JPH10166417A - Production of thermoplastic resin molded object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molded object from a hardly moldable resin with high productivity without taking labor for removing or recovering an org. solvent and generating the reduction of a mol. wt. at a time of molding. SOLUTION: A hardly moldable resin is supplied to an extruder 1 from a pressure-resistant hopper 2 to be transformed from a solid phase to a molten phase within the extruder and this molten resin is introduced into a mold 3 to be extruded and shaped. In this case, the difficult-to-mold resin is transformed while non-reactive gas held to a high pressure state is dissolved in the resin to produce a thermoplastic resin molded object. The molten resin is pref. introduced into the mold 3 while held to a pressurized state. It is pref. to supply the non-reactive gas to the region from the pressure-resistant hopper 2 to the solid transport part of the extruder 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermoplastic resin, particularly a resin having a high melt viscosity, which is difficult to melt-extrude, a resin which is easily thermally decomposed, an additive having a low boiling point or an additive which is easily thermally decomposed. The present invention relates to a method for producing a molded article of a difficult-to-mold resin such as a resin to be formed.

[0002]

2. Description of the Related Art Resins such as ultrahigh molecular weight polyethylene and ultrahigh polymerization degree polyvinyl chloride are very difficult to mold because of their high melt viscosity and easy decomposition, and are generally called difficult-to-mold resins. Have been.

Conventionally, in the case of such a difficult-to-mold resin having a very high melt viscosity, the following method has been employed for producing a molded article from the resin.

(1) A method of forming a plate-like or rod-like molded body by compression molding or ram extrusion molding, and shaping the molded body into a desired product by cutting out such as cutting;
(2) A method of dissolving a difficult-to-mold resin in an organic solvent and forming a film or a sheet by a casting method; (3) A method of adding an organic solvent to a powder of a difficult-to-mold resin as described in Japanese Patent Publication No. Hei 4-47608. A method in which the resulting dispersion or mixture is heated and melted, then extruded, and the organic solvent is volatilized after the molding.

[0005] However, the method (1) has a disadvantage that productivity is extremely low. In addition, the above (2) and
In the method (3), if the solvent remains in the molded body, the physical properties of the molded body are deteriorated.Therefore, it is necessary to heat the molded body to evaporate the solvent. It requires a large-scale device, requires a long time, and also has low productivity. In addition, if the solvent is volatilized in the air as it is, there is a risk of causing pollution. Therefore, the solvent must be recovered, and there is a problem that the equipment cost of the recovery equipment and the like increases.

In the case of a difficult-to-mold resin whose decomposition temperature and molding temperature are close to each other, a method has been adopted in which a stabilizer or a plasticizer is added to the resin to minimize the decomposition of the resin. However, in this method, the physical properties of the resin decrease in proportion to the amount of the stabilizer or plasticizer added. Conversely, when the resin is molded without adding the stabilizer or plasticizer, the appearance of the molded article is deteriorated due to decomposition of the resin. Inevitably, the quality of the molded product is deteriorated due to the decrease in the molecular weight.

[0007]

According to the present invention, it is possible to obtain a difficult-to-mold resin molded product with high productivity without requiring the trouble of removing and recovering the organic solvent and without causing a decrease in the molecular weight at the time of molding. An object of the present invention is to provide a method for producing a difficult-to-mold resin molded article.

[0008]

SUMMARY OF THE INVENTION The method for producing a difficult-to-mold resin molded article according to the present invention has been devised in order to achieve the above object, and supplies the difficult-to-mold resin to an extruder from a pressure-resistant hopper. In the step of transforming the solid phase into a molten phase, and introducing the molten resin into a mold for extrusion molding, the resin is transformed while dissolving a non-reactive gas in a high-pressure state in the difficult-to-mold resin. Is what you do.

Examples of the difficult-to-mold resin in the present invention include a resin having a high melt viscosity, which is difficult to be melt-extruded, a resin which is easily decomposed by heat, a resin having a low boiling point additive or an additive which is easily decomposed by heat. Can be

Examples of the resin having a high melt viscosity that are difficult to melt-extrude include engineering plastics such as ultrahigh molecular weight polyethylene, ultrahigh polymerization degree polyvinyl chloride, polytetrafluoroethylene, and polyimide, so-called super engineering plastic resins. No.

Examples of the resin which is easily decomposed by heat include biodegradable resins such as polyvinyl chloride and polylactic acid having a high degree of chlorination, and polyacrylonitrile.

The non-reactive gas used in the present invention can be used without particular limitation as long as it is a gas at normal temperature and normal pressure and does not react with the difficult-to-mold resin and does not deteriorate the resin. For example, carbon dioxide, nitrogen, argon, neon, helium, oxygen and the like can be mentioned. These may be used alone or in combination of two or more. Of these, carbon dioxide is most preferable because it has high solubility in the resin and the melt viscosity of the resin is greatly reduced.

The specific method for dissolving the non-reactive gas in the resin is not particularly limited. For example, the non-reactive gas is supplied to the region from the pressure hopper of the molding apparatus to the solid transport section of the extruder to supply the non-reactive gas. And a method of dissolving it in the solution. For the supply of the non-reactive gas to the above-mentioned region, the gas may be supplied directly from the gas cylinder to the extruder, or may be supplied at a high pressure using a pressure pump or the like.

In order to maintain the high pressure state of the non-reactive gas, it is preferable to incorporate a screw drive shaft and a pressure-resistant seal structure of a hopper into the extruder. Further, by installing the screw drive shaft on the tip side of the extruder, it is relatively easy to make the drive shaft a pressure-resistant seal structure for molten resin. This method is more preferable for increasing the pressure resistance.

The amount of the non-reactive gas dissolved is not particularly limited as long as the melt viscosity of the resin becomes a viscosity suitable for molding by dissolution, and is appropriately selected depending on the type of the resin and the type of the non-reactive gas. can do.

Next, when introducing the molten resin into the mold, it is preferable to keep the resin in a pressurized state. Once the pressure is reduced, the non-reactive gas dissolved in the molten resin may volatilize or bubble. In such a case, the amount of non-reactive gas dissolved in the resin decreases during the flow of the molten resin in the mold, and the melt viscosity increases, making shaping difficult. Further, a non-foamed molded article as described later cannot be obtained, or the foamed molded article becomes a molded article having a variable cell diameter.

The method for producing a molded article according to the present invention comprises:
It can be applied to the production of both foamed and non-foamed molded products.

In order to obtain a foamed molded product, a mold having a conventional structure for extrusion foaming may be used at the time of extrusion molding. The mold shape, resin flow viscosity, Alternatively, the bubble shape and bubble diameter can be controlled by appropriately setting the molding conditions such as the mold temperature and the extrusion amount.

On the other hand, when a non-foamed molded article is obtained, the following method can be adopted.

(1) A method in which the resin is sufficiently cooled in a mold and extruded in a solidified state. In this method, it is also preferable to take measures such as using a liquid lubricant to reduce the resin flow resistance in the mold, or applying vibration to the mold to reduce the frictional resistance between the wall surface and the resin surface. . (2) A method of performing rapid cooling sizing while maintaining the pressure from the mold outlet. (3) A method of removing air bubbles from a molded article by applying pressure in a temperature range of plastic deformation when forming a foamed article from a mold outlet.

As the method using a liquid lubricant in the above method (1), a conventionally known method can be arbitrarily applied.
As a liquid lubricant used in this method, decomposition, boiling and the like are unlikely to occur at the molding temperature, and do not dissolve in the resin,
A chemically stable substance that does not promote the deterioration of the resin is preferable. Examples of the lubricant satisfying such conditions include liquid polysiloxane, polyhydric alcohol such as ethylene glycol, and its alkyl ester and alkyl ether, polyoxyalkylene and its alkyl ester, and alkyl ether, polyoxyalkylene and Examples thereof include random, block or graft copolymers of two or more alkylene oxides. Above all, water-soluble lubricants such as the above-mentioned polyhydric alcohols are preferable in that they are easily removed after adhering to the surface of the molded article.

In order to uniformly cover the resin surface with the lubricant, it is desirable that the wall surface of the mold is made of a porous material. Examples of the material of the porous body include a metal material mainly composed of aluminum, stainless steel, titanium, gold, silver, copper and the like, and a nonmetallic material mainly composed of alumina, mullite, silicic acid, zirconia and the like. The pressure and flow rate required for lubricant supply are determined by the type of lubricant used and the pore diameter, porosity, and mold wall thickness of the porous body constituting the mold wall.

In order to uniformly apply the lubricant to the resin interface, it is preferable to select a porous body having a sharp pore distribution curve and uniformly dispersed pores as the porous body constituting the mold wall surface. . As a porous body satisfying such conditions, it is desirable to use a non-ferrous metal-based material.

As means for applying vibration to the mold,
Conventionally known ones can be applied, for example, a vibration motor,
Vibration is given to the mold using a vibrator, ultrasonic waves or the like. In this case, the frequency of the vibration is not particularly limited,
Preferably it is 100 to 100,000 Hz, more preferably, 500 to 30,000 Hz. If the frequency is less than 100 Hz, the frictional resistance on the wall surface cannot be sufficiently reduced, and extrusion may not be possible. If the frequency is more than 100,000 Hz, a large amount of energy is required to apply vibration, and the production cost may increase.

On the other hand, the amplitude of the vibration is preferably 0.5 to 1
000 μm, more preferably 1 to 500 μm. If the amplitude is less than 0.5 μm, the friction resistance on the wall surface cannot be sufficiently reduced, and extrusion may not be possible. If the amplitude exceeds 1000 μm, the appearance of the molded article may be deteriorated.

In the above method (3), when the difficult-to-mold resin is a crystalline resin, the temperature range of the plastic deformation is preferably in the range of (melting point−20 ° C.) to (melting point + 100 ° C.)
The temperature range is more preferably from (melting point) to (melting point + 50 ° C.). If the molded body is shaped at a temperature lower than (melting point −20 ° C.), foam may remain inside the resin, and a molded body having a uniform shape may not be obtained, and desired physical properties may not be sufficiently exhibited. If the temperature is higher than (° C.), it may be difficult to peel off the molded articles stacked after shaping.

On the other hand, when the difficult-to-mold resin is an amorphous resin, the plastic deformation temperature range is preferably in the range of (glass transition temperature -10 ° C.) to (glass transition temperature + 150 ° C.), more preferably (glass transition temperature + 150 ° C.). (Glass transition temperature) to (glass transition temperature + 80 ° C.). (Glass transition temperature-
If the molded body is formed at a temperature lower than (10 ° C.), foam may remain inside the resin, and a uniform-shaped molded body may not be obtained, and the desired physical properties may not be sufficiently exhibited. If the ratio is higher than the above range, it may be difficult to peel off the formed body after the shaping.

The pressure applied to the compact during shaping is preferably ^{2 to} 300 kgf / cm ² , more preferably 5 to 300 kgf / cm ² .
250 kgf / cm ² , particularly preferably 10 to 200 k
gf / cm ² . The pressure is not obtained molded body having a uniform shape remainder foam inside the resin is less than 2 kgf / cm ^2, there may not be sufficiently exhibited even desired properties, exceeds 300 kgf / cm ^2, molding The body may be rolled excessively and the desired thickness accuracy may not be obtained.

The time required for shaping under pressure (hereinafter referred to as "shaping time") is preferably at least 1 second, more preferably at least 5 seconds. If the shaping time is less than 1 second, foaming remains in the resin, a molded article having a uniform shape cannot be obtained, and desired physical properties may not be sufficiently exhibited. There is no particular upper limit on the shaping time, but if this time is too long, the productivity is lowered, which is not preferable.

The method for applying pressure to the compact is not particularly limited as long as the above-mentioned predetermined pressure and shaping time can be satisfied. For example, the compact is shaped by a surface pressure such as a double belt press. , A method of shaping between a belt and a roll, a method of shaping between a roll and a roll, and the like.

Further, by forming an uneven pattern such as an embossed pattern on the surface of a roll or a belt at the time of shaping, the uneven pattern is transferred to the surface of the molded article, and a difficult-to-mold resin molded article having excellent decorativeness can be obtained. Can be.

The cooling temperature after shaping is lower than the heat deformation temperature of the resin. If the cooling temperature is equal to or higher than the heat deformation temperature, the molded body may be deformed in a process such as winding.

(Function) The present invention is characterized by transforming a resin from a solid phase to a molten phase while dissolving a high-pressure non-reactive gas in the difficult-to-mold resin, for the following reasons. is there.

When a non-reactive gas is dissolved in a solid phase, for example, a resin in a pellet or powder state, and then the resin is heated and melted in the absence of the non-reactive gas, the process of increasing the temperature involves diffusion into the resin by diffusion. The dissolved non-reactive gas may volatilize or foam. Also, when dissolving the non-reactive gas in the molten resin, in the case of a resin having a very high melt viscosity, for example, when plasticizing the resin with the screw, the screw becomes unrotatable due to a sudden increase in torque. In the case of a resin that is very sensitive to heat, the decomposition of the resin may proceed before the non-reactive gas is dissolved in a molten state.

In the method according to the present invention, while the resin is being transformed from the solid phase to the molten phase, the non-reactive gas under high pressure is dissolved in the difficult-to-mold resin, and the completely compatible state of the resin and the non-reactive gas is changed. Due to the formation, the non-reactive gas dissolved in the resin does not volatilize or foam from the resin before the resin is melted. Accordingly, the energy required for plasticizing the resin by the non-reactive gas is reduced, the torque is reduced, the screw can be rotated smoothly, and the molding temperature during melting can be reduced. Moreover, since the non-reactive gas maintains the dissolved state in the difficult-to-mold resin, the melt viscosity of the resin decreases, and the molten resin can be extruded smoothly from the extruder. Further, the molding temperature can be reduced depending on the degree of decrease in the melt viscosity.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings.

FIG. 1 schematically shows an example of a molding apparatus used in the method for producing a difficult-to-mold resin molded article of the present invention.

Referring to FIG. 1, the molding apparatus (A) mainly comprises an extruder (1), a pressure hopper (2) and a lubricating cooling mold (3). Extruder (1) is a cylinder (11)
And a screw (12) arranged inside the cylinder. (11) The lower end of the pressure-resistant hopper (2) is located at the base end of the cylinder (11).
And a lubricating cooling mold (3) is attached to the tip of the cylinder (11). Further, a gas supply port (13) is provided in a solid transport section at the base end of the cylinder (11). Non-reactive gas is supplied from gas cylinder (15) to pressurized pump (16)
The gas is supplied to the gas supply port (13) and the pressure-resistant hopper (2) through the open / close valves (14) and (22) at a high pressure. The screw shaft has a pressure-resistant seal structure, and can maintain the supplied non-reactive gas in a high pressure state.

The lubricating cooling mold (3) extrudes a molten resin raw material, which is guided from the extruder (1) while maintaining a pressurized state, while forming it into a desired shape. A lubricant can be supplied to the mold inner surface (32) from a lubricant supply port (31) provided on the outer wall surface of the mold. Here extruder (1)
Each of the lubricating and cooling molds (3) is provided with a temperature control device (not shown) so that it can be controlled to a predetermined temperature.

In the method for producing a difficult-to-mold resin molded article according to the present invention, first, a pressure hopper is
The difficult-to-form resin (4) filled in (2) is supplied into a cylinder (11) and melted while being transported forward by a screw (12) in the cylinder (11).

At this time, by opening the on-off valve (14),
A non-reactive gas is supplied at a high pressure from the gas supply hole (13) into the solid transport section of the cylinder (11), and the same occurs when the difficult-to-mold resin (4) transforms from the solid phase to the molten phase in the cylinder (11). The non-reactive gas is dissolved in the resin under high pressure. Also, if necessary, open the on-off valve (22) so that the resin
A non-reactive gas is injected at a high pressure into the pressure-resistant hopper (2) filled with (4) to dissolve the non-reactive gas in the difficult-to-mold resin (4).

The molten resin in which the non-reactive gas is dissolved is completely melted by the screw (12), and supplied to the lubricating cooling mold (3) while maintaining the pressurized state. It is cooled and solidified to obtain a predetermined molded body (5).

In this production method, as described above, the extruder
Before the hard-to-mold resin (4) is melted and kneaded in (1), since the non-reactive gas is dissolved in the hard-to-mold resin (4) in advance, the hard-to-mold resin (4) is The energy is reduced during plasticization, the torque is reduced, the screw (12) can rotate smoothly, and the temperature of the molten resin can be reduced. In addition, since the non-reactive gas maintains the dissolved state even after being dissolved in the difficult-to-mold resin, the melt viscosity decreases, and the molten resin is smoothly introduced from the extruder (1) into the lubrication cooling mold (3). Then, extrusion molding can be performed from here. Further, the molding temperature can be reduced depending on the degree of decrease in the melt viscosity.

Since the lubricating cooling mold (2) is kept at a low temperature by the temperature control device, the lubricating cooling mold (2)
The molten resin guided to (3) is rapidly cooled in the mold, and the non-reactive gas dissolved in the molten resin does not volatilize and expand in the mold. Furthermore, the quenching of the molten resin in the mold (2) increases the melt viscosity and decreases the fluidity, but the lubricant is supplied to the mold (2), and this lubricant reduces the fluidity. A laminar flow is generated between the melted resin and the inner wall surface of the mold (2), thereby reducing wall resistance and enabling smooth extrusion.

Accordingly, the extruded molded body (5) has no foaming and has a smooth surface conforming to the shape of the mold (2).

In addition, although the non-reactive gas is dissolved in the obtained molded body, the non-reactive gas spontaneously escapes from the resin. A solvent recovery step is not required, productivity is high, and downsizing of equipment and reduction of manufacturing cost are possible.

[0047]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 As an ultrahigh-viscosity resin, an ultrahigh molecular weight polyethylene resin, HIZEX Million 240M (manufactured by Mitsui Petrochemical Co.
The weight-average molecular weight of 2.3 million and the melting point of 136 ° C.) were supplied to a single screw extruder (1) (screw diameter: 40 mm, L / D = 30) from a pressure hopper (2) of a molding apparatus (A) shown in FIG. Carbon dioxide gas is used as the non-reactive gas, and this is supplied to the gas supply port (13).
From the extruder at a pressure of 200 kg / cm ² . At this time, the extruder (1) maintained a high-pressure state of carbon dioxide gas by a high-pressure shaft seal mechanism driven by a screw shaft and a pressure-resistant hopper structure. The resin supplied to the extruder (1) could be sufficiently melt-kneaded under the conditions of an extrusion rate of 2 kg / h, a screw rotation speed of 30 rpm, and a barrel setting temperature of 200 ° C.

Subsequently, the molten resin was introduced into a lubricating cooling mold (3) set at 80 ° C., and polyalkylene glycol was supplied as a lubricant at a rate of 5 cc / min to the mold. The molten resin was cooled and solidified in a mold during extrusion molding to obtain an ultrahigh molecular weight polyethylene rod. In this mold, the lubricant is uniformly applied to the molten resin over the entire periphery of the interface with the molten resin from the reservoir through the porous body on the mold wall.

The obtained ultra high molecular weight polyethylene rod had a diameter of 20 mm, and when its cross section was observed with a microscope, no bubbles or a layer structure were confirmed, and the surface was smooth and uniform.

Example 2 As a resin easily decomposed by heat, RESO which is a polylactic acid resin is used.
Using MER L209 (manufactured by Boehringer Ingelheim, weight average molecular weight: 500,000), the pressure for injecting carbon dioxide into the solid transporting section was set to 150 kg / cm ² , and the barrel setting temperature was set to 1
Molding was performed under the same conditions as in Example 1 except that the temperature was set to 50 ° C., and a polylactic acid rod was obtained.

The obtained polylactic acid rod had a diameter of 10 mm.
Microscopic observation of the cross section revealed no bubbles or layer structure, and the surface was smooth and uniform. Further, when the molecular weight was measured by gel permeation chromatography, no decrease in the molecular weight was observed before and after the extrusion, and it was found that thermal decomposition of the resin did not occur.

[0053]

According to the method of the present invention, the non-reactive gas is dissolved under high pressure in a state where the resin is transformed from a solid phase to a molten phase, so that the resin can be effectively plasticized. Melt extrusion of a high-viscosity resin and low-temperature molding of a resin that easily undergoes thermal decomposition are possible. In addition, since the non-reactive gas naturally escapes from the resin after extrusion, a solvent recovery step such as the conventional method of plasticizing with an organic solvent is not required. In addition, foamed and non-foamed molded articles can be arbitrarily provided depending on the shape of the mold, molding conditions, post-processing, and the like.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a molding apparatus used in Examples 1 and 2 of the present invention.

[Explanation of symbols]

 (A): Molding device (1): Extruder (2): Pressure hopper (3): Lubrication cooling mold (11): Cylinder (12): Screw (13): Gas supply port (14): On-off valve ( 22): On-off valve (15): Gas cylinder (16): Pressurizing pump (31): Lubricant supply port (32): Mold inner surface

Claims (3)

[Claims] 1. A hard-to-mold resin is supplied from a pressure hopper to an extruder to be transformed from a solid phase to a molten phase in the extruder, and the molten resin is introduced into a mold for extrusion molding. A method for producing a thermoplastic resin article, comprising transforming a resin while dissolving a non-reactive gas in a high pressure state. 2. The method for producing a thermoplastic resin article according to claim 1, wherein the molten resin is introduced into a mold while being maintained in a pressurized state. 3. The method for producing a thermoplastic resin article according to claim 1, wherein the non-reactive gas is supplied to a region from the pressure hopper to a solid transport section of the extruder.