JP4166315B2 - Pellets made of rubber-modified polystyrene resin and melt extrusion method using the same - Google Patents

Description

【００２８】
【効果】
本発明のペレットを用いることで、ゴム変性ポリスチレン系樹脂を溶融押出成形する際の目ヤニ発生を、従来のゴム変性ポリスチレン系樹脂ペレットに比べ、著しく抑えることができるため、従来以上に連続生産が可能になる。又、得られる成形品中の目ヤニによる汚染が少なくなるため連続生産が可能となる。
【図面の簡単な説明】
【図１】目ヤニ発生係数の測定に使用した押出機の概念図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel pellet made of a rubber-modified polystyrene resin and a melt extrusion method for suppressing the generation of eyes from the die lip of the used extruder when melt extrusion is performed using the pellet.
[0002]
[Prior art]
Rubber-modified polystyrene resin is excellent in extrusion moldability and injection moldability, is easy to perform secondary processing, and is one of the cheapest plastic materials, so it can be used in a wide range of applications such as home appliances, OA, and food packaging materials. in use. In particular, it has high rigidity, moisture absorption resistance, and cold resistance in addition to easy processability, and it is indispensable for food packaging applications (mainly extruded products) because it can produce very thin containers. It is a material.
[0003]
Rubber-modified polystyrene resins are mainly used as extruded products such as sheets and films. However, when continuous molding over a long period of time or molding at a relatively high resin temperature, pigments and other coloring fillers are blended. In the case of molding, for example, a deposit called “eyes” accumulates on the die lip of the extruder, and if the amount of the deposit is remarkably large, the product is contaminated. For this reason, it is necessary to frequently clean the die lip as a measure to prevent product contamination, and in some cases, it may be necessary to interrupt production. Become. It is unclear about the cause of the occurrence of eye burrs. However, it is empirically known that the amount of eye burrs generated is relatively small when a rubber-modified polystyrene resin material having a small amount of rubber is used. However, when the amount of rubber is greatly reduced, it is clear that the product strength is lowered, and there is a limitation in product design and application.
[0004]
[Problems to be solved by the invention]
In the present invention, even when a rubber-modified polystyrene-based resin with a large amount of rubber is continuously molded for a long time, molded at a high temperature, or added with a pigment, the molding is performed under conditions that are likely to cause eye strain. The present invention provides a pellet and a method for producing the same that can significantly suppress the occurrence of eye-cracking and prevent the production efficiency from decreasing and the generation of defective products.
[0005]
[Means for Solving the Problems]
As a result of intensive studies on the above problems, the present inventors have found that the moisture content is not more than a specific amount, or by using pellets made of rubber-modified polystyrene having a specific pellet size and a specific melt viscosity, Succeeded in suppressing the occurrence. The invention has been made based on such findings. That is, the present invention
(1) It is made of a rubber-modified polystyrene resin having a rubber-like substance content of 3 to 15% by weight, a resin temperature of 200 ° C., and a melt viscosity of 1000 to 1500 Pa · sec at a shear rate of 100 / sec, and the pellet particle size is Pellets that are 300-800 pieces / 10 g.
(2) The pellet of (1) obtained by drying for 0.5 to 4 hours with a hopper dryer maintained at 70 ° C. or higher and 95 ° C. or lower, and having a pellet moisture content of 150 ppm or less.
(3) When melt-extruding using pellets, the Dry-Hot or Wet-Hot eye crack generation coefficient represented by the formula ( 1 ) at the die lip of the following extruder is 0.5 mg / min · mm or less The pellet of (1) or (2).
Eye creep generation coefficient = M / 20T (mg / min · mm) ( 1 )
In the formula, T represents the extrusion time (minutes), and M represents the weight of the eyes (mg) collected with a 20 mm wide die lip collected by the following extruder.
(Extruder used for measurement of eye spear generation coefficient and its setting condition)
(I) Full flight screw 35mm diameter, screw L / D = 26, one pitch = 35mm, flight width 4 mm, the rotational speed 115 rpm, compression ratio 3.5, a feed / compression / metering = 305/410/250 mm ,
(ii) Die coat: Hanger die: Die width 300mm, lip opening 0.45mm, orifice 3.5, no mesh
(V) Hopper: Open system, no hopper dryer,
(iv) Heater set temperature: Die temperature 260 ° C, adapter 250 ° C, metering 230 ° C , Compression 210 ℃, feed part 190 ℃, resin temperature 250 ℃
(Pellet condition adjustment method)
(I) Dry-Hot: Put pellets in a paper bag and dry in a large dryer at 70 ° C. for 3 hours.
(ii) Wet-Hot: Pellets are put in a paper bag and conditioned for 12 hours or more in a large temperature and humidity chamber at 60 ° C. and a relative humidity of 80% .
(4) A melt-extrusion method for a rubber-modified polystyrene resin, wherein the resin temperature is 180 ° C. or higher when melt-extruding using the pellets according to any one of (1) to (3).
(5) The method for melt extrusion of a rubber-modified polystyrene resin according to (4), wherein an extruder having no degassing equipment is used.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
1. The pellet made of the rubber-modified polystyrene resin of the present invention The rubber-modified polystyrene resin used in the present invention is not particularly limited, and is a known method, for example, a styrene-dissolved rubber-like substance, a bulk polymerization method, a suspension polymerization method or a bulk- Examples thereof include those produced by a graft polymerization method such as a suspension two-stage polymerization method.
[0007]
The rubber content in the rubber-modified polystyrene resin is preferably 3 to 15% by weight, more preferably 5 to 15% by weight, and particularly preferably 6 to 15% by weight based on 100% by weight of the resin. If the rubber content is less than 3% by weight, the strength of the product after molding (impact resistance, etc.) may not be improved and the meaning of rubber modification may be lost. If it exceeds 15% by weight, the rigidity is insufficient and the production is also difficult. It can be difficult.
[0008]
The area average particle diameter of the rubber particles is preferably 0.5 to 5.0 μm, more preferably 2 to 4 μm.
If the area average particle size is less than 0.5μm, the strength of the product after molding (impact resistance, etc.) may not be improved and the meaning of rubber modification may be lost. May be inferior. The average rubber particle diameter can be variously adjusted according to the rotational speed of the stirrer, the amount of chain transfer agent used, and the reaction temperature.
[0009]
The melt viscosity is 1000-1500 Pa · sec under the conditions of 200 ° C. and a shear rate of 100 / sec. When the melt viscosity is less than 1000 Pa · sec, the possibility of generation of eyes is generally reduced, but since the viscosity is low, the extrusion stability is deteriorated, the product strength is lowered, and the product design and use are restricted. When it is larger than 1500 Pa · sec, the discharge amount at the time of melt extrusion becomes small and the productivity is lowered. In order to avoid a decrease in productivity, the extrusion temperature has to be raised, so that the eyes become prone to occur.
[0010]
Styrene monomers used when polymerizing the rubber-modified polystyrene resin of the present invention are styrene, o-methyl styrene, p-methyl styrene, m-methyl styrene, 2,4-dimethyl styrene, p-tert-butyl butyl. Examples thereof include α-alkyl-substituted styrene such as nuclear alkyl-substituted styrene such as styrene, α-methylstyrene, α-methyl-p-methylstyrene, and the like. Among these, styrene can be preferably used.
[0011]
Examples of the rubber-like substance include various conjugated diene compounds such as polybutadiene, styrene / butadiene copolymer, polyisoprene, and natural rubber. Among these, polybutadiene and styrene / butadiene copolymer can be preferably used.
The pellet of the present invention is obtained by pelletizing the above rubber-modified polystyrene resin so that the pellet moisture content is 150 ppm or less, or the pellet particle size is 300 to 800 pieces / 10 g, the pellet moisture content is 150 ppm or less, and A better product can be obtained by pelletizing so that the pellet particle size satisfies 300 to 800 pieces / 10 g.
[0012]
The pellet moisture content in the present application is a value representing the moisture adhering to the pellet as a ratio to the weight of the pellet itself.
The pellet water content is preferably 120 ppm or less, more preferably 100 ppm or less. When the pellet moisture content is more than 150 ppm, it may be difficult to suppress the generation of eyes, especially using an extruder that does not have equipment (such as a vent) for degassing moisture and volatile matter, It becomes even more difficult when extruding at resin temperature.
[0013]
Note that the pellet moisture content is preferably 150 ppm or less for the pellet itself supplied to the hopper, but even if the pellet moisture content exceeds 150 ppm, the moisture is removed in the hopper and If the moisture content is 150 ppm or less immediately before entering the cylinder of the machine, it is possible to suppress generation of eyes. The pellet particle size is preferably 400 to 700 pieces / 10 g. If the pellet particle size is out of the range of 300 to 800 pieces / 10g, it may be difficult to suppress the generation of eyes, especially using an extruder that does not have equipment (such as a vent) for degassing moisture and volatile matter. Thus, it becomes more difficult to extrude at a resin temperature of 200 ° C. or higher.
[0014]
In order to obtain pellets whose water content satisfies the requirements of the present invention, for example, the following method may be mentioned.
For example, the pellets may be dried with a hopper dryer maintained at 70 ° C. or higher and 95 ° C. or lower. The drying time is 0.5 to 4 hours, preferably 2 to 4 hours.
When the drying temperature is higher than 95 ° C, there is a risk that the pellets are fused with each other. When the drying temperature is lower than 70 ° C, the drying efficiency is deteriorated. If the drying time is shorter than 0.5 hour, the removal of water is insufficient, and if it exceeds 4 hours, the production efficiency is deteriorated.
[0015]
In addition to the hopper dryer described above, a vacuum hopper that evacuates the hopper may be used, or a dehumidified hopper dryer may be used by circulating dehumidified dry air.
Further, when the pellets are air-fed from the storage silo to the extruder through a hose or the like, it is more preferable to air-feed using dehumidified and / or heated dry air.
[0016]
Usually, water adhesion to the rubber-modified polystyrene resin occurs at a stage before being applied to the extruder, that is, at the pellet stage. Therefore, it is effective to keep the pellet water content at 150 ppm or less, preferably 100 ppm or less as in the present invention. However, when using an extruder with deaeration equipment, such as when the inside of the extruder is depressurized and / or there are multiple vents for degassing, Even if the amount of water exceeds 150 ppm, it may be possible to prevent eyes from being damaged.
[0017]
By using the pellets of the present invention, it is possible to remarkably suppress the occurrence of eye scum even when melt-extruding pellets such as rubber-modified polystyrene resins having a high rubber content that are likely to generate eye scum using an extruder without the above degassing equipment. .
The pellet particle size may be adjusted by a known method, for example, by extruding a resin from an extruder to produce a strand and cutting it into an appropriate length with a cutter. Therefore, since the hole diameter of the die of the extruder, the take-up speed of the strand, and the cutter speed mainly affect the pellet particle size, pellets having the pellet size of the present application can be obtained by appropriately adjusting them.
[0018]
The pellets according to the present invention are optionally filled with various known additives as long as the object of the present invention is not impaired, such as calcium carbonate, talc, mica, silica, asbestos, glass fiber, carbon fiber and metal whisker. Lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide, organic polysiloxane, mineral oil, or 2,6-di-t-butyl-4 -Methylphenol, stearyl-β- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, triethylene glycol-bis-3- (3-tert-butyl-4-hydroxy-5-methylphenyl) Hindered phenols such as propionate and tris (2,4-t- Butylphenyl) phosphite. Phosphorous antioxidants such as 4,4′-butylidenebis (3-methyl-6-tert-butylphenyl-di-tridecyl) phosphite, ultraviolet absorbers, flame retardants, antistatic agents, mold release agents, plasticizers, Dyes, pigments, other polymers, etc. can be added.
[0019]
2. The melt extrusion method of the present invention The melt extrusion method of the present invention is characterized in that the pellet is used for melt extrusion at a resin temperature of 180 ° C. or higher, preferably 180 to 280 ° C., more preferably 200 to 260 ° C.
When the resin temperature is higher than 280 ° C., it is difficult to suppress foaming due to moisture, and there is a risk that the spear will be easily generated. When the resin temperature is lower than 180 ° C., extrusion becomes difficult.
[0020]
3. Evaluation Method of Eye Dwarf Generation Prevention Performance In the present invention, the ease of generation of eye burrs is defined by the eye burrs generation coefficient of the following equation (1).
Eye creep generation coefficient = M / 20T (mg / mm · min.) (1)
T is the extrusion time (minutes), “20” is the width (mm) of the die lip part from which the spear was collected, and M is the weight (mg) of the spear sampled at the part in T minutes. Extrusion conditions and the like are as described in the examples.
Since the die lip portion where the eye sag is generated is irregular, the eye sag generation coefficient is calculated by collecting the eye scum from the site where the eye scum is most generated.
[0021]
The pellet of the present invention has 0.5 mg / mm · min. Or less, preferably 0.15 mg / mm · min. It is as follows.
[0022]
【Example】
1. Measurement method of eye sprout generation coefficient (1) Extruder used for measurement of eye sprout generation coefficient and its setting condition (1) Full flight screw 35 mm diameter, screw L / D = 26
1 pitch = 35 mm, flight width 4 mm, rotation speed 115 rpm,
Compression ratio 3.5
Feed / compression / metering = 305/410/250 mm
(2) Die coat hanger die, die width 300mm, lip opening 0.45mm,
Orifice 3.5, no mesh (3) Hopper open system, no hopper dryer.
(4) Heater set temperature Die temperature 260 ° C, Adapter 250 ° C, Metering 230 ° C
Compression 210 ° C, Feed section 190 ° C, Resin temperature 250 ° C
[0023]
(2) Condition adjustment method of pellets used for measurement (1) Dry-Hot: The pellets were put in a paper bag and dried in a large dryer at 70 ° C. for 3 hours.
(2) Wet-Hot: Pellets were put in a paper bag and conditioned for 12 hours or more in a large temperature and humidity chamber at 60 ° C. and a relative humidity of 80%.
[0024]
(3) The apparatus shown in FIG. 1 was assembled using the extruder described in the measurement operation (1) (hereinafter referred to as an extruder), and the purge of the extruder and the cleaning of the die lip were sufficiently performed before the measurement. The pellet to be measured was put into an extruder and continued to be extruded under the above-mentioned extrusion conditions for 60 minutes. The eye spear was scraped off from the site (width 20 mm) where die sprinkling was most frequent on the die lip, and the weight (Mmg) was measured. The eye crack generation coefficient was obtained from the above formula.
[0025]
2. Method for measuring melt viscosity: Measured with a Capillograph 1B manufactured by Toyo Seiki.
Resin temperature 200 ° C., shear rate 100 / sec.
3. Method for Measuring Moisture Content in Pellets Pellets collected from the hopper of the extruder were sealed in a glass container, and samples stored in a desiccator were measured by the Karl Fischer method.
[0026]
4). Examples 1 to 4 and Comparative Example 1
The rubber-modified polystyrene resin powder described in Table 1 was applied to a twin screw extruder, melt kneaded at a resin temperature of 250 ° C., extruded as a strand, cooled with water, and cut with a pelletizer to obtain pellets in Table 1.
After the state of the obtained rubber-modified polystyrene resin pellets was adjusted under the dry-hot or wet-hot conditioning conditions, the water content was measured and the eye dust generation coefficient was measured. The results are shown in Table 1.
[0027]
[Table 1]

[0028]
【effect】
By using the pellets of the present invention, it is possible to remarkably suppress the generation of eyes when melt-extrusion molding of rubber-modified polystyrene resin, compared to conventional rubber-modified polystyrene resin pellets, so continuous production is more than conventional. It becomes possible. In addition, continuous production is possible because there is less contamination from the eyes in the resulting molded product.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an extruder used for measurement of an eye crack generation coefficient.

Claims (5)

A pellet made of a rubber-modified polystyrene resin having a rubber-like substance content of 3 to 15% by weight, a resin temperature of 200 ° C., and a melt viscosity of 1000 to 1500 Pa · sec at a shear rate of 100 / sec. Pellet that is ˜800 / 10 g. The pellet according to claim 1, which is obtained by drying for 0.5 to 4 hours with a hopper dryer maintained at 70 ° C or higher and 95 ° C or lower, and has a pellet water content of 150 ppm or less. When melt-extruding using pellets, the dry-hot or wet-hot eye-gear generation coefficient represented by formula (1) is 0.5 mg / min · mm or less in the die lip of the following extruder: Item 3. The pellet according to Item 1 or 2.
Eye creep generation coefficient = M / 20T (mg / min · mm) (1)
In the formula, T represents the extrusion time (minutes), and M represents the weight of the eyes (mg) collected with a 20 mm wide die lip collected by the following extruder.
(Extruder used for measurement of eye spear generation coefficient and its setting condition)
(I) Full flight screw 35mm diameter, screw L / D = 26, one pitch = 35mm, flight width 4 mm, the rotational speed 115 rpm, compression ratio 3.5, a feed / compression / metering = 305/410/250 mm ,
(ii) Die: Coat hanger die: Die width 300mm, lip opening 0.45mm, orifice 3.5, no mesh
(iii) Hopper: Open system, no hopper dryer,
(iv) Heater set temperature: Die temperature 260 ° C, adapter 250 ° C, metering 230 ° C , Compression 210 ℃, feed part 190 ℃, resin temperature 250 ℃
(Pellet condition adjustment method)
(I) Dry-Hot: Put pellets in a paper bag and dry in a large dryer at 70 ° C. for 3 hours.
(ii) Wet-Hot: Pellets are put in a paper bag and conditioned for 12 hours or more in a large temperature and humidity chamber at 60 ° C. and a relative humidity of 80%. A melt extrusion method for a rubber-modified polystyrene-based resin, wherein the resin temperature is 180 ° C or higher when melt extrusion molding is performed using the pellets according to any one of claims 1 to 3. 5. The method for melt extrusion of a rubber-modified polystyrene resin according to claim 4, wherein an extruder having no degassing equipment is used.

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