KR102121622B1 - An extruder for polypropylene foam sheet - Google Patents

Abstract

The present invention relates to a processing equipment for foaming a thermoplastic polymer polypropylene (polypropylene) resin in a sheet form, that is, a foam sheet extruder, specifically, a foam sheet generated in a process of extrusion foaming a polypropylene resin having a low melt strength. It relates to an extruder for the production of polypropylene foam sheet that can solve problems such as thickness non-uniformity, rupture occurrence, strength reduction, surface characteristics degradation, open cell mass production.

Description

Polypropylene foam sheet extruder {An extruder for polypropylene foam sheet}

The present invention relates to a processing equipment for foaming a thermoplastic polymer polypropylene (polypropylene) resin in a sheet form, that is, a foam sheet extruder, specifically, a foam sheet generated in a process of extrusion foaming a polypropylene resin having a low melt strength. It relates to an extruder for the production of polypropylene foam sheet that can solve problems such as thickness non-uniformity, rupture occurrence, strength reduction, surface characteristics degradation, open cell mass production.

Styrofoam, a typical disposable food container widely used in the world, is produced by thermoforming a foam sheet formed by extruding and foaming polystyrene resin.

Since the polystyrene resin is non-crystalline, the process window of foam extrusion is wide, a high foaming magnification of about 20 times can be obtained, and the melt strength of the resin is high, so that the process of extrusion foaming in a sheet form is very easy.

However, unlike the amorphous resin, most of the crystalline resins have a low melt strength, and the window of the foaming process is narrow, so the process of extruding in the form of a foam sheet is very difficult, and it is known that it is extremely difficult to obtain a high foaming ratio. .

In particular, polypropylene, which is a typical general-purpose crystalline resin, is unable to produce a normal foam sheet in a conventional polystyrene foam extruder.

Polypropylene resin has been tried to foam and use it as a food container because of its harmlessness and eco-friendliness, but it is extremely rare to succeed in commercialization due to the difficulty of the foam sheet manufacturing process.

In this connection, Korean Patent Publication No. 10-2010-0024814 foams polypropylene using a foaming agent to produce a sheet-like foam sheet to be used for automobile interior materials. The method is disclosed.

However, the above technology cannot produce a foam sheet of uniform thickness due to tearing or sagging of the foam sheet in the extrusion process, and the foaming rate is low and the strength is reduced.

Korean Patent Publication No. 10-2010-0024814

The present invention is to solve the problems of the prior art, the low melt strength and the foam extrusion process window is narrow, so it is very difficult to produce a high-quality foam sheet extrusion polypropylene resin foam can be extruded into a foam sheet of high foaming rate The purpose is to provide a sheet extruder.

In addition, the present invention provides a foam sheet extruder capable of maintaining a uniform thickness in both the length and width directions without tearing or sagging of the foam sheet by placing the die and mandrel perpendicular to the extruder so that the foam sheet is discharged in the gravity direction. It aims to do.

In addition, the present invention is by immersing the cylindrical mandrel in the cooling water in the cooling water chamber, the foam sheet is rapidly cooled while passing through the mandrel and the cooling water to form an independent cell inside the foam sheet, and the size of the formed foam cell is uniform and An object of the present invention is to provide a foam sheet extruder having improved strength.

In order to achieve the above object, the present invention is a primary extruder in which a composition comprising a polypropylene resin, a nucleating agent and a blowing agent is introduced and melted and kneaded; A secondary extruder that receives and cools the melted mixture kneaded in the primary extruder; A die which is melted and cooled in the secondary extruder and discharged in the form of a tube to the outside of the extruder to foam, and is disposed perpendicular to the longitudinal direction of the secondary extruder; And a cylindrical mandrel which is installed parallel to the die under the die and stretched while the foamed sheet discharged in the form of a tube is cooled, and the cylindrical mandrel is immersed in cooling water in a cooling water chamber, and the length of the secondary extruder. It is possible to maintain a uniform thickness without tearing or sagging the foam sheet by a die and a mandrel arranged perpendicular to the direction, and the foam sheet is rapidly cooled while passing through the mandrel and the coolant, so that the size of the foam cell inside the foam sheet is uniform. And it provides a foam sheet extruder characterized in that the strength of the foam sheet is improved.

In one embodiment of the invention, the ratio of the die lip diameter and the mandrel diameter is characterized in that 1:1.5 ~ 4.5.

In one embodiment of the present invention, it is characterized in that it further comprises a static mixer between the secondary extruder and the die.

In one embodiment of the present invention, the foam sheet is characterized in that the thickness variation in the width direction is 10% or less.

In one embodiment of the present invention, the foam sheet is characterized in that the independent bubble rate is 60% or more.

The present invention can provide a foam sheet extruder capable of extruding a polypropylene resin, which is very difficult to extrusion-produce a high-quality foam sheet due to low melt strength and a narrow foam extrusion process window, into a foam sheet having a high foaming rate.

In addition, the present invention by placing the die and the mandrel perpendicular to the extruder so that the foam sheet is discharged to free fall in the direction of gravity, the foam sheet can maintain a uniform thickness in both the longitudinal and width directions without tearing or sagging. Extruders can be provided.

In addition, the present invention is by immersing the cylindrical mandrel in the cooling water in the cooling water chamber, the foam sheet is rapidly cooled while passing through the mandrel and the cooling water to form an independent cell inside the foam sheet, and the size of the formed foam cell is uniform and It is possible to provide a foam sheet extruder having improved strength.

In addition, according to the present invention, by placing the die and the mandrel perpendicular to the extruder, the foam sheet is discharged in the gravity direction, so that the foam sheet can maintain a uniform thickness in both the length and width directions without tearing or sagging. Since the polypropylene resin can be used in a high content, the manufacturing cost of the foam sheet can be reduced.

In general, in order to manufacture a polypropylene foam sheet, in order to prevent the sagging phenomenon of the foam sheet generated in the extrusion process is used by adding a high solid content high strength melt strength polypropylene, in the extruder of the present invention, Since the sagging phenomenon is minimized, a general polypropylene can be used in a high content, so that the manufacturing cost of the foam sheet can be reduced.

In addition, since the cooling efficiency of the foamed sheet is very high by using a water-cooled cooling process in which the mandrel is immersed in the cooling water as the cooling process of the foamed sheet, it is possible to increase the discharge rate per unit time and obtain high productivity. .

In addition, the polypropylene foam sheet of the present invention is an eco-friendly material that is harmless to the human body, and uses a method such as thermoforming or a paper cup assembly method to disposable food packaging containers, coffee/beverage containers, instant food containers capable of heating microwave ovens, cup ramen It can be used for containers, automobile head liners, trunk liners, dashboards, automobile air ducts, and the like.

1 shows a conventional horizontally arranged foam sheet extruder.
Figure 2 shows the vertically arranged foam sheet extruder of the present invention.

Hereinafter, the present invention will be described in detail based on examples. The terms, examples, and the like used in the present invention are merely exemplified in order to explain the present invention in more detail and help a person skilled in the art understand, and the scope of the present invention should not be interpreted as being limited thereto.

Technical terms and scientific terms used in the present invention, unless otherwise defined, refer to meanings commonly understood by those skilled in the art to which this invention belongs.

The present invention relates to an extruder for producing a foam sheet of polypropylene resin, which is a general-purpose plastic that is not harmful to the human body, is environmentally friendly, and is safe to heat in a microwave oven.

Styrofoam foamed food containers, which are widely used around the world, cannot be used as microwave heating containers due to the risk of elution of styrene monomer, a carcinogen.

Polypropylene foam containers have been considered as a viable alternative to overcome the limitations of these Styrofoam foam containers, but the inherent rheological properties of polypropylene resins are not suitable for the foam extrusion process, and the foam sheet manufacturing process is very demanding and equipment It is a situation that requires a lot of improvement.

The present invention aims to propose an optimized new facility structure capable of extruding a high-quality polypropylene foam sheet.

The present invention is a primary extruder in which a composition comprising a polypropylene resin, a nucleating agent and a blowing agent is introduced and melted and kneaded; A secondary extruder that receives and cools the melted mixture kneaded in the primary extruder; A die which is melted and cooled in the secondary extruder and discharged in the form of a tube to the outside of the extruder to foam, and is disposed perpendicular to the longitudinal direction of the secondary extruder; And it is installed in parallel to the die below the die and relates to a polypropylene foam sheet extruder comprising a cylindrical mandrel stretched while the foam sheet discharged in the form of a tube is cooled (FIG. 2).

The structure of the conventional extruder for foam sheet production is as shown in FIG. 1, the primary extruder 10 and the secondary extruder 11 are used in tandem extruder (tandem extruder) connected in series, foamed at the end of the secondary extruder 11 The circular die 14 through which the sheet 16 is discharged and the cylindrical mandrel 15 are arranged horizontally.

As shown in FIG. 1, in the conventional foam extrusion sheet manufacturing apparatus, the die 14 through which the sheet is discharged and the mandrel 15 for cooling are arranged horizontally, and cooling of the sheet in the mandrel is air-cooled using compressed air. It is done in a way.

The foam sheet 16 discharged from the circular die moves horizontally and wraps around a cylindrical mandrel to cool and pass. The high-temperature foam sheet discharged from the die is cooled while being in contact with the mandrel surface through which cooling water is circulated, and is also air-cooled by external compressed air.

At this time, the foam sheet can withstand the tensile force pulled from the winder by increasing the strength while cooling. If the cooling in the mandrel is insufficient, the sheet may be torn, sagging, or stretched by the winder tension. In the case of polystyrene, the glass transition temperature is as high as 105°C, so that the strength can be sufficiently improved by cooling. However, in the case of polypropylene resin, since the glass transition temperature is around 0°C, much higher efficiency of cooling is required.

In the case of an amorphous resin including a polystyrene resin having a high melt strength and excellent foaming characteristics, a high-quality foam sheet can be easily produced through the equipment configuration and arrangement of the foam extruder as shown in FIG. 1.

In particular, since the polystyrene resin has a glass transition temperature of about 105° C., the foam sheet discharged from the circular die through the extruder is cooled while passing through a mandrel and falls below the glass transition temperature. At this time, the cooled foam sheet has high strength and there is no problem in withstanding the tension pulled from the winder.

However, when the polypropylene foam sheet is manufactured using the extruder of FIG. 1, the glass transition temperature of the polypropylene resin is 0° C. or less, and thus, despite the crystallization during cooling, the produced foam sheet is not sufficiently cooled, so that the winder is insufficient. It does not have enough strength to withstand tension.

In addition, by discharging the foam sheet by placing the die and mandrel horizontally with the extruder, the foam sheet is torn, stretched or sagged by gravity due to the low strength of the foam sheet, resulting in variations in thickness in both the length and width directions. Occurs and the quality of the polypropylene foam sheet deteriorates.

On the other hand, as the foam sheet is discharged from the die, a foam cell is formed and the formed foam cell grows. At this time, the grown foam cell is cooled and stops growing to form an independent cell of uniform size, resulting in low surface roughness and excellent surface quality. Foam sheets can be produced.

However, when the polypropylene foam sheet is manufactured using the extruder of FIG. 1, the cooling is not sufficiently performed due to air-cooling, so that the sheet surface is rough, the thickness uniformity of the sheet is poor, and the surface quality of the foam sheet is poor.

That is, as the cooling is delayed, the formed foam cell bursts to form an open cell, thereby lowering the strength of the foam sheet, lowering the surface roughness, and poor appearance quality.

The present invention is a composition comprising a polypropylene resin, a nucleating agent and a blowing agent is injected and melted and kneaded primary extruder 10; A secondary extruder 11 for receiving and cooling the melted mixture kneaded in the primary extruder 10; A die 14 discharged from the secondary extruder 11 in the form of a tube and discharged to the outside of the extruder to be foamed, and disposed vertically to the longitudinal direction of the secondary extruder 11; And a cylindrical mandrel (15) which is installed parallel to the die (14) under the die (14) and stretched while the foamed sheet (16) discharged in the form of a tube is cooled. will be.

2, the die 14 and the mandrel 15 are arranged in a vertical form suitable for foam extrusion of a polypropylene resin having low melt strength and rapid cooling, rather than a conventional horizontal arrangement. Then, by submerging the mandrel (15) in the cooling water (18) in the cooling water chamber (17), the foam sheet (16) passes through the mandrel (15) and the cooling water (18) by using water-cooled cooling. High quality polypropylene foam sheet can be produced.

The primary extruder 10 is introduced and mixed with a composition comprising a polypropylene resin, a nucleating agent and a blowing agent.

The secondary extruder 11 cools the kneaded resin melt to maximize the melt strength of the melt to the level required for foaming properties.

In the present invention, the die 14 is bent in the vertical direction with respect to the longitudinal direction of the secondary extruder 11 to induce the ejection of the foam sheet in a downward direction, and the cylindrical mandrel 15 is set vertically, not horizontally, in a downward ejection die. The resulting foam sheet is cooled. At this time, the mandrel 15 and the foam sheet 16 are immersed in the cooling water 18 in the cooling water chamber 17 to induce rapid cooling of the foam sheet.

That is, the die 14 and the mandrel 15 are vertically disposed, and a polypropylene foam sheet can be manufactured using water-cooled cooling that immerses the mandrel in cooling water.

By setting the positions of the primary and secondary extruders of the foam extruder high, and disposing the sheets horizontally, rather than horizontally, in the die for foaming, the entire circular sheet is uniform without counteracting gravity. Place the extruder under the influence of one gravity.

In addition, in order to solve the low cooling efficiency of the existing air-cooled cooling device, a water-cooled cooling method of rapidly cooling the polypropylene foam sheet by submerging the cylindrical mandrel in the cooling water 18 in the cooling water chamber 17 is used.

That is, the present invention is a new foam extruding device capable of stably foaming a polypropylene resin, which is very difficult to extrude, and consists of a die 14 and a mandrel 15 in a vertical arrangement rather than a conventional horizontal arrangement. And, it is a technical feature that the air-cooled cooling method with low cooling efficiency is improved to water-cooled cooling with high cooling efficiency.

By forming the die 14 and the mandrel 15 in a vertical arrangement with respect to the longitudinal direction of the secondary extruder, when the polypropylene resin having low melt strength is discharged from the die, the foam sheet is lowered downward, so that the foam sheet The direction of travel and the direction of gravity coincide. Therefore, the entire circular foam sheet is affected by the same gravity, so that no sagging occurs in any direction and the entire tensile force is applied. Due to this, the thickness variation in the width direction and the length direction of the foam sheet is reduced without tearing or sagging of the foam sheet, thereby significantly improving the thickness uniformity of the entire foam sheet.

In addition, by using a water-cooled cooling in which the mandrel 15 is immersed vertically in the cooling water 18 in the cooling water chamber 17, the foam sheet 16 is rapidly cooled while passing through the mandrel 15 and the cooling water 18, The polypropylene foam sheet can be rapidly cooled to show high strength.

At this time, as the foam sheet is discharged from the die, a foam cell is formed, and the formed foam cell gradually grows, while the foam cell growing through rapid cooling of the foam sheet while stabilizing the mandrel 15 and the cooling water 18 is stabilized. Can be.

That is, as the polypropylene foam sheet is discharged from the die, a foam cell is formed and the formed foam cell is grown. At this time, the grown foam cell is rapidly cooled by water-cooled cooling to stop growth, so that an independent cell of uniform size is obtained. Formed, it is possible to manufacture a foam sheet having a low surface roughness and excellent surface quality.

When the polypropylene foam sheet is manufactured using the extruder of FIG. 2, the cooling of the sheet is rapid due to water-cooled cooling to maintain an independent cell having a uniform size, the surface roughness of the sheet is low, and the thickness uniformity of the sheet It improves and the strength of the sheet increases.

At this time, the thickness of the foam sheet in the longitudinal and width directions is preferably 10% or less, more preferably 5% or less.

The composition comprising a polypropylene resin, a nucleating agent, a pigment imparting color, and the like is dry kneaded and injected into the raw material supply hopper 12 of the primary extruder.

As the polypropylene resin, general polypropylene resin, high melt strength polypropylene resin, and the like can be used without limitation.

Since the polypropylene resin has a low melt strength, it is easily ejected from the extruder die and stretched to a cylindrical mandrel where cooling is performed, so that the sheet is liable to tear during unfolding. In addition, even if the sheet is not torn, since the sheet sags due to gravity, thickness variations in the width direction and the length direction of the sheet may occur, thereby deteriorating the quality of the sheet.

To solve this problem, a polypropylene resin having high melt strength and high melt strength may be used.

The high melt strength polypropylene resin is a general polypropylene resin modified to improve melt strength, and has improved foaming properties, but has a higher cost than the general polypropylene resin.

The present invention can be used by mixing a general polypropylene resin and a high-melting strength polypropylene resin, wherein the content of the general polypropylene resin is preferably 30 to 70% by weight, more preferably 50 to 70% by weight is used good. Within the above numerical range, the thickness uniformity and the sheet quality of the foam sheet can be maximized.

In general, it is advantageous to lower the cost by increasing the content of the general polypropylene resin mixed with the high melt strength polypropylene resin, but when the general polypropylene resin is used at a high content, the melt strength is lowered and the foaming process and foaming characteristics are lowered. , When using the extruder of Figure 1, it is inevitable to lower the addition ratio of the general polypropylene resin to 10 to 20% by weight.

However, the present invention allows the foam sheet to be discharged in the direction of gravity by placing the die and the mandrel perpendicular to the extruder, so that the foam sheet can maintain a uniform thickness in both the length and width directions without tearing or sagging, so the unit cost is low. Since the polypropylene resin can be used in a high content (30 to 70% by weight), the manufacturing cost of the foam sheet can be reduced.

In general, in order to manufacture a polypropylene foam sheet, in order to prevent the sagging phenomenon of the foam sheet generated in the extrusion process, high-melting-strength polypropylene having a high unit price is added and used in a high content (80% by weight or more). In the extruder of, since the sagging phenomenon of the foam sheet is minimized, the general polypropylene can be used in a high content, thereby reducing the manufacturing cost of the foam sheet.

The nucleating agent usually uses talc, and the talc is preferably 0.5 to 3 parts by weight based on 100 parts by weight of the polypropylene resin. Within the above numerical range, the thickness uniformity and the sheet quality of the foam sheet can be maximized.

The blowing agent injection hole 13 is located in the middle of the cylinder of the primary extruder, and the blowing agent is introduced into the extruder through the injection hole.

Foaming agents that can be used for foaming of polypropylene resin include carbon dioxide, nitrogen, butane, pentane, propane, chlorodifluoromethane, chlorodifluoroethane, difluoroethane, tetrafluoroethane, ethanol, dimethyl ether, etc. There is, it can be used by selecting one of them or by mixing two or more blowing agents.

The content of the foaming agent is preferably 1 to 10 parts by weight based on 100 parts by weight of the polypropylene resin. Within the above numerical range, the thickness uniformity and the sheet quality of the foam sheet can be maximized.

The raw materials are injected into a primary extruder and uniformly kneaded, and in particular, the blowing agent is dissolved in a resin melt in an environment of high temperature and pressure. In the secondary extruder connected to the primary extruder, the resin melt is cooled.

In the secondary extruder, the melt strength of the resin melt can be maximized through cooling, and the improved melt strength is necessary to form an independent bubble structure without bursting the foam cells, and is a very important factor to lower the density of the foam sheet.

The structure of the screw used in the secondary extruder maximizes cooling efficiency, minimizes heat generation of the resin melt, and requires a special design to obtain a uniform temperature. In particular, in the case of plastics having a high crystallization rate such as polypropylene resin, the structural design of the secondary extruder screw is more important.

The resin melt cooled in the secondary extruder is discharged through a circular die to reduce the wrinkle problem. At this time, the blowing agent dissolved in the resin melt is phase-separated due to thermodynamic instability, i.e., reduced solubility through pressure reduction, to form a foam cell. do. At this time, a small number of foam cells are generated due to the nucleating agent present in the melt, and the foam cells are grown through diffusion of the foam gas.

The temperature of the polypropylene foam sheet discharged from the die is preferably 140 to 170°C.

Also, the ratio of the die lip diameter and the mandrel diameter is preferably 1:1.5 to 4.5, and more preferably 1:2.5 to 4.5. Within the above numerical range, the thickness uniformity and the sheet quality of the foam sheet can be maximized.

In the conventional horizontal die and mandrel arrangement structure as shown in FIG. 1, the thickness of the foam sheet is easily circumferential due to the problem of sagging due to gravity, and the work itself on the mandrel by stretching the sheet is also easy. no. For this reason, the ratio of the die lip diameter and the mandrel diameter through which the sheet is discharged must be lowered to a level of 1:1 to 2.5, thereby deteriorating the quality of the foam sheet.

In the present invention, as shown in FIG. 2, the sheet discharged die is placed downwardly, and the circular mandrel is also disposed vertically accordingly, so that the tube-shaped foamed sheet discharged downward has the effect of uniform gravity in the circumferential direction. To receive. By doing so, it is possible to obtain a uniform sheet thickness and a foam cell structure without sagging the foam sheet in the circumferential direction.

In addition, despite the low melt strength, the foam sheet is naturally stretched without tearing or sagging, making the process of passing through the cylindrical mandrel body easier.

In addition, the present invention may also be provided with a static mixer (static mixer) between the secondary extruder and the die to improve the kneading degree of the melt.

By arranging the cylindrical mandrel to be immersed in the cooling water in the cooling water chamber, the polypropylene foam sheet is rapidly cooled to improve strength and quality.

At this time, the cylindrical mandrel is preferably arranged so that 50 to 90% of the body length is immersed in the cooling water in the cooling water chamber, and more preferably, 60 to 80% of the body length is immersed in the cooling water. Within the above numerical range, the thickness uniformity and the sheet quality of the foam sheet can be maximized.

In addition, the temperature of the cooling water contained in the cooling water chamber is preferably 30 to 70°C, more preferably 40 to 60°C. Within the above numerical range, thickness uniformity and sheet quality of the foam sheet may be maximized.

At this time, as the foam sheet is discharged from the die, a foam cell is formed, and the formed foam cell gradually grows, while the foam cell growing through rapid cooling of the foam sheet while stabilizing the mandrel 15 and the cooling water 18 is stabilized. Can be.

That is, as the polypropylene foam sheet is discharged from the die, a foam cell is formed and the formed foam cell is grown. At this time, the grown foam cell is rapidly cooled by water-cooled cooling to stop growth, so that an independent cell of uniform size is obtained. Formed, it is possible to manufacture a foam sheet having a low surface roughness and excellent surface quality.

When the polypropylene foam sheet is manufactured using the extruder of FIG. 2, the cooling of the sheet is rapid due to water-cooled cooling to maintain an independent cell having a uniform size, the surface roughness of the sheet is low, and the thickness uniformity of the sheet It improves and the strength of the sheet increases.

In addition, because of the high cooling efficiency through the water-cooled cooling process, the discharge rate and the production speed can be increased, so that the overall productivity of the foam sheet can be greatly improved.

The thickness of the polypropylene foam sheet produced by the above method is preferably 0.6 to 6 mm, and the density is preferably 20 to 600 kg/m ³ .

In addition, the size of the foam cell of the foam sheet is preferably 50 ~ 500 ㎛, the independent bubble rate is preferably 60% or more, more preferably 70% or more.

Hereinafter, the present invention will be described in detail through examples and comparative examples. The following examples are only exemplified for the practice of the present invention, and the contents of the present invention are not limited by the following examples.

(Example 1)

The polypropylene resin composition and the blowing agent were injected into a tandem foam extruder having the structure of FIG. 2 to continuously produce a single-layer polypropylene foam sheet.

The tandem foam extruder has a structure in which a single screw extruder (primary extruder, L/D=32) having a screw diameter of 100 mm and a single screw extruder (secondary extruder, L/D=32) having a screw diameter of 130 mm are connected in series. Liquid butane is injected into the middle of the barrel of the primary extruder to knead the molten resin.

After the resin melt is gradually cooled in the secondary extruder, the foam sheet is discharged through a top-down circular die. The foam sheet is rapidly cooled as it passes through a cylindrical mandrel, in which 70% of the body is immersed in the coolant in the coolant chamber. At this time, the cooling water contained in the cooling water chamber was controlled to be maintained at a temperature of 50°C.

After mixing 1 part by weight of the nucleating agent talc with respect to 100 parts by weight of the polypropylene resin in a mixer, it was put into a primary extruder. At this time, 3 parts by weight of butane, a blowing agent, was supplied into the primary extruder and kneaded, and the kneaded melt was transferred to a secondary extruder to prepare a foam sheet having a thickness of 4 mm.

The foam sheet discharged from the die to the bottom was rapidly cooled by cooling water by hanging on a cylindrical mandrel to produce a polypropylene foam sheet having a uniform thickness without tearing or sagging. At this time, the ratio of the die lip diameter and the mandrel diameter was maintained at 1:3.

The prepared foam sheet had an independent bubble rate of 85% and a density of 100 kg/m ³ .

(Example 2)

A polypropylene foam sheet was prepared in the same manner as in Example 1, except that 45% of the mandrel body length was immersed in the cooling water in the cooling water chamber.

(Example 3)

A polypropylene foam sheet was prepared in the same manner as in Example 1, except that 95% of the mandrel body length was immersed in the cooling water in the cooling water chamber.

(Example 4)

A polypropylene foam sheet was prepared in the same manner as in Example 1, except that the temperature of the cooling water was maintained at 20°C.

(Example 5)

A polypropylene foam sheet was prepared in the same manner as in Example 1, except that the temperature of the cooling water was maintained at 80°C.

(Comparative Example 1)

A polypropylene foam sheet was prepared in the same manner as in Example 1, except that both the extrusion die and the cylindrical mandrel were placed in the horizontal direction, and the foam sheet was cooled by air cooling.

The prepared foam sheet had an independent bubble rate of 50% and a density of 150 kg/m ³ .

(evaluation)

(1) Thickness uniformity

Deviation in the width direction of the foam sheet prepared in Examples and Comparative Examples was measured.

(2) sheet quality

By checking the appearance of the foam sheet prepared in Examples and Comparative Examples, the degree of tearing or sagging of the sheet and the roughness of the sheet surface were marked as excellent, excellent, normal, or poor.

division Example Comparative example One 2 3 4 5 One Thickness uniformity
(%) 4.8 10.5 9.8 11.4 10.1 18.1 Sheet quality eminence Great usually Great usually Bad

As can be seen in Table 1, Examples 1 to 5 according to the present invention exhibited excellent thickness uniformity and sheet quality, and in particular, Example 1 showed the best characteristics.

On the other hand, in the case of Comparative Example 1, the thickness uniformity and sheet quality were lowered compared to the Examples.

10: primary extruder 11: secondary extruder
12: Raw material supply hopper 13: Foaming agent inlet
14: die 15: mandrel
16: Foam sheet 17: Cooling water chamber
18: coolant

Claims (5)

A primary extruder in which a composition comprising a polypropylene resin, a nucleating agent and a blowing agent is introduced and melted and kneaded;
A secondary extruder that receives and cools the melted mixture kneaded in the primary extruder;
A die discharged in the form of a tube to the outside of the extruder to cool the melt cooled in the secondary extruder, and disposed vertically to the longitudinal direction of the secondary extruder; And
In the foam sheet extruder including a cylindrical mandrel which is installed parallel to the die under the die and discharged in a tube form while being cooled and stretched,
The cylindrical mandrel is immersed in the coolant in the coolant chamber,
It is possible to maintain a uniform thickness without tearing or sagging the foam sheet by a die and a mandrel disposed perpendicular to the longitudinal direction of the secondary extruder,
The foam sheet is quenched while passing through the mandrel and the cooling water, so that the foam cell size inside the foam sheet is uniform, and the strength of the foam sheet is improved.
The ratio of the die lip diameter and the mandrel diameter is 1:1.5 to 4.5,
The cylindrical mandrel is a foam sheet extruder, characterized in that 50 to 90% of the body length is arranged to be immersed in the cooling water of the cooling water chamber.
delete According to claim 1,
Foam sheet extruder, characterized in that it further comprises a static mixer between the secondary extruder and the die.
According to claim 3,
The foam sheet extruder of a foam sheet, characterized in that the thickness variation in the width direction is 10% or less.
The method of claim 4,
The foam sheet is a foam sheet extruder, characterized in that the independent bubble rate is 60% or more.

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