JP2012072353A - Polyvinyl alcohol film, and method for producing polyvinyl alcohol film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film excellent in flame retardancy, and to provide a method for producing the polyvinyl alcohol film.SOLUTION: The polyvinyl alcohol film is characterized in that the boron atom content in the polyvinyl alcohol film is 3000-50000 mg/kg.

Description

  The present invention relates to a polyvinyl alcohol film, and more particularly to a polyvinyl alcohol film excellent in flame retardancy and transparency.

In general, polyvinyl alcohol-based films have properties such as hydrophilicity, organic solvent resistance, moisture permeability, and releasability, and are widely used.
However, due to its chemical structure, the polyvinyl alcohol film itself is flammable and has a serious problem of being easily ignited and burned.
On the other hand, recently, from the viewpoint of safety and security, flame retarding of structures, interior materials, sheets, etc. has been demanded. Especially, interior products such as curtains, industrial materials such as construction sheets, curing sheets, ropes, There is an increasing demand for flame retardants for textile products such as tents and canvases. When applying polyvinyl alcohol films for these applications, it is essential to provide flame retardancy. ing.

  Conventionally, in order to impart flame retardancy to polyvinyl alcohol, it is generally known to blend halogen-containing organic compounds, phosphorus-containing organic compounds, sulfur-containing compounds, nitrogen-containing compounds, inorganic compounds, etc. Halogen organic compounds are often restricted in their use due to environmental considerations, and are required to be halogen-free. For example, flame retardants containing sodium polyborate mixed in a resin composition. A functional resin composition has been proposed (see, for example, Patent Document 1).

JP 2010-24281 A

  However, the technique disclosed in Patent Document 1 kneads sodium polyborate into a resin. For example, when polyvinyl alcohol is used as the resin, the viscosity increases during kneading and sufficient uniform mixing cannot be performed. Furthermore, it was very difficult to form a polyvinyl alcohol film. Therefore, there is still room for improvement in order to obtain a polyvinyl alcohol film excellent in flame retardancy.

  Therefore, in the present invention, in such a background, an object is to provide a polyvinyl alcohol film excellent in flame retardancy, and further provide a method for producing the polyvinyl alcohol film. .

  However, as a result of intensive studies in view of such circumstances, the present inventor has found that the boron content in the polyvinyl alcohol film greatly contributes to flame retardancy, and completed the present invention.

  That is, the gist of the present invention relates to a polyvinyl alcohol film having a boron atom content in the polyvinyl alcohol film of 3000 to 50000 mg / kg.

  In the present invention, the polyvinyl alcohol resin is not simply made to contain a flame retardant in the polyvinyl alcohol resin, but is formed by immersing the once formed polyvinyl alcohol film in a boron compound solution. Boron atoms can be effectively contained in the system film, which is preferable in terms of productivity.

  The polyvinyl alcohol-based film of the present invention has an effect excellent in flame retardancy and transparency, and is particularly used for industrial materials and building materials (for example, curing used in an environment where flammable substances are used). Sheet) and interior materials.

The present invention is described in detail below.
The polyvinyl alcohol film of the present invention (hereinafter, polyvinyl alcohol may be abbreviated as PVA) has a boron atom content in the PVA film of 3000 to 50000 mg.

  In the present invention, if the boron atom content in the PVA film is too small, a sufficient flame retardant effect cannot be obtained, and if it is too much, the film becomes too brittle. The preferable range of the boron atom content in the PVA film is 5000 to 40000 mg / kg, and the particularly preferable range is 8000 to 30000 mg / kg.

In addition, content of the boron atom in the PVA-type film of this invention is measured as follows.
That is, about 1 g of a PVA film containing boron atoms is melt-decomposed with 8 g of alkali (potassium sodium carbonate), and the volume is adjusted to 250 ml. ICP (inductively coupled plasma) light emission from Thermo Fisher Scientific Co., Ltd. The boron content in the film is quantified by introducing into a spectroscopic analyzer.

  In the present invention, examples of the boron atom contained in the PVA-based film include those derived from boron compounds such as boric acid, borax, and polyboric acid metal salts. For example, sodium polyborate, potassium metal borate and the like can be mentioned. Among these, a boron compound having good water solubility is preferable in that a boron atom can be easily contained in the PVA film.

  Examples of the method for containing boron atoms in the PVA film include (1) a method in which a boron compound is contained in a PVA resin before forming the PVA film, and the resin solution is formed into a film. However, such a method makes it difficult to form a polyvinyl alcohol film due to problems such as high viscosity during kneading and insufficient uniform mixing. Therefore, for example, (2) A method of immersing the PVA film in a boron compound solution after producing a PVA film by previously forming a film from a PVA resin, and (3) a boron compound solution in a previously produced PVA film. (4) A method in which a PVA-based film produced in advance is coated with a boron compound solution. The method (2) is more preferable in that the boron compound can be efficiently contained.

  Moreover, about the PVA-type film of this invention, it is preferable from the point of shape stability or a process appropriateness that the weight reduction rate after being immersed in 30 degreeC water for 10 minutes is 20% or less. If the weight reduction rate is too high, the shape of the film is greatly changed compared with that before immersion, and the shape as a film cannot be maintained, and the immersion process in the boron compound solution tends to be hindered. The preferred range of such weight loss rate is 15% or less, particularly preferably 10% or less. The lower limit value of the weight reduction rate is usually 0.1%.

Here, the weight reduction rate is measured as follows.
That is, a film having a size of 100 mm × 100 mm is cut out, the cut film is dried in an environment of 100 ° C. for 5 minutes, and the weight (α) is measured. Then, after immersing the film in water at 30 ° C. for 10 minutes, the film is taken out from the water, dried as it is in an environment of 100 ° C. for 10 minutes, and its weight (β) is measured. From the measured weight (α) and weight (β), the weight reduction rate is calculated according to the following formula.
Weight reduction rate (%) = [(α) − (β) / (α)] × 100

The PVA film of the present invention is produced as follows using a PVA resin.
The PVA resin used in the present invention is obtained by polymerizing a vinyl ester compound and then saponifying it in accordance with a conventional method. In the present invention, the PVA resin may be used alone or in combination of two or more as required.

  Examples of the vinyl ester compounds include vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl versatate, vinyl palmitate, and vinyl stearate. . These may be used alone or in combination of two or more, but vinyl acetate is preferably used practically.

  In addition, as the PVA resin used in the present invention, it is usually preferable to use an unmodified PVA resin, but a partially modified PVA resin may be used. Examples of the modified PVA resin include those obtained by copolymerizing a small amount of other monomers with a vinyl ester compound, and the ratio of the monomers in this case is in a range that does not inhibit the effect of the present invention. The mol% or less, preferably 7 mol% or less.

  Examples of the other monomers include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itacone. Unsaturated acids such as acids or salts thereof, mono- or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, olefin sulfones such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid Acids or salts thereof, alkyl vinyl ethers, polyoxyethylene (meth) allyl ether, polyoxyalkylene (meth) allyl ether such as polyoxypropylene (meth) allyl ether, polyoxyethylene (meth) acrylate Polyoxyalkylene (meth) acrylates such as polyoxypropylene (meth) acrylate, polyoxyalkylene (meth) acrylamides such as polyoxyethylene (meth) acrylamide, polyoxyethylene (meth) acrylamide, and polyoxyethylene [1- (meta ) Acrylamide-1,1-dimethylpropyl] ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, diacrylacetone amide, N -Acrylamide methyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyldiallylammonium chloride Dimethylallyl vinyl ketone, N- vinylpyrrolidone, vinyl chloride, vinylidene chloride and the like. These other monomers may be used alone or in combination of two or more. In the present invention, (meth) allyl means allyl or methallyl, (meth) acryl means acryl or methacryl, and (meth) acrylate means acrylate or methacrylate.

  The polymerization (or copolymerization) using the vinyl ester compound is not particularly limited and a known polymerization method is used. Usually, an alcohol such as methanol, ethanol or isopropyl alcohol is used as a solvent. Solution polymerization is performed. In addition to solution polymerization, emulsion polymerization and suspension polymerization are also possible.

  The polymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, and the reaction temperature is usually 35 ° C. to boiling point, more preferably 50 It is selected from a range of about ~ 80 ° C.

  Next, when the obtained vinyl ester polymer is saponified, the vinyl ester polymer is dissolved in an alcohol in the presence of an alkali catalyst. Examples of the alcohol include methanol, ethanol, butanol, and the concentration of the vinyl ester copolymer in the alcohol is appropriately selected within a range of 20 to 50% by weight.

As the alkali catalyst during the saponification, alkali catalysts such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate and potassium methylate can be used. What is necessary is just to select the usage-amount of the said alkali catalyst suitably in the range of 1-100 millimol equivalent with respect to a vinyl ester polymer. In some cases, saponification with an acid catalyst is also possible.
In this way, a PVA resin is obtained.

  Further, as the PVA resin, it is also preferable to use a PVA resin having a 1,2-diol bond in the side chain, and the PVA resin having a 1,2-diol bond in the side chain is, for example, (a) acetic acid A method of saponifying a copolymer of vinyl and 3,4-diacetoxy-1-butene, (a) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinyl ethylene carbonate, and (c) vinyl acetate. Of saponifying and deketalizing a copolymer of 2,2-dialkyl-4-vinyl-1,3-dioxolane, and (d) saponifying a copolymer of vinyl acetate and glycerol monoallyl ether. Obtained by a method, etc.

  In the present invention, the average saponification degree of the PVA-based resin is preferably 90 mol% or more, particularly 93 to 99.9 mol%, more preferably 95 to 99.9 mol%, particularly 96 to 99. It is preferably 9 mol%. If the average saponification degree of the PVA-based resin is too low, when the boron atom is contained, when it is immersed in the boron compound aqueous solution, the shape tends to be maintained depending on the water temperature. The average degree of saponification is measured according to JIS K 6726.

  Furthermore, the average viscosity of a 4 wt% aqueous solution of the PVA resin at 20 ° C. is preferably in the range of 5 to 70 mPa · s, more preferably in the range of 15 to 60 mPa · s. If the average viscosity of the 4% by weight aqueous solution is too low, the strength of the film tends to decrease. On the other hand, if the average viscosity of the 4% by weight aqueous solution is too high, the viscosity tends to be high and it becomes difficult to form a film. The average viscosity of the 4% by weight aqueous solution at 20 ° C. is measured according to JIS K 6726.

  And although a PVA-type film is manufactured by forming into a film using the said PVA-type resin, in addition to the case where it consists only of this PVA-type resin, a plasticizer, surfactant, filler is added to this PVA-type resin. It is also preferable to produce the film by appropriately blending and the like.

  Examples of the plasticizer include glycerins such as glycerin, diglycerin, and triglycerin, alkylene glycols such as triethylene glycol, polyethylene glycol, polypropylene glycol, and dipropylin glycol, and trimethylolpropane. These may be used alone or in combination of two or more.

  It is preferable that the compounding quantity of the plasticizer mix | blended with the said PVA-type resin is 30 weight part or less with respect to 100 weight part of PVA-type resin, Most preferably, it is 20 weight part or less. If the amount of the plasticizer is too large, the film tends to become dull and difficult to handle.

  The surfactant is blended for the purpose of improving the peelability between a metal surface such as a drum or belt, which is a film forming apparatus for a PVA film, and the film formed. Examples of the surfactant include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl nonyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan mono Polyoxyethylene alkylamines such as palmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyalkylene alkyl ether phosphate monoethanolamine salt, polyoxyethylene laurylamine, polyoxyethylene stearylamine Etc. These may be used alone or in combination of two or more. Among these, it is preferable to use polyoxyalkylene alkyl ether phosphate monoethanolamine salt, polyoxyethylene alkylamine, and polyoxyethylene sorbitan monolaurate from the viewpoint of peelability.

  About content of the said surfactant, it is preferable that it is 0.01-5 weight part with respect to 100 weight part of PVA-type resin, and it is more preferable that it is 0.03-3 weight part. If the content of the surfactant is too small, the peelability between the metal surface of the film forming apparatus, such as a drum or belt, and the film formed tends to be difficult to produce, and conversely if too large, bleeding occurs. It tends to cause a decrease in surface properties such as whitening of the surface.

  Examples of the filler include starch (not only various raw products but also etherified, oxidized, and modified products), organic powders such as polymethyl methacrylate, inorganic powders such as talc, mica, and silica. These may be used alone or in combination of two or more. Of these, starch is preferably used.

  The amount of filler to be blended in the PVA resin is preferably 0.1 to 20 parts by weight, more preferably 0.3 to 10 parts by weight, particularly preferably 100 parts by weight of the PVA resin. Is 0.5-8 parts by weight. If the blending amount of the filler is too small, blocking tends to occur, and conversely if too large, the film strength tends to decrease.

  Furthermore, as long as the effects of the present invention are not hindered, antioxidants (phenolic, amine-based, etc.), stabilizers (phosphate esters, etc.), coloring agents, fragrances, extenders, antifoaming agents, rust inhibitors, Other additives such as ultraviolet absorbers and other water-soluble polymer compounds (polysodium acrylate, polyethylene oxide, polyvinylpyrrolidone, dextrin, chitosan, chitin, methylcellulose, hydroxyethylcellulose, etc.) may be appropriately blended. .

The manufacturing method of the polyvinyl alcohol film of the present invention will be further described in detail as follows.
First, a film-forming material is prepared by blending the PVA-based resin and, if necessary, a plasticizer, a surfactant, a filler, other additives, and the like in a predetermined blending amount. Next, a film-forming material is cast from a T-die onto a film-forming belt or film-forming drum, dried to form a film, and further heat-treated as necessary.

  Here, the film-forming belt has an endless belt that runs across a pair of rolls, and the film-forming material flowing out from the T-die is cast on the endless belt and dried. The endless belt is preferably made of, for example, stainless steel, and its outer peripheral surface is mirror-finished.

The film-forming drum is a rotating drum-type roll, and the film-forming material flowing out from the T-die is cast onto one or more rotary drum-type rolls and dried.
About a drying temperature, when using a film forming belt, it is preferable that it is 80-160 degreeC normally, and 90-150 degreeC is especially preferable. If the drying temperature is too low, drying tends to be insufficient and peeling from the belt tends to be heavy, while if it is too high, the moisture content tends to be too low and the film tends to become brittle.

  Moreover, when using a film forming drum, it is preferable that film forming first drum is 80-80 degreeC normally, and it is especially preferable that it is 82-99 degreeC. If the drying temperature is too low, drying tends to be insufficient, and peeling from the drum tends to be heavy. Here, the film-forming first drum is a drum-type roll located on the most upstream side where the film forming material flowing out from the T die is cast.

  After the drying, heat treatment is performed as necessary. Examples of the heat treatment method include a hot roll (including a calender roll), hot air, far infrared rays, and dielectric heating. Further, the surface to be heat-treated is preferably a surface opposite to the surface in contact with the film forming belt or the film forming drum, but there is no problem even if it is nipped. Moreover, it is preferable that the water content of the film which heat-processes is about 4 to 8 weight% normally. Furthermore, the water content of the film after the heat treatment is usually preferably 2 to 6% by weight. The moisture content of the PVA film can be measured using, for example, a Karl Fischer moisture meter (“MKS-210” manufactured by Kyoto Electronics Industry Co., Ltd.).

  It is preferable to perform heat processing by the said heat processing apparatus normally at 50-130 degreeC, More preferably, it is 60-120 degreeC. That is, if the temperature of the heat treatment is too low, curling of the surface in contact with the film forming belt or the first drum of the film forming tends to be difficult to handle, and if the temperature of the heat treatment is too high, the film becomes soft and wrinkles occur. If the wire is pulled so as to be wound, the orientation in the longitudinal direction becomes stronger and the width tends to be reduced. Further, in the case of a heat treatment roll, the time required for the heat treatment is usually 0.2 to 15 seconds, preferably 0.5 to 12 seconds, although it depends on the surface temperature. The heat treatment is usually performed as a separate heat treatment roll or embossing roll following the drying roll treatment for drying the film.

  The embossing treatment by the embossing roll may be performed for the purpose of preventing blocking. However, since the transparency is lowered, not only silk embossing but also satin embossing may be used.

  Although the PVA-type film is obtained by the above method, the moisture content of the obtained PVA-type film is preferably in the range of 2 to 6% by weight, more preferably 2.3 to 5.5% by weight. . If the moisture content is too low, it tends to be brittle, and the tendency is particularly high when the amount of plasticizer is small. Conversely, if the moisture content is too high, blocking tends to occur.

  Examples of the method for adjusting the moisture content of the PVA film include the following methods. That is, according to the moisture content adjustment method described below, it is possible to set the moisture content of the PVA film within the above range.

(1) The moisture content is adjusted by a method of increasing or decreasing the dryer temperature when the dope in which the PVA resin is dissolved is dried to form a film, thereby humidifying and dehumidifying the PVA film. The temperature of the dope is adjusted within the range of 70 to 98 ° C. because the temperature affects the drying efficiency. Further, the drying is preferably performed in at least two or more hot air dryers having a temperature gradient between 150 and 50 ° C., more preferably between 145 and 60 ° C. It is preferable from the viewpoint of moisture adjustment to dry for 1 minute, more preferably 1 to 11 minutes.

  If the gradient range of the drying temperature is too large or the drying time is too long, there is a tendency to overdry, and conversely if the gradient range of the drying temperature is too small or the drying time is too short, the drying is insufficient. Tend to be.

  The above temperature gradient gradually changes the drying temperature between 150 and 50 ° C. Usually, the temperature is gradually increased from the start of drying and once set until a predetermined moisture content is reached. It is effective to reach the highest moisture temperature in the drying temperature range, and then gradually lower the drying temperature to finally achieve the desired moisture content. This is performed to control crystallinity, releasability, productivity, and the like. For example, 120 ° C-130 ° C-115 ° C-100 ° C, 130 ° C-120 ° C-110 ° C, 115 ° C-120 ° C. The temperature gradient is set such as −110 ° C. to 90 ° C., and is appropriately selected and executed.

(2) The PVA film is humidified and dehumidified by passing it through a humidity control tank before winding the PVA film, and the moisture content is adjusted.

(3) Before or after winding the PVA film, heat treatment is performed to dehumidify the PVA film and adjust the moisture content.

  Next, the haze of the PVA film is preferably 40% or less, more preferably 35% or less. If the haze is too high, not only does the strength of the PVA film decrease, but the concealability tends to increase too much. The lower limit of haze is usually about 0.1%. The haze of the PVA-based film can be measured using, for example, a haze meter (Nippon Denshoku Industries Co., Ltd., NDH 2000).

  In addition, the elongation at break of the PVA film is preferably 150% or more, more preferably 180% or more under 23 ° C. and 50% RH humidity control conditions. If the elongation at break is too low, it tends to break during use. The upper limit of elongation at break is usually 350%. Here, the breaking elongation of the film is measured according to JIS K 7127 (1999).

  In this way, the PVA film used in the present invention is obtained. The film thickness of such a PVA-based film is preferably 10 to 120 μm, particularly 20 to 100 μm, and more preferably 30 to 80 μm from the viewpoints of ease of handling and easy incorporation of boron atoms.

  In the present invention, the PVA-based film may be stretched in that mechanical strength can be stably imparted, and the stretching method will be described below.

  In stretching, the film may be uniaxially stretched in the longitudinal (machine) direction, but biaxially stretching in both the longitudinal and lateral directions is preferable in terms of further improving the above physical properties.

  Such biaxial stretching may be either sequential biaxial stretching or simultaneous biaxial stretching. In biaxial stretching, the water content of the polyvinyl alcohol film obtained above is adjusted to 3 to 30% by weight. It is preferable to adjust to 5 to 30% by weight. If the water content is too low or too high, the draw ratio tends not to be sufficiently increased. In adjusting the moisture content, for example, the moisture content is adjusted at the time of drying the polyvinyl alcohol film, or the polyvinyl alcohol film having a moisture content of less than 3% by weight is immersed in water, sprayed with water, or conditioned. A method for adjusting the water content can be mentioned.

  After biaxial stretching, it is preferable to perform heat setting, and the temperature of the heat setting is preferably selected to be lower than the melting point of the polyvinyl alcohol resin. However, when the temperature is lower than the melting point by 80 ° C. or more, the dimensional stability is poor and the shrinkage rate is increased. On the other hand, when the temperature is higher than the melting point, the film thickness tends to increase. For example, when the polyvinyl alcohol-based resin is a saponified product of vinyl acetate homopolymer, the heat setting temperature is preferably 140 to 250 ° C, more preferably 150 to 230 ° C, and the heat setting time is 1 to 30. It is preferable that it is second, More preferably, it is 5 to 10 second.

  Although there is no restriction | limiting in particular about a draw ratio, It is preferable that the draw ratio of a vertical direction is 1.1-5 times, It is more preferable that it is 3-4.5 times, The draw ratio of a horizontal direction is 1. It is preferably 1 to 5 times, and more preferably 3 to 4 times. If the stretching ratio in the machine direction is too low, it tends to be difficult to improve physical properties by stretching, and if it is too high, the film tends to tear in the machine direction. Moreover, when the draw ratio of a horizontal direction is too low, there exists a tendency for the physical property improvement by extending | stretching to be difficult to obtain, and when too high, there exists a tendency for a film to fracture | rupture.

  Thus, the PVA film used in the present invention is obtained. In the present invention, the PVA film is contained so that the boron atom content in the PVA film becomes the above predetermined content. A method of immersing the boron compound solution in the prepared PVA film is preferable.

  In immersing the boron compound solution in the PVA-based film, the solvent used as the boron compound solution may be any solvent that dissolves the boron compound, but water is preferred because it can easily swell the PVA-based film.

  Further, the concentration of the boron compound solution is preferably 0.05 to 5% by weight, particularly 0.1 to 4% by weight, and more preferably 0.2% in that the PVA film can contain boron atoms efficiently. ~ 3 wt% is preferred. If the concentration is too low, it tends to be difficult to efficiently contain boron atoms, and if it is too high, the boron atom content in the film tends to vary.

  Furthermore, the immersion temperature is preferably 10 to 50 ° C, particularly 20 to 50 ° C, more preferably 30 to 50 ° C. If the immersion temperature is too low, it tends to be difficult to contain boron atoms efficiently, and if it is too high, the moisture in the immersion tank volatilizes and the concentration tends to change.

  The immersion time is usually in the range of 30 seconds to 2 hours, although depending on the immersion temperature, it is preferably 1 minute to 1 hour, more preferably 2 minutes to 30 minutes. If the immersion time is too short, the boron atom content tends to decrease, and if it is too long, the boron atom tends to be contained so that the film tends to become brittle, and the production efficiency tends to decrease.

  The PVA film of the present invention thus obtained (PVA film containing boron atoms) is a film having flame retardancy and excellent transparency, and is used for industrial materials and building materials. (For example, a curing sheet used in an environment where flammable substances are used) and interior materials are very useful.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
In the examples, “parts” and “%” mean weight basis.

Example 1
20% (average saponification degree 99 mol%, 4% average viscosity (20 ° C.) of 28 mPa · s PVA 100 parts, glycerin 10 parts, surfactant (polyoxyethylene sorbitan monolaurate) 0.3 parts The dope with a solid content concentration) is discharged from a T-die onto a rotating stainless steel endless belt whose surface temperature is adjusted to 90 ° C., cast into a film, and subsequently heat treated with a satin embossing roll adjusted to 120 ° C. The PVA film having a thickness of 50 μm was obtained.
The obtained PVA film was immersed in a 2% boric acid aqueous solution adjusted to 40 ° C. for 15 minutes, and then dried in an 80 ° C. dryer for 5 minutes as it was without particularly wiping off the film surface. When the boron atom content contained in the obtained boron-containing PVA film was quantified, it was 17000 mg / kg.

The boron atom content was measured as follows.
About 1 g of the boron-containing PVA film is melt-decomposed with 8 g of alkali (manufactured by Wako Pure Chemical Industries, Ltd., potassium potassium carbonate (special grade)), and the volume is adjusted to 250 ml. ICP (Inductively Coupled Plasma manufactured by Thermo Fisher Scientific) ) It was introduced into an emission spectroscopic analyzer and the boron content in the film was quantified.

Moreover, about the obtained boron containing PVA film, it was 6% when the weight decreasing rate after being immersed in 30 degreeC water for 10 minutes was measured.
The weight reduction rate was measured as follows.
A film having a size of 100 mm × 100 mm was cut out, and the cut film was dried in an environment of 100 ° C. for 5 minutes, and then its weight (α) was measured. Then, after immersing the film in water at 30 ° C. for 10 minutes, the film was taken out from the water, and the film surface was dried for 10 minutes in an environment at 100 ° C. without wiping off, and the weight (β) was measured. From the measured weight (α) and weight (β), the weight reduction rate was calculated according to the following formula.
Weight reduction rate (%) = [(α) − (β) / (α)] × 100

The following evaluation was performed about the obtained boron containing PVA film.
<Combustion test>
Cut the boron-containing PVA film into a strip of width 25 mm x length 150 mm, pinch one end with tweezers, apply a flame of a candle lit from the other end (bottom end) for 3 seconds, observe the fire spread state of the film, Evaluation was performed according to the criteria.
(Judgment)
X: The flame that ignited once spread and burned out completely within 10 seconds (no self-extinguishing property).
Δ: The flame disappeared within 5 seconds although it ignited and burned once.
○: Even if ignited, it did not spread and disappeared.

Example 2
A PVA film was obtained in the same manner as in Example 1 except that glycerin was not added.
The obtained PVA film was immersed in a water bath adjusted to 40 ° C. for 3 minutes, then immersed in a 1% sodium polyborate aqueous solution adjusted to 40 ° C. for 30 minutes, and then left as it was without particularly wiping the film surface. In the state, it was dried in an 80 ° C. dryer for 5 minutes. When the boron atom content contained in the obtained boron-containing PVA film was quantified, it was 20000 mg / kg.
Moreover, when the weight decreasing rate was measured about the obtained boron containing PVA film, it was 3%.
About the obtained boron containing PVA film, evaluation similar to Example 1 was performed.

Example 3
Average saponification degree 99 mol%, 4% aqueous solution average viscosity (20 ° C.) 28 mPa · s PVA 100 parts, surfactant (polyoxyethylene sorbitan monolaurate) 0.3 parts 20% (solid content concentration) The dope was discharged from a T-die onto a rotating stainless steel endless belt whose surface temperature was adjusted to 90 ° C. to obtain an unstretched film by casting, and then 3 × 3 times by a biaxial stretching machine. Was biaxially stretched to obtain a biaxially stretched PVA film having a thickness of 30 μm.
After the obtained biaxially stretched PVA film was immersed in a 2% aqueous sodium polyborate solution adjusted to 50 ° C. for 30 minutes, it was dried in an 80 ° C. dryer for 5 minutes without wiping off the film surface. It was. When the boron atom content contained in the obtained boron-containing biaxially stretched PVA film was quantified, it was 20000 mg / kg.
Moreover, when the weight decreasing rate was measured about the obtained boron containing PVA film, it was 2%.
About the obtained boron containing PVA film, evaluation similar to Example 1 was performed.

Example 4
Using the same PVA film as in Example 1, it was immersed in a water bath adjusted to 40 ° C. for 3 minutes, then immersed in a 2% boric acid aqueous solution adjusted to 20 ° C. for 30 minutes, and then the surface of the film was particularly wiped off. It was made to dry for 5 minutes in an 80 degreeC dryer as it was, without leaving. When the boron atom content contained in the obtained boron-containing PVA film was quantified, it was 13000 mg / kg.
Moreover, when the weight decreasing rate was measured about the obtained boron containing PVA film, it was 6%.
About the obtained boron containing PVA film, evaluation similar to Example 1 was performed.

Comparative Example 1
A PVA film was obtained in the same manner as in Example 1 except that PVA was changed to PVA having an average saponification degree of 99 mol% and a 4% aqueous solution average viscosity (20 ° C.) of 63 mPa · s.
Moreover, when the weight decreasing rate was measured about the obtained PVA film, it was 9%.
Evaluation similar to Example 1 was performed with respect to the obtained PVA film, without performing a boron compound solution process.

Comparative Example 2
A PVA film was obtained in the same manner as in Example 1 except that PVA was changed to PVA having an average saponification degree of 99 mol% and a 4% aqueous solution average viscosity (20 ° C.) of 63 mPa · s.
The obtained PVA film was immersed in a 1% sodium polyborate aqueous solution adjusted to 5 ° C. for 3 minutes, and then dried in an 80 ° C. drier for 5 minutes without wiping off the film surface. When the boron atom content contained in the obtained boron-containing PVA film was quantified, it was 2000 mg / kg.
Moreover, when the weight decreasing rate was measured about the obtained boron containing PVA film, it was 8%.
About the obtained boron containing PVA film, evaluation similar to Example 1 was performed.
The evaluation results of Examples and Comparative Examples are shown in Table 1.

  From the above results, the PVA film of Comparative Example 1 alone or the PVA film of Comparative Example 2 in which the amount of boron atoms is less than a predetermined amount is in contact with the flame and spreads at once, but as in the Examples It can be seen that a PVA-based film containing a certain amount of boron atoms has a result that the flame disappears without spreading and has flame retardancy and can suppress the spread of fire.

  The polyvinyl alcohol-based film of the present invention has an effect excellent in flame retardancy and transparency, and is particularly used for industrial materials and building materials (for example, curing used in an environment where flammable substances are used). Sheet) and interior materials.

Claims (12)

A polyvinyl alcohol film having a boron atom content in the polyvinyl alcohol film of 3000 to 50000 mg / kg. The polyvinyl alcohol-based film according to claim 1, wherein the weight reduction rate after being immersed in water at 30 ° C for 10 minutes is 20% or less. 3. The polyvinyl alcohol-based resin according to claim 1, wherein the polyvinyl alcohol-based resin has an average degree of saponification of 90 mol% or more and an average viscosity of a 4% by weight aqueous solution at 20 ° C. of 5 to 70 mPa · s. the film. The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the polyvinyl alcohol film is a uniaxially or biaxially stretched polyvinyl alcohol film. The polyvinyl alcohol film according to any one of claims 1 to 4, wherein a boron atom in the polyvinyl alcohol film is derived from a polyboric acid metal salt. The polyvinyl alcohol film according to any one of claims 1 to 5, wherein a boron atom is contained in the polyvinyl alcohol film by immersing the polyvinyl alcohol film in a boron compound solution. The polyvinyl alcohol film according to claim 6, wherein the polyvinyl alcohol film is previously swollen in water and then immersed in a boron compound solution. The polyvinyl alcohol film according to claim 6 or 7, wherein the concentration of the boron compound solution is 0.05 to 5% by weight. The method for producing a polyvinyl alcohol film according to any one of claims 1 to 8, wherein a boron atom is contained in the polyvinyl alcohol film by immersing the polyvinyl alcohol film in a boron compound solution. The method for producing a polyvinyl alcohol film according to claim 9, wherein the polyvinyl alcohol film is previously swollen in water and then immersed in a boron compound solution. A method for producing a polyvinyl alcohol film, comprising immersing a polyvinyl alcohol film in a boron compound solution to contain boron atoms in the polyvinyl alcohol film. The method for producing a polyvinyl alcohol film according to claim 11, wherein the polyvinyl alcohol film is swollen in advance and then immersed in the boron compound solution.