JPH0532720A - Acrylic resin premix and production of acrylic scagliolia - Google Patents

Abstract

PURPOSE:To provide the subject premix containing a specified ratio of unsaturated monomers composed mainly of methyl methacrylate, an inorganic powder and a specified resin fine powder and capable of producing a scagliolia having an excellent glossy surface and excellent in transparency even by short-time molding. CONSTITUTION:An objective premix composed of (A) 20-60wt.% unsaturated monomers composed mainly of methyl methacrylate, (B) 80-40wt.% inorganic powder preferably composed of aluminum hydroxide and having 0.1-100mum (especially preferably 1-30mum) particle size in general and (C)1-25wt.% fine powder of a methyl methacrylate-based resin having 3-5 times degree of swelling to methyl methacrylate (MMA), insoluble in MMA and preferably containing crosslinkages introduced thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an acrylic resin premix and an acrylic artificial marble, and more particularly to an acrylic resin premix having excellent moldability and an efficient method for producing an acrylic artificial marble using the same. .

[0002]

2. Description of the Related Art Acrylic artificial marble, which is acrylic resin filled with inorganic powder, makes use of its beautiful appearance and excellent characteristics to make use of kitchen tops, countertops, vanities, shower trays, and waterproofing. It is used for bread, flooring, wall materials, partition boards, etc. This product is generally produced by dispersing and containing an inorganic powder in an unsaturated monomer mainly composed of methyl methacrylate or its syrup to form a slurry, and polymerizing and curing the slurry along a mold. . However, since methyl methacrylate has a low boiling point, the polymerization temperature is inevitably low, which causes a problem that the polymerization and curing are slow and the molding time is on the order of hour unit.

On the other hand, some unsaturated polyester resin type artificial marbles are efficiently molded at high temperature under pressure for a short time, which is said to be within 1 minute per 1 mm of the wall thickness of the molded product from the premix, Also in the case of acrylic, a method of polymerizing and curing a highly viscous mixture of an unsaturated monomer mainly composed of methyl methacrylate and an inorganic powder, that is, a premix at high temperature under pressure has been attempted. However, acrylic resin premix cannot be thickened easily like unsaturated polyester, so in order to prevent stickiness and improve handleability, unsaturated monomer mainly composed of methyl methacrylate is made into a high viscosity syrup, Further, although the amount of unsaturated monomer used is reduced and the inorganic powder is highly filled, the high filling of the inorganic powder has a drawback that the transparency of the molded product is impaired and the high-grade feeling is lost. Even if such an acrylic resin premix uses a mirror surface mold, the molded product surface lacks gloss in short-time molding, and even if it is glossy, if it is taken out of the mold and allowed to cool, the gloss will gradually be lost. There was also.

Therefore, an object of the present invention is to provide an acrylic resin premix which gives an acrylic artificial marble having a beautiful glossy surface which faithfully transfers the mirror surface of the mold even in a short time molding and which is excellent in transparency. Another object of the present invention is to provide an efficient method for producing an acrylic artificial marble excellent in surface gloss and transparency using the premix.

[0005]

Means for Solving the Problems As a result of intensive investigations by the present inventors by paying attention to the composition of an acrylic resin premix in order to solve the above-mentioned problems, as a result, resin fine particles insoluble in methyl methacrylate and having swelling property were found. By adding, it is possible to obtain a non-sticky acrylic resin premix without using high-concentration syrup or high-filling with inorganic powder, and the molded product has excellent transparency and mirror-like transferability. The present invention has been completed by finding out that it is improved. That is, the above-mentioned object is the present invention, that is, (a) 20 to 60% by weight of an unsaturated monomer mainly composed of methyl methacrylate, (b) 80 to 40% by weight of inorganic powder, and (c) swelling with respect to methyl methacrylate. Acrylic resin premix consisting of 1 to 25% by weight of resin fine particles having a degree of 3 to 15 times and insoluble in methyl methacrylate, and production of an acrylic artificial marble by shaping the premix under pressure to polymerize and cure. Achieved by the method.

The present invention will be described in detail below.

The premix is generally a putty-like molding material made by kneading a liquid thermosetting resin, particularly an unsaturated polyester resin, with a reinforcing material, a filler, a curing agent, a coloring agent and the like. The acrylic resin premix of the present invention is an unsaturated monomer mainly composed of methyl methacrylate,
A putty-like molding material obtained by mixing inorganic powder, a curing agent, and the like.

The unsaturated monomer mainly composed of methyl methacrylate used in the present invention means methyl methacrylate alone, a mixture of methyl methacrylate and another unsaturated monomer, or a polymer substance thereof. Refers to the dissolved and contained syrup, including the methyl methacrylate that is a constituent of the polymeric substance, the proportion of methyl methacrylate in the unsaturated monomer mainly methyl methacrylate,
It is 50% by weight or more, preferably 60% by weight or more, more preferably 75% by weight or more. If the proportion of methyl methacrylate is less than 50% by weight, the weather resistance and stain resistance of the acrylic artificial marble deteriorate, which is not preferable.

The other unsaturated monomer which can be used in combination with these methyl methacrylates is one that can be homopolymerized or copolymerized with other components in the unsaturated monomer mainly containing methyl methacrylate. , There is no particular limitation. Examples of such compounds include esters of monohydric alcohols or monohydric phenols with acrylic acid or methacrylic acid having 2 to 18 carbon atoms in one molecule, and those having 2 to 4 carbon atoms in one molecule. Monoester of dihydric alcohol and acrylic acid or methacrylic acid, acrylic acid, methacrylic acid, methyl acrylate, acrylonitrile, methacrylonitrile, acrylamide, styrene, α-methylstyrene,
Monofunctional unsaturated monomers such as vinyl acetate, vinyl chloride, vinylidene fluoride, vinylidene chloride, ethylene, maleic anhydride, maleic acid, fumaric acid, glycidyl methacrylate, acrylic acid and / or methacrylic acid and ethylene glycol, Polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, tetramethylolmethane, dimethylolethane, trimethylolethane, dimethylolpropane, Trimethylolpropane,
Polyesters with polyhydric alcohols such as pentaerythritol and dipentaerythritol, divinylbenzene,
Examples thereof include polyfunctional unsaturated monomers such as triallyl isocyanurate. It is also possible to use two or more types of other unsaturated monomers used in combination with these methyl methacrylates. Heat resistance of acrylic artificial marble,
In order to improve the stain resistance and the like, it is desirable to use a polyfunctional unsaturated monomer in combination. As the polyfunctional unsaturated monomer, the above-mentioned ones can be used, but among them, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate and the like are preferable. is there. The amount of the polyfunctional unsaturated monomer used is 0.1 to 25% by weight, preferably 2 to 10% by weight, based on the total amount of unsaturated monomers mainly composed of methyl methacrylate. If the amount used is less than 0.1% by weight, the effect of improving the heat resistance and stain resistance of the acrylic artificial marble is poor, while if it exceeds 25% by weight, the acrylic artificial marble becomes brittle.

The unsaturated monomer mainly containing methyl methacrylate is a syrup containing a polymer substance so that the acrylic resin premix has a viscosity and a good fluidity at the time of molding. Is desirable. In such syrup, the ratio of the polymeric substance to the total amount of syrup is
The lower limit is 5% by weight or more, preferably 20% by weight or more, more preferably 35% by weight or more, and the upper limit is 60% by weight or less, preferably 50% by weight or less, more preferably 45% by weight or less. If the proportion of the polymer substance is less than 5% by weight, the premix may be poor in fluidity or the polymerization and curing time may be long, while if it exceeds 60% by weight, the molded product is kept at a high molding temperature from the mold. When taken out, part of the surface of the molded product adheres to the mold and remains, so that so-called mold adhesion occurs in which the smoothness and gloss of the surface of the molded product is lost. The syrup viscosity is not particularly limited as long as it does not hinder the kneading with the inorganic powder, and includes low-viscosity fluid with a high fluidity and high-viscosity fluid with a low fluidity. Is poor in handleability, and therefore, those having 1 to 600 poises are usually preferable.
As the polymer substance dissolved and contained in the syrup, any substance such as a natural polymer substance, a synthetic polymer substance or a semi-synthetic polymer substance can be used, but if the content in the syrup is large, it is attached to the mold. In order to prevent this, a resin having heat resistance that does not melt at the molding temperature of the premix is preferable. It is also possible to use two or more types of these polymeric substances in combination.

Acrylic artificial marble is required to have a transparent feeling in order to have a high-grade appearance. For that purpose, the polymer substance contained in the syrup and the polymer of the unsaturated monomer of the syrup are transparently combined. It is preferable to dissolve. Such a combination generally requires that the composition of the polymeric substance and the composition of the unsaturated syrup polymer are the same or similar. There is no particular limitation on the method for producing the syrup, and the syrup can be produced by any method, but those requiring transparency are methyl methacrylate alone or a mixture of methyl methacrylate and another unsaturated monomer. A part of the polymer is dissolved in the remaining part, methyl methacrylate alone or a mixture of methyl methacrylate and another unsaturated monomer is partially polymerized, methyl methacrylate alone or methyl methacrylate and others It can be advantageously produced by a method of partially polymerizing a part of the mixture with the unsaturated monomer and dissolving it in the remaining part. In addition to these, acrylonitrile-styrene copolymer resin, vinyl chloride-vinylidene fluoride copolymer resin, ethylene-vinylidene fluoride copolymer resin and a combination of methyl methacrylate, etc. However, such combinations are not so limited.

The amount of the unsaturated monomer composed mainly of methyl methacrylate used is 20 to 60% by weight, preferably 2 based on the total amount of the unsaturated monomer, the inorganic powder and the resin fine particles.
It is 2 to 50% by weight, more preferably 25 to 40% by weight. If the amount of the unsaturated monomer composed mainly of methyl methacrylate is less than 20% by weight, the desired amount of the inorganic powder cannot be filled, or even if it is filled, the fluidity of the premix is poor, or the acrylic It is not preferable because the transparency of the artificial marble is lost. On the other hand, if it exceeds 60% by weight, the premix is not easy to handle, the curing is slow, and the heat resistance of the resulting acrylic artificial marble is deteriorated, which is not preferable.

The inorganic powder used in the present invention is not particularly limited as long as it is insoluble in the unsaturated monomer composed mainly of methyl methacrylate and does not interfere with the polymerization and curing thereof, aluminum hydroxide, aluminum oxide, Calcium carbonate,
Powders of calcium silicate, calcium aluminate, calcium sulfate, magnesium hydroxide, silica, talc, clay, glass and the like can be used, but are not limited thereto. However, aluminum hydroxide, magnesium hydroxide, and silica, particularly aluminum hydroxide, are preferably used from the viewpoints of the high-grade feeling, stain resistance, and processing performance of the acrylic artificial marble. It is also possible to use two or more kinds of these inorganic powders in combination.

The particle size of the inorganic powder is usually 0.1 to 100 μm.
m, preferably 0.5 to 50 μm, more preferably 1 to
It is 30 μm. If the particle size exceeds 100 μm, unclear and minute spots may appear on the acrylic artificial marble, which may impair the appearance. If the particle size is less than 0.1 μm,
It is not preferable because the transparency is lost and the filling amount is limited.

The filling amount of the inorganic powder is determined by the performance required for the acrylic artificial marble, etc., but is usually based on the total amount of unsaturated monomers mainly composed of methyl methacrylate, resin fine particles and the inorganic powder. 80 to 40% by weight, preferably 75 to 50% by weight, more preferably 70
˜55 wt%. When the filling amount of the inorganic powder exceeds 80% by weight, the filling is difficult, the fluidity of the premix is deteriorated, and the properties such as transparency and strength of the acrylic artificial marble are deteriorated. However, the hardness and heat resistance of the acrylic artificial marble are deteriorated, and the marble-like appearance is impaired, which is not preferable.

The fine resin particles used in the present invention are insoluble in methyl methacrylate and have a swelling property.
The term “having swellability” as used herein means that the degree of swelling expressed by the ratio of the bulk volume when swollen by immersing in a large amount of methyl methacrylate for 1 hour at 25 ° C. is 3 to
It means 15 times, preferably 5 to 10 times.
If the degree of swelling is less than 3 times or completely insoluble, the addition effect is small, and the acrylic artificial marble obtained by molding for a short time has a cloudy surface even if a mirror surface type is used, and even if a mirror surface is obtained. When removed from the mold and allowed to cool, it gradually loses its luster. On the other hand, if the amount exceeds 15 times or that is dissolved in methyl methacrylate is used, the surface of the molded product is inferior in smoothness and gloss due to the adhesion of the mold, and in any case, the transferability of the mirror surface is insufficient, which is not preferable.

Any material can be used as the material of the resin fine particles, regardless of whether it is a synthetic polymer substance, a natural polymer substance, a semi-synthetic polymer substance, etc., as long as it satisfies the above swelling property. The most suitable is a synthetic polymer that is dissolved in methyl methacrylate and is insolubilized by lightly introducing a cross-linking bond. There is no particular limitation on the method of introducing cross-linking,
It can be carried out by any method, but the method of copolymerizing a polyfunctional unsaturated monomer is convenient. The copolymerization amount of the polyfunctional unsaturated monomer is 0.01 to 2% by weight, preferably 0.1.
05-1% by weight is suitable. If the amount of the polyfunctional unsaturated monomer used is less than 0.01% by weight, the degree of swelling will be too large, and if it exceeds 2% by weight, the degree of swelling will be small, such being undesirable. At that time, it is effective to copolymerize an unsaturated monomer having a high affinity with methyl methacrylate, such as an acrylic ester, in order to impart swelling property. Examples of the resin fine particles introduced with cross-linking include cross-linked polystyrene-based resin, cross-linked polymethyl methacrylate-based resin, cross-linked methyl methacrylate-styrene copolymer-based resin, etc., but the resulting acrylic artificial marble is transparent. A methyl methacrylate resin is advantageous in terms of feeling and weather resistance.

The particle size of the present resin fine particles is 0.1 to 100.
μm, preferably 1 to 50 μm, more preferably 10
It is 30 μm. If the particle size exceeds 100 μm, the surface properties of the acrylic artificial marble molded product will be poor, and if it is less than 0.1 μm, the handleability will be poor and the production will be difficult, such being undesirable.

The amount of the resin particles to be added is 1 to 25% by weight, preferably 3 to 20% by weight, based on the total amount of the unsaturated monomer mainly containing methyl methacrylate, the inorganic powder and the resin particles. It is more preferably 5 to 15% by weight. If the addition amount is less than 1% by weight, the effect of addition is poor,
If it exceeds 25% by weight, it becomes expensive, which is not preferable.

The method for obtaining the acrylic resin premix of the present invention is not particularly limited, and each component can be manufactured at once or by mixing in any order. When a syrup containing a polymer substance is used, the step of dissolving the polymer substance in methyl methacrylate or a mixture of methyl methacrylate and another unsaturated monomer to form a syrup is omitted, and other components are omitted. It is possible to mix it directly with
It is advantageous to use once as a syrup because uniform mixing is easy. Since the syrup used in the present invention usually has a high viscosity in many cases, the present premix can be preferably produced by a method of stirring and dissolving with a kneader, adding other components to the kneader and kneading.

The hardness of the acrylic resin premix of the present invention is 5 to 9 in terms of hardness at 25 ° C. measured by an Asker rubber hardness meter C type (Japan Rubber Association standard SRIS-0101).
It is 0 degree, preferably 20 to 50 degrees. If the hardness is less than 5 degrees, there is a lot of leakage from the fitting part of the mold when press molding, it is not possible to press, the extrusion or injection by the screw type molding machine is not possible, and the molded product with the shape like the bottom of the bucket There are disadvantages such as difficulty in defoaming and stickiness and poor handleability. On the other hand, when it exceeds 90 degrees, the fluidity becomes poor and filling failure occurs, which is not preferable.

In the present invention, the fact that a mold is applied under pressure to polymerize and cure means that the acrylic resin premix described above is pressed and applied in a mold, and at the same time, unsaturated containing methyl methacrylate as a main component. Means to polymerize and cure the monomer. Specifically, compression molding, injection molding, extrusion molding,
It can be performed by transfer molding or the like, but is not limited thereto. The polymerization does not necessarily have to be completed in this step, and can be completed in a post-cure step provided separately, if necessary. Pressure at pressurization is 10 to 500 kg / cm ² , preferably ² to 250 kg /
It can be selected in the range of cm ² .

The material of the mold surface used in the present invention is not particularly limited, and any material such as metal, glass, ceramics and resin can be used. The structure of the mold is also not particularly limited, and as described above, it is possible to use any one such as a compression molding mold, an injection molding mold, an extrusion molding die, and a transfer molding mold.

The method of polymerizing and curing the acrylic resin premix in the present invention is not particularly limited, and for example, a method of heating in the presence or absence of a radical polymerization initiator,
Examples thereof include a so-called redox system method comprising a radical polymerization initiator and an accelerator, and a method of irradiating ultraviolet rays or radiation. However, in the present invention, the method of heating in the presence of a radical polymerization initiator is advantageous. In that case, the heating temperature can be selected in the range of 75 to 150 ° C, preferably 80 to 140 ° C, more preferably 90 to 130 ° C. It is advantageous that the heating temperature is high for rapid curing, but at a high temperature, die attachment tends to occur.

The radical polymerization initiator is not particularly limited as long as it decomposes at the heating temperature, and any one can be used, but in order to achieve a high polymerization rate in a short time, the concentration is 0. When a benzene solution of 1 mol / liter is heated for 10 hours, a temperature at which half of the initial amount decomposes (hereinafter referred to as 10-hour half-life temperature) is 60 ° C. or less, and 60 ° C. It is advantageous to use a high temperature active radical polymerization initiator in excess. Examples of the low temperature active radical polymerization initiator include cumyl peroxy neodecanoate, diisopropyl peroxy dicarbonate, di (2-ethylhexyl) peroxy dicarbonate, t-butyl peroxy neodecanoate,
2,4-dichlorobenzoyl peroxide, t-butylperoxypivalate, 2,2'-azobis- (2,2
4-dimethylvaleronitrile), 2,2'-azobis-
Examples thereof include (4-methoxy-2,4-dimethylvaleronitrile), but the invention is not limited thereto. As the high temperature active radical polymerization initiator, one having a 10-hour half-life temperature within a heating temperature range of ± 10 ° C is more suitable. Therefore, if the heating temperature is 90 ° C., the 10-hour half-life temperature is 80 to 100 ° C.
A temperature of 120 ° C is advantageous. Examples of the high temperature active radical polymerization initiator include benzoyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, cyclohexanone peroxide, t-
Examples thereof include butyl peroxybenzoate, dicumyl peroxide, and 2,5-dimethylhexane-2,5-dihydroperoxide, but are not limited thereto.

Two or more radical polymerization initiators can be used in combination. Therefore, two or more kinds of each of the above-mentioned low temperature active and high temperature active radical polymerization initiators can be used in combination, and when a low temperature active radical polymerization initiator and a high temperature active radical polymerization initiator corresponding to the heating temperature are used. In addition, it is also possible to use a radical polymerization initiator which does not correspond to these. The amount of these radical polymerization initiators used is usually 0.01 to 9 parts by weight, preferably 0.05 to 4 parts by weight, preferably 0.05 to 1.5 parts by weight, based on 100 parts by weight of the unsaturated monomer. Parts and 0.02 to 5 parts by weight of a high temperature active radical polymerization initiator, preferably 0.1.
05 to 2 parts by weight can be usually used together.

If necessary, the acrylic resin premix of the present invention may include dyes and pigments, reinforcing materials, modifiers, stabilizers, ultraviolet absorbers, mold release agents, flame retardants, polymerization initiators and polymerization regulators. ,
Furthermore, it is possible to add organic fillers such as wood powder and bamboo powder.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Examples 1 to 5 A mixed solution of styrene and divinylbenzene was suspension polymerized to obtain polystyrene crosslinked beads having an average particle diameter of 12 µm and having a swelling degree as shown in Table 1. The degree of swelling is the volume when the cross-linked beads are put into a graduated cylinder at 25 ° C., the graduated cylinder is lightly tapped several times, and the volume when swelled for one hour by adding a sufficient amount of methyl methacrylate thereto. Expressed as the ratio of

8.8 parts by weight of a methacrylic resin containing 1% by weight of methyl acrylate unit and having an average degree of polymerization of 1000 is dissolved in 13.2 parts by weight of methyl methacrylate, and then 3 parts by weight of neopentyl glycol dimethacrylate and Stearic acid 1.5 parts by weight, 85% by weight phosphoric acid aqueous solution 1.5 parts by weight, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole 0.15 parts by weight, 2,2
-Bis (t-butylperoxy) butane 3 parts by weight, bis- (4-t-butylcyclohexyl) peroxydicarbonate 0.5 parts by weight, dicumyl peroxide 0.4
3 parts by weight of aluminum hydroxide powder having an average particle diameter of 3 μm, 5 parts by weight of glass fibers having a cut length of 3 mm, and amorphous fine powder silica (Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.) 2 Parts by weight, and 5 parts by weight of the polystyrene crosslinked beads are added and kneaded with a kneader,
An acrylic resin premix having no stickiness and good handleability was obtained. The hardness of these obtained premixes at 25 ° C. (measured with Asker rubber hardness meter C type manufactured by Kobunshi Keiki Co., Ltd.) was 30 to 50 degrees. Using a 150 mm square flat plate mold with a chrome-plated surface, the mold temperature is 10
The above premix is adjusted to 0 ° C and 0.5 to 10 kg / cm ² .
Then, the pressure was increased to 100 kg / cm ² for 4.5 minutes to obtain an acrylic artificial marble flat plate having a thickness of 5 mm. All of the obtained flat plates had no defective filling and were highly transparent.
As can be seen from the 60 degree gloss value, a beautiful glossy surface was obtained by faithfully transferring the mold surface.

[0030] Comparative Example 1 By the same method as in Examples 1 to 5, except that polystyrene swelling beads having a swelling degree of 2 were used.
An acrylic artificial marble plate was obtained. When the obtained flat plate was taken out of the mold and allowed to cool, the gloss gradually lost and the 60-degree gloss value became 53%. Comparative Example 2 An acrylic artificial marble flat plate was obtained by the same method as in Examples 1 to 5 except that polystyrene crosslinked beads having a swelling degree of 25 times were used. The obtained flat plate surface was inferior in smoothness and gloss due to the die attachment. Comparative Example 3 An acrylic resin premix was obtained by performing the method of Examples 1 to 5 without using the polystyrene crosslinked beads in Examples 1 to 5. This premix had stickiness and poor handleability, and the hardness was less than 5 degrees. Comparative Example 4 Example 1 was used instead of 5 parts by weight of polystyrene crosslinked beads.
Acrylic resin premixes were obtained by the same method as in Examples 1 to 5, except that 5 parts by weight of the same aluminum hydroxide powder as in Examples 1 to 5 was used. This premix had stickiness and poor handleability, and the hardness was less than 5 degrees. Example 6 A small amount of neopentyl glycol dimethacrylate was mixed with methyl methacrylate and suspension polymerization was carried out to obtain polymethyl methacrylate crosslinked beads having a particle size of 10 μm. The degree of swelling of these beads by the same measurement method as in Examples 1 to 5 was 5.6 times.

Example 1 was added to 15 parts by weight of methyl methacrylate partially polymerized syrup having a degree of polymerization of about 8000 and a rate of polymerization of about 8%.
7 parts by weight of methacrylic resin and 3 parts by weight of neopentylglycol dimethacrylate, which are the same as those of Nos. 5 and 5, were kneaded with a kneader to dissolve the methacrylic resin. To this, 1.5 parts by weight of stearic acid, 1.5 parts by weight of 85% by weight phosphoric acid aqueous solution, 2- (2'-hydroxy-5'-methylphenyl)
Benzotriazole 0.15 parts by weight, 2,2-bis (t
-Butylperoxy) butane 3 parts by weight, bis- (4-t
-Butylcyclohexyl) peroxydicarbonate (0.5 parts by weight) and dicumyl peroxide (0.4 parts by weight) were dissolved, and further 50 parts by weight of aluminum hydroxide powder having an average particle size of 50 μm, the same glass fiber as in Examples 1-5. 10 parts by weight and the above polymethylmethacrylate crosslinked beads 15
By adding parts by weight and kneading, an acrylic resin premix having no stickiness and good handleability was obtained. The hardness of this premix measured by the same method as in Examples 1 to 5 was 42 degrees.

The flat plates obtained from this premix by the same method as in Examples 1 to 5 were rich in transparency, did not have a rough surface due to the adhesion of the mold, and did not lose their gloss even when left to cool. The value was 79%. Comparative Example 5 The surface of a flat plate obtained by the same method as in Example 6 except that non-crosslinked beads were used instead of polymethylmethacrylate crosslinked beads was inferior in smoothness and gloss due to die attachment. Met. Comparative Example 6 A flat plate obtained by the same method as in Example 6 except that polymethylmethacrylate crosslinked beads having a swelling degree of 5.6 times was used instead of the polymethylmethacrylate crosslinked beads having a swelling degree of 5.6. When it was taken out of the mold and allowed to cool, it gradually became cloudy and the 60-degree gloss value became 40%.

[0033]

Effect of the Invention Unlike the unsaturated polyester premix, the acrylic resin premix is difficult to thicken, so stickiness is prevented by high filling of the inorganic powder. Therefore, there is a defect that the molded product lacks transparency. In terms of moldability, when molding at high temperature to increase molding efficiency, the surface becomes dirty due to the adhesion of the mold, and in short time molding the transferability of the mold surface is poor and the molded product obtained even if a mirror surface mold is used It became cloudy, and even if a provisional mirror surface product was obtained, there was a drawback that the gloss was lost if it was left to cool for a while after molding.

On the other hand, the acrylic resin premix according to the present invention obtained by adding resin particles which are insoluble and swellable to the unsaturated monomer mainly containing methyl methacrylate is
Stickiness is prevented without high filling of inorganic powder,
Also, the molded product is excellent in transparency and does not adhere to the mold, and even if molding is performed for a short time, the resulting molded product faithfully transfers the mirror surface of the mold and has a beautiful glossy surface. It does not lose its gloss when left unattended. Therefore, by using the acrylic resin premix of the present invention, it becomes possible to efficiently mold an acrylic artificial marble excellent in surface gloss, smoothness and transparency by short-time molding.

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Claims (2)

[Claims] 1. (a) 20 to 60% by weight of an unsaturated monomer composed mainly of methyl methacrylate, (b) 80 to 80% of inorganic powder.
An acrylic resin premix comprising 40% by weight and (c) 1 to 25% by weight of resin fine particles having a swelling degree with respect to methyl methacrylate of 3 to 15 times and insoluble in methyl methacrylate. 2. (a) 20 to 60% by weight of an unsaturated monomer mainly composed of methyl methacrylate, (b) 80 to 80% inorganic powder.
An acrylic resin premix consisting of 40% by weight and (c) 1 to 25% by weight of resin fine particles having a swelling degree with respect to methyl methacrylate of 3 to 15 times and insoluble in methyl methacrylate is shaped under pressure. A method for producing an acrylic artificial marble, which comprises polymerizing and hardening.