JP4090934B2 - Insolubilized polyvinyl alcohol fiber aggregate and method for producing the same - Google Patents

Description

【００６２】
【表２】

【００６３】
表１及び表２の結果から、α−ヒドロキシ酸と同様にカルボキシル基を有するグルタル酸（比較例１）やマロン酸（比較例２）を添加しても、沸騰水浸漬減量率が４％以下という十分に不溶化した不溶化ＰＶＡ繊維集合体を得ることは困難であり、α−ヒドロキシ酸を用いることによる優位性が確認された。また、α−ヒドロキシ酸を添加した場合であっても、加熱が不十分な場合（比較例３、４）には、沸騰水浸漬減量率が４％以下という十分に不溶化した不溶化ＰＶＡ繊維集合体を得ることは困難であり、α−ヒドロキシ酸の融点以上の温度で加熱することの優位性も確認された。
【００６４】
【発明の効果】
本発明の不溶化ポリビニルアルコール繊維集合体は、安全性が高く、十分に不溶化したものであるため、各種用途に適用できるものである。
【００６５】
本発明の不溶化ポリビニルアルコール繊維集合体の製造方法は、安全性が高く、十分に不溶化した不溶化ポリビニルアルコール繊維集合体を製造することができる。
【図面の簡単な説明】
【図１】 静電紡糸装置の模式的断面図
【符号の説明】
１ 溶解液供給器
２ ノズル
３ 電圧印加装置
４ 捕集体
５ 密閉容器
６ 湿度調節器
６ａ バルブ又は弁
７ 排気装置
７ａ バルブ又は弁[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an insolubilized polyvinyl alcohol fiber assembly and a method for producing the same.
[0002]
[Prior art]
Polyvinyl alcohol fibers can be spun using an aqueous polyvinyl alcohol solution that uses water as a solvent instead of an organic solvent as a spinning stock solution, and even insolubilized polyvinyl alcohol fibers are hydrophilic and easy to adapt to water. Alcohol fiber aggregates have heretofore been suitably used.
[0003]
For example, “a thin film-like polyvinyl alcohol-based fine fiber sheet in which continuous fine fibers having a fiber diameter of 1 μm or less are stacked and intersected with each other, and an opening between the fibers is 1 μm or less” (Patent Document) 1) is known. However, since this fine fiber sheet is melted by moisture such as hand sweat, it is not only difficult to handle, but also when used for various applications such as filter media (particularly liquid filter). In some cases, it dissolved and did not work.
[0004]
Therefore, acetalization (or formalization) using aldehydes as in the past, or acetalization with an aromatic compound having two aldehyde groups has been considered (Patent Document 2). However, since aldehydes have toxicity and carcinogenicity, it is preferable that they are fiber aggregates composed of polyvinyl alcohol fibers insolubilized without using aldehydes.
[0005]
[Patent Document 1]
Japanese Patent Publication No. 3-79467 (Claims etc.)
[Patent Document 2]
Japanese Examined Patent Publication No. 29-6145 (claims, etc.)
[0006]
[Problems to be solved by the invention]
Therefore, the present invention provides an insolubilized polyvinyl alcohol fiber assembly that does not use aldehydes, has no concerns about toxicity and carcinogenicity, is hardly dissolved by moisture, and can be applied to various uses, and a method for producing the same. For the purpose.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention is “a fiber assembly in which insolubilized polyvinyl alcohol fibers in which polyvinyl alcohol is insolubilized with α-hydroxy acid are assembled, and this fiber assembly is reduced in boiling water immersion as defined by the following: An insolubilized polyvinyl alcohol fiber aggregate characterized by a rate (Ra) of 4% or less.
Record
Ra = {(Mab−Maa) / Mab} × 100
Ra: Weight loss rate of the fiber aggregate immersed in boiling water
Mab: Mass of the fiber assembly before being immersed in boiling water for 20 minutes
“Maa: Mass of fiber assembly after immersion in boiling water for 20 minutes”. Since α-hydroxy acid is highly safe and can be used as a food additive, aggregates of insolubilized polyvinyl alcohol fibers insolubilized with α-hydroxy acid are safe and have no concern about toxicity or carcinogenicity. It is expensive. In addition, even when immersed in boiling water, the rate of decrease in mass is small, it is sufficiently insolubilized, and is difficult to dissolve due to moisture or the like, so that it can be applied to various applications.
[0008]
The invention according to claim 2 of the present invention is the “insolubilized polyvinyl alcohol fiber assembly according to claim 1, wherein the polyvinyl alcohol before insolubilization is composed of unmodified polyvinyl alcohol”. Since the polyvinyl alcohol is unmodified, it is a fiber assembly that does not generate odor due to decomposition or the like.
[0009]
The invention according to claim 3 of the present invention is as follows: “The α-hydroxy acid is composed of one or more kinds selected from malic acid, tartaric acid, and citric acid. Is an insolubilized polyvinyl alcohol fiber aggregate. It can be effectively insolubilized by using these α-hydroxy acids. In addition, malic acid, tartaric acid, and citric acid are preferable because they have two or more carboxyl groups in one molecule and are easily insolubilized.
[0010]
The invention according to claim 4 of the present invention is the “insolubilized polyvinyl alcohol fiber assembly according to any one of claims 1 to 3, wherein the fiber diameter of the insolubilized polyvinyl alcohol fiber is 1 μm or less”. It is. Since the fiber diameter is small in this way, it is excellent in various performances such as separation performance, liquid retention performance, wiping performance, concealability, insulation, or flexibility, so it can be applied to various applications and has a wide range of applications. It is.
[0011]
The invention according to claim 5 of the present invention is as follows: “(1) A step of preparing a solution in which polyvinyl alcohol and α-hydroxy acid are dissolved in a solvent capable of dissolving both, (2) the dissolution (3) by heating the polyvinyl alcohol fiber, the boiling water immersion weight loss rate (Rf) defined by the following is insolubilized to 4% or less, thereby insolubilizing the polyvinyl alcohol fiber. (4) A process for producing a fiber aggregate by aggregating the insolubilized polyvinyl alcohol fibers. A method for producing an insolubilized polyvinyl alcohol fiber aggregate.
Record
Rf = {(Mfb−Mfa) / Mfb} × 100
Rf: Weight loss ratio of fibers immersed in boiling water
Mfb: the mass of the fiber before being immersed in boiling water for 20 minutes
Mfa: the mass of the fiber after being immersed in boiling water for 20 minutes. According to this production method, it is possible to produce a fiber assembly that is highly safe and sufficiently insolubilized and can be applied to various uses without using aldehydes.
[0012]
The invention according to claim 6 of the present invention is: (1) a step of preparing a solution in which polyvinyl alcohol and α-hydroxy acid are dissolved in a solvent capable of dissolving both, (2) the dissolution A step of aggregating the polyvinyl alcohol fibers spun using the liquid to form a polyvinyl alcohol fiber aggregate; (3) heating the polyvinyl alcohol fiber aggregate to reduce the weight loss by boiling water defined by the following ( Ra) is insolubilized to 4% or less, and a process for producing an insolubilized polyvinyl alcohol fiber aggregate is provided. A method for producing an insolubilized polyvinyl alcohol fiber aggregate.
Record
Ra = {(Mab−Maa) / Mab} × 100
Ra: Weight loss rate of the fiber aggregate immersed in boiling water
Mab: Mass of the fiber assembly before being immersed in boiling water for 20 minutes
“Maa: Mass of fiber assembly after immersion in boiling water for 20 minutes”. According to this production method, it is possible to produce a fiber assembly that is highly safe and sufficiently insolubilized and can be applied to various uses without using aldehydes.
[0013]
The invention according to claim 7 of the present invention is as follows: “Additional amount of α-hydroxy acid is 0.005 mol or more with respect to 1 mol of monomer unit of polyvinyl alcohol. 6. A method for producing an insolubilized polyvinyl alcohol fiber assembly according to item 6. By making the amount of α-hydroxy acid added within the above range, it is easy to produce a fiber assembly having a boiling water immersion loss rate of 4% or less.
[0014]
The invention according to claim 8 of the present invention is as follows: “The insolubilized polyvinyl alcohol fiber assembly according to any one of claims 5 to 7, wherein the heating temperature is equal to or higher than the melting point of α-hydroxy acid. It is a manufacturing method of a body. By heating at a temperature equal to or higher than the melting point of α-hydroxy acid, it is easy to produce a fiber assembly having a boiling water immersion loss rate of 4% or less.
[0015]
The invention according to claim 9 of the present invention is “insolubilized polyvinyl alcohol according to any one of claims 5 to 8, characterized in that a polyvinyl alcohol fiber is spun by an electrospinning method using a solution. "Production method of fiber assembly". Spinning by the electrostatic spinning method makes it easy to produce aggregates of insolubilized polyvinyl alcohol fibers with a fiber diameter of 1 μm or less. As a result, various properties such as separation performance, liquid retention performance, wiping performance, concealability, insulation, or flexibility It is easy to manufacture a fiber assembly that has excellent performance and can be applied to various applications.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The insolubilized polyvinyl alcohol fiber (hereinafter sometimes referred to as “insolubilized PVA fiber”) constituting the insolubilized polyvinyl alcohol fiber aggregate (hereinafter simply referred to as “fiber aggregate”) of the present invention is obtained by converting polyvinyl alcohol to α-hydroxy. Insolubilized with acid. As the polyvinyl alcohol before insolubilization, a polyvinyl alcohol polymer having a vinyl alcohol unit can be used. Usually, since it cannot superpose | polymerize directly from vinyl alcohol, the polyvinyl alcohol produced by saponifying a vinyl acetate polymer can be used. In addition to 100 mol% saponified polyvinyl alcohol, partially saponified polyvinyl alcohol in which vinyl acetate remains can also be used. The degree of saponification of the partially saponified polyvinyl alcohol is not particularly limited, but is preferably 50 mol% or more, more preferably 65 mol% or more, and further preferably 80 mol% or more. Moreover, even if it is the reacetylation thing which has the saponification degree of these ranges, it can be used. In addition, a cation-modified polyvinyl alcohol formed by copolymerizing a quaternary ammonium salt or reacting a low molecular weight compound having a quaternary ammonium group and a reactive group such as an aldehyde group with polyvinyl alcohol is used. However, since cation-modified polyvinyl alcohol may decompose and generate odor, it is unmodified polyvinyl alcohol (100 mol% saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, or re-acetylated product). preferable.
[0017]
The average degree of polymerization of the polyvinyl alcohol that can be used in the present invention is not particularly limited, but is preferably 200 or more, more preferably 300 or more so that the strength of the insolubilized PVA fiber is excellent. . Further, if the average degree of polymerization is too high, the solubility in a solvent is lowered, and the productivity may be inferior. Therefore, it is preferably 30,000 or less, more preferably 20,000 or less, More preferably, it is 000 or less. The “degree of saponification” and “average degree of polymerization” in the present invention refer to values measured according to JIS K6726. In addition, even if it is a case where a saponification degree is less than about 70 mol%, the value measured according to the said JIS specification is said.
[0018]
Since the insolubilized PVA fiber of the present invention is obtained by insolubilizing polyvinyl alcohol as described above with α-hydroxy acid, unlike acetalization (or formalization) using aldehydes, there are concerns about toxicity and carcinogenicity. There is no high safety.
[0019]
The details of the insolubilization with α-hydroxy acid are not clear, but it is presumed that the insolubilization may be caused by a chemical reaction (esterification) between the hydroxyl group of polyvinyl alcohol and the carboxyl group of α-hydroxy acid. is doing. In addition, in α-hydroxy acids having two or more carboxyl groups, it is speculated that this reaction occurs not only within the molecule but also between the molecules, and crosslinking also occurs.
[0020]
The α-hydroxy acid is an organic compound in which a hydroxyl group and a carboxyl group are bonded to the same carbon atom, and is also used as a food additive or a cosmetic raw material, and has high safety and low environmental problems. Examples of the α-hydroxy acid (more specifically, α-hydroxycarboxylic acid) include glycolic acid, lactic acid, malic acid, citric acid, and tartaric acid. Among α-hydroxy acids, those that are solid at room temperature and normal pressure have excellent spinnability, and the fibers do not stick even after spinning and drying. it can. Among these α-hydroxy acids, malic acid, tartaric acid, and citric acid, which are easily insolubilized because they have two or more carboxyl groups in one molecule and are solid at normal temperature and pressure, can be suitably used. The α-hydroxy acid can be insolubilized by using one kind or two or more kinds in combination, and it is particularly preferable to insolubilize malic acid, tartaric acid and citric acid by using one kind or two or more kinds in combination. Some of these α-hydroxy acids have asymmetric carbon atoms, and isomers exist. However, in the present invention, α-hydroxy acids may be used, and the isomers are not particularly limited.
[0021]
The fiber diameter of the insolubilized PVA fiber constituting the fiber assembly of the present invention is not particularly limited, but is excellent in various performances such as separation performance, liquid retention performance, wiping performance, concealing performance, insulation, or flexibility. Thus, the fiber diameter is preferably 1 μm or less, and the smaller the fiber diameter of the insolubilized PVA fiber, the better the various characteristics. Therefore, it is more preferably 0.8 μm or less, and 0.6 μm or less. More preferably. The lower limit of the fiber diameter of the insolubilized PVA fiber is not particularly limited, but about 1 nm is appropriate. “Fiber diameter” in the present invention means a diameter in a cross section of a fiber obtained by measurement from an electron micrograph of a fiber assembly. When the cross section is non-circular, the same area as the cross section is obtained. The diameter of the circle is considered as the fiber diameter.
[0022]
The fiber length of the insolubilized PVA fiber constituting the fiber assembly of the present invention is not particularly limited, but it is preferably 0.1 mm or more so that the insolubilized PVA fiber does not easily fall off. In particular, it is preferable that the insolubilized PVA fiber is a continuous fiber in terms of the ability to prevent dropping.
[0023]
The fiber assembly of the present invention is a collection of insolubilized PVA fibers as described above. The fiber assembly has a boiling water immersion loss rate (Ra) defined by the following of 4% or less. As is apparent from the following formula, the boiling water immersion loss rate is a percentage of the mass change of the fiber assembly before and after being immersed in boiling water. It is an index that indirectly indicates that it is difficult to dissolve by, for example. Since the fiber assembly of the present invention is difficult to dissolve in water or the like having a boiling water immersion loss rate of 4% or less, it can be used without problems in water and can be applied to various applications. . The fact that the value of the boiling water immersion weight loss is small means that it is difficult to dissolve with water or the like. Therefore, the boiling water immersion weight loss is preferably 3% or less, more preferably 2% or less. Preferably, it is 1% or less, more preferably 0.5% or less, and ideally 0%.
Record
Ra = {(Mab−Maa) / Mab} × 100
Ra: Weight loss rate of the fiber aggregate immersed in boiling water
Mab: Mass of the fiber assembly before being immersed in boiling water for 20 minutes
Maa: Mass of the fiber assembly after being immersed in boiling water for 20 minutes
[0024]
In addition, the aggregate state of the insolubilized PVA fiber in the fiber assembly of the present invention is not particularly limited. That is, the insolubilized PVA fibers may be in a regularly assembled state (for example, a woven form, a knitted form, a net form, etc.) or an irregularly assembled state (for example, a non-woven form). It can be a collective state depending on the application. The fiber assembly of the present invention is, for example, a filter medium for liquid or gas, a separator for various secondary batteries such as an alkaline battery or a lithium battery, or a separator for a primary battery, an interlining, a mask, a scratching material, and for holding various indicators. It can use suitably for uses, such as a substrate and a wiper, and when applying to these uses, it is preferred to consist of a nonwoven fabric form.
[0025]
The basis weight of the fiber assembly of the present invention (value measured as 10 cm × 10 cm according to JIS L1085) is not particularly limited, but is 0.1 to 20 g / m. ² Preferably, 0.5 to 18 g / m ² 1 to 15 g / m ² It is more preferable that The thickness of the fiber assembly is a value (μm) measured using a micrometer, and is preferably 1 to 100 μm, and more preferably 2 to 80 μm.
[0026]
The fiber assembly of the present invention can be produced, for example, as follows.
[0027]
(First manufacturing method)
First, (1) a step of preparing a solution obtained by dissolving polyvinyl alcohol and α-hydroxy acid in a solvent capable of dissolving both of them. For this purpose, a polyvinyl alcohol and an α-hydroxy acid as described above and a solvent capable of dissolving both of them are prepared. If this solvent cannot dissolve only one or both of polyvinyl alcohol and α-hydroxy acid, it becomes difficult to mix uniformly, and a fiber aggregate having a boiling water immersion loss rate of 4% or less is obtained. Because it becomes difficult. The solvent is not particularly limited as long as it can dissolve both polyvinyl alcohol and α-hydroxy acid. For example, water, alcohols, and other organic solvents can be used. . Among these, it is preferable to use water in view of problems in the manufacturing environment.
[0028]
These prepared polyvinyl alcohol and α-hydroxy acid are dissolved in the prepared solvent to prepare a solution. The amount of α-hydroxy acid added to polyvinyl alcohol is 0.005 mol or more with respect to 1 mol of polyvinyl alcohol monomer unit so that a fiber aggregate having a boiling water immersion loss rate of 4% or less can be easily produced. Preferably, it is 0.01 mol or more, more preferably 0.02 mol or more, and further preferably 0.03 mol or more. On the other hand, the upper limit of the amount of α-hydroxy acid added to the polyvinyl alcohol can be arbitrarily set within a range that does not impair the spinnability of the polyvinyl alcohol fiber, but it is 1 mol or less with respect to 1 mol of the polyvinyl alcohol monomer unit. Is preferably 0.8 mol or less, and more preferably 0.5 mol or less. Moreover, the density | concentration of the polyvinyl alcohol in a solution is not specifically limited as long as it is below the density | concentration which both polyvinyl alcohol and alpha-hydroxy acid can melt | dissolve, It can set arbitrarily. In general, it is preferably 0.1 to 50%.
[0029]
Next, (2) a step of spinning polyvinyl alcohol fiber using the solution is performed. As a spinning method of the polyvinyl alcohol fiber, a conventionally known spinning method can be adopted, and for example, it can be spun by a wet spinning method, a dry spinning method, a flash spinning method, a centrifugal spinning method, an electrostatic spinning method, or the like. . Among these, according to the electrospinning method, it is easy to produce polyvinyl alcohol fibers having a fiber diameter of 1 μm or less. In any case, it is preferable to dry after spinning.
[0030]
Next, (3) by heating the polyvinyl alcohol fiber, the boiling water immersion weight loss rate (Rf) defined by the following is insolubilized to 4% or less to produce an insolubilized polyvinyl alcohol fiber.
Record
Rf = {(Mfb−Mfa) / Mfb} × 100
Rf: Weight loss ratio of fibers immersed in boiling water
Mfb: the mass of the fiber before being immersed in boiling water for 20 minutes
Mfa: the mass of the fiber after being immersed in boiling water for 20 minutes
[0031]
The temperature of the heat treatment is not particularly limited as long as the temperature can be sufficiently insolubilized until the boiling water immersion loss rate is 4% or less, but heating is performed at a temperature equal to or higher than the melting point of α-hydroxy acid. It is preferable to heat at a temperature higher than the melting point by 5 ° C. or more. When two or more kinds of α-hydroxy acids are included, it is preferable to heat at a temperature equal to or higher than the melting point of the α-hydroxy acid having the highest melting point, and more preferable to heat at a temperature higher by 5 ° C. than the melting point. In any case, the upper limit of the heating temperature is a temperature at which α-hydroxy acid and polyvinyl alcohol are not decomposed. Further, the heating time may be a time when the boiling water immersion weight loss rate is 4% or less, and is not particularly limited, but is preferably 1 minute or more, more preferably 3 minutes or more, More preferably, it is 5 minutes or more. On the other hand, even if heated for a too long time, no change is seen in the effect of insolubilization, so that it is preferably within 1 hour, more preferably within 45 minutes.
[0032]
The “melting point” in the present invention refers to a temperature that gives a maximum value of a melting endothermic curve obtained by using a differential scanning calorimeter at a temperature rising temperature of 10 ° C./min and raising the temperature from room temperature. When there are two or more maximum values, the highest temperature maximum value is taken as the melting point.
[0033]
As described above, the insolubilized PVA fiber having a boiling water immersion loss rate of 4% or less is, for example, a heating temperature in which the addition amount of α-hydroxy acid is 0.005 mol or more with respect to 1 mol of polyvinyl alcohol monomer unit. By adjusting the conditions such that the temperature is higher than the melting point of the α-hydroxy acid, the heating time is 1 minute or more, etc., by making the conditions more suitable conditions Insolubilized PVA fibers having a smaller weight loss by immersion in boiling water can be produced.
[0034]
And (4) The process of collecting the said insolubilized polyvinyl alcohol fiber and manufacturing a fiber assembly is implemented. This method of assembling the insolubilized PVA fibers can be carried out by a conventionally known method. For example, a fiber assembly in a woven form can be manufactured using a tappet loom, dobby loom, jacquard loom, fly shuttle loom, shuttleless loom, etc., and a fiber assembly in a knitted form is a weft knitting machine or a circular knitting machine. Can be manufactured using full-fashion machines, tricot machines, Milanese machines, Russell machines, etc., and non-woven fiber assemblies are wet papermaking, resin bond, needle punch, fluid flow (for example, water flow) entanglement Etc. can be manufactured.
[0035]
If necessary, various post-treatments can be performed so that the fiber assembly is suitable for various applications. For example, a calendar process for densification, a hydrophilic process, a water repellent process, a surfactant adhesion process, a pure water cleaning process, and the like can be performed.
[0036]
(Second manufacturing method)
First, (1) a step of preparing a solution obtained by dissolving polyvinyl alcohol and α-hydroxy acid in a solvent capable of dissolving both of them. Since this step can be performed in exactly the same manner as the first manufacturing method, a detailed description is omitted.
[0037]
Next, (2) a step of collecting polyvinyl alcohol fibers spun using the solution to form a polyvinyl alcohol fiber aggregate is performed. This step differs from the first production method in that the spun fibers are directly assembled to form a polyvinyl alcohol fiber aggregate. As a method for directly assembling the spun fibers, for example, a flash spinning method, a centrifugal spinning method, an electrostatic spinning method, or the like can be used. Among these, the electrospinning method makes it easy to produce a fiber assembly made of polyvinyl alcohol fibers having a fiber diameter of 1 μm or less. In any case, it is preferable to dry after forming the fiber assembly.
[0038]
Here, a suitable electrospinning method will be described with reference to FIG.
[0039]
First, the solution is supplied as a spinning solution from the solution supply device 1 to the nozzle 2 and pushed out from the nozzle 2. A voltage is applied by the voltage application device 3, and an electric field is applied to the extruded solution to form a fiber. To do. The direction of extrusion of the solution is not particularly limited, but it is preferable that the direction of extrusion from the nozzle does not match the direction of action of gravity so that the solution does not easily drop. In particular, it is preferable to extrude the solution in a direction opposite to the direction of gravity or in a direction perpendicular to the direction of gravity.
[0040]
The diameter of the nozzle 2 for extruding this solution varies depending on the fiber diameter of the insolubilized PVA fiber, but the diameter (inner diameter) of the nozzle 2 is 0.05 so that the fiber diameter of the insolubilized PVA fiber can be 1 μm or less. It is preferable to be about ~ 1.5 mm.
[0041]
The nozzle 2 may be made of metal or non-metal. If the nozzle 2 is made of metal, the nozzle 2 can be used as one of the electrodes. If the nozzle 2 is made of non-metal, an electrode is placed inside the nozzle 2 so that the extruded solution An electric field can be applied.
[0042]
After extruding the solution from the nozzle 2, the solution is drawn and made into fibers by applying an electric field to the extruded solution. This electric field varies depending on the fiber diameter of the insolubilized PVA fiber, the distance between the nozzle 2 and the collector 4 that collects the fibers, the viscosity of the solution, and the like. In order to make it 1 micrometer or less, it is preferable that it is 0.2-5 kV / cm. If the electric field to be applied is large, the fiber diameter of the insolubilized PVA fiber tends to become thin as the electric field value increases, but if it exceeds 5 kV / cm, it is not preferable because air breakdown tends to occur. Moreover, if it is less than 0.2 kV / cm, it is difficult to form a fiber shape.
[0043]
By applying an electric field to the extruded solution as described above, an electrostatic charge is accumulated in the solution, and is electrically pulled and stretched by the electrode on the collector 4 side to be fiberized. Since the fibers are electrically stretched, the speed of the fibers is accelerated by the electric field as the fibers approach the collector 4, and polyvinyl alcohol fibers having a smaller fiber diameter are obtained. Moreover, it is thought that it becomes thin by evaporation of the solvent, the electrostatic density is increased, it is split by the electric repulsive force, and it becomes a polyvinyl alcohol fiber having a smaller fiber diameter.
[0044]
Such an electric field is generated by, for example, generating a potential difference between the nozzle 2 (in the case of a metal nozzle, the nozzle itself, in the case of a non-metallic nozzle such as glass or resin, an electrode inside the nozzle) and the collector 4. It can be made to act by providing. For example, as shown in FIG. 1, a potential difference can be provided by applying a voltage to the nozzle 2 and grounding the collector 4. Conversely, applying a voltage to the collector 4 and grounding the nozzle 2. A potential difference can also be provided.
[0045]
The voltage application device 3 is not particularly limited, but a direct current high voltage generator can be used, and a Van de Graf electromotive machine can also be used. The applied voltage is not particularly limited as long as the electric field intensity can be set as described above, but is preferably about 5 to 50 KV. Note that the polarity of the applied voltage may be either positive or negative. However, it is preferable to make the nozzle 2 side have a positive potential so that the fibers can be prevented from spreading and gathered in a state where the hole diameter is small and the hole diameter distribution is narrow. In particular, it is preferable that the counter electrode on the collector 4 side is grounded, the nozzle 2 side is applied positively, and the nozzle 2 side has a positive potential so that corona discharge during voltage application can be easily suppressed. .
[0046]
The collector 4 used for collecting the spun polyvinyl alcohol fibers is not particularly limited as long as the polyvinyl alcohol fibers can be collected. For example, a drum, a nonwoven fabric, A conductive material made of metal or carbon having a woven fabric, knitted fabric, net, flat plate, or belt shape, or a nonconductive material made of organic polymer or the like can be used. In some cases, a liquid such as water or an organic solvent can be used as a collector.
[0047]
As described above, when the collector 4 is used as the other electrode, the collector 4 has a volume resistance of 10. ⁹ It is preferably made of a conductive material (for example, made of metal) of Ω or less. On the other hand, when the conductive material is disposed as the counter electrode behind the collector 4 as viewed from the nozzle 2 side, the collector 4 does not necessarily need to be a conductive material. As in the latter case, when the counter electrode is disposed behind the collector, the collector and the counter electrode may be in contact with each other or may be separated from each other.
[0048]
In addition, it is preferable to implement the electrospinning to collect the spun polyvinyl alcohol fibers in an atmosphere with a relative humidity of 30 to 80%. This is because when the relative humidity is less than 30%, the solution at the nozzle outlet dries quickly and tends to solidify and close the nozzle. When the relative humidity exceeds 80%, it is difficult to dry. It is because it tends to become difficult to form fibers, and more preferably 35 to 70%. Therefore, in FIG. 1, while installing the nozzle 2 and the collection body 4 in the airtight container 5, the humidity controller 6 is connected via the valve or the valve 6a, humidity-conditioned air is sent, The humidity can be adjusted within the above range. In FIG. 1, an exhaust device 7 is connected to the sealed container 5 via a valve or a valve 7a so as not to raise the pressure in the sealed container and to discharge the solvent volatilized from the solution. .
[0049]
And (3) by heating the polyvinyl alcohol fiber aggregate, the boiling water immersion weight loss rate (Ra) defined by the following is insolubilized to 4% or less, and the step of producing the insolubilized polyvinyl alcohol fiber aggregate: carry out.
Record
Ra = {(Mab−Maa) / Mab} × 100
Ra: Weight loss rate of the fiber aggregate immersed in boiling water
Mab: Mass of the fiber assembly before being immersed in boiling water for 20 minutes
Maa: Mass of the fiber assembly after being immersed in boiling water for 20 minutes
[0050]
Since the heat treatment temperature and the heat treatment time are exactly the same as those in the first manufacturing method, a detailed description is omitted. The fiber aggregate having a boiling water immersion loss rate of 4% or less is, for example, that the addition amount of α-hydroxy acid is 0.005 mol or more with respect to 1 mol of polyvinyl alcohol monomer unit, and the heating temperature is α-. It is easy to produce by adjusting conditions such as a temperature higher than the melting point of the hydroxy acid and a heating time of 1 minute or more. By making the conditions more suitable, boiling water A fiber assembly having a smaller immersion weight loss rate can be produced.
[0051]
If necessary, various post-treatments can be performed so that the fiber assembly is suitable for various applications. For example, a calendar process for densification, a hydrophilic process, a water repellent process, a surfactant adhesion process, a pure water cleaning process, and the like can be performed.
[0052]
Examples of the present invention will be described below, but the present invention is not limited to the following examples.
[0053]
【Example】
(Examples 1-8, Comparative Examples 1-4)
Polyvinyl alcohol (made by Wako Pure Chemical Industries, Ltd., polyvinyl alcohol 2,800, partially saponified type, polyvinyl alcohol 1,000, fully saponified type, or polyvinyl alcohol 1,000, partially saponified type) as shown in Table 1 As shown in Table 1, an α-hydroxy acid and an organic acid having two carboxyl groups were prepared.
[0054]
Next, after the polyvinyl alcohol is dissolved in pure water so as to have a predetermined concentration as shown in Table 1, the α-hydroxy acid or organic acid is added to the polyvinyl alcohol aqueous solution by a predetermined amount as shown in Table 1. Was added and completely dissolved to prepare a solution.
[0055]
Here, an electrostatic spinning apparatus as shown in FIG. 1 was prepared. That is, a polytetrafluoroethylene tube was connected to the solution supply device 1, and a stainless steel nozzle 2 having an inner diameter of 0.6 mm was attached to the tip of the tube to obtain a spinning device. Next, a voltage applying device 3 was connected to the nozzle 2. Furthermore, a drum (collector 4, grounding) having a stainless steel thin plate with conductive fluorine processing on the surface thereof was installed at a position 10 cm away from the nozzle 2.
[0056]
Air that was humidity-controlled (relative humidity: 50 to 55%) with the humidity controller 6 was introduced into the sealed container 5 and exhausted from the exhaust device 7 to keep the humidity inside the sealed container 5 constant. Next, each of the dissolved solutions is pushed out from the nozzle 2 in a direction perpendicular to the direction of gravity by using the dissolved solution feeder 1, and the drum 4 is rotated at a constant speed (surface speed: 0.9 m / min). However, a voltage of +18 kV was applied from the voltage application device 3 to the nozzle 2, and an electric field was applied to the extruded solution to form a fiber. Polyvinyl alcohol fibers (polyvinyl alcohol / α-hydroxy) were formed on the stainless steel thin plate of the drum 4. Acid mixed fiber or polyvinyl alcohol / organic acid mixed fiber). When assembling the polyvinyl alcohol fibers, the nozzle 2 is reciprocally swung at a constant speed (moving speed: 2.5 cm / min) in a direction perpendicular to the rotation direction of the drum 4 to increase the dispersibility of the polyvinyl alcohol fibers. Increased. Subsequently, the obtained fiber assembly was dried at a temperature of 105 ° C. to form a dry polyvinyl alcohol fiber assembly.
[0057]
Next, this dry polyvinyl alcohol fiber aggregate is subjected to heat treatment under the conditions shown in Table 1, and insoluble PVA fiber aggregates in the form of nonwoven fabric (weight per unit, thickness) comprising insolubilized PVA fibers having fiber diameters as shown in Table 2. Was obtained as shown in Table 2. Any insolubilized PVA fiber was a continuous fiber.
[0058]
Then, after measuring the mass (Mab) of the insolubilized PVA fiber aggregate, the insolubilized PVA fiber aggregate is immersed in pure water maintained in a boiling state for 20 minutes and dried, and then the mass of the insolubilized PVA fiber aggregate is measured. (Maa) was measured. And the boiling water immersion weight loss rate (Ra) was computed by the following formula. These results are shown in Table 2.
Ra = {(Mab−Maa) / Mab} × 100
[0059]
(Comparative Example 5)
A solution was prepared using only polyvinyl alcohol (polyvinyl alcohol 1,000, partially saponified type, manufactured by Wako Pure Chemical Industries, Ltd.) without adding α-hydroxy acid, and then dried in the same manner as in Example 1. A polyvinyl alcohol fiber aggregate was formed. Thereafter, heat treatment was performed under the conditions described in Table 1, and a heat-treated PVA fiber assembly in the form of a nonwoven fabric (weight per unit: 4 g / m) composed of heat-treated PVA fibers (fiber diameter: 0.21 μm, continuous fibers). ² , Thickness: 19 μm).
[0060]
Then, after measuring the mass (Mab) of the heat-treated PVA fiber assembly, after immersing the heat-treated PVA fiber assembly in pure water maintained in a boiling state for 20 minutes, the mass of the heat-treated PVA fiber assembly An attempt was made to measure (Maa), but it was completely dissolved and the mass could not be measured.
[0061]
[Table 1]

[0062]
[Table 2]

[0063]
From the results of Tables 1 and 2, even when glutaric acid having a carboxyl group (Comparative Example 1) or malonic acid (Comparative Example 2) is added in the same manner as the α-hydroxy acid, the boiling water immersion loss rate is 4% or less. It was difficult to obtain a sufficiently insolubilized insolubilized PVA fiber assembly, and the superiority of using α-hydroxy acid was confirmed. Further, even when α-hydroxy acid is added, when heating is insufficient (Comparative Examples 3 and 4), the sufficiently insolubilized insolubilized PVA fiber aggregate having a boiling water immersion loss rate of 4% or less is used. It was difficult to obtain the above, and the superiority of heating at a temperature equal to or higher than the melting point of the α-hydroxy acid was also confirmed.
[0064]
【The invention's effect】
Since the insolubilized polyvinyl alcohol fiber aggregate of the present invention is highly safe and sufficiently insolubilized, it can be applied to various uses.
[0065]
The method for producing an insolubilized polyvinyl alcohol fiber aggregate of the present invention is highly safe and can produce a sufficiently insolubilized insolubilized polyvinyl alcohol fiber aggregate.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an electrospinning apparatus.
[Explanation of symbols]
1 Solution supply unit
2 nozzles
3 Voltage application device
4 collectors
5 Sealed container
6 Humidity controller
6a Valve or valve
7 Exhaust device
7a Valve or valve

Claims (9)

Polyvinyl alcohol is a fiber assembly in which insolubilized polyvinyl alcohol fibers are insolubilized with α-hydroxy acid, and this fiber assembly has a boiling water immersion loss rate (Ra) defined by the following that is 4% or less. A feature of the insolubilized polyvinyl alcohol fiber assembly.
Ra = {(Mab−Maa) / Mab} × 100
Ra: Weight loss ratio of fiber aggregate immersed in boiling water Mab: Mass of fiber aggregate before being immersed in boiling water for 20 minutes Maa: Mass of fiber aggregate after being immersed in boiling water for 20 minutes The insolubilized polyvinyl alcohol fiber assembly according to claim 1, wherein the polyvinyl alcohol before insolubilization comprises unmodified polyvinyl alcohol. The insolubilized polyvinyl alcohol fiber assembly according to claim 1 or 2, wherein the α-hydroxy acid comprises at least one selected from malic acid, tartaric acid and citric acid. The insolubilized polyvinyl alcohol fiber assembly according to any one of claims 1 to 3, wherein the fiber diameter of the insolubilized polyvinyl alcohol fiber is 1 µm or less. (1) A step of preparing a solution in which polyvinyl alcohol and α-hydroxy acid are dissolved in a solvent that can dissolve both of them,
(2) a step of spinning polyvinyl alcohol fiber using the solution;
(3) A step of heating the polyvinyl alcohol fiber so that the boiling water immersion weight loss rate (Rf) defined by the following is insolubilized to 4% or less to produce an insolubilized polyvinyl alcohol fiber,
(4) a step of producing a fiber assembly by aggregating the insolubilized polyvinyl alcohol fibers;
And a method for producing an insolubilized polyvinyl alcohol fiber assembly.
Rf = {(Mfb−Mfa) / Mfb} × 100
Rf: Weight loss ratio of fibers immersed in boiling water Mfb: Mass of fibers before being immersed in boiling water for 20 minutes Mfa: Mass of fibers after being immersed in boiling water for 20 minutes (1) A step of preparing a solution in which polyvinyl alcohol and α-hydroxy acid are dissolved in a solvent that can dissolve both of them,
(2) collecting polyvinyl alcohol fibers spun using the solution to form a polyvinyl alcohol fiber aggregate;
(3) A step of heating the polyvinyl alcohol fiber aggregate so that the boiling water immersion weight loss rate (Ra) defined by the following is insolubilized to 4% or less to produce an insolubilized polyvinyl alcohol fiber aggregate;
And a method for producing an insolubilized polyvinyl alcohol fiber assembly.
Ra = {(Mab−Maa) / Mab} × 100
Ra: Weight loss ratio of fiber aggregate immersed in boiling water Mab: Mass of fiber aggregate before being immersed in boiling water for 20 minutes Maa: Mass of fiber aggregate after being immersed in boiling water for 20 minutes The insoluble polyvinyl alcohol fiber assembly according to claim 5 or 6, wherein the amount of α-hydroxy acid added is 0.005 mol or more per mol of polyvinyl alcohol monomer unit. Method. The method for producing an insolubilized polyvinyl alcohol fiber assembly according to any one of claims 5 to 7, wherein the heating temperature is a temperature equal to or higher than the melting point of the α-hydroxy acid. The method for producing an insolubilized polyvinyl alcohol fiber assembly according to any one of claims 5 to 8, wherein a polyvinyl alcohol fiber is spun by an electrospinning method using a solution.

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