JP3856771B2 - Method for preventing thermal degradation products - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing the generation of thermally deteriorated products in the production of extruded products such as resin films, sheets, foams, and profile extrusions.
[0002]
[Prior art]
In general, in the molding of extruded products such as resin films, sheets, foams, and profile extrusions, heat is applied to solid resin raw materials and additives to make the resin flow deformed, and the resin is extruded from an extrusion die. As a result, it is formed into a film, a sheet, a foam, a profile extrusion product, or the like. At that time, in order to prevent the heat-deteriorated foreign matter produced by heat-deteriorating the resin and additives from entering the molded film, sheet, foam, profile extrusion product, etc., which is the product, A foreign matter filtering device is provided upstream of the extrusion die. However, heat-deteriorated foreign matter may also occur in an extrusion die downstream of the foreign matter filtering device. In that case, the foreign matter filtering device does not remove the molded film, sheet, foam, or profile extrusion. It will be mixed inside. Conventionally, as a countermeasure against contamination of heat-deteriorated foreign matter generated in such an extrusion die, the production amount per hour has been reduced, or the frequency of disassembly and cleaning of the extrusion die has been significantly increased. , Manufacturing methods that significantly impede production efficiency.
[0003]
Conventionally, it has been considered that the heat-deteriorated foreign matter in the extrusion die is generated due to a long residence time of the molten resin in the extrusion die as disclosed in JP-A-9-155949. . For this reason, the flow path shape of the extrusion die is narrowed, the flow wall surface has no corners so that no molten resin stays, or the metal surface of the molten resin flow wall surface of the extrusion die. Residue of molten resin on the surface of the extrusion die channel wall surface by using a surface treatment material with low adhesion or adhesion to the molten resin as the treatment material, or shortening the flow passage in the extrusion die The generation of heat-deteriorated foreign matter has been suppressed by reducing the time.
However, the current situation is that heat-deteriorated foreign matter generation in an extrusion die cannot be suppressed only by preventing heat deterioration by reducing the residence time of the molten resin, which is a conventional technique.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-155949
[Problems to be solved by the invention]
The present invention suppresses the generation of foreign matter due to thermal degradation of the molten resin in the extrusion molding die, so that they are mixed into the extrusion molded product such as a resin film, sheet, foam, and profile extrusion product. It aims to provide a method to prevent.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor has made the present invention. That is, the present invention is as follows.
(1) When extruding the resin, the shear rate on the flow path wall surface of the molten resin flowing in the extrusion die is 40 sec ^{−1 at} 60% or more of the total flow path wall surface area of the extrusion die. and ~10sec ^-1, and thermal degradation products formation preventing method which is characterized in that a 40 sec ^-1 or less on the entire flow path wall surface.
(2) the shear rate on the flow path wall surface of the molten resin, 80% or more odor of the total flow path wall surface of the extrusion within-die and 40 ^{sec -1} ~10sec -1, and total flow wall surface The method for preventing thermal degradation product generation according to (1), wherein the thermal degradation product is 40 sec ⁻¹ or less .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The most different point of the present invention from the prior art is that the conventional technique suppresses the generation of thermally deteriorated foreign matter in the resin extrusion die by reducing the residence time of the molten resin. In the invention, regardless of the residence time, the generation of heat-deteriorated foreign matter can be suppressed by controlling the shear rate of the molten resin on the channel wall surface inside the die.
[0008]
As a result of studying the relationship between the residence time of the molten resin in the extrusion die and the generation of heat-deteriorated foreign matter, the inventor found that the heat-degraded foreign matter was generated even at a position where the residence time was short in the extrusion die. We found a state where there is no heat-deteriorated foreign matter with a part where the residence time is clearly long. FIG. 1 shows an example of the generation and adhesion of the thermally deteriorated foreign matter, taking a spiral die as an example. In the figure, heat-deteriorated foreign matter like 15 and 16 was generated on the outer surface of the 11 inner die ring. Further, heat-deteriorated foreign matter was also generated on the surface on the opposite side of the inner surface of the outer die ring 12 on the opposite side of the resin flow path 15 and 16. However, no heat-deteriorated foreign matter is generated in the portion 17 where the residence time is clearly longer than 15 and 16 in FIG.
[0009]
Furthermore, heat-deteriorated foreign matter is generated under the condition that the flow path of the molten resin is narrow, the speed passing through the flow path is higher than a certain level, a large shear stress is applied to the molten resin, and the molten resin causes a large amount of self-heating. I discovered that. In any part of the flow path in the extrusion die, there is a distribution in the shear stress applied to the molten resin in the cross-sectional direction of the flow path. Resins, additives, and the like generate a large amount of self-heating, and a large amount of thermally deteriorated foreign matter such as carbon is generated. Then, heat-deteriorated foreign matter adheres and solidifies on the wall surface of the extrusion molding die flow path of the molten resin flow path, and the heat-degraded foreign matter such as carbon grows in a layered manner, thereby reducing the thickness of the extrusion die flow path. As a result, the passage speed of the molten resin increases, and the shear stress applied to the molten resin and additives increases on the surface of the die flow path wall for extrusion molding, and self-heating of the molten resin and additives increases. In addition, the rate of generation of heat-degraded foreign matter such as carbon is promoted.
[0010]
Then, when the shear stress of the molten resin increased by narrowing the flow path through which the molten resin passes due to the heat-degraded foreign material lamination exceeds the adhesive force between the generated heat-degraded foreign material and the extrusion die channel wall surface, The heat-deteriorated foreign matter that has been laminated is peeled off, flows out from the extrusion die outlet, and is mixed into the product resin film, sheet, foam, profile extrusion product, and the like.
In resin extrusion molding, molding is performed under a temperature condition that is higher than the melting point of each resin and about 100 ° C. higher than the melting point so that the resin can flow, but self-heating of the resin and additives locally in the extrusion die. If this happens, the heat-degraded foreign matter is locally generated due to the property that the heat conduction of the molten resin is very poor. In addition, the molding temperature is often lowered to prevent thermal degradation. However, when the temperature of the molten resin decreases, the viscosity of the molten resin increases and the local shear heating value increases, and the heat conduction of the molten resin increases. On the other hand, the generation of heat-deteriorated foreign matter is increased due to the property of being very bad.
[0011]
In order to prevent the generation of heat-degraded foreign matter due to self-heating of the resin and additives in the extrusion die, it is desirable not to apply a large shear stress and shear rate to the resin. Resin films, sheets, foams, profile extrusions For example, the extrusion die should be designed, manufactured and used at a shear rate of 100 sec ^-1 or less on the surface of the extrusion die channel wall. Preferably, 70 sec ^-1 or less, more preferably 40 sec ^-1 or less. However, if the shear rate is too low, there will be a problem of heat-degraded foreign matter due to local stagnation on the wall surface of the flow path inside the die for extrusion molding. 10 sec ⁻¹ or more is preferable on the road wall surface.
[0012]
In addition, the amount of heat-degraded foreign matter generated and the amount mixed into the molded product increases the ratio of the channel wall surface area with the above optimum shear rate to the total channel wall surface area in the extrusion die. By doing so, it is possible to reduce. The ratio of the channel wall surface area having the optimum shear rate to the total channel wall surface area in the extrusion die is preferably 60% or more, more preferably 80% or more, and gradually approaches 100%. Is most preferred. In the present invention, the flow path wall surface means a cross section of the flow path through which the molten resin constituting the extrusion die flows or a cross section perpendicular to the streamline is a circular cross section flow path, a substantially circular cross section flow path, a semicircular cross section. It refers to all parts of the flow path, such as a flow path, a plane or slit cross section flow path, a cylindrical cross section flow path, a rectangular cross section flow path, a substantially rectangular cross section flow path, and a slit cross section flow path.
[0013]
Extruded materials used in the present invention are thermoplastic resins and blended resins thereof, for example, polyethylene, polypropylene, polystyrene, vinyl chloride, vinylidene chloride, methacryl, polyethylene terephthalate, Ethylene vinyl alcohol, ionomer, styrene acrylate, styrene butadiene, styrene acrylonitrile, acrylate butadiene styrene, polyamide, polyacetal, polycarbonate, polyphenylene ether, polybutylene ether, polysulfone, polyether sulfone , Polyphenylene sulfide, polyacrylate, polyimide, polyether ketone, liquid crystal polymer, fluororesin, polymer alloy, thermoplastic elastomer System, a thermoplastic polyurethane, and the like. In addition, thermoplastic resins and blended resins obtained by adding additives such as heat stabilizers, antioxidants, UV absorbers, surfactants, microballoons, metal powders, inorganic powders, and wood chip powders to the above resins are used. May be.
[0014]
These extrusion materials are usually plasticized and melted by an extruder, kneaded and homogenized, and passed through a pipe called a foreign matter filtering device or a polymer pipe at a temperature higher than the melting point of each resin and about 100 ° C. higher than the melting point. Then, it is led to an extrusion die and formed into a resin film, a sheet, a foam, a profile extrusion product, and the like by the extrusion die. The application of the preferred shear rate of the present invention is also applicable to foreign matter filtration devices and polymer pipes downstream from the extruder, but the shear rates are compared in order to obtain a uniform extruded product downstream of the foreign matter filtration device. The extrusion die has a relatively large flow channel wall surface area of the molten resin and is easy to generate carbon, and is very effective.
[0015]
The die used in the present invention varies in die form depending on the specifications of the extruded product, but any type of extrusion die can be used. For example, spider dies, spiral dies, crosshead dies, etc., which are cylindrical dies for resin extrusion molding, T-dies, coat hanger dies, fish tail dies, etc., which are flat dies, and profile extrusion dies. A single layer die or a multilayer die of those dies can also be used.
[0016]
A method for controlling the shear rate on the flow path wall surface through which the molten resin of the extrusion die flows is to increase the flow passage cross-sectional area of the molten resin of the extrusion die with respect to the flow rate of the molten resin. There is a simple method such as reducing the amount of extrusion, but this would reduce the production efficiency, which is not industrially preferable. In most extrusion dies, the shear rate tends to be large in a flat or slit-like flow path or cylindrical cross-section flow path, and heat-deteriorated foreign matter is generated on the flow path wall surface at this site and peeled off. In many cases, the traces made are observed. In order to reduce the shear rate to an appropriate value in a plane, slit-like cross-section flow path, or cylindrical cross-section flow path, control can be performed by increasing the thickness of the flow paths. The shear rate can also be controlled by increasing the diameter of the cylindrical cross-sectional flow path in the cylindrical die or by increasing the width of the flat or slit-shaped cross-sectional flow path in the planar die.
[0017]
However, in an extrusion die, the thickness of the slit channel may be reduced as appropriate in order to maintain a certain thickness accuracy in films, sheets, foams, profile extrusions, etc. Decreasing the thickness increases the shear stress and shear rate applied to the molten resin, increases the self-heating of the molten resin, and increases the amount of heat-deteriorated foreign matter generated. It is preferable to lengthen or devise a channel upstream from the slit channel to maintain the thickness accuracy of necessary resin films, sheets, foams, profile extrusions, and the like.
[0018]
In addition, the material of the channel wall surface in the extrusion die through which the molten resin flows is usually a metal or ceramic material, but the molten resin can be selected by selecting a material with poor adhesion to the molten resin. It becomes easy to control the shear rate on the flow channel wall surface. In other words, by selecting a channel wall surface material with low adhesion to the molten resin, slippage occurs between the channel wall surface material and the molten resin, resulting in a shear rate of the molten resin on the channel wall surface. Can be lowered to an appropriate value. If the flow path wall surface material is a surface treatment material, it is chromium, ceramic, nickel, nickel blend, electropolishing, nickel-Teflon (registered trademark), passive treatment, For example, nitriding treatment base materials are used as the base material of the resin flow path. Copper, aluminum, titanium, tungsten, nickel, stainless, ceramic, chromium, molybdenum, and their blends The material is mentioned.
[0019]
However, even if the shear rate on the flow path wall surface of the molten resin can be reduced, if the frictional heat generation due to the slip between the flow path wall surface material and the molten resin increases, the heat of the resin or additive in that portion Since a deteriorated foreign matter is generated, it is preferable to appropriately select a material with little frictional heat generation. Similarly, by reducing the surface finish roughness of the flow path component, the shear rate of the molten resin on the flow path wall surface can be lowered to an appropriate value. The surface finish roughness value is preferably 0.3 μm or less. For this purpose, it is preferable to perform surface treatment such as buffing, lapping and electrolytic polishing. In addition, in order to reduce the shear rate on the flow channel wall surface of the molten resin to an appropriate value, a material having poor adhesion to a metal represented by Teflon (registered trademark) is mixed with the material to be extruded. As a result, slippage occurs between the molten resin and the material constituting the flow path of the molten resin on the resin flow path wall surface, and the same effect as using the above-mentioned optimal flow path wall surface material can be obtained. It becomes possible.
[0020]
There are two methods for calculating the shear rate on the resin flow path wall surface, the condition that the resin does not slide on the resin flow path wall surface and the condition of sliding.
In the condition that the resin does not slip on the resin channel wall surface, the shear rate calculation method on the resin channel wall surface is, for example, as shown in FIG. The calculation method is preferable, and the shear rate on the wall surface of the other cross-sectional channel is preferably calculated in detail and accurately using a numerical analysis method such as a finite element method or a difference method.
[0021]
When molten resin slides on the surface of the flow path wall surface against the material constituting the surface of the extruded flow path wall surface, the shear rate calculation method on the surface of the resin flow path wall surface is based on the slip characteristics of the extruded material and the flow path wall surface material. For example, the calculation method shown in FIG. 3 is preferable for the tubular cross-section flow channel and the planar cross-section flow channel, and the shear rate on the wall surface of the other cross-sectional flow channels is a finite element. It is preferable to perform flow calculation in detail and accurately using a numerical analysis method such as a method or a difference method.
[0022]
【Example】
[Example]
The exit diameter of the molten resin is 200 mm, and the extrusion rate is 500 kg / hr, the power law approximation coefficient of the viscosity of the molten resin is n = 0.6, the melt density of the resin is 760 kg / m ³ , the flow The surface of the wall surface is 4.8 mm, the wall surface is made of hard chrome plating, and the surface of the wall surface (598,378 mm ² ) is 97% of the total surface area of the molten resin flow channel wall (616,885 mm ² ). using the spiral die for multilayer resin extrusion shear rate shear rate on 92.6Sec ^-1 and the wall surface had a channel shape which is 100 sec ^-1 or less of the above polyethylene-based molten resin additive containing A resin film was produced by melt extrusion at an extrusion rate of 500 kg / hr and a set temperature of 200 ° C. Using this extrusion die, a film can be produced, which enables a continuous production operation for about 12 months, and the productivity is greatly improved. In addition, there was no contamination of the heat-degraded foreign matter into the resin film or sheet, and there was no disposal amount due to the contamination of the heat-degraded foreign matter of the resin film or sheet in the shipping inspection.
[0023]
[Comparative example]
The conditions other than the shear rate on the flow path wall surface of the molten resin are the same as in the above example, and in the flow path through which the molten resin passes, the flow path of the molten resin is reduced by reducing the flow path thickness. The residence time in the extrusion die is reduced, and the amount of extrusion is 500 kg / hr, the power law approximation coefficient of the viscosity of the molten resin is n = 0.6, and the melt density of the resin is at a slit portion of a cylindrical channel having a diameter of φ200 mm. 760kg / m ³ , channel thickness dimension is 4.4mm, channel wall surface material is hard chrome plating, the channel wall surface area is 50% of the total channel wall surface area and the shear rate on the wall surface is 110 The resin was extruded using a spiral die having a channel shape in which the shear rate applied to the resin on the channel wall surface was ¹ sec ⁻¹ and 110 sec ⁻¹ or more. Then, when this extrusion die is used for about 1.5 months or more, a large amount of heat-degraded foreign matter suddenly enters the resin film, and the disposal amount of the resin film in the shipping inspection is extremely increased. The yield of the resin film was greatly reduced. Further, it was found that this extrusion die required to be disassembled and cleaned in less than one month of continuous use in order to prevent the heat-degraded foreign matter from flowing out into the resin film, which significantly hindered productivity.
[0024]
【The invention's effect】
By suppressing the generation of the heat-deteriorated foreign matter of the molten resin in the extrusion molding die, it is possible to prevent the heat-deteriorated foreign matter from being mixed into the resin film, sheet, foam, modified extrusion product and the like.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a state of adhesion of thermally deteriorated foreign matter on a spiral die.
FIG. 2 is a schematic view showing an example of a method for calculating a shear rate on the resin flow path wall surface.
FIG. 3 is a schematic diagram showing another example of a method for calculating the shear rate on the resin flow path wall surface.
FIG. 4 is a graph showing an example of viscosity coefficient calculation when using power law approximation of a molten resin.
[Explanation of symbols]
11: Spiral die inner die ring 12: Spiral die outer die ring 13: Resin flow channel inlet 14 to the extrusion molding die 14: Resin flow channel outlet 15 of the extrusion molding die 17: Location 17 where no thermally deteriorated foreign matter is attached Location 18 where heat degradation foreign matter is generated and attached upstream: Location 18 where heat degradation foreign matter is generated upstream of location 18 where no thermal degradation foreign matter is attached 17: Location 18 where no thermal degradation foreign matter is attached 18: Location 19 where no thermal degradation foreign matter is attached : Heat-deteriorated foreign matter generation and adhesion site 21: Channel wall surface 31: Channel wall surface γ _{dot # wall} : For molten resin and additive on the channel wall surface of the extrusion die at various positions in the resin channel The shear rate [sec ^-1 ]
M _dot : Extrusion flow rate at various positions in the resin flow path [m ³ / sec]
H: Thickness of slit channel at various positions of resin channel [m]
W: width of the plane cross-sectional flow path in the direction perpendicular to the main flow direction where M _dots flow at various positions of the resin flow path, or circumferential length [m] if the cross-section flow path is cylindrical
R: Radius [m] of the circular cross section channel
V _wall : speed at which molten resin and additive slide on the flow path wall surface of the extrusion die [m / s]
n: Coefficient of viscosity of molten resin including additives, if any, for example, viscosity coefficient by power law approximation γ _dot0 : Shear rate and resin viscosity in extrusion die, for example, power law approximation Lower limit of shear rate [sec ^-1 ] that can be expressed approximately when using
γ _dot1 : The upper limit of the shear rate [sec ^-1 ] that can approximately represent the shear rate and resin viscosity in the extrusion die when using, for example, the power law approximation
μ ₀ : Melt resin viscosity [Pa · sec] at shear rate γ _dot0
μ ₁ : Melted resin viscosity [Pa · sec] at shear rate γ _dot1

Claims (2)

When extruding a resin, the shear rate on the flow path wall surface of the molten resin flowing through the extrusion molding in a die, 40 sec at 60% or more of the total flow path wall surface of the extrusion die ^{-1 ~10sec - 1} and 40 sec ⁻¹ or less on the entire wall surface of the flow path . The shear rate on the flow path wall surface of the molten resin, 80% or more odor of the total flow path wall surface of the extrusion within-die and 40 ^{sec -1} ~10sec -1, and 40sec on total flow wall surface ^{- The} method for preventing thermal degradation product generation according to claim 1, wherein the thermal degradation product generation method is ¹ or less .

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