JP2941311B2 - Casting method for synthetic resin - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a casting method, and more particularly to a casting method using an ultraviolet-curable liquid resin.

(Prior art) Conventionally, a casting method has been developed in which a liquid synthetic resin is injected and cured into a cavity of a silicone rubber mold molded with RTV silicone rubber based on a master to obtain a molded product.

Molding of parts by the casting method has become widespread in the field of high-mix low-volume production and molding of prototypes because the production of molds can be done in a short time at low cost.

The synthetic resin used in the conventional casting method is a two-pack type polyurethane resin or epoxy resin composed of a main agent and a curing agent. Recently, there has been a case where a rubber mold is a transparent rubber mold obtained by molding a master with a transparent rubber, and an ultraviolet curable liquid resin is used as a synthetic resin for casting.

(Problems to be solved by the invention) In the case of casting using a conventional two-component synthetic resin,
When mixing two liquids, air must be mixed in the resin liquid, so that the mixing must be performed in a vacuum. In addition, since the curing reaction proceeds rapidly due to the mixing of the two liquids, the pot life is short, and the casting operation must be performed quickly. Was needed.

In addition, when casting with a two-component synthetic resin, even if a resin with a high curing speed is used, the molded product will not be completely cured unless heated and cured at 60 ° C. for 1 to 2 hours after casting. Cannot be removed from

For this reason, when trying to obtain a small amount (about 50 to 100) of molded products, it takes a considerable time to obtain all the molded products unless a large number of molds are prepared. In the case of casting using a UV-curable liquid resin, since the resin liquid is a one-liquid type, there is no need to worry about the pot life and the workability is improved. However, conventional UV-curable liquid resins have been developed for paints, inks, adhesives, and the like, and are hardly suitable for casting. That is, the conventional ultraviolet curable liquid resin has a high viscosity and poor castability, and is diluted with a diluent to decrease the viscosity in order to enhance the castability. As a result, the curability decreases and it takes a considerable time for about 10 to 30 minutes to cure, and furthermore, thick products cannot be cured, molding shrinkage is large, not only the appearance quality of the molded product is reduced, but also the physical properties Many drawbacks such as lowering occurred, and it was difficult to put it to practical use.

The present invention was created as a result of repeated studies on casting with a one-pack type and fast-curing synthetic resin in order to solve the above-mentioned drawbacks of the prior art.

(Means for Solving the Problems) That is, the present invention relates to a method of casting a synthetic resin, in which an ultraviolet-curable liquid resin is injected into a cavity of a transparent silicone rubber mold having a master and is cured by ultraviolet irradiation. The ultraviolet-curable liquid resin is a mixture of a diacrylate of bisphenol A ethylene oxide adduct and an acrylate of phenylglycidyl ether, and the photopolymerization initiator is 2-benzyl-2-dimethylamino-1- (4- (Morpholinophenyl) -butane-1 is a method for casting a synthetic resin.

(Function) The present invention is configured as described above, and its function is to use an ultraviolet curing type as a synthetic resin liquid used for casting, so that the resin liquid is a one-part resin liquid, and the working time required for the mixing operation is used. No need to worry about. Further, since the ultraviolet curing liquid resin to be used has a low viscosity and is particularly suitable for casting, it is necessary to dilute with a diluent in order to enhance the casting property as in the case of the conventional ultraviolet curing liquid resin. In addition, casting can be performed while taking advantage of its excellent properties such as curability, molding shrinkage, and physical properties. This makes it possible to cure the ultraviolet ray in a very short time of about 5 minutes or less even if the thickness is large, and to produce a molded article which has very good appearance quality and excellent physical properties because of almost no molding shrinkage, and which can withstand practical use sufficiently. It can be easily obtained.

(Examples) Ultraviolet curing type synthetic resins are roughly classified into radical polymerization type and cationic polymerization type according to their curing mechanism.

Currently, UV curable synthetic resins are being put to practical use.
In the fields of paints, inks, adhesives, and imaging materials, the ones that are mainly used here are those that use radical polymerization of (meth) acrylic monomers. Epoxy acrylate (bisphenol A type vinyl ester, trade name: Lipoxy [Showa Kobunshi]) which is an addition reaction product of acrylonitrile and acrylic acid.

Although this synthetic resin has excellent chemical resistance, curability, heat resistance, etc., it has high viscosity and is difficult to cast, so it is hardened by adding various polysynthetic monomers and reactive diluents to lower the viscosity. However, hardening could not be performed even though the wall thickness was large, and the molding shrinkage was large, so that a good cast product could not be obtained.

Also, cationic polymerization synthetic resin, although may not cure is inhibited by oxygen, molding shrinkage has the advantage such as low, the gas such as N ₂ upon curing occurs, thick molded articles In the case of (1), air bubbles were contained inside, so that it was not suitable for casting.

Under these circumstances, we first examined the selection of UV-curable synthetic resin suitable for casting, and cured the acrylate of bisphenol A ethylene oxide adduct (hereafter referred to as monomer I) with a relatively low viscosity of 800-1400 CPS. It has been found that it is a synthetic resin which is excellent in heat resistance, cures thick-walled products uniformly, has a low molding shrinkage ratio, and has excellent heat resistance and hardness and is suitable for casting.

Specific examples of such a synthetic resin include the following.

Such a cast product obtained by curing the monomer I by ultraviolet curing is insufficient in flexibility, elongation, and toughness. Therefore, a monomer which is blended with the monomer I to improve these properties was studied.

As a result, the acrylate ester of phenylglycidyl ether (hereinafter referred to as monomer II) is well compatible with monomer I and has the effect of improving the above-mentioned physical properties, and has a low viscosity of 150 CPS, excellent curability, and a high molding shrinkage. It is also found that the resin has excellent properties as a casting resin because of its low properties.

Specific examples of the monomer II include the following.

Next, as a study of the photopolymerization initiator for the monomer described above, 2-benzyl-2-dimethylamino-1- (4-
Morpholinophenyl) -butane-1 (hereinafter referred to as initiator A); 1-hydroxycyclohexyl phenyl ketone (hereinafter referred to as initiator B) Was compared.

KAYARAD R5 of monomer I as a UV-curable synthetic resin
Using 51, 4KW, 80W / cm (high pressure mercury lamp), height 21cm, 1
FIG. 1 shows the results of examining the relationship between the photopolymerization initiator concentration and the curing depth by performing ultraviolet curing under irradiation conditions of minute irradiation.

According to the results, the initiator A is much more effective than the initiator B. The concentration is not shown here, but may be 0.5 to 2% by weight in consideration of the relationship between the concentration and physical properties. I found it favorable.

Next, FIG. 2 to FIG. 6 show the results of examining the physical properties of the cured product when the mixing ratio of the monomer II to the monomer I was changed from time to time and the type of the initiator was also changed.

According to the results, the impact strength and elongation were improved by blending the monomer II with the monomer I, and the tensile strength, the bending strength and the hardness tended to decrease. From these results, the blending ratio was 9% by weight. : 1 to 6: 4 was found to be preferable, and the addition of initiator A was found to be preferable for improving the impact strength.

The test conditions in the above examination were as follows:
Using KAYARAD R551, the monomer II and the initiators A and B were the same as the products listed above, and the dumbbell-shaped test piece was 4 KW.
Curing was performed under the conditions of 80 W / cm, a high-pressure mercury lamp, a height of 21 cm, and irradiation for 2 minutes.

When dissolving the photopolymerization initiator in the monomer by heating, it is necessary to add a polymerization inhibitor in order to prevent the monomer from being polymerized by heat, and this may be any of commonly used polymerization inhibitors, for example, It is preferable to mix hydroquinone monomethyl ether in the range of 100 to 200 PPM.

In addition, in the case of casting with a UV-curable synthetic resin, injection is performed at a degree of vacuum of about 10 mmHg in order to completely inject the resin into the cavity of the mold, so that bubbles are not mixed into the molded product. The water content in the synthetic resin liquid needs to be 0.05% by weight or less.

Therefore, at the time of compounding the synthetic resin liquid, a predetermined amount of a photopolymerization initiator, a polymerization inhibitor, and the like are mixed in the monomer, and a porous bag filled with a heat-absorbing agent (for example, Bayrit made by Bayer) is placed. After stirring and mixing at 40-60 ° C for about 5 minutes,
When dewatering is performed for 30 minutes while maintaining a vacuum of 10 mmHg or more, and then cooled to room temperature, the water content in the synthetic resin liquid becomes 0.05% by weight or less.

The mold used for casting has excellent transferability of the master, and is transparent to facilitate the release of complicated shaped products.
It is preferably formed of RTV silicone rubber.

As a transparent RTV silicone rubber, for example, CX52-084 from Toray Silicone Co., Ltd. has good transparency and hardness JISA4
5, the tensile strength of 48 kg / cm _2, elongation 320%, tear strength JISA11
kg / cm, which had enough material for casting.

The ultraviolet curing of the synthetic resin liquid is performed with ultraviolet light having a wavelength of 2000 to 8000 A, and low-pressure or high-pressure mercury lamps, metal halide lamps, xenon lamps, and the like are available as lamps that emit such ultraviolet light.If a high-pressure mercury lamp or metal halide lamp is used, The curing efficiency is good and a thick molded product can be cured in a short time.

An example in which molding is actually performed by ultraviolet curing based on the results of the various studies described above will be described below.

Example 1-Synthetic resin liquid Monomer I (KAYARAD R551) 90 g Monomer II 10 g Initiator A 1 g Polymerization inhibitor (hydroquinone monomethyl ether) 100 PPM-Rubber mold Transparent 300 mm thick dumbbell specimen with 3 mm thickness Silicone rubber mold ・ Injection of synthetic resin solution Vacuum injection at a degree of vacuum of 10 mmHg ・ Curing 2 minutes under high pressure mercury lamp with 80 W / cm strength ・ Result A good cured product with no stickiness or cracks on the surface was obtained.

Example 2 Synthetic resin liquid Monomer I (KAYARADR551) 140 g Monomer II 60 g Initiator A 2 g Polymerization inhibitor (hydroquinone monomethyl ether) 100 PPM Rubber type 155 x 85 x 40 mm as shown in Fig. 7 and thickness max3m
The thickness max of the circuit case as a sewing machine part of m
60mm transparent silicone rubber mold.

-Injection and curing of synthetic resin liquid This was performed by an ultraviolet irradiation type vacuum injection device shown in Fig. 8 described later.

・ Result The molded product is obtained in a good cured state. This molded product is coated with a two-pack type acrylic urethane paint (Nippon Paint, max Superior), and a coating film with good adhesion is obtained by heating at 60 ° C. for 30 minutes. Was done. The silicone rubber mold gradually turned yellow by irradiation with ultraviolet light, but there was no problem in molding about 50 to 100 pieces.

Referring to the ultraviolet irradiation type vacuum injection apparatus shown in FIG. 8, reference numeral 1 denotes a vacuum box having an exhaust port 12 and a reflective plate 2 adhered to the inner surface thereof. A mold mounting table 3 is provided, and a polycup mounting table 5 having a shaft 6 that is rotatable and slidable in the left-right direction is provided, and a light transmission window 7 is provided on one surface of the wall.

Reference numeral 8 denotes an ultraviolet ray generation chamber adjacent to the vacuum box 1, in which a high-pressure mercury lamp 9 covered with a cold mirror 10 for reflecting ultraviolet light is provided. Is provided with a shutter 11 for opening and closing irradiation with respect to.

Reference numeral 18 denotes an exhaust port for cooling the exhaust in the ultraviolet irradiation chamber 8 and the high-pressure mercury lamp 9, reference numeral 19 denotes an intake port, and reference numeral 13 denotes a vacuum pump (not shown) for opening and closing the exhaust port 12 of the vacuum box 1. )
Is a vacuum on-off valve provided in an exhaust pipe connected to.

The operation of injecting and curing the synthetic resin liquid using the apparatus configured as described above is performed as follows.

First, the vacuum cup 1 is closed in a state where the polycup 16 having the synthetic resin liquid 17 measured is mounted on the polycup mounting base 5 and the transparent silicone rubber die 14 having the injection port 15 mounted on the die mounting base 3 is mounted.

Next, the mold mounting table 3 is moved up and down to set the transparent silicone rubber mold.
The position is adjusted so that 14 is at a height facing the high-pressure mercury lamp 9, and the polycup mounting base 5 is also slid left and right to align with the injection port 15 of the transparent silicone rubber mold 14.

After that, the vacuum opening / closing valve 13 is opened to evacuate the inside of the vacuum box 1 to a degree of vacuum of about 10 mmHg, and at the same time, the polycup mounting base 5 is rotated. And then return to normal pressure in the vacuum box 1.

Finally, the shutter 11 is opened, and ultraviolet light from the high-pressure mercury lamp 9 is irradiated on the transparent silicone rubber mold 14 rotating by the rotation of the mold mounting table 3 for about 4 minutes to cure the synthetic resin liquid 17 injected into the cavity. To complete the work.

(Effects) The present invention has the above configuration and operation,
This effect is evident from the comparison of the working process with the conventional method of thermosetting a two-pack type synthetic resin shown in FIG.

That is, in the conventional method, in order to obtain a molded product free of air bubbles, the work must be constantly performed in a vacuum, and after the two-liquid mixing, the curing reaction is progressing, so that this can be effectively performed in a short time. Although it was necessary to carry out the method, the ultraviolet curing method of the present invention does not require such considerations at all, and the working process is extremely simple.

The curing time is about 5 minutes or less even for a thick wall, and it takes 10 to 30 minutes for a thin wall, of course, as compared with the case where a two-pack synthetic resin requires 1 to 2 hours. This is greatly reduced as compared with the case where a conventional ultraviolet curable liquid resin is used. Furthermore, the quality of the appearance and physical properties of the molded product is extremely superior to that of the conventional UV-curable liquid resin, no matter what the shape and thickness, and when the two-component synthetic resin is used. There is no inferiority to that of the above, and it is sufficiently practical.

As described above, the present invention provides a casting method capable of extremely efficiently molding a synthetic resin, and has a great effect on the formation of prototypes and small-lot production of many kinds.

[Brief description of the drawings]

FIG. 1 is a diagram showing the curability of the photopolymerization initiator of the present invention.
6 to 6 show the relationship between the composition of the synthetic resin liquid of the present invention and the physical properties. FIG. 2 shows impact strength, FIG. 3 shows tensile strength, FIG. 4 shows elongation, FIG. Figure 6 shows the bending strength,
FIG. 7 is a perspective view of an ultraviolet-cured molded product, FIG. 8 is a diagram showing an ultraviolet-curing injection device, and FIG. 9 is a diagram comparing working steps between the conventional method and the present invention.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI B29K 105: 24 (56) References JP-A-58-80587 (JP, A) JP-A-60-25710 (JP, A) ( 58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 39/02 B29C 39/26-39/34 B29C 33/38-33/40

Claims (1)

(57) [Claims] 1. A method of casting a synthetic resin in which an ultraviolet-curable liquid resin is injected into a cavity of a transparent silicone rubber mold in which a master is cast and cured by irradiation with ultraviolet light, wherein the ultraviolet-curable liquid resin comprises a monomer. A mixture of a diacrylate of bisphenol A ethylene oxide adduct and an acrylate of phenylglycidyl ether was used, and the photopolymerization initiator was 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butane-
A method for casting a synthetic resin, wherein the composition is a composition as described in 1.