JPH10264229A - Die for extrusion molding, extrusion molding method and film manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly mitigate the quantity of residue sticking to the extrusion face of a die and reduce the frequency of lip cleaning for scraping off residue by making the maximum height of the surface roughness or the arithmetic mean roughness of a die face exposed to an atmosphere larger than the maximum height of the surface roughness or the arithmetic mean roughness of a face coming into contact with a liquid. SOLUTION: The maximum height Ryb or the arithmetic means roughness of JISB 0601 (1994) as the surface roughness of a die face 6 exposed to an atmosphere is made larger than the maximum height Rya of the surface roughness or the arithmetic mean roughness of a die face 5 coming into contact with a liquid respectively. Further, the equation of Ryb/Rya=1.50-1 is to be established, and Rya=0.025 μm-1.25 μm, Ryb=0.16 μm-2.0 μm are preferably to be established. Especially the face 6 exposed to an atmosphere is preferably honed, and further, the face 5 coming into a liquid or the face 6 exposed to an atmosphere is preferably to be plated with either of TiN, TiCN, TiC, CrN, DLC, cBN or amorphous HCr as a surface treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die for extrusion molding of a thermoplastic resin and an extrusion molding method using the die. More specifically, the present invention relates to an extrusion die for stably producing a high-quality molded product and a die for the extrusion. It relates to the extrusion molding method used.

[0002]

2. Description of the Related Art A die is used when a thermoplastic resin is melted and extruded into a sheet. As a material of the die, a material mainly containing iron, such as S45C and SS400, has been used. However, in recent years, corrosion has occurred in a flow path of a thermoplastic resin.
2. SUS630 has come to be used.

[0003] However, when extrusion molding is performed using a die made of these materials, a quality defect called "eyes" is often generated. This is because deterioration of the thermoplastic resin and some of the additives, or oxides and decomposition products of the thermoplastic resin adhere to the surface open to the atmosphere like eyes, accumulate on the surface open to the air during sheet molding, This is a phenomenon in which the attached material comes into contact with a sheet-like material extruded from a die, and a convex or concave streak is formed on the surface of the sheet-like material.
At the initial stage of the occurrence of the "eye", the "eye" tends to form concave streaks on the surface of the sheet.
When the “eye” is developed, on the contrary, the “eye” becomes a core, and the thermoplastic resin adjacent thereto tends to be drawn into a convex streak.

As a countermeasure for preventing this "eye flaw", Japanese Patent Publication No. 4-55369 proposes a method of using a zirconia sintered body to which plastic does not easily adhere as a die material. However, ceramics generally have high hardness, but are poor in toughness, and have a disadvantage that they are easily chipped when subjected to an impact, and there is a problem that chipping occurs at a lip tip when used for a long time, and the lip cannot be used.

Japanese Patent Application Laid-Open No. Hei 6-315966 proposes a die in which the hardness of the inner surface of the die-lip in contact with the molten resin, the outer surface adjacent to the inner surface, and the ridge formed by both surfaces are HRC45 or more. doing. In this proposal, it is necessary to break the sheet by die cleaning in order to remove the "eyes", and there is a problem that productivity is reduced.

In Japanese Patent Application Laid-Open No. Hei 2-261622, the dimensions from the end of the flat surface of the resin flow path on the side of the traverse to the extension of the outer surface of the lip are described. It is proposed that the dimension from the end on the side to the extension of the surface on the resin flow path side is both 0.005 to 0.1 mm. In other words, this proposal means that the radius R of the lip tip 7 shown in FIG. 2 is set to 0.005 to 0.1 mm. However, according to the test of the present inventors, it was not possible to sufficiently prevent the occurrence of "eye frays" and to reduce the number of times of cleaning the base by simply adding R, which was the object of the present invention. .

Japanese Patent Laid-Open Publication No. 4-201227 and the like propose a die coated with a nitride or carbide ceramic having a thickness of 0.3 to 5 μm. However, according to the tests of the present inventors, simply coating with a nitride or carbide-based ceramic, the object of the present invention, a sufficient effect to prevent the occurrence of "eye fray",
It was not possible to reduce the number of base cleanings.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to greatly reduce "eyes and eyes" adhering to the extrusion surface of a die, reduce the number of times of lip cleaning for scraping "eyes and eyes", and reduce the damage to the die. An object of the present invention is to provide an extrusion die capable of producing a good product over a long period of time without adding a die, and an extrusion molding method using the die.

[0009]

The present invention employs the following configuration to achieve the above object.

That is, the extrusion die according to the present invention is characterized in that a pair of lips having a liquid contact surface with which the molten thermoplastic resin of the die lip contacts, and an air opening surface adjacent to the liquid contact surface and open to the atmosphere are provided. In an extrusion die for forming a gap and extruding a thermoplastic resin, the maximum height (Ryb) in JIS B0601 (1994) as the surface roughness of the surface open to the atmosphere is the maximum height of the surface roughness of the liquid contact surface. (Rya), or the arithmetic average roughness (Rab) of the surface roughness of the surface open to the atmosphere is larger than the arithmetic average roughness (Raa) of the surface roughness of the liquid contact surface. I do. In particular, it is preferable that the liquid contact surface and the air opening surface are formed so as to be substantially perpendicular to each other.

More specifically, as specific numerical values, when the maximum height of the surface roughness of the liquid contact surface is Rya and the maximum height of the surface roughness of the surface open to the atmosphere is Ryb, Ryb / Rya
= 1.5 to 10 and the maximum height Rya of the surface roughness of the liquid contact surface is 0.025 μm to 1.25 μm
And the maximum height R of the surface roughness of the surface open to the atmosphere
It is preferable that yb = 0.16 μm to 2.0 μm.

In particular, it is more effective to finish the surface open to the atmosphere with honing.

It is also preferable that the radius of curvature R of the corner formed by the intersection of the liquid contact surface and the open air surface is 40 μm or less.

Further, as a surface treatment, TiN, TiCN, TiC, CrN,
It is preferable to apply any of DLC, cBN and amorphous HCr plating. Here, TiN, TiCN, T
iC is a titanium compound, CrN is chromium nitride, DLC is diamond-like carbon, cBN
Means cubic boron nitride.

In particular, it is more effective to apply the above-mentioned die to film production.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In order to prevent the occurrence of "eyes", the present inventors have found that a thermoplastic resin adheres to an air-exposed surface which is substantially perpendicular to the liquid-contact surface of the thermoplastic resin and is open to the atmosphere. It has been found that the surface roughness is important for this purpose. The present invention prevents the occurrence of "glazing" by adjusting the surface roughness of the air-exposed surface, which is open to the atmosphere in the vicinity of the liquid-contact surface and the liquid-contact surface of the thermoplastic resin, to prevent the occurrence of "glazing" during production. An object of the present invention is to provide an extrusion die capable of producing a sheet having no surface defects for a long time without breaking the sheet and cleaning the die.

Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings.

FIG. 1 is a front view showing an embodiment of an extrusion die according to the present invention, and FIG. 2 is a cross-sectional view of a central portion viewed from a side surface of FIG.

The die includes a die hopper 1 forming a manifold, a pair of A lips 2 and B lips 3 forming a lip gap, and a side plate 4 sealing both sides of the A and B lips. The discharge amount distribution in the die width direction
It is determined only by the balance between the pressure loss of the die hopper and the pressure loss of the lip.
In particular, it is greatly affected by the surface condition near the lip tip.

FIG. 3 is an enlarged view of the vicinity of the lip. Factors that determine the surface condition of the sheet material include the material of the lip, the surface treatment of the lip, the R of the lip tip 7, and the surface roughness of the lip. However, we have:
It has been found that the surface roughness of the open-to-atmosphere surface 6 is particularly important for achieving the object of the present invention.

In other words, the mechanism of the generation of "eyes" is as follows. When the thermoplastic resin compressed in the die is extruded from the die and released to the atmosphere, it expands due to the ballast effect, adheres to the atmosphere-exposed surface 6, and grows. If it adheres for a long period of time, it deteriorates due to heat, hardens, comes into contact with the sheet-like material, and gives a convex or concave streak on the surface of the sheet-like material, causing quality defects. It turned out to be one.

Therefore, it is important that the state of the open-to-atmosphere surface 6 is such that the thermoplastic resin is not easily adhered in order to prevent the occurrence of "eye fog". Therefore, samples having different surface treatments and surface roughnesses as shown in Table 1 were manufactured, and evaluation was made on the difficulty of attaching the thermoplastic resin, that is, the releasability.

FIG. 4 shows an evaluation method. SUS as material
Sample 11 of 50 × 25 × t2 was manufactured using 420J2. This surface was subjected to various surface treatments and finished to a predetermined surface roughness. A chip 12 of polyethylene terephthalate (PET) as an example of a thermoplastic resin was placed on this surface, the temperature was maintained at 280 ° C. for 5 minutes, and the magnitude of the force F for peeling off the chip was measured. The results are shown in Table 1.

Here, the honing is a method in which the surface is finished to have a satin finish by a liquid honing process. In addition,
Each surface treatment + honing means a base material (here, SUS4
20J2) means that each surface treatment was performed after the surface was honed. The surface roughness is J
Maximum height Ry in IS B 0601 (1994)
It was measured in.

[0025]

[Table 1] As a result, the type of surface treatment has almost no effect,
The rougher the surface roughness, the more easily the PET resin comes off,
In particular, it was found that the surface roughness of about 0.8 after the liquid honing treatment was very easy to peel off.

Since the liquid contact surface 5 of the thermoplastic resin of the A lip and the B lip forming the lip gap is an important surface for determining the surface forming of the sheet, the maximum surface roughness of the liquid contact surface 5 is high. Assuming that Rya is Rya, it is important that the maximum height of the surface roughness of the liquid contact surface 5 is at least Rya = 1.25 μm or less. However, when the surface roughness of the liquid contact surface 5 is reduced to some extent, the smoothness of the surface of the sheet-like material reaches a plateau, and no further improvement is made. Therefore, from the viewpoint of the die processing cost, at most Rya = 0.025 μm
m is the limit.

On the other hand, from the results shown in Table 1, the surface roughness of the air-exposed surface 6 which is substantially perpendicular to the liquid-contact surface 5 is better to some extent. Let Rya be the maximum height of the surface roughness of Ryb, and Ryb be the maximum height of the surface roughness of the open-to-atmosphere surface 6, Ryb / Rya =
It is preferably in the range of 1.5 to 10.

When the maximum height (Rya) of the surface roughness of the liquid contact surface 5 of the thermoplastic resin is in the range of 0.025 to 1.25, the maximum height (Ryb) of the surface roughness of the open air surface 6 is set. ) Is preferably in the range of 0.16 to 2.0, and 0.4 to 2.0.
A range of 0 is more preferred. In particular, it is more effective to uniformly roughen the air opening surface 6 by the honing process.

In the above embodiment, only the maximum surface roughness (Ry) has been described, but the arithmetic average roughness (Ra) of the surface roughness may be used. If the surface has many scratches and the surface roughness curve extremely increases or decreases, Ra
You should evaluate in.

The radius of curvature R of the corner formed by the contact surface 5 of the thermoplastic resin and the surface 6 open to the atmosphere, that is, the radius R of the lip tip 7 indicates that the release of the lip from the thermoplastic resin is good. In order to reduce the variation in the die width direction, the thickness is preferably set to 40 μm or less.

Further, before starting the production, a copper plate or the like is applied to the lower surface of the die to clean the lip, so that the liquid contacting surface 5, the atmosphere opening surface 6, and the R surface of the lip tip 7 are treated with TiN, TiCN, TiC, CrN, DLC, cBN,
One of amorphous HCr plating 0.1 to 5 μm
It is preferable to increase the hardness by applying a certain amount. Here, the coating thickness is preferably 0.1 μm or more in order to exhibit the performance of the hardness of the coating, and in order to maintain a predetermined surface roughness and a predetermined lip tip R, It is preferable that the thickness be 5 μm or less.
Other coatings have a Vickers hardness (HV) described in JIS Z 2244 (1992) with a film thickness of about 0.1 to 5 μm, without significantly changing the state of surface roughness. If HV = 1000 or more, it can be used.

Examples of the thermoplastic resin in the present invention include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyamide resins such as nylon 6 and nylon 66; polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and polyethylene. A polyethylene resin such as -1,4-cyclohexane dimethylene terephthalate, a polyacetal resin, a polyphenylene sulfide resin, and the like can be used. Further, these resins may be homopolymer resins, or may be copolymers or blends. In addition, known various additives such as an antioxidant, an antistatic agent, a crystal nucleating agent, and inorganic particles may be attached to these resins.

The extrusion die according to the present invention is used for forming not only T dies such as T dies, coat hanger dies and fish tail dies shown in FIGS. 1 and 2, but also a tube-shaped sheet material. The same effect can be achieved with a circular die.

Although not specifically shown in FIG. 1, thermal expansion,
A lip gap automatic control mechanism using a change in viscosity of the polymer, a lip gap manual adjustment mechanism using a differential screw or the like, or a lip gap adjustment mechanism in which both are overlapped may be provided.

Although FIG. 1 shows a single-layer die, the same effect can be obtained by using a composite die.

In FIG. 1, a lip in which the liquid contact surface and the air opening surface are formed so as to be substantially perpendicular to each other has been described as an example, but as shown in FIGS. 5A and 5B, The case where the liquid contact surface 5 and the atmosphere opening surface 6 are acute angles may be used. In addition,
FIG. 5B is an enlarged view of the lip tip of FIG. 5A. Further, as shown in FIGS. 6A and 6B, the liquid contact surface 5 and the air opening surface 6 are almost in contact with each other at a right angle, and the length of the air opening surface 6 in the portion contacting the right angle is 1 mm or less. If so, the open-to-atmosphere surface 6 next to the open-to-atmosphere surface 6 in contact with the liquid contact surface 5 is also included in the open-to-atmosphere surface described in the present invention. FIG. 6 (B)
FIG. 7 is an enlarged view of the lip tip of FIG. In the embodiment shown in FIGS. 5 and 6, FIGS.
As shown in (B), it is preferable to provide R at the lip tip 7.

[0037]

As described above, the extrusion die according to the present invention can properly adjust the surface roughness of the air-exposed surface, which is substantially perpendicular to the liquid contact surface of the thermoplastic resin and is open to the atmosphere. By doing so, it is possible to prevent the occurrence of "eyes" and to produce a sheet-like material having no surface defects for a long period of time without breaking the sheet-like material during production and cleaning the die.

[Brief description of the drawings]

FIG. 1 is a front view showing one embodiment of an extrusion die according to the present invention.

FIG. 2 is a cross-sectional view of a central portion of the extrusion die as viewed from the side in FIG.

FIG. 3 is an enlarged view of a lip tip of FIG. 2;

FIG. 4 is a schematic diagram of an evaluation test.

FIG. 5 is a central sectional view showing another embodiment of the extrusion die according to the present invention.

FIG. 6 is a central sectional view showing still another embodiment of the extrusion die according to the present invention.

[Explanation of symbols]

 1: die hopper 2: A lip 3: B lip 4: side plate 5: liquid contact surface of thermoplastic resin 6: open air surface 7: lip tip R 8: manifold 9: lip gap 11: sample for evaluation 12: thermoplastic resin

Claims (8)

[Claims] 1. A pair of lips having a liquid contact surface with which a molten thermoplastic resin of a die lip contacts, and an air open surface adjacent to the liquid contact surface and open to the atmosphere, form a lip gap, and form a thermoplastic resin. In the extrusion die for extrusion,
The surface roughness of the surface open to the atmosphere is JIS B 0601
(1994) that the maximum height (Ryb) is greater than the maximum height (Rya) of the surface roughness of the liquid contact surface, or the arithmetic average roughness (Ra) of the surface roughness of the surface open to the atmosphere.
b) is the arithmetic average roughness of the surface roughness of the liquid contact surface (Raa)
An extrusion die characterized in that it is larger than the die. 2. The extrusion die according to claim 1, wherein the liquid contact surface and the air opening surface are formed so as to be substantially perpendicular to each other. 3. A maximum height (Ry) of the surface roughness of the liquid contact surface.
a) and the maximum height of the surface roughness of the open air surface (Ryb)
(Ryb / Rya) is in the range of 1.5 to 20, and the maximum height (Rya) of the surface roughness of the liquid contact surface
3 is 0.025 to 1.25, and the maximum height (Ryb) of the surface roughness of the open air surface is 0.16 to 2.0. Extrusion die. 4. The extrusion molding die according to claim 1, wherein said surface open to the atmosphere is honed. 5. The extrusion die according to claim 1, wherein a radius of curvature R of an angle formed by intersecting the liquid contact surface and the air opening surface is 40 μm or less. 6. A surface treatment of TiN, TiCN, TiC, CrN, DL on the liquid contact surface or the open air surface.
The extrusion die according to any one of claims 1 to 5, wherein one of C, cBN, and amorphous HCr plating is applied. 7. An extrusion molding method using an extrusion die according to claim 1, which is applied to the production of a film. 8. A method for producing a film, comprising melting and discharging a thermoplastic resin using the die for extrusion molding according to claim 1, to produce a film.