JPH04290720A - Mold for extrusion molding of vinyl chloride resin - Google Patents

Abstract

PURPOSE:To obtain an extrusion mold having high surface hardness and excellent in corrosion resistance by forming a ceramics film to at least the surface coming into contact with a molten vinyl chloride resin of a mold by ion plating. CONSTITUTION:A ceramics film is formed to the surface of the base material of an extrusion mold using an ion plating method wherein a metal constituting the ceramics film is evaporated to form evaporated particles which are, in turn, ionized and the ionized metal particles are reacted with reactive gas (e.g., nitrogen gas in the case of a nitride film, hydrocarbon gas such as methane gas or acetylene gas in the case of a carbide film). The ceramics film is composed of ceramics selected from a group consisting of nitride, carbide, carbonitride and oxide of a metal selected from Ti, Zr, Cr, Hf, B, Si, V or the like.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for extrusion molding a vinyl chloride resin.

0002

[Prior Art] Conventionally, hard chromium plating or nickel plating has been used to impart wear resistance to the surface of plastic extrusion molds and to improve extrusion moldability by reducing the frictional force with the molten resin. is being carried out.

However, the above-mentioned plating is susceptible to wear on the plated surface due to long-term use, scratches on the plated surface due to buffing during maintenance, and corrosion of the plated surface due to acid gas (for example, hydrochloric acid) generated during thermal decomposition of the resin. As a result, the smoothness of the plated surface is impaired, and as a result, scratches occur on the surface of the molded product, making it impossible to obtain a good product.

On the other hand, it has been proposed to form a ceramic coating on the mold surface in order to impart wear resistance, corrosion resistance, etc.
An injection mold is described in which a ceramic coating is formed on part or all of the injection molding surface of the injection mold by a vacuum deposition method or a CVD method.

However, in the above-mentioned injection mold, when the ceramic coating is formed by vacuum evaporation, the adhesion between the ceramic coating and the mold base material, and the formation of the ceramic coating on the uneven surface of the mold base material are poor. It has the disadvantage of poor film thickness uniformity, surface hardness, etc. When a ceramic film is formed using the CVD method, the mold base material undergoes dimensional changes due to heat due to the high film formation temperature, resulting in a molded object having a predetermined shape. The drawback was that it was not available.

[0006]

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to improve the adhesion to the mold base material and to improve the uniformity of the film thickness on the uneven surface of the mold base material. To provide a mold for extrusion molding of a vinyl chloride resin, which has a high surface hardness and excellent corrosion resistance, in which a ceramic coating having excellent properties, etc. is formed on the surface of the mold that contacts the molten resin.

[0007]

[Means for Solving the Problems] The vinyl chloride resin extrusion mold of the present invention is obtained by forming a ceramic coating on the surface of the mold base material of the extrusion mold using an ion plating method. and the above ceramic coating is
It is formed at least on the surface of the mold base material that comes into contact with the molten vinyl chloride resin.

The extrusion mold described above is not particularly limited, and examples include a monofilament extrusion mold, a film extrusion mold, a pipe extrusion mold, and the like.

The material of the mold base material is not particularly limited, and materials conventionally known for plastic molds can be used, such as carbon steel, stainless steel,
Examples include alloy steels such as chromium molybdenum steel, nickel chromium molybdenum steel, hot die steel, and age hardening alloy steel, copper alloys, aluminum alloys, and zinc alloys.

[0010] Examples of the above ceramic coating include:
Examples include one or more ceramics selected from the group consisting of nitrides, carbides, carbonitrides, and oxides of metals such as Ti, Zr, Cr, Hf, B, Si, and V.

[0011] When the thickness of the ceramic coating becomes thin, the surface hardness of the coated surface decreases and pinholes occur in the coating, resulting in a decrease in corrosion resistance, and when it becomes thick, the adhesion to the mold base material decreases. 0.5 to 10.
It is preferably μm, more preferably 1 to 7 μm.

[0012] In order to form the above-mentioned ceramic coating by the ion plating method, the metal constituting the ceramic coating is evaporated, and the evaporated particles are further ionized.
The ionized metal is transferred to a reactive gas (for example, nitrogen gas if the film to be formed is a nitride, hydrocarbon gas such as methane gas or acetylene gas if the film is a carbide, or a mixture of nitrogen gas and hydrocarbon gas if the film is a carbonitride) It may be reacted with a gas (oxygen gas in the case of an oxide).

The above ion plating method is not particularly limited, and conventionally known methods can be used.
For example, direct current discharge method, hollow cathode discharge method (hereinafter referred to as HCD method), high frequency excitation method (hereinafter referred to as RF method),
For example, the HCD method, the RF method, and the AIP method are preferred because they can form a ceramic film on a surface with a complicated surface shape. . The difference between these methods is that the method of evaporating the metal and the method of ionizing the evaporated particles are different.

[0014] As a process for forming a ceramic coating on a mold base material using each of the above methods, for example, the mold base material is supplied into a vacuum container, the mold base material is heated, and the inside of the vacuum container is heated. The pressure is reduced to a predetermined degree of vacuum, and then the metal to be reacted is evaporated and further ionized, while a reactive gas is introduced into the vacuum container to a predetermined reaction pressure (however, HC
In the case of method D, it is necessary to introduce an inert gas such as Ar gas in addition to the reactive gas, so the partial pressure of the reactive gas in the total pressure is set as the reaction pressure), and a DC voltage is applied to the mold base material. Another example is a process in which an ionized metal is reacted with a reactive gas to form a desired ceramic coating on a mold base material.

In the above process, when the heating temperature of the mold base material is low, the adhesion between the obtained ceramic coating and the mold base material decreases, and when it becomes high, the mold base material is deformed, and the dimensional accuracy of the mold is deteriorated. The temperature is preferably 200 to 800°C, more preferably 250 to 550°C. If the degree of vacuum in the vacuum container is low, impurities will be mixed into the resulting ceramic coating and the hardness of the coating will decrease. 5×1
It is preferably 0-5 Torr or less. Note that the reaction pressure varies depending on the ion plating method used and the type of ceramic film to be formed, but if the reaction pressure is too high or too low, the ionization of the evaporated particles will be insufficient and the hardness of the ceramic film obtained will decrease. decreases, so
In the case of DC discharge method, 5 x 10-4 to 1 x 10-2 Tor
r is preferred, and in the case of RF method and AIP method, 1×10
-5 to 1 x 10-3 Torr is preferable, and in the case of the HCD method, 1 x 10-5 to 5 x 10-3 Torr is preferable. Within these reaction pressure ranges, a more preferable range of reaction pressure is determined as appropriate depending on the type of ceramic coating to be formed. For example, HCD method and A
5 for TiN coating or TiC coating by IP method
×10 −5 to 1×10 −3 Torr.

Furthermore, the DC voltage applied to the mold base material varies greatly depending on the ion plating method used and the type of ceramic coating to be formed, and the DC voltage applied to the mold base material may be too high or too low. However, since the hardness of the film obtained also decreases, the preferable range is appropriately determined depending on the ion plating method and the type of film. For example, TiN coating by HCD method or Ti
In the case of C coating, it is +10 to -300V, and in the case of TiN coating or TiC coating by AIP method, it is -20V.
It is 0 to -600V.

The vinyl chloride resin extrusion mold of the present invention can be obtained by the method described above, but in order to improve the adhesion between the obtained ceramic film and the mold base material, before forming the ceramic film, In advance, the surface of the mold base material on which the film is to be formed is cleaned with an organic solvent, and then bombarded with an inert gas such as Ar gas or metal ions such as Ti under reduced pressure to form the film on the mold base material. It is preferable to keep the surface clean.

As the vinyl chloride resin to be extruded using the vinyl chloride resin extrusion mold of the present invention, conventionally known resins used as extrusion molded products may be used. In addition to homopolymers, copolymers in which vinyl chloride and polymerizable monomers other than vinyl chloride are copolymerized, graft copolymers in which vinyl chloride is grafted onto polymers other than vinyl chloride, and the like can be used.

Examples of the polymerizable monomer include α-olefins such as ethylene, propylene and butylene, and vinyl esters such as vinyl acetate and vinyl propionate. These may be used alone or in combination of two or more.

Examples of polymers other than vinyl chloride include ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and the like.

[0021]

[Examples] Examples of the present invention will be described below.

Example 1 FIG. 1 is a schematic cross-sectional view of the center of the extrusion axis direction of a vinyl chloride resin pipe extrusion mold used in this example. In FIG. 1, 1 is the outer mold of the mold, 2 is the inner mold of the mold, and 3 is the contact surface with the molten vinyl chloride resin.

The outer mold 1 and inner mold 2 (the mold base material is S45C carbon steel) shown in FIG. ting device (manufactured by Nippon Vacuum Technology Co., Ltd., model: IP
B60/60), and a TiN film was formed on the contact surface 3 under the following film forming conditions.

(Film forming conditions) (1) Initial degree of vacuum: 1 x 10-5 Torr (2) Mold base material heating temperature: 500°C (3) Ar gas pressure during Ar bombardment: 0.1 Torr ( 4) Metal as evaporation source: Ti (purity 99.7%) (5) Reactive gas: N
2 gas (combined with Ar gas) (6) N2 gas pressure during film formation: 0.8 x 10-3 Torr (7) DC applied voltage to mold base material: -100V (8) Film formation time: 20 minutes

The thickness and surface hardness of the obtained TiN coating were evaluated based on the following evaluation criteria, and the results are shown in Table 1. (Evaluation criteria) Five test pieces of 50 x 50 x 2 mm made of the same material as the above mold were placed at approximately the same position as the surface on which the TiN coating was to be formed on the mold, and the TiN coating was formed at the same time as the mold. The TiN film formed on the mold base material was evaluated based on the film thickness and surface hardness of the evaluation sample measured by the following measurement method.

(Measurement method) (1) The film thickness evaluation sample was subjected to a fluorescent X-ray micro film thickness meter (manufactured by Seiko Electronics Co., Ltd., model: SFT-157), and one evaluation sample was measured at three locations (5 The film thickness was measured at 15 locations, and the average value and variation were calculated.

(2) Surface hardness evaluation The sample was subjected to a Vickers microhardness meter (manufactured by Akashi Seisakusho Co., Ltd., model: Microhardness Tester MVK-E),
The surface hardness of each evaluation sample was measured at three locations (5 locations, 15 locations), and the average value was calculated.

Next, the vinyl chloride resin pipe extrusion mold (inner mold and outer mold) on which the TiN coating was formed was set in an extruder (manufactured by Toshiba Machine Co., Ltd., model: TEM-50).
Melted vinyl chloride resin (polymerization degree 1000
), the vinyl chloride resin was allowed to stay in the mold for 20 minutes, the resin in the mold was extruded, and the mold was cooled. After disassembling the mold after cooling and buffing the surface of the mold base material on which the TiN film was formed, the condition of the surface of the mold base material on which the TiN film was formed was observed and evaluated based on the following evaluation criteria. Corrosion resistance was evaluated and the results are shown in Table 1.

(Evaluation criteria) ○: No corrosion on the mold base material surface △: Corrosion occurs in a part of the mold base material surface ×: Corrosion occurs on the entire surface of the mold base material

[0029] Further, the mold after the above corrosion resistance evaluation was set in the extruder (manufactured by Toshiba Machine Co., Ltd., model: TEM-50) again, and vinyl chloride resin (degree of polymerization 1000) was extruded at 180°C. The surface properties of the pipe molded products were evaluated based on the following evaluation criteria, and the results are shown in Table 1. (Evaluation criteria) ○: No scratches on the surface ×: There are scratches on the surface

Example 2 A mold on which a TiN film was formed was obtained in the same manner as in Example 1 except that the film forming time was changed to 50 minutes.

The film thickness, surface hardness, and corrosion resistance of the mold obtained, as well as the surface properties of the pipe molded product obtained using the mold, were evaluated in the same manner as in Example 1, and the results are shown in Table 1. .

Example 3 In Example 1, the reaction gas was changed to acetylene gas,
T was conducted in the same manner as in Example 1 except that the film formation time was 40 minutes.
A mold with an iC coating formed thereon was obtained.

The film thickness, surface hardness, and corrosion resistance of the mold obtained, as well as the surface properties of the pipe molded product obtained using the mold, were evaluated in the same manner as in Example 1, and the results are shown in Table 1. .

Example 4 In Example 1, A was used as the ion plating apparatus.
A mold on which a TiN film was formed was obtained in the same manner as in Example 1, except that an IP method ion plating apparatus (manufactured by Kobe Steel, model: AIP1000) was used and the film forming conditions were changed to the following conditions.

(Film forming conditions) (1) Initial degree of vacuum: 1×10 −5 Torr (2) Mold base material heating temperature: 500° C. (3) Ar gas pressure during Ar bombardment treatment: 0.1 Torr ( 4) Metal as evaporation source: Ti (purity 99.7%) (5) Reactive gas: N
2 gas (6) N2 gas pressure during film formation: 0.4×1
0-3 Torr (7) DC applied voltage to mold base material: -
500V (8) Film forming time: 30 minutes The film thickness, surface hardness, and corrosion resistance of the obtained mold and the surface properties of the pipe molded product obtained using the mold were evaluated in the same manner as in Example 1, The results are shown in Table 1.

Example 5 A mold on which a TiN film was formed was obtained in the same manner as in Example 4, except that the film forming time was changed to 60 minutes.

The film thickness, surface hardness, and corrosion resistance of the mold obtained, as well as the surface properties of the pipe molded product obtained using the mold, were evaluated in the same manner as in Example 1, and the results are shown in Table 1. .

Comparative Example 1 In Example 1, a vacuum evaporation device (manufactured by Showa Shinku Co., Ltd., model: SGC-22W) was used instead of the ion plating device.
A mold on which a TiN film was formed was obtained in the same manner as in Example 1 except that A) was used and the film forming conditions were changed to the following conditions.

(Film forming conditions) (1) Initial degree of vacuum: 1 x 10-5 Torr (2) Mold base material heating temperature: 500°C (3) Ar gas pressure during Ar bombardment treatment: 0.1 Torr ( 4) Metal as evaporation source: Ti (purity 99.7%) (5) Reactive gas: N
2 gas (6) N2 gas pressure during film formation: 0.4×1
0-3 Torr (7) Film forming time: 40 minutes The film thickness, surface hardness, and corrosion resistance of the mold obtained and the surface properties of the pipe molded product obtained using the mold were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 The mold used in Example 1 was plated with hard chromium to a thickness of 30 μm to obtain a mold with a hard chromium plating film formed thereon.

The corrosion resistance of the mold obtained and the surface properties of the pipe molded product obtained using the mold were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 3 The mold used in Example 1 was electroless nickel plated to a thickness of 20 μm to obtain a mold with a nickel plating film formed thereon.

The corrosion resistance of the obtained mold and the surface properties of the pipe molded product obtained using the mold were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0044]

[Table 1]

[0045]

Effects of the Invention The structure of the vinyl chloride resin extrusion mold of the present invention is as described above, and the ion plating method is used to coat a specific ceramic coating with at least the molten vinyl chloride resin of the mold base material. The vinyl chloride-based Resin extrusion molds can be buffed during maintenance to prevent scratches and corrosion caused by acid gas.

As a result, the surface of the vinyl chloride resin extrusion molded product obtained using the vinyl chloride resin extrusion mold does not suffer from appearance defects such as streaks or scratches even during long-term running. .

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the center of a mold for extrusion molding a vinyl chloride resin pipe in the extrusion axis direction.

[Explanation of symbols]

1. Outer mold of the mold 2 Inner mold of the mold

Claims (1)

[Claims] 1. A mold for extrusion molding a vinyl chloride resin, wherein a ceramic coating is formed by an ion plating method on at least the surface of the mold that comes into contact with the molten vinyl chloride resin. A mold for extrusion molding of vinyl chloride resin.