JP2538716B2 - Polymer melt molding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polymer melt-molding method, and more particularly to suppressing adhesion of polymer deterioration products, a part of additives and the like to the extrusion surface of an extrusion die. The present invention relates to a polymer melt molding method for stably molding a high quality molded article.

[Prior Art] When a polymer is melted and extrusion-molded, a die is used. Conventionally, a material having iron as a main component such as S45C and SS41 has been used as a material of the die. However, corrosion occurs in the polymer flow path, which causes problems such as streak-like defects on the surface of the molded product.
20J2 or SUS630 is used, and for example, Japanese Patent Laid-Open No. 183825/1988 proposes rustproof coating by plating with Cr, Ni, etc., sputtering film with TiN, SiC, etc.

However, when extrusion molding is performed using a die made of any of these materials, a molding defect called an "eye stitch" often occurs. This is because polymer deterioration products, part of compounding agents, or their oxidation and decomposition products adhere to the extrusion surface of the die like "eye crocodile", and accumulate and stick to the extrusion surface (outer surface of the tip) of the die during molding. However, it is further deteriorated by heat, and this adhered material comes into contact with the molded product extruded from the die and causes a phenomenon that a convex scratch is formed on the surface of the molded product.

As a method for solving this problem, for example, Japanese Patent Laid-Open No. 63-
No. 153112 proposes that the surface layer of Cr plating covering the die is Cr ₂ O ₃ , but it is generally difficult to obtain a satisfactory Cr ₂ O ₃ film only by changing the plating conditions. Similarly, in JP-A-1-280525, the chemical composition of chromium in the surface layer is 5 mol% of metallic chromium, 50 mol% of chromium oxide, hydroxide + sulfate.
Proposes 33%. As a method of embodying this, there is a method of heat-treating at 550 ° C. in air, but when heat-treating chrome plating at such a high temperature, chrome-plating generally causes stress cracking and micro-cracking, which is an important characteristic of the die. It is not practical because it causes new problems such as a significant decrease in surface hardness.

As another means, JP-A-63-293032 discloses that the composition ratio of chromium in the die is 12 to 100% by weight in the flow path of the polymer and 0 to 11% by weight on the lower surface of the die. −3020
No. 16 proposes that the chromium composition ratio of the die is 0 to 18% by weight in the polymer channel and 30 to 100% by weight on the lower surface of the die. According to the additional test by the present inventor, no remarkable effect was found.

Generally, the easiness of inventing the "eye candy" greatly varies depending on the heat resistance of the polymer, the melt viscosity, the compounding agent contained in the polymer, the filler, etc. even if the die is made of the same material. Therefore, when the "eye seal" grows and a defect is likely to occur in the molded product, the production of the molded product is interrupted and the "eye seal" is scraped off with a spatula of a soft metal such as copper. .

On the other hand, the tip shape of the die when the polymer passes through the inside of the die and is discharged into the air has a great influence on the surface shape of the molded product, and therefore, it is generally finished to have an extremely sharp edge. Japanese Patent Application Laid-Open No. 1-281916 proposes a die coated with a ceramic having a wetting angle of 70 ° C. or more between a polymer and a heated die. Ceramics generally have high hardness but poor toughness, and impact It is a material that is liable to chip when receiving it, and therefore when scratching the tip of a sharp-edge die covered with ceramics with a metal spatula,
Occasionally, problems such as scratching or missing of the ceramic coating on the edge are likely to occur.

Further, JP-A-1-281915 and JP-A-2-162010 propose a slit die made of a noble metal such as gold, platinum or tantalum, but the material is expensive and the hardness of the material is small. There is a problem that the base is easily scratched.

[Object of the Invention] The object of the present invention is not particularly difficult to materialize as in the above-mentioned prior art, and it is possible to significantly reduce the “eye dent” attached to the extrusion surface of the die, and An object of the present invention is to propose a method capable of forming a good product for a long period of time with almost no damage to the die even by a scraping operation of the "eye seal".

[Configuration of the Invention] The present invention has the following configurations in order to achieve the above object.

In a method of extruding a molten polymer from a die, the surface of the channel and / or the extrusion surface of the molten polymer used as the die has a wetting angle of 40 ° C. with triethylene glycol.
A method for melt-molding a polymer, characterized in that a die coated with a metallic glass having a temperature of ≧ ° is used.

The polymer in the present invention is a thermoplastic polymer, for example, polyester such as polyethylene terephthalate, polyolefin such as polypropylene, vinyl polymer such as polyvinyl chloride, polyamide such as nylon 6, acrylic polymer such as polymethylmethacrylate. Etc. can be mentioned. Of these, polyester is particularly preferable.

The die in the present invention is a die for spinning out a fiber, an inflation die or a straight die for extruding a film, an extrusion die for wire coating, and the like.

The “wetting angle with triethylene glycol” in the present invention means that the droplet of triethylene glycol of a reagent grade under a 20 ° C. atmosphere is between the material forming the surface of the die which contacts the molten polymer, for example, metallic glass. This is the contact angle created by.

According to the empirical fact of the present inventor, the surface characteristics of the material, particularly metallic glass, are specified by triethylene glycol in the present invention. The wetting angle is more correlated.

On the other hand, the wetting angle with the molten polymer is not suitable as a scale because of poor reproducibility of data due to the following reasons. That is, the melt viscosity of the thermoplastic polymer changes depending on the molecular weight of the polymer or the heating temperature, and in addition, the melted polymer may be decomposed by the heat or the atmospheric gas, and the crosslinking reaction may proceed in parallel, which is highly accurate. It is difficult to obtain reproducible data. For the above reasons, triethylene glycol is convenient.

The "metallic glass" in the present invention is also referred to as an amorphous alloy, and generally, the alloy is periodically quenched and solidified from a molten state, or is periodically formed in the process of solid formation such as sputter deposition. A glass-like structure that does not have a crystalline structure even in a solid state and is similar to a liquid can be obtained by performing a treatment for preventing the formation of order or a treatment for breaking the periodic order by ion implantation or the like.

Since metallic glass is physically and chemically homogeneous,
It is said that a uniform and dense passivation film with corrosion resistance is formed on the surface.

In the die coated with the metallic glass of the present invention, the reason why the "eye dent" is unlikely to occur, the cause is not clear, but it has the unique physical and chemical homogeneous and dense corrosion resistance of metallic glass. The passivation film may suppress the generation of degradation products of the polymer that is the cause of eye blemishes and decomposition products from the compounding agent, and may further weaken the adhesion of the degradation products to the die. Presumed.

Examples of the metallic glass suitable for the purpose of the present invention include Ta-based amorphous alloys, W-based amorphous alloys, Ti-based amorphous alloys, Cr amorphous alloys, and the like.
These alloys contain Ta, W, Ti and / or C as the first component.
r and the second and other components such as Cr, Ni, F
It is composed of one or more elements selected from e, Al, Si, Zr, Mo, Co, Cu, P, C and B. Specific examples of such alloys include JP-A-61-266549, JP-A-61-210143, JP-A-63-270435, JP-A-63-79932 and JP-A-6.
3-79928, JP-A-62-33736, JP-A-62-3
Examples thereof include those disclosed in Japanese Patent No. 3735. Of these, those having a “wetting angle with triethylene glycol” of 40 ° or more are used.

For coating the metallic glass, for example, gas phase reactivity such as a sputtering method, a bulk processing method using a laser, a plating method, or the like can be used.

It is preferable that the metallic glass of the present invention is heat-treated at a temperature lower than the temperature at which crystallization starts and in an oxidizing atmosphere, because the passivation film on the surface may be more inactivated.

The structural form of metallic glass can be confirmed by a conventional method of X-ray diffraction.

The base material coated with metallic glass in the present invention may be one conventionally used as a die material, for example, carbon steel such as S45C, SS41, SUS420J2, SUS630.
Can be rust-free steel like.

[Examples] Hereinafter, the present invention will be further described with reference to Examples.

Example 1 and Comparative Example 1 A flow path surface of molten polymer of a die made of SUS420J2,
A metal glass film having a film thickness of about 5 μm and made of Ta50% (atomic%), Fe36%, Ni5%, and Cr9% was formed on the extrusion surface of the die which was in contact with the surface and extruded into the air of the polymer. The wetting angle of this coating with triethylene glycol was 59 ° (note that the wetting angle of Teflon was 85 °).

This die was assembled into a die having a slit width of 1.5 mm and a width of 500 mm, polyethylene terephthalate having a resin temperature of 290 ° C. was extruded, and a sheet having a thickness of 150 μm was extruded onto a cooling roll at a speed of about 30 m / min and taken out.

The streak-like defect due to the eye-like resin at the tip of the die was hardly recognized even 72 hours after the start of extrusion.

On the other hand, as for the die whose die material was SUS420J2 and which was not surface-treated in particular, the sheet was extruded under the same conditions as in the above-mentioned examples, and as a result, a streak-like defect due to eye bleeding was revealed 36 hours after the start of extrusion.

[Effects of the Invention] According to the present invention, the polymer channel surface and the polymer extruded surface of the die are coated with metallic glass having low wettability, which suppresses the occurrence of "eye dents" on the extruded surface of the die. Then
It is possible to stably form a high-quality extruded product without streaky defects.

Claims (2)

(57) [Claims] 1. A method of extruding a molten polymer from a die, wherein the surface of the channel and / or the extrusion surface of the molten polymer as the die is coated with metallic glass having a wetting angle of 40 ° or more with triethylene glycol. 1. A method for melt-molding a polymer, which comprises using a die. 2. The polymer melt-molding method according to claim 1, wherein the metallic glass is a Ta-based amorphous alloy.