JP7332368B2 - Resin composition pellet and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a resin composition pellet and a method for producing the same, and more particularly to a resin composition pellet having improved transparency and suitable for use as a medical substrate such as a PTP packaging sheet, and a method for producing the same.

In recent years, as a package for medicines, etc., the contents such as medicines and food are stored in pockets made by thermoforming plastic sheets, and aluminum foil coated with adhesive is heated so as to seal the openings. Sealed press-through pack packaging (hereinafter sometimes referred to as "PTP packaging") is widely used. In a PTP package, the contents such as medicines and foods are taken out by pressing the pocket from the outside with a finger and breaking the foil with the contents.

A PTP packaging sheet used for PTP packaging is required to be transparent so that the state of the contents can be checked.

In the past, polyvinyl chloride resin was used as a material for PTP packaging sheets, but in recent years it has become difficult to use due to the environmental problem of generating harmful chlorine-containing substances when incinerated. . For this reason, polypropylene-based resins have begun to be used as materials to replace polyvinyl chloride resins.
A petroleum resin is added to the polypropylene resin sheet for PTP packaging for the purpose of improving transparency (Patent Documents 1 to 4).

JP-A-5-137776 JP-A-5-253288 JP-A-7-76641 JP-A-2003-41072

However, a resin composition obtained by adding a petroleum-based resin to a polypropylene-based resin has a problem that a product with insufficient transparency may be obtained depending on manufacturing conditions.
Furthermore, medical substrates such as polypropylene-based resin sheets for PTP packaging are required to have even greater transparency.
Accordingly, an object of the present invention is to provide a resin composition pellet that is excellent in transparency and suitable for use as a medical base material such as a polypropylene resin sheet for PTP packaging.
Another object of the present invention is to provide a method for stably producing the resin composition pellets having excellent transparency.

In order to solve the above-mentioned problems, the inventors of the present invention have conducted studies, and as a result, it is possible to provide a step of cooling the resin composition extruded from the nozzle of the extruder under specific conditions in the process of producing resin composition pellets. They found that it was effective, and completed the present invention. That is, the present invention
(1) A pellet made of a resin composition containing 50 to 99% by mass of a propylene-based polymer and 1 to 50% by mass of a petroleum resin, and having a whiteness Lc of 75 or less.
(2) The pellet according to (1), which has a pellet mass of 0.50 g/30 grains or less.
(3) Made of a resin composition containing 50% by mass or more and 99% by mass or less of a propylene-based polymer and 1% by mass or more and 50% by mass or less of a petroleum resin, having a whiteness Lc of 75 or less and a pellet mass of 0.5% by mass or less. A method for producing pellets of 50 g/30 grains or less,
After extruding a strand composed of the resin composition from a plurality of nozzles provided on the die of the extruder with an extrusion rate per nozzle (one hole) of 140 g / min or more and 280 g / min or less, the strand is heated to 5 ° C. or higher. A method for producing pellets, comprising a step of contacting a refrigerant of 30° C. or less for 6.00 m or more.

ADVANTAGE OF THE INVENTION According to this invention, it is excellent in transparency and can provide stably the resin composition pellet suitable for the use of medical substrates, such as a polypropylene-type resin sheet for PTP packaging.

Preferred embodiments of the present invention will be described below.
The pellets of the present invention are made of a resin composition containing 50% by mass or more and 99% by mass or less of a propylene polymer and 1% by mass or more and 50% by mass or less of a petroleum resin, and have a whiteness Lc of 75 or less. and preferably, the mass of the pellet is 0.50 g/30 grains or less.

The pellet has a whiteness Lc of 75 or less. When the whiteness Lc is 75 or less, a PTP sheet with excellent transparency can be obtained.
In the present invention, the whiteness Lc refers to a value determined by a spectrophotometer based on ASTM D2244, specifically a value measured by the method described in Examples.

The pellet preferably has a haze of 5% or less, more preferably 3% or less. When the haze is 3% or less, a sheet with excellent transparency can be obtained.
The haze is a value determined by the method for determining haze of plastic-transparent materials (JIS K 7136), and specifically, it is a value measured by the method described in Examples.

Although the propylene-based polymer used in the present invention is not particularly limited, it may be, for example, a homopolymer of propylene or a copolymer of propylene containing propylene as a main component and other monomer components, and preferable polypropylene. Examples of the base resin include homopolymers of propylene, random copolymers or block copolymers of propylene and ethylene, random copolymers or block copolymers of propylene and α-olefins such as butene, pentene, hexene and heptene. A propylene homopolymer or a propylene/α-olefin random copolymer is preferred from the viewpoint of compatibility with petroleum resins.

The α-olefin in the propylene/α-olefin random copolymer includes α-olefins having 2 to 8 carbon atoms, specifically α-olefins such as ethylene and butene, pentene, hexene, heptene, and octene. A copolymer consisting of

The propylene-based polymer preferably has a melting point of 150°C or higher and 170°C or lower.

The propylene-based polymer has a melt flow rate (MFR) at 190° C. and a load of 2,160 g (according to JIS K7120-1999). /10 minutes or less is preferable, and 1 g/10 minutes or more and 10 g/10 minutes or less is more preferable.

The propylene-based polymer is mainly composed of isotactic polypropylene obtained by using a stereoregular polymerization catalyst such as a Ziegler-Natta catalyst, and is homopolypropylene or a copolymer composed mainly of this. These are appropriately selected depending on the application.

A petroleum resin is used in the present invention. Petroleum resins include synthetic resin-based petroleum resins and natural product-based petroleum resins, and synthetic resin-based petroleum resins are preferred in the present invention.
Examples of synthetic resin petroleum resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, alicyclic saturated hydrocarbon resins, and copolymer petroleum resins. , alicyclic saturated hydrocarbon resin-based petroleum resins are preferred.

The petroleum resin preferably has a softening point of 100°C or higher and 150°C or lower.

The weight average molecular weight (Mw) of the petroleum resin is preferably 900 or less, more preferably 400 or more and 700 or less, from the viewpoint of compatibility with the polypropylene polymer. In addition, in this invention, a weight average molecular weight is a value calculated|required by a gel permeation chromatography (Gel Permeation Chromatography).

Typical commercial products of petroleum resins include Alcon (Arakawa Chemical) and T-REZ (JXTG Energy Co., Ltd.).

In the resin composition according to the present invention, the content of the propylene-based polymer is 50% by mass or more and 99% by mass or less, preferably 70% by mass or more and 85% by mass or less. The petroleum resin content is 1% by mass or more and 50% by mass or less, preferably 15% by mass or more and 30% by mass or less. In the present invention, the contents of the propylene-based polymer and the petroleum resin are within the above range, so that a material having excellent gas barrier properties and transparency can be obtained.

The resin composition pellets of the present invention may contain additives other than the propylene-based polymer and the petroleum resin as long as the effects of the present invention are not impaired.
Examples of additives include antioxidants, ultraviolet absorbers, light stabilizers, lubricants, antiblocking agents, antistatic agents, surfactants, dyes, pigments, retardants, and plasticizers.

Next, a preferred method for producing the resin composition pellets of the present invention described above will be described.
According to the study of the present inventors, in the production of resin composition pellets containing a propylene-based polymer and a petroleum resin, it was found that cloudy resin composition pellets were obtained.
In the resin composition pellet, the role of the petroleum resin is to constrain the molecular chains of polypropylene and reduce the degree of crystallinity. As a result, the transparency of polypropylene is improved. It has been found that the state of spherulites (crystals) differs between cloudy pellets and transparent pellets. Since the cloudy pellets and the transparent pellets should be different in (1) the element that grows the spherulites or (2) the structural element that becomes the crystal nucleus, after specifying the above (1) "element to crystallize", the crystal It was thought that it was necessary to take measures to prevent the generation and mixing of elements that cause crystallization in the first place, or to adjust the conditions and standards in anticipation of the generation and mixing of elements that cause crystallization. As a result of further studies, it has been found that the above (1) "factor for crystallization" is the separation of polypropylene and petroleum resin during the strand cooling process. In other words, it was found that when the polypropylene and the petroleum resin were separated during the strand cooling process, crystallization occurred and cloudy pellets were formed.
Within the extruder, the polypropylene and the petroleum resin are mutually dissolved due to shear flow, but once they are extruded from the extruder, the shear rate becomes zero from that moment, and the polypropylene and the petroleum resin begin to separate. be done.
Therefore, it was found that it is effective to rapidly lower the temperature of the pellets immediately after coming out of the extruder to prevent the separation of the polypropylene and the petroleum resin.
That is, the resin composition pellets of the present invention are extruded from a plurality of nozzles provided on a die of an extruder with an extrusion rate per nozzle (one hole) of 140 g / min or more and 280 g / min or less, and strands made of the resin composition After extruding, the strand is preferably produced by a production method comprising a step of contacting a refrigerant of 5 ° C. or higher and 30 ° C. or lower for 6.00 m or more. A specific description will be given below.

(Melting kneading process)
In the present invention, a propylene-based polymer and a petroleum resin are heated and melt-kneaded in a melt extruder. The melt extruder used for melt kneading should be capable of kneading the propylene polymer and petroleum resin in a molten state and extruding this kneaded product from a plurality of nozzles provided on the die at the tip of the melt extruder. There are no particular restrictions. For example, it may be either a single-screw or twin-screw melt extruder. Further, there are no particular restrictions on the configuration of the screw of the melt extruder, the number of revolutions, and the presence or absence of vents.
The temperature in the cylinder of the melt extruder during melt kneading may be any temperature at which the propylene-based polymer and the petroleum resin melt, but is preferably 180° C. or higher and 290° C. or lower, more preferably 200° C. or higher and 250° C. or lower. . When the content is at least the lower limit, it is possible to efficiently knead the propylene-based polymer and the petroleum resin. Moreover, when it is set to the upper limit or less, the propylene-based polymer and the petroleum resin can be melt-kneaded without being thermally decomposed.

(Molten strand forming step)
The kneaded product melt-kneaded in the melt-kneading step is continuously extruded from a plurality of nozzles provided on a die at the tip of the melt extruder to form a melt strand. The extrusion rate per nozzle (one hole) is 140 g/min or more and 280 g/min or less. If the extrusion rate per nozzle (one hole) is 140 g/min or more and 280 g/min or less, a sufficient cooling effect in the water cooling bath can be obtained, and separation of the polypropylene resin and the petroleum resin can be suppressed.
The outer diameter of the molten strand extruded from the nozzle is preferably 1 mm or more and 10 mm or less, more preferably 2 mm or more and 5 mm or less. If the molten strand has an outer diameter of 10 mm or less, a sufficient cooling effect can be obtained up to the center of the strand.

(Molten strand quenching process)
A molten strand extruded from a plurality of nozzles provided on the die is quenched. Separation of the polypropylene and the petroleum resin starts from the moment the molten strand is extruded from the nozzle. Therefore, in the present invention, by rapidly cooling the molten strand and fixing the structure before separation, the separation of the polypropylene and the petroleum resin can be suppressed and the clouding of the pellets can be prevented.
The means for rapidly cooling the molten strand is to contact a coolant of 5° C. or more and 30° C. or less for 6.00 m or more. If the temperature of the coolant is 5° C. or higher and 30° C. or lower, the strand can be rapidly cooled down to the central portion, and the separation of the polypropylene and the petroleum resin can be suppressed. Also, the molten strand and the coolant are in contact with each other over a distance of 6.00 m or more, preferably 8.00 m or more. By contacting for 6.00 m or longer, the polypropylene and the petroleum resin can be cooled before separation and the morphology can be fixed.
Moreover, the distance from the tip of the nozzle provided on the die to the contact of the molten strand with the quenching means is preferably 0.5 m or less, more preferably 0.3 m or less. Separation of the polypropylene and the petroleum resin can be suppressed if the distance from the tip of the nozzle to the quenching means is 0.5 m or less.
The resin temperature at the tip of the nozzle is preferably 190° C. or higher and 270° C. or lower, more preferably 205° C. or higher and 250° C. or lower. If the temperature of the resin at the tip of the nozzle is 270° C. or less, separation that occurs during cooling can be suppressed.
The cooling medium for the quenching means for the melted strands is not particularly limited as long as the temperature can be set within the range of 5°C or higher and 30°C or lower, but water is preferable from the viewpoints of cooling efficiency and economy.

(Fragmentation step)
The melted strand solidified by the melted strand quenching process described above is cut to the length of the desired polymer pellet, or the melted strand is crushed by a crusher to be fragmented. When the molten strand is cut, it is generally cut perpendicular to the length of the solidified molten strand. According to this method, it is possible to obtain pellets having a uniform length such as cylindrical or prismatic shape. The pellet length is appropriately selected depending on the use of the polymer pellet, etc., but it can be usually about 2 mm or more and 10 mm or less, preferably about 3 mm or more and 8 mm or less.

The device used for cutting the molten strand may be any device provided with a cutter for cutting the molten strand, such as a pelletizer that cuts the molten strand with a rotary blade and a fixed blade.

On the other hand, when the molten strand is crushed, it is possible to obtain particulate pellets having a desired average particle size. The average particle size of the granular polymer pellets obtained by crushing is preferably about 1 mm or more and 10 mm or less, more preferably 3 mm or more and 5 mm or less. The average particle diameter is defined as the median diameter when the cumulative distribution is determined using a sieving method conforming to JIS K0069.

Examples of crushers include shredders, jaw crushers, cone crushers, hammer crushers, roll crushers, roll mills, stamp mills, hammer mills, cutter mills, rod mills, cascade mills, speed mills, and oscillator-type granulators.

The resin composition pellets described above are particularly excellent in transparency, and are publicly used as medical substrates such as polypropylene-based resin sheets for PTP packaging.

(Example 1)
Raw material polypropylene F102P (propylene homopolymer, manufactured by Prime Polymer Co., Ltd., MFR 2 g / 10 min, melting point 162 ° C.) (hereinafter also referred to as "PP-1") 75 parts by mass and petroleum resin OP501 (manufactured by JXTG Nippon Oil & Energy Corporation , trade name T-REZ OP501, Mw 650) (hereinafter also referred to as “petroleum resin-1”) was put into a Henschel mixer and kneaded to obtain a mixture. The resulting mixture was put into a single-screw extruder (φ100 mm) (NVC100 manufactured by Nakatani Kikai Co., Ltd.) and melt-kneaded at a cylinder temperature of 200-210° C. and a screw rotation speed of 120-140 rpm. A strand composed of the resin composition was extruded from a plurality of nozzles (hole diameter φ3.5 mm) provided on a die at an extrusion rate of 150 g/min per nozzle (one hole). At this time, the temperature of the resin composition extruded from the nozzle was about 210°C. Next, the strand-shaped resin composition extruded from the die is cooled by contacting a refrigerant of 20 ° C. for 8.00 m, and then cut using a pelletizer to obtain a pellet-shaped polypropylene-petroleum resin composition 1. Ta. The mass of 30 pellets obtained was 0.45 g/30 pellets. The obtained pellets were evaluated as follows. Table 1 shows the results.
(Evaluation method)
・Whiteness Lc
The whiteness Lc of the obtained pellets was measured with a spectrophotometer according to ASTM D2244.
• Haze The obtained pellets were formed into a sheet having a thickness of 350 µm by a T-die extruder, and the total haze was measured with a haze meter (method for determining haze of transparent materials (JIS K 7136)).

(Example 2)
In Example 1, the cylinder temperature of the single-screw extruder was set to 260-270°C, and the temperature of the resin composition extruded from the nozzle was changed to about 240°C, in the same manner as in Example 1. , a polypropylene-petroleum resin composition 2 in the form of pellets was obtained. The mass of 30 pellets obtained was 0.45 g/30 pellets. The obtained pellets were evaluated in the same manner as in Example 1. Table 1 shows the results.

(Example 3)
In Example 1, from the plurality of nozzles provided on the die of the single-screw extruder, pelletized in the same manner as in Example 1, except that the extrusion rate per nozzle (one hole) was changed to 260 g / min. A polypropylene-petroleum resin composition 3 was obtained. The mass of 30 pellets obtained was 0.45 g/30 pellets. The obtained pellets were evaluated for whiteness Lc in the same manner as in Example 1. Table 1 shows the results.

(Comparative example 1)
In Example 1, pellet-like polypropylene-petroleum resin composition 4 was prepared in the same manner as in Example 1, except that the mass per 30 pellets obtained was changed to 0.65 g/30 pellets. Obtained. The obtained pellets were evaluated in the same manner as in Example 1. Table 1 shows the results.

(Comparative example 2)
In Example 1, pellet-shaped polypropylene-petroleum resin was prepared in the same manner as in Example 1, except that the strand-shaped resin composition extruded from the die was cooled by contacting a coolant of 10 ° C. for 4.00 m. Composition 4 was obtained. The mass of 30 pellets obtained was 0.45 g/30 pellets. The obtained pellets were evaluated in the same manner as in Example 1. Table 1 shows the results.

(Comparative Example 3)
A pellet-shaped polypropylene-petroleum resin composition 5 was obtained in the same manner as in Example 1, except that the strand-shaped resin composition extruded from the die was cooled with a 40° C. refrigerant. The mass of 30 pellets obtained was 0.45 g/30 pellets. The obtained pellets were evaluated for whiteness Lc in the same manner as in Example 1. Table 1 shows the results.

(Comparative Example 4)
A polypropylene-petroleum resin composition 6 in the form of pellets was obtained in the same manner as in Example 1, except that the extrusion rate per nozzle (one hole) was changed to 350 g/min. The mass of 30 pellets obtained was 0.45 g/30 pellets. The obtained pellets were evaluated for whiteness Lc in the same manner as in Example 1. Table 1 shows the results.

Claims (2)

A resin composition containing 50% by mass or more and 99% by mass or less of a propylene polymer and 1% by mass or more and 50% by mass or less of a petroleum resin, and has a whiteness Lc of 75 as determined by a spectrophotometer based on ASTM D2244. and

Pellets having a pellet mass of 0.50 g/30 grains or less . A resin composition containing 50% by mass or more and 99% by mass or less of a propylene polymer and 1% by mass or more and 50% by mass or less of a petroleum resin, and has a whiteness Lc of 75 as determined by a spectrophotometer based on ASTM D2244. A method for producing pellets having a pellet mass of 0.50 g/30 grains or less,

After extruding a strand composed of the resin composition from a plurality of nozzles provided on the die of the extruder with an extrusion rate per nozzle (one hole) of 140 g / min or more and 280 g / min or less, the strand is heated to 5 ° C. or higher. A step of contacting a refrigerant of 30 ° C or less for 6.00 m or more ,
The outer diameter of the strand extruded from the tip of the nozzle is 1 mm or more and 10 mm or less,
The method for producing pellets , wherein the distance until the strand extruded from the tip of the nozzle comes into contact with the refrigerant is 0.5 m or less .