JPH1071637A - Apparatus for melt molding of chlorine type resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the pyrolysis of a resin effectively to a degree eliminating the adverse effect on a product and to facilitate machine work by constituting one of structural members coming into contact with a molten resin of surface modified stainless steel receiving surface cleaning treatment and heat treatment in an oxidative atmosphere. SOLUTION: Base material stainless steel is subjected to surface cleaning treatment by mechanical or electrolytic polishing and further subjected to heat treatment in an oxidative atmosphere such as atmospheric non-dehydrated steam to form an oxide film layer. In one example of an inflation molding extruder, a barrel 2 heated by a heater 1 and the screw 3 inserted into the barrel are provided. A chlorine type resin introduced in a powdery or pellet like form from a hopper 4 is sent to the right by the screw 3 rotationally driven by a left drive part 5 and receives melting and kneading treatment in the process passing through the barrel 2 heated by a heater 1 to be formed into a molten resin stream 6 which is, in turn, downwardly extruded through a flange 7 and a die 8 to be formed into a parison 6a and this parison is subjected to inflation treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vinyl chloride resin,
The present invention relates to a melt-forming apparatus for chlorine-based resin such as vinylidene chloride resin, and more particularly to a melt-forming apparatus for suppressing thermal decomposition of chlorine-based resin.

[0002]

2. Description of the Related Art Similar to other thermoplastic resins, chlorine-based resins such as vinyl chloride resin and vinylidene chloride resin also form polymerization products into pellets suitable for secondary molding such as injection molding. To form a composition alone or with a colorant, a heat stabilizer, an antioxidant, an ultraviolet absorber, a plasticizer, and the like.
The treatment is performed using a melt-kneading device such as a single-screw or twin-screw extruder or a kneader. Further, the chlorine-based resin after the melt-kneading treatment is further subjected to secondary melt molding such as injection molding and blow molding.

Here, as a problem in melt-forming a chlorine-based resin, a chlorine-based resin generally has poor thermal stability, and active chlorine generated by thermal decomposition reacts with the surface of a melt-forming apparatus to generate heat. Surface conditions that promote decomposition tend to be created. This tendency is remarkable especially in a vinylidene chloride resin in which the thermal decomposition temperature and the melt-kneading temperature are close to each other. Then, once the thermal decomposition occurs, a product defect such as a mixture of the thermal decomposition product in the product or a resin appearance in the melting flow path resulting in poor appearance is caused. In particular, in the extrusion process of vinylidene chloride resin, a film of a thermal decomposition product of vinylidene chloride resin is formed on a metal member surface of the extruder,
There is a problem in that this peels off intermittently and mixes into the product, causing a product defect.

[0004] For example, in vinylidene chloride resin, in order to avoid the above-mentioned thermal decomposition during melt molding, the degree of polymerization is reduced or additives are increased to generate heat of the resin during melt molding (in particular, melt kneading). Attempts have also been made to suppress However, the vinylidene chloride resin having a decreased degree of polymerization also has a reduced strength, and is easily broken when applying tension to the film for elongating the film wrinkles during packaging, which deteriorates the suitability of the packaging machine, and also reduces the cold resistance. . In addition, an increase in the amount of the additive leads to a decrease in the gas barrier property, which is a main characteristic of vinylidene chloride resin.

In order to systematically suppress the thermal decomposition of chlorine-based resin in a melt-forming apparatus such as the above-described extruder, for example, in an extruder, a metal member such as a screw or a die that comes into contact with the chlorine-based resin to be melt-formed. A method of plating the surface with chromium, a method of coating with a heat-resistant release resin such as Teflon, and a method of forming these metal members with a nickel alloy have also been proposed. Each of these methods exerts a certain effect from the viewpoint of suppressing the thermal decomposition of the chlorine-based resin, but has a problem and cannot be a versatile solution. For example, chrome-plated members are unlikely to cause thermal decomposition of chlorine-based resin,
For example, due to the stagnation of resin on the structure of the device,
Once the thermal decomposition of the chlorine-based resin is generated, the effect of suppressing the thermal decomposition is almost lost, and there is a problem that it is difficult to continue the production. Although the nickel-plated member is not as large as the chrome-plated member, the same problem still occurs.

Although the use of a Teflon-coated member is extremely effective in suppressing the thermal decomposition of a chlorine-based resin, it is not practical for moving parts and members that have a strong frictional force due to severe wear.

Further, the use of a nickel alloy member has disadvantages in that it is difficult to perform cutting work because of the high hardness of the alloy and that it is difficult to obtain dimensional accuracy, and there is a problem in general use because the material cost of the alloy is high.

[0008]

SUMMARY OF THE INVENTION Accordingly, a main object of the present invention is to effectively suppress the thermal decomposition of a chlorine-based resin so as not to adversely affect the product and to melt the chlorine-based resin easily machined. It is to provide a molding device.

[0009]

SUMMARY OF THE INVENTION The present inventors have tested various metallic materials in combination with various surface treatments for the above-mentioned purpose, and as a result, they have undergone a surface cleaning treatment and a heat treatment in an oxidizing atmosphere. The present inventors have found that stainless steel effectively suppresses the thermal decomposition of a chlorine-based resin, even if initially used, over time, and arrived at the present invention.

That is, in the chlorine-based resin melt-molding apparatus of the present invention, at least one of the structural members in contact with the chlorine-based resin to be melt-molded is subjected to a surface cleaning treatment and a heat treatment in an oxidizing atmosphere. It is characterized by being made of high quality stainless steel.

The above-mentioned cleaning treatment is preferably performed as an electropolishing treatment, and it is also preferable to dissolve and remove a part of the generated oxide film following the heat treatment in an oxidizing atmosphere. The surface-modified stainless steel that has been subjected to such a cleaning treatment and a heat treatment in an oxidizing atmosphere is itself known as a constituent material of a pure water treatment apparatus or the like that suppresses elution of iron ions (Japanese Patent Publication No. HEI 9-222). 2-1916). This suggests that the effect of suppressing the elution of iron ions from the surface-modified stainless steel also contributes to the effect of suppressing the thermal decomposition of the chlorine-based resin in the chlorine-based resin melt molding apparatus of the present invention. Probably, but details are unknown.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the surface-modified stainless steel used in the present invention is a known stainless steel in which elution of iron ions is suppressed (Japanese Patent Publication No. 2-1).
916) describes the outline of the manufacturing process as follows.

Austenitic stainless steel containing Fe as a base material, containing Cr for improving rust resistance, and further containing Ni is preferably used as the base material. Specific examples include SUS304, SU
S316, SUS317, SUS385, and the like.

The base stainless steel is preferably surface-treated through the following steps.

(1) Surface cleaning treatment Mechanical polishing (machine tool polishing, buff polishing) and / or electrolytic polishing (a substrate connected to an anode of a DC power supply is opposed to a cathode in an electrolytic solution, and a predetermined external current is applied. To remove fine irregularities on the surface of the base material and make the surface glossy). It is preferable to perform a cleaning process including electrolytic polishing.

If necessary, post-treatment such as pre-cleaning (high-pressure cleaning, ultrasonic cleaning) and ultra-pure water cleaning (high-temperature ultra-pure water cleaning, high-purity nitrogen gas cleaning) is performed.

(2) Heat treatment in an oxidizing atmosphere A heat treatment is performed at 350-700 ° C., for example, for about 10 minutes to 10 hours in an oxidizing atmosphere such as non-dewatered steam or water. A colored (gold) oxide film layer is formed to a certain degree.

It is believed that the colored oxide film layer formed in this manner or the chromium oxide layer thereunder suppresses the elution of Fe ions, and the present invention also contributes to the suppression of thermal decomposition of the chlorine-based resin by magnetic force. It is thought that it is doing.

(3) Removal of Surface Layer Next, part or all of the colored oxide film formed as described above is removed (dissolved) with an acid or the like to form a surface layer having an increased concentration of chromium oxide. Is effective at least in suppressing the initial thermal decomposition of the chlorine-based resin.

Further, the surface-modified stainless steel obtained as described above may be subjected to post-washing (acid solution washing,
Post-processing such as high-pressure ultrapure water cleaning, (high-temperature) ultrapure water cleaning, and drying (high-purity nitrogen gas drying) is performed.

In the melt-forming apparatus of the present invention, the surface-modified stainless steel obtained as described above is used to constitute at least one of the structural members in contact with the chlorine-based resin to be melt-formed. Examples of the melt molding apparatus include an extruder, a kneader, and an injection molding machine including an extruder, a blow molding machine, and the like. Preferred examples of the structural member made of surface-modified stainless steel include a screw of the extruder. , A barrel, a die, and a mold for injection molding. Among them, it is most preferable to configure an extruder barrel, a die, and a screw that come into direct contact with a chlorine-based resin that is melt-kneaded at a high temperature for a long time, particularly an extruder screw that is suitable for surface treatment after processing.

FIG. 1 is a schematic sectional view of an inflation molding extruder as a preferred example of a chlorine-based resin melt-molding apparatus of the present invention. The extruder includes a barrel 2 heated by a heater 1 and a screw 3 inserted through the barrel 2.
Having. The chlorine-based resin introduced in the form of powder or pellets from the hopper 4 is sent to the right by the screw 1 rotated and driven by the left driving unit 5, and passes through the barrel 2 heated by the heater 1. The molten resin is subjected to a melt-kneading process to form a molten resin flow 6, and is extruded downward through a flange 7 and a die 8 to form a parison 6a, which is further subjected to an inflation process.

According to the present invention, at least one of the (cylinder) barrel 2, screw 3 and die 7, preferably one of barrel 2 and screw 3, particularly preferably screw 3, is made of the above-mentioned surface-modified stainless steel. It is formed.

Examples of a chlorine-based resin suitable for molding using the apparatus of the present invention include a vinylidene chloride resin and a vinyl chloride resin.

The vinylidene chloride resin includes a homopolymer of vinylidene chloride and a copolymer of vinylidene chloride and at least one other monomer copolymerizable with vinylidene chloride. The amount of the other monomer in the copolymer is 40 to 2% by weight, and preferably 35 to 4% by weight in view of the balance between extrudability and gas barrier properties. Other monomers include vinyl chloride, vinyl acetate, vinyl propionate, alkyl acrylate, alkyl methacrylate, acrylic acid,
Includes methacrylic acid, itaconic acid, acrylonitrile, methacrylonitrile, acrylamide, vinyl alkyl ether, vinyl alkyl ketone, acrolein, allyl esters and ethers, butadiene, chloroprene. It may be a ternary, quaternary or higher copolymer. Preferably, vinyl chloride, an alkyl acrylate having an alkyl group having 1 to 12 carbon atoms and an alkyl methacrylate are used, and as the latter, methyl acrylate, ethyl acrylate and methyl methacrylate are particularly preferable.

A mixture of vinylidene chloride copolymers having different reduced viscosities may be used. Mixing of the vinylidene chloride copolymer having a small reduced viscosity is considered from the viewpoint of extrusion processability and cold resistance.
5% by weight is preferred.

The vinyl chloride resin is a copolymer of vinyl chloride resin or vinyl chloride with a copolymerizable monomer of not more than 30% by weight of vinyl bromide, vinylidene chloride, vinyl acetate, ethylene, acrylic acid, methacrylic acid and the like. Polymers or chlorinated vinyl chloride resins and mixtures thereof. The polymerization degree of the vinyl chloride resin is 500 to 3000. Usually, for rigid containers, sheets and films,
800, 800 to 1300 for pipes and irregular molding, and 700 to 2500 for soft sheets and films.

Examples of the chlorine-based resin include ethylene copolymers, that is, vinyl acetate, (meth) acrylic acid, its alkyl ester copolymer (particularly, alkyl ester having 1 to 4 carbon atoms), MBS resin, At least one selected from auxiliaries may be mixed.

The vinyl chloride resin is mixed with MBS resin (Kureha BTA, HIA, Paraloid KM series, etc., manufactured by Kureha Chemical Industry), chlorinated polyethylene, and the like. The addition amount for imparting the impact strength is about 2 to 20 parts by weight.

Processing aids, especially acrylic processing aids,
It is polymerized from a monomer containing at least 50% by weight of at least one ester of (meth) acrylic acid (for example, an alkyl group having 1 to 4 carbon atoms) and has a weight average molecular weight of at least 100,000. Typically, Rohm and Haas paraloid K-125 is mentioned.
Paraloid K-130, K-175 and the like. Also, an ethylene-vinyl acetate copolymer is preferably used.

The processing aid to be added to the vinylidene chloride copolymer is preferably 0.05 to 3 parts by weight per type. If the addition amount is too large, the motor load fluctuates and becomes unstable, and the extrusion processability such as increased adhesion and decomposition at the die outlet decreases. Conversely, if the mixing amount is too small, it becomes difficult to maintain the outflow of decomposition products, cold resistance and gas barrier properties. By adding an appropriate amount, it is possible to maintain a balance between extrudability, suitability for a packaging machine, and gas barrier properties as well as cold resistance.

The processing aid to be added to the vinyl chloride resin is preferably added in an amount of 0.05 to 5 parts by weight, so that the extrudability is improved.

As for the vinylidene chloride copolymer, the thermal decomposition of the vinylidene chloride copolymer and the extrusion temperature are close to each other, it is difficult to improve the thermal stability of the vinylidene chloride copolymer itself, and a method of suppressing the heat generation of the resin is often adopted. You. For example, it is conceivable to reduce the degree of polymerization or add more additives. The former is
The strength of the vinylidene chloride copolymer is weakened, and the vinylidene chloride copolymer is easily broken at the time of applying a film tension for elongating the film wrinkles during packaging, so that the suitability of the packaging machine is deteriorated and the cold resistance is also lowered. In the latter, the gas barrier properties are reduced. Extrudability is closely related to suitability for packaging machines. Large fluctuations in the extrusion motor load cause unevenness in the amount of extrusion, which in turn causes unevenness in the film thickness and changes the energy per unit thickness given to the film when sealing.If the film is too thin, the film will melt. As a result, a pinhole is broken, and if the film is too thick, a trouble occurs in which a seal cannot be formed. The outflow of the decomposition product sparks the seal electrode by the decomposition product, and the film is finely broken to form a pinhole.
Adhesion and decomposition of the die outlet causes minute unevenness in the width direction of the film thickness, which causes minute wrinkles of the film and causes a decrease in sealing failure and the like.

When the same copolymer component is used in a mixed system of a vinylidene chloride copolymer, it is easy to uniformly melt inside the extruder,
The generation of fish eyes generated by thermal decomposition, unmelting, and the like of the resin, which is not preferable in the quality of the formed film, is reduced.

The use of the extruding apparatus of the present invention, in which the metal material is surface-treated, can be effectively contributed to the improvement of the extrusion process of the vinylidene chloride copolymer.

The chlorine-based resin of the present invention contains known plasticizers, stabilizers, lubricants, antioxidants, surfactants, light stabilizers, pigments,
Additives such as fillers can be blended. Specifically, dioctyl phthalate, acetyl tributyl citrate, dibutyl sebacate, dioctyl sebacate, diisobutyl adipate, acetylated monoglyceride, adipic acid-based polyester (weight average molecular weight of 100
0-4000), epoxidized oils such as soybean oil, linseed oil and epoxy group-containing resins, magnesium hydroxide, magnesium oxide, calcium hydroxyphosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, primary phosphoric acid Inorganic bases such as sodium, stabilizers such as ethylenediaminetetraacetic acid salts, polyolefin oxides such as polyethylene oxide, paraffin wax, polyethylene wax, various waxes such as montanic acid ester wax, fatty acid esters such as glycerin monoester, fatty acid monoester and the like. Lubricants such as bisamide derivatives, triethylene glycol bis-3- (3-tert-butyl-4-
(Hydroxy-5-methylphenyl) propionate (for example, IRGANOX 245 manufactured by Ciba Geigy), octadecyl 3,5-ditert-butyl-4-hydroxyhydrocinnamate, various tocophenols of α, β, γ, and δ and mixtures thereof, butylhydroxyl Examples thereof include antioxidants such as toluene and antioxidants such as alkyl thiodipropionates having 12 to 18 carbon atoms in the alkyl group (e.g., dilauryl thiodipropionate and distearyl thiodipropionate). Surfactants such as sorbitan fatty acid ester type and polyoxyethylene sorbitan fatty acid ester type.

As particularly preferred examples of the vinylidene chloride copolymer, ethylenediaminetetraacetic acid or a salt thereof, at least one salt of a non-alkene weak acid (particularly, a phosphate or a derivative thereof) and, if necessary, triethylene glycol bis- 3- (3-tert-butyl-4-hydroxy-
5-methyl-phenyl) propionate, vitamin E,
Vinylidene chloride is polymerized in the presence of an auxiliary selected from the group of thiodipropionic acid alkyl esters. The preferred range of the addition amount is 0.0005 to 0.25 parts by weight of ethylenediaminetetraacetic acid or a salt thereof, 0.001 to 15 parts by weight of at least one salt of a non-alkene weak acid, and if necessary, triethylene glycol bis 0.0005 to 0.55 parts by weight of -3- (3-tert-butyl-4-hydroxy-5-methyl-phenyl) propionate, 0.0005 to 0.2 parts by weight of vitamin E, alkyl thiodipropionate of 0. Vinylidene chloride is polymerized in the presence of an auxiliary selected from the group of 0005 to 0.2 parts by weight. It is particularly effective for improving color tone.

[0038] Among the additives, the additives of the plasticizer and the stabilizer are 1 to 10 parts by weight, more preferably 2 to 6 parts by weight.
Some of these additives may be added during the polymerization or may be mixed in powder form. The additives are adsorbed or absorbed by the ethylene copolymer, MBS resin, and acrylic processing aid, and a good balance between extrudability and gas barrier properties can be obtained together with a synergistic effect of mixing with the vinylidene chloride copolymer. Additives other than plasticizers and stabilizers are used as needed.

Examples of the mixing device include known mixing devices such as a blade blender, a ribbon blender, and a Henschel mixer. Mixing can also be performed using a screw feeder or the like in an on-machine hopper device of an extruder.

The chlorine-based resin is supplied to the melt molding apparatus of the present invention in the form of powder or in the form of pellets.

For a chlorine-based resin, particularly a vinylidene chloride copolymer, it is effective to use a combination of extrusion processing methods in which an extruder is supplied to an extruder via a vacuum hopper, and the present invention suppresses thermal decomposition. , The color tone is improved.

A recycled resin may be contained in the chlorine-based resin. It is possible to mix and recycle pulverized chlorine resin. A new ethylene copolymer, that is, vinyl acetate, (meth) acrylic acid, an alkyl ester copolymer thereof (particularly, an alkyl ester having 1 to 4 carbon atoms) and an MBS resin polymer may be mixed, Specially, a recycled product of a multilayer film and a casing containing them may be mixed. Extrudability can be improved. In the case of a multilayer, a resin containing recycled material may be disposed as an independent layer. Since the apparatus of the present invention can suppress the occurrence of thermal decomposition and can effectively use recycled resin, the generation of environmentally harmful resin waste can be reduced.

The chlorine-based resin is melt-molded and stretched if necessary. Vinylidene chloride copolymer is used for film,
It is made into products such as casings and sheets. Vinyl chloride resin is made into products such as pipes, molds, containers, sheets, and films. Examples of the molding method include inflation molding using a circular die, T-die molding,
Extrusion molding methods such as blow molding and injection molding can be applied. Usually, a film obtained by stretching and orientation has heat shrinkability and is used as a retortable casing film. The heat shrinkage of the vinylidene chloride copolymer casing is usually about 30 to about 60% in both the vertical and horizontal directions (measured at 120 ° C.). The retort condition is about 120 ° C. (pressure 0.245 MPa). The thickness of the film and casing is preferably about 10 to about 30 as a single film.
It is about μm and is usually used as a double film.

The resulting film, casing, pipe, profile, container, and sheet may be a multilayer product of the same type of chlorine-based resin or another resin extrudable therefrom.

Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples.

[0046]

EXAMPLE A test piece of SUS316 stainless steel (50 m
mx50mmx45mmt) Comparative Examples 1 to 3 and Examples 1 to 6 were each subjected to the following surface treatments.
Two test pieces were prepared.

[0047] Comparative Example 1 buffing finish Comparative Example 2 buff polished + electropolished Example 1 buff polished + electropolished + oxidation treatment in an air atmosphere (formation of oxide coloring (Gold) coating) Example 2 Buffing finish + Electropolishing + Oxidation treatment in air atmosphere + Dissolution and removal (whitening) of oxidized colored film (gold) by acid Comparative example 3 Buffing finish + Chrome plating (10 μm) treatment Comparative example 4 Teflon separately A Teflon sheet test piece having a thickness of 2 mm was prepared to give thermal stability corresponding to the coating material.

COMPARATIVE EXAMPLE 5 A nickel alloy test piece of the same dimensions (50 mm × 50 mm × 4.5 mmt) (Ni> 93.00%, Al, S
(i, Fe: small amount) was prepared.

(Test 1) The test pieces of the above Examples and Comparative Examples were brought into contact with a vinylidene chloride resin under heat and pressure, and the degree of thermal decomposition of the vinylidene chloride resin was determined based on the degree of coloring.

The vinylidene chloride resin used was prepared by mixing 100 parts by weight of a vinylidene chloride / vinyl chloride (81/19 (charge ratio by weight)) copolymer (intrinsic viscosity: 0.063 g / 10 dl) with ethylene / vinyl acetate (75/25). (Weight ratio) The composition was obtained by adding 2.0 parts by weight of the copolymer, 3 parts by weight of DBS, and 2.0 parts by weight of epoxidized linseed oil.

First, each test piece was sufficiently heated (10 minutes) on a hot press heated to 180 ° C.
mm SUS plate, and then a Teflon frame plate (frame size 30 mm x 30 mm, thickness 0.5 mm) is placed on the test piece, and then about 1.2 g of the above vinylidene chloride resin is put into the frame portion. A laminate obtained by placing a Teflon plate having a thickness of 0.5 mm and a SUS plate having a thickness of 1 mm was sandwiched by a hot press, and was heated at 180 ° C. for 1 minute at a gauge pressure of 0 MPa and then at 9 MPa at a gauge pressure of 1 MPa. After pressurizing for 1 minute, it was taken out of the hot press and cooled for 1 minute at room temperature.

The vinylidene chloride resin sheet treated with the test piece under heat and pressure as described above was peeled off from the test piece,
A color difference meter (“CR-200” manufactured by Minolta Co., Ltd.) is used to visually determine the color and to show a yellow to light yellow color without discoloring to black or brownish brown by thermal decomposition. The thermal stability was numerically evaluated (a lower value in the range of approximately 5 to 30 indicates a lighter color and better thermal stability).

The results are summarized in Table 1 below.

[0054]

[Table 1]

The above results indicate that the surface-modified stainless steel of the present invention obtained by subjecting SUS316 material to buffing, electrolytic polishing, oxidation treatment, and removal of an oxide film,
This shows that the use of Cr plating, Teflon sheet, Ni alloy material, and the like is rather inferior to the effect of suppressing the thermal decomposition of the chlorine-based resin without showing any particular effect.

(Test 2) However, the present inventors
Empirically, the thermal changes of chlorinated resins, especially during extrusion,
It was recognized that the initial evaluation alone was inaccurate and that it was necessary to evaluate over time.

Therefore, the same treatment of contacting the vinylidene chloride resin, heating and pressurizing each test piece of Test 1 described above was performed twice (a total of three times including Test 1).
The results are shown in Table 2 below together with the results of the first test in Test 1 described above.

[0058]

[Table 2]

The results shown in Table 2 above show that the surface-modified stainless steel of the present invention (Examples 1 and 2) differs from the results of the first thermal stability test and shows that the thermal stability significantly improved in the repeated tests. Therefore, the Teflon sheet test showing remarkably good thermal stability as compared with the chromium plated test piece (Comparative Example 3) having deteriorated thermal stability in the repeated test, and having a problem in mechanical durability as a coating material. This shows that the same thermal stability as that of the test piece (Comparative Example 4) or the Ni alloy test piece having a problem in machining (Comparative Example 5) can be obtained.

(Test 3) On the basis of the results of the above Test 2, a screw 3 of a 25 mm diameter extruder (manufactured by Plastic Engineering Laboratory) having a sectional structure essentially as shown in FIG. SUS316 stainless steel only)
And Example 2 (SUS316 steel subjected to buffing + electrolytic polishing + oxidation heating + oxide film removal treatment), respectively, and is formed from Hastelloy (manufactured by Hitachi Metals, Ltd.), which has relatively good thermal decomposition resistance of chlorine-based resin. Two types of extruders were constructed in combination with the barrel thus obtained, and a continuous extrusion test of the vinylidene chloride resin used in Test 1 was performed.

The screw has 22 pitches (L / D = 2
2), CR = 3.5, pitch distribution is transport / compression / weighing =
6/12/4, combined with a 0.5 mm × 20 mm slit type die. The set temperatures are as follows: Cylinder 1 / Cylinder 2 / Cylinder 3 / Flange / Die = 115/155/175/165/160 ° C. As a result of a continuous extrusion operation at 25 rpm for 6 hours, coloring of the extruded resin was recognized in both cases. No run-off of the pyrolysis product occurred after 6 hours of operation.

The external sketches of the screws taken out of each extruder after the above operation are as shown in FIG. 2 (a) (screw of Comparative Example 1) and FIG. 2 (b) (screw of Example 2). While the screw of Example 1 formed a black film (indicated by cross wasp) due to remarkable thermal decomposition in about half of the tip (pitch 13 to 22),
It can be seen that the screw of Example 2 had only a brown pyrolysis film formed at the very tip, and the thermal decomposition of the vinylidene chloride resin was significantly suppressed. Empirically Comparative Example 1
When the operation is further continued, the thermal decomposition film as shown in (1) is peeled off and may be mixed into the product.

[0063]

In the above description, a vinylidene chloride resin having a particularly remarkable thermal decomposability has been mainly described as an example.
It can be easily understood that a similar effect can be obtained also with a vinyl chloride resin which also contains chlorine, forms similar chemical conditions under melt contact, and has thermal decomposability.

As described above, according to the present invention, a stainless steel which is easily machined is subjected to a surface treatment to effectively suppress the thermal decomposition of the chlorine-based resin. The present invention provides a chlorine-based resin melt-molding apparatus that effectively suppresses chlorination.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an extruder as a preferred example of a melt molding apparatus of the present invention.

FIGS. 2A and 2B are sketches showing the state of formation of a thermal decomposition film after continuous operation of extruder screws according to a comparative example and an example, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 Barrel (cylinder) 3 Screw 4 Hopper 5 Screw drive part 6 Molten resin flow (6a: parison) 7 Flange 8 Die

Claims (7)

[Claims] At least one of structural members in contact with a chlorine-based resin to be melt-molded is made of a surface-modified stainless steel that has been subjected to a surface cleaning treatment and a heat treatment in an oxidizing atmosphere. Resin melt molding equipment. 2. The apparatus according to claim 1, wherein a structural member made of surface-modified stainless steel further subjected to a surface melting treatment after a heat treatment in an oxidizing atmosphere is used. 3. The apparatus according to claim 1, which is an extruder. 4. The apparatus of claim 3 wherein said structural member is an extruder screw. 5. The apparatus according to claim 1, wherein the chlorine-based resin is a vinylidene chloride resin. 6. A method for melt-molding a chlorine-based resin using the apparatus according to claim 1. 7. A chlorine-based resin film or sheet produced by the method of claim 6.