JP2503554B2 - Cast molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to cast molding. In particular, it relates to a method for preventing entrapment of air bubbles in producing a molded product related to light transmission refraction by cast molding.

<Prior Art> The reaction injection molding method, which is a typical example of the casting method, is a known molding method. Regarding the method and the apparatus, Plastic Age, Vol. 25, No. 3, (1979), Plastic Age Co., Ltd., p. 62- The method is described in the literature such as “Technology and apparatus for various internal and external RIM systems” on page 69.

In such a reaction injection molding, as a method for preventing bubbles from being entrapped in the cavity, a method of using a mold having a structure for reducing the flow rate at the time of injecting the raw material liquid into the mold is disclosed in JP-A- 61462, JP-A-54-52171, JP-A-56-3440, and JP-A-59-12 as a method for collecting bubbles in a raw material liquid by providing a branch collection chamber in a runner portion in a mold.
No. 824, JP-A No. 60-120023, and JP-A No. 56-123850 have been proposed as an apparatus capable of changing the injection rate of the reaction raw material liquid into the mold.

Further, as a transparent molded article, JP-A-60-258219 discloses a method for obtaining a disk substrate by polymerizing a monomer containing methyl methacrylate as a main component in a mold.

<Problems to be Solved by the Invention> The presence of air bubbles in a molded product that requires transparency, such as a molded product with a marble pattern, which is involved in light transmission and refraction, is a major obstacle even if it is small.

A mold having a complicated structure is required in the method of using a mold having a structure for reducing the flow velocity when injecting the raw material liquid into the mold.

Even if there is a collection chamber, it is not possible to deal with air bubbles generated after passing through the collection chamber. Therefore, changing the injection speed into the mold without using the above-mentioned special mold, without entraining air bubbles,
An object of the present invention is to provide a molding method of an excellent molded product relating to light transmission refraction.

<Means for Solving Problems> That is, in the present invention, in a molding method of injecting a raw material liquid into a mold and polymerizing and curing the raw material liquid, vinyl and / or vinylidene simple substance is contained in the raw material liquid with or without a polymer. It is a cast molding which is mainly composed of a polymer and is characterized by changing the injection rate of the raw material liquid into the mold in at least two stages.

In the present invention, the raw material liquid mainly containing vinyl and / or vinylidene monomer with or without a polymer means a monomer mainly used from vinyl and / or vinylidene monomer or a soluble in these monomers. The main component is a monomer composition containing the above polymer, and a polymerization initiator and, if necessary, various auxiliary agents and additives.

The vinyl or vinylidene monomer means a monomer having at least one polymerizable unsaturated carbon bond such as an acryloyl group, a methacryloyl group, and a vinyl group in the molecule, and the unsaturated carbon bond has one monomer. As the monomer, methyl (meth) acrylate, ethyl (meth) acrylate,
Butyl (meth) acrylate, isopropyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate,
Fatty alcohols such as bornyl (meth) acrylate, furfuryl (meth) acrylate, isobornyl (meth) acrylate, adamantane (meth) acrylate, etc., alicyclic alcohols, heterocyclic alcohols, aromatic alcohols or (Meth) acrylic acid esters with phenols; acrylonitrile, methacrylonitrile,
Vinyl nitriles such as crotonitrile; vinyl acetate,
Vinyl esters such as vinyl propionate and vinyl benzoate; aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene; 2-chlorostyrene,
Aromatic vinyl compounds having halogen-substituted aromatic rings such as 4-bromostyrene, 4-bromophenyl (meth) acrylate, and 2,4,6-tribromophenyl (meth) acrylic acid, halogen-containing (meth) acrylic acid Esters; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride and anhydrides thereof; and the like.

Further, such vinyl or vinylidene monomers can be used alone or in combination, and further other copolymerizable monomers can be used in combination.

The polyfunctional monomer having two or more unsaturated carbon bonds in the molecule, ethylene glycol, propylene glycol or their oligomers, other dihydric or higher alcohols or phenols and their alkylene oxide adducts and acrylic acid or Esters with methacrylic acid; and ring-opening adducts of dihydric or polyhydric alcohols with glycidyl group-containing (meth) acrylates; and ring-opening adducts of dibasic acids with glycidyl group-containing (meth) acrylates; and aryl Methacrylate, vidinylbenzene and the like can be mentioned.

The polyfunctional monomer has the effect of improving the strength, chemical resistance and heat resistance of the molded product, and is preferably used in the range of 0.1 to 30% by weight in the raw material liquid.

The vinyl or vinylidene monomer can be used as a monomer as it is, but can be used as a monomer composition in which a polymer is dissolved (commonly called syrup).

The amount of the polymer contained in this monomer composition is limited by the fluidity of the raw material liquid, but is approximately 50% by weight in the raw material liquid.
To the extent.

This polymer can be arbitrarily selected depending on the physical properties of the molded product as long as it is soluble in the monomer.

As the polymerization initiator, known radical initiators are used, for example, benzoyl peroxide, lauroyl peroxide, diacyl peroxide such as disuccinic acid peroxide: di-t-butyl peroxide, t-butyl cumyl peroxide, Dialkyl peroxide such as dicumyl peroxide: -t
-Peroxy ester such as butyl peroxyacetate, t-butyl peroxypivalate, t-butyl peroxybenzoate: Hydroperoxide such as t-butyl hydroperoxide, cumene hydroperoxide: ketone peroxide such as methyl ethyl ketone peroxide Organic peroxides such as oxides and 2,2-
Examples thereof include azo compounds such as azobisisobutyronitrile and 2,2-azobis (2,4-dimethylvaleronitrile).

The amount of such a polymerization initiator is 0.01 to 10% by weight in the raw material liquid.

Further, in the present invention, in addition to the above-mentioned polymerization initiator, a polymerization accelerator and an auxiliary component of the polymerization accelerator can be used if necessary, and such a polymerization accelerator corresponds to a reducing substance.

As the auxiliary component of the polymerization accelerator, there are a metal-containing compound, an amine or an amine-halogen compound and the like.

As the polymerization accelerator, lauryl mercaptan, octyl mercaptan, 2-ethylhexylmethylcaptan,
Mercaptans such as glycol dimercaptoacetate and glycol dimercaptopropionate: thioureas such as dibutylthiourea and tetramethylthiourea: trimethylphosphite, phosphite esters such as chilli-n-butylphosphite, etc. .

Examples of the metal compound include organic acid salts or organic complexes of metals selected from iron, copper, cobalt, nickel, tin, aluminum, palladium, antimony and the like.

Examples of amines or amine-halogen compounds include primary amines, secondary amines, tertiary amines, hydrogen halide salts thereof, and quaternary ammonium halides.

The amount of the polymerization accelerator and its auxiliary component is 0.00001 to 1% by weight in the raw material liquid.

Further, the reactive raw material liquid mainly composed of the vinyl and / or vinylidene monomer used in the present invention,
In addition to the above-mentioned polymerization initiator and polymerization accelerator, an ultraviolet absorber, a heat stabilizer, a lubricant, a release agent, a colorant, and a filler can be added, if necessary.

When a polymerization accelerator is used, if it is mixed with the polymerization initiator in the raw material liquid in advance, the polymerization may proceed immediately and smooth formation may not be possible.

In such a case, the basic method of reaction injection molding in which the raw material liquid is divided into two parts, the polymerization initiator is dissolved in one side and the polymerization accelerator is dissolved in the other side, and the usage is mixed immediately before the injection into the mold is performed. You can use it.

In this case, the auxiliary component of the polymerization accelerator and various additives may be mixed in either one.

The mold used in the present invention has a well-known and publicly-used structure used for reaction injection molding.

That is, it has a cavity corresponding to the shape of the molded product and an injection path for introducing the raw material into this cavity.

This injection path has a runner section and a gate section, and the runner section may have an after-mixer if necessary.

In cast molding represented by reaction injection molding, it is generally desired that the injection rate of the raw material liquid into the mold be as high as possible in view of the economical efficiency of the molding and the reactivity of the raw material liquid.

That is, if the speed is kept low, the raw material liquid may be reactively hardened in the middle of the injection path, and smooth molding may be difficult. Even if molding is possible, it takes a long time, which is economically inferior.

However, at high speeds, gas is entrained in the raw material liquid at various places in the mold, and especially at the tip of the flow, the gas becomes bubbles and remains in the molded product, so that a proper molded product can be obtained. Can not.

In the present invention, the rate of injecting the raw material liquid into the mold is changed in at least two steps.

Specifically, the change in the injection rate is preferably in the order of low speed-high speed.

That is, it is preferable that the injection passage in the mold is filled at a low speed until it is filled with the raw material liquid, and then at a high speed when the raw material liquid begins to enter the cavity.

When the shape inside the cavity is complicated, it is more preferable to further change the injection speed in the order of low speed-high speed-low speed.

That is, the injection path in the frame is filled with the raw material liquid at a low speed, and when the raw material begins to enter the inside, the cavity portion is injected at a high speed, and when the inside of the cavity portion is close to being filled with the raw material liquid, It is preferable to reduce the speed again.

When the inside of the cavity is close to being completely filled with the raw material liquid is before it is completely filled, and when the volume corresponding to 1/20 to 1/10 of the space volume of the cavity of the mold is left. Say.

Lowering the velocity near the end of this injection has a curative to eliminate gas in the cavity, especially if the geometry in the cavity is complex.

 It is also effective in limiting the occurrence of burrs.

In the present invention, the injection rate can be expressed as cm ³ / sec in the injection volume of the raw material liquid per unit time.

And low velocity V _L (cm ³ / sec), high layer V _H (cm ³ / sec)
And the viscosity ρ (centipoise) of the raw material liquid, and the minimum spatial cross-sectional area perpendicular to the average flow direction in the injection channel in the mold is S _G (cm
² ) It is desirable that the injection velocity satisfies the following equations (i) and (ii), where S _C (cm ² ) is the minimum spatial sectional area perpendicular to the average flow direction in the cavity.

V _L = (50 to 3,000) / (S _G · logρ) (i) V _H = (3,000 to 30,000) / (S _C · logρ) (ii) Low speed is slower than the lower limit shown in equation (i) If
The injection speed is likely to be unstable, there is a problem in the uniform supply of the raw material liquid, and the time required for the injection is only long. If the upper limit is exceeded, the raw material liquid passes through and the raw material enters the cavity. It becomes easy for air bubbles to be entrained before the liquid flows in.

If the high speed is slower than the lower limit expressed by the equation (ii), the time required for injection becomes long, and if it exceeds the upper limit, it becomes easy to entrap bubbles in the cavity.

As long as the above-mentioned expressions (i) and (ii) are satisfied, the change can be made in each of the high speed and low speed ranges.

Further, in the change of low speed-high speed, the change of high speed-low speed, or the change of high speed-low speed, it is possible to make a rapid change, but it is preferable that the change of speed is gentle.

In order to inject the raw material liquid into the mold, a well-known quantitative liquid feeding device may be used.

Further, the flow rate may be adjusted by using a known device and method suitable for the liquid feeding device.

In the present invention, a raw material liquid mainly containing a vinyl and / or vinylidene monomer containing or not containing the polymer to be used is injected into the frame, and if necessary, heated and pressurized to polymerize and cure.

The heating condition is preferably in the range of 50 to 150 ° C., more preferably in the range of 70 to 100 ° C. Further, after curing, heat treatment can be performed.

The pressure condition is 1 to 100 kg / cm ² G during polymerization and curing.

<Effects of the Invention> According to the present invention, without using a special formwork structure,
There are no bubbles entrapped on the surface or inside of the obtained molded product,
The shape and surface condition of the mold can be accurately transferred, and large molded products can also be applied to produce beautiful, transparent molded products.

Examples of products in which the present invention is used include general-purpose lenses, Fresnel lenses, projector screens,
Optical elements such as optical discs, prisms, mirrors, large parts such as automobile windows, pillars, sunroofs, front grills, lamps and lenses, and bathtubs, washbasins, counter tops, table tops, doors, signs. , Building materials such as water tanks, furniture.

<Examples> The present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto.

(Preparation of stock solution) Methyl methacrylate resin was dissolved in methyl methacrylate so as to be 10% by weight, 20% by weight and 30% by weight to prepare stock solutions A, -B and -C, respectively.

(Preparation of Raw Material Liquid) Component A; 20 g of lauroyl peroxide was dissolved in 1000 g of the above stock solution-A to prepare Component A.

Component B: Component B was prepared by dissolving 10 g of lauryl mercaptan in 1000 g of the above stock solution-A.

Component-C; Stock solution B (900 g) was mixed and dissolved with 100 g of neopentyl glycol dimethacrylate, 20 g of t-butyl peroxybenzoate, and 2 g of dimethylstearylamine hydrochloride to prepare Component-C.

Component-D: 0.002 g of acetylacetone copper for 1000 g of stock solution B
Component-D was prepared by mixing and dissolving 10 g of glycol dimercaptopropionate.

Component-E: 100 g of the stock solution C, 800 g of tetraethylene glycol dimethacrylate, 15 g of t-butyl peroxybenzoate, and 2 g of dimethylstearylamine hydrochloride were mixed and dissolved to prepare a component-E.

Ingredient-F: 0.02 g of copper naphthenate, n-
Component-F was prepared by mixing and dissolving 20 g of octyl mercaptan.

(Form) The properties and constitutions shown in the sectional view of FIG. 1 and the plan view of the mating surface of the form of FIG. 2 were used.

The cavities 1 and 5 are flat plates of 500 mm × 500 mm × 2 mm.

Gates 2 and 6 are 5 cm ² in cross section perpendicular to the average flow direction.

3 and 7 are runners, and the cross-sectional area perpendicular to the flow direction is
1.5 cm ² .

 4 and 8 are mixing devices.

 Is.

Examples 1-8, Comparative Examples 1-3 (molding) The mold was kept at a temperature of 80 ° C. Two components each shown in Table 1 were delivered by two piston pumps at an equal weight ratio of 1: 1 so that the injection speeds shown in Table 1 were obtained, and the mixture was injected while collision-mixing to perform molding.

The viscosity of the raw material liquid obtained by mixing the components A and B in equal weight ratio was 10 centipoise.

The viscosity of the stock solution in which the components C and D were mixed in equal weight ratios was 100 centipoise, and the viscosity of the stock solution in which the components E and F were mixed in equal weight ratios was 1000 centipoises.

After pouring into the mold, the inside was kept at 10 kg / cm ² G, and after 5 minutes, the polymerized and cured molded product was taken out and evaluated for appearance.

 The results are shown in Table 1.

Example 9 Component-C and component-D were used as the raw material liquid, and the mixture was poured into the mold while mixing at a weight ratio of 1: 1 as in Example 1.

The mold has a cavity with a cross-sectional area of 28 cm ² and a bottom 50 cm square 5.
The same shape as in Example 1 was used except that the rising portion around the thickness of 5 mm had a height of 5 cm and the box had a thickness of 3 mm, and was used while the temperature was kept at 90 ° C.

The injection speed of the mixed raw material liquid is 200 cm ³ / sec until the injection channel is filled, then 500 cm ³ / sec, and 1/10 of the space volume of the cavity before the completion of filling the cavity. From the time of leaving 155 cm ³ , it was set to 50 cm ³ / sec.

After pouring into the mold, the inside was kept at 15 kg / cm ² and after 5 minutes, a molded article having a polymerization effect was obtained.

No bubbles were observed in the obtained molded product, which was good.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of the mold used in the examples. FIG. 2 is a plan view of a mating surface of the same mold. The symbols in FIG. 1 and FIG. 1 represent 1 and 5 ... Cavity part 2 and 6 ... Gate part 3 and 7 ... Runner part 4 and 8 ... Mixing device.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location B29L 31:10 B29L 31:10 31:44 31:44 (72) Inventor Takanobu Fujita 5 Sokai-cho, Niihama-shi, Ehime Prefecture No. 1 In Sumitomo Chemical Co., Ltd. (72) Inventor Yukio Kojo 2-10-1 Tsukahara, Takatsuki City, Osaka Sumitomo Chemical Co., Ltd.

Claims (5)

(57) [Claims] 1. A casting method for injecting a raw material liquid into a mold to polymerize and harden it, wherein the raw material liquid mainly comprises vinyl and / or vinylidene monomers containing or not containing a polymer, and is placed in the mold. The casting method, wherein the injection speed of the raw material liquid is changed in at least two steps. 2. The method according to claim 1, wherein the change of the injection speed comprises a change in the order of low speed-high speed.
The cast molding method described in the item. 3. The casting method according to claim 1, wherein the change of the injection speed comprises a change in the order of low speed-high speed-low speed. 4. The pouring speed is set low until the raw material liquid fills the pouring path in the mold, the pouring speed in the cavity is high, and the pouring speed becomes low again when the cavity is filled with the raw material liquid. The casting method according to claim (3), characterized in that the speed is set. 5. A low pouring speed is V _L (cm ³ / sec), a high pouring speed is V _H (cm ³ / sec), and the viscosity of the raw material liquid is ρ (centipoise). When the minimum spatial sectional area perpendicular to the average flow direction is S _G (cm ² ) and the minimum spatial sectional area perpendicular to the average flow direction in the cavity S _C (cm ² ) is defined by the following formulas (i) and (ii): Claims (2) defined,
The cast molding method according to any one of (3) and (4). V _L = (50 to 3,000) / (S _G · logρ) (i) V _H = (3,000 to 30,000) / (S _C · logρ) (ii)