JP2003206369A - Foam injection holding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foam injection molding mainly composed of a polyolefin resin and having dense, uniform, and minute expanded cells. <P>SOLUTION: This molding is manufactured by permeating 0.1-20 pts.wt. supercritical gas to 100 pts.wt. polyolefin molding material, then it is, while kept in the supercritical condition, injected and filled into a mold, then expanded by degassing. The polyolefin molding material comprises 100 pts.wt. resin component (A) comprising 50-99 wt.% polyolefin resin (a) and 50-1 wt.% thermoplastic elastomer (b) which is not completely compatible with the polyolefin resin, and 0-100 pts.wt. inorganic filler (B). The maximum diameter of the expanded cell of this foaming extrusion molding is not greater than 100 μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foam injection molded article. More specifically, the present invention relates to a foam injection-molded article having a dense and uniform fine foam cell mainly composed of a polyolefin resin.

[0002]

2. Description of the Related Art Polyolefin-based materials are lightweight and have relatively good mechanical properties, and are therefore widely used in various fields such as office automation equipment, electric / electronic equipment parts and automobile parts. In recent years, demands for further weight reduction and high physical properties have been increasing. By the way, in the field of thermoplastic resin foams, in addition to the conventional chemical foaming method and physical foaming method, a supercritical foaming method for producing a foam having fine cells with a high cell density by using a supercritical gas. Is being developed.

Although this method can suppress deterioration of physical properties as compared with a chemical foaming method using a chemical foaming agent, when it is applied to a polyolefin resin, supercritical carbon dioxide, nitrogen, etc. permeate the resin. Since it is difficult, it is difficult to obtain a foam having dense and fine foam cells, and there is a problem that the weight cannot be sufficiently reduced. On the other hand, a method has been proposed in which a supercritical gas is permeated into a resin composition containing a resin component composed mainly of a styrene resin and a polypropylene resin mixed therein, and then degassed to foam. JP-A-10-24476). However, in this method, although a foam having a dense and homogeneous foam cell can be obtained, since the resin composition mainly containing styrene resin is used, the obtained foam has mechanical properties and chemical resistance. It is inferior to the above, and it is unavoidable that its applications are limited.

Further, a supercritical gas is impregnated with a resin composition containing a resin component obtained by blending a crystalline thermoplastic resin such as a polypropylene resin with an amorphous thermoplastic resin such as a thermoplastic elastomer. After that, a method of releasing the supercritical gas-impregnated resin composition from a pressurized state and foaming it has been proposed (Japanese Patent Laid-Open No. 2001-40130). However, in this method, although a foam having a dense and homogeneous foam cell is obtained, first, after molding the resin composition, the molded body is impregnated with a supercritical gas, and then foamed, There are problems with productivity, variety of shapes, and dimensional stability.

[0005]

Under such circumstances, the present invention is mainly composed of a polyolefin resin and has fine and uniform fine foam cells, and has good mechanical properties, chemical resistance and dimensional stability. It is an object of the present invention to provide a foamed injection-molded article having, for example,

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a polyolefin resin is blended with a thermoplastic elastomer which is not completely compatible with it at a specific ratio. Thereby improving the melt tension of the polyolefin-based resin, and improving the affinity with carbon dioxide and nitrogen that are commonly used as supercritical gases, and a molding material containing the polyolefin-based resin and a thermoplastic elastomer. It has been found that a foam molded article obtained by injection foam molding using a supercritical gas can meet the purpose. Further, in this foam injection-molded article, a supercritical gas is allowed to permeate the molding material at a specific ratio, and this is injected and filled in a mold while maintaining the supercritical state, and then degassed to foam. According to the above, it was found that it can be obtained in an arbitrary shape with high productivity. The present invention is
It was completed based on this knowledge.

That is, in the present invention, (A) (a) 50 to 99% by weight of a polyolefin resin and (b) a thermoplastic elastomer 5 which is not completely compatible with the polyolefin resin 5
A resin component consisting of 0 to 1% by weight, and a polyolefin-based molding material containing 0 to 100 parts by weight of the inorganic filler (B) per 100 parts by weight, and having a maximum foam cell diameter of 100 μm or less. A characteristic foamed injection molded article is provided. The foamed injection-molded article was made to infiltrate 0.1 to 20 parts by weight of a supercritical gas into 100 parts by weight of the polyolefin-based molding material, and then injection-filled this into a mold while maintaining the supercritical state. After that,
It can be suitably manufactured by degassing and foaming.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The foamed injection-molded article of the present invention comprises:
(A) A foam molding comprising a polyolefin-based molding material containing (a) a polyolefin resin and (b) a thermoplastic elastomer resin component, and (B) an inorganic filler optionally used. In the polyolefin-based molding material (hereinafter, may be simply referred to as a molding material), the (a) component polyolefin-based resin used as the main component in the (A) resin component is not particularly limited and includes, for example, ethylene, Propylene, butene-1,3
-Α-olefin homopolymers such as methylbutene-1,3-methylpentene-1,4-methylpentene-1 and their copolymers, or between these and other copolymerizable unsaturated monomers Examples thereof include copolymers. Typical examples are high density, medium density, low density polyethylene and linear low density polyethylene, ultra high molecular weight polyethylene, polyethylenes such as ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, propylene alone. Polymers, polypropylenes such as propylene-ethylene block copolymers and random copolymers, propylene-ethylene-diene compound copolymers, polybutene-1, poly-4-
Methyl pentene-1 etc. can be mentioned.

Among the above polypropylenes, a crystalline polypropylene-based resin is preferable. Examples of the crystalline polypropylene-based resin include crystalline isotactic propylene homopolymer and propylene-containing a small amount of ethylene units. Ethylene random copolymer, a propylene block copolymer composed of a homo part consisting of a propylene homopolymer and a copolymer part consisting of an ethylene-propylene random copolymer having a relatively large content of ethylene units, and further A crystalline propylene-ethylene-α-olefin copolymer or the like in which each homo- or copolymerized part in the propylene block copolymer is further formed by copolymerizing an α-olefin such as butene-1.

Among these polyolefin resins,
Polyethylenes and polypropylenes are preferred. Further, a resin that is less likely to be compatible with the supercritical gas has a great effect of applying the present invention. Therefore, among polypropylenes, a propylene block copolymer or a propylene-ethylene random copolymer is preferable to a propylene homopolymer because a foamed molded product having dense and fine foam cells can be obtained. Further, the polyolefin resin used in the present invention has a melt flow index (MI) measured by standard loading conditions and methods of each resin of 0.1 to 200 g / 10 minutes, preferably 1 to 100 g /
Those in the range of 10 minutes are advantageous. The standard measurement conditions are those specified by ASTM. For example, in the case of polypropylenes, the temperature is 230
℃, load 21.17N, polyethylene 190 ℃, load 21.17N, other ASTM
The measurement is performed according to the measurement conditions defined in D1238. In the present invention, one type of the polyolefin resin as the component (a) may be used alone, or two or more types may be used in combination.

On the other hand, in the resin component (A), the thermoplastic elastomer of the component (b) used as another component is an elastomer which is not completely compatible with the polyolefin resin of the component (a). The material is not particularly limited, but a material that forms a sea-island structure when melt-kneaded with the polyolefin resin is preferable. When this thermoplastic elastomer is dispersed in sea islands, the dispersed elastomer becomes a kind of foaming core, and a fine and homogeneous foamed body is obtained. Further, since the melt tension is improved, the foamability is improved. Since the supercritical gas easily penetrates into the elastomer component from the polyolefin resin portion, the expansion ratio becomes high.

Examples of such thermoplastic elastomers include butadiene rubber, styrene-butadiene rubber, ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), hydrogenated styrene-butadiene copolymer elastomer (HSBR). ), Styrene- (ethylene / butylene) -ethylene block copolymer elastomer (SEBC), ethylene- (ethylene / butylene) -ethylene block copolymer elastomer (C
EBC), silicone rubber, fluororubber, ethylene-acrylic rubber and the like. Among these, hydrogenated styrene-butadiene copolymer elastomer, styrene- (ethylene / butylene) -ethylene block copolymer elastomer and ethylene- (ethylene / butylene) -ethylene block copolymer elastomer are particularly preferable.

In the present invention, the thermoplastic elastomer as the component (b) may be used alone or in combination of two or more. In the polyolefin-based molding material of the present invention, as the resin component of the component (A), the polyolefin-based resin 50 of the component (a) is used.
To 99% by weight and component (b) thermoplastic elastomer 50
-1% by weight is used. If the amount of the component (b) is less than 1% by weight, the effect of improving foaming properties and physical properties will not be sufficiently exhibited, and if it exceeds 50% by weight, the melt tension will be unnecessarily high and foaming will be difficult. A preferred blending ratio is 60 to 98% by weight of the component (a),
The component (b) is in the range of 40 to 2% by weight.

In the present invention, the molding material may optionally contain an inorganic filler as the component (B). Examples of this inorganic filler, talc, calcium carbonate, nano-dispersed layered silicate, clay, magnesium oxide, zinc oxide, glass powder, titanium oxide, carbon black, inorganic powder such as anhydrous silica, whiskers, glass fiber, Inorganic fibers such as carbon fibers and aramid fibers can be mentioned. Among these inorganic fillers, inorganic powders having an average particle diameter of 10 μm or less, plate-like materials such as talc having an average particle diameter of 10 μm or less, nano-dispersed layered silicate and clay are preferable, and talc is particularly preferable. is there.

In the present invention, one kind of the inorganic filler as the component (B) may be used alone, or two or more kinds thereof may be used in combination. Moreover, the compounding quantity is 0 to 1 with respect to 100 parts by weight of the resin component which is the component (A).
It is selected in the range of 00 parts by weight. If this amount exceeds 100 parts by weight, the effect of weight reduction due to foaming cannot be sufficiently exhibited. On the other hand, if the amount is too small, the effect of improving physical properties and the effect as a foam core cannot be expected. The preferable blending amount of the component (B) is 1 to 40 parts by weight, and the range of 2 to 25 parts by weight is particularly preferable.

The polyolefin-based molding material in the present invention is prepared by a conventionally known method, for example, the above-mentioned polyolefin-based resin, thermoplastic elastomer, and optionally an inorganic filler, further an antioxidant, a heat stabilizer, and an ultraviolet ray. Absorbents, light stabilizers, chlorine scavengers, flame retardants, flame retardant aids, lubricants, colorants, softeners, other thermoplastic resins and the like, and mixed with a tumbler blender, hexshell mixer, or the like, or After mixing, it can be further carried out by melt-kneading using a Banbury mixer, a single-screw extruder, a multi-screw extruder or the like.

The foamed injection-molded article of the present invention comprises the above-mentioned polyolefin-based molding material, and has a maximum foam cell diameter of 10.
It is a fine foamed molded product having a size of 0 μm or less. Here, the maximum foam cell diameter means the cross section of the foam molded article by a scanning electron microscope (S
EM) means the maximum diameter of a cell that can be seen in a cross-sectional photograph taken at 1000 times. If the maximum cell diameter exceeds 100 μm, the average cell diameter also becomes coarse, and the merit of the fine foam molded article that physical properties such as strength are less likely to deteriorate even if foamed may be impaired. When the maximum foamed cell diameter is 100 μm or less, the average cell diameter is often 30 μm or less, and since the average cell diameter is usually 15 μm or less, the above disadvantage does not occur. It should be noted that the reason why the maximum cell diameter is focused in the present invention is that the average cell diameter is difficult to calculate because the shape of the cells is not constant. In the case of the maximum cell diameter, if there is an SEM photograph, it can be immediately obtained using the scale shown with the cell image,
It's simple.

As a method for producing a foamed injection-molded article having such properties, a step of infiltrating a supercritical gas into the polyolefin-based molding material (a step of making them compatible) and a degassing of the gas-infiltrated molding material. The method is not particularly limited as long as it is a method having a step of
The methods described in US Pat. No. 73,665, US Pat. No. 5,158,986 and the like can be used,
A desired foamed injection-molded article can be efficiently produced by the method described below.

In a preferred manufacturing method, first, a supercritical gas is permeated into the above-mentioned polyolefin-based molding material. The gas used at this time is not particularly limited as long as it can be dissolved in the molding material and is inert, but from the viewpoint of safety and cost, carbon dioxide and / or
Or nitrogen is preferable. The critical gas is permeated and compatibilized in the range of 0.1 to 20 parts by weight, preferably 0.2 to 10 parts by weight, based on 100 parts by weight of the molding material.
If the amount of supercritical gas is less than 0.1 parts by weight, uniform foam cells will not be formed and the expansion ratio will not be so high. On the other hand, if it exceeds 20 parts by weight, the appearance of the surface of the foamed molded product will be poor, and it will be difficult to obtain a beautiful surface appearance, and coarse cells will be generated.

The supercritical gas is preferably permeated into a molten polyolefin-based molding material in a kneader,
Examples of the method include a method of injecting an inert gas in a gaseous state directly or in a pressurized or depressurized state, a method of injecting an inactive gas in a liquid state with a plunger pump or the like. When permeating the supercritical gas into the molding material, the gas pressure must be maintained above the critical pressure of the permeating gas, at least until the step of introducing into the mold is completed, and the permeation rate is further improved. For this purpose, the pressure is preferably 15 MPa or higher, particularly preferably 20 MPa or higher.

Next, the molding material thus impregnated with the supercritical gas is injected and filled into the mold while maintaining the supercritical state, and then degassed to foam. Before injection molding the molding material impregnated with supercritical gas into the mold,
If the supercritical state cannot be maintained, foaming will be difficult and silver will be generated. When a molding material impregnated with a supercritical gas is injected into a mold and the polyolefin resin in the molding material is a crystalline resin, the actual mold temperature is the crystallization temperature of the resin ± 20 ° C. When kept within a certain range at least until the degassing treatment is completed, the molding material impregnated with the supercritical gas transfers to the mold at a high transfer rate, and then a skin layer is formed sooner, so that the gas is on the surface of the molded body. A foamed injection-molded body having a maximum foamed cell diameter of 100 μm or less, which has high transferability, high gloss, and does not have an appearance defect such as silver generation without being retained on the mold cavity surface.

However, when the appearance is not a problem, even if the mold temperature is set from room temperature to less than [crystallization temperature-20] ° C, when the polyolefin-based molding material according to the present invention is used, coarse foaming occurs. There is an advantage that generation can be prevented and the molding cycle can be shortened. After filling the molding material impregnated with a supercritical gas into the mold, while at least a part of the molding material in the mold is in a molten state, the pressure in the mold is rapidly lowered, A large number of foam nuclei are generated, and the foam cells grow around them to obtain a high-transfer, high-gloss foam molding having uniform foam cells. As a method of rapidly lowering the pressure in the mold, (1) the mold clamping pressure is loosened, (2) the mold material before being filled with a molding material impregnated with a supercritical gas is -20 MPa is filled with an inert gas, the inert gas is removed immediately after the molding material is introduced, (3) the mold temperature is rapidly lowered, (4) the molding material in the mold is a metal mold. The surface layer in contact with the mold forms a skin layer, and some or all of the mold may be retracted while the inside is in a molten state.

Among these, the operation (4) is particularly preferable. In the operation of (4), by performing core back at the above timing, the average foam cell diameter tends to be slightly increased, but the distribution of the foam cell diameter is reduced, and particularly, in the vicinity of the gate and the end portion of the molded body. Variations in foam cell diameter are reduced. The rate of retracting the mold may be selected according to the required expansion ratio. The expansion ratio is usually about 1.1 to 3 times. A known injection molding or injection compression molding die unit can be used as the mechanism for retracting the die.

[0024]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. The foamed cell distribution and the foaming ratio of the foamed molded product obtained in each example were measured according to the methods described below to evaluate the foamed state.

(1) A SEM photograph of a cross section in the thickness direction of a foamed cell distribution molded body is taken, and the minimum foamed cell diameter (denoted as A) and the maximum foamed cell diameter (denoted as B) shown in the photograph are taken. It was designated as A to B to give the foamed cell distribution. (SEM magnification is 1000 times) (2) Foaming ratio (thickness of molded product after foaming-thickness of molded product before foaming) / thickness of molded product before foaming. However, the measurement site of the thickness is the same place. Further, in each example, a foam injection molded article was manufactured using the foam injection molded article manufacturing apparatus shown in the schematic configuration diagram of FIG. 1. In FIG. 1, reference numeral 1 is an injection molding machine with a supercritical gas injection mechanism (MuCell molding machine “J1” manufactured by JSW).
80ELIII-180H-MuCell "), 2
Is an OA housing mold having a 170 mm × 250 mm × 1.2 mm core back mechanism (not shown). 3 is a hopper, 4 and 4'is a gas cylinder, 5 is a booster, 6 and 6'is a pressure control valve, and 7 is an opening / closing valve.

Comparative Example 1 (1) Injection foam molding method 1 (without core back) Homopolypropylene [Idemitsu Petrochemical Co., Ltd. "Idemitsu Polypro J-3003GV", MI = 30 g / 10 min]
It is put into the injection molding machine 1 from the hopper 3. Resin temperature 2
While melting and kneading at 00 ° C, in the plasticizing region of the kneader,
Nitrogen discharged from the gas cylinder 4 is adiabatically compressed to 20 MPa by the pressure booster 5 to raise the temperature and pressure, and is blown in using the control valve 6, whereby the nitrogen gas is heated to about 200 ° C. and the homopolypropylene is supercritical. Permeated with nitrogen. The opening degree of the control valve 6 was adjusted so that the impregnated amount of nitrogen gas was 0.6 parts by weight with respect to 100 parts by weight of homopolypropylene.

The homopolypropylene impregnated with the supercritical gas in this manner was used at a resin temperature of 200 ° C. and a mold temperature of 4
Insulation-free mold 2 at 5 ° C (thickness 1.2 mm and 5M
Nitrogen gas of Pa is filled from the cylinder 4'through the control valve 6 '. A mold thickness equivalent to 1 mm was injected into the bracket) at a speed of 100 mm / sec. After the injection was completed, the nitrogen gas was removed and the pressure in the mold was reduced to cause foaming, whereby a foam injection-molded article having a foaming ratio of 1.2 times was obtained. Table 1 shows the evaluation results of the foamed state of this foamed molded product.

(2) Injection foam molding method 2 (with core back) The polypropylene used, the injection molding apparatus, and the method of permeating the polypropylene in the kneader with the supercritical gas are the same as those in (1) above. Homopolypropylene impregnated with supercritical gas is used at a resin temperature of 200 ° C and a mold temperature of 45 ° C.
It was injected into the heat-insulating non-mold 2 (1.2 mm thick) at a full shot at a speed of 100 mm / sec. No counter pressure was applied. One second after the completion of injection, the mold was retracted so that the cavity interval was 1.8 mm, whereby a foam injection-molded article having a foaming ratio of 1.5 times was obtained. Table 1 shows the evaluation results of the foamed state of this foamed molded product.

Examples 1 to 9 and Comparative Examples 2 to 5 In Comparative Example 1, instead of the homopolypropylene "Idemitsu Polypro J3003GV", a molding material consisting of a single polyolefin resin of the type shown in Table 1, or Table 1 was used. Except that a molding material containing the components in the types and amounts shown in was used,
The same operations as in (1) and (2) of Comparative Example 1 were performed to produce a foamed injection-molded article. Table 1 shows the evaluation results of the foaming state of each foamed molded product.

[0030]

[Table 1]

(Note) J-3003GV: "Idemitsu Polypro J-3003GV" manufactured by Idemitsu Petrochemical Co., Ltd., homopolypropylene, MI = 3
0-30 minutes J-3054H: "Idemitsu Polychemical J-3054H" manufactured by Idemitsu Petrochemical Co., Ltd., block polypropylene, MI = 3
0g / 10min 210J: “Idemitsu Polyethylene 210” manufactured by Idemitsu Petrochemical Co., Ltd.
J ”, high density polyethylene, MI = 5 g / 10 min, density 0.968 g / cm ³ HSBR:“ Dyalon 1320P ”manufactured by JSR, hydrogenated styrene-butadiene rubber SEBC:“ Dyalon 4600P ”manufactured by JSR, styrene- ( Ethylene / butylene) -ethylene block copolymer elastomer CEBC: "Dyaron 6200P" manufactured by JSR, ethylene- (ethylene / butylene) -ethylene block copolymer elastomer talc: JM209 manufactured by Asada Flour Mills, average particle size 4 µm

[0032]

[Table 2]

(Note) The molding conditions are a resin temperature of 200 ° C., a mold temperature of 45 ° C., an injection speed of 100 mm / min, and a nitrogen impregnation amount of 0.6% by weight based on a polyolefin molding material. First
As can be seen from the table, the foamed molded articles of Examples 1 to 9 all have a fine foamed cell structure having a maximum cell diameter of 50 μm or less and a narrow cell diameter distribution. On the other hand, the foamed molded articles of Comparative Examples 1 to 5 all had a maximum cell diameter of 30.
The cell diameter was as large as 0 μm or more and had a wide cell diameter distribution, and silver was remarkably generated.

That is, according to the present invention, it can be seen that a foamed injection-molded article having a fine and uniform foamed cell diameter of a level which has hitherto been difficult to achieve with a polyolefin-based molding material can be obtained. In particular, the foamed injection-molded article of the present invention has a difficulty in permeating the supercritical gas into the resin.
It can be preferably produced by a foam molding method in which the "degassing step" is continuously performed. In addition, although there is an example in which the distribution of the foam cells is slightly increased in the examples in which the core back is performed, it is relatively uniform and the expansion ratio can be further increased, so that the weight reduction effect is great.

[0035]

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a foamed injection-molded article having dense and uniform fine foam cells with high productivity by injection foam-molding using a polyolefin-based molding material and supercritical gas. You can This foam injection-molded article is used, for example, in the field of automobiles for exterior parts, interior parts,
It can be preferably used for parts in engine rooms, refrigerators, washing machines, various panels, built-in parts in the field of office automation equipment and home appliances, and various parts such as toilet units and bath units in the field of housing. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a foam injection-molded article manufacturing apparatus in Examples and Comparative Examples.

[Explanation of symbols]

1 injection molding machine 2 mold 3 hopper 4,4 'gas cylinder 5 booster 6,6 'pressure control valve 7 open / close valve

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C08L 101: 00) C08L 15:00 (C08L 23/00 53:00 15:00 B29K 105: 04 53:00 ) B29K 105: 04 F-term (reference) 4F074 AA13 AA16 AA17B AA24 AA26B AA32B AA97 AA98 AC00 AC36 AG01 BA33 CA26 CC04X CC10X DA02 DA03 DA35 DA45 DA47 4F206 AA03 AA45 AA47E AB11 AG20 J25 JN1 JN20 JN12 JN1 JNJ04 JFJJN J04 J04 JFJJN J04 JFJJN J04 J04 J27 JQJAR JJA JJNJ04 J26 JF4 J07 JQJARJ JN04 BB061 BB071 BB072 BB121 BB141 BB151 BB152 BB171 BD122 BP021 BP032 CL063 CP032 DA016 DA036 DE076 DE106 DE236 DJ006 DJ016 DJ036 DJ046 DL006 FA016 FA043 FA046 FA066 FD013 FD016 GC00 GL00 GN00 GQ00

Claims (3)

[Claims] 1. (A) (a) polyolefin resin 50
To 99% by weight and (b) 50 to 1% by weight of a thermoplastic elastomer not completely compatible with the polyolefin resin, and (B) 0 to 100 parts by weight of an inorganic filler per 100 parts by weight thereof. A foamed injection-molded article comprising a polyolefin-based molding material containing the same and having a maximum foam cell diameter of 100 μm or less. 2. The thermoplastic elastomer as the component (A) or (b) is a hydrogenated styrene-butadiene copolymer elastomer, a styrene- (ethylene / butylene) -ethylene block copolymer elastomer, or ethylene- (ethylene / butylene). -The foamed injection-molded article according to claim 1, which is at least one selected from ethylene block copolymer elastomers. 3. The inorganic filler as component (B) has an average particle size of 1
The foamed injection-molded article according to claim 1 or 2, which is talc having a size of 0 µm or less.