JPH05279575A - Artifical marble containing transparent particles dispersed therein - Google Patents

Abstract

PURPOSE:To provide an artificial marble of high-quality design having an appearance close to that of natural marble by dispersing transparent particles comprising a resin compsn. and an inorg. filler in an opaque matrix comprising a resin compsn. and an inorg. filler. CONSTITUTION:Substantially transparent particles of 0.2 to 5mm in diameter comprising 15-60wt.% resin compsn. and 40-85wt.% inorg. filler are dispersed in an opaque matrix comprising 15-60wt.% resin compsn. and 40-85wt.% inorg. filler. An artificial marble comprises 20-99.5wt.% matrix and 0.5-80wt.% transparent particles. The resin compsn. in the matrix pref. comprises polymethyl methacrylate or a polymer having methyl methacrylate monomer units as the main structural units and comonomer units, while an example of the inorg. filler in the matrix is aluminum hydroxide. An example of the resin compsn. in the substantially transparent particles is a copolymer of an unsatd. polyester with styrene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial marble having a stone pattern.

Artificial marble has an elegant texture, excellent strength,
Due to weather resistance and ease of construction and processing, it is used in many applications such as kitchen tops, vanities, tables, furniture, wall materials, floor materials, interior accessories, seals, bathtubs, window frames, and indirect lighting panels. Its usage is increasing more and more.

[0003] In recent years, as the lifestyle has become more sophisticated, the stone-grained artificial marble having an appearance similar to that of natural stone has become popular, and in particular, the stone-grained artificial marble in which transparent particles are dispersed is closer to natural stone. Since it has an external appearance and matches well with a vanity, a bathroom, etc., it is highly demanded by users, and it is attracting attention as a new application of artificial marble. By dispersing transparent particles, the stone-grained artificial marble of the present invention has a completely new appearance and fashionability not found in conventional artificial marble, and has a conventional artificial nature such as processability and ease of maintenance. Since it has the characteristics of marble, it can be used not only as an artificial marble but also as a natural marble which has not been used in the conventional artificial marble in terms of appearance.

[0004]

2. Description of the Related Art Natural marble has been used for a long time as a wall material, floor material, and various top plates due to its elegance, but it is heavy and hard, making construction and processing difficult, and its surface is porous. Since it is difficult to remove dirt, it is difficult to obtain long ones, and it has seams.

As a marble-like artificial material, a melamine decorative board, a gel-coated artificial marble whose surface is patterned,
There are acrylic artificial marble and polyester artificial marble. Compared to natural marble, these are lighter and non-porous, but the former two have the drawbacks that they are difficult to process and repair because they have a pattern only on the surface, and they are weak against impact.

[0006] Acrylic artificial marble and polyester artificial marble have an elegant texture peculiar to solid materials, easy workability, excellent strength, and impact resistance. In particular, acrylic artificial marble has excellent weather resistance. It has many advantages.

The technique relating to the stone-grained artificial marble in which transparent particles are dispersed, which is the object of the present invention, is disclosed in, for example, Japanese Patent Publication No.
No. 24,357, and in this technique, transparent particles are quartz, glass, peacock stone, marble,
It is a crushed stone such as mica or obsidian, or a crushed resin such as ABS resin, epoxy resin, melamine resin or phenol resin.

Another example of the prior art is Japanese Patent Application No. 53-4.
No. 6668, the transparent particles of this technology are mica flakes and crushed cold water stones, and another example is Japanese Patent Application No. 63-615.
In No. 11, the transparent particles are crushed natural stones and glass particles. There is no known technique comprising a mixture of the resin composition and the inorganic filler according to the present invention. If the transparent particles in the prior art consist of hard materials such as quartz, mica, and crushed glass,
It is difficult to process the artificial marble containing the particles, especially when the surface is ground or cut, and sometimes the processing tool is damaged.

When the particles are made of a resin composition such as an epoxy resin or a melamine resin, static electricity is generated due to friction between the particles and the inner wall of the pipe in the step of transporting the particles by a pipeline, or a bag of particles, In the transfer process from the container, static electricity is generated due to friction between the particles and the bag and the container and peeling of the contact surface. When the transparent particles are made by crushing the resin composition, static electricity is generated by collision and friction between the resin composition and the crusher, and static electricity is similarly generated when the crushed material needs to be sieved.

When static electricity is generated in these steps, the particles adhere to and agglomerate on the wall surface, etc., which not only does not carry well, but also causes mixing of different particles. Electric field strength (about 30KV / c
Above m), a discharge phenomenon may occur and a dust explosion may occur. Also, when the particles are put in a volatile organic solvent, a polymerizable unsaturated monomer, etc., an explosion occurs due to the discharge phenomenon of the particles,
It may also cause a fire.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. The object of the present invention is to disperse substantially transparent particles and to use a conventional acrylic artificial material. A stone-grained artificial material that has the characteristics that marble has, that is, a homogeneous and non-porous solid material, construction and workability equivalent to hard wood, easy maintenance, impact resistance, weather resistance, flame retardancy, etc. To provide technology related to marble.

The term "substantially transparent" as used herein means that the particles have a transparent appearance with a design property, and a preferable state thereof is JIS-K7105.
According to the above, the value of the parallel light transmittance of a 2 mm thick sheet measured by measuring method A is 8% or more, and more preferably 10% or more. On the other hand, when the matrix is not more transparent, it means that the transparent appearance is low depending on the degree to which the substantially transparent particles are dispersed to have a designable contrast, and the preferred state thereof is JIS-K7105. According to the above method, the parallel light transmittance of a 2 mm thick sheet measured by measuring method A is 1% or more lower than the parallel light transmittance of substantially transparent particles.

[0013]

Means for Solving the Problems In the present invention, as a means for solving the above problems, a particle size of 0.5 to 60% by weight of a resin composition and 40 to 85% by weight of an inorganic filler is used.
2 to 5 mm of substantially transparent particles (B) are the resin composition 1
Dispersed in a less transparent matrix (A) consisting of 5 to 60% by weight and 40 to 85% by weight of inorganic filler,
The total amount of the matrix (A) and the particles (B) is 100% by weight.
In this case, the artificial marble is characterized by comprising 20 to 99.5% by weight of the matrix (A) and 0.5 to 80% by weight of the particles (B).

The resin composition of the matrix (A) of the present invention is preferably polymethylmethacrylate or a polymer having methylmethacrylate as a main constituent unit and a copolymer compound unit.

By adding a copolymerization compound to the resin material of the main constituent unit of the matrix (A) and copolymerizing it, there is an effect of increasing the strength and stain resistance of the artificial marble.
Excessive addition of a copolymer compound deteriorates workability and processability.

Therefore, in the case of a polymer having methyl methacrylate as a main constituent unit and a copolymer compound unit, when the polymer is 100% by weight, 90% by weight or more of the methyl methacrylate unit and 10 copolymer compound units are included. It is preferably not more than wt%.

Preferred examples of the copolymer compound include (meth) acrylic acid esters (meaning acrylic acid ester or methacrylic acid ester; the same applies hereinafter) excluding methyl methacrylate, styrene and ethylene glycol dimethacrylate. The compound which has a polymeric double bond is mentioned.

Examples of the inorganic filler of the matrix (A) of the present invention include aluminum hydroxide, calcium hydroxide,
Magnesium hydroxide, powdered talc, powdered quartz, fine silica, diatomaceous earth, gypsum, powdered glass, clay minerals, powdered chalk, marble, limestone, colloidal asbestos, aluminum silicate, aluminum stearate, mullite, calcium silicate , Anhydrite, manganite, borax, etc.

Of these, aluminum hydroxide, calcium hydroxide, magnesium hydroxide and the like are preferable, but aluminum hydroxide is most preferable. These hydroxides release water of crystallization at high temperatures and effectively act to improve the flame retardancy of artificial marble.

The size of this inorganic filler depends on the matrix
The particle size is preferably 1 to 150 μm, and the center particle size of the particle size distribution is preferably 10 to 100 μm, because it affects the light-transmitting property of (A) and the viscosity increase when mixed with the polymerizable resin raw material. ..

In order to improve the flame retardancy, it is necessary to fill the inorganic filler in a sufficient amount, but excessive filling causes a decrease in the strength of the matrix (A).

Therefore, the inorganic filling amount in the matrix (A) is preferably 40 to 85% by weight when the total amount of the matrix (A) is 100% by weight. Further, the surface of the inorganic filler treated with, for example, a silane coupling agent, a titanate coupling agent, stearic acid or the like can be treated in the same manner.

Various additives other than the inorganic filler may be added to the matrix (A). Examples thereof include colorants such as pigments and dyes, ultraviolet absorbers, flame retardants, release agents, fluidizers, thickeners, and the like.

The matrix (A) must have a low transparency due to the degree to which it gives a design contrast when substantially transparent particles are dispersed.
As a preferable state, the value when the parallel light transmittance is measured by the measuring method A in a 2 mm thick sheet according to JIS-K7105 is lower than the parallel light transmittance of the substantially transparent particle (B) by 1% or more. That is. When the difference in the parallel light transmittance between the matrix (A) and the particles (B) is less than 1%, the contrast between the matrix (A) and the particles (B) becomes small, and the appearance lacks in design.

One of the preferable examples of the resin composition of the substantially transparent particles (B) of the present invention is a copolymer cured product of unsaturated polyester and styrene. The unsaturated polyester can be produced by a polycondensation reaction of an unsaturated dicarboxylic acid such as maleic acid or fumaric acid with a glycol such as ethylene glycol or diethylene glycol. As another preferable example, poly (benzyl methacrylate),
Alternatively, a polymer having benzyl methacrylate as a main constituent unit can be used.

Preferred examples of the compound copolymerizable with benzyl methacrylate are (meth) other than benzyl methacrylate.
Examples thereof include compounds having a plurality of polymerizable double bonds in the molecule such as acrylic acid ester, styrene and ethylene glycol dimethacrylate.

Of these, it is more preferable to use 50 to 70% by weight of unsaturated polyester and 30 to 50 of styrene.
Copolymer with wt% or benzyl methacrylate 90
To 99.9% by weight and 0.1 to 10% by weight of a compound having a plurality of polymerizable double bonds in the molecule such as ethylene glycol dimethacrylate.

Examples of the inorganic filler of the substantially transparent particles (B) of the present invention include aluminum hydroxide, calcium hydroxide, magnesium hydroxide, powdered talc, powdered quartz, fine silica, diatomaceous earth, gypsum. , Powdered glass, clay minerals, powdered chalk, marble, limestone, colloidal asbestos,
Examples include aluminum silicate, aluminum stearate, mullite, calcium silicate, anhydrite, borax, and borax.

Of these, aluminum hydroxide, calcium hydroxide and magnesium hydroxide are preferred, and aluminum hydroxide is most preferred. These hydroxides release water of crystallization at high temperatures, and act particularly effectively for improving the flame retardancy of artificial marble.

Since the size of the inorganic filler affects the light-transmitting property of the particles (B) and the increase in viscosity when mixed with the polymerizable resin raw material, the particle size is preferably 1 to 150 μm, and the center of the particle size distribution. The particle size is preferably 10 to 100 μm.

In order to improve the flame retardancy and to reduce the electrostatic charge capacity, it is necessary to fill the inorganic filler in a sufficient amount. On the other hand, excessive filling causes a decrease in the strength of the particles (B),
It is easy to cause a decrease in transparency. The inorganic filling amount in the particles (B) is
When the total amount of particles (B) is 100% by weight, 40 to 8
It is preferably 5% by weight. In addition, the surface of the inorganic filler treated with, for example, a silane coupling agent, stearic acid or the like can be treated in the same manner.

Various additives other than the inorganic filler may be added to the particles (B). Examples thereof include colorants such as pigments and dyes, ultraviolet absorbers, flame retardants, release agents, fluidizing agents, thickeners, and the like.

The particles (B) are required to have a transparent appearance with a design property, and the preferable state is to measure the parallel light transmittance with a 2 mm thick sheet according to JIS-K7105. The value when measured by Method A is 8
% Or more. When the parallel light transmittance is lower than this value, the transparency of the particles (B) is insufficient and a novel artificial marble cannot be produced. More preferably, the parallel light transmittance is 10% or more.

Further, the substantially transparent particles (B) are preferably those having a small electrostatic charge amount, and JIS-K69
When the surface resistivity is measured according to 11, the surface resistivity is preferably 2.0 × 10 ¹⁵ Ω or less. this is,
If the surface resistivity of the particles exceeds 2.0 × 10 ¹⁵ Ω, static electricity will be generated during the particle transporting process or crushing process, and the particles will not adhere to the surface.
This is because dust and explosion may occur due to the occurrence of a discharge phenomenon as well as agglomeration and mixing of foreign matter. The surface resistivity (ρs) is calculated by the following formula.

[0035]

[Equation 1] However, d: outer diameter of inner circle of surface electrode (cm) D: inner diameter of surface annular electrode (cm) Rs: surface resistance (MΩ)

The larger size of the substantially transparent particles (B) gives an appearance closer to that of natural stone, but it is difficult in the manufacturing process of artificial marble. Ie, substantially transparent particles
The artificial marble in which (B) is dispersed has particles on the surface of the artificial marble when the surface is ground to a depth that is half the particle diameter of the particles (B).
Since (B) is pulled out and a more preferable appearance is obtained, the smaller the size of the particles (B), the easier the grinding.

From this, the size of the particles (B) is preferably 0.2 to 5 mm.

Among the methods for producing the artificial marble of the present invention, the method for producing the particles (B) is as follows: the inorganic filler is uniformly dispersed in the polymerizable resin raw material to perform bulk polymerization and then pulverize with a pulverizer. Or a method of uniformly dispersing the inorganic filler in the polymerizable resin raw material and performing suspension polymerization in an aqueous medium, and the like.However, the inorganic filler is uniformly dispersed in the polymerizable resin raw material. A method of pulverizing with a pulverizer after bulk polymerization is preferable.

Examples of the method for polymerizing the polymerizable resin raw material of the substantially transparent particles (B) include redox polymerization, or a method of heating polymerization after adding a polymerization initiator.

The redox polymerization of a polymer having benzyl methacrylate as a main constituent unit is carried out by acyl peroxide such as benzoyl peroxide and N, N-dimethylaniline, N,
A combination with an amine compound such as N-diethylaniline or N, N-dimethylparaidine, or a combination of a peroxyl compound such as tert-butyl peroxymaleic acid and a mercaptan compound such as glycol dimercaptoacetate is used.

In the redox polymerization of a polymer having an unsaturated polyester as a main constituent unit, a vinyl compound such as styrene is mixed with the unsaturated polyester, and a peroxide catalyst such as methyl ethyl ketone peroxide or cyclohexanone peroxide and naphthenic acid are mixed. It is performed by adding a promoter such as cobalt. The grinding method for obtaining substantially transparent particles (B) includes a ball mill, a rod mill, a tower grinder, a vibration mill, a roll mill, a brake crusher, a roll crusher, a hammer mill, a jet mill, and a fluidized grinding. There is also a method of using these in combination.

The shape of the particles crushed by the crusher is more angular than the shape of the particles obtained by suspension polymerization, and gives a more natural appearance. Therefore, the one crushed by the crusher is preferable. In addition, the desired particle size can be obtained by changing the crushing conditions of the crusher, which is particularly effective when obtaining a large size.

Examples of the method for polymerizing the polymerizable resin raw material constituting the matrix (A) include a redox polymerization method and a method of heating polymerization after adding a thermal initiator.

Redox polymerization of a polymer having methyl methacrylate as a main constituent unit is carried out by acyl peroxide such as benzoyl peroxide and N, N-dimethylaniline, N, N
-A combination with an amine compound such as diethylaniline or N, N-dimethylparaidine, or a combination of a peroxyl compound such as tertiary butyl peroxymaleic acid and a mercaptan compound such as glycol dimercaptoacetate.

When polymerizing the polymerizable raw material, it is often preferable to use pre-polymerized syrup.

In order to obtain syrup, a method of polymerizing a methyl methacrylate monomer and stopping the polymerization on the way, or a polymer having methyl methacrylate as a main constituent unit prepolymerized by bulk polymerization or suspension polymerization is used. , There is a method of dissolving in a methyl methacrylate monomer.

The advantages of using syrup are as follows: 1) Polymerizable raw material, inorganic filler, and substantially transparent particles.
When adding (B), sedimentation of these fillers can be prevented by controlling the viscosity of the syrup which is a polymerizable raw material. 2) The curing time of the polymerizable raw material can be shortened.

The artificial marble in which substantially transparent particles are dispersed increases the size of the particles appearing on the surface by grinding the surface, and gives an appearance closer to natural stone. For that purpose, it is preferable to grind the surface at a depth of at least half the particle diameter of the largest of the substantially transparent particles (B).

More preferably, particles which are substantially transparent to the matrix (A) by increasing the surface gloss.
The contrast of (B) is increased, the transparency of the particles (B) is increased, and the designability can be further improved.

The present invention is further illustrated by the following examples, which do not limit the present invention.

Here,% means weight%. Example 1 (A) Production of substantially transparent particles 37.2% of unsaturated polyester resin (Polymer 3308PS manufactured by Takeda Pharmaceutical Co., Ltd.), methyl ethyl ketone peroxide (Permec N manufactured by NOF CORPORATION) 0.5
%, 62.3% of aluminum hydroxide powder (Higelite H-210 manufactured by Showa Denko KK) having a central particle diameter of 30 μm are mixed, stirred, poured into a mold, and cured at room temperature to give a substantially transparent curing. The product (I) was obtained.

The parallel light transmittance of this cured product (I) is JIS
According to K7105, when a 2 mm thick sheet was measured by measuring method A, it was 11.9% and was substantially transparent.
The surface resistivity measured according to JIS-K6911 was 1.8 × 10 ¹⁵ Ω. The cured product (I) was pulverized with a pulverizer and then sieved to obtain a particle size of 5.0.
~ 0.2 mm of substantially transparent particles (I) were prepared. At that time, the particles (I) did not adhere to the wall surface of the crusher or the sieve, and it was not observed that the particles (I) were electrostatically charged.

(B) Manufacture of artificial marble A syrup (viscosity of 50 centipoise at 25 ° C.) consisting of 20% of poly (methyl methacrylate) and 80% of methyl methacrylate was prepared, and this syrup was 33.3% and the central particle diameter was 30 μm. Aluminum hydroxide powder (Showa Denko KK)
Hydilite H-210) 44.0%, tertiary butyl peroxymaleic acid (NOF Corporation Perbutyl MA) 0.3%, ethylene glycol dimethacrylate (Mitsubishi Rayon Co., Ltd. Acryester ED) 0.35.
%, Ethylene glycol dimercaptoacetate (GDMA, Yodo Chemical Co., Ltd.) 0.15%, deionized water 0.1%, white pigment (Harwick Chemical Corporation Stan-
Tone White) 0.9% and 20.9% of substantially transparent particles (I) produced in (A) were mixed and vacuum degassed with stirring.

Pour the vacuum degassed mixture into a mold,
By curing at room temperature, an artificial marble having a thickness of 13 mm, in which substantially transparent particles were uniformly dispersed on the surface of the sheet, was manufactured. This artificial marble had an appearance closer to that of natural stone than conventional artificial marble, and had high designability.

In order to measure the parallel light transmittance of the matrix portion of this artificial marble, a sheet having a thickness of 2 mm was prepared in the same manner as described above without adding substantially transparent particles (I). The parallel light transmittance was measured by measuring method A according to JIS-K7105, and it was 5.8%.

(C) Processing of artificial marble The surface of the artificial marble produced in (B) was ground to a depth of about 0.5 mm with a planer for woodworking, and then the surface was sequentially sandpapered to No. 600 finish surface. Polished.

Before surface grinding and polishing, the size of the transparent particles visible on the surface of the artificial marble was less than half of the actual particle diameter and it looked blurry. The size of the transparent particles that were visible was the same as the actual particle size, and they were clearly visible, giving an appearance closer to that of natural stone.

Furthermore, after polishing with No. 800 sandpaper and polishing to a mirror surface with a polishing compound, the contrast between the transparent particles and the matrix becomes large, and the substantially transparent particles look more transparent and are excellent in design. It could be processed into artificial marble.

Example 2 (A) Production of Substantially Transparent Particles Benzyl Methacrylate (Mitsubishi Rayon Co., Ltd.) 36.9
%, Aluminum hydroxide powder (the same as in Example 1) 6
2.3%, tertiary butyl peroxymaleic acid (the same as in Example 1) 0.15%, ethylene glycol dimethacrylate (the same as in Example 1) 0.5%,
Ethylene glycol dimethylcaptoacetate (the same as in Example 1) 0.1%, deionized water 0.05%,
Vacuum degassed with stirring.

Pour the vacuum degassed mixture into a mold,
By curing at room temperature, a substantially transparent cured product (II) was obtained. The parallel light transmittance of this cured product (II) is JI.
According to S-K7105, when a 2 mm thick sheet was measured by measuring method A, it was 12.3% and was substantially transparent.
Further, the surface resistivity was measured according to JIS-K6911 and found to be 1.4 × 10 ¹⁵ Ω.

The cured product (II) was crushed with a crusher and then sieved to obtain substantially transparent particles (II) having a particle size of 5.0 to 0.2 mm. At that time, the particles (II) did not adhere to the wall surface of the crusher or the sieve, and it was not observed that the particles (II) were electrostatically charged.

(B) Manufacture of Artificial Marble In the method for manufacturing (B) artificial marble of Example 1, particles are used.
By using the particles (II) instead of (I), an artificial marble having a thickness of 13 mm in which the particles (II) were uniformly dispersed in the sheet surface and in the depth direction was manufactured in the same manner as in Example 1.

Similar to the artificial marble produced in Example 1, this artificial marble also had an appearance close to that of natural stone and high designability.

Comparative Example 1 (A) Production of Particles The raw materials used in the production of the artificial marble (B) of Example 1 were mixed in the following proportions and vacuum degassed while stirring.

Raw Material Weight% Methyl Methacrylate Syrup 36.9% Aluminum Hydroxide Powder 62.3% Tertiary Butyl Peroxymaleic Acid 0.15% Ethylene Glycol Dimethacrylate 0.5% Ethylene Glycol Dimethyl Captoacetate 0.1% 1% deionized water 0.05% 100% A cured product was obtained by injecting this vacuum degassed mixture into a mold and curing at room temperature.

The parallel light transmittance of this cured product was measured according to JIS-K.
According to 7105, when a 2 mm thick sheet was measured by measuring method A, it was 6.6% and was not substantially transparent.

After crushing this cured product, particles (III) having a particle size of 5 to 0.2 mm were prepared.

(B) Manufacture of Artificial Marble In the method for manufacturing (B) artificial marble of Example 1, particles are used.
By using the particles (III) instead of (I), an artificial marble having a thickness of 13 mm in which the particles (III) were uniformly dispersed in the sheet surface and in the depth direction was prepared in the same manner as in Example 1. Was not different from the conventional stone-grained artificial marble in appearance and was not novel.

Examples 3-5 Example 1 (A) Example 1 except that the proportion of the raw materials used in the production of the substantially transparent particles was changed as shown in Table 1.
The same experiment was performed. The results obtained in these examples are
It had an appearance similar to that of natural stone, and was of high design quality.

[0070]

[Table 1]

Examples 6 to 8 Example 2 except that the proportion of the raw materials used in the production of the (A) substantially transparent particles of Example 2 was changed as shown in Table 2.
The same experiment was performed. The results obtained in these examples are
It had an appearance similar to that of natural stone, and was of high design quality.

[0072]

[Table 2]

Examples 9-14 Particles (I) prepared by (A) Preparation of substantially transparent particles of Example 1 or (A) Preparation of substantially transparent particles of Example 2 were prepared. An artificial marble was produced in the same manner as in the production of the (B) artificial marble of Example 1 except that the ratio of the matrix and the substantially transparent particles was changed as shown in Table 3 using the particles (II). did. The products obtained in these examples had an appearance close to that of natural stone and were of high designability.

[0074]

[Table 3]

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Claims (3)

[Claims] 1. A particle size of 0.2 to 5 mm comprising 15 to 60% by weight of a resin composition and 40 to 85% by weight of an inorganic filler.
Substantially transparent particles (B) of the resin composition 15 to 6
The matrix (A) and the particles (B) are dispersed in a less transparent matrix (A) consisting of 0% by weight and 40 to 85% by weight of an inorganic filler, and the total amount of the matrix (A) and the particles (B) is 100% by weight. A) 20 to 99.5% by weight and particles
(B) An artificial marble characterized by being composed of 0.5 to 80% by weight. 2. The artificial marble according to claim 1, wherein the substantially transparent particles (B) have a parallel light transmittance of 8% or more. 3. The surface resistivity of the substantially transparent particles (B) is 2.0 × 10 ¹⁵ Ω or less.
The described artificial marble.