JPH082578B2 - Clean container and its molding method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clean chemical container made of a polymer and resistant to mechanical shock, and a method for molding the same.

[0002]

Polymers such as polyethylene have great resistance to chemicals, are excellent in swelling resistance, oxidation resistance and stress cracking resistance, are lightweight and relatively resistant to impact, and are widely used as various chemical containers. ing.

Polyethylene polymer molded containers are also used in the semiconductor field, for example. Particularly in the field of semiconductors, it is required that stored high-purity chemicals can be stored in high purity for a long period of time. For example, hydrogen fluoride water, ammonium fluoride water, sulfuric acid, hydrochloric acid, nitric acid, hydrogen peroxide water, ammonia water and the like are widely used for etching and cleaning semiconductor wafers, and high purity is required. Impure particulates should rarely leach into the stored chemicals from the resin forming the container during storage. If the amount of the impure fine particles in the chemical is large, the quality and the yield of semiconductors are significantly adversely affected.

As a container for high-purity chemicals capable of maintaining a high-purity state for a long time, the density is 0.940 to 0.970 g / cm ³ , the melt index showing the melt viscosity is 0.1 to 0.5 g / 10 minutes, and the cleanness is 300 pieces / High-density polyethylene containers of less than ml are known. The melt index is measured according to JIS K 6760, and the larger the molecular weight of the resin and the greater the fluidity, the larger the value.

The cleanliness is the degree to which the contents of a container are stored in a container for a long period of time, during which impure particles are leached from the resin forming the container into the contents, and the resin of the container impures the contents. Say. After a certain period of time, calculate and find out how many fine particles with a particle size of 0.3 μm or more exist in 1 ml of water stored in a resin container. Specifically, it is defined by the following equation.

[0006]

[Formula 1]

Where a is the volume of the container to be inspected.
b is the amount of ultrapure water sampled from the container to be inspected. Sampling water is collected as follows. Half of the volume, a / 2 (ml), of ultrapure water is put into a container to be inspected having a volume of aml, shaken for 15 seconds each time to be discharged, and the inside of the container is washed. After repeating washing by shaking 5 times, put a / 2 (ml) of ultrapure water into the a (ml) container again, leave it at room temperature for 1 week, shake it for another 15 seconds, and shake it in the container. Let water stand for 20 minutes. Sampling water is collected from the static water. C is a value obtained by counting fine particles having a particle diameter of 0.3 μm or more contained in the total amount of sampling water with a particle counter.

Among such high-density polyethylene containers, the density of the resin used to mold the container is 0.940.
When it is up to 0.970 g / cm ^3, it is preferable because it is relatively rigid and strong against impact. When the melt index is 0.1 to 0.5 g / 10 minutes, the extrusion moldability is good and the molding does not collapse.

Many attempts have been made so far in an attempt to reduce the number of fine particles that leach into the stored liquid during storage of chemicals. The leachable particulates are often the low molecular weight component of the resin forming the container. In order to reduce the amount of low-molecular-weight polyethylene from the molding resin as much as possible, a method of devising polymerization conditions or removing only low-molecular-weight polyethylene from the resin has been adopted.

Additives which may cause fine particles,
For example, measures have been taken to suppress the leaching of catalysts, neutralizing agents, stabilizers and the like. In addition, in order to maintain the cleanliness of the container, container manufacturers perform blow molding in a clean environment with few floating particles, and immediately after molding the container so that contaminants from the outside cannot be mixed in, the cap is closed immediately under a clean environment. It is packaged in a clean film and shipped to drug makers and semiconductor makers.

The demand for containers with less contamination of their contents is ever increasing. In addition to this, recently
International Standards for the Transport of Dangerous Goods and Drugs (United Nations, Recommendations on t
he Transport of DangerousGoods) has been set to a stricter level. Many of the chemicals used for etching or cleaning semiconductor wafers are chemicals of dangerous substances, and unless they are containers that pass the above standards or domestic voluntary regulation standards conforming to them (UN standard passing containers), etching or cleaning liquids, etc. It cannot be used as a storage container.

In order to be used as a storage container for etching or cleaning liquid, the container itself has a new IMDG code (International Maritime Dangerous) in view of swelling resistance to chemicals, oxidation resistance, stress cracking resistance and mechanical strength. Goods Code) Must pass the test criteria. At present, polyethylene containers that satisfy this condition have a weight average molecular weight of 200,000 or more, a density of 0.940 to 0.970 g / cm ³ , and a melt index of 0.
Only high density high molecular weight polyethylene container of less than 09g / 10 minutes. In the case of this kind of high-density high-molecular-weight polyethylene container, there is a problem that stored chemicals may be contaminated with fine particles and cannot be used as a storage and storage container for high-purity chemicals for semiconductors. Moreover, the melt index is small, and it is very difficult to mold the container at a high speed.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, in which the leaching of fine particle impurities into the stored chemicals is extremely small, and the chemical resistance is excellent. It is an object of the present invention to provide a clean container which has mechanical strength and can sufficiently meet the international standard for transportation of dangerous substances and chemicals, and to provide a method for forming a clean container capable of easily manufacturing such a clean container. And

[0014]

Means for Solving the Problems The clean container of the present invention made to achieve the above-mentioned object is a polymer (a) and a polymer (b) each of which is polyethylene or an ethylene / α-olefin copolymer. The polymer (a) having a weight average molecular weight of 200,000 or more, a density of 0.940 to 0.970 g / cm ³ , and a melt index of 0.09 g / 10 min or less based on JIS K6760 is ³⁰ % in the total weight. ~ 95% by weight, covering the outer surface substantially, having a weight average molecular weight of 30,000 or more and less than 200,000, a density of 0.930 to 0.970 g / cm ³ , and a melt index of 0.1 to 1.0 g / 10 based on the same JIS standards. Polymer (b) which is
Occupies 5 to 70% by weight and substantially covers the inner surface.

The method for molding a clean container according to the present invention uses a polymer (a) and a polymer (b), both of which are polyethylene or an ethylene / α-olefin copolymer, and has a weight average molecular weight of 20.
A polymer (a) having a density of 0.940 to 0.970 g / cm ³ , a melt index of 0.09 g / 10 min or less based on JIS K 6760, and a weight average molecular weight of 30,000 to less than 200,000 and a density of 0.93.
0 to 0.970 g / cm ³ , and the polymer (b) having a melt index of 0.1 to 1.0 g / 10 min based on the same JIS standard are mixed at a mixing ratio of 30 to 95% by weight of the polymer (a). Polymer (b) is 5
Mix to ~ 70 wt% and blow mold.

The polymer (a) and the polymer (b) are JI
It is more preferable that the ratio η (a) / η (b) with respect to the apparent viscosity η based on SK 7210, temperature 190 ° C., shear rate γ = 18 sec ⁻¹ is 1.3 or more.

Polymer (a) used in the present invention, polymer
Examples of (b) include ethylene homopolymers and copolymers of ethylene with other α-olefins.

The α-olefin copolymerizable with ethylene includes propylene, butene-1,4-methyl-pentene-1,
Examples include hexene-1 and octene-1.

The content of α-olefin in the copolymer is 15
It is preferably not more than wt%.

The molecular structure of the copolymer may be atactic, isotactic or syndiotactic. The polymerization method may be either a low pressure method or an intermediate pressure method. Further, as additives, if necessary, a catalyst, a neutralizing agent, a stabilizer and the like may be appropriately used in predetermined amounts.

The weight average molecular weight of the polymer (a) is 200,000 or more. The density is 0.940 to 0.970 g / cm ³ , and the melt index based on JIS K 6760 is 0.09 g / 10 minutes or less. The weight average molecular weight of the polymer (b) is 30,000 or more and less than 200,000. The density is 0.930 to 0.970 g / cm ³ , and the melt index based on JIS K6760 is 0.1 to 1.0 g / 10 minutes.

The cleanliness of the polymer (b) is less than 300 pieces / ml. The degree of cleanliness is obtained by first forming an inspection container, storing water in the formed inspection container for one week, and calculating how many trace particles with a particle size of 0.3 μm or more are present in 1 ml of the water. That is, half the volume of ultrapure water is put into the container to be inspected, shaken for 15 seconds each time to be discharged, and the inside of the container is washed. After repeating the washing with shaking 5 times, put half of the inner volume of ultrapure water into the container again and keep it at room temperature for 1 hour.
Leave it for a week, shake it for another 15 seconds, and allow the water in the shaken container to stand for 20 minutes. Sampling water is collected from the water that has been left standing for 20 minutes. Particle size included in sampling water 0.3 μ
Fine particles of m or more are counted by a particle counter, and the above numerical formula 1 is used to obtain the value.

The ratio of the apparent viscosity of the polymer (a) to the apparent viscosity of the polymer (b), η (a) / η (b), is preferably 1.3 or more. When it is 1.3 or more, it becomes easy to form a two-layer structure particularly in molding. The apparent viscosity is measured according to JIS K 7210 at a temperature of 190 ° C and a shear rate of γ = 18 sec ^-1 .

In the clean container of the present invention, the polymer (a) as described above accounts for 30 to 95% by weight of the total weight and substantially covers the outer surface, and the polymer (b) is 5 to 70% by weight. Occupy substantially the inner surface to cover the inner surface, so to speak, so to speak, a two-layer structure.

Such a clean container is formed, for example, by the following method.

The above polymer (a) and the polymer (b) are mixed. The mixing ratio is 30 to 95% by weight of the polymer (a), the polymer (b)
Is 5 to 70% by weight, preferably 40 to 90% by weight of the polymer (a) and 10 to 60% by weight of the polymer (b). Polymer
If the proportion of (b) is less than 5% by weight, a container obtained by molding cannot be provided with sufficient cleanliness, which is not preferable. If it exceeds 70% by weight, sufficient resistance to chemicals and mechanical strength cannot be obtained.

The method of mixing the polymer (a) and the polymer (b) is not particularly limited, and examples thereof include a method of dry blending pellets, a method of melt mixing and extruding, and a method of pelletizing.

The extruder used for melt extrusion molding may be an ordinary single-screw extruder, and any screw may be used as long as it gives an appropriate shearing force. However, it is not preferable to apply excessive shearing force.

The resin is melted by an extruder and extruded into a cylindrical parison, and the extruded parison is sandwiched between molds, blown with a pressurized gas from a blow pin, cooled, and molded.

[0030]

The function of the clean container of the present invention is polyethylene or an ethylene / α-olefin copolymer that exhibits chemical resistance.

The polymer (a) covers the outside to realize mechanical strength and physical strength, and the polymer (b) covers the inside,
Prevents fine particles from leaching into the container from (a).

In the method for molding a clean container of the present invention, the polymer (b) having a large melt index is easily melted,
The polymer (a) with a small melt index is difficult to melt, so the polymer (a) goes around the outer circumference and the polymer (b) goes around the inner circumference due to the difference in the flow method during blow molding, resulting in a two-layer structure. it is conceivable that.

In extruding resin and blow molding,
Polymers with a low melt index (a) generally have low extrudability, but polymers with a high melt index.
By being combined with (b) , the moldability is improved.

[0034]

Embodiments of the present invention will be described below.

Example 1 Pellets of polyethylene (a) having a weight average molecular weight of 250,000, a density of 0.956 g / cm ³ and a melt index of 0.02 g / 10 min were obtained. Weight average molecular weight 150,000, density 0.956g / cm
^3. Pellets of polyethylene (b) having a melt index of 0.17 g / 10 min were obtained. When a test container was molded with polyethylene (b), the cleanliness was 49 pieces / ml (Comparative Example 2). The apparent viscosity η was measured. Polyethylene (a)
Apparent viscosity η (a) of polyethylene and that of polyethylene (b) η
The ratio η (a) / η (b) with (b) was 2.1. Such polyethylene (a) and polyethylene (b)
Dry blending was carried out at a weight ratio of (a) / polyethylene (b) of 40/60. This mixed pellet is 75m / m, L / D = 24
It was melted at 200 ° C. in an extruder (D: screw diameter, L: effective screw length) and extruded into a cylindrical parison.
Insert the extruded parison with a mold and use the blow pin to
Compressed air of Kg / cm ² was blown and cooled with a mold cooled to 20 ° C. to form a square can container having a capacity of 20 liters and a weight of 1.7 Kg. It was found that the fluidity of the resin at the time of molding was good and that it could be molded at high speed.

The molded containers were inspected for cleanliness.

10 L of ultrapure water (trade name, Trepure LV-10T (manufactured by Toray Industries, Inc.)) was placed in a molding container having a capacity of 20 L, and washed by shaking for 15 seconds. Then, 10 liters of ultrapure water was similarly added, shaken and washed for 15 seconds each time and drained. Shaking wash was repeated 5 times. 5 ml was collected from the fifth wash water, and the number of fine particles of 0.3 μm or more leached therein was measured with a particle counter (type: KS-58 (manufactured by Lion Corporation)).

The number of fine particles in water (particles / ml) was calculated by the same formula 2 as the formula 1.

[0039]

[Formula 2]

The results are shown in Table 1.

[0041]

[Table 1]

10 liters of ultrapure water was placed again in the above container, shaken for 15 seconds, and allowed to stand at room temperature for 1 week. 1
Shake the water after a week for 15 seconds again,
Then, it was left still for another 20 minutes. From the water that has been left standing for 20 minutes
Collect 5 ml and in the same manner as above, the number of fine particles in water (pieces / ml)
Was calculated.

The results are shown in Table 1.

The number of fine particles in water after one week is 100
Below, it turned out to be extremely clean.

Three typical chemicals, namely kerosene (JI
SK 2203 No. 1), nitric acid (69 wt%), acetic acid (98 wt%) are sequentially filled in the above-mentioned container at a volume ratio of 98% or more.
Accelerated tempering was carried out at a temperature of 40 ° C. for 35 days, and a predetermined test was conducted according to the IMDG code test standard.

The results are shown in Table 2.

[0047]

[Table 2]

In Table 2, ∘ indicates pass, and x indicates disapproval.

Satisfactory results were obtained in all of the drop test, stacking test, airtight test and hydraulic test.

Examples 2, 3 The mixing ratio of polyethylene (a) and polyethylene (b) was 60 /
Same as Example 1 except 40 and 80/20.

Comparative Example 1 A rectangular can container having a capacity of 20 liters and a weight of 1.7 Kg was formed by using polyethylene (a) used in the examples alone, as in the case of the examples.

With respect to the obtained square can container, the same test as in the example was conducted.

The results are shown in Tables 1 and 2.

Satisfactory results were obtained in all of the drop test, the stacking test, the airtight test and the water pressure test, but it was found that a large amount of fine particles were leached in the stored water.

In molding, it was also found that the resin has a low fluidity compared to any of the examples and that extrusion molding is difficult.

Comparative Example 2 The procedure of Comparative Example 1 was repeated except that polyethylene (b) was used instead of polyethylene (a). The results are shown in Tables 1 and 2.

It has been found that the resin has good fluidity during molding and high-speed molding is possible. The number of fine particles in the water after one week was 100 or less, and it was also found to be extremely clean.

Satisfactory results were not obtained in any of the drop test, the stacking test, the airtight test and the water pressure test.

[0059]

As described above in detail, in the clean container of the present invention, the leaching of fine particle impurities into the stored chemicals is extremely small as in the conventional products, and further, the chemical resistance is excellent. It also has sufficient mechanical strength to meet the latest stringent international standards for dangerous goods and drug transport containers.

The method of manufacturing a clean container of the present invention can easily form such a clean container.

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Claims (2)

[Claims] 1. All of them are polyethylene or ethylene / α.
-Comprising the polymer (a) and the polymer (b) which are olefin copolymers, having a weight average molecular weight of 200,000 or more and a density of 0.940 to 0.9.
The polymer (a) having a melt index of 70 g / cm ³ and JIS K 6760 of 0.09 g / 10 min or less is 30% in the total weight.
Occupies ~ 95% by weight and substantially covers the outer surface, and has a weight average molecular weight of 30,000 or more and less than 200,000 and a density of 0.930 to 0.970 g / cm3.
³ , the melt index based on the same JIS standard is 0.1
A clean container characterized by having a structure in which the polymer (b) having an amount of 1.0 g / 10 min. Accounts for 5 to 70% by weight and substantially covers the inner surface. 2. All of them are polyethylene or ethylene / α.
-Polymer (a) and polymer (b) which are olefin copolymers
With a weight average molecular weight of 200,000 or more and a density of 0.940 to 0.970 g / cm
³ , 0.09g melt index based on JIS K 6760
Polymer (a) having a weight average molecular weight of 30,000 or more and less than 200,000, a density of 0.930 to 0.970 g / cm ³ , and a melt index of 0.1 to 1.0 g / 10 minutes based on the same JIS standard. Polymer (b) and, in a mixing ratio, the polymer (a) is 30 ~ 95
%, And the polymer (b) is mixed in an amount of 5 to 70% by weight, and the mixture is blow-molded.