JPH04301409A - Manufacture of polyvinyl alcohol base molded form - Google Patents

Abstract

PURPOSE:To provide the economical manufacture of a polyvinyl alcohol base molded form by a simplified process from the mixture of polyvinyl alcohol and water. CONSTITUTION:The polyvinyl alcohol base molded form is manufactured in such a manner that the mixture of polyvinyl alcohol and water is formed in a beltlike substance, in which the mixture is fed substantially between at least one pair of compression rollers 4 and flocculated, and the beltlike substance is crushed or cut after slitting and pelletized, and melt-extruded and molded by using an extruder 7.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molded articles made of polyvinyl alcohol resin, particularly sheet, plate and film shaped articles.

0002

[Prior Art] In the production of polyvinyl alcohol film using the melt extrusion method, since a mixture of polyvinyl alcohol and water tends to cause a blocking phenomenon and also tends to solidify under pressure, it has traditionally been difficult to efficiently feed this mixture to an extruder. Various efforts have been made to produce high-quality products. For example, Japanese Patent Publication No. 44-11026 discloses that in order to improve the homogeneity of the stock solution for manufacturing molded products, the above mixture is melted or semi-melted by kneading, stirring, etc. under heating, and then pulverized. , JP-A-51-89562 discloses a method of preparing pellets with low apparent density and low polyvinyl alcohol concentration, supplying them to an extruder, and dissolving them. A method is described in which polyvinyl alcohol whose alcohol content is kept within a predetermined range is used, and after mixing, the polyvinyl alcohol is fed to an extruder and melted within a predetermined time. However, these methods are complicated or not sufficiently effective, and even if the mixture can be supplied into the extruder by some method, problems such as extrusion fluctuation and foaming will occur in this state. It was difficult to mold using a general-purpose extruder. In addition, intense heating, shearing, etc. to melt or semi-melt the resin and additives will promote deterioration, thermal decomposition, alteration, etc. of the resin and additives, and these will become foreign substances in the extruder and cause clogging of the filter.
It also adversely affects the appearance and performance of the final product. On the other hand,
Various improvements have been made to the extruder itself. For example, in Japanese Patent Publication No. 57-32663, the above-mentioned mixture introduced into the machine is melted at high temperature and pressure using an extruder using a special screw, and then the temperature and pressure are lowered while stirring, and then the mixture is cooled. Japanese Patent Publication No. 2-31661 describes a method for preventing quality deterioration due to foaming of molded products by discharging the material from an extruder as a molten material. A method is disclosed in which the materials are homogenized while being mixed, transported, heated and melted, volatile components are removed, and the materials are extruded from an extruder. However, these are not common because they require a special extruder.

0003

SUMMARY OF THE INVENTION It is therefore an object of the present invention to economically produce polyvinyl alcohol-based moldings, in particular moldings such as sheets, plates and films, in a simplified process from a mixture of polyvinyl alcohol and water. The purpose of this paper is to provide a method for manufacturing the same.

0004

[Means for Solving the Problems] The method for producing polyvinyl alcohol-based molded products according to the present invention is to prepare a mixture of polyvinyl alcohol and water preferably at a temperature of 60° C. or lower, more preferably at room temperature, and preferably at a rate of 1 to 80 kg/kg. cm,
More preferably, the material is fed between at least a pair of compression rollers pressurized at 2 to 67 kg/cm with substantially no back pressure to form an agglomerated band, which is crushed or slit and then cut into pellets. It is characterized in that it is melt-extruded using an extruder.

[0005] To explain this, the present inventors have developed a mixture of polyvinyl alcohol and water according to Japanese Patent Application Laid-open No. 50-1296.
As shown in Publication No. 47, we focused on the fact that it tends to harden under pressure, and as a result of our research, we found that when a mixture of polyvinyl alcohol and water is passed between compression rollers without back pressure, it will harden at around room temperature. The present invention was achieved based on the discovery that it can be easily and stably aggregated. In the present invention, a mixture of polyvinyl alcohol and water is first fed between at least a pair of compression rollers with substantially no back pressure to form an agglomerated strip. It varies depending on the degree of polymerization, degree of saponification, moisture content, etc., but at a temperature of 60°C or lower, especially at room temperature, it is 1 to 80 kg/cm, especially 2 to 67 kg/cm.
It is preferable that the pressure is applied to cm. This pressure is 1k
If it is less than g/cm 2 , aggregation will be insufficient. Furthermore, if the temperature of the compression roller exceeds 60° C., the mixture of polyvinyl alcohol and water will adhere to the roller, making stable supply impossible. In the present invention, "substantially no back pressure" refers to a state in which when polyvinyl alcohol powder is supplied by a screw or the like, the screw does not apply any pressure other than its own weight to the powder, and refers to an acceleration of 1.2 G or less. Further, it is preferable that the mixture of polyvinyl alcohol and water contains 10 to 100 parts by weight of water per 100 parts by weight of polyvinyl alcohol, and within this range, aggregation of 80 kg/cm or less is possible. In the present invention, agglomeration refers to a state in which polyvinyl alcohol powders stick together to form a sheet shape, cannot be easily torn off with fingers, etc., and the powders are connected.

[0006] The strips agglomerated between the rollers can be fed as they are to the extruder, but for stable production it is necessary to form them into pellets. For this purpose, the strip may be crushed as it is in a crusher into pellets of a certain size, or the strip may be slit to a certain width and then cut with a rotating blade to form pellets. The size of the pellets is preferably about 0.5 mm 3 to 2 cm 3 in consideration of blocking in the hopper when fed to the extruder.

The extruder used to melt extrude the mixture of pelletized polyvinyl alcohol and water is
A common single-screw type general-purpose extruder for molding thermoplastic resins is sufficient, but of course twin-screw and multi-screw extruders may also be used. The structure of the screw used in an extruder generally has a compression ratio of 1.5 to
7.0 times the range is used, and there are also known ones with various length distributions of the supply section, compression section, and metering section, and the ratio of screw diameter/shaft length, etc., but these The numerical value may be selected and adopted as appropriate depending on the desired extrusion capacity, efficiency, etc., and the present invention is not limited to the structure, type, etc. of the extruder.

As the polyvinyl alcohol used in the present invention, polyvinyl alcohol having various degrees of polymerization and saponification can be used as described above, but in addition, olefins such as ethylene and propylene, crotonic acid, acrylic acid, It is also possible to use polyvinyl alcohol modified with a small amount of unsaturated carboxylic acids such as methacrylic acid, maleic acid, and itaconic acid, or alkyl esters thereof, methyl methacrylate, acrylamide, vinyl sulfonic acid, and vinyl stearate. The polyvinyl alcohol may also optionally contain surfactants such as funnel oil, lubricants such as stearic acid, monoglycerin, fillers such as talc, calcium carbonate, plasticizers such as diethylene glycol, magnesium sulfate, zinc sulfate, or 35
- It is also possible to add reinforcing or coloring substances such as coloring inhibitors, organic or inorganic acids, titanium oxide, various pigments such as carbon black, dyes, etc., as described in Japanese Patent No. 1669, etc.

Next, the method of producing a polyvinyl alcohol molded article from a mixture of polyvinyl alcohol and water according to the present invention will be explained with reference to FIG. After polyvinyl alcohol and water are mixed in a mixer (not shown), they are put into a hopper 2 of a compression molding machine 1, extruded by a screw 3, and molded into an agglomerated strip by a compression roller 4. The temperature of the compression roller is preferably 60°C or lower, more preferably 0 to room temperature, and the pressure is preferably 1 to 80 kg/cm.
, more preferably maintained within the range of 2 to 67 kg/cm 2 . The obtained agglomerated strip is punched metal 5
It is sent to a crusher 6 equipped with a
It is ground into pellet-like compacts with a size of m3. The pellet-like molded product is fed to an extruder 7 heated to a cylinder temperature of 50 to 150°C and a die temperature of 70 to 130°C, melted and kneaded, and then passed through a die 8 into a sheet on a metal or plastic belt 9. A polyvinyl alcohol molded product is obtained. The pressure between the rolls in the present invention is defined as linear pressure P by the following equation 1. In addition, in the formula, M: own weight of the roll, A: pressure, L:
It is the tangent length.

0010

[Math 1]

[0011]

[Effect] 1. Agglomeration can be achieved by compressing the mixture. 2. The agglomerated material has a rubber-like appearance and can be easily crushed. 3. Since no blocking occurs during feeding to the extruder, stable feeding is possible. 4. Because the degree of heat treatment and shear applied to the mixture of polyvinyl alcohol and water during the pelletizing process is low, dissolution in the extruder is easy and uniform, and discoloration due to resin deterioration and generation of undissolved substances can be avoided. can.

0012

[Examples] Specific embodiments of the present invention will be explained below with reference to Examples and Comparative Examples. Example: Step 1: Each sample shown in Table 1 consisting of polyvinyl alcohol, water, and glycerin was put into the mixer in the apparatus A shown in FIG.
It was put into hopper 2 inside. After charging, the mixture was extruded using a conical screw 3 so that there was no back pressure at the inlet of the compression roller, and a band-shaped product was agglomerated using the compression roller 4 under the conditions shown in Table 1. The strip was pulverized by a pulverizer 6 equipped with a 5φ punching metal 5 to obtain a pellet-like molded product having a size of approximately 5 mm 2 .

[0013]

[Table 1]

Step 2: Sample No. obtained in the previous step. 5
The pellet-shaped molded product is processed in the apparatus B shown in FIG.
It is fed to a 40 mm general-purpose single screw extruder 7 using a full-flight screw with L/D = 28 and a compression ratio of 3 times, where it is melt-kneaded, extruded into a sheet form from a die 8 onto a belt 9, and dried to produce a polyvinyl alcohol film. was manufactured. Table 2 shows the set temperatures of the cylinder and die of the extruder at this time. The obtained polyvinyl alcohol film showed no foaming phenomenon, undissolved matter, or thermal decomposition products, and had extremely excellent transparency and smoothness.

[0015]

[Table 2]

Comparative Example: In the illustrated apparatus, when a mixture of polyvinyl alcohol and water was supplied to the compression roller 4 by the screw 3 in the hopper 2 of the compression molding machine 1, the back of the compression roller 4 was oversupplied. Pressure was generated, and the mixture of polyvinyl alcohol and water coagulated between the screw 3 and the compression roller 4 and could no longer be fed to the compression roller 4. From this, it was found that a mixture of polyvinyl alcohol and water could not form a flocculated band under conditions where back pressure was present.

[0017]

[Effects of the Invention] The method of molding a pellet-shaped product from a mixture of polyvinyl alcohol and water in the present invention includes the following steps:
Unlike conventional methods, there is no complicated or extra process such as melting or semi-melting a mixture of polyvinyl alcohol and water using a kneading extruder, etc., and by simply compression molding the mixture continuously, a large amount can be produced from the mixture in a short time. This method has the advantage of being able to easily and economically obtain pellet-like molded products, and is an extremely suitable method for producing pellet-like molded products. Therefore, when manufacturing a polyvinyl alcohol molded product from a mixture of polyvinyl alcohol and water, by using this method of molding a pellet-like molded product, the manufacturing process can be significantly shortened and workability can be improved, as well as the above-mentioned method. Pellet-like molded products can be easily made into polyvinyl alcohol-based molded products using a general-purpose extruder without using a special extruder, so it is possible to provide molded products that are cheaper than conventional polyvinyl alcohol-based molded products. This is a very industrially advantageous method.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an apparatus for implementing the method of the present invention.

[Explanation of symbols]

4... Compression roller, 6... Pulverizer, 7... Extruder.

Claims (2)

[Claims] Claim 1: A mixture of polyvinyl alcohol and water,
The method includes supplying the material between at least a pair of compression rollers with substantially no back pressure to form an agglomerated band, which is crushed or slit and then cut into pellets, and then melt-extruded using an extruder. A method for producing a characteristic polyvinyl alcohol molded product. Claim 2: The compression roller has a temperature of 1 to 60°C or less.
The method for producing a polyvinyl alcohol molded article according to claim 1, wherein the polyvinyl alcohol molded article is pressurized at 80 kg/cm.