JP2993047B2 - Method for emulsifying thermoplastic resin composition - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for industrially and inexpensively producing thermoplastic resin powders and emulsions.

[Prior Art] There are several methods for producing powders and emulsions of thermoplastic resins. Examples of the method include powder production methods represented by mechanical pulverization and chemical pulverization, and emulsion production methods represented by emulsion polymerization, suspension polymerization, and post-emulsification.

In the powder production method, mechanical pulverization can be said to be an inexpensive production method, but has the disadvantage that the particle size is relatively large and the particle shape is poor.

On the other hand, chemical pulverization is said to be relatively small in particle size and good in particle shape, but has the drawback that it is expensive and may cause environmental pollution because a large amount of organic solvent is used. I have.

In the emulsion production method, polymers obtained by emulsion polymerization or suspension polymerization typified by an ethylene-vinyl acetate copolymer generally have only a low ethylene content, and the ethylene content exceeds 50% by weight. Such a process is a high-pressure process in which the reaction pressure is several hundred kg / cm ² or more, which is practically difficult to implement from the viewpoint of cost and safety, and the ethylene content of the ethylene-vinyl acetate copolymer obtained by these methods is high. The upper limit is 40 wt%.

On the other hand, the method using post-emulsification is excellent as a method for emulsifying a polymer having a high olefin content because a thermoplastic resin which is usually a solid is dispersed in water in a post-process.

For the post-emulsification method, it is conceivable that a solvent may or may not be used, but the former is a method in which a solution in which a thermoplastic resin is dissolved in an appropriate organic solvent and an emulsifier aqueous solution are mixed and emulsified.
This is a method for recovering the solvent. According to this method, it is possible to emulsify a thermoplastic resin having a relatively high molecular weight, but it is technically difficult to recover the solvent, and it can be said that this is a low-productivity and high-cost production method. It is also not preferable from the viewpoint of environmental problems.

Regarding the latter method, a method has been proposed in which a composition of a polyolefin and a carboxyl group-containing polyolefin is melted, and a basic substance and the composition are dispersed in water at 140 to 300 ° C. (for example, Japanese Patent Publication No. 58-42207). I have. Although the use of an emulsifier is excellent in that the physical properties of the resin are not impaired, a sufficient effect cannot be expected unless a carboxyl group-containing polyolefin is used. Further, when producing fine particles, the influence of the melt viscosity of the resin is large, and it is a high-temperature and high-pressure process that is not suitable for emulsifying a relatively high-molecular-weight resin, and is disadvantageous in terms of energy. As still another method, an aqueous dispersion is produced by melt-kneading an olefin resin and an aqueous solution of partially saponified polyvinyl alcohol with a multi-screw extruder (for example, Japanese Patent Publication No. Sho 62
-29447). In this method, since fine particles cannot be obtained unless a high viscosity aqueous solution of partially saponified polyvinyl alcohol is used, the partially saponified polyvinyl alcohol used is limited to those having a high degree of polymerization. Also, preparation of a high-viscosity partially saponified polyvinyl alcohol aqueous solution is a difficult operation, and it is also difficult to supply this to an extruder. In this method, fine particles cannot be obtained unless the aqueous solution is supplied to the compression zone of the multi-screw extruder. The screws of a multi-screw extruder with a compression zone are very special and not widely used.

[Problems to be Solved by the Invention] Unlike the conventional method, the present invention is very stable only by supplying water in the middle of a general-purpose twin-screw extruder without using a special emulsifier or dispersant. An object of the present invention is to produce an aqueous dispersion of a thermoplastic resin continuously, inexpensively and easily.

[Means for Solving the Problems] In view of the above situation, the present inventors have conducted intensive studies and found that the use of a thermoplastic resin composition obtained by melt-mixing a general-purpose polyvinyl alcohol with a thermoplastic resin is extremely stable. The inventors have found that an aqueous dispersion of a thermoplastic resin can be produced continuously, inexpensively and easily, and have completed the present invention.

That is, in the present invention, a thermoplastic resin composition obtained by melt-mixing 80 to 98 wt% of a thermoplastic resin and 2 to 20 wt% of polyvinyl alcohol is supplied from a hopper of a twin-screw extruder, and is provided after a melting zone of the composition. The present invention relates to a method for emulsifying a thermoplastic resin composition, wherein water is supplied from at least one supply port and melt-kneaded with the composition.

 Hereinafter, the present invention will be described in detail.

The twin-screw extruder used in the present invention has at least one or more water supply ports after the melting zone of the composition, and is a general-purpose two-screw extruder as long as it exhibits high shearing force. A shaft extruder may be used, and the rotation direction may be the same or different.

FIG. 1 shows an example of the apparatus. In the drawing, reference numeral 1 denotes a screw disk type, 1-1 feed kneading disk, 1-2 return kneading disk, 1-3 neutral kneading disk, 1-4 flight disk,
In the figure, reference numeral 2 denotes a twin-screw extruder for emulsification, a 2-1 feeder, a 2-2 hopper, a 2-3 motor, a 2-4 gear box, a 2-5 cylinder (with a heating device), a 2-6 screw, 2-7 nozzle, 2-8 plunger pump,
In the configuration of the 2-9 heating water tank and the 2-6 screw, A is a feed zone, B is a melting zone, C is a kneading zone, and D is a measuring zone. E1, E2, and E3 are water inlets. Here, the melting zone refers to a kneading disk portion used for melting the resin in the screw configuration from the hopper to the first injection port E1, and the resin temperature needs to be at least the melting point. Also, the kneading zone refers to the region from the first injection port to the last kneading disk in the screw configuration.

After a certain amount of resin is supplied from the feeder and completely melted in the melting zone of part B, the resin is forcibly kneaded and emulsified with a certain amount of water supplied in a kneading zone of C having one or more liquid injection ports. , D, to obtain a continuous product.

Particularly preferred is a twin-screw extruder of the type in which a screw dimension having two or three kneading discs having an L / D of 20 or more can be easily changed.
As shown in the figure, a screw configuration using a combination of a flight type disk and a kneading type disk is preferable, and a configuration in which feed / neutral / return is performed for each of a melting zone and a kneading zone is preferable. Further, the water supply position is preferably a strong kneading portion on the kneading disk in the kneading zone, and the ratio of the kneading disk after the first water injection port needs to be at least 10% of L / D. L / D used herein is a value obtained by dividing the length L of the screw by the diameter D.

As the thermoplastic resin used in the present invention, for example,
Low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, fully or partially saponified ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene -Various metal salts of acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-acrylic acid ester-maleic anhydride terpolymer, ethylene-methacrylic acid ester copolymer Examples thereof include a polymer, polypropylene, a random or block copolymer of ethylene-polypropylene, a terpolymer of ethylene-polypropylene-α-olefin, and a mixture of polystyrene and the like at an arbitrary ratio. Further, for various purposes, a small amount of additives, for example, at least one or more of rosin, petroleum resin, polyamide, wax, surfactant and the like may be used in combination.

The polyvinyl alcohol used in the present invention refers to a completely or partially saponified polyvinyl acetate, and may be a general-purpose one used for ordinary emulsion polymerization, and has a polymerization degree of 200 to 2
A range of 000 is preferred. Particularly preferred is a partially saponified polyvinyl alcohol, the degree of saponification of which is 65 to 95.
Molar% is preferred. If the saponification degree is less than 65 mol%, sufficient emulsification cannot be performed, and a stable aqueous dispersion cannot be obtained.

The thermoplastic resin composition used in the present invention refers to a material obtained by melting and mixing the above-mentioned thermoplastic resin and polyvinyl alcohol, and the mixing ratio of the thermoplastic resin and polyvinyl alcohol is 80 to 98 wt% of the thermoplastic resin. Polyvinyl alcohol is in the range of 2 to 20% by weight. If the polyvinyl alcohol content is less than 2% by weight, no emulsification occurs and no aqueous dispersion can be obtained. On the other hand, when the content exceeds 20% by weight, when the aqueous dispersion is formed into a heat-dried film, the water resistance is remarkably lowered and the cost is increased, which is not preferable.

Further, as a method of supplying the thermoplastic resin composition to the twin-screw extruder for emulsification, for example, a method of supplying after melt-mixing in a separate step in advance, a method of dry blending and supplying the thermoplastic resin and polyvinyl alcohol There is a method of dry-blending a small amount of a mixture obtained by melting and mixing a high concentration of polyvinyl alcohol with a thermoplastic resin, and supplying the resulting mixture. In any case, it is sufficient if the mixture is supplied to the hopper of the twin-screw extruder for emulsification and completely melt-mixed in the melting zone of B.

Further, as a method of melt-mixing the thermoplastic resin and polyvinyl alcohol, a twin-screw extruder having a strongly kneaded portion is preferable from the viewpoint of dispersibility, and the melt-mixing temperature is not limited as long as the polyvinyl alcohol is sufficiently dispersed. Particularly preferably above the melting point of polyvinyl alcohol, below the decomposition temperature
A range from 190 to 220 ° C is preferred.

In the present invention, the number of water inlets is one or more, particularly preferably two or more. The reason for supplying at two or more locations is that the viscosity difference between the molten resin water and the resin is large, and if a large amount is supplied at one location, slip occurs between the screw and the resin, making it difficult to knead. This tendency is remarkable for a resin with a high melt viscosity. A resin with a high melt viscosity that cannot be injected at one place and can be emulsified by supplying it at two or more places can be emulsified. It is preferable to increase the number of locations. Another effect is that an emulsion having a smaller particle size can be stably produced. Although the reason for this phenomenon is not always clear, it is speculated that the W / O emulsion is first formed from the water injection in multiple stages, and then the phase transition to the O / W emulsion progresses in stages. Is done. However, such a presumption does not limit the present invention in any way.

As for the temperature of the water supplied to the twin-screw extruder, it is preferable that the temperature difference with the molten resin is small, and it is more preferable that the temperature is the same as the molten resin temperature. If the temperature of the supply water is too low, the molten resin is quenched at the water injection portion, so that the melt viscosity becomes high, the emulsification becomes difficult, and the particle shape becomes poor. Also,
When emulsification at a high temperature is required, such as a decrease in melt viscosity or emulsification of a high melting point resin, it is not preferable to increase the water temperature more than necessary to use pressurized hot water, because the apparatus becomes large-scale.

Further, in the case of emulsifying an acid copolymer such as acrylic acid, an aqueous solution using an appropriate amount of a base for neutralizing the acid may be supplied to the extruder instead of the supplied water. When emulsifying a resin having a high melt viscosity, a high-viscosity aqueous solution of a water-soluble polymer such as sodium polyacrylate or carboxymethyl cellulose is supplied instead of water in order to prevent the screw from slipping with the resin. No problem.

In the present invention, the ratio of water to the thermoplastic resin composition supplied to the twin-screw extruder is such that the resin 10
Water is preferably 5 to 20 parts by weight with respect to 0 parts by weight, and water 10
A range of ~ 15 parts by weight is preferred. If the amount is less than 5 parts by weight, no phase transition to the emulsion occurs and no product can be obtained. Also,
If the amount exceeds 20 parts by weight, the amount of water supplied is too large, a slip occurs between the resin and the screw, and the resin cannot be kneaded and cannot be emulsified. However, when injecting at two or more locations, the amount of water supplied can be greatly changed as compared to when injecting at one location, and water is preferably 5 to 200 parts by weight per 100 parts by weight of resin, and more preferably 10 to 100 parts by weight of water. A range of parts by weight is preferred. If the amount is less than 5 parts by weight, no phase transfer to the emulsion occurs and no product can be obtained. On the other hand, if it exceeds 200 parts by weight, the resulting emulsion has a low solid content, so that it is not industrially useful.

In this way, an emulsion of a thermoplastic resin can be continuously produced easily and at low cost.

Further, by drying the thus obtained emulsion by a method such as spray drying, it is possible to obtain a thermoplastic resin powder.

[Examples] Next, examples of the present invention and comparative examples corresponding thereto will be described, but the present invention is not limited thereto.

Reference Example As a method of melting and mixing a thermoplastic resin composition,
Granulation was performed using a screw extruder (manufactured by Kobe Steel Ltd .: 2NCM granulator) under the condition that the molten resin temperature was 190 ° C.

Example 1 Twin screw extruder (manufactured by Kobe Steel Ltd .: KTX-37, L / D = 30)
In accordance with the reference example, an ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE720, vinyl acetate content: 28 wt%, melt flow rate (190 ° C.): 150 g / 10 mi)
n) A mixture of 90 wt% and 10 wt% of polyvinyl alcohol (Gosenol KL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
It was supplied at 10 kg / h. 90 ° C. water was supplied at a rate of 1 kg / h from the plunger pump P1 of 2-8 in the figure. Extrusion was performed at a heating temperature of 120 ° C. (cylinder temperature until the first liquid injection), a kneading temperature of 90 ° C. (cylinder temperature after the first liquid injection), and a rotation speed of 250 rpm. As a result, a milky white solid was obtained. This solid was dispersed in water using a homogenizer to prepare a solid content of 50% by weight to obtain a product.

The average particle size, stability, appearance of the heat-dried film, and water resistance of the obtained product were evaluated, and the results were summarized in Table 1.

The average particle size was measured using a laser diffraction type particle size distribution analyzer, SK Laser Micron Sizer (manufactured by Seishin Enterprise Co., Ltd.).

For stability, take a 100 cc emulsion on a flat bottom tester with an inner diameter of 25 mmφ, seal tightly so that water does not evaporate,
Let sit for a week. For those that do not separate into an emulsion layer and an aqueous layer after standing, ○ is given, and for those that have undergone phase separation, the ratio of the separated aqueous layer to the whole is expressed as a percentage.

For the preparation of a heat-dried film, a certain amount of emulsion is applied on a slide glass and dried at a temperature of 20 ° C. or higher, which is the melting point of the resin, until moisture is completely eliminated, thereby producing a continuous film.

The appearance is visually observed to see whether the coating is a uniform continuous coating. Good products are indicated by "O" and bad products are indicated by "X".

Regarding water resistance, the heat-dried film is immersed in water for 30 minutes, then dried at room temperature, and the appearance is similarly observed.

Example 2 In Example 1, an ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE710, vinyl acetate content: 28)
wt%, melt flow rate: 18g / 10min) 80wt% and polyvinyl alcohol (Gosenol KM-11, manufactured by Nippon Synthetic Chemical Industry Co., Ltd .: 20wt%) Extrusion was carried out in exactly the same manner to obtain a milky white solid. This solid was dispersed in water using a homogenizer to prepare a solid content of 50% to obtain a product.

Example 3 Twin screw extruder (manufactured by Kobe Steel Ltd .: KTX-37, L / D = 30)
According to the reference example, 90 wt% of ethylene vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE751, vinyl acetate content: 28 wt%, melt flow rate: 6 g / 10 min) and polyvinyl alcohol (Nippon Synthetic Chemical Industry Co., Ltd .: Gohsenol KL-05) A mixture of 10 wt% was supplied at 10 kg / h. From the plunger pumps P1, P2, P3 in 2-8 in the figure
90 ° C water was supplied at 0.5 kg / h, 0.7 kg / h and 5 kg / h, respectively. Extrusion was performed at a heating temperature of 160 ° C. (cylinder temperature until the first liquid injection), a kneading temperature of 90 ° C. (cylinder temperature after the first liquid injection), and a rotation speed of 250 rpm. As a result, a milky liquid was obtained. This liquid was dispersed in water using a homogenizer to prepare a solid content of 50% by weight to obtain a product.

Example 4 In Example 3, 98 wt% of an ethylene-acrylic acid copolymer (manufactured by Dow Chemical: Primacol 3460, acrylic acid content: 9 wt%, melt flow rate: 20 g / 10 min) and polyvinyl alcohol (Kuraray Co., Ltd.) PVA-110) 2wt%
Was supplied to a hopper of a twin-screw extruder. Also, instead of the water supplied to the extruder, 10wt
Extrusion was carried out in exactly the same manner except that an aqueous solution of sodium hydroxide was used to obtain a milky white solid. This solid was dispersed in water using a homogenizer to prepare a solid content of 50% by weight to obtain a product.

Example 5 In Example 3, low-density polyethylene (manufactured by Tosoh Corporation: Petrocene 356, melt flow rate: 100 g / 1)
0 min, density: 0.914 g / cm ³ ) 90 wt% of polyvinyl alcohol (Kuraray Co., Ltd .: PVA-110) 10 wt% according to the reference example, except that the mixture is fed to a hopper of a twin screw extruder. Extrusion was carried out by the technique to obtain a milky white liquid. This liquid was dispersed in water using a homogenizer to prepare a solid content of 50% by weight to obtain a product.

Example 6 In Example 3, 90 wt% of a partially saponified ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation: Mersen H-6410, melt flow rate: 16 g / 10 min) and polyvinyl alcohol (manufactured by Kuraray Co., Ltd.) : PVA-205) Extrusion was carried out in exactly the same manner except that a mixture of 10 wt% according to the reference example was supplied to the hopper of a twin-screw extruder to obtain a milky liquid. This liquid was dispersed in water using a homogenizer to prepare a solid content of 50% by weight to obtain a product.

Comparative Example 1 In Example 1, 99 wt% of ethylene vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE720) and 1 wt% of polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd .: Gohsenol KL-05) were used as reference examples. The mixture was extruded in exactly the same manner except that the mixture was supplied to the hopper of a twin-screw extruder to obtain a milky white solid. When this solid was dispersed in water using a homogenizer, no dispersion occurred.

Comparative Example 2 Extrusion was performed in exactly the same manner as in Example 1 except that water was supplied by a plunger pump to the center of the melting zone in B in the figure, to a position where the resin was in a semi-molten state. Slip occurred between the samples, and sufficient kneading could not be performed, and a product could not be obtained.

Comparative Example 3 Extrusion was performed in exactly the same manner as in Example 1 except that a single-screw extruder (Placo Co., Ltd .: 50 mmφ) was used instead of the twin-screw extruder. Slip occurred and sufficient kneading could not be performed to obtain a product.

Comparative Example 4 In Example 3, 75 wt% of an ethylene vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE751) and 25 wt% of polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd .: Gohsenol KL-05) were mixed. Extrusion was carried out in exactly the same manner except that the mixture was supplied to the hopper of a twin-screw extruder, according to the Reference Example, to obtain a milky liquid.
Disperse this liquid in water using a homogenizer and solidify
The product was prepared by adjusting to 50 wt%.

Comparative Example 5 In Example 1, an ethylene vinyl acetate copolymer (manufactured by Tosoh Corporation: Ultracene UE720) was supplied at 10 kg / h to a hopper of a twin-screw extruder, and polyvinyl alcohol (Japan) was used instead of water. Extrusion was carried out in exactly the same manner except that a 10 wt% aqueous solution of Gohsenol KH-20 (manufactured by Synthetic Chemical Industry Co., Ltd.) was supplied at 5 kg / h, to obtain a milky liquid. This liquid was dispersed in water using a homogenizer to prepare a solid content of 50% by weight to obtain a product.

[Effects of the Invention] As is apparent from the above description, according to the present invention, a specially shaped screw is not required, and continuous and easy heat is supplied only by supplying water to a general-purpose twin-screw extruder. An emulsion of a plastic resin can be obtained. In addition, since it does not require high temperature and pressure and does not use organic solvents, it is advantageous in terms of energy and environmental pollution, is a safe and low-cost process, and provides an inexpensive thermoplastic resin emulsion. You can do it.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an emulsion production facility. In the figure, reference numeral 1 denotes a disk type of a screw segment of a twin screw extruder. 1-1 kneading disk, 1-2 return kneading disk, 1-3 neutral kneading disk, and 1-4 flight disk. In the figure, reference numeral 2 is a schematic diagram of a twin-screw extruder, which is an example of a case where water is injected from three places. 2-1 feeder, 2
-2 hopper, 2-3 motor, 2-4 gear box, 2-5 cylinder (with heating device), 2-6 screw, 2-7 nozzle, 2-8 plunger pump, 2-
9 heating water tanks, and E1, E2, E3 are water inlets. The present invention is not limited by this drawing.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C08J 3/00-3/28 B29B 7/00-7/94

Claims (1)

(57) [Claims] A thermoplastic resin composition obtained by melting and mixing 80 to 98% by weight of a thermoplastic resin and 2 to 20% by weight of polyvinyl alcohol is supplied from a hopper of a twin-screw extruder and provided after a melting zone of the composition. A method for emulsifying a thermoplastic resin composition, comprising supplying water from at least one supply port and melt-kneading the composition with the composition.