JP2015214652A - Production method of polyvinyl alcohol resin-made pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a polyvinyl alcohol resin-made pellet which enables pelletization of the water-soluble resins, i.e. polyvinyl alcohol resins.SOLUTION: A production method of a polyvinyl alcohol resin-made pellet includes a step of melt-extruding a polyvinyl alcohol resin by a melt extruder 1 to form a strand 5 and a step of cutting the strand 5 to pellets. The step of cutting the strand 5 to pellets is conducted under conditions of a temperature of the strand 5 of 35-95°C and a water content of the strand 5 of lower than 0.1 wt.%.

Description

  The present invention relates to a method for producing pellets made of polyvinyl alcohol resin (hereinafter referred to as “PVA”) that can be used as a molding material for various molded products.

  Conventionally, a hydrophobic thermoplastic resin can be pelletized by extruding the thermoplastic resin into a strand by melt-kneading, water contact cooling (water flow immersion), and then cutting into a pellet shape with a cutting device. The obtained pellets are used for various molding materials. As described above, the thermoplastic resin exhibiting hydrophobicity can be cooled by the water contact cooling method as described above, and pellets can be easily produced. However, PVA, which is a water-soluble resin, will be dissolved when trying to cool by water contact cooling after being extruded into a strand as described above, and cannot be cooled effectively. It was difficult to cut into a pellet shape.

  For this reason, pelletization of PVA, which is a water-soluble resin, has been studied. For example, after preparing PVA from which volatile components have been removed and extruding it into a strand shape on a belt, the PVA extruded onto the belt is air-cooled or air-cooled and pelletized by a cutting device such as a pelletizer. It has been proposed (see Patent Document 1).

JP 2012-149144 A

  In the production method of Patent Document 1, a method for cooling a hot strand extruded by melting and kneading is to produce a desired pellet by cutting a product cooled by air cooling or air cooling. The strands could not be sufficiently cooled within the air cooling time or the air cooling time, and it was difficult to efficiently cut into the desired pellets even if the air cooling time was sufficiently long. Thus, as for the manufacturing method of pelletizing the PVA which is a water-soluble resin as a raw material, the actual situation is that the actual manufacturing method has not yet been established.

  This invention is made | formed in view of such a situation, The objective is to provide the manufacturing method of the pellet made from PVA which enables the pelletization of PVA which is water-soluble resin.

  In view of the above circumstances, the present inventor conducted a series of studies in order to obtain PVA pellets, which are water-soluble resins that were conventionally difficult to produce industrially. And research was advanced centering on the cutting conditions of the strand which makes it possible to cut | disconnect the high temperature strand formed by melt-extruding PVA powder which is water-soluble resin into a pellet form without a problem. As a result, the temperature of the strand is set to 35 to 95 ° C., and the moisture content is less than 0.1% by weight, so that the strand can be cut into pellets having a good shape without causing any trouble. As a result, the present invention has been reached.

  That is, in order to achieve the above object, the method for producing PVA pellets of the present invention is a method for producing PVA pellets comprising a step of melt-extruding PVA to form strands and a step of cutting the strands into pellets. And the process of cut | disconnecting the said strand to a pellet form takes the structure that the temperature of a strand is 35-95 degreeC, and the water content is performed on the conditions of less than 0.1 weight%.

  By using the method for producing PVA pellets of the present invention, it is possible to cut the strands into pellets having a good shape without causing any problems when the strands are cut.

It is process drawing which shows typically an example of the manufacturing method of the pellet made from PVA of this invention.

  Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

The manufacturing method of the PVA pellets of the present invention is as follows:
(1) a step of melt-extruding PVA to form a strand;
(2) A method for producing a PVA pellet comprising a step of cutting the strand into a pellet. And in this invention, in such a manufacturing method, as mentioned above, the process of cut | disconnecting the said strand to a pellet form is performed under specific conditions (temperature and water content of a strand). is there.

First, PVA used as a raw material in the method for producing PVA pellets of the present invention will be described.
<< PVA >>
The PVA used in the method for producing the PVA pellets of the present invention is usually in the form of a powder and may be either unmodified PVA or modified PVA. Examples of the modified PVA include acetoacetylated PVA, oxyalkylene group-containing PVA, PVA having a 1,2-diol structural unit in the side chain, and carboxylic acid-modified PVA. Among them, PVA having a 1,2-diol structural unit in the side chain is particularly preferable because it has a low melting point and can be melted at a relatively low temperature when melt-molding.

  The saponification degree of the PVA is usually 70 to 100 mol%, preferably 80 to 99.9 mol%, particularly preferably 90 to 99 mol%. If the degree of saponification is too high, the molding temperature becomes high, the melt molding temperature range becomes narrow and melt molding tends to be difficult, and if it is too low, the flexibility becomes too high and the molded product has a sticky surface. There is a tendency to be able to.

  The average degree of polymerization of PVA (based on JIS K6726) is usually 300 to 1100, particularly 350 to 800, and more preferably 400 to 650. If the average degree of polymerization is too large, shear heat generation tends to occur during melt molding, and the resin tends to thermally decompose. Conversely, if the average degree of polymerization is too small, the strength of the resulting molded product is low and brittle molding There is a tendency to make things.

  Furthermore, the PVA is usually in the form of a powder, and the average particle size is usually 50 to 2000 μm, preferably 100 to 1700 μm, and particularly preferably 150 to 1500 μm.

  Here, the average particle size means that the PVA particles are sieved with an opening of 1700 μm, 1000 μm, 850 μm, 500 μm, 250 μm, and 150 μm, and the particle size is 1700 μm or more, 1000 μm or more and less than 1700 μm, 850 μm using a sieve shaker. The particle size is classified into particles having a cumulative particle size distribution of 50% by weight, which is classified into those having a particle size distribution of less than 1000 μm, 500 μm or more and less than 850 μm, 250 μm or more and less than 500 μm, or 150 μm or more and less than 250 μm.

  The PVA, which is the raw material, usually contains a volatile component, and the volatile component is derived from a reaction product generated in the PVA manufacturing process or a residue of the raw material used in the PVA manufacturing. Examples thereof include water, methyl alcohol, and methyl acetate. Content of the said volatile component is about 3 to 5 weight% normally in PVA which is a raw material.

  The PVA is produced by polymerizing a vinyl ester monomer and further saponifying it. Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl versatate. , Aliphatic vinyl esters such as vinyl trifluoroacetate, and aromatic vinyl esters such as vinyl benzoate, etc., and usually have 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, particularly preferably 4 to 7 carbon atoms. Group vinyl ester. From the economical viewpoint, vinyl acetate is particularly preferably used. These are usually used alone, but a plurality of them may be used simultaneously as necessary.

  The modified PVA is produced by saponifying a polymer of a vinyl ester monomer and another unsaturated monomer, or by post-modifying polyvinyl alcohol.

  Examples of the other unsaturated monomer include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene, acrylic acid, methacrylic acid, crotonic acid, maleic acid, and maleic anhydride. , Unsaturated acids such as itaconic acid or salts thereof, mono- or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, etc. Olefin sulfonic acids or salts thereof, alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinyl chloride Polyoxyalkylene (meth) allyl ethers such as denene, polyoxyethylene (meth) allyl ether and polyoxypropylene (meth) allyl ether, polyoxyalkylenes such as polyoxyethylene (meth) acrylate and polyoxypropylene (meth) acrylate (Meth) acrylate, polyoxyethylene (meth) acrylamide, polyoxyalkylene (meth) acrylamide such as polyoxypropylene (meth) acrylamide, polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester, Polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene Nbiniruamin and the like.

  Examples of the post-modification method include acetoacetate esterification, acetalization, urethanization, etherification, grafting, phosphate esterification, and oxyalkyleneation.

  As described above, the PVA used in the present invention has a low melting point and can be melted at a relatively low temperature during melt molding, so that it has a 1,2-diol structural unit in the side chain. Is preferably used.

<PVA having a 1,2-diol structural unit in the side chain>
The PVA having a 1,2-diol structural unit in the side chain is specifically a PVA having a 1,2-diol structural unit in the side chain represented by the following general formula (1). In 1), R ¹ , R ² , and R ³ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, X represents a single bond or a bonded chain, R ⁴ , R ⁵ , and R ⁶ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

  In addition, the content of the 1,2-diol structural unit represented by the above formula (1) of the PVA having the 1,2-diol structural unit in the side chain is usually 0.3 to 20 mol%, preferably 1 -10 mol%, particularly preferably 4-8 mol%. The remaining part is composed of a vinyl alcohol structural unit and a slight amount of vinyl acetate structural unit in the same manner as a normal PVA resin.

All of R ^{1 to} R ³ and R ^{4 to} R ⁶ in the 1,2-diol structural unit represented by the above formula (1) are preferably hydrogen atoms, but the resin properties are not significantly impaired. The amount may be substituted with an alkyl group having 1 to 4 carbon atoms, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, etc. Are preferable, and may have a substituent such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group, if necessary.

Further, X in the 1,2-diol structural unit represented by the above formula (1) is typically a single bond, and is most preferably a single bond in terms of thermal stability. As long as it does not inhibit the above, a bond chain may be used, and the bond chain is not particularly limited, but hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, naphthylene (these hydrocarbons include fluorine, chlorine, bromine, etc.) other, -O of may be substituted by a _{halogen) -, - (CH 2 O} ) m -, - (OCH 2) m -, - (CH 2 O) m CH 2 -, - CO-, _{-COCO -, - CO (CH 2} ) m CO -, - CO (C 6 H 4) CO -, - S -, - CS -, - SO -, - SO 2 -, - NR -, - CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO _{4 -, - Si (OR)} 2 -, - OSi (OR) 2 -, - OSi (OR) 2 O -, - Ti (OR) 2 -, - OTi (OR) 2 -, - OTi (OR) 2 O-, -Al (OR)-, -OAl (OR)-, -OAl (OR) O-, etc. are mentioned (R is each independently an arbitrary substituent, preferably a hydrogen atom or an alkyl group, Of these, m is a natural number). Among them, an alkylene group having 6 or less carbon atoms, particularly a methylene group, or —CH ₂ OCH ₂ — is preferable from the viewpoint of stability during production or use.

  The PVA having a 1,2-diol structural unit in the side chain can be produced by, for example, a known method described in paragraphs [0014] to [0037] of JP-A-2008-163179.

<< PVA pellet manufacturing method >>
The method for producing the PVA pellets of the present invention is carried out as follows using the powdery PVA.
As described above, the method for producing the PVA pellets of the present invention is as follows.
(1) a step of melt-extruding PVA to form a strand;
(2) A manufacturing method comprising a step of cutting the strand into pellets, wherein the strand is cut into pellets at a temperature of 35 to 95 ° C. and the water content of the strand is 0. Performed under specific conditions of less than 1% by weight.

  An example of the process for producing the PVA pellets of the present invention will be described step by step based on the process diagram shown in FIG. However, in the method for producing PVA pellets of the present invention, the step of cutting the strands into pellets may be performed under the specific conditions described above, and is not limited to the steps shown in FIG.

<Melt extrusion process>
A powdery PVA is charged into the charging port 2 of the melt extruder 1 shown in FIG. 1, melt-kneaded, and extruded into one or a plurality of substantially rod-shaped strands 5. The diameter of the strand 5 extruded at this time is appropriately set depending on the size of the hole of the mold attached to the extrusion port of the melt extruder 1, but is usually 0.5 to 4 mm, preferably 1 to 3 mm. Particularly preferably, the thickness is 1.5 to 2.5 mm.

  The temperature condition for the melt kneading is preferably set to 250 ° C. or less, more preferably 150 to 240 ° C., and particularly preferably 180 to 230 ° C. If the melt kneading temperature is too high, the PVA will be thermally decomposed, making it difficult to extrude the desired strand 5.

The melt extruder 1 is not particularly limited in appearance and the like, and even if it is a twin screw type, the bottom of the hopper is a biaxial screw, and thereafter, it is a single screw type toward the tip. Although an extruder referred to as a 5-axis may be used, a twin-screw type melt extruder is usually used.
Among these, those provided with a vent 3 for degassing volatile components contained in the charged PVA are preferable. One or more vents 3 may be provided, but preferably one is provided.

  The vent 3 may be installed at a position after the PVA starts to melt and before it is completely melted, but is preferably a position immediately before the melt from about half of the melt. If the installation position of the vent 3 is before the molten state, unmelted raw material may be blown out, and the generated volatile component flows backward at the installation position after being completely melted and blown out from the inlet as back pressure. There is a possibility that raw materials cannot be input.

The shape of the opening (mouth) of the vent 3 is usually a circle, an ellipse, a polygon such as a triangle, a quadrangle, or a pentagon, and is preferably a circle or a quadrangle. The size of such a mouth, usually 1～150Cm ^2, preferably 2～80Cm ^2, particularly preferably 3 to 10 cm ^2. If the mouth is too large, the unmelted powder PVA raw material tends to be ejected, and if it is too small, the unmelted powder PVA raw material tends to be clogged immediately.

  Further, in addition to the vent 3, a general vent (a degassing port, a vacuum vent port) 4 can be provided. In addition, the said general vent 4 may be provided in two or more several multistage.

  In addition, after the PVA starts to melt and before it completely melts, specifically, a part of the PVA powder starts to melt, and the unmelted powder is kneaded into the melted resin. It is a rare white viscous substance, and can actually be confirmed by visual observation or the like.

<Strand cooling process>
As shown in FIG. 1, the melt-extruded strand 5 is cooled. Conventionally known methods such as air cooling and air cooling can be used. However, since PVA is water-soluble, it can be used by a water bath or shower. It cannot be cooled. Among them, a method of cooling using a water-cooled metal endless belt 6 and fog is preferable. Specifically, the strand 5 is placed on the surface of the water-cooled metal endless belt 6, and the contact surface with the strand 5 is cooled by moving the strand 5 by rotational driving of the metal endless belt 6. At the same time, the entire strand 5 is cooled by spraying mist on the surface of the strand 5.

  As the water-cooled metal endless belt 6, for example, a stainless steel belt that employs a conventionally known water-cooling method is preferably used. In the drawing, the cooling process using the metal endless belt 6 is provided in one place, but the present invention is not limited to this, and the cooling process using the metal endless belt 6 may be provided in two or more places in a continuous manner. Good.

  The surface temperature of the water-cooled metal endless belt 6 is preferably 2 to 80 ° C, more preferably 5 to 60 ° C, and particularly preferably 20 to 40 ° C. If the surface temperature is too high, it is difficult to cool the strand 5 in a short time and effectively.

On the other hand, as a method of cooling the entire strand 5 by spraying mist on the surface of the strand 5, for example, as shown in FIG. 1, above the strand 5 moving by the rotational drive of the metal endless belt 6, A spraying device 7 for spraying mist is provided, and mist is sprayed on the surface of the strand 5 from the upper part to allow moisture to adhere to the surface of the strand 5, which evaporates with the heat of the strand, and efficiently cools the latent heat of vaporization. How to do. When using the spraying device 7, the amount of sprayed mist varies depending on the speed of the cooling belt, but is usually 0.5 to 10 L / hr, preferably 1 to 4 L / hr, particularly preferably 2 to 3 L / hr. It is.
Moreover, the average water droplet particle diameter of the water to spray is 0.1-30 micrometers normally, Preferably it is 0.5-20 micrometers, Most preferably, it is 1-10 micrometers. If the particle diameter is too large, the strand 5 may get wet and the PVA may melt or the water content of the strand 5 may increase.
The mist as described above can be sprayed by using, for example, a two-fluid spray nozzle (for example, AKIJET manufactured by Ikeuchi Co., Ltd.) that sprays compressed air and water simultaneously.

Next, it is preferable to cool the surface of the strand 5 based on latent heat of vaporization by injecting a dry gas 8 onto the strand 5 that has passed through the cooling step. Examples of the dry gas 8 include air and inert gas (for example, nitrogen gas, carbon dioxide gas, etc.). Preferably, an air cooling system by injecting air is employed. The gas volume of the drying gas 8, typically, 5~5m ³ / min, preferably 10 to 40 m ³ / min, particularly preferably 20 to 30 m ³ / min. Moreover, as temperature of the dry gas 8 to be used, it is 5-40 degreeC normally, Preferably it is 10-30 degreeC, Most preferably, it is 15-25 degreeC.

  The cooling distance in the cooling step of spraying the mist and injecting the dry gas is usually 4 to 20 m, preferably 6 to 15 m, particularly preferably 8 to 10 m. If the cooling distance is too short, the cooling is insufficient. Therefore, the strand 5 tends to be unable to be cut with a pelletizer or the like, and if it is too long, the workability during production tends to deteriorate.

  The temperature of the strand 5 formed through the cooling step and the dry gas injection step is set in a range of 35 to 95 ° C. More preferably, it is 60-95 degreeC, Most preferably, it is 70-90 degreeC. If the temperature of the strand 5 is too high, the strand 5 in the next step cannot be cut and pelletized efficiently. Specifically, if the temperature of the strand 5 is too high, when the strand 5 is cut into pellets in the next step, the strand 5 is too soft to produce a pellet having a uniform cut surface or to cut. May wrap around a cutter or gear. On the other hand, if the temperature of the strand 5 is too low, the strand 5 is too hard and fine powder is generated at the time of cutting, or a defect occurs on the cut surface.

Further, the water content of the strand 5 formed through the cooling step and the dry gas injection step is less than 0.10% by weight, more preferably 0.08% by weight or less, particularly preferably 0.05% by weight or less. It is. Usually, the lower limit of the water content is 0.02% by weight. If the water content is too large, when the strand 5 is cut into a pellet, it is too soft to produce a pellet having a uniform cut surface.
Thus, as a method of obtaining the strand 5 having a water content of less than 0.10% by weight, in addition to the method described in the above <Strand cooling step>, a method of air cooling, air cooling, etc. in a low humidity environment, etc. Can be given.

<Strand cutting (pelletizing) process>
In the present invention, the greatest feature is that the step of cutting and forming the strand 5 into pellets is performed under specific conditions in which the strand temperature is 35 to 95 ° C. and the water content is less than 0.10% by weight. To do. By supplying the strand 5 cooled by the said process to the cutting device 9 for cut | disconnecting in a pellet form, the strand 5 is cut and formed into a pellet form (pelletizing process). Examples of the cutting device 9 include a device that continuously cuts the strand 5 into a pellet shape with a rotary blade, such as a pelletizer. And in this cutting | disconnection, in order to suppress the temperature rise of the strand 5 resulting from the frictional heat at the time of a cutting | disconnection, and to cool to an appropriate temperature, the cooling gas 10 is supplied to a cutting part. Examples of the cooling gas 10 include air and inert gas (for example, nitrogen gas, carbon dioxide gas, etc.), for example, as in the case of the dry gas described above. Preferably, an air cooling method by injecting air is employed. The The supply gas amount of the cooling gas 10 is usually 150 to 1200 NL / min, preferably 300 to 1000 NL / min, and particularly preferably 500 to 800 NL / min. Further, the temperature of the cooling gas 10 to be supplied is usually 5 to 30 ° C, preferably 8 to 20 ° C, and particularly preferably 10 to 15 ° C.
By cutting the strands 5 into pellets under the above conditions, the cutting operation can be performed without hindrance, and pellets with a good appearance can be obtained.

<Pellet cooling process>
PVA pellets (hereinafter also simply referred to as “pellets”) 11 cut and formed by passing through the strand cutting (pelletizing) step are subjected to a pellet cooling step in order to fix the pelletized shape. It is preferable. As the pellet cooling step, for example, as shown in FIG. 1, the pellet 11 cut and formed in the pellet cooling device 14 is placed on the metal mesh 12 and moved in the direction of the arrow while moving the metal mesh 12. The mode of vibrating itself is preferable from the viewpoint of preventing adhesion of the pellet 11 to the surface of the metal net 12 and effective cooling. In addition, as a cooling method, the cooling gas 13 is supplied to the pellet 11 through the metal mesh 12 from below the metal mesh 12, and the cooling gas 13 is circulated outside the device from above the pellet cooling device 14. Accordingly, it is preferable from the viewpoint of cooling the pellet 11 that the cooling gas 13 is not retained in the pellet cooling device 14. Examples of the cooling gas 13 include air and an inert gas (for example, nitrogen gas, carbon dioxide gas, etc.), for example, similar to the above-mentioned dry gas, and preferably air. The gas volume of the cooling gas 13, typically, 5~60m ³ / min, preferably 20 to 50 m ³ / min, particularly preferably 30 to 40 m ³ / min. Moreover, as cooling gas 13 temperature to supply, it is 5-35 degreeC normally, Preferably it is 10-30 degreeC, Most preferably, it is 15-25 degreeC.

  The pellet 11 cooled via the pellet cooling device 14 is preferably, for example, less than 35 ° C., more preferably 10 to 30 ° C., and particularly preferably 20 to 25 ° C. If the temperature of the cooled pellet 11 is too high, it is difficult to efficiently classify the pellet 11 in the next step, and the accuracy of classification tends to be reduced.

<Classification process>
The cooled pellets 11 are usually sorted into a desired shape and size through a classification process. In this way, a pellet 11 made of PVA as a final product is obtained.

  The finally obtained pellet 11 is generally a substantially cylindrical shape. Moreover, although the magnitude | size of the pellet 11 is suitably set according to a use etc., it is 0.5-4 mm in diameter normally, Preferably it is 1-3 mm, Most preferably, it is 2-2.5 mm, The length of the pellet 11 is preferable. The thickness is usually 0.5 to 4 mm, preferably 1 to 3 mm, particularly preferably 1.5 to 2.5 mm.

  PVA pellets obtained by the method for producing PVA pellets of the present invention are used for various molding materials, but have not been industrially produced as PVA pellets. Extrusion molding, injection molding, film molding (inflation film / T-die cast film), profile molding, melt coating, blow molding, melt spinning, nonwoven fabric molding (spunbond, meltblown), etc. that could not be used as material applications Used for various molding materials.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the examples, “parts” and “%” mean weight basis unless otherwise specified.

[Example 1]
Based on the process chart shown in FIG. 1, PVA pellets were produced as follows.

  A reaction vessel equipped with a reflux condenser, a dropping funnel and a stirrer was charged with 68.0 parts of vinyl acetate, 23.8 parts of methanol, and 8.2 parts of 3,4-diacetoxy-1-butene, and azobisisobutyro Nitrile was added in an amount of 0.3 mol% (vs. vinyl acetate charged), and the temperature was raised under a nitrogen stream while stirring to initiate polymerization. When the polymerization rate of vinyl acetate reaches 90%, m-dinitrobenzene is added to complete the polymerization, and then unreacted vinyl acetate monomer is removed out of the system by blowing methanol vapor. A combined methanol solution was obtained.

  Next, the methanol solution was further diluted with methanol, adjusted to a concentration of 45%, charged into a kneader, and a 2% methanol solution of sodium hydroxide was added to the vinyl acetate structural unit in the copolymer while maintaining the solution temperature at 35 ° C. And saponification was performed by adding 10.5 mmol with respect to 1 mol of the total amount of 3,4-diacetoxy-1-butene structural units. When saponification progresses, saponification precipitates and forms particles, and is separated by filtration, washed well with methanol and dried in a hot air dryer to produce the target PVA resin (particle size 920 μm) did.

The saponification degree of the obtained PVA was 98.9 mol% when analyzed by the alkali consumption required for hydrolysis of residual vinyl acetate and 3,4-diacetoxy-1-butene. The average degree of polymerization was 450 when analyzed according to JIS K 6726. The content of the 1,2-diol structural unit represented by the general formula (1) is ¹ H-NMR (300 MHz proton NMR, d6-DMSO solution, internal standard substance: tetramethylsilane, 50 ° C.). It was 6 mol% when computed from the measured integral value. The volatile component contained 3%.

<Melt extrusion process>
The powdered PVA obtained above is charged into the inlet 2 of a melt extruder (2-screw type: TEM-58BS manufactured by Toshiba Machine Co., Ltd.), melted and kneaded, and a single substantially rod-shaped strand under the following conditions: 5 (diameter 2.0 mm).

Diameter (D) 58mm, L / D = 45
Screw rotation speed: 150rpm
Set temperature: C1 / C2 / C3 / C4 / C5 / C6 / C7 / C8 / A / D = 90/120/150/180/200/205/210/210/210/210 ° C.
Screw pattern: 2 kneaded screws Screen mesh: 90/120/90 mesh
Discharge rate: 200kg / hr
Vent 3 position: C4 (caliber 100mm)
Vent 4 position: C8 (caliber 100mm)
The temperature condition for the melt kneading was 250 ° C.

<Strand cooling process>
The melt-extruded strand 5 of about 250 ° C. is placed on the surface of a water-cooled (cooling water temperature 5 ° C.) stainless steel belt 6 (length: 10 m). The lower side of the strand 5 was cooled by moving it. At the same time, as shown in FIG. 1, a spray device 7 for spraying mist (AKIJET AKIJET nozzle) is provided above the strand 5 that is moved by the rotational drive of the stainless steel belt 6, and the mist is sprayed on the surface of the strand 5 from above. Then, water was adhered to the surface of the strand 5 to cool the entire strand 5. The surface temperature of the water-cooled stainless steel belt 6 was 10 ° C. Further, when the spray device 7 was used, the water spray amount was 3 L / hr.

Next, the surface of the strand 5 was cooled by injecting air as the dry gas 8 to the strand 5 that passed through the cooling step. The gas amount of the dry gas 8 was set to 45 m ³ / min, and the temperature of the dry gas 8 was set to 25 ° C.

  The temperature of the strand 5 which passed through the said cooling process and dry gas injection process was 95 degreeC. Moreover, the moisture content of the strand 5 which passed through the said cooling process and dry gas injection process was 0.03%. The temperature of the strand 5 was measured using a non-contact laser thermometer. On the other hand, the water content of the strand 5 was measured with a Karl Fischer moisture meter.

<Strand cutting (pelletizing) process>
In order to cut the strand 5 having a water content of 0.03% at 95 ° C. cooled by the above process into pellets, the strand 5 is cut into pellets by feeding it to a pelletizer 9 (TSL-450 type, manufactured by Tanaka). (Pelletizing step). At the same time, when cutting into the pellets, air was injected and supplied as a cooling gas 10 to the cut portion. The supply amount of the cooling gas (air) 10 was set to 800 NL / min, and the temperature of the supplied cooling gas 10 was set to 15 ° C.

<Pellet cooling process>
Next, the pellet 11 formed by going through the strand cutting (pelletizing) step was passed through the pellet cooling step. In the pellet cooling step, as shown in FIG. 1, the pellet 11 cut and molded in a pellet cooling device (Mistral ASC type manufactured by Tanaka) 14 is placed on a stainless steel mesh 12, and the stainless steel mesh 12 itself. The pellet 11 was sequentially moved in the direction of the arrow while vibrating. In addition, the cooling gas 13 is supplied from below the stainless steel mesh 12 through the stainless steel mesh 12 and supplied to the pellet 11, and the cooling gas 13 is supplied from above the pellet cooling device 14 to the outside of the device so that the cooling gas 13 is not retained. 13 was distributed. The cooling gas 13 was normal air, the gas amount of the cooling gas 13 was set to 40 m ³ / min, and the temperature of the cooling gas 13 to be supplied was set to 20 ° C.

  The temperature of the pellet 11 cooled via the pellet cooling device 14 was 27 ° C. The temperature of the pellet 11 was measured using a non-contact laser thermometer as described above.

<Classification process>
Next, the cooled pellets 11 were classified using a vibration type pellet sorter (PSL-300A manufactured by Tanaka). The finally obtained pellet 11 was substantially cylindrical, and the size was 2.0 mm diameter × 2.0 mm length.

[Example 2]
In Example 1, pellets 11 were produced in the same manner as in Example 1 except that the water temperature of the cooling water of the water-cooled stainless steel belt 6 was 60 ° C. and the discharge rate was 100 kg / hr. The temperature of the strand 5 that passed through the cooling step and the dry gas injection step was 90 ° C., the water content was 0.08%, and the obtained pellet 11 was substantially cylindrical as in Example 1 and had a diameter of 2 A pellet 11 having a size of 0.0 mm × length 2.0 mm was obtained. The results are shown in Table 1 below.

[Example 3]
In Example 1, pellets 11 were prepared in the same manner as in Example 1 except that the water temperature of the cooling water of the water-cooled stainless steel belt 6 was 25 ° C., no mist was sprayed, and the discharge rate was 70 kg / hr. Manufactured. The temperature of the strand 5 that passed through the cooling step and the dry gas injection step was 75 ° C., the water content was 0.05%, and the obtained pellet 11 was substantially cylindrical, as in Example 1, and had a diameter of 2 A pellet 11 having a size of 0.0 mm × length 2.0 mm was obtained. The results are shown in Table 1 below.

[Example 4]
In Example 1, pellets 11 were produced in the same manner as in Example 1 except that the mist was not sprayed and the discharge rate was 50 kg / hr. The temperature of the strand 5 that passed through the cooling step and the dry gas injection step was 40 ° C., the water content was 0.04%, and the obtained pellet 11 was substantially cylindrical, as in Example 1, and had a diameter of 2 A pellet 11 having a size of 0.0 mm × length 2.0 mm was obtained. The results are shown in Table 1 below.

[Comparative Example 1]
In Example 1, pellets were produced in the same manner as in Example 1 except that the amount of mist spray was changed from 3 L / hr to 10 L / hr and the discharge rate was adjusted from 200 kg / hr to 50 kg / hr. As a result, the cooling capacity was too high for the discharge amount, so that the water from the sprayed water could not be completely evaporated, and the strand surface was water-soluble and sticky, resulting in mutual adhesion. Furthermore, since the strand was cooled too much, it became a glass-like resin, and many cracks were generated by cutting with a pelletizer.

[Comparative Example 2]
In Example 3, pellets were produced in the same manner as in Example 3 except that the amount of sprayed mist was 10 L / hr. As a result, the cooling capacity was too high for the discharge amount, so that the water from the sprayed water could not be completely evaporated, and the strand surface was water-soluble and sticky, resulting in mutual adhesion.

[Comparative Example 3]
In Example 2, pellets were produced in the same manner as in Example 2 except that the mist was not sprayed and the discharge rate was increased to 200 kg / hr. As a result, since the discharge amount was large, the cooling was not in time, the cooling of the strands was insufficient, and the strands remained flexible. The flexible strand could not be cut in the pelletizer, and the pelletizer stopped due to entanglement with the rotating part in the apparatus.

[Comparative Example 4]
In Example 1, pellets were produced in the same manner as in Example 1 except that the temperature of the cooling water of the water-cooled stainless steel belt 6 was 25 ° C. As a result, although the discharge amount was large, the cooling capacity was too low, so the temperature of the pellets was too high, and the pellets were stuck together in the pelletizer.

  As is clear from the above results, in all Examples, PVA pellets having no problem in appearance or the like could be efficiently produced through the production process of the PVA pellets. On the other hand, in the manufacturing method of the PVA pellets described in the above comparative examples, the above-described problems occur, and thus the desired PVA pellets cannot be obtained.

  PVA pellets obtained by the PVA pellet manufacturing method of the present invention include, for example, extrusion molding, injection molding, film molding (inflation film / T-die cast film), profile molding, melt coating, blow molding, melt spinning, and nonwoven fabric molding. (Spunbond, meltblown) and the like can be used for molding material applications.

DESCRIPTION OF SYMBOLS 1 Melt extruder 3 Vent 5 Strand 6 Metal endless belt 7 Spraying device 9 Cutting device 11 PVA pellet (pellet)
12 Metal mesh 14 Pellet cooling device

Claims (2)

  A method for producing a polyvinyl alcohol-based resin pellet comprising a step of melt-extruding a polyvinyl alcohol-based resin to form a strand, and a step of cutting the strand into a pellet, and the step of cutting the strand into a pellet The method for producing pellets made of polyvinyl alcohol resin, wherein the strand temperature is 35 to 95 ° C. and the water content is less than 0.1% by weight.   2. The method for producing a polyvinyl alcohol resin pellet according to claim 1, wherein a cooling gas is supplied to the cut portion in the step of cutting the strand into a pellet.

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