JPS63212515A - Manufacture of molded object of artificial marble - Google Patents

Abstract

PURPOSE:To obtain appearance excellent in smoothness, luster and the similarity to a natural marble by a method in which thermal softening material is held by pinching in between the end edges of a bottom force and a top force, and the temperature of the bottom force is kept higher than that of the top force, and then said material is polymerized and cured, while pressurizing it. CONSTITUTION:Thermal softening material 3 is held by pinching in between each end edges 1', 2' of a bottom force and a top force 2, and the top force 2 is pressurized against the bottom force 1 with small pressurizing force. A space 4 is filled with the resin composition for molding. Next, heating medium is charged in a space 6 from a heating medium inlet 7, and is taken out from a heating medium outlet 8, whereby the heating medium is circulated. Then, since the temperature of the bottom force 1 is caused to be higher than that of the top force 2 and is kept at the curing temperature of the resin composition, the resin composition, which is positioned the more adjacently to the bottom force, the more quickly is polymerized and cured, and the resin composition which is positioned the more adjacently to the top force 2, the longer peeps its fluid condition. Accordingly, the shrinkage due to polymerizing and curing process is absorbed in the part of fluid condition, whereby the unevenness or wrinkle does not entirely occur on the surface of a resin molded object in contact with the bottom force. Since the top force 2 is always brought in contact with the resin composition under pressure, unevenness does not occur on the contact surface.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an artificial marble molded product, and more specifically, to a method for easily manufacturing an artificial marble molded product with a beautiful external surface. This article relates to a method for manufacturing artificial marble molded products.

(Prior Art and its Problems) Conventionally, a molded article called artificial marble has been manufactured from a composition of an unsaturated polyester resin syrup or acrylic resin syrup and an inorganic filler. These artificial marble products are widely used for wall materials, table and counter tops, and various shelf materials as substitutes for natural marble products, which have a constant appearance and are difficult to obtain uniform products. The manufacturing method for these artificial marble products involves placing a composition of a resin syrup in which monomers are partially polymerized and an inorganic filler into a mold and polymerizing and hardening it to form a molded product in a predetermined shape. Methods of manufacturing are known.

However, when manufacturing artificial marble molded products, especially molded products with a three-dimensional shape, by such a method,
The molded product shrinks as the resin syrup polymerizes and hardens, but this shrinkage occurs in the internal direction of the molded product, so the outer surface of the molded product, that is, the visible surface that is the external appearance of the molded product, and the inner surface of the molding die are A gap is created in between. During the shrinkage process, peeling between the outer surface of the molded product and the inner surface of the molding die does not occur uniformly over the entire surface, so the visible surface of the molded product becomes uneven, creating a mottled pattern and losing its commercial value. In order to suppress this shrinkage, it is possible to add a thermally expandable polymer to reduce the amount of shrinkage, but in that case, there are problems such as a decrease in the physical properties of the molded product and an increase in cost. There is.

Furthermore, in the case of thick-walled products, it is difficult to remove the polymerization heat due to the wall thickness, and the temperature inside the composition rises too much, causing unreacted monomer to vaporize, resulting in voids inside the molded product. This results in a decrease in mechanical strength, or voids break near the outer surface of the molded product, causing the outer surface of the molded product to become aputter-like, resulting in a molded product with no commercial value. This phenomenon is particularly likely to occur when using an acrylic resin syrup whose main raw material is methyl methacrylate, which has a boiling point of about 100°C.

Artificial marble molded products made using acrylic resin are prized as high-grade molded products because of their excellent appearance in terms of smoothness, gloss, and resemblance to natural stone.
The appearance of a molded product is particularly important, and if the visible surface of the molded product is uneven or has a mottled pattern, it cannot be used as a product.

(Object of the Invention) The object of the present invention is to easily produce thermosetting resin-based artificial marble having an excellent appearance (visible surface of molded product) in terms of smoothness, gloss, resemblance to natural marble, etc. The aim is to provide a method that can be used.

(Structure of the Invention) The present invention relates to a method for producing an artificial marble molded product in which a composition containing a thermosetting resin component and an inorganic filler is hardened and molded by a press molding method using upper and lower molds. A heat-softening material is sandwiched between the edge of the lower mold and the edge of the upper mold to form the visible part of the product, and the space formed by the upper mold and the lower mold is The temperature of the lower mold is maintained higher than that of the upper mold and at the curing temperature of the composition, and the composition is polymerized and cured while pressing the upper mold against the lower mold. This is a method for manufacturing an artificial marble molded product, which is characterized by:

(Preferred Embodiment of the Invention) The thermosetting resin component used in the present invention is a thermosetting resin known per se used for manufacturing artificial marble molded products, and is an acrylic resin or an unsaturated resin. Polyester resins are preferred, and are generally used in the form of a so-called syrup, which is a partially polymerized product.For example, acrylic resin syrup is preferably used, for example, by adding a small amount of radical polymerization to a monomer mainly composed of methyl methacrylate. The material is added and heated in a prepolymerization pot until the partial polymerization rate is 10 to 30.
% by partial polymerization.

This resin syrup generally has a viscosity of 500 to 2,000 centipoise (cps), although it varies depending on the miscibility with inorganic fillers and other components, cast moldability of the molding material, and post-polymerization curing properties. This is desirable. The monomer may consist only of methyl methacrylate, or one or more ethylenically unsaturated monomers copolymerizable with methyl methacrylate within the range of 1 to 25% by weight based on the total monomers. It may also be a mixture of other monomers having double bonds and methyl methacrylate. Examples of monomers copolymerizable with methyl methacrylate include styrene monomers such as styrene, vinyltoluene, and α-methylstyrene;
Methacrylic acid, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, glycidyl methacrylate, acrylic acid, methyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, ethylene glycol dimethacrylate, dimethacrylate Examples include (meth)acrylic monomers such as 1,3-butylene glycol acid, trimethylolpropane trimethacrylate, and allyl methacrylate, diallyl phthalate, and allyl glycol carbonate. In particular, in order to improve the heat resistance of the molded article, it is preferable to contain a monomer having 2 to 3 ethylenically unsaturated double bonds in an amount of 1 to 5% by weight based on the total monomers.

In addition, unsaturated polyester resin syrup is made by adding a monomer having the ethylenically unsaturated double bond such as styrene to a partially condensed metal compound of an unsaturated acid such as maleic anhydride and a diol such as ethylene glycol. It is. The viscosity of the unsaturated polyester resin syrup is preferably similar to the viscosity of the acrylic resin syrup.

As the inorganic filler used in the present invention, all those conventionally used for manufacturing artificial marble molded products can be used. Examples of inorganic fillers include:
Fine powder products such as calcium silicate, talc, silica, calcium carbonate, and alumina trihydrate (for example, Tyler mark *i
; i is about 150 meshes to 350 meshes).

The blending amount of the inorganic filler is preferably such that it is contained in the composition of the thermosetting resin component and the inorganic filler in an amount of 30 to 901i%.
If the amount is less than 90% by weight, the filling effect of the filler as artificial marble will not be sufficiently exhibited. If the amount is more than i%, the mechanical strength of the artificial marble molded product will decrease.

In the present invention, the radical polymerization initiator used for producing the resin syrup and for polymerizing and curing the composition of the thermosetting resin component and the inorganic filler is usually used for polymerizing these resins. All radical polymerization initiators known per se used in , tertiary butylperoxy-2-ethylhexanoate, and other organic peroxides, and azo compounds such as azobisisobutyronitrile, singly or in mixtures. A small amount of the radical polymerization initiator is sufficient based on the acrylic resin syrup, but it is generally 0.05 to 3% by weight, particularly 0.2 to 2% by weight, based on the acrylic resin syrup.
It is.

In the present invention, a composition of a thermosetting resin component, an inorganic filler material, and a radical polymerization initiator as described above is used as a material for producing an artificial marble molded article. This composition may further include a silane coupling agent, a dispersant such as an organic carboxylic acid salt, a mold release agent, a coloring agent, etc. Additives can be added. It is desirable to defoamer before molding.

The invention will now be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a molding apparatus used in one embodiment of the present invention, and FIG. 2 is a cross-sectional view of a molding apparatus used in another embodiment of the present invention.

In FIG. 1, a thermosoftening material 3 is sandwiched between an edge 1' of a lower mold 1 and an edge 2' of an upper mold 2. As shown in FIG. The composition is injected into the space 4 formed by the lower mold 1 and the upper mold 2 and polymerized and hardened to produce a molded product. Therefore, the lower mold 1 and the upper mold 2 are manufactured so that the space 4 matches the shape of the desired molded product. The lower mold 1 and the upper mold 2 are
It may be made of metal or heat-resistant resin, or a combination of both. The surface 5 of the lower mold 1 facing the space 4 forms the visible appearance of the molded product, and may have a mirror finish or a matte finish, depending on the desired molded product. A cavity 6 for passing a heating medium is provided inside the lower mold 1 so that the distance It (thickness of the inner surface of the lower mold) from the back surface 5 facing the space 4 is approximately equal. and
A heating medium at a desired temperature is charged into the cavity 6 from the heating medium lower part, and the heating medium is discharged from the heating medium outlet 8.

The upper mold 2 is provided with one or more thermosetting resin composition injection ports 9 and one or more air vent holes 10.

The heat-softening material 3 has a heat distortion temperature in the temperature range at which the resin composition starts to shrink due to polymerization and curing, preferably 70 to 8
It is a material with a heat distortion temperature of 0°C. A preferred thermosoftening material is a thermoplastic resin having a heat distortion temperature in the above temperature range. As such a thermoplastic resin, ethylene-vinyl acetate copolymer, polystyrene, high-density polyethylene, polyvinyl chloride, and other arbitrary resins can be used, but for the reasons described below, particularly preferred resins are: It is an ethylene-vinyl acetate copolymer.

When manufacturing an artificial marble molded product using the manufacturing method of the present invention, first, as shown in FIG. Edge 2' of mold 2
The heat-softening material 3 is sandwiched between the molds and the entire outer periphery of the mold, and the material is assembled by a pressurizing machine, an elastic member, or other pressurizing means (not shown) at a pressure of 2 to 3 Kg/cm2. Press the upper mold 2 against the lower mold 1 with a weak pressure of
The resin composition is injected into the valve 1 to fill the space 4 with the resin composition.
Close 1. Next, from the heating medium man lower, 70 to 8
A heating medium at a temperature of 0° C., such as hot water or hot oil, is charged into the cavity 6 and taken out from the heating medium outlet 8, and the heating medium is circulated between the heater (not shown) and the lower plate. Maintain mold at desired temperature.

The resin composition in the space 4 begins to polymerize and harden and shrinks, and at the same time, the heat-softening material 3 softens, and the lower mold 1 of the upper mold 2
The thickness of the heat-softening material 3 gradually decreases due to the pressure applied to the resin composition, and the volume of the space 4 also decreases following the shrinkage of the resin composition.

In the present invention, the temperature of the lower mold 1 is higher than the temperature of the upper mold 2 and is maintained at the curing temperature of the resin composition, so that the resin composition in the space 4 is close to the lower mold. The parts polymerize and harden quickly. The resin composition in the portion near the upper mold 2 maintains a fluid state for the longest time. Therefore, shrinkage caused by polymerization and curing of the resin composition is absorbed by the fluidized portion of the resin composition, so even if only the above-mentioned weak pressing force is applied to the resin composition during polymerization and curing, the resin in contact with the lower mold will shrink. The surface of the molded product is not affected by the above-mentioned shrinkage, and no unevenness or wrinkles occur at all. Since the resin composition hardens from the side that comes into contact with the lower mold 1, shrinkage of the resin composition is absorbed by the fluidized portion of the resin composition, and the upper mold 2 is cured by the softening and thinning of the heat-softening material 3. During polymerization and curing of the composition, since the resin composition is always in pressure contact, almost no unevenness occurs on the surface that comes into contact with the upper mold 2. Even if irregularities appear on the surface of the molded product that contacts the upper mold 2, the surface of the molded product that comes into contact with the upper mold 2 is an invisible portion and will not impair the commercial value of the molded product.

In the present invention, since a finished ship product is manufactured as described above, the heat-softening material 3 has excellent sealing properties between the upper mold 2 and the lower mold 1, and a resin composition. It softens and deforms with weak force in the polymerization and curing temperature range of , and even when softened, it does not easily leak out from the edge of the mold and sticks closely to the mold to prevent leakage of the resin composition. It is required to be able to do the following. As a heat-softening material that can satisfy all of these requirements, an ethylene-vinyl acetate copolymer is preferable, especially containing 10 to 40% by weight of units derived from vinyl acetate, more particularly 15 to 25% by weight of units derived from vinyl acetate. % of ethylene-vinyl acetate copolymer is preferred. The heat distortion temperature of such an ethylene-vinyl acetate copolymer can be changed by changing the content of units derived from vinyl acetate and the degree of polymerization. If the content of units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is higher than the above range, the adhesion to the mold will be too strong and it will be difficult to separate it from the mold after producing the molded product. If the amount is less than the above range, the elasticity at a temperature lower than the heat deformation temperature will be reduced, and the sealing performance of the space 4 will be reduced.

The thickness of the thermosoftening material can be adjusted as appropriate depending on the size of the space 4, the shrinkage rate of the resin composition used, etc.
Generally preferred is 0.8 to 2+u+, and the width of the heat softenable material is generally preferred to be 5 to 40+n.

In the present invention, the temperature of the upper mold 2 is maintained lower than the temperature of the lower mold 1, and normally the above state can be maintained without providing special heating means for the upper mold 2. Optionally, heating means may be provided to achieve the above state.

In FIG. 2, the lower mold 1 includes a cavity 6 shown in FIG.
An electric heater 12 is provided in place of the heating medium lower and the heating medium outlet. In the embodiment shown in FIG. 2, the structure of the mold, the method of manufacturing the molded product, etc. are the same as those described with reference to FIG. 1, except that the heating means for the lower mold 1 is different.

The present invention produces not only flat plate-like molded products but also molded products with three-dimensional shapes, such as kitchen sinks, counters with integrated kitchen sinks, washbowls, vanities with integrated washbowls, bathtubs, and other artificial marble molded products. Therefore, it is possible to easily produce the molded product with an extremely clean visible surface.

(Effects of the Invention) In the present invention, upper and lower molds in which a thermosetting material is sandwiched between their edges are used, and the temperature of the lower mold is higher than that of the upper mold, and the thermosetting material for molding is The thermosetting resin composition is polymerized and cured while maintaining the curing temperature of the resin composition and pressurizing the upper mold against the lower mold, so that the polymerization and curing of the resin composition will occur on the visible surface of the molded product. The shrinkage during curing is absorbed by the fluid part during curing, and as the resin composition shrinks, the upper mold approaches the lower mold and the molded product is manufactured with the resin composition always under pressure. As a result, the visible surface of the obtained molded product is extremely clean, with no unevenness caused by shrinkage.

Example 1 Acrylic resin syrup 30 prepared by partially polymerizing a monomer mixture consisting of 80% by weight of methyl methacrylate and 20% by weight of styrene until the viscosity reached 500 cp.
To the parts by weight, 70 parts by weight of fine silica powder (trade name: "Crystallite A-AJ ■ manufactured by Tatsumori), 1.0 parts by weight of tertiary butyl peroxy-2-ethylhexanoate, and an appropriate amount of pigment were added. The resin composition obtained by addition, mixing, and defoaming treatment was injected into a light groove in the space 4 of the mold shown in FIG.

The heat-softening material 3 is made of ethylene-vinyl acetate copolymer (containing 20% by weight of units derived from vinyl acetate) having a thickness of 1. (A low sheet was used. A press pressure of 2 g/cta was applied to the upper mold 2, and the heating medium population) to 8
The lower mold 1 was heated by circulating hot water at 0° C. into the cavity 6. The temperature of the surface 5 in contact with the composition of the lower mold 1 is approximately 75°C.
From the time when the ethylene-vinyl acetate copolymer sheet exceeds The amount decreased to 0.2 to 0.3 and did not decrease thereafter. Thereafter, cold water was circulated in the cavity 6 to cool the mold to around room temperature, and then the molded product was taken out from the mold. The visible surface (concavity forming surface) of the obtained artificial marble molded product had no irregularities due to shrinkage and had an extremely good appearance.

Comparative Example 1 A molded article was produced in the same manner as in Example 1, except that the upper mold and lower mold were first temporarily clamped and no press pressure was applied during curing of the composition. .

The visible surface of the obtained molded product had unevenness partially due to shrinkage, and had a poor appearance.

Comparative Example 2 A molded article was produced in the same manner as in Comparative Example 1, except that no heat-softening material was used and the edges of the upper mold and the lower mold were brought into direct contact.

The visible surface of the obtained molded product had irregularities caused by shrinkage everywhere, and had a poor appearance.

[Brief explanation of the drawing]

FIG. 1 is a front view of a molding device used in one embodiment of the present invention, and FIG. 2 is a sectional view of a molding device used in another embodiment of the present invention. 1 is the lower mold, 1' is the edge of the lower mold, 2 is the upper mold, 2'
is the edge of the upper mold, 3 is the heat-softening material, 4 is the space, 5 is the surface facing the space of the lower mold, 6 is the cavity, F is the heating medium inlet, 8 is the heating medium outlet, 9 is the The resin composition injection port 12 is an electric heater.

Claims (18)

[Claims] (1) In a method for producing an artificial marble molded product, in which a composition containing a thermosetting resin component and an inorganic filler is hardened and molded by a press molding method using upper and lower molds, the visible part of the molded product is formed. A heat-softening material is sandwiched between the edge of the lower mold and the edge of the upper mold, and the composition is injected into the space formed by the upper mold and the lower mold. The temperature of the lower mold is maintained higher than the temperature of the upper mold and at the curing temperature of the composition, and the composition is polymerized and cured while pressing the upper mold against the lower mold. Manufacturing method for artificial marble molded products. (2) The manufacturing method according to claim 1, wherein the thermosetting resin component is a partially polymerized syrup of an acrylic resin or an unsaturated polyester resin. (3) A patent claim characterized in that the acrylic resin is obtained by polymerizing a monomer containing one or more lower alkyl esters of acrylic acid or methacrylic acid as a main component using a radical polymerization initiator. The manufacturing method according to item 2 of the scope. (4) the acrylic resin contains one or more lower alkyl esters of acrylic acid or methacrylic acid;
A patent claim characterized in that a mixture with a monomer having one or more ethylenically unsaturated double bonds, which accounts for 25% by weight or less of the total monomers, is polymerized using a radical polymerization initiator. The manufacturing method described in Scope 2. (5) The production method according to any one of claims 3 and 4, wherein the lower alkyl ester of methacrylic acid is methyl methacrylate. (6) The monomer having the ethylenically unsaturated double bond,
Styrene, vinyltoluene, α-methylstyrene, methacrylic acid, ethyl methacrylate, butyl methacrylate,
2-ethylhexyl methacrylate, lauryl methacrylate, glycidyl methacrylate, acrylic acid, 2-ethylhexyl acrylate, lauryl acrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate, allyl methacrylate, diallyl phthalate and allyl glycol carbonate. (7) Claims 1 to 6 characterized in that the composition contains a radical polymerization initiator.
The manufacturing method described in any one of paragraphs. (8) The manufacturing method according to claim 1, wherein the content of the inorganic filler in the composition is 30 to 90% by weight. (9) The manufacturing method according to claim 1, wherein the thermosoftening material is a thermoplastic resin. (10) The manufacturing method according to claim 1, wherein the heat-softening material is a heat-softening material having a heat distortion temperature of 70 to 80°C. (11) The manufacturing method according to claim 9, wherein the thermoplastic resin is an ethylene-vinyl acetate copolymer. (12) Claim 11, characterized in that the ethylene-vinyl acetate copolymer is an ethylene-vinyl acetate copolymer containing 10 to 40% by weight of units derived from vinyl acetate. manufacturing method. (13) The manufacturing method according to claim 1, wherein the heat-softening material is a plate-shaped body having a thickness of 0.8 to 2 mm. (14) The manufacturing method according to claim 1, characterized in that the temperature of the lower mold is maintained at 70 to 100°C. (15) The temperature of the upper mold is 10% lower than the temperature of the lower mold.
The manufacturing method according to claim 1, characterized in that the temperature is maintained at a temperature lower than 40°C. (16) The manufacturing method according to claim 1, wherein the lower mold is heated by passing a heating medium through a cavity provided in the lower mold. (17) The manufacturing method according to claim 1, wherein the lower mold is heated by a heater selected from the group consisting of an electric heater and an infrared heater. (18) The upper mold is pressurized against the lower mold by one or more pressure means selected from the group consisting of a pressure machine, an elastic member, and the dead weight of the upper mold. A manufacturing method according to claim 1.