JP2007031468A - Rotational molding powder composition and skin material - Google Patents

Abstract

Using a powder composition having a particle size of 1000 μm or more, which does not impose a production cost, a molded product having no pinholes and excellent surface properties and releasability is obtained by rotational molding.
SOLUTION: Polypropylene is added to a styrenic block copolymer to impart hardness. At this time, a high-flowing polypropylene that does not impair rotational moldability is used, and the compatibility between the styrenic block copolymer and polypropylene is further improved. In order to improve the above, an ethylene-ethylene-butylene-ethylene block copolymer is added.
[Selection figure] None

Description

  The present invention relates to a powder composition used for rotational molding and a skin material obtained by rotational molding of the powder composition.

BACKGROUND OF THE INVENTION
Rotational molding is a molding method useful for molding a skin material such as a toy ball. For example, since this type of skin material requires flexibility, it is a powder mainly composed of a thermoplastic elastomer. A body composition is used as the material.

[Conventional technology]
Conventionally, as this type of composition, a composition in which paraffin oil is blended as a softening agent in a styrene block copolymer (for example, Patent Document 1), and a composition in which a polypropylene homopolymer is blended in a styrene block copolymer ( For example, Patent Document 2), or a thermoplastic elastomer composition powder such as olefin-based or polyurethane-based elastomer (for example, Patent Document 3) is provided.

Japanese Patent No. 3335737 Japanese Patent No. 3000165 JP 2002-363417 A

In the above conventional formulation, a polypropylene homopolymer is added to the styrene block copolymer to adjust the hardness, but the styrene block copolymer and the polypropylene homopolymer are not sufficiently compatible, The melt of polypropylene homopolymer has poor fluidity, and the surface property of the molded product is poor when it is rotationally molded.
Furthermore, when rotational molding is performed using the powder composition having an average particle size of 1000 μm or more, it is difficult to obtain a molded product without a pinhole, and to obtain a molded product without a pinhole. If the average particle size is 500 μm or less, the cost for pulverization increases and the production volume also decreases, resulting in an increase in production cost.

As a means for solving the above-mentioned conventional problems, the present invention comprises a styrene block copolymer, an ethylene-ethylene-butylene-ethylene block copolymer, a polypropylene homopolymer, a high-fluidity polypropylene, and a softening agent. A powder composition for rotational molding is provided.
The average particle size of the powder composition is preferably 1000 μm or more, and it is desirable that an impact-resistant polystyrene and / or ethylene / α-octene copolymer is further added to the composition.
The molding powder composition is used for producing a skin material, particularly by rotational molding.

[Action]
The ethylene-ethylene-butylene-ethylene block copolymer acts as a compatibilizer between the styrenic block copolymer and polypropylene, and improves the impact resistance of the composition. Moreover, when a high flow polypropylene is added to a polypropylene homopolymer as polypropylene, the hardness of the composition can be increased without increasing the melt viscosity of the composition.
When the average particle size of the powder composition is 1000 μm or more, the average surface area of the powder is reduced without increasing the production cost, and the addition amount of an anti-blocking agent such as silica can be reduced. In the present invention, since the compatibility between the styrene block copolymer and the polypropylene is improved by the ethylene-ethylene / butylene-ethylene block copolymer, the rotational molding obtained can be obtained even when the particle size of the powder composition is 1000 μm or more. There is no pinhole on the product surface.
When impact-resistant polystyrene is added to the composition, the hardness of the molded product can be further increased without increasing the melt viscosity of the composition. In addition, the elongation of the composition can be improved by adding an ethylene-α-octene copolymer.

〔effect〕
If the composition of the present invention is rotationally molded, a molded product having a smooth surface and high hardness without a pinhole can be obtained.

Hereinafter, the present invention will be described in detail.
[Styrene block copolymer]
Examples of the styrene block copolymer used in the present invention include a styrene-butadiene-styrene block copolymer (SBS), a styrene-ethylene-butadiene block copolymer (SEBS), and a styrene-butylene-butylene-styrene block copolymer. Examples thereof include a polymer (SBBS), an epoxy group-containing SBS, an epoxy group-containing SEBS, an epoxy group-containing EEA, a carboxyl group-containing SBS, and a carboxyl group-containing SEBS.
Desirable as the styrenic block copolymer is a combined use of SEBS and SBBS. SEBS has good compatibility with polypropylene and gives a molded article favorable weather resistance, and SBBS is a molded article. Gives favorable paintability. The mixing ratio of the SEBS and SBBS is usually 90:10 to 70:30 mass ratio, desirably 85:15 to 75:25 mass ratio.

[Polypropylene (PP)]
In the present invention, polypropylene homopolymer and high flow polypropylene are used in combination as polypropylene. Polypropylene homopolymer has an MFR of 1 to 100 g / 10 min. However, a high flow polypropylene has an MFR of 1500 to 2000 g / 10 min, and the addition of the high flow polypropylene does not increase the melt viscosity of the composition. Hardness can be increased. However, when a high-fluidity polypropylene alone is used, it is difficult to impart high hardness to the molded article when a softening agent is added, so a polypropylene homopolymer is used in combination.

[Ethylene-ethylene-butylene-ethylene block copolymer (CEBC)]
CEBC is an elastomer obtained by polymerizing butadiene with a living catalyst and then hydrogenating and saturating the double bond of the butadiene moiety.
CEBC improves the compatibility of the styrenic block copolymer with polypropylene and improves the impact resistance of the composition.

[Softener]
In the present invention, a softening agent is added to adjust the hardness. As the softening agent used in the present invention, naphthenic hydrocarbons, paraffinic hydrocarbons, process oils, extenders, higher fatty acids, pine oil, etc. are used. It is desirable to use paraffinic hydrocarbons that perform.

[Impact-resistant polystyrene (HIPS)]
HIPS has improved impact resistance by mixing butadiene rubber, styrene graft butadiene rubber (PS-g-PBR), etc. with polystyrene. By adding HIPS to the composition of the present invention, HIPS The hardness of the molded product can be increased without impairing fluidity and without deteriorating physical properties such as impact resistance of the molded product.

[Ethylene-α-octene copolymer]
The ethylene-α-octene copolymer improves the extensibility of the composition of the present invention.

[Lubricant]
In order to impart releasability to the mold of the molded product in the composition of the present invention, it is desirable to add a lubricant to ensure the surface smoothness and antistatic property of the molded product. As the lubricant, a nonionic surfactant, erucic acid amide or the like is used.

[Other ingredients]
Other than the above components, for example, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, calcium sulfite, calcium phosphate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, magnesium oxide, titanium oxide, iron oxide, zinc oxide, alumina, silica , Diatomite, dolomite, gypsum, talc, clay, asbestos, mica, glass fiber, carbon fiber, calcium silicate, bennite, white carbon, carbon black, iron powder, aluminum powder, stone powder, blast furnace slag, fly ash, cement , Inorganic fillers such as zirconia powder, natural fibers such as cotton, hemp, bamboo fiber, palm fiber, wool, silk, polyamide fiber, polyester fiber, acrylic fiber, viscose fiber, acetate fiber, vinyl chloride fiber, vinylidene chloride fiber , Vinylon Organic synthetic fibers such as fibers, acetate fibers, asbestos fibers, glass fibers, carbon fibers, ceramic fibers, metal fibers, inorganic fibers such as whiskers, fillers such as organic fillers such as wood powder and palm powder, pigments and dyes, Antioxidants, antistatic agents, flame retardants, flame retardants, anti-aging agents, and ultraviolet absorbers may be added. These components may be added singly or in combination of two or more.

[Combination]
Desirable blend ratios of the above components are as follows.
Styrene block copolymer 100 parts by mass CEBC 25-45 〃
Polypropylene homopolymer 5-15 〃
High flow polypropylene 30-80 〃
Softener 110-170〃
HIPS 5-15 〃
Ethylene-α-octene copolymer 10-35〃
Lubricant (nonionic surfactant) 1-2
Lubricant (erucic acid amide) 1-1.5〃
When the amount of CEBC is less than 25 parts by mass in the above blending ratio, the surface property of the obtained molded product is deteriorated and the release property may be deteriorated. Further, when the amount of CEBC exceeds 45 parts by mass, there is a possibility that pinholes are generated on the surface of the obtained molded product. Further, when the amount of the high fluid polypropylene is less than 30 parts by mass, the hardness is low (A hardness 50 or less), and when the amount of the high fluid polypropylene exceeds 80 parts by mass, the surface property is deteriorated and the releasability is also deteriorated. There is a fear. Furthermore, when the addition amount of the softening agent exceeds 170 parts by mass, the hardness is lowered and the release property may be deteriorated.

[Powder composition]
The above components are mixed at the above blending ratio, heated and melt-kneaded by an extruder set at a cylinder temperature of about 160 to 180 ° C., extruded from a fine die, cut into water by a pelletizer, and a powder composition It becomes.
In the case of the present invention, since the average particle size of the powder composition is 1000 μm or more, there is no need to use an expensive pulverization method such as freeze pulverization, and the pelletizing method can be applied. Cost does not increase. As described above, even when the powder composition of the present invention has a thickness of 1000 μm or more, preferably 1200 μm or more, generation of pinholes on the surface of the molded product is prevented by the compatibilizing effect of CEBC as described above.
The average particle size was measured by measuring the particle size of 50 or more spherical powder compositions extracted indiscriminately using an optical microscope, and determining the average value. When the shape of the powder composition is cylindrical or elliptical, the lengths of the longest and shortest portions of the granules are measured, and the average value is taken as the average particle size.

[Post-processing]
In order for the powder composition to prevent blocking, inorganic fine powders such as silica fine powder and talc are adhered to the surface. A desirable inorganic fine powder is hydrophobic micronized silica.
In order to attach the inorganic fine powder to the surface of the powder composition, dry blending is performed with a super mixer or the like. The amount of the inorganic fine powder added is usually 0.3 to 0.5 parts by mass with respect to 100 parts by mass of the powder composition.

(Rotational molding)
In general, the rotational mold is made of aluminum or nickel, and a predetermined amount of the powder composition is filled into the mold at room temperature, and the mold filled with the powder composition is about 300 to 350. Place in a heating furnace maintained at ℃, and apply the biaxial rotation in the horizontal direction and the vertical direction to the mold in the heating furnace to adhere the powder composition filled in the mold to the inner wall of the mold The mixture is heated and melted and defoamed, and heated until the mold temperature reaches 240 to 280 ° C. Thereafter, the mold is cooled with water or air to cool the mold until the mold temperature reaches about 40 ° C., the rotation of the mold is stopped, the mold is opened, and the molded product is taken out.
The rotational speed of the mold in the rotational molding is usually 2 to 20 rpm.
Examples of the present invention will be described below.

[Examples 1 to 4, Comparative Examples 1 to 5]
The raw materials used in this example are shown in Table 1.

  Using the raw materials, powder composition samples of Examples 1 to 4 and Comparative Examples 1 to 5 were prepared according to the formulation shown in Table 2.

The physical properties of the above samples were measured by the following method. The results are shown in Table 2.
[Method for measuring physical properties]
1. Method of measuring A hardness The measurement of A hardness is based on JIS-K-6253A.
The test piece used was a stack of three 2000 μm thick sheets prepared by heat compression molding using the above samples.
2. Evaluation method of “paintability” Urethane paint was used as the paint. The test piece used was a 2000 μm thick sheet prepared by the “A hardness measurement method”.
The surface of the sheet was wiped with methanol, and then applied with a brush so that the thickness of the coating film was about 100 μm or less. At this time, pretreatment such as ozone treatment and plasma treatment was not performed.
Place a total of 100 10 × 10 grids at 1000 μm intervals with a cutter on the painted surface of the painted sheet, apply cellophane tape on it, peel it off perpendicularly to the painted surface, and paint Observed the state of the grid that remained on the surface,
○: not peeled ×: even one peeled ○ has good paintability. X evaluated that paintability was bad.
3. Evaluation method of “sheet preparation”, “presence / absence of pinhole”, “surface property”, “release property” “Sheet preparation” is performed, and evaluation is performed by checking the state of the molded product obtained there. I did it.
(1) “Production of sheet”
Each of the above powder composition samples was put into a plast mill, heated and kneaded at a heating medium oil temperature of 180 ° C. for about 10 minutes, and the resulting resin mass was heated and compressed using a press machine to form a sheet having a thickness of 2000 μm. Was made. The sheet is cut into about 10,000 μm × 10000 μm square (40 g), arranged evenly on an aluminum pad, put in an oven kept at about 250 ° C., and heated for 15 minutes in a bath. Thereafter, the aluminum pad was cooled to about 40 ° C. by water cooling.
(2) Evaluation method of “presence / absence of pinholes” The state of the surface of the sheet (molded product) obtained in “Preparation of sheet” (the surface in contact with the aluminum pad) was visually observed. Evaluation was performed according to the following criteria.
No: No pinholes can be seen (0)
Small: few pinholes (1-10)
Existence: Large incidence of pinholes (11 or more)
(3) “Surface property” evaluation method The surface state of the surface of the sheet (molded product) obtained in “Preparation of sheet” (the surface in contact with the aluminum pad) was visually observed. Evaluation was performed according to the following criteria.
○: Uniformly mixed.
X: White powder is raised.
(4) Evaluation method of “Releasability” The surface state of the released aluminum pad of the sheet (molded product) obtained in “Preparation of sheet” was visually observed. Evaluation was performed according to the following criteria.
○: No trace is left on the aluminum pad.
Δ: Resin marks remain on the aluminum pad but are easy to remove.
×: Resin marks remain on the aluminum pad and are difficult to remove.

  When Table 2 is examined, in Comparative Example 1 in which the addition amount of high-flow polypropylene is 30 parts by mass or less (15 parts by mass), the A hardness is 50 or less (40), and the addition amount of high-fluid polypropylene exceeds 80 parts by mass. (90 parts by mass) Comparative Example 2 has poor surface properties and poor releasability. In Comparative Example 3 in which the amount of CEBC added was 25 parts by mass or less (20 parts by mass), both surface properties and releasability deteriorated, and the amount of CEBC added exceeded 45 parts by mass (50 parts by mass). There is a pinhole. Further, in Comparative Example 5, the amount of the softener added exceeds 170 parts by mass (180 parts by mass), the A hardness is 50 or less (47), and the releasability is also poor.

  On the other hand, the samples of Examples 1 to 4 have high hardness, good paintability, surface property and releasability, and no pinholes.

Further, for the powder compositions of Examples 1 to 4, a skin material having a thickness of 3 mm was produced by the method described in [Rotational molding]. The temperature conditions are a heating furnace temperature of about 335 ° C. and a mold temperature of 260 ° C.
As a result of measuring the physical properties of the skin material by the same method, as shown in Table 2, there was no occurrence of pinholes, and both surface properties and releasability were good.

In the present invention, the production cost of the powder composition can be reduced, and a skin material free from pinholes, good in surface properties and releasability and sufficiently high in hardness can be obtained by rotational molding.

Claims (4)

  A powder composition for rotational molding comprising a styrenic block copolymer, an ethylene-ethylene-butylene-ethylene block copolymer, a polypropylene homopolymer, a high-flowing polypropylene, and a softening agent.   The powder composition for rotational molding according to claim 1, wherein the powder composition has an average particle size of 1000 μm or more.   The powder composition for rotational molding according to claim 1 or 2, wherein impact-resistant polystyrene and / or ethylene / α-octene copolymer is further added to the composition.   A skin material produced by rotationally molding the powder composition for rotational molding according to any one of claims 1 to 3.