water solubility have been disclosed by blending various additives such as plasticizers or using modified polyvinyl alcohol (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When manufacturing a water-soluble film, a method is generally used in which a film-forming stock solution containing PVA and a solvent is cast onto a support such as a metal roll or a drum, and the solvent is evaporated and removed to obtain a film. However, hydrophilic PVA generally has a higher affinity for metals than resins such as polyolefin, and tends to be difficult to peel off from the support. When the peeling from the support is poor, uneven film thickness, and uneven physical properties such as mechanical strength and solubility occur. To improve the peelability of the water-soluble film from the support, a method of adding a surfactant to the film-forming stock solution of the water-soluble film is known.

[0006] However, when a surfactant having a high affinity for PVA is added to the film-forming stock solution of the water-soluble film, it is necessary to add a large amount of the surfactant to obtain sufficient peelability, which is not preferable from the viewpoint of economy. In addition, due to the addition of a large amount of the surfactant, the surfactant tends to bleed out to the surface of the water-soluble film, and the films are likely to block each other. On the other hand, when a surfactant having a low affinity for PVA is added to the film-forming stock solution of the water-soluble film, the peelability of the film is improved even with a small amount of the surfactant added. However, since PVA and the surfactant undergo phase separation in the film-forming stock solution and fine particles of the surfactant are dispersed in the film, the transparency of the film tends to decrease. Therefore, even when the amount of the surfactant added to the film-forming stock solution is reduced and the content of the surfactant in the water-soluble film is reduced, a water-soluble film excellent in peelability from the support and having good transparency has been desired.

[0007] An object of the present invention is to provide a water-soluble film having good peelability from a support with a smaller surfactant content and good transparency.

Means for Solving the Problems

[0008] As a method for analyzing components present on the surface of a film and components present inside the film in the depth direction, there is time-of-flight secondary ion mass spectrometry (hereinafter sometimes referred to as TOF-SIMS). In this analysis method, it is possible to grasp the distribution of various additive components on the film surface by identifying fragment ions derived from various additives. Further, by etching the film surface and analyzing, it is also possible to grasp the distribution of various additive components in the film depth direction.

[0009] For example, by focusing on and analyzing the signal of fragment ions derived from the surfactant contained in the film, it is possible to estimate the segregation state of the surfactant in the surface portion of the film, that is, the segregation state on the surface of the film and the surface obtained by etching in the depth direction of the film, by comparing the signal intensities.

[0010] Based on the findings of the detailed analysis of the segregation state of surfactants in various water-soluble films by the above-mentioned TOF-SIMS, the inventors have conducted intensive studies. As a result, it has been found that the above object can be achieved by a water-soluble film in which the segregation state of the surfactant on the film surface satisfies a specific relationship, and based on this finding, further studies have been conducted to complete the present invention.

[0011] That is, the present invention relates to [1] A water-soluble film containing a polyvinyl alcohol resin and a surfactant, wherein the content of the surfactant is 0.005 to 1 part by mass with respect to 100 parts by mass of the polyvinyl alcohol resin, and on at least one surface of the water-soluble film, the ratio S(0) / S(32) of the abundance S(0) of the surfactant on at least one surface of the water-soluble film measured by the count number of fragment ions derived from the surfactant detected by time-of-flight secondary ion mass spectrometry to the abundance S(32) of the surfactant on the plane at a depth position of 32 nm from the surface of the water-soluble film is in the range of 100 to 500. relates to.

[0012] Furthermore, the present invention relates to [2] The water-soluble film according to [1], wherein the surfactant is a nitrogen-containing surfactant. [3] The water-soluble film according to [2], wherein the nitrogen-containing surfactant contains at least one selected from the group consisting of alkylamine-based surfactants, alkylamide-based surfactants, and alkylalkanolamide-based surfactants. [4] The water-soluble film according to [3], wherein the alkylamine-based surfactant is a polyoxyethylene alkylamine-based surfactant and the alkylamide-based surfactant is a higher fatty acid diethanolamide-based surfactant. [5] The water-soluble film according to any one of [1] to [4] above, containing a filler and [6] The water-soluble film according to [5] above, wherein the filler is inorganic particles relates to

[0013] Furthermore, the present invention [7] A package in which the water-soluble film according to any one of [1] to [6] above contains a drug [8] The package according to [7] above, wherein the drug is a pesticide, a detergent or a disinfectant and [9] The package according to [7] or [8] above, wherein the drug is in a liquid state relates to

Advantages of the Invention

[0014] According to the present invention, a water-soluble film having good peelability from a support with a smaller surfactant content and good transparency is provided.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be specifically described. The water-soluble film of the present invention contains PVA and a surfactant. Further, the water-soluble film may contain other resins and components other than PVA, such as additives such as plasticizers.

[0016] <Surfactant> In the present invention, the water-soluble film contains a surfactant in order to obtain good peelability from the support. The content of the surfactant in the water-soluble film needs to be from 0.005 to 1 part by mass with respect to 100 parts by mass of PVA. When the content of the surfactant is less than 0.005 part by mass, problems such as poor peelability of the water-soluble film from the support during the production of the water-soluble film or blocking between water-soluble films are likely to occur. From this perspective, the content of the surfactant in the water-soluble film is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, and even more preferably 0.05 part by mass or more. On the other hand, when the content of the surfactant exceeds 1 part by mass, bleeding out of the surfactant to the surface of the water-soluble film and a decrease in the transparency of the water-soluble film due to aggregation of the surfactant are likely to occur. From this perspective, the content of the surfactant in the water-soluble film is preferably 0.8 part by mass or less, more preferably 0.6 part by mass or less, even more preferably 0.4 part by mass or less, and particularly preferably 0.3 part by mass or less. Here, the content of the surfactant in the water-soluble film is the ratio of the mass of the surfactant to the mass of PVA contained in the entire water-soluble film. Generally, the surfactant is non-volatile, and the content of the surfactant in the water-soluble film substantially coincides with the mass of the surfactant with respect to the mass of PVA in the film-forming stock solution of the water-soluble film. For a volatile surfactant, the content of the surfactant in the water-soluble film can be measured by a method such as dissolving the water-soluble film in a good solvent for PVA such as hexafluoroisopropanol, adding a poor solvent for PVA such as methanol to reprecipitate and remove PVA, and quantifying the surfactant concentration in the solvent by liquid chromatography analysis.

[0017] There is no particular limitation on the type of the surfactant. For example, anionic surfactants, nonionic surfactants, etc. can be used, but it is preferable to have an appropriate affinity with the PVA contained in the water-soluble film. When the affinity with PVA is too high, the surfactant is likely to be uniformly dispersed in PVA, so the amount of the surfactant present on the surface of the water-soluble film may be insufficient, and the peelability of the water-soluble film from the support may be poor. On the one hand, when the affinity with PVA is too low, in the film-forming stock solution of the water-soluble film or in the process of drying and solidifying the film-forming stock solution on the support, the surfactant is phase-separated from PVA to form droplets, which easily leads to a decrease in the transparency of the film and roughness on the surface of the film.

[0018] As a surfactant having an appropriate affinity with PVA, a nitrogen-containing surfactant Agent is preferred, and alkylamine surfactants, alkylamide surfactants, and alkylalkanolamide surfactants are exemplified. Therefore, the water-soluble film of the present invention preferably contains at least one surfactant selected from the group consisting of alkylamine surfactants, alkylamide surfactants, and alkylalkanolamide surfactants. Examples of alkylamine surfactants include higher fatty acid amine salts such as oleylamine acetate, and polyoxyalkylene alkylamine surfactants such as polyoxyethylene laurylamine. Examples of alkylamide surfactants include polyoxyalkylene alkylamide surfactants such as polyoxyethylene laurylamide. Examples of alkylalkanolamide surfactants include higher fatty acid alkanolamide surfactants such as alkanolamide laurate. Among these, from the viewpoint that a water-soluble film excellent in peelability from the support can be easily obtained under a wider range of production conditions, polyoxyethylene alkylamine surfactants or higher fatty acid alkanolamide surfactants are more preferred, and polyoxyethylene alkylamine surfactants are even more preferred. These surfactants may be used alone or in combination of two or more.

[0019] <TOF-SIMS measurement> In the present invention, on at least one surface of the water-soluble film, the ratio of the abundance S(0) of the surfactant on at least one surface of the water-soluble film, measured by the number of fragment ions derived from the surfactant in the water-soluble film detected by TOF-SIMS, to the abundance S(32) of the surfactant on the plane at a depth position of 32 nm from the surface of the water-soluble film is in the range of 100 to 500. However, the ratio of the abundance S(0) on the above surface to the abundance S(32) on the plane at a depth position of 32 nm from the surface of the water-soluble film is a value obtained by dividing S(0) by S(32) (hereinafter sometimes referred to as S(0) / S(32)). S(0) is the abundance of the surfactant on at least one surface, measured by the number of fragment ions derived from the surfactant detected when analyzing at least one surface of the water-soluble film by TOF-SIMS. On the other hand, S(32) is the abundance of the surfactant on the plane at a depth position of 32 nm from the surface of the water-soluble film (hereinafter sometimes referred to as the etching plane) detected when analyzing the plane at a depth position of 32 nm from the surface of the water-soluble film exposed by etching after performing an etching treatment of 32 nm in the depth direction from the surface of the water-soluble film (the same surface as the surface on which S(0) was measured) by TOF-SIMS, measured by the number of fragment ions derived from the surfactant detected. That S(0) / S(32) is 100 or more indicates that the abundance of the surfactant on the surface of the water-soluble film is 100 times or more the abundance of the surfactant on the plane at a depth position of 32 nm from the surface of the water-soluble film. If S(0) / S(32) is small, it means that the segregation of the surfactant on the surface of the water-soluble film is insufficient, and it is likely to cause a decrease in the peelability of the water-soluble film from the support or a decrease in the transparency of the water-soluble film. S(0) / S(32) is preferably 150 or more, more preferably 200 or more, and even more preferably 250 or more. On the one hand, when S(0) / S(32) is large, it means that the segregation of the surfactant on the surface of the water-soluble film is large, the surface of the water-soluble film becomes sticky, and blocking between films and a decrease in transportability are likely to occur. S(0) / S(32) is preferably 450 or less, more preferably 400 or less, and even more preferably 350 or less. The count numbers of S(0) and S(32) are not particularly limited as long as they can be distinguished from other fragment ions, but in order to make the influence of noise and the like negligible, it is preferably 50 or more, more preferably 100 or more, and even more preferably 1000 or more.

[0020] From the above, the water-soluble film of the present invention can ensure good peelability from the support by suppressing the addition amount of the surfactant and segregating the surfactant on the surface of the film. In addition, a decrease in the transparency of the film caused by excessive addition of the surfactant can be avoided.

[0021] As a method for controlling S(0) / S(32) within the above range, in addition to selecting the type and content of the surfactant having an appropriate affinity with the above-mentioned PVA, the film-forming conditions of the water-soluble film such as the adjustment conditions, extrusion conditions, and drying conditions of the film-forming stock solution described later can be selected. By combining these methods, the water-soluble film of the present invention can be obtained.

[0022] Hereinafter, a specific method for performing TOF-SIMS measurement will be described. <Sample preparation> The water-soluble film was cut into a size of 5 mm × 5 mm and set on the measurement pedestal via a conductive double-sided tape. In the measurement, the surface of the film without etching treatment and the etching surface at a depth position of 32 nm from the surface of the film obtained by etching the surface of the film were used as the measurement targets, and TOF-SIMS measurement was performed under the following <TOF-SIMS measurement conditions> respectively. The depth position of 32 nm from the surface of the film was defined as the 200th analysis position when etching was performed under the following <etching treatment conditions>.

[0023] <TOF-SIMS Measurement Conditions> Measurement apparatus: TOF-SIMS 5 (manufactured by ION-TOF) Analysis software: Surface Lab 6 (manufactured by ION-TOF) Primary ion source: Bi 3 ++ Measurement current: 0.2 pA at 25 keV (10 kHz) Measurement range: 200 μm × 200 μm Number of measurement pixels: 128 Pix × 128 Pix Charge neutralization condition: Without using a neutralizing electron gun Measurement of the count number: The number of fragments captured by the detector (detector intensity)

[0024] <Etching Treatment Conditions> Etching mode: GCIB Etching source: Ar cluster Raster Size: 500 μm × 500 μm Current: 0.26 nA After etching a total of 0.16 nm in the depth direction from the surface of the water-soluble film by etching three times under the above <Etching Treatment Conditions>, the cycle of performing TOF-SIMS measurement once was repeated. Therefore, it means that 0.16 nm of depth is etched for each TOF-SIMS measurement, and the value at a depth position of 32 nm from the surface of the water-soluble film is the analysis result of the 200th point (etching rate: 0.16 nm / 1 scan). This etching rate (0.16 nm / 1 scan) was obtained assuming that it is the same as the etching rate (0.16 nm / 1 scan) when etching a sample of a water-soluble film with a known film thickness measured separately with an ellipsometer or the like under the same conditions.

[0025] <Method for Selecting Fragment Ions Derived from Surfactant> When a water-soluble film is measured by TOF-SIMS, a wide variety of fragment ions are counted. Among them, fragment ions characteristic of the surfactant contained in the water-soluble film are selected, and the count number thereof is measured. The fragment ions characteristic of the surfactant are, for example, fragment ions having a strong intensity and considered not to be generated from other components in the water-soluble film. As a specific selection method, a water-soluble film not containing a surfactant is measured by TOF-SIMS under the same conditions as above, and strong-intensity fragment ions or fragment ions independent of other fragment ions are selected from among the fragment ions that hardly appear in the water-soluble film not containing a surfactant but appear in the water-soluble film containing a surfactant. For the selected fragment ions, the count numbers at the surface of the water-soluble film and at the etched surface at a depth position of 32 nm from the surface of the water-soluble film were measured and designated as S(0) and S(32), respectively.

[0026] <Polyvinyl alcohol resin> The water-soluble film of the present invention contains PVA. As the PVA, those produced by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer can be used. Examples of the vinyl ester-based monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, etc. Among these, vinyl acetate is preferable.

[0027] The above vinyl ester-based polymer is preferably obtained using only one or more vinyl ester-based monomers as monomers, more preferably obtained using only one vinyl ester-based monomer as a monomer, but may also be a copolymer of one or more vinyl ester-based monomers and other monomers copolymerizable therewith.

[0028] Examples of other monomers copolymerizable with such vinyl ester monomers include ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc.; acrylic acid esters; methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc.; methacrylic acid esters; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamidepropanesulfonic acid or its salts, acrylamidepropyldimethylamine or its salts, N-methylolacrylamide or its derivatives; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or its salts, methacrylamidepropyldimethylamine or its salts, N-methylolmethacrylamide or its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters, or acid anhydrides; itaconic acid or its salts, esters, or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate, etc.The above vinyl ester polymer can have structural units derived from one or more of these other monomers.

[0029] From the viewpoints of water solubility and film strength, the proportion of the structural units derived from the above other monomers in the above vinyl ester polymer is preferably 15 mol% or less, more preferably 5 mol% or less, based on the number of moles of all the structural units constituting the vinyl ester polymer.

[0030] There is no particular limitation on the degree of polymerization of PVA. From the viewpoint of film strength, the lower limit of the degree of polymerization is preferably 200 or more, more preferably 300 or more, and even more preferably 500 or more. On the other hand, from the viewpoints of the productivity of PVA and the productivity of the water-soluble film, etc., the upper limit of the degree of polymerization is preferably 8,000 or less, more preferably 5,000 or less, and even more preferably 3,000 or less. Here, the degree of polymerization means the average degree of polymerization (Po) measured in accordance with the description in JIS K6726-1994, and is obtained from the limiting viscosity [η] (unit: deciliter / g) measured in water at 30°C after saponifying and purifying PVA by the following formula. Po = ([η]×10 4 / 8.29) (1 / 0.62)

[0031] In the present invention, the saponification degree of PVA is preferably from 64 to 99.9 mol%. By adjusting the saponification degree within this range, it is easier to achieve both water solubility and mechanical properties of the film. The saponification degree is more preferably 70 mol% or more, and even more preferably 75 mol% or more. On the other hand, the saponification degree is more preferably 99.6 mol% or less, and even more preferably 99.3 mol% or less. Here, the saponification degree of PVA refers to the ratio (mol%) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester monomer units) that can be converted into vinyl alcohol units by saponification and vinyl alcohol units in PVA. The saponification degree of the PVA-based polymer can be measured according to the description in JIS K6726-1994.

[0032] In the water-soluble film of the present invention, one type of PVA may be used alone as PVA, or two or more types of PVA having different degrees of polymerization, saponification, or modification degree may be blended and used.

[0033] In the present invention, as the upper limit of the content of PVA in the water-soluble film, 100% by mass is preferable. On the other hand, as the lower limit of the content of the above PVA, 50% by mass is preferable, 80% by mass is more preferable, and 85% by mass is even more preferable.

[0034] <Filler> In the present invention, in order to improve the peelability of the water-soluble film from the support, it is preferable to contain a filler in the water-soluble film. The average particle size of the filler is preferably from 0.5 to 50 μm. When the average particle size of the filler is less than 0.5 μm, the effect of improving the peelability may not be sufficient, and when it exceeds 50 μm, the transparency of the water-soluble film may decrease. The average particle size of the filler is more preferably from 1 to 30 μm, and even more preferably from 1.5 to 15 μm. The material of the filler is not particularly limited, and it may be an inorganic filler or an organic filler. Examples include clay, talc, alumina, starch, acrylic resin fine particles, etc. Among them, inorganic fine particles are preferred in terms of cost and handleability.

[0035] The content of the filler in the water-soluble film is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, based on 100 parts by mass of PVA. If the content is greater than 15 parts by mass, the processability may deteriorate. On the other hand, if the content is too low, sufficient effects may not be obtained. The content of the filler is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more.

[0036] <Plasticizer> A film containing PVA is rigid compared to other plastic films when it does not contain a plasticizer, and mechanical properties such as impact strength and processability during secondary processing may deteriorate. To prevent this, it is preferable to contain a plasticizer in the water-soluble film of the present invention. Preferred plasticizers include polyhydric alcohols. Specifically, for example, polyhydric alcohols such as ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and sorbitol can be mentioned. These plasticizers may be used alone or in combination of two or more. Among these plasticizers, ethylene glycol or glycerin is preferred, and glycerin is more preferred, from the viewpoint of less likely to cause bleed-out on the surface of the water-soluble film.

[0037] When the water-soluble film of the present invention contains a plasticizer, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more with respect to 100 parts by mass of PVA contained in the water-soluble film. Also, the content of the plasticizer is preferably 70 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less. If the above content is less than 1 part by mass, the effect of improving mechanical properties such as the impact strength of the water-soluble film may not be sufficient. On the other hand, if the above content exceeds 70 parts by mass, the water-soluble film may become too flexible, resulting in a decrease in handleability or bleed-out on the surface of the water-soluble film.

[0038] <Water-soluble polymer> For the purpose of imparting mechanical strength to the water-soluble film, maintaining moisture resistance when handling the film, or adjusting the rate of softening due to water absorption when dissolving the film, etc., the water-soluble film of the present invention may contain a water-soluble polymer other than PVA.

[0039] Examples of water-soluble polymers other than PVA include dextrin, gelatin, glue, casein, shellac, gum arabic, polyacrylamide, sodium polyacrylate, polyvinyl methyl ether, a copolymer of methyl vinyl ether and maleic anhydride, a copolymer of vinyl acetate and itaconic acid, polyvinyl pyrrolidone, cellulose, acetyl cellulose, acetyl butyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, sodium alginate, and the like.

[0040] The content of the water-soluble polymer other than PVA in the water-soluble film is preferably 15 parts by mass or less, more preferably 10 parts by mass or less with respect to 100 parts by mass of PVA. If the content is greater than 15 parts by mass, the water solubility of the film may decrease.

[0041] <Other components> The water-soluble film of the present invention may contain components such as surfactants, plasticizers, water-soluble polymers other than PVA, as well as water, antioxidants, ultraviolet absorbers, lubricants, crosslinking agents, colorants, fillers, preservatives, fungicides, and other polymer compounds, as long as the effects of the present invention are not impaired. The proportion of the total mass of PVA, surfactant, and the above plasticizer and water-soluble polymer other than PVA in the total mass of the water-soluble film of the present invention is preferably in the range of 60 to 100% by mass, more preferably in the range of 80 to 100% by mass, and even more preferably in the range of 90 to 100% by mass.

[0042] <Water-soluble film> The water-soluble film of the present invention preferably has a complete dissolution time of 150 seconds or less when immersed in water at 10°C. When the complete dissolution time is 150 seconds or less, it can be suitably used as a packaging film for drugs and the like. The complete dissolution time is more preferably 90 seconds or less, even more preferably 60 seconds or less, and particularly preferably 45 seconds or less. On the other hand, there is no particular limitation on the lower limit of the complete dissolution time. However, a water-soluble film with too short a complete dissolution time tends to easily cause problems such as blocking between films due to moisture absorption of moisture in the atmosphere and a decrease in film strength. Therefore, it is preferably 5 seconds or more, more preferably 10 seconds or more, even more preferably 15 seconds or more, and particularly preferably 20 seconds or more.

[0043] The thickness of the water-soluble film of the present invention is not particularly limited. However, if the thickness is too thick, the secondary processability of the water-soluble film tends to deteriorate. Therefore, it is preferably 200 μm or less, more preferably 150 μm or less, still more preferably 100 μm or less, and particularly preferably 50 μm or less. On the other hand, if the thickness is too thin, the mechanical strength of the water-soluble film may decrease. Therefore, it is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 15 μm or more, and particularly preferably 20 μm or more. The thickness of the water-soluble film can be determined as the average value by measuring the thickness at any 10 locations (for example, any 10 locations on a straight line drawn in the length direction of the water-soluble film).

[0044] <Method for producing water-soluble film> In the present invention, the method for producing a water-soluble film can be any method such as (i) a casting film formation method, (ii) a wet film formation method in which a film-forming stock solution obtained by adding a solvent, a surfactant, etc. to PVA and homogenizing it is discharged into a poor solvent, (iii) a dry-wet film formation method, (iv) a gel film formation method in which the film-forming stock solution is once cooled and gelled and then the solvent is extracted and removed to obtain a PVA film, or (v) a method of forming a film by combining these, (vi) a melt extrusion film formation method in which the film-forming stock solution is extruded from a T-die or the like using an extruder, or (vii) an inflation molding method. Among these, since a homogeneous water-soluble film can be obtained with good productivity, (i) the casting film formation method or (vi) the melt extrusion film formation method is preferred. Hereinafter, the (i) casting film formation method or (vi) melt extrusion film formation method of the water-soluble film will be described.

[0045] When a water-soluble film is formed by the (i) casting film formation method or the (vi) melt extrusion film formation method, the film-forming stock solution is cast in a film shape onto a support such as a metal roll or a metal belt, heated to remove the solvent, and then solidified to form a film. The solidified film is peeled off from the support, dried by a drying roll, a drying furnace, etc. as necessary, further heat-treated as necessary, and wound up, whereby a long water-soluble film in roll form can be obtained.

[0046] It is considered that the surfactant in the film-forming stock solution gradually phase-separates in the film-forming stock solution to form fine droplets, except for surfactants having a very high affinity with PVA. When such a film-forming stock solution is flowed in a pipe, due to the shear rate distribution from the center of the pipe to the pipe wall surface, the surfactant tends to gradually move toward the vicinity of the pipe wall surface. As a result, the concentration of the surfactant in the vicinity of the pipe wall surface tends to increase, so that the concentration of the surfactant on the film surface of the film-forming stock solution cast onto the support becomes high, and the abundance S(0) and S(32) of the surfactant in the surface portion of the obtained water-soluble film tend to increase. Therefore, by adjusting the moving speed of the surfactant in the pipe, the abundance S(0) and S(32) of the surfactant in the surface portion of the obtained water-soluble film can be adjusted. Here, this moving speed of the surfactant is affected by film-forming conditions such as the dispersion state of the surfactant immediately after adjusting the film-forming stock solution, the temperature (viscosity) of the film-forming stock solution, the shear rate in the flow path pipe, the presence or absence of a kneading device such as a static mixer, and the drying speed of the cast film-forming stock solution, in addition to the affinity of the surfactant with respect to PVA. Therefore, by adjusting these factors, the abundance S(0) and S(32) of the surfactant in the surface portion of the water-soluble film of the present invention can be adjusted.

[0047] Examples of the method for adjusting the film-forming stock solution include a method of dissolving PVA, a surfactant, and additives such as a plasticizer as necessary in a dissolution tank, etc., and a method of melt-kneading water-containing PVA using a single-screw or twin-screw extruder and melt-kneading with a surfactant and additives such as a plasticizer as necessary.

[0048] When adjusting the casting dope, if the shear rate is too low, the dispersion of the surfactant may be poor, and the transparency of the water-soluble film may decrease. On the other hand, if the shear rate is too high, the surfactant may be overly dispersed, and segregation of the surfactant on the surface of the water-soluble film may be insufficient. The shear rate when adjusting the casting dope is preferably from 10 to 300 s -1 and more preferably from 20 to 250 s -1 and even more preferably from 30 to 200 s -1 Here, the above shear rate refers to the maximum shear rate in the casting dope adjustment device. For example, when adjusting while stirring with a stirring blade in a tank, it is the value obtained by dividing the speed at the tip of the stirring blade by the distance between the tip of the stirring blade and the tank wall surface. In the case of a single-screw extruder, it is the value obtained by dividing the linear velocity at the bottom surface of the groove in the screw metering section (usually the tip of the screw) by the groove depth.

[0049] The volatile content concentration of the casting dope is preferably in the range of 50 to 90% by mass, and more preferably in the range of 55 to 80% by mass. The volatile content concentration refers to the concentration of volatile components such as solvents that are removed by volatilization or evaporation during film formation. If the volatile content concentration is less than 50% by mass, the viscosity of the casting dope may increase, making film formation difficult. On the other hand, if the volatile content concentration exceeds 90% by mass, the viscosity may decrease, and the uniformity of the film thickness that can be obtained is likely to be impaired. Here, the "volatile content fraction of the casting dope" in this specification is determined by the following formula. Volatile content fraction of the casting dope (% by mass) = {(Wa - Wb) / Wa} × 100 (In the formula, Wa represents the mass (g) of the casting dope, and Wb represents the mass (g) when Wa (g) of the casting dope is dried in an electric drying oven at 105°C for 16 hours.)

[0050] The adjusted film-forming stock solution is sent through pipes or the like to a T-die or the like and discharged in a film form. Filters can be installed in the pipes or the like to remove droplets of the surfactant, or static mixers or the like can be installed to change the dispersion state of the droplets of the surfactant. However, if the dispersion state of the droplets of the surfactant is overly homogenized as described above, the degree of segregation of the surfactant on the surface of the water-soluble film may decrease.

[0051] If the temperature of the film-forming stock solution in the pipes and the T-die or the like is too high, the surfactant may overly segregate on the surface of the water-soluble film, which may reduce the transparency of the water-soluble film. If it is too low, the segregation of the surfactant on the surface of the water-soluble film may not be sufficient. The temperature of the film-forming stock solution in the pipes and the T-die or the like is preferably from 70 to 130 °C, more preferably from 80 to 120 °C, and even more preferably from 85 to 110 °C.

[0052] The shear rate in the T-die or the like has a great influence on the segregation state of the surfactant on the surface of the water-soluble film. If it is too high, the surfactant may overly segregate on the surface of the water-soluble film, which may reduce the transparency of the water-soluble film. If it is too low, the segregation of the surfactant on the surface of the water-soluble film may not be sufficient, and the peelability of the water-soluble film from the support may become insufficient. The shear rate in the T-die is preferably from 100 to 1000 s -1 and more preferably from 150 to 850 s -1 and even more preferably from 200 to 700 s -1

[0053] The film-forming stock solution discharged in a film form from the T-die or the like onto the support is dried and solidified on the support and in the subsequent drying process. During this period, the segregation of the surfactant on the surface of the water-soluble film gradually progresses. ​The surface temperature of the first drying roll or the first drying belt (hereinafter sometimes referred to as the first drying roll, etc.), which is the first support for casting the film-forming stock solution, is preferably 50 to 110°C. When the surface temperature is less than 50°C, not only is there a risk that the segregation of the surfactant on the surface of the water-soluble film will proceed excessively due to slow drying, but also the peelability of the water-soluble film may deteriorate due to insufficient drying. On the other hand, when the surface temperature exceeds 110°C, there is a risk of causing abnormalities on the film surface of the water-soluble film such as foaming, and there is also a risk that the segregation of the surfactant on the surface of the water-soluble film will not be sufficient due to rapid drying. The surface temperature of the first drying roll is preferably 60 to 100°C, and more preferably 65 to 95°C.

[0054] At the same time as heating the film-like PVA on the first drying roll, etc., hot air with a wind speed of 1 to 10 m / s may be uniformly blown onto the entire non-contact surface side of the film-like PVA with respect to the first drying roll, etc. to adjust the drying rate. The temperature of the hot air blown onto the non-contact surface side is preferably 50 to 150°C, and more preferably 70 to 120°C, from the viewpoints of drying efficiency and drying uniformity.

[0055] The water-soluble film peeled off from the first drying roll or the like is subsequently dried preferably to a volatile content of 5 to 50% by mass on a subsequent support (hereinafter may be referred to as a drying roll or the like, and when there are two or more, may be sequentially referred to as the second drying roll, the third drying roll, or the second drying belt, the third drying belt). After drying to the preferred range of the volatile content, it is peeled off and further dried as necessary. There is no particular limitation on the drying method, and a method using a drying furnace may be mentioned in addition to the method of bringing it into contact with a drying roll or the like. When drying with a plurality of drying rolls or the like, it is preferable to alternately bring one side and the other side of the film into contact with the second drying roll and subsequent rolls in order to equalize both sides. For example, the number of rolls after the second drying roll is preferably 3 or more including the second drying roll, more preferably 4 or more, and even more preferably 5 to 30. The temperature after the drying furnace, the second drying roll or the second drying belt is preferably 40°C or higher and 110°C or lower. The upper limit of the temperature after the drying furnace, the second drying roll or the second drying belt is more preferably 100°C or lower, even more preferably 90°C or lower, and still more preferably 85°C or lower.

[0056] The water-soluble film can be further heat-treated as necessary. By performing the heat treatment, the strength, water solubility, birefringence, etc. of the film can be adjusted. The heat treatment temperature is preferably 60°C or higher and 135°C or lower. The upper limit of the heat treatment temperature is more preferably 130°C or lower. If the heat treatment temperature is too high, the water solubility of the water-soluble film may decrease.

[0057] The water-soluble film produced in this way can be further subjected to humidity conditioning treatment, cutting of both ends (ears) of the film, etc. as necessary. i It is wound into a roll on a cylindrical core, moisture-proof packaged, and becomes a product.

[0058] The volatile content of the water-soluble film finally obtained by the above series of treatments is preferably in the range of 1 to 5% by mass, and more preferably in the range of 2 to 4% by mass.

[0059] <Application> The water-soluble film of the present invention can be suitably used for various water-soluble film applications. Examples of such water-soluble films include drug packaging film, hydraulic transfer base film, embroidery substrate film, release film for artificial marble molding, seed packaging film, and waste storage bag film. Among these, the water-soluble film of the present invention is preferably used as drug packaging film.

[0060] When the water-soluble film of the present invention is used as a drug packaging film, the types of drug include agricultural chemicals, detergents (including bleaching agents), disinfectants, etc. There is no particular limit to the physical properties of the drug, and the drug may be acidic, neutral, or alkaline. The drug may also contain a boron-containing compound. The drug may be in any form, such as powder, lump, gel, or liquid. There is no particular limit to the packaging form, but a unit packaging form in which the drug is packaged (preferably sealed) in unit amounts is preferred. The package of the present invention can be obtained by packaging the drug using the water-soluble film of the present invention as a drug packaging film. EXAMPLES

[0061] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples. The evaluation items and methods adopted in the following examples and comparative examples are as follows.

[0062] [TOF-SIMS measurement] Using the above-mentioned apparatus and conditions, S(0) and S(32) of the films obtained in the following Examples and Comparative Examples were measured to calculate S(0) / S(32).

[0063] [Removability of water-soluble film] In the examples and comparative examples, the peelability of the film from the support during the formation of the water-soluble film was evaluated according to the following criteria: The support for the evaluation of peelability was the first drying roll. A: At the circumferential position of the support, the position where the film separates from the film-forming support is approximately the same position in the width direction, and the positions where it peels off are substantially in a straight line when viewed in the width direction, enabling stable film formation. B: The position where the film separates from the support varies slightly in the width direction, and the positions where it peels off are uneven when viewed in the width direction, but stable film formation is possible. C: The position where the film separates from the support varies greatly in the width direction, and distinct thickness unevenness can be seen in the film, but continuous film formation is possible. D: It is difficult to stably peel the film from the support, and continuous film formation cannot be achieved.

[0064] [Haze value of water-soluble film] On the water-soluble film obtained in the following examples or comparative examples, a straight line was drawn perpendicular to the film end in the width direction (TD) of the film. Excluding 5 cm from each end of the film along the straight line, the remaining part was divided into 20 equal parts. Using the central part of each of the 20 equal parts as the measurement point, the haze value at that measurement point was measured in accordance with ASTM D1003 - 61 using a haze meter "HZ-1" manufactured by Suga Test Instruments Co., Ltd. In the following examples and comparative examples, since a film with a width of 170 cm was formed, the center of each section with a width of 8 cm obtained by dividing 160 cm (excluding 5 cm from each end) into 20 equal parts was measured. The average value of the 20 measured haze values was determined and taken as the haze value of the water-soluble film.

[0065] <Example 1> 100 parts by mass of maleic acid methyl (MA) - modified PVA (saponification degree 99 mol%, polymerization degree 1700, MA modification degree 5 mol%) obtained by saponifying polyvinyl acetate, 10 parts by mass of glycerin as a plasticizer, 0.2 parts by mass of polyoxyethylene laurylamine as a surfactant, and water were charged into a dissolution tank and mixed at a maximum shear rate of 150 s -1 to adjust a film-forming stock solution with a volatile fraction of 60% by mass. The obtained film-forming stock solution was filtered, adjusted to a temperature of 95 °C, and a maximum shear rate of 360 s -1From the T-die, it was discharged in a film form onto the first drying roll with a surface temperature of 85°C, and on the first drying roll, hot air at 85°C was blown at a speed of 5 m / s over the entire non-contact surface with the first drying roll for drying, and then it was peeled off from the first drying roll. The peelability of the water-soluble film was A. Drying was carried out such that one surface and the other surface of the film peeled off from the first drying roll sequentially and alternately contacted the subsequent drying rolls, and it was wound up to obtain a water-soluble film (thickness 35 μm, width 170 cm). The surface temperature of each subsequent drying roll was adjusted to 75°C.

[0066] When TOF-SIMS measurement of the obtained water-soluble film was carried out, compared with the water-soluble film obtained in the same manner as above without adding a surfactant (hereinafter sometimes referred to as a control film), C 3 H 7 N 2 O + ions were characteristically detected, and from the count number of these ions, S(0) was 1,980,000 and S(32) was 6,390. Therefore, S(0) / S(32) was 310. Also, the haze of this water-soluble film was 0.6%.

[0067] <Comparative Example 1> In Example 1, the shape of the paddle-type stirring blade during the preparation of the film-forming stock solution was changed so that the maximum shear rate was 350 s -1 to, the temperature of the film-forming stock solution at the T-die was set to 85°C, and the lip opening of the T-die was changed so that the maximum shear rate in the T-die was 80 s -1 except for changing to, a water-soluble film was formed in the same manner as in Example 1. The TOF-SIMS measurement results, the peelability and haze of the water-soluble film are shown in Table 1. In the TOF-SIMS measurement, compared with the control film, C 3 H 7 N 2 O + ions were characteristically detected.

[0068] <Comparative Example 2> The film-forming stock solution was prepared in the same manner as in Example 1 except that the amount of the surfactant was changed to 0.001 part by mass, and a film was attempted to be formed. However, the peelability of the water-soluble film from the first drying roll was D, and a stable water-soluble film could not be obtained. Therefore, TOF-SIMS measurement and haze measurement could not be performed.

[0069] <Comparative Example 3> A water-soluble film was formed in the same manner as in Example 1 except that the amount of the surfactant was changed to 3 parts by mass. The TOF-SIMS measurement results, the peelability of the water-soluble film, and the haze are shown in Table 1. In the TOF-SIMS measurement, C 3 H 7 N 2 O + ions were characteristically detected.

[0070] <Example 2> A water-soluble film was formed in the same manner as in Example 1 except that the surfactant was changed to lauric acid diethanolamide. When TOF-SIMS measurement of the obtained water-soluble film was performed, C 4 H 10 NO 2 + ions were characteristically detected, and S(0) / S(32) was 440 from the count number of these ions. The peelability and haze of the water-soluble film are shown in Table 1.

[0071] <Example 3> A water-soluble film was formed in the same manner as in Example 1 except that PVA was changed to non-modified PVA (saponification degree: 88 mol%, degree of polymerization: 1700) obtained by saponifying polyvinyl acetate. The TOF-SIMS measurement results, the peelability of the water-soluble film, and the haze are shown in Table 1. In the TOF-SIMS measurement, C 3 H 7 N 2 O + ions were characteristically detected.

[0072] <Example 4> A water-soluble film was formed in the same manner as in Example 2, except that the amount of the surfactant was changed to 0.08 parts by mass. The TOF-SIMS measurement results, peelability, and haze of the water-soluble film are shown in Table 1. In the TOF-SIMS measurement, C 4 H 10 NO 2 + ions were characteristically detected.

[0073] <Example 5> A water-soluble film was formed in the same manner as in Example 4, except that 3 parts by mass of talc having an average particle diameter of 3 μm was added as a filler to the film-forming stock solution. The TOF-SIMS measurement results, peelability, and haze of the water-soluble film are shown in Table 1. In the TOF-SIMS measurement, C 4 H 10 NO 2 + ions were characteristically detected.

[0074] <Comparative Example 4> In Example 2, the amount of the surfactant was changed to 0.8 parts by mass, the shape of the paddle-type stirring blade during the preparation of the film-forming stock solution was changed, and the maximum shear rate was 75 s -1 The lip opening of the T-die was changed to change the shear rate in the T-die to 1030 s -1 A water-soluble film was formed in the same manner as in Example 2, except for the above changes. The TOF-SIMS measurement results, peelability, and haze of the water-soluble film are shown in Table 1. In the TOF-SIMS measurement, C 4 H 10 NO 2 + ions were characteristically detected.

[0075]

Table 1

[0076] As is clear from Table 1, the water-soluble film of the present invention has good peelability even with a relatively low surfactant content, and has low haze, so that it has good transparency. The obtained water-soluble film can be suitably used for various applications of water-soluble films. In particular, the water-soluble film of the present invention is suitable for a film for drug packaging, and is suitable for a package for packaging agricultural chemicals, detergents (including bleaching agents), disinfectants, and the like.

Claims

1. A water-soluble film containing a polyvinyl alcohol resin and a surfactant, wherein the content of the surfactant is from 0.005 to 1 part by mass with respect to 100 parts by mass of the polyvinyl alcohol resin, and on at least one surface of the water-soluble film, the ratio of the abundance S(0) of the surfactant on at least one surface of the water-soluble film to the abundance S(32) of the surfactant on the plane at a depth position of 32 nm from the surface of the water-soluble film, measured by the number of fragment ions derived from the surfactant detected by time-of-flight secondary ion mass spectrometry, S(0) / S(32), is in the range of 100 to 500. A water-soluble film.

2. The water-soluble film according to claim 1, wherein the surfactant is a nitrogen-containing surfactant.

3. The water-soluble film according to claim 2, wherein the nitrogen-containing surfactant contains at least one selected from the group consisting of alkylamine surfactants, alkylamide surfactants, and alkylalkanolamide surfactants.

4. The water-soluble film according to claim 3, wherein the alkylamine surfactant is a polyoxyethylene alkylamine surfactant and the alkylamide surfactant is a higher fatty acid diethanolamide surfactant.

5. The water-soluble film according to any one of claims 1 to 4, containing a filler.

6. The water-soluble film according to claim 5, wherein the filler is inorganic particles.

7. A package in which the water-soluble film according to any one of claims 1 to 6 contains a drug.

8. The package according to claim 7, wherein the drug is a pesticide, a detergent, or a disinfectant.

9. The package according to claim 7 or 8, wherein the drug is in a liquid state.

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