JP3250769B2 - Polybutylene terephthalate resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polybutylene terephthalate resin composition containing a polybutylene terephthalate resin and a specific modified block copolymer as main components. The polybutylene terephthalate resin composition has excellent impact resistance and melt fluidity (moldability), and is useful as a material for electric / electronic parts, automobile parts, and the like.

[0002]

2. Description of the Related Art Polybutylene terephthalate resin is used in a wide range of fields such as electric / electronic parts and automobile parts by utilizing its excellent properties such as moldability, heat resistance, chemical resistance, and high elongation. ing. However, polybutylene terephthalate resin has a drawback of low impact strength, and improvement thereof is desired. As a method for improving the impact resistance of a polybutylene terephthalate-based resin, it has been proposed to mix an elastomer with the polybutylene terephthalate-based resin (for example, Japanese Patent Publication No. 46-5224, Japanese Patent Publication No. 46-5225, Kosho 46-522
No. 7, JP-B-46-32866, etc.).

[0003]

In the case where a resin composition is prepared by mixing different kinds of polymers, there are generally very few combinations having good compatibility. Even in the resin composition obtained by mixing the elastomer with the above polybutylene terephthalate resin, in many cases, non-uniformity due to poor compatibility,
Problems such as phase separation occur, and the fact is that the impact resistance of polybutylene terephthalate resin is not so much improved. An object of the present invention is to significantly improve the impact resistance deficient with polybutylene terephthalate-based resins and to improve the original excellent performance of polybutylene terephthalate-based resins such as melt fluidity (moldability) and elongation. An object of the present invention is to provide a polybutylene terephthalate-based resin composition held at a standard level.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have reached the present invention. That is, the present invention provides (1) a polycondensation reaction of a polybutylene terephthalate-based resin, which comprises a polymer block A composed of a monomer unit mainly composed of a vinyl aromatic compound unit and a monomer unit mainly composed of a conjugated diene unit, and The resin composition obtained by performing in the presence of a modified block copolymer comprising a hydrogenated polymer block B and having a hydroxyl group at a terminal, and (2) a polybutylene terephthalate-based resin are melted. It is a polybutylene terephthalate-based resin composition obtained by mixing.

In the present invention, polybutylene terephthalate resin (hereinafter referred to as "PBT resin") refers to an acid component mainly composed of terephthalic acid or an ester-forming derivative thereof (lower alkyl esters such as methyl ester and ethyl ester). And a polyester obtained by reacting a diol component mainly composed of 1,4-butanediol, and a typical example thereof is polybutylene terephthalate (hereinafter, referred to as “PBT”).

An acid component for producing a PBT resin is as follows:
It may consist solely of terephthalic acid or its ester-forming derivative, but may optionally contain small amounts (usually 20 mol% or less) of other acid components. Examples of such acid components that can be used in combination include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and bis (p-carboxyphenyl).
Aromatic dicarboxylic acids such as methane, anthracene dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, and dodecandioic acid; -Cyclohexanedicarboxylic acid,
Alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; ester-forming derivatives of these dicarboxylic acids (lower alkyl esters such as methyl ester and ethyl ester); These acid components may be used alone or in combination of two or more.

The diol component for producing the PBT resin may be composed of only 1,4-butanediol, but if necessary, a small amount (usually 20 mol% or less) of other diol components may be used. May be included. Examples of such diol components that can be used in combination include ethylene glycol, propylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, 1,5-
Aliphatic diols having 2 to 10 carbon atoms, such as pentanediol, cyclohexanedimethanol, and cyclohexanediol; polyalkylene glycols having a molecular weight of 6,000 or less, such as diethylene glycol, polyethylene glycol, polytrimethylene glycol, and polytetramethylene glycol, can be given. . These diol components which can be used in combination may be only one kind or two or more kinds.

Further, the PBT-based resin may contain a small amount of trifunctional or higher functional monomer components such as glycerin, trimethylolpropane, pentaerythritol, trimellitic acid, and pyromellitic acid, as long as the properties thereof are not significantly adversely affected. Good.

The modified block copolymer used in the present invention comprises a polymer block A composed mainly of a vinyl aromatic compound unit and a monomer block composed mainly of a conjugated diene unit, and comprises at least a part thereof. And a hydrogenated polymer block B at the molecular main chain terminal. The modified block copolymer contains at least one polymer block A and one polymer block B in its molecule, but preferably contains two or more polymer blocks A.

It is preferable that the vinyl aromatic compound unit is contained in a ratio of 10 to 90% by weight based on the weight of the block copolymer before hydrogenation. When the proportion of the vinyl aromatic compound unit is 10% by weight or more based on the weight of the block copolymer before hydrogenation, the heat resistance of the PBT-based resin composition of the present invention is good, while 90% If it is less than 10% by weight, the impact resistance of the composition is particularly good.
The ratio of the vinyl aromatic compound unit in the modified block copolymer was set at 20 based on the weight of the block copolymer before hydrogenation.
It is particularly preferred that the content is set to 70% by weight.

The degree of unsaturation in the polymer block B of the modified block copolymer is preferably 10% or less. When the polymer block B is hydrogenated to an unsaturation degree of 10% or less, the PBT-based resin composition and the molded article obtained therefrom can prevent the development of tackiness. And it is convenient in handling of the molded article.

As the modified block copolymer, for example,
What is shown by each following formula is mentioned. (XY) _k -OH (YX) ₁ -OH X- (YZ) _m -OH Y- (XY) _n -OH (in each formula, X and Z each represent a polymer block A. Y represents a polymer block B, k, l, m and n
Represents an integer of 1 or more, and OH represents a hydroxyl group. ) Polymer block A in modified block copolymer
And the number of repetitions k, l, m and n of the polymer block B are
Usually, it is preferably within the range of 1 to 5, respectively.

Particularly preferred as modified block copolymers are those of the formula XYZZOH, where X, Y, Z and O
H is as defined above. ) Is a modified triblock copolymer. When this modified triblock copolymer is used, the PBT resin composition of the present invention exhibits particularly excellent impact resistance.

The vinyl aromatic compound which gives the vinyl aromatic compound unit in the polymer block A is styrene;
α-methylstyrene; o-, m- or p-methylstyrene; 2,4-dimethylstyrene; vinylnaphthalene; vinylanthracene and the like, among which styrene and / or α-methylstyrene are preferred. The polymer block A may be composed of only one type of vinyl aromatic compound unit, or may be composed of two or more types of vinyl aromatic compound units.

The conjugated diene compound which gives a conjugated diene compound unit in the polymer block B includes isoprene, 1,3-butadiene, 2,3-dimethyl-1,3-
Examples thereof include butadiene, 1,3-pentadiene, and 1,3-hexadiene. Of these, 1,3-butadiene and / or isoprene are preferred. Polymer block B
May be composed of only one type of conjugated diene compound unit or may be composed of two or more types of conjugated diene compound units. When the polymer block B is composed of two or more types of conjugated diene compound units (for example, a butadiene unit and an isoprene unit), the arrangement of each unit is random, block, or tapered block. It may be.

The hydroxyl group of the modified block copolymer may be located at either the terminal of the polymer block A or the terminal of the polymer block B, but is located at the terminal of the polymer block A which is a hard block. Is preferred. The content of the terminal hydroxyl group of the modified block copolymer is, on average,
The number is preferably 0.5 or more per molecule.
More preferably, it is within the range of 7 to 2. Even if a block copolymer containing no terminal hydroxyl group is present in the polymerization reaction system of the PBT-based resin, the particle size of the block copolymer dispersed in the obtained resin composition is large, and as a result, A PBT resin composition having good impact properties cannot be obtained.

The number average molecular weight of the polymer block A is 500
It is preferably in the range of 0 to 50,000. The number average molecular weight of the polymer block B is preferably in the range of 10,000 to 100,000. Further, the number average molecular weight of the modified block copolymer is preferably in the range of 15,000 to 150,000. The modified block copolymer used may be only one kind, or two or more kinds.

The PBT resin composition of the present invention comprises (1) P
The polycondensation reaction of the BT-based resin is carried out by reacting a polymer block A comprising a monomer unit mainly comprising a vinyl aromatic compound unit and a polymer block B comprising a monomer unit mainly comprising a conjugated diene unit and being hydrogenated. And a resin composition (hereinafter referred to as "precursor resin composition") obtained by performing the reaction in the presence of a modified block copolymer having a hydroxyl group at a terminal and (2) a PBT-based resin under melting conditions. It is manufactured by doing. The precursor resin composition comprises PBT
It is produced by performing a polycondensation reaction to obtain a system resin under conditions such that the modified block copolymer is kneaded in the reaction system. That is, the precursor resin composition is produced by an arbitrary method similar to that in the synthesis of a general PBT-based resin except that a modified block copolymer is added. As a typical example of a method for synthesizing a PBT-based resin that can be employed, when the dicarboxylic acid component is a dicarboxylic acid such as terephthalic acid, an esterification reaction with glycol is performed, and when a dicarboxylic acid ester such as dimethyl terephthalate is used. Performs a transesterification reaction with glycol, and converts the product obtained by the esterification reaction or the transesterification reaction into
Next, a method of subjecting to a polycondensation reaction at a high temperature under reduced pressure may be mentioned. Here, the modified block copolymer is added at a time until the polycondensation reaction for producing the PBT-based resin is completed. The addition time of the modified block copolymer depends on the PBT
If it is time until the polycondensation reaction of the system resin is completed, without particular limitation, for example, before the esterification reaction, during the esterification reaction, before the transesterification reaction, during the transesterification reaction, before the polycondensation reaction, It may be at any time, such as during a polycondensation reaction. In the production of the precursor resin composition, the amount of the modified block copolymer to be added to the PBT resin synthesis reaction system is
PB in the case where the modified block copolymer is not added
The relative value to the theoretical amount of the T-based resin (the ratio of the theoretical amount of the PBT-based resin / the weight of the added amount of the modified block copolymer) is preferably in the range of 96/4 to 40/60, It is more preferable to be in the range of 95/5 to 60/40. If the amount of the modified block copolymer is too large, the resulting PBT-based resin composition may lose excellent properties such as heat resistance, moldability, and high elongation inherent in the PBT-based resin. If the amount is too small, the improvement in impact resistance may be insufficient.

The above-mentioned precursor resin composition has a constitution in which fine particles mainly composed of a modified block copolymer are dispersed in a matrix resin mainly composed of a PBT resin, due to the production method. Have. The average particle diameter of the particles mainly composed of the modified block copolymer is usually 1.0 μm or less, and a PBT-based resin composition having particularly excellent impact resistance is obtained.
Is preferably within the range. The precursor resin composition is presumed to be produced as a result of a part of the modified block copolymer used reacting in the PBT-based resin synthesis reaction system.
It contains a small amount of a copolymer of a modified block copolymer and a PBT-based resin.

When the polymerization reaction of the PBT-based resin in the presence of the modified block copolymer is sufficiently performed, the precursor resin composition can exhibit high impact resistance. Due to the increase in the intrinsic viscosity of the PBT-based matrix resin, the melt fluidity (moldability) tends to decrease. Since the PBT-based resin composition of the present invention is a mixture of the precursor resin composition and the PBT-based resin under melting conditions, the PBT-based resin composition lacks the melt flowability (moldability) of the precursor resin composition. As a result of being improved by mixing the resin, both excellent impact resistance and melt fluidity (moldability) can be achieved. A precursor resin composition in which the PBT resin has an intrinsic viscosity (measured at 30 ° C. using an equal weight mixture of phenol / tetrachloroethane as a solvent) of 0.95 dl / g or more usually exhibits extremely excellent impact resistance. However, since the melt fluidity (moldability) is significantly reduced, the PBT resin has a precursor resin composition having an intrinsic viscosity of 0.95 dl / g or more and a precursor resin composition having an intrinsic viscosity of 0.90 dl / g or less. In the PBT-based resin composition obtained by melt-kneading the PBT-based resin, the effects of the present invention are particularly remarkably exhibited.

When the precursor resin composition and the PBT resin are mixed under melting conditions, the PBT resin forms a uniform matrix phase with the PBT resin contained in the precursor resin composition, Particles mainly composed of the modified block copolymer maintain their fine particle diameter or are further refined. Therefore, the PBT-based resin composition of the present invention is usually obtained by dispersing particles having an average particle diameter of 1.0 μm or less mainly composed of a modified block copolymer in a matrix resin mainly composed of two or more PBT resins. Has an existing configuration. The average particle diameter of the particles mainly composed of the modified block copolymer is preferably in the range of 0.01 to 0.7 μm from the viewpoint of impact resistance. The PBT resin composition of the present invention contains, as a small amount of a component, a copolymer of a modified block copolymer and a PBT resin.

The method of mixing the precursor resin composition and the PBT resin under the melting conditions for producing the PBT resin composition of the present invention is not particularly limited, and any method can be adopted. it can. For example, the PB of the present invention
Using a kneader such as a single-screw extruder, a twin-screw extruder, a kneader, and a Banbury mixer, the T-based resin composition is used to simultaneously form the precursor resin composition, the PBT-based resin, and if necessary, other additives. Alternatively, it is manufactured by melt-kneading sequentially. Further, the PBT-based resin composition of the present invention is produced by adding a PBT-based resin produced in advance at the end of the polycondensation reaction in which the precursor resin composition has been formed, and kneading the two in a polymerization tank. You can also.

In the PBT resin composition of the present invention,
In the ratio of the total weight of the PBT resin and the melt-mixed PBT resin in the precursor resin composition to the weight of the modified block copolymer (the ratio of the total weight of the PBT resin to the weight of the modified block copolymer), It is preferable that it is contained in a ratio of 97/3 to 65/35. If the content of the modified block copolymer is too high, the excellent heat resistance and moldability inherently possessed by the PBT-based resin may not be exhibited, whereas if the content is too low, the impact resistance may be reduced. Becomes insufficient.

The PBT resin composition of the present invention comprises an antioxidant, a thermal decomposition inhibitor, an ultraviolet absorber, a crystallization nucleating agent, a crystallization accelerator, a coloring agent, a flame retardant, a reinforcing agent, a filler, Mold,
A plasticizer, an antistatic agent, an anti-hydrolysis agent, an adhesion aid, a pressure-sensitive adhesive, and other polymers may optionally be contained.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The modified block copolymer used was
The following abbreviations are used.

EPS-OH: diblock of hydrogenated polyisoprene block (number average molecular weight: 20,000) / polystyrene block (number average molecular weight: 10,000) having a hydroxyl group at a polystyrene block terminal (hydroxyl content:
0.8 styrene / molecule; Styrene unit content based on modified block copolymer before hydrogenation: 33% by weight; Unsaturation degree based on hydrogenated polyisoprene block: 5%; Number average molecular weight: 300
00) SEBS-OH: polystyrene block (number average molecular weight: 6000) / hydrogenated poly (1,3-butadiene) block (number average molecular weight: 28000) / polystyrene block (number average) having a hydroxyl group at one polystyrene block terminal Triblock (molecular weight: 6000) (hydroxyl content: 0.8 / molecule; styrene unit content based on the modified block copolymer before hydrogenation: 30% by weight; hydrogenated poly (1,3-butadiene) block Reference Unsaturation:
5%; number average molecular weight: 40000) SEPS-OH: polystyrene block having a hydroxyl group at one polystyrene block terminal (number average molecular weight: 6000) / hydrogenated polyisoprene block (number average molecular weight: 28000) /
Triblock of polystyrene block (number average molecular weight: 6000) (hydroxyl content: 0.8 / molecule; styrene unit content based on modified block copolymer before hydrogenation: 30)
% By weight; degree of unsaturation based on hydrogenated polyisoprene block:
5%; number average molecular weight: 40000)

The precursor resin composition obtained in Reference Example and P
BT, the PBT-based resin composition obtained in the example, and the PBT obtained in the comparative example were evaluated by the following measurement methods.

(1) PBT, PBT in the precursor resin composition
Of intrinsic viscosity of PBT and PBT in PBT resin composition: phenol / tetrachloroethane (weight ratio: 1 /
It was measured in the mixed solvent of 1) at 30 ° C. (2) Evaluation of impact resistance of PBT-based resin composition and PBT: Notched Izod impact strength was measured at 23 ° C. according to JIS K 7110 using an injection molded product. (3) Measurement of PBT resin composition and elongation of PBT:
The elongation was measured using an injection molded product according to JIS K7113. (4) Measurement of melt viscosity of PBT resin composition and PBT: The melt viscosity was measured at a temperature of 250 ° C. and a shear rate of 1000 sec ⁻¹ using a Capillograph manufactured by Toyo Seiki Co., Ltd. Under these conditions, if it has a melt viscosity of 2500 poise or less, it can be determined that it has a melt fluidity suitable for molding. (5) Measurement of the average size of the modified block copolymer particles in the precursor resin composition and the PBT-based resin composition: A part of the test piece was broken, and the modified block copolymer dispersed in the form of particles was treated with toluene. After extraction, the fracture surface was observed using a scanning electron microscope. The average particle diameter was determined by image processing of the fractured surface.

Reference Example 1 Production of Precursor Resin Composition (a-1) 76.6 parts by weight of dimethyl terephthalate, 42.6 parts by weight of 1,4-butanediol and 0.03 part by weight of tetraisopropyl titanate were reacted. Charged in a tank (theoretical amount of PBT: 87 parts by weight), 170 to 230 ° C under normal pressure
The ester exchange reaction was carried out by heating while gradually increasing the temperature until the ester exchange reaction was stopped when 24.4 parts by weight of methanol was distilled off. Thereafter, 13 parts by weight of EPS-OH was added, and then the system was evacuated to a polycondensation reaction system. That is, it took about 30 minutes to raise the reaction temperature from 230 ° C. to 250 ° C. and reduce the pressure from normal pressure to 0.2 mmHg. At this reaction temperature and pressure, the polycondensation reaction took about 60 minutes. Next, the polycondensation reaction was stopped by supplying nitrogen gas to the reaction tank to return the system to normal pressure, and the precursor resin composition (a-1)
I got The precursor resin composition had a structure in which particles mainly composed of EPS-OH having an average particle diameter of 0.3 μm were uniformly dispersed in a matrix mainly composed of PBT. The intrinsic viscosity of PBT contained in the precursor resin composition was 1.01 dl / g.

Reference Example 2 Production of Precursor Resin Composition (a-2) SEBS-OH was used instead of EPS-OH, and the weight ratio of the theoretical amount of PBT / the amount of SEBS-OH added was 87/1.
A transesterification reaction and a polycondensation reaction were carried out in the same manner as in Reference Example 1 except that 3 was added. The obtained precursor resin composition (a-2) had a structure in which particles composed mainly of SEBS-OH and having an average particle diameter of 0.3 μm were uniformly dispersed in a matrix composed mainly of PBT. The intrinsic viscosity of PBT contained in the precursor resin composition was 1.01 dl / g.

Reference Example 3 Production of Precursor Resin Composition (a-3) SEPS-OH was used instead of EPS-OH, and the weight ratio of the theoretical amount of PBT / the amount of SEPS-OH added was 87/1.
A transesterification reaction and a polycondensation reaction were carried out in the same manner as in Reference Example 1 except that 3 was added. The obtained precursor resin composition (a-3) had a structure in which particles mainly composed of SEPS-OH and having an average particle diameter of 0.3 μm were uniformly dispersed in a matrix mainly composed of PBT. The intrinsic viscosity of PBT contained in the precursor resin composition was 1.01 dl / g.

Reference Example 4 Production of Precursor Resin Composition (a-4) The amount of SEPS-OH added was calculated as the theoretical amount of PBT / SEP.
A transesterification reaction and a polycondensation reaction were carried out in the same manner as in Reference Example 3 except that the weight ratio of the added amount of S-OH was changed to 80/20. The obtained precursor resin composition (a-4) has an average particle size of 0.3 mainly composed of SEPS-OH in a matrix mainly composed of PBT.
The particles had a structure in which μm particles were uniformly dispersed. The intrinsic viscosity of PBT contained in the precursor resin composition is
0.97 dl / g.

(Reference Example 5) Production of PBT (b-1) 88 parts by weight of dimethyl terephthalate, 49 parts by weight of 1,4-butanediol and 0.035 part by weight of tetraisopropyl titanate were charged into a reaction vessel, and the mixture was placed under normal pressure. 170 ° C
The mixture was heated while gradually raising the temperature to 230 ° C. to perform a transesterification reaction, and the transesterification reaction was stopped when 28 parts by weight of methanol was distilled off. Thereafter, the system was evacuated to a polycondensation reaction system. That is, it took about 30 minutes to raise the reaction temperature from 230 ° C. to 250 ° C. and reduce the pressure from normal pressure to 0.2 mmHg. At this reaction temperature and pressure, the polycondensation reaction took about 45 minutes. Next, PBT (b-1) was obtained by stopping the polycondensation reaction by supplying nitrogen gas to the reaction tank and returning the system to normal pressure. The intrinsic viscosity of the obtained PBT was 0.80 dl / g.

(Reference Example 6) Production of PBT (b-2) The transesterification and the transesterification were carried out in the same manner as in Reference Example 5 except that the polycondensation time at 250 ° C. and 0.2 mmHg was changed from about 45 minutes to about 50 minutes. A polycondensation reaction is performed and the intrinsic viscosity is 0.8
5 dl / g of PBT (b-2) was obtained.

(Examples 1 to 5) Production of PBT resin composition Precursor resin compositions and PBT obtained in Reference Examples 1 to 6
(All in the form of pellets) were premixed using a Henschel mixer, and then melt-kneaded with a twin-screw extruder under the condition of a cylinder temperature of 250 ° C. to obtain a PB
A T-based resin composition was obtained. Using this PBT-based resin composition, injection molding was performed at a cylinder temperature of 250 ° C and a mold temperature of 50 ° C. The obtained injection molded product was used for evaluation of physical properties. The type of the precursor resin composition and the PBT used and the mixing ratio thereof are shown in Table 1 below. In addition, the obtained PBT
Table 2 below shows the evaluation results of the resin composition.

[0036]

[Table 1]

In each of the obtained PBT resin compositions, a matrix mainly composed of PBT has an average particle diameter of 0.3 mainly composed of a modified block copolymer.
The particles had a structure in which μm particles were uniformly dispersed.

Comparative Example 1 Preparation of PBT Transesterification and polycondensation were carried out in the same manner as in Reference Example 5 except that the polycondensation time at 250 ° C. and 0.2 mmHg was changed from about 45 minutes to about 55 minutes. , Intrinsic viscosity 0.9
3 dl / g of PBT was obtained. The obtained PBT was prepared in Example 1.
The evaluation was performed in the same manner as in the above. The results are shown in Table 2 below.

[0039]

[Table 2]

The weight of PBT in the "weight ratio of PBT / modified block copolymer" in Table 2 is the total weight of the precursor resin composition used for melt mixing and the PBT introduced from PBT.

[0041]

According to the present invention, there is provided a PBT resin composition excellent in both impact resistance and melt fluidity (moldability). The resin composition can be used for a wide range of applications as a material for electric / electronic parts, automobile parts, etc. by utilizing its features.

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 53/02 C08L 67/00-67/02

Claims (2)

(57) [Claims] (1) A polycondensation reaction of a polybutylene terephthalate-based resin comprises a polymer block A comprising a monomer unit mainly comprising a vinyl aromatic compound unit and a monomer unit mainly comprising a conjugated diene unit, and The resin composition obtained by performing in the presence of a modified block copolymer comprising a hydrogenated polymer block B and having a hydroxyl group at a terminal, and (2) a polybutylene terephthalate-based resin are melted. A polybutylene terephthalate-based resin composition obtained by mixing. (1) In a matrix resin mainly composed of two or more kinds of polybutylene terephthalate resins,
(2) A polymer block A mainly composed of a monomer unit mainly composed of a vinyl aromatic compound unit and a polymer block B mainly composed of a monomer unit mainly composed of a conjugated diene unit and being hydrogenated. A polybutylene terephthalate-based resin composition, wherein particles of a modified block copolymer having a hydroxyl group and having an average particle diameter of 1.0 μm or less are dispersed and present.