JPS6141730B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a straight manifold type coat hanger die with excellent flow characteristics. Conventionally, there are two methods for extrusion of plastic films or sheets: one is a so-called inflation film using a circular die, and the other is extrusion using a flat die. The die used in extrusion using a flat die is T.
There are three main types: dies, coat hanger dies, and fish tail dies. These dies are used in various ways depending on the type of resin, sheet thickness, width, etc. Fishertail dies are generally used to manufacture narrow sheets made of materials that have poor fluidity and are prone to thermal decomposition, such as hard vinyl chloride resins, while T dies are generally used to manufacture sheets of materials such as polyethylene, polypropylene, It is widely used to extrude wide sheets or films of polystyrene, nylon, etc. When trying to extrude a wide product, the fish tail die should be used in the machine direction (perpendicular to the die width).
It becomes noticeably longer and bulkier. Also T
- The residence time of the molten resin flow that flows around the die side end of the manifold is significantly longer than the residence time of the resin flow that flows out the shortest distance along the die center line. The resin that flows out from near both ends undergoes more thermal decomposition than the resin that flows out from the middle of the width of the die, and as a result the quality at both ends in the width direction deteriorates. Or, it was often seen when the molding temperature was high. In order to overcome these drawbacks of the die, a so-called coat hanger die, in which the boundary line between the manifold and the downstream slit is in the shape of a coat hanger, was developed and has been widely used. There are several shapes of coat hanger dies, but the most common shapes are shown in Figures 1 and 2. FIG. 1 is a plan view showing a channel through which resin flows in the coat hanger die, and FIG. 2 is a sectional view of the channel along the die center line A. In Figure 1, manifold 3 and slit 5
A die with a linear boundary line 4 will be referred to as a straight manifold type coat hanger die.
To explain the flow of resin and the names of each part one by one, molten resin flows from die inlet 1 on die center line A,
It flows into the manifold 3 from the manifold inlet 2, flows in the direction of the manifold center line, sequentially changes direction from the boundary line 4 between the manifold 3 and the slit 5, flows into the slit 5, and inside the slit, flows in the machine direction, It flows in a direction parallel to the die center line, reaches the slit bottom line 6, flows further in the machine direction through the die lip 7, and is extruded out of the die through the die opening 8. If an arbitrary streamline flowing as described above is illustrated in FIG. 1, it will look like line B with arrows attached at the beginning and end. It is necessary for the volumetric flow rate per unit die width of the sheet-shaped molten resin flow extruded from such a coat hanger die to be uniform in the die width direction. The flow resistance in the die lip is often finely adjusted for each position in the die width direction by pushing or pulling, but since the molten resin is so-called viscoelastic, the above-mentioned pressure is already applied at the stage of flowing from the slit 5 to the die lip 7. The uniformity of the thickness of the extruded sheet or film is better when the uniformity of the flow rate is achieved. Therefore, in a straight manifold type coat hanger die as shown in Figure 1,
A geometry design method has been proposed to obtain uniformity of flow rate by selecting a way to gradually reduce the radius of the manifold [CTChung & DT]
Lohkamp, “Modern Plastics”, Mar.P−52–55
(1976), Kiyoshi Ito, “Design of Dies for Plastic Extrusion Molding,” Kogyo Choshukai (1971)]. Furthermore, in order to improve the quality deterioration at both ends of the extruded product in the width direction due to the poor uniformity of the internal residence time distribution, which is a drawback of the T-die mentioned above, the shape shown in Fig. 1, that is, the straight manifold shape was adopted. A design method for the shape and dimensions of a coat hanger die that makes the distribution of residence time in the die uniform across the width of the die in addition to uniformity of flow rate by making the boundary line between the manifold and the slit a calculated curve. was reported, and a coat hanger die with a curved line between the manifold and the slit as shown in Figure 3 was proposed (Masayoshi Ito, Plastics Co., Ltd.).
Vol.28, No.2, P-43-47 (1977), Yutaka
Matsubara, Polymer Engineering and
Science, Fed., 1979, Vol.19, No.3, P-169~
172). However, the coat hanger die described above, which satisfies the two uniformity requirements at the same time, has a longer slit height, that is, a longer flow path in the machine direction of the die than the current coat hanger die, and is therefore bulky. This method has the drawback that the manifold-to-slit boundary line is curved, making it more difficult to construct the flow path within the die. By the way, the third
The internal angle of the fan-shaped opening of the slit part in the figure is 137.4 degrees, but the current coat hanger die is closer to 170 degrees. The inventor of the present invention found that uniformity of the flow rate in the width direction of the die is very important for flat dies that extrude films and sheets, but the uniformity of the residence time distribution within the die is determined by the heat of the molten resin within the die. Considering that the residence time distribution can be spread to some extent as long as the decomposition is not too severe, the residence time distribution in the die width direction in the straight manifold type coat hanger die as shown in Figure 1 is as follows. In addition, we examined the quality deterioration in the width direction of extruded products and found that if the residence time distribution is kept within a certain allowable spread, it will be possible to maintain flow uniformity, prevent quality deterioration at both ends of the width direction, and reduce the bulk of the die in the machine direction. The present invention was completed by discovering that all of the above problems can be overcome. That is, in the present invention, the gap between the slits immediately downstream of the manifold is constant, the boundary line between the manifold and the slit is a straight line, and this boundary line extends toward the die side end at a certain angle with respect to the die opening line. In a coat hanger die that is inclined and whose manifold cross-sectional area decreases toward the die side end, select a and H such that the value of m at Z=0 in equation (2) is 1 to 20, and the value of R. The gist of this is a coat hanger die determined by equation (1) according to different values of Z. (However, R is the radius of the cross-sectional circle of the manifold, and is determined by the above formula according to the Z coordinate of the point between the cross-sectional circle and the above boundary line for any cross-sectional circle. If it is not yen,
Let R be the radius of a circular cross section that is hydrodynamically equivalent to that cross section. n is the flow index at the molding temperature of the raw resin melt flowing in the die. Usually a value greater than 1. L is half the width of the die flow path, that is, Z of the die center line
The coordinates are values determined by the width of the extruded product, H is the gap between the slits, a is the tangent of the angle that the boundary line between the manifold and the slits takes with respect to the die width direction, that is, the die opening line direction, and Z is the manifold width. The horizontal coordinate m taken from the old side edge toward the inside of the die along the die width direction is the flow from the manifold inlet in the manifold axial direction, flowing into the slit from the coordinate Z on the above boundary line, and flowing inside the slit. Regarding the flux flowing perpendicular to the die width direction, the average residence time from the manifold inlet to the downstream end of the slit is calculated as the average residence time of the flux that flows immediately from the manifold inlet to the slit and flows down the slit along the die center line. The quotient divided by the average residence time of the bundle in the slit. ) The present invention will be explained in detail below. In the linear manifold type coat hanger die shown in Fig. 1, the conditions for making the volumetric flow rate per unit die width uniform at the downstream end 6 of the slit are as follows:
[CIChung & DT
Lohkamp, “Modern Plastics”, Mar, P52−55
(1976); Masaru Ito, “Design of Dies for Plastic Extrusion Molding,” Kogyo Kenkyukai (1971)]. Equation (1) means that the dependence of R on Z is determined by n, H, a, and the dimension given by the right side of Equation (1) can be taken as the manifold radius at each position (Z coordinate). This means that uniformity in flow rate can be obtained. The present inventor further studied the flow characteristics of the straight manifold type coat hanger die shown in Fig. 1, and found that after flowing through the manifold in the direction of its center line, it flows into the slit from a point on the boundary line and flows along the die center line. A manifold with an arbitrary flow velocity that flows parallel to the slit and reaches the downstream end of the slit, and a center that flows directly into the slit from the manifold inlet with an average residence time in the slit, flows down the die center line, and reaches the downstream end of the slit. They found that the ratio of the flow velocity to the average residence time in the slit is expressed by equation (2), and that this can be used as a design parameter. The meaning of equation (2) is that when the Z coordinate of a point on the manifold-to-slit boundary line is Z, the ratio of the average residence time of the flux that changes direction from this point and flows from the manifold to the slit is Z Depends on
The way it is determined depends on n, H, a, and L. For example, if you do the following, you can design a straight manifold type coat hanger die with a uniform flow rate using equations (1) and (2). That is, polyvinyl chloride was used as the raw resin, the flow index n was 4 according to known data, the extrusion flow rate was determined from the die lip gap to 170 Kg/hr, the specific gravity of the molten resin was 1.4 according to known data, and the die half width L was the extruded product. The width of the manifold is set to 100cm based on the width of the manifold, and the manifold slope is kept low to 0.06, and the average flow velocity of the resin at the manifold inlet cross section is suppressed to 80cm/mm to prevent the flow line from being disturbed by the kinetic energy of the resin. The old entrance radius R _L is determined to be 2.0065 cm using the following equation. πR ² _L × 80 [cm/min] = 170/2 [Kg/hr] × 1/60 [hr/min] × 1000/1.4 [cm ³ /
Kg] Next, to equation (1), R = 2.0065, a = 0.06, n = 4, Z
By substituting =100, we get H=0.21198cm. With this, the required geometric dimensions L, a, and H are aligned, and the change in R depending on Z can be determined as shown in the following sequence using equation (1).

[Table] Next, calculate the change in m according to Z by substituting the above values of n, L, a, and H into equation (2), and calculate the distribution of the residence time ratio m of a die with such a shape and size. When you ask,
The arrangement will look like this:

[Table] If the molten resin with a flow index n of 4 is extruded through the coat hanger die having the above-mentioned dimensions L, a, H, and R, the flow rate will be uniform in the width direction of the die; The distribution of the residence time ratio m is determined. In the linear manifold type coat hanger die of the present invention, the value of m at Z=0 (hereinafter m ₀
By selecting a combination of a and H such that the value (referred to as . Also, the slope a of the manifold-to-slit boundary line
That is, considering that when tanφ=0.1, the internal angle of the fan-shaped opening at the slit part is 2 × (90° - arctan0.1) = 168.5°, when m ₀ becomes about 20, the internal angle of the fan-shaped opening becomes quite large, and the die machine Directional bulk can also be reduced. Since the coat hanger die according to the present invention has a straight line between the manifold and the slit, the die is easy to work. In addition, the cross-sectional shape of the coat hanger die in the present invention is not only a circle but also a formula (1).
Any cross-section that is hydrodynamically equivalent to the circular cross-section with the radius required by It is sufficient if the area is equal to the cross-sectional area of the radius. In Figure 4, A is the formula
(1) is the cross-sectional circle at a certain coordinate Z required by equation (1), and b is the cross-sectional circle at the coordinate L required by equation (1), that is, the manifold inlet. ,
C is a combined arcuate cross section replacing A, and the radius of the arc of C is equal to the radius of B and the area of C. This shape is easier to work with than a manifold with a circular cross section. When a film or sheet is formed by extrusion molding of a thermoplastic resin using the linear manifold type coat hanger die of the present invention, the quality of the molded product obtained is constant in the width direction of the die, and the thickness is uniform. is obtained. As the thermoplastic resin used in the present invention, polyvinyl chloride, polyolefin, polyamide, polyester, polystyrene polyvinylidene chloride, and ABS resin are used. The present invention will be explained below with reference to Examples. Example 1-2, Comparative Example 1-2 Polypropylene (MFR=9) as raw resin
n, L, a, shown in the table at a molding temperature of 240℃ using
Determine the value of H, and then substitute this value into equation (1) to calculate R at the manifold inlet, that is, R _L , and equation (2).
A film with a thickness of 30 μm was formed by extrusion using a straight manifold type coat hanger die with m ₀ determined, and the physical properties of the film in the width direction of the die were measured. The measurement results (average of the measurements of the five samples) are shown in the table and FIG. 5. From FIG. 5, it can be seen that when the value of m ₀ is 20 or less, a constant quality film with less difference in physical properties between the center and edges of the film can be obtained. Example 3-4, Comparative Example 3 A soft vinyl chloride compound (average degree of polymerization = 1050, plasticizer 45 PHR) was used as the raw material resin, and the values of n, L, a, and H shown in the table were determined at a molding temperature of 190°C. By substituting the value into equation (1) and determining R at the manifold inlet, that is, R _L , and m ₀ using equation (2), the thickness was determined using a straight manifold type coat hanger die.
A 50μ film was formed by extrusion, and the physical properties of the film in the die width direction were measured. The measurement results (average of the measured values of 5 samples) are shown in the table and FIG. 5. From FIG. 5, it can be seen that when the value of m ₀ is 20 or less, a constant quality film with less difference in physical properties between the center and edges of the film can be obtained.

【table】 [Brief explanation of the drawing]

Fig. 1 is a plan view of a straight manifold type coat hanger die of the present invention, Fig. 2 is a sectional view taken along line A in Fig. 1, and Fig. 3 is a coat hanger die with a curved manifold-slit boundary; The figure shows a cross section of a manifold, and FIG. 5 shows the relationship between the physical property difference of the film obtained by a straight manifold type coat hanger die and the average residence time ratio m ₀ of the resin at the die side end. 1...Die inlet, 2...Manifold inlet,
3... Manifold part, 4... Boundary line between manifold part and slit part, 5... Slit part,
6...Slit lower end line, 7...Die lip part, 8
...Die opening, A...Die center line, B...Examples of arbitrary streamlines or fluxes.

Claims (1)

[Claims] 1. The gap between the slits immediately downstream of the manifold is constant, the boundary line between the manifold and the slits is a straight line, and this boundary line is directed toward the die side end at a certain angle with respect to the die opening line. In a coat hanger die where the manifold cross-sectional area decreases toward the die side end, Z=
A coat hanger die in which a and H are selected so that the value of m at 0 is 1 to 20, and the value of R is determined by formula (1) according to the different values of Z. (where R is the radius of the cross-sectional circle of the manifold or the radius of the hydrodynamically equivalent circle, n is the flow index of the raw resin melt flowing in the die at its molding temperature, L is the half width of the die flow path, and H is The gap between the slits, a, is the tangent of the angle that the boundary line between the manifold and the slit takes with the die width direction, that is, the die opening line direction, and Z is the gap from the manifold side edge toward the inside of the die along the die width direction. and m are the flow velocity from the manifold inlet to the manifold axial direction, flowing into the slit from the coordinate Z on the boundary line, and flowing through the slit at right angles to the die width direction, from the manifold inlet to the downstream end of the slit. (The quotient obtained by dividing the average residence time until the flux reaches the slit by the average residence time in the slit of the flux that immediately flows into the slit from the manifold inlet and flows down the slit along the die center line.)