KR101815833B1 - An extruder for extruding porous plastics - Google Patents

Abstract

The present invention relates to a foam extruder, and more particularly to a barrel cooling system for an extruder for the production of porous plastic articles, which comprises a porous plastic sheet, a board, a profile and a bead an extruder capable of continuously producing a bead at a high discharge speed and a foam produced therefrom.
The present invention can maximize the melt strength of a melt by uniformly maintaining the temperature of the melt without causing crystallization or solidification due to the supercooling of the melt, and is capable of increasing the cell structure of the foam and improving the foaming rate An extruder can be provided.
Further, the present invention can provide a foam extruder capable of producing a foam of high quality at a high discharge speed by using a complex barrel cooling system in which a water cooling type cooling part and a oil cooling type cooling part are combined.

Description

[0001] An extruder for extruding porous plastics [0002]

The present invention relates to a foam extruder, and more particularly to a barrel cooling system for an extruder for the production of porous plastic articles, which comprises a porous plastic sheet, a board, a profile and a bead an extruder capable of continuously producing a bead at a high discharge speed and a foam produced therefrom.

Porous plastic products are lightweight materials that can reduce manufacturing costs and are widely used in various fields because of their excellent properties such as heat insulation, sound insulation, impact resistance, light reflectivity, and absorbency.

Particularly, porous plastic, which is expanded at a high magnification with a volume of three times or more, is in the spotlight as a high-value-added material that can be used in various applications.

Widely commercialized plastic materials for foaming are polystyrene and polyethylene, and are widely used in impact protective packaging, disposable food containers, insulation, automotive parts and other industrial applications.

The porous plastic product may be manufactured in various forms such as a sheet, a board, a profile, a bead, and the like and may be applied to an application.

Due to the various advantages offered by the porous cell structure, studies on the technology of continuously extruding general plastic or engineering plastic materials to impart porosity have been rapidly increasing in industry.

Particularly, as the demand for energy-saving environmentally friendly vehicles has increased recently, weight reduction of parts using porous plastic has become a very important research and development task.

However, despite the increasing demand and development efforts of porous plastic, which is increasing in various industries, the technology to continuously extrude high quality foamed plastic products is very scarce.

On the other hand, it is essential to maximize the melt strength through cooling of the melt due to the characteristics of the foaming process. For this purpose, it is very important to construct an efficient and precise extruder barrel cooling system.

However, the related research and technical solutions are still at a fundamental stage, because the foamed polystyrene, which has been widely manufactured over a long period of time, can be very easily foamed with a very wide foaming process window, This is because it was not required to be large.

Particularly, in the case of semi-crystalline polymers such as polypropylene, polyethylene terephthalate, polyamide and polylactic acid, since the window of the foaming process is very narrow due to the crystallization behavior, in order to continuously extrude excellent porous foamed products, There are technical limitations with extruders.

Also, there is a technical problem to uniformly cool the melt temperature in order to obtain a small and uniform cell structure even in continuous extrusion foaming process of amorphous polymer.

Korean Patent Publication Nos. 10-2001-0067785, Korean Patent No. 10-0453808 and Korean Patent No. 10-0699202 disclose a foam extruder.

However, in the case of using the extruder disclosed in the above document, crystallization or solidification occurs due to supercooling of the melt in the cooling step, the temperature of the melt can not be kept uniform and the melt strength of the melt can not be maximized, So that a foam having a high foaming ratio can not be obtained.

Korean Patent Publication No. 10-2001-0067785 Korean Patent No. 10-0453808 Korean Patent No. 10-0699202

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art, and it is an object of the present invention to maximize the melt strength of a melt by maintaining the temperature of the melt uniformly without crystallization or solidification due to supercooling of the melt, And to provide a foam extruder capable of uniformly increasing the foaming ratio.

Another object of the present invention is to provide a foam extruder capable of producing a high quality foam at a high discharge speed by using a complex barrel cooling system in which a water cooling type cooling part and a oil cooling type cooling part are combined.

In order to achieve the above object, the present invention provides a process for producing a thermoplastic resin composition, which comprises: a primary extruder into which a composition containing a thermoplastic resin and a foaming agent is charged and melted and kneaded; A secondary extruder for transferring and cooling the molten mixture kneaded in the primary extruder; And a die for discharging the molten material cooled in the secondary extruder to the outside of the extruder for foaming, wherein a cooling part for cooling the molten material is provided on a barrel surface of the secondary extruder, the front end of the cooling part is a water- The cooling-type cooling unit is configured to cool the high-temperature molten material to a target temperature in a short period of time. The lubricating-type cooling unit reaches the target temperature of the molten material cooled to a temperature close to the target temperature, Characterized in that crystallization or solidification due to supercooling does not occur and the temperature of the melt is uniformly maintained to maximize the melt strength of the melt and to make the cell structure of the foam uniform and improve the foaming ratio .

In one embodiment of the present invention, the length of the oil-cooling type cooling part is 5 to 85% of the entire length of the cooling part.

In one embodiment of the present invention, the lubricating and cooling type cooling unit includes a method of installing an aluminum cast jacket including an oil circulation coil, a method of cooling a barrel by winding a groove in a barrel surface and then winding an oil circulation coil in a groove, A method of simultaneously using an aluminum cast jacket including an oil circulating coil and an oil circulating coil wound around a groove on the surface of a barrel, or a method of circulating oil in a space between a surface of a barrel having an unevenness and a housing surrounding the barrel, And the molten material is cooled by a wet liner method.

The present invention also relates to a method for producing a thermoplastic resin composition, which comprises mixing a composition containing a thermoplastic resin and a foaming agent, A cooling unit for transferring and cooling the molten mixture kneaded in the mixing unit; And a die for discharging the molten material cooled in the cooling unit to the outside of the extruder for foaming, wherein cooling means for cooling the molten material is provided on the surface of the cooling unit, the front end of the cooling unit is a water cooling type cooling unit, Cooling type cooling section, wherein the water-cooled type cooling section cools the high temperature molten material to a target temperature in a short period of time, and the lubricating type cooling section reaches the target temperature by cooling the molten material to a temperature close to the target temperature, Characterized in that crystallization or solidification does not occur and the melt temperature of the melt is uniformly maintained to maximize the melt strength of the melt and to make the cell structure of the foam uniform and to improve the foaming ratio.

In an embodiment of the present invention, L / D (L: screw length, D: barrel inner diameter) of the foam extruder is 30 to 60.

In an embodiment of the present invention, the length of the cooling part is 20 to 70% of the length of the screw included in the extruder.

In one embodiment of the present invention, the length of the oil-cooling type cooling part is 5 to 85% of the entire length of the cooling part.

In one embodiment of the present invention, the lubricating and cooling type cooling unit includes a method of installing an aluminum cast jacket including an oil circulation coil, a method of cooling a barrel by winding a groove in a barrel surface and then winding an oil circulation coil in a groove, A method of simultaneously using an aluminum cast jacket including an oil circulating coil and an oil circulating coil wound around a groove on the surface of a barrel, or a method of circulating oil in a space between a surface of a barrel having an unevenness and a housing surrounding the barrel, And the molten material is cooled by a wet liner method.

The present invention also provides a foam produced by the above-mentioned foam extruder, wherein the foam is in the form of sheet, board, bead or profile.

In one embodiment of the present invention, the foam has a closed cell ratio of 70 to 100% and a foaming ratio of 3 to 50 times.

In one embodiment of the present invention, the foam is characterized in that it has an open cell form in which the closed cell ratio of the foam is 0 to 30% and the foaming ratio is 3 to 50 times.

The present invention can maximize the melt strength of a melt by uniformly maintaining the temperature of the melt without causing crystallization or solidification due to the supercooling of the melt, and is capable of increasing the cell structure of the foam and improving the foaming rate An extruder can be provided.

Further, the present invention can provide a foam extruder capable of producing a foam of high quality at a high discharge speed by using a complex barrel cooling system in which a water cooling type cooling part and a oil cooling type cooling part are combined.

In addition, the present invention can provide a foam having a high expansion ratio through a continuous extrusion process of plastic materials which are difficult to foam by conventional extruders.

Further, the present invention can prevent the crystallization or solidification of the melt by the supercooling even in the case of a quasi-crystalline polymer having a narrow process window, thereby providing a high-quality porous plastic.

Figure 1 shows a tandem foam extruder in which two single screw extruders are connected in series.
2 shows a tandem foam extruder in which a twin screw extruder and a single screw extruder are sequentially connected.
Figure 3 shows a foam extruder with a single screw.
Figure 4 shows a foam extruder with twin screws.
Figure 5 shows a foam extruder with a water-cooled cooling system on the barrel surface of the secondary extruder.

Hereinafter, the present invention will be described in detail based on examples. It is to be understood that the terminology, examples and the like used in the present invention are merely illustrative of the present invention in order to more clearly explain the present invention and to facilitate understanding of the ordinary artisan, and should not be construed as being limited thereto.

Technical terms and scientific terms used in the present invention mean what the person skilled in the art would normally understand unless otherwise defined.

The present invention relates to a primary extruder in which a composition comprising a thermoplastic resin and a foaming agent is charged and melted and kneaded; A secondary extruder for transferring and cooling the molten mixture kneaded in the primary extruder; And a die for discharging the molten material cooled in the secondary extruder to the outside of the extruder for foaming (Figs. 1 and 2).

The barrel surface of the secondary extruder is provided with a cooling section for cooling the molten material. The front end of the cooling section is a water cooling type cooling section, and the downstream end of the cooling section is a cooling type cooling section.

Wherein the water cooled type cooling unit is configured to cool the high temperature molten material to a temperature close to the target temperature in a short period of time so that the temperature of the molten material cooled to near the target temperature reaches the target temperature and the crystallization or solidification due to the supercooling of the molten material does not occur And the melt temperature of the melt is kept uniform, thereby maximizing the melt strength of the melt, making the cell structure of the foam uniform, and improving the expansion ratio.

And the length of the oil-cooling type cooling part is 5 to 85% of the entire length of the cooling part.

A method of installing an aluminum cast jacket including an oil circulating coil, a method of cooling a barrel by winding a oil circulating coil inside a groove after making a groove on the surface of the barrel, an aluminum cast jacket including an oil circulating coil And the oil circulation coil wound around the groove of the barrel surface, or a wet liner method of directly cooling the barrel surface by circulating the oil in a space between the surface of the barrel having the concavo-convex shape and the housing surrounding the barrel, Is cooled.

Further, the front end of the cooling section may be a water-cooled cooling section, the cooling section may be a lubricant cooling type cooling section, and the rear end of the cooling section may be a water cooling type cooling section.

By forming the water cooling type cooling part at the rear end of the cooling part, the melt strength can be maximized to make the cell structure of the foam uniform and improve the expansion ratio.

The present invention also relates to a method for producing a thermoplastic resin composition, which comprises mixing a composition containing a thermoplastic resin and a foaming agent, A cooling unit for transferring and cooling the molten mixture kneaded in the mixing unit; And a die for discharging the molten material cooled in the cooling section to the outside of the extruder and foaming the molten material (FIGS. 3 and 4).

A cooling unit for cooling the molten metal is provided on the surface of the cooling unit, the front end of the cooling unit is a water cooling type cooling unit, and the rear end of the cooling unit is a cooling type cooling unit.

Wherein the water cooled type cooling unit is configured to cool the high temperature molten material to a temperature close to the target temperature in a short period of time so that the temperature of the molten material cooled to near the target temperature reaches the target temperature and the crystallization or solidification due to the supercooling of the molten material does not occur And the melt temperature of the melt is kept uniform, thereby maximizing the melt strength of the melt, making the cell structure of the foam uniform, and improving the expansion ratio.

The L / D (L: screw length, D: barrel inner diameter) of the foam extruder is 30 to 60.

The length of the cooling part is 20 to 70% of the length of the screw included in the extruder.

And the length of the oil-cooling type cooling part is 5 to 85% of the entire length of the cooling part.

A method of installing an aluminum cast jacket including an oil circulating coil, a method of cooling a barrel by winding a oil circulating coil inside a groove after making a groove on the surface of the barrel, an aluminum cast jacket including an oil circulating coil And the oil circulation coil wound around the groove of the barrel surface, or a wet liner method of directly cooling the barrel surface by circulating the oil in a space between the surface of the barrel having the concavo-convex shape and the housing surrounding the barrel, Is cooled.

The present invention also relates to a foam produced through the foam extruder.

The foam may be in the form of a sheet, board, bead or profile.

The foam has an independent void ratio of 70 to 100% and a foaming ratio of 3 to 50.

The foam may also be in the form of an open cell having a closed cell ratio of 0 to 30% and a foaming ratio of 3 to 50 times.

A commonly used extruder for the production of foamed plastics at a ratio of 3 times or more has a barrel cooling system at the rear end of the extruder.

The barrel cooling system maximizes the melt strength by cooling the melt in which the foam gas is dissolved, thereby helping the foam cell to form well in the instantaneous volume expansion process that occurs when the melt passes through the extruder die .

In addition, the barrel cooling system may function to uniformly form open cells depending on applications.

On the other hand, conventional extruders use a water-cooled barrel cooling system or a liquid-cooled barrel cooling system.

The water-cooled barrel cooling system is a method of circulating cooling water by injecting a circulating coil into a jacket made of aluminum casting. In this case, the amount of cooling water flowing into the aluminum jacket of each cooling zone is controlled, So that rapid and rapid cooling is possible.

However, even if the extruder barrel is shut off at the moment when the desired set temperature of the extruder barrel is reached, excessive cooling of the barrel may occur due to absorption of the heat of evaporation of the cooling water already remaining inside the aluminum cooling jacket.

At this time, the excessive cooling of the barrel may cause the crystallization or solidification of the melt, and the temperature distribution of the melt may become large, resulting in a significant increase in the melt strength deviation of the melt.

As a result, a heterogeneous foam cell structure is obtained, and the loss of the foam gas during the process of popping the cells becomes very large, so that a product with a high expansion ratio can not be produced.

Even when a porous plastic having open cells other than the open cells is produced, a plastic having a uniform open cell can be produced only by obtaining a melt having a narrow temperature distribution. Therefore, a conventional foam extruder having a water- It has a limit.

On the other hand, the oil-cooled barrel cooling system using oil as a refrigerant has advantages of precisely controlling the oil temperature and injecting and circulating the oil into the aluminum jacket so that the temperature can be controlled very precisely. However, the laminar flow behavior of the oil, The cooling efficiency is lowered, so that the discharge speed of the foamed plastic is lowered and the productivity is remarkably reduced.

The present invention uses a complex barrel cooling system combining a water cooled barrel cooling system and a cooled barrel cooling system to produce a foam.

That is, in the configuration of the cooling system which must be installed at the rear end of the extruder for foaming, a water-cooled cooling jacket is provided at the front end of the cooling system to rapidly cool the molten material, The temperature of the melt to be obtained can be controlled very precisely.

By arranging the two cooling systems at appropriate positions, only the respective merits can be selectively utilized, and a high-quality porous plastic product can be manufactured with high productivity.

Figure 1 shows a tandem foam extruder in which two single screw extruders are connected in series and a composite barrel cooling system is installed in the barrel of the secondary extruder to enable rapid cooling and precise temperature control simultaneously.

Wherein the foam extruder comprises a primary extruder into which a composition containing a thermoplastic resin and a foaming agent is charged and melted and kneaded; A secondary extruder for transferring and cooling the molten mixture kneaded in the primary extruder; And a die for discharging the molten material cooled in the secondary extruder to the outside of the extruder for foaming.

The primary extruder melts the plastic material, kneads it with the foaming gas, and transfers it to the secondary extruder.

The secondary extruder serves to cool the melted material mixed in the primary extruder and cool it.

The present invention uses a complex barrel cooling system in which a water-cooled cooling system is installed at the front end of the secondary extruder and a cooling system is provided at the rear end of the secondary extruder.

In the water-cooled cooling system, there is a method in which an aluminum jacket is wound around a barrel or a groove is formed on the surface of a barrel, and then a cooling water circulating coil is wound inside the groove to cool the barrel. In some cases, Two methods are used at the same time.

In addition, an electric band heater may be installed in the cooling zone for heating prior to plant operation.

There are four types of oil cooling type cooling system. There are four ways of installing the aluminum cast jacket including the oil circulation coil, the method of cooling the barrel by winding the oil circulation coil inside the groove after making the groove on the barrel surface, A wet liner for directly cooling the barrel surface by circulating oil in a space between the aluminum cast jacket including the circulating coil and the oil circulating coil wound around the groove on the surface of the barrel or between the surface of the barrel having the concavo- the melt can be cooled by a wet liner method.

By using a complex barrel cooling system, very high temperature melts can be cooled to near the target temperature at the front end of the secondary extruder in a short time.

The temperature of the circulating oil is injected into the aluminum jacket and the circulating coil at the downstream end of the secondary extruder so that the temperature of the molten material cooled to near the target temperature reaches the target temperature, Crystallization or solidification can be prevented from occurring.

That is, since the barrel temperature is kept constant at the set target temperature value, there is no risk of supercooling of the molten material, the melt temperature of the molten material can be uniformly maintained and the melt strength of the molten material can be maximized, the cell structure of the foamed material can be made uniform, Can be improved.

It is also possible to lower the set temperature of the barrel to a lower temperature which can maximize the melt strength without crystallization or solidification.

The oil-cooled cooling zone of the secondary extruder is preferably 5 to 85% of the total cooling zone, more preferably 20 to 60%. When the oil cooling type cooling zone has an upper limit value range, the melt has a uniform temperature distribution and a high melt strength, and the cell structure of the foam is uniform and the foaming ratio can be maximized.

A melt having a uniform temperature distribution and a high melt strength can form a highly uniform cell structure when subjected to volume expansion through an extruder die and can be processed into a porous plastic product with a foam expansion rate as high as 50 times .

The foam extruder of the present invention can exhibit a very large effect in a high magnification foaming process of a quasi-crystalline polymer such as polyester, polyamide, polyolefin, and engineering plastic having a narrow process window due to crystallization.

The foaming agent may be a chemical foaming agent or a physical foaming agent. The chemical foaming agent may be injected through the hopper together with the plastic raw material, and the physical foaming agent may be injected through the barrel of the primary extruder.

The present invention can control the closed cell ratio and the cell structure as desired while maintaining a high expansion ratio according to the application.

The foams of the present invention may be in sheet, board, bead or profile form.

The foam has an independent void ratio of 70 to 100% and a foaming ratio of 3 to 50.

The foam may also be in the form of an open cell having a closed cell ratio of 0 to 30% and a foaming ratio of 3 to 50 times.

FIG. 2 shows a tandem foam extruder in which a twin screw extruder and a single screw extruder are connected in sequence, and a composite barrel cooling system is installed in the barrel of the second extruder to enable rapid cooling and precise temperature control at the same time.

The primary extruder melts the plastic material, kneads it with the foaming gas, and transfers it to the secondary extruder.

The secondary extruder serves to cool the melted material mixed in the primary extruder and cool it.

Since the primary extruder is a twin screw extruder, the kneading degree of the raw material is increased and the dissolution of the foaming gas occurs in a short time.

Fig. 3 shows a foam extruder having a single screw, and a composite barrel cooling system is installed at the rear end of the extruder to enable rapid cooling and precise temperature control at the same time.

Wherein the foam extruder comprises: a mixing portion into which a composition containing a thermoplastic resin and a foaming agent is charged and melted and kneaded; A cooling unit for transferring and cooling the molten mixture kneaded in the mixing unit; And a die for discharging the molten material cooled in the cooling section to the outside of the extruder and foaming it.

L / D (L: screw length, D: barrel inner diameter) of the extruder is preferably 30 to 60, since kneading and cooling of the raw material must occur simultaneously in one extruder. When the L / D of the extruder has an upper limit value range, the melt has a uniform temperature distribution and a high melt strength, the cell structure of the foam is uniform, and the foaming ratio can be maximized.

The present invention uses a complex barrel cooling system in which a water-cooled cooling system is installed at the front end of the cooling unit and a cooling system is provided at the rear end of the cooling unit.

The length of the cooling part is preferably 20 to 70% of the length of the screw included in the extruder. When the length of the cooling part has an upper limit value range, the molten material has a uniform temperature distribution and a high melt strength, and the cell structure of the produced foam can be uniform and the foaming ratio can be maximized.

Also, the oil-cooled cooling zone of the extruder is preferably 5 to 85%, more preferably 20 to 60% of the entire cooling zone. When the oil cooling type cooling zone has an upper limit value range, the melt has a uniform temperature distribution and a high melt strength, and the cell structure of the foam is uniform and the foaming ratio can be maximized.

A melt having a uniform temperature distribution and a high melt strength can form a highly uniform cell structure when subjected to volume expansion through an extruder die and can be processed into a porous plastic product with a foam expansion rate as high as 50 times .

The foam extruder of the present invention can exhibit a very large effect in a high magnification foaming process of a quasi-crystalline polymer such as polyester, polyamide, polyolefin, and engineering plastic having a narrow process window due to crystallization.

The foaming agent may be a chemical foaming agent or a physical foaming agent. The chemical foaming agent may be injected through the hopper together with the plastic raw material, and the physical foaming agent may be injected through the barrel of the extruder.

The present invention can control the closed cell ratio and the cell structure as desired while maintaining a high expansion ratio according to the application.

The foams of the present invention may be in sheet, board, bead or profile form.

The foam has an independent void ratio of 70 to 100% and a foaming ratio of 3 to 50.

The foam may also be in the form of an open cell having a closed cell ratio of 0 to 30% and a foaming ratio of 3 to 50 times.

Fig. 4 shows a foam extruder having a twin screw, and a composite barrel cooling system is installed at the rear end of the extruder, enabling rapid cooling and precise temperature control at the same time.

Since the extruder has a twin screw, the kneading degree of the raw material is increased and the dissolution of the foaming gas occurs in a short time.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. The following examples are intended to illustrate the practice of the present invention and are not intended to limit the scope of the present invention.

(Example 1)

A semi-crystalline polylactic acid resin composition and a physical foaming agent were injected into a tandem foam extruder to continuously produce a single-layer foam sheet.

The tandem foam extruder has a structure in which a single screw extruder (primary extruder, L / D = 32) with a screw diameter of 100 mm and a single screw extruder (secondary extruder, L / D = 32) with a screw diameter of 130 mm are connected in series.

Liquid butane is injected into the middle of the barrel of the primary extruder and kneaded with the melted resin.

A complex barrel cooling system was used in which a water-cooled aluminum jacket was installed in the front 60% of the extruder of the second extruder and a oil-cooled aluminum jacket was installed in the rear 40% area to control the oil temperature to 140 ° C accurately.

To 100 parts by weight of the polylactic acid resin, 1 part by weight of talc, which is a foaming nucleus, was mixed in a mixer and then charged into a primary extruder.

At this time, 5 parts by weight of butane was fed into the primary extruder and kneaded, and the kneaded melt was transferred to a secondary extruder and cooled to prepare a foam sheet having a thickness of 4 mm.

Since the crystallization by the supercooling does not occur in the secondary extruder, the set temperature can be operated as low as 140 캜, thereby stably producing the polylactic acid foam sheet having the closed cell ratio of 85 to 90% and the expansion ratio of 18 times Could.

The discharge rate of the foam sheet per hour was as high as 350 kg, and the polylactic acid foam sheet can be used as a meat tray or various types of food packaging containers after an additional thermoforming process.

(Example 2)

A polypropylene resin composition having a high melt strength and azodicarbonamide as a chemical foaming agent were charged into a long single screw extruder to continuously produce a single-layer foam sheet.

The single screw foaming extruder has a screw diameter of 100 mm and an L / D of 54. In the extruder front end (27D length), the mixing, melting and kneading of the raw material takes place and the composite cooling system Respectively.

A water-cooled aluminum jacket is installed in a front region 14D of the cooling system and a lubricating cooling system of a wet liner type is installed in the rear region 13D to accurately control the temperature of the oil to 155 DEG C, And circulated.

0.7 parts by weight of talc as a foaming nucleus and 3 parts by weight of azodicarbonamide as a chemical foaming agent were added to 100 parts by weight of a polypropylene resin and kneaded through a hopper. The kneaded mixture was transferred to a cooling portion and cooled. Was prepared.

Since the crystallization due to the supercooling does not occur at the rear end of the extruder, the set temperature can be operated as low as 155 캜, thereby making it possible to stably produce a foam sheet having a closed cell ratio of 70 to 80% and a foaming magnification of 5 times there was.

The discharge rate per hour of the foam sheet was as high as 300 kg, and the polypropylene foam sheet can be used as a meat tray or various types of food packaging containers after an additional thermoforming process.

(Example 3)

A semi-crystalline polylactic acid resin composition and butane, a physical foaming agent, were injected into a tandem foam extruder to continuously produce a single-layer foam sheet.

The tandem foam extruder has a structure in which a single screw extruder (primary extruder, L / D = 32) with a screw diameter of 100 mm and a single screw extruder (secondary extruder, L / D = 32) with a screw diameter of 130 mm are connected in series.

Carbon dioxide is injected in the middle of the barrel of the primary extruder and kneaded with the melted resin.

A combined barrel cooling system was used in which a water-cooled aluminum jacket was installed in the front 55% of the extruder of the second extruder and a oil-cooled aluminum jacket was installed in the rear 45% area to precisely control the oil temperature to 140 ° C.

1 part by weight of talc, which is a foaming nucleus, and 20 parts by weight of an open cell forming additive were mixed in a mixer with respect to 100 parts by weight of the polylactic acid resin, and then the mixture was introduced into a first extruder.

At this time, 8 parts by weight of carbon dioxide was fed into the primary extruder, kneaded, and the kneaded melt was transferred to a secondary extruder and cooled to prepare an open cell foam sheet having a thickness of 5 mm.

Since the crystallization by the supercooling does not occur in the secondary extruder, the polylactic acid open cell foam sheet having a closed cell ratio of 1 to 10% and a foaming magnification of 20 times can be stably operated . ≪ / RTI >

The discharge rate per hour of the foam sheet was as high as 330 kg, and the polylactic acid open cell foam sheet can be used as a scaffold material which is a medical artificial biomaterial.

(Comparative Example 1)

A polylactic acid foam sheet was prepared in the same manner as in Example 1 except that a water-cooled aluminum jacket was provided in the entire area of the barrel of the secondary extruder (FIG. 5).

The foamed sheet was crystallized by a supercooling in a secondary extruder, and thus had a closed cell ratio of 55% and a foaming magnification of 3 times.

10: Primary extruder 20: Secondary extruder
21: water-cooled cooling water 22:
30: die 40: foam
50: extruder 60: foaming agent

Claims (10)

A primary extruder into which a composition containing a thermoplastic resin and a foaming agent is charged and melted and kneaded;
A secondary extruder for transferring and cooling the molten mixture kneaded in the primary extruder; And
And a die for discharging the molten material cooled in the secondary extruder to the outside of the extruder for foaming,
A cooling section for cooling the molten material is provided on the barrel surface of the secondary extruder,
Wherein the front end of the cooling section is a water-cooled cooling section, and the rear end of the cooling section is a cooling-
Wherein the water-cooled cooling section cools the hot melt to a temperature close to the target temperature in a short time,
The cooling and cooling type cooling unit reaches the target temperature by cooling the molten material to the target temperature so as not to cause crystallization or solidification due to the supercooling degree of the molten material and to maintain the temperature of the molten material uniformly to maximize the melting strength of the molten material , The cell structure of the foam is made uniform, the foaming ratio is improved,
Characterized in that the cooling section is capable of lowering the temperature of the melt to a temperature at which the melt strength can be maximized without crystallization or solidification taking place,
Wherein the length of the oil-cooling type cooling part is 5 to 85% of the entire length of the cooling part.
A mixing portion to which a composition containing a thermoplastic resin and a foaming agent is added and melted and kneaded;
A cooling unit for transferring and cooling the molten mixture kneaded in the mixing unit; And
And a die for discharging the molten material cooled in the cooling section to the outside of the extruder for foaming,
A cooling means for cooling the molten metal is provided on the surface of the cooling section,
Wherein the front end of the cooling section is a water-cooled cooling section, and the rear end of the cooling section is a cooling-
Wherein the water-cooled cooling section cools the hot melt to a temperature close to the target temperature in a short time,
The cooling and cooling type cooling unit reaches the target temperature by cooling the molten material to the target temperature so as not to cause crystallization or solidification due to the supercooling degree of the molten material and to maintain the temperature of the molten material uniformly to maximize the melting strength of the molten material , The cell structure of the foam is made uniform, the foaming ratio is improved,
Characterized in that the cooling section is capable of lowering the temperature of the melt to a temperature at which the melt strength can be maximized without crystallization or solidification taking place,
Wherein the length of the oil-cooling type cooling part is 5 to 85% of the entire length of the cooling part.
delete 3. The method of claim 2,
Wherein L / D (L: screw length, D: inner diameter of barrel) of said foam extruder is 30 to 60.
3. The method of claim 2,
Wherein the length of the cooling part is 20 to 70% of the length of the screw included in the extruder.
delete 3. The method according to claim 1 or 2,
A method of installing an aluminum cast jacket including an oil circulating coil, a method of cooling a barrel by winding a oil circulating coil inside a groove after making a groove on the surface of the barrel, an aluminum cast jacket including an oil circulating coil And the oil circulation coil wound around the groove of the barrel surface, or a wet liner method of directly cooling the barrel surface by circulating the oil in a space between the surface of the barrel having the concavo-convex shape and the housing surrounding the barrel, Is cooled.
delete delete delete

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