JP2554715B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for molding a plastic cast material used as a kitchen work top, a table top, a wash basin top, a wall material, a floor material, and the like. Relates to a cast molding method capable of producing the cast product with high precision and beauty.

[Prior Art] Plate-shaped hard molded articles obtained by curing and molding a thermosetting composition such as an unsaturated polyester resin composition or an acrylic resin composition into a certain shape have been recently used as artificial marble boards. It is widely used in the field of housing equipment and equipment. As a method for producing the above-mentioned plate-shaped hard molded product, there are a casting method, a press molding method, a continuous molding method and the like, which are carried out on an industrial level, respectively, but all have many problems.

Of these, the cast molding method has long been used as a manufacturing method for liquid resin compositions and is suitable for producing small to medium quantities of a wide variety of products. It has the highest degree of popularity because it can be easily changed and adjusted (thickness, thickness, color tone, patterning, etc.) and is used as a method of manufacturing hard molded products for many types of housing equipment and equipment.

There are two types of casting molds, one is a horizontal type and the other is a vertical type. Generally, the horizontal type is used because it is easy to handle. However, when a liquid resin composition containing a filler is formed by casting, the specific gravity of the filler particles and the specific gravity of the resin liquid in the liquid resin composition are different, and in many cases the specific gravity of the filler particles is large. As a result, the filler settles at the bottom of the casting space, and the shrinkage rate upon curing differs between the top and bottom of the casting space. Therefore, warpage occurs in the molded product. In the case of producing a plate-shaped cast-molded product, the shrinkage rate is different on both sides of the plate in the flat-casting cast-molding method, resulting in significant warpage and low commercial value.
On the other hand, in the vertical type, there is no difference in shrinkage rate between both surfaces of the plate, and warpage does not occur.

FIG. 4 is a vertical cross-sectional explanatory view showing a vertical casting mold 1 used to manufacture a flat plate casting. Two rigid casting plates 2a, 2b are erected and face each other, and the casting plates 2a, 2b
Spacers 5 made of metal, synthetic resin, or wood are arranged on the left and right side edges and the bottom edge, and the casting space 3 is formed by the casting plates 2a, 2b and the spacers 5. The two casting mold plates 2a and 2b are clamped by a clamp 4 at a part of their peripheral edges. The casting mold 1 is immersed in a heated liquid bath (mainly water) bath in a liquid bath, and the casting method is manufactured according to the following sequence.

After cleaning the casting mold plates 2a, 2b, etc. and applying mold release agents to the opposite surfaces respectively, the spacer 5 is sandwiched to form the casting space 3 and the casting is performed by the clamp 4 as shown in FIG. Type 1
Assemble.

Immerse the casting mold 1 in the vertical position in the liquid bath.

The liquid material for molding is filled into the casting mold space 3 (the process may be reversed).

The entire casting mold 1 is heated by introducing a high temperature liquid into the liquid bath or by heating the liquid in the liquid bath to polymerize and cure the liquid raw material.

Take out the casting mold 1 from the liquid bath, disassemble and take out the molded product.

[Problems to be Solved by the Invention] As the molding liquid raw material, an acrylic resin-based composition containing an inorganic filler, an unsaturated polyester resin-based composition, or the like is used. Shrinkage of about 2 to 20% occurs. That is, as shown in FIG. 4 and FIG. 5 (plan sectional view), the liquid raw material 6A shrinks in the three-dimensional direction in the process of being processed into the cured molded product 6B, and the wall surface of the cured molded product 6B and the casting space 3 The gaps S ₁ and S ₂ are formed between and. The gap S ₁ may be formed separately on the side of the casting molds 2a and 2b, but it is generally formed in a biased manner on the casting plate having the better releasability.

Due to such volume contraction, a gap is generated between the template and the resin composition being polymerized, and the monomer component having a relatively low boiling point in the liquid raw material evaporates from the surface of the molded article being polymerized, so that the surface of the molded article is The composition is different from the inside,
If the surface of the molded product contacts the evaporated monomer or oxygen in the air and the curing is impaired, or the heat of polymerization from the molded product on the side where the gap is generated will not be transferred by heat transfer. There was an unfavorable state in which whitening, cloudiness, and uneven luster occurred and the transparency was lost, impairing the appearance. Since the whitening, cloudiness, and glossiness cannot be eliminated by after-cure, the surface of the molded product had to be ground and removed.

Therefore, the present inventors compensate for the mold release from the casting due to curing shrinkage by some means, and complete the curing without the mold release, whereby the appearance is beautiful and the dimensional uniformity is high. The present invention has been completed as a result of various studies on a casting method capable of obtaining

[Means for Solving the Problems] In the present invention which achieves the above object, the spacers arranged at both side edges and bottom edges of facing vertical casting plates are made of elastic tubes, and Introduce a pressurized fluid to form a sealed state, immerse it in a liquid bath, and then fill the casting space composed of the casting plate with the liquid material for casting to start the curing reaction. Inject the liquid raw material for casting into the casting space in which the sealing state is formed, and then immerse it in the liquid bath to start the curing reaction, and consider the progress of gelation of the liquid raw material. Meanwhile, it is a gist to discharge the pressurized fluid in the elastic tube and press the casting plate in the approaching direction by the liquid head pressure in the liquid bath to reach the completion of curing.

[Operations and Examples] FIG. 1 is a partially cutaway explanatory view showing an example of the casting mold 1 used in the casting mold forming method of the present invention, which is different from the conventional example shown in FIG. The points are as follows. That is, the spacer provided between the casting plates 2a and 2b is replaced with the elastic tube 8, and the pressure fluid is taken in and out of the elastic tube 8 to exert a sealing function in balance with the liquid head pressure in the liquid bath. At the same time, the casting mold plates 2a and 2b are configured so that the distance between them can be adjusted. The elastic tube 8 is formed of vinyl chloride resin, polyethylene resin, or the like, and in addition to the cylindrical tube shown in the drawing, a hollow tube having a rectangular or elliptical cross section is used.
One end 8a of the elastic tube 8 is closed and the other end 8b is connected to a pressurized fluid supply source (not shown). When manufacturing a synthetic resin plate using this casting mold 1, for example, the following procedure is performed.

First, the casting mold plates 2a and 2b are erected so as to face each other, and the elastic tube 8 is sandwiched between both side edges and the bottom edge of the casting mold plates 2a and 2b, and is clamped from the outside by the clamp 4 so that the casting mold 1 is formed. Assemble.

At this time, a pressurized fluid is introduced into the elastic tube 8 so that both side edges and bottom edges of the casting mold plates 2a and 2b are connected to the elastic tube 8
To completely block it.

The casting liquid space 6 is filled with the molding liquid raw material 6A from the upper opening of the casting mold 1 [state shown in FIG. 2 (A)]. Due to the liquid pressure of the liquid raw material, the casting plates 2a and 2b exert a force in a direction in which they are separated from each other, but the clamps 4 mounted on the four circumferences keep the molding space interval constant, and the elastic tube is slightly spaced from the molding space interval. Sufficient sealing pressure can be obtained by increasing the elastic repulsion force by deforming the elastic tube 8 to a predetermined distance and introducing a pressurized fluid into the elastic tube 8 (usually ² to 3 kg / cm ² ). Although water or air can be used as the pressurized fluid, water having good thermal conductivity is more preferable.

The casting mold 1 is immersed in the liquid in the liquid bath in the vertical state so that the upper opening is projected from the liquid surface. At this time, the casting heads 2a, 2b receive a force in a direction in which they approach each other due to the bath head pressure of the liquid, but the head pressure of the casting liquid raw material opposes this force, and as a result, they do not approach each other.

By heating the liquid in the liquid tank to 40 to 80 ° C., the entire casting mold 1 is heated to accelerate the polymerization reaction of the hardening component in the liquid raw material 6A.

As the polymerization progresses, the liquid raw material starts to gel, the hydraulic pressure acting on the inner surfaces of the casting plates 2a and 2b begins to decrease, and finally solidifies, the hydraulic pressure becomes zero, and further volume contraction begins. . The pressurized fluid in the elastic tube 8 is discharged while monitoring the progress of gelation of the molding liquid raw material 6A, and the pressure is made lower than the liquid head pressure in the liquid tank, for example, atmospheric pressure or less. Cast template
2a and 2b are moved toward each other by the head pressure.

The movement of the casting plates 2a, 2b is performed by the head pressure in the liquid tank, and the elastic tube 8 is deformed according to the movement of the casting plates 2a, 2b. The sealing properties of the plates 2a and 2b are not impaired.

Take out the casting mold 1 from the liquid tank and, if necessary, 80 to 130 ℃
After heating and performing after-cure, the casting mold 1 is disassembled and the molded product is recovered.

The molded products produced by the above-mentioned (1) to (3) are continuously pressed and clamped by the casting plates 2a and 2b until the end of curing, and the inner surfaces of the casting plates 2a and 2b are in contact with the outer surfaces of the cured molded products. Therefore, inconveniences such as variations in plate thickness and warpage do not occur, and defects such as whitening, clouding, and gloss unevenness do not occur in the appearance of the molded product, and beautiful molding can be performed. As a result, it has become possible to reduce mechanical secondary processing such as grinding and cutting.

FIG. 3 (A) is a plan view showing another casting mold 1 used for carrying out the method of the present invention, and FIG. 3 (B) is a sectional view showing still another casting mold. With the mold 1, a synthetic resin plate having an L-shaped cross section can be molded.

Example 1 A casting mold 1 having the shape shown in FIG.
The dimensions were 12 mm in thickness, 1000 mm in width and 1000 mm in height.

Next, in a resin solution prepared by dissolving 25 parts of polymethylmethacrylate resin (Sumitomo Chemical Co., Ltd., Sumipex B (LG)) in 75 parts of methyl methacrylate, aluminum hydroxide (Showa Light Metal Co., Ltd., Heidi 200 parts of Light H320) and 1 part of a curing catalyst (Kayaester O manufactured by Kayaku Nouri Co., Ltd.) were mixed to obtain a resin composition (1).

Next, air is injected into the inside of the elastic tube 8 at an air pressure of ² kg / cm ² to form the casting space 3, the above resin composition (1) is injected, and the resin composition is held in a water tank at 60 ° C. and cured. After about 25 minutes, it stopped flowing. At this time, the air injected into the elastic tube 8 was evacuated to atmospheric pressure, and subsequently cured in a water bath at 60 ° C. for 35 minutes.

Next, the cured product was taken out from the casting mold and subjected to after-curing at 120 ° C. for 2 hours to obtain a milky white translucent marble-like cured product. No defects such as whitening of the surface, cloudiness, and uneven gloss were observed.

As the molding raw material applied in carrying out the method of the present invention, a liquid polymerizable resin composition may be used, and in addition to the acrylic resins shown in the above examples, unsaturated polyester resins, vinyl ester resins, Curable compositions, such as an epoxy resin, can be mentioned.

[Effects of the Invention] Since the method of the present invention can complete the curing of a molded product while maintaining the close contact between the inner surface of the casting mold and the outer surface of the molded product, the casting with a beautiful appearance and high dimensional accuracy can be achieved. Shaped products are now available.

[Brief description of drawings]

FIG. 1 is a partially broken explanatory view of a casting mold used in the present invention, FIGS. 2 (A) and 2 (B) are side sectional views showing a manufacturing process of the present invention, and FIG. 3 (A) is the present invention. FIG. 3 (B) is a cross-sectional view showing another casting mold applied to the present invention, FIG. 3 (B) is a vertical sectional view showing still another casting mold applied to the present invention, and FIG. 4 is a vertical section showing a conventional casting mold. FIG. 5 is a cross sectional view of FIG. 1 ... Casting mold, 2a, 2b ... Casting mold plate 3 ... Casting mold space part, 4 ... Clamp 5 ... Spacer, 6A ... Liquid raw material for molding 6B ... Hardened molded product, 8 ... … Elastic tube

Claims (1)

(57) [Claims] 1. In the casting method, spacers arranged at both side edges and bottom edges of facing vertical casting plates are made of elastic tubes, and a pressurized fluid is introduced into the elastic tubes. Liquid material for casting is filled in the casting space that is formed by forming a sealed state, and the curing reaction is started in the state of being immersed in the liquid bath, and the degree of gelation of the liquid raw material is considered. Meanwhile, the pressurized fluid in the elastic tube is discharged, and the completion of curing is reached by pressing the casting plate in the proximity direction by the liquid head pressure in the liquid bath.