JP2002052596A - Method for preventing mixture of colored foreign matter with molding by extrusion molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing a mixture of a colored foreign matter of a resin carbide or the like in a molding when interrupted extrusion molding is restarted. SOLUTION: The method for preventing the mixture of the colored foreign matter with the molding by extrusion molding comprises the steps of storing a resin composition in a cylinder 11 of an extruder 10 during a period until the interrupted extrusion molding is restarted, and maintaining a temperature of the composition at a temperature higher by 30 to 100 deg.C than a glass transition temperature of the resin. The method also comprises the step of sealing a lip 19 of a die 18 during a period while the extrusion molding is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a resin by extrusion molding, and more particularly, to a method for preventing colored foreign matter from being mixed into a processed product by extrusion molding when restarting interrupted extrusion molding. About.

[0002]

2. Description of the Related Art Polymethyl methacrylate (PMMA)
Molding of thermoplastic resin such as acrylic resin, polyvinyl chloride (PVC) resin, polystyrene (PS) resin, polycarbonate (PC) resin, etc.
A so-called extrusion molding method is widely used in which the resin composition is melted in a cylinder 11 of an extruder (extrusion molding machine) 10 and then forcedly extruded from a die 18 to continuously obtain a processed product ( (See FIG. 1).

The operation of the extruder 10 is generally performed by the extruder 10
It is performed continuously except when performing maintenance inspection and cleaning of the inside of the cylinder 11 or when there is little demand for processed products.
Here, when the operation of the extruder 10 is stopped for the former reason, the resin composition remaining in the cylinder 11 is removed. However, when the operation is temporarily stopped for the latter reason, the resin composition is removed. It is general that the resin composition in the cylinder 11 is left in place without being removed from the viewpoint of the trouble of removing and the work efficiency at the time of restarting operation. In the latter case, the heating of the cylinder 11 is stopped from the viewpoint of cost reduction,
Allowed to cool.

[0004]

However, if the operation of the extruder is temporarily stopped and the cylinder 11 is allowed to cool, then when the operation of the extruder is restarted, black spot foreign matter is generated in the processed product. There was a problem of doing. In particular, with regard to processed products such as PMMA, the generation of black spot foreign matter will impair the excellent transparency and decorativeness inherent in the resin,
This causes the commercial value of the processed product to be significantly reduced.

Accordingly, an object of the present invention is to provide a method for preventing black spot foreign matter from being generated in a processed product when the interrupted extrusion is restarted.

[0006]

Means for Solving the Problems and Effects of the Invention In the study for solving the above problems, the present inventors have found that black spot foreign matter is generated in the processed product after the operation of the extruder is temporarily suspended. , For the following reasons. That is, when the resin composition is allowed to cool without being removed from the cylinder of the extruder, a gap is generated between the cylinder and the resin composition due to a difference in the thermal shrinkage rate between the cylinder and the resin composition, and air is generated in the gap. Get in. As a result, the resin composition is oxidized and decomposed, and furthermore, the oxidized and decomposed resin composition is carbonized by the residual heat of the cylinder and the like, and finally, the carbide of the resin adheres to the inner wall of the cylinder. When the operation of the extruder is resumed with the resin carbide adhered to the inner wall of the cylinder, the carbide is separated from the inner wall and mixed into the molten resin composition. Usually, the discharge port 1 of the cylinder 11
5 is connected to a screen 16 (see FIG. 1), but carbides fined by kneading in the cylinder 11 may pass through the screen 16 and eventually enter the processed product and become small. It becomes black spot foreign matter.

[0007] The inventors of the present invention have continued to study to prevent the generation of resin carbide, and while the operation of the extruder has been stopped, the heating of the cylinder has been continued, and the inside of the cylinder has been heated. If the stored resin composition is kept at a predetermined temperature, the resin composition can be prevented from being thermally contracted during the stoppage of operation, and therefore, the gap between the cylinder and the resin composition can be suppressed. The generation of parts was suppressed, and the idea of preventing the occurrence of resin carbide and the incorporation of colored foreign matter into processed products was obtained, and further studies were repeated.
As a result, when the resin composition in the cylinder is kept at a temperature 30 to 100 ° C. higher than the glass transition temperature of the resin to be extruded, unexpectedly, the generation of carbides and The present inventors have found a new fact that mixing can be effectively prevented, and furthermore, deterioration of the resin due to continuous heating of the resin composition can be prevented, and the present invention has been completed.

That is, in order to solve the above-mentioned problems, the method for preventing colored foreign matter from being mixed into a processed product by extrusion according to the present invention is provided in a cylinder of an extruder until the interrupted extrusion is restarted. The resin composition is stored, and the temperature of the resin composition in at least the molten portion of the cylinder is maintained at a temperature higher by 30 to 100 ° C. than the glass transition temperature of the resin. Generally, the temperature of the resin composition at the time of extrusion molding varies depending on the type of the resin to be molded, but is one point lower than the glass transition temperature of the resin.
Temperatures as high as 30-200 ° C., more typically 150
The temperature is set to about 180 ° C. higher. Therefore, if the resin composition stored in the cylinder is kept at the above-mentioned temperature and kept warm, there is no gap between the cylinder and the resin composition, and therefore the generation of resin carbide and the accompanying No colored foreign matter is mixed into the processed product.
However, the glass transition temperature of the resin is 130 to 20
If the resin composition is kept in the cylinder at a temperature as high as 0 ° C. for a long time, thermal deterioration may occur and yellowing of the resin may be caused. On the other hand, when the resin composition is stored in the cylinder at a temperature lower than about the glass transition temperature of the resin (more specifically, a temperature about 10 to 20 ° C. higher than the glass transition temperature), the shrinkage of the resin composition is reduced. Because it occurs remarkably,
It is unavoidable that a void is formed between the cylinder and the resin composition.

On the other hand, according to the method of the present invention,
The temperature of the resin composition stored in the cylinder is maintained at a temperature 30 to 100 ° C. higher than the glass transition temperature of the resin. This is because when the temperature of the resin composition is kept in the above temperature range, there is a remarkable difference in the volume of the resin composition between the time of actually performing the extrusion molding and the time of keeping the resin composition in the cylinder. This is because it does not occur. Moreover,
Since it is not necessary to raise the temperature of the cylinder to such an extent that the extrusion is actually performed, not only the cost required for heating the cylinder but also the deterioration of the resin due to the heating can be minimized.

In the method of the present invention, the resin to be subjected to extrusion molding includes polymethyl methacrylate. Since polymethyl methacrylate is originally a resin having extremely high transparency, the effect obtained by preventing the contamination of colored foreign matter by the method of the present invention is extremely large.
In the method of the present invention, the die lip of the extruder is preferably sealed while the extrusion is interrupted. By sealing the die lip, it is possible to prevent the resin melt inside the die from coming into contact with air. Therefore, even if the die is continuously mounted on the extruder when the operation of the extruder is stopped, it is possible to suppress the oxidative deterioration of the resin composition remaining in the die and the generation of resin carbide. When a resin carbide is generated on the inner wall of the die, a scaly or massive clear brown to black foreign substance may be mixed into the processed product.

Further, conventionally, in order to prevent carbonization of the resin composition on the inner wall surface of the die, it has been required to remove the die every time the operation of the extruder is stopped. According to the method of the invention, it is possible to save extra labor due to the removal of the die, and the above-described effect can be obtained only by performing a simple treatment of bringing the sealing member into contact with the die lip portion. In addition, when the die is of a vertical type, the resin composition dissipates inside the die when the operation of the extruder is stopped, but if the resin composition adheres slightly to the inner wall surface of the die, the resin is It is easy to carbonize and causes black spot foreign matter to be generated remarkably when the operation is resumed. On the other hand, sealing the die lip prevents the resin composition from dissipating when the operation is stopped, and even if the resin composition shrinks due to the cooling of the cylinder, the die inner wall surface and the resin composition Air can be suppressed from entering between them, and the occurrence of black spot foreign matter can be more reliably prevented.

On the other hand, when the die is of a horizontal type, although the amount of the resin composition dissipated inside the die is small, it is possible to prevent air from entering the inside of the die by sealing the die lip. As in the case (1), the generation of black spot foreign matter can be more reliably prevented.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method of preventing colored foreign matter from mixing into a processed product by extrusion molding according to the present invention will be described in detail. Examples of the resin constituting the resin composition applicable to the method of the present invention include polymethyl methacrylate (PMMA); impact-resistant (meth) acrylic resin containing rubber; methyl acrylate, ethyl acrylate, butyl acrylate as a comonomer; A (meth) acrylic resin such as a (meth) acrylic resin containing styrene or the like can be used. In addition to the (meth) acrylic resin, various conventionally known thermoplastic resins such as a polyvinyl chloride (PVC) resin, a polystyrene (PS) resin, and a polycarbonate (PC) resin are exemplified. Can be

The thermoplastic resin may contain various conventionally known additives such as a cross-linking agent and a reinforcing agent, depending on the use of the extruded sheet and the required properties. The type and amount of the additive may be set according to a conventional method. [Insulating Temperature of Resin Composition] In the method of the present invention, the temperature of the resin composition at the time of temporarily stopping the extrusion (hereinafter, referred to as “insulating temperature of the resin composition”) is at least in the melting portion of the cylinder. The temperature is set to be 30 to 100 ° C. higher than the glass transition temperature Tg of the molten resin. For example, when the resin to be subjected to extrusion molding is PMMA, the glass transition temperature Tg is around 100 ° C., more specifically 85 to 85 ° C., although it depends on the molecular weight of PMMA.
Since the temperature is about 105 ° C., the temperature for keeping the resin composition is determined based on the Tg.

FIG. 1 is a schematic sectional view showing an example of an extruder. Generally, the extruder 10 has a screw 1 inside.
4 includes a cylinder 11, a gear pump 17 for adjusting the discharge amount of the resin melt, a die 18 connected to the discharge port 15 of the cylinder via the gear pump 17, a hopper 20 for supplying the resin composition into the cylinder 11, and the like. ing. The resin composition (usually in the form of pellets) supplied from the hopper 20 is supplied to the discharge port 15 by the driving force of the screw 14.
Side, and is heated by a heater 13 provided on the outer peripheral surface of the cylinder 11. Further, as the resin composition moves from the supply section 11b on the hopper 20 side of the cylinder to the melting section 11a on the discharge port 15 side of the cylinder 11, the resin composition becomes in a molten state.

In the present invention, at least the molten portion 11
It is required that the temperature for keeping the resin composition (a) (the so-called extrusion temperature or outlet temperature) satisfy the above range. Therefore, the cylinder temperature in a region other than the melting portion 11a, such as the supply portion 11b, is not particularly limited. The heat retaining temperature of the resin composition in such a region may be appropriately set within a temperature range that does not cause thermal deterioration. The temperature at which the resin composition is kept warm (° C.)
If the temperature is lower than Tg + 30 (° C.), the resin composition significantly shrinks and a void is formed between the cylinder and the resin composition. Cannot be prevented from being mixed. Conversely, the temperature at which the resin composition is kept warm (° C.) is Tg + 100.
When the temperature exceeds (° C.), although there is little possibility that a void is formed between the cylinder and the resin composition, the resin composition tends to undergo thermal deterioration while the operation of the extruder is stopped, The risk of yellowing of the resin and the like increases.

The temperature for keeping the resin composition (° C.) is preferably Tg + 30 to Tg + 80 (° C.), and more preferably Tg + 40 to Tg + 60 (° C.). Although not particularly limited,
It is more preferable that the heat retaining temperature be lower within the above range from the viewpoint of reducing the cost required for heating the cylinder. [Other application examples of the present invention] The method of the present invention is, for example, as follows.
In the case where a resin laminate is manufactured by extruding separate resin compositions from one cylinder, extrusion from one cylinder is temporarily interrupted to form a single-layer body, and if necessary, two cylinder resins are formed again. The present invention is also applicable to a case where a laminate is formed. That is, for the cylinder on which the extrusion is temporarily suspended, by setting the temperature of the resin composition stored in the cylinder in the above range until the extrusion is restarted, the laminated body after the restart of the operation The incorporation of colored foreign matter can be sufficiently suppressed.

[Sealing of Die Lip] In the method of the present invention, the member for sealing the lip of the die when the extrusion is temporarily stopped is not particularly limited, and the shape of the die lip is not particularly limited. What is necessary is just to design suitably according to the etc. In general, a suitable shape for the sealing member 21 of the die lip portion is, for example, as shown in FIG.
9 is provided with a receiving portion 23 that can close the opening by pressing the resin composition 9 and that can store the resin composition 22 leaked from the die lip portion 19.

[0019]

(Effect of temperature control of resin composition)

Example 1 A general-purpose polymethyl methacrylate (PMMA, trade name “SUMIPEX EX” manufactured by Sumitomo Chemical Co., Ltd., glass transition temperature Tg: 102 ° C.) was melted in a cylinder of a commercially available extruder, and the extruder was operated. After forming the sheet, the temperature of the resin composition in the cylinder fusion zone was raised to 150
C., and kept (warmed) for 24 hours. At the time of keeping the temperature, the die was removed in advance.

After a lapse of 24 hours, the die is attached, and
The temperature of the cylinder was raised to about 250 ° C., and sheets were continuously manufactured by extrusion. From the sheets thus obtained, samples were taken every 10 minutes after the operation of the extruder was restarted. For this sample,
Ten points in a range of 00 × 200 mm were arbitrarily selected, and the occurrence of colored foreign matters in the range was observed with a microscope. Thus, the time required for reducing the generation of the resin carbide and reducing the mixing of the colored foreign matter to a range that does not pose a practical problem was determined.

Comparative Examples 1 and 2 A small extruder for testing was used in place of a commercially available extruder, and the temperature of the resin composition at the melting portion of the cylinder was 260 ° C. (Comparative Example 1) or 50 ° C. (Comparative Example 2). In the same manner as in Example 1, the sheet was formed, the operation was interrupted and the cylinder was kept warm (24 hours), and the sheet was formed after the operation was restarted. Further, the occurrence of colored foreign matter was observed on the obtained sheet.

[Effect of Attaching Cover of Die Lip] Example 2 A general-purpose PMMA (the above-mentioned “SUMIPEX EX”, glass transition temperature Tg: 102 ° C.) was charged into a commercially available extruder to form a sheet. At this time, the temperature of the resin composition in the cylinder melting part was about 250 ° C. Next, the operation of the extruder was temporarily stopped, the temperature of the resin composition in the cylinder melting portion was set to 150 ° C., and a sealing member (cover) was attached to the lip portion of the extruder while the die was attached. After maintaining this state for 24 hours, the temperature of the cylinder was raised again to about 250 ° C., and a sheet was formed by extrusion.

From the sheet thus obtained, 200 × 2
Ten points in a range of 00 mm were arbitrarily selected, and the occurrence of colored foreign matter in the sheet was observed with a microscope. Comparative Example 3 While the operation of the extruder was temporarily stopped, the sheet was formed in the same manner as in Example 2 except that the sealing member was not attached to the lip portion while the die was attached. Was.

In Examples 1 and 2 and Comparative Examples 1 to 3, based on the results obtained by observing the occurrence of colored foreign matter in the formed sheet, the foreign matter was re-started after the extruder was restarted. The amount of time required for the amount of contaminants to be reduced to a level that does not pose a practical problem (the time for disappearance of contaminating foreign substances) was determined. Table 1 shows the results.

[0025]

[Table 1]

As is evident from Table 1, Example 1 in which the temperature for keeping the resin composition in the cylinder melting portion was set higher than the glass transition temperature of the resin in the range of 30 to 100 ° C.,
Further, in Example 2, in which the die lip portion was sealed when the operation of the extruder was interrupted, the time required for reducing the amount of the brown or black foreign matter mixed to such an extent that no practical problem was caused was extremely short. On the other hand, in Comparative Example 1 in which the heat retaining temperature of the resin composition in the cylinder melting portion was too high, yellowing of the resin occurred, and consequently, mainly brownish foreign matter was significantly mixed. Conversely, in Comparative Example 2 in which the temperature of keeping the resin composition in the cylinder fusion zone was too low, the mixing of mainly black foreign substances was remarkable. In Comparative Example 3 in which the lip was not sealed while the die was attached when the operation of the extruder was stopped, mainly brownish foreign matter was conspicuously produced.

In each of the above comparative examples, it took a very long time for the amount of foreign matter to be reduced to such an extent that no practical problem occurred.

[Brief description of the drawings]

FIG. 1 is a front view showing an example of an extruder.

FIG. 2 is a cross-sectional view illustrating an example of a sealing member of a die lip portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Extruder 11 Cylinder 11a Melting part 18 Die 19 Lip part 21 Sealing member

Claims (3)

[Claims] 1. Until the interrupted extrusion is restarted,
Extrusion, wherein the resin composition is stored in a cylinder of the extruder, and the temperature of the resin composition in at least a molten portion of the cylinder is maintained at a temperature higher by 30 to 100 ° C. than the glass transition temperature of the resin. A method for preventing colored foreign matter from mixing into processed products by molding. 2. The method according to claim 1, wherein said resin is polymethyl methacrylate. 3. The method according to claim 1, wherein the die lip of the extruder is sealed while the extrusion is interrupted.