JPS601333B2 - Method for producing polyvinyl alcohol aqueous solution - Google Patents

Description

[Detailed description of the invention] The present invention relates to polyvinyl alcohol (hereinafter referred to as PVA).

) Regarding a method for producing an aqueous solution. Conventionally, many proposals have been made regarding the production of concentrated aqueous solutions of PVA, but because the decomposition point is lower than the melting point of the polymer, they are processed in a semi-molten state as an aqueous solution. It has been implemented.

I The extrusion port scale method (hereinafter referred to as
This is called the blended powder method.

). 2. Made by an extrusion melting method using raw materials that are slightly more melted than the raw materials in 1, cooled and crushed.

3. A method in which extrusion melting is carried out by shortening the heating holding time of 1, forming a hydrous pellet, and extruding and dissolving the pellet.

(Hereinafter referred to as the Berett method) 4 A method in which PVA raw material powder, water, additives, plasticizers, etc. are placed in a pressurized tank, melted under pressure, defoamed, and transferred with a pump (hereinafter referred to as the pressurized tank melting method) ).

Batch-type methods such as the blended powder method in 1 or the method in 2 are prone to variations between batches, especially in the powder properties, angle of repose, bulk specific gravity, etc. of the PVA water-containing raw material. Fluctuations in conditions affect dissolution and kneading.

As a result, not only does this hinder quality stability over a long period of time, but also the bulk specific gravity of the raw material is small, so the stock space for heating and holding time, cooling time, etc. becomes large. In the 3rd pellet method,
Cutting cannot be performed unless sufficient gelation time has been allowed after strand formation, making it uneconomical and inefficient (the moisture content of the hydrous pellets must also be maintained at a constant level).

Furthermore, since it is more efficient to produce pellets at higher concentrations, the moisture content must be readjusted before processing. The pressurized tank dissolution method described in No. 4 is a batch system, and the concentration limit in operations such as melting and defoaming is about 45 to 48%, and higher concentration dissolution is practically impossible.

In addition, since the melting and degassing time is limited, when operating in a two-tank switching system, if the throughput per unit time becomes large, the tank capacity becomes extremely large, which tends to become uneconomical.
Furthermore, troubles when switching tank fluids cannot be ignored. As described above, conventional methods have problems such as being unsuitable for continuous production and high concentration, and requiring uneconomical steps to adjust the moisture-containing raw materials fed into the extruder for molding. .

Such problems are thought to be caused by the characteristics of the PVA raw material described below.

In other words, PVA raw materials are generally more heterogeneous than other polymers; for example, they may have undergone a high local heat history during the polymer drying process or heat treatment process, or they may contain other parts that are difficult to dissolve. In addition, the particle size of the raw material varies depending on the process, but it is widely distributed from a few meshes to fine particles.

Therefore, in the case of semi-melt extrusion, a slow rate of dissolution occurs for these heterogeneous raw materials. For this purpose, the product is melted under pressure for a long time (tank melting), once formed into a pellet shape and then final processed, or swollen with sufficient water or plasticizer etc. in a powder or similar state. It was necessary to process it as a raw material and make the aqueous solution uniform. on the one hand,
A water-containing raw material in a powder or a state close to it has different characteristics as a powder or granule depending on its degree of swelling.

In other words, the bulk specific gravity and angle of repose change depending on the heating temperature, time, cooling process, etc. after adding water, and subtle changes in these conditions affect the transport characteristics of the water-containing material in the powder castle in the extruder. This results in loss of quality and inhomogeneity of the solution. In addition, the loss that occurs during the process, especially the edge trimming shoulder of films, slit loss, etc., has a high degree of crystallinity, and the crystallinity is high, and this is crushed and mixed with new raw materials and melted. This tends to result in a non-homogeneous solution, making it difficult to control the concentration and limiting the amount of recovered products to be mixed. The present inventor studied various problems related to the production of a highly concentrated PVA aqueous solution related to the film production process, and based on these backgrounds, repeated various experiments and arrived at the present invention. The present invention is not a batch method as described above, and the raw material PVA is prepared in advance.
To provide a method for continuously producing a high-concentration PVA aqueous solution in which the loss generated within the system can be recovered as a high-quality aqueous solution without impregnating the powder with water corresponding to the required concentration.

That is, in the present invention, a fixed amount of polyvinyl alcohol powder that has not undergone a special hydration and swelling process is injected into the barrel through the inlet provided at the base of the high-speed plastic-meshing two-ball extruder, and the powder is transferred into the barrel by the powder transfer function of the screw. After forming a powder transfer castle at a constant speed, water or a polyvinyl alcohol aqueous solution having a polyvinyl alcohol content of 25% by weight or less is metered and added at low pressure from an inlet provided downstream of the inlet, and the polyvinyl alcohol content is 5% by weight. A homogeneous polyvinyl alcohol aqueous solution having a weight percent or more of polyvinyl alcohol is melt-kneaded, and further water or a polyvinyl alcohol aqueous solution having a polyvinyl alcohol content of 25% or less is metered and mixed through an injection port provided downstream of the injection port, and mixed at the high speed. This is a method for producing a polyvinyl alcohol aqueous solution, which is characterized in that a homogeneous polyvinyl alcohol aqueous solution is obtained in one step from the tip of a cutting-meshing twin-screw extruder. The PVA used in the present invention is preferably completely saponified PVA or partially saponified PVA, and generally the residual moisture content is controlled at a constant value of about 5 to 7%.

The liquid added to PVA powder is water or low concentration PVA
An aqueous solution in which appropriate amounts of plasticizers, additives, etc. are mixed and dispersed is used.

One of the features of the present invention is that a PVA aqueous solution can be used as the hydrating liquid.

That is, in the Friend Powder method, the Haberett method, etc., there are various difficulties in simply recycling process losses from the molding process and other defective products into the system.
In the present invention, even loss with foreign matter is dissolved as a low concentration aqueous solution, and by performing a sufficiently high furnace filtration with low viscosity, it can be recovered as a homogeneous aqueous solution and used as an additive for PVA.For example, PVA concentration 5 ~25%, 8
The aqueous solution maintained at 5 to 93 qo as added water further increases the stability of the system in this method. Another feature of the present invention is to obtain a homogeneous aqueous solution containing no unmelted materials from a PVA raw material having heterogeneous elements.

For example, in the commonly practiced aqueous solution production method mentioned at the beginning, even raw materials that have been sufficiently swollen with water or plasticizers before extrusion are processed as an aqueous solution with a concentration of 42 to 48%. Small amounts of unmelted material were generated everywhere,
This will reduce the value of the product. This tendency is particularly strong for polymers with a high degree of saponification. Generally, it is not easy to eliminate this melt. Moreover, it will be understood that it would be quite difficult to directly prepare an aqueous solution in a short period of time if conventional methods were followed. In this regard, the inventors repeated various experiments and succeeded in realizing this by first carrying out the first stage of dissolution as a highly concentrated aqueous solution, and then performing dilution dissolution in the second stage to reduce the concentration to the desired concentration. did. The method for producing the PVA aqueous solution of the present invention uses a high-speed interlocking two-event extruder (hereinafter referred to as
It is simply called an extruder.

) PVA powder is introduced through the inlet provided at the base of the barrel, and after forming a steady state of powder transfer within the barrel, water or a low concentration PVA aqueous solution is metered and injected to melt and mix the PVA content. to prepare a PVA aqueous solution with a PVA content of 50% by weight or more, and then add PVA with a PVA content of 25% by weight from an additive water inlet provided further downstream of the extruder.
A high concentration (P
By accurately controlling the transfer amount of the PVA aqueous solution (with a VA content of 50% by weight or more) and the transfer amount of the added solution added later, the two are mixed at a predetermined ratio to form fine unmelted particles. It is possible to obtain a concentrated aqueous PVA solution with no substances and a constant concentration. The reason why the additive liquid is brought into contact with the PVA raw powder under low pressure is that if the two come into contact under high pressure, the steady transfer of the powder may be inhibited by the pressure of the additive solution, or conversely, the amount of the additive liquid may change due to the powder being transferred. Because it does. Here, low pressure is in the range of normal pressure to 5 atmospheres.

When the PVA raw material powder and the additive liquid are brought into contact with each other at low pressure, the apparent volume increases rapidly, but this must be reliably and quickly transferred downstream of the extruder. For this purpose, the extruder used in the present invention changes the thread pitch of the extrusion screw near the raw material input port and the thread pitch of the extrusion screw downstream of the additive liquid injection port, depending on the conditions in each region. The screw pitch is set. As a result, the PVA raw material powder and the additive liquid are transferred and mixed at a constant ratio. When the additive liquid is a PVA aqueous solution, it goes without saying that its temperature and concentration should be kept constant, and furthermore, that the flow rates of both should be accurately controlled. The PVA aqueous solution transferred by the extrusion screw in this way is
Along the downstream side of the extruder, mixing, generation of transfer pressure, and generation of mixing transfer pressure are successively repeated until the mixture reaches a defoaming section provided downstream of the extruder.

The temperature distribution in the transfer section from the raw material input port to this defoaming section is maintained at about 75 to 90°C in the early stage of mixing, giving sufficient depth in the high viscosity state for heating, melting, and drilling. ,
Next, make sure that a homogeneous PVA aqueous solution is obtained when diluted. In addition, in the area immediately before defoaming, the viscosity is increased to about 11,000 to lower the viscosity and facilitate defoaming.
The air mixed in at the raw material input port is defoamed in a flash manner at the degassing hole of the defoaming section to obtain a good degassing effect. The evaporation of water from the degassing holes is small and quantitative, and no special means for maintaining equilibrium is required. Further, the liquid added to the PVA raw material powder may be water or a low concentration PVA aqueous solution mixed and dispersed with appropriate amounts of plasticizers, additives, etc. as necessary.

Furthermore, as an additive solution, the PVA concentration is 5 to 25% by weight.
It is preferable that it is maintained at about 85 to 9y0. This is because a PVA aqueous solution having such a concentration can be easily dissolved and defoamed using simple equipment. The twin-screw extruder used in the present invention is preferably a high-speed shunting type twin-screw extruder having a self-cleaning function of a two-wheel mesh type.

This twin-screw extruder has a surface self-cleaning function in all of the internal channels, and the outer circumferential speed of the extrusion screw is as high as 40 mm/mm or more. In other words, it is sufficient that each part of the interior of the aircraft can be controlled to a high degree and has the function of quickly absorbing heat generated by internal friction. In addition, for the transfer part, solid phase,
Needless to say, it has a reliable transport force at each stage of the mixed phase and liquid phase. In addition, if the initial moisture content of the raw material, the concentration, temperature, flow rate, and feed rate of the raw material are individually controlled accurately, and the above-mentioned items are properly implemented, continuous concentration control in the first stage can be achieved. It is possible.

Next, an example of a high-speed interlocking type twin-screw extruder used in the present invention will be explained with reference to the drawings.

FIG. 1 is a partially cutaway plan view showing the main parts of a high-speed cutting and meshing type two-ball extruder, and FIG. 2 is a side view of the same extruder. In the figure, 1 is the extruder main body, and inside the extruder main body 1 there are transfer elements 2a, 2b, 2d, 2f, 2h, 2i, 2j with male threads formed at different pitches in predetermined sections, and columnar bodies with smooth surfaces. Mixed elements 2c, 2e,
Two extrusion screws 3 having a weight of 2 g are arranged side by side so that their threaded portions mesh with each other. The extrusion screw 3 is rotated at a desired rotational speed by a drive mechanism 4 provided at the rear of the extruder main body 1. A raw material inlet 5 is provided at the rear end of the extruder main body 1 . A transfer element 2a having threads formed at a predetermined pitch is provided in the extrusion screw 3 section directly below the raw material input port 5 to ensure that the input raw material powder 6 is continuously and steadily transferred forward. There is. The raw material inlet 5 is provided with a chute 7, and the raw material powder is led from the raw material hopper 8 provided above the drive mechanism 4 to the vibrating feeder 101 via the feeder 9 formed by an endless belt. 6 is reliably supplied to the raw material input port 5. The raw material powder 6 supplied from the raw material hopper 8 to the feeder 9 is continuously transferred and guided to the chute 7 while being accurately measured by the feeder 9. Raw material input port 5
An additive water inlet 11 into which water or a low concentration PVA aqueous solution is injected is provided downstream. Water or a low concentration PVA aqueous solution pressurized by a metering pump 13 is introduced into the additive water injection row 1 from a tank 12 via a flow rate compensator 14. In addition, the extruder main body 1
Further downstream, a second additive water inlet 17 is provided for injecting additive water led from the tank 12 through a metering pump 15 and a flow rate compensator 16 in sequence. This second
A deaeration hole 18 is provided near the added water inlet 17 . In the deaeration hole 18, the air in the PVA aqueous solution maintained at a predetermined temperature and introduced by the extrusion screw 3 is removed together with water bubbling. In addition, deaeration hole 1
The amount of moisture evaporated in step 8 is small and constant, and there is no need to provide any means to keep the amount of evaporation in equilibrium.However, in order to further reduce the amount of evaporation, a condensation pipe is installed in the degassing hole 18 to condense the water. The water may flow down the wall surface and return into the degassing hole 18.

Further, a transfer element 2a provided on the extrusion screw 3,
2b, 2d, 2f, 2h, 2i, and 2j are desirably set in number and thread pitch depending on the concentration of the PVA aqueous solution produced by this extruder.

In addition, the mixing elements 2c, 2e, and 2g may be of a columnar shape with a smooth surface or may be of any type having the function of kneading the PVA aqueous solution. PVA powder is input from raw material input port 5 of the machine, and
A PVA aqueous solution is injected from the additive water inlet 11 of the extrusion screw 3 and mixed, mixed, and melted using the mixing elements 2c, 2e, and 2g of the extrusion screw 3 to produce a PVA aqueous solution containing more than 5% by weight of PVA. While maintaining the temperature and transferring it downstream by the extrusion screw 3, the second
water or less than 25% by weight of PV from the added water inlet 17 of
By injecting a low concentration PVA aqueous solution containing A, mixing it with the extrusion screw 3, and extruding it downstream, it is possible to obtain a polyvinyl alcohol concentrated aqueous solution with a uniform concentration that does not contain minute unmelted substances. .

Next, the number of mixing elements in the high-speed acid-interlocking twin-screw extruder was varied, and the relationship between the concentration and specific power of the PVA aqueous solution injected from the inlet provided at the rear end of the extruder was investigated. An experimental example will be explained.

A first additive water inlet 11 is located 18 meters downstream from the center of the extruded rock raw material input port 5 shown in FIGS. A mixing element 2b having an added water inlet 17 and having a length of 100 ribs between the first added water inlet 11 and the second added water inlet 17.
2 double extrusion screws 3 on the diameter 53 side with 2...... and 4 types of 2 screws with different numbers of 3, 4, and 5 mixing elements 2b of the same shape. Using a high-speed cutting mesh type twin-screw extruder that can be installed by replacing the extrusion screw 3, P with a degree of saponification of 98 hol% or more, a degree of polymerization of 1650 to 17.00, and a final concentration of 45 to 60% by weight is used.
When the relationship between the concentration of the VA solution and the specific power was investigated, the results shown in FIG. 3 were obtained.

The rotational speed of the extrusion screw 3 is 30mm. p. m. Met.

Further, the specific power (kW.H/k9) is the value obtained by dividing the power (kW) given from the motor of the extruder by the amount of PVA raw material powder and added water at that time (extrusion amount k9'H). We investigated the state of the PVA aqueous solution while driving the extruder, and found that as the concentration and specific power of the PVA solution produced at the rear end of the extruder increased, the extrusion of the foamed surface of the extruded PVA solution improved. Microscopic unmelted substances floating on the surface of the large, thin foam were no longer observed.

Where this melt no longer exists, the specific power is 0.2
At kWH/kg or more, the PVA concentration was 50% by weight or more. Next, examples of the present invention will be described.

Example 1 As shown in FIGS. 1 and 2, the input port 5 of the extruder main body 1
It has a first added water injection row 1 at a position 18 downstream from the added water inlet, and further has a second added water inlet 17 at a downstream 1440 side of this added water inlet 11, and
A high-speed interlocking type in which a two-bag extrusion screw 3 made of willow with a diameter of 53 is inserted, which has five stages of mixing elements 2c between the added water inlet 11 and the second added water inlet. Using a twin-screw extruder, the polymerization degree is 17 at the raw material input port 5.
00, PVA with saponification degree of 98 mol% and initial moisture content of 6.8%
Raw material powder is introduced at a rate of 40k9 per hour, and then the first
The scrap of the PVA raw material powder was melted through the added water inlet 11, and the temperature was adjusted to 8 to 0 by degassing in the furnace, and the PVA concentration was 1.
9. A PVA aqueous solution of % by weight of the base was injected, and the 2-koji extrusion screw 3 was turned for 30 minutes. p. m. A PVA aqueous solution having a PVA concentration of approximately 58% by weight was prepared by rotating the container and extruding it forward.

Next, the same PVA aqueous solution as the PVA aqueous solution injected at the first added water inlet 11 is injected into this PVA aqueous solution from the second added water inlet 17, and this is further poured into the PVA aqueous solution from the second added water inlet 17 to the front 720 side. The PV with a PVA concentration of 47.5% by weight was guided to the extrusion port provided at the position while being mixed.
A aqueous solution was obtained. When this PVA aqueous solution was weighed under pressure and continuously formed into a film to form a film with a thickness of 60 mm, no unmelted material was observed by visual observation. The specific power in the primary melting section of the extruder (between the first added water inlet 11 and the second added water inlet 17) is 0.28.
It was kWH'kg. In addition, the temperature of the primary melting section is controlled by four temperature control zones, and the temperature of each zone is 7, 8, 0, 10,000, and 11,600 from the first added water inlet 11 side.
It is. Example 2 The same high-speed shear mesh type twin-screw extruder as in Example 1 was used, and the initial moisture content was 5.6% at the raw material input port 5.
, PVA raw material powder with a degree of polymerization of 1650 and a degree of saponification of 99.9% was introduced, and while being transported forward at a rate of 43.5k9/hour, scraps of the raw material powder were melted from the first water injection row 1. The obtained PVA concentration was 21.4% by weight.
The VA aqueous solution was injected while keeping the temperature at 8,500 ℃.

The primary dissolving part from the first added water inlet 11 to the second added water inlet 17 is 700 m from the first added water inlet 11 side.
The temperature was controlled in temperature control bands of 80°C, 92°C, and 11,800°C. As a result, the PVA concentration in the primary melting zone was approximately 56.1
A PVA aqueous solution of % by weight was obtained. The specific power of the primary melting section was 0.298 kWH/k9. Next, P was introduced from the second added water inlet 17 to the first added water inlet 11.
The same PVA aqueous solution as the VA aqueous solution is injected, and the PV
A concentration is 49. A PVA aqueous solution of round weight % was obtained.

This PVA aqueous solution was weighed under pressure to form a film with a thickness of about 145 mm.

Next, this was dried to a film moisture content of 19%, and then biaxially stretched. The longitudinal thickness distribution of this film is ±5%.
It was easy to keep the melting temperature within 100 mL, and it was extremely homogeneous, with no unmelted material to the extent that it would cause problems in practical use. As explained above, according to the method for producing a polyvinyl alcohol aqueous solution according to the present invention, by directly melting and kneading the PVA raw material powder and water or PVA aqueous solution using a high-speed interlocking two-ball extruder, high This method has remarkable effects such as being able to easily obtain a high-quality PVA aqueous solution.

[Brief explanation of drawings]

FIG. 1 is a plan view of an example of a high-speed cutting and interlocking double-sided extruder used in the method for producing a concentrated aqueous solution of polyvinyl alcohol of the present invention, and FIG. 2 is a side view of the same extruder. FIG. 3 is a characteristic diagram showing the relationship between specific power and PVA concentration when the present invention is carried out using the same extruder, 1.
...Extruder main body, 5... Raw material input port, 6...
... PVA raw material powder, 11 ... Added water inlet, 1
7... Added water immersion port. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A fixed amount of polyvinyl alcohol powder that has not gone through a special hydration and swelling process is injected into the input port provided at the base of the high-speed shear meshing twin-screw extruder, and the powder is transferred at a constant rate into the barrel by the powder transfer function of the screw. After forming the transfer zone, water or a polyvinyl alcohol aqueous solution having a polyvinyl alcohol content of 25% by weight or less is metered and added at low pressure from an injection port provided downstream of the inlet to form a homogeneous material with a polyvinyl alcohol content of 50% by weight or more. The polyvinyl alcohol aqueous solution is melt-kneaded, and then water or a polyvinyl alcohol aqueous solution having a polyvinyl alcohol content of 25% or less is metered and mixed through an injection port provided downstream of the injection port, and the high-speed shear meshing type twin-screw extrusion is performed. A method for producing a polyvinyl alcohol aqueous solution, characterized in that a homogeneous polyvinyl alcohol aqueous solution is obtained from the tip of a machine in one step.