JPS60137623A - Manufacture of resin mold for injection molding product excellent in luster - Google Patents

Abstract

PURPOSE:To obtain the mold made of epoxy resin for injection molding, which enables the product excellent in luster to be obtained by causing epoxy resin fluidized under reduced pressure after the epoxy resin containing a specified diluent and curing agent has been cast, etc. in the mold made of methacryl. CONSTITUTION:The epoxy resin containing the low viscous and reactive diluent with at least one epoxy radical in one molecule and amine group curing agent, is used. Bath diluent and curing agent have vapour pressure equal to or lower than 1mm.Hg at 30 deg.C and the thermal deformation temperature equal to or higher than 60 deg.C after curing. This resin is cast into the master form model made of methacryl resin, or the master form model is gel-coated with the epoxy resin, and then said resin is cured after it has been caused to fluidize under reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a resin mold for injection molding, and an object thereof is to obtain an injection molded product with excellent gloss using this resin mold for injection molding. It is something.

Generally, one metal mold is used as a mold for injection molding. However, the molds have the drawbacks of being extremely expensive and requiring many days to manufacture.

When developing a new product that is an injection molded product, it is common practice to make a prototype of the molded product in advance. If a mold is used at the prototype stage, the cost of the mold increases and it takes many days to manufacture the mold.

Particularly in relation to automobiles and electrical products, shortening the trial production period for a certain part in relation to other parts will shorten the trial production period for the entire product, leading to a reduction in trial production costs. therefore.

Simple molds for injection molding are attracting attention because they are cheaper to manufacture and take less time to manufacture than molds. Epoxy resin molds, electroforming molds, metal spray molds, and casting molds made of fusible metal are known as simple molds for injection molding.

Each of these simplified types has its own advantages and disadvantages.

For example, electroforming molds have advantages such as extremely faithful reproduction of the original mold, good surface finish of injection molded products, and excellent 1-dimensional accuracy, but the disadvantage is that it takes a considerable number of days to produce the electroformed shell. .

Metal spray molds are often suitable for prototyping as they can produce simple molds with high dimensional accuracy and fidelity in a short time.

It is difficult to manufacture items with particularly severe unevenness or deep grooves. In addition, the mold has a short lifespan.

These electroforming molds and metal spray molds are usually used with their respective shells lined with a mixture of fusible metal or epoxy resin mixed with aluminum powder or granular aluminum. Casting molds made from fusible alloys have good fidelity, but have the drawback of having problems with dimensional accuracy and surface roughness compared to other molds. All of these simple types require appropriate equipment to manufacture.

On the other hand, epoxy resin molds do not require any equipment, can be manufactured at low cost in a short period of time, have good mold fidelity and dimensional accuracy, and are hardly influenced by shape. However, since epoxy resin does not have strong mechanical strength under hot conditions, the epoxy resin mold may be damaged during molding of the elbow. In addition.

The disadvantage is that injection molded products do not have the same gloss.

Normally, the number of injection molded products required for trial production is 300 or less, but at one time, several hundred to several thousand molded products, which can be considered as small-volume production, may be produced. 'In recent years, social and economic needs have become increasingly diverse.

As products become fashionable, high-mix, low-volume production with frequent model changes is progressing.

In such cases, the mold is generally economically problematic. That is, high manufacturing cost, design requiring experience, and long manufacturing period. On the other hand, when manufacturing molds for mass production, prototypes are often made in order to consider problems in mass production in advance. In other words, in such cases, a simplified version is required.

Once a mold is made, it is often difficult to modify it, so before making two molds, make a prototype of the desired molded product and assemble it alone or with other parts to determine the quality of the overall design shape. or judge.

There are defects in the product design and mold design.

Conduct strength tests and learn about shape defects. We also determine the general shrinkage of the materials used in molded products, commercialize products ahead of other companies and offer user hair peels, or perform limited marketing.

The cost required for prototyping of injection molded products is low.

The current situation is that the time required to obtain molded products is short (and beautiful molded products as close to those molded in a mold as possible) are required.

Furthermore, as a small-volume production type, in addition to the low manufacturing cost of the mold, since it is a finished product, a molded product that is more beautiful than a prototype is required.

For the reasons mentioned above, the present invention uses an epoxy resin mold as a substitute for a mold during trial production and small-scale production, is low cost, requires a short production period, and can be used to mold products injection-molded using a mold. The present invention relates to a method for manufacturing an epoxy resin mold that can produce molded products with excellent gloss.

Epoxy resin molds utilize the phenomenon that the shape and dimensions of a prototype model that is to become a product can be easily replicated as a negative mold by casting alone or by brushing gel coat and backing with resin or the like. Methods of lining include pouring epoxy resin, laminating epoxy resin with heat-resistant fibers such as glass cloth, carbon cloth, or aromatic polyamide, or using resin concrete such as Evo-xy resin and silica sand with one grain of aluminum. .

The present inventors have been involved in the development of resin molds for injection molding in which the basic structure of the mold is made of epoxy resin for many years, but one of the major drawbacks of epoxy resin molds is that the injection molded product is not glossy. As a result, they discovered a method for producing an injection molding resin ηL that gives a molded product with excellent gloss.

That is, the epoxy resin that makes up the resin mold.

The reactive diluent contained in the epoxy resin before curing and the amine compound constituting the curing agent both have a vapor pressure of 1 mmHg or less at 30CK, and are composed of components whose heat distortion temperature after curing is 60°C or higher. This is a method in which the resin is cast or gel coated onto a methacrylic prototype model and then evacuated under reduced pressure to cause the resin to flow.

The epoxy resin before curing used in the present invention is not particularly limited, except for alicyclic epoxy, and includes epoxy resins synthesized from bisphenol A, bisphenol F, novolak resins, halogenated compounds thereof, and epichlorohydrin. When a cycloaliphatic epoxy resin is used, the curing temperature becomes high and exceeds the heat resistance (approximately 100 to 110° C.) of the methacrylic resin of the original model, so it is practically unusable.

The epoxy resin used in resin molds for injection molding is used as a gel coat by casting or brushing, so one job is 1 K.
It is necessary to have a viscosity of 3WJ.

Reactive diluents are used to adjust the viscosity. The reactive diluent used in this invention must be resistant to evaporation. This is because after the resin is cast or gel coated, it is evacuated by applying a vacuum of 1. When the vapor pressure of the reactive diluent is high, bubbles are constantly generated during evacuation, resulting in bubbles remaining in the cured product. In addition, the viscosity of the epoxy resin increases due to the evaporation of the reactive diluent, making it less compatible with the original model, and when the resin mold is removed from the original model after the resin has hardened, the surface of the resin mold may become uneven. This results in non-uniformity, and when injection molded, the molded product has a dull surface and shatters.

For the same reason, the amine curing agent used in the present invention preferably has a low vapor pressure.

As a result of intensive research, the present inventors have found that the vapor pressure of both the reactive diluent and the curing agent is 30CK and 1 mmHg or less, preferably 0.
．． It has been found that it is necessary to be 1+++nHg or less.

Examples of reactive diluents that can be used include 1,4-butanediol diglycidyl ether, phenylglycidyl ether, diglycidyl ether at both ends of an addition copolymer of ethylene oxide and epichlorohydrin, aniline, and
-) Glycidylamine, which is a reaction product of luidine and epichlorohydrin, and diglycidyl ether of polyalkylene glycol.

Butyl glycidyl ether, allyl glycidyl ether, etc. have a vapor pressure of 1 mmHg or more at 30° C., so they cannot be used as two-reactive diluents in the present invention.

Preferred amine curing agents include aliphatic polyamines such as triethylenetetramine and tetraethylenepentamine, adducts of aliphatic amines or aromatic amines such as ethylene oxide or propylene oxide, and polyamide amines. These curing agents can be used alone or in combination.

Dimethylamine propylamine, diethylaminopropylamine, 1.3 diaminopropane, etc.

In either case, the vapor pressure at 30°C is 1+nmHg or more, so they cannot be used as amine curing agents.

In the present invention, the epoxy resin and curing agent used must be composed of components such that the heat deformation temperature of the curing resin is 60°C or higher, preferably 70°C or higher.

The present inventors have discovered that 11
I learned that the surface temperature of the fat mold usually reaches 60-110C. Therefore, to withstand high injection pressure (around 5001 t/rd) at such temperatures.

Epoxy resin needs to be heat resistant. Heat distortion temperature 60℃
Molten polymer is injected into the resin mold, which can also include the following resins →
As a result, the surface of the mold becomes semi-molten and does not fuse with the molding material, increasing the mold release resistance of the molded product. When the mold is released, the molded product is pulled from the surface of the mold, so the surface of the molded product becomes uneven and loses its luster.

Another feature of the invention is the use of a model made of methacrylic resin. Methacrylic resin can be easily shaped into the desired shape by thermoforming, and can be easily polished to give a uniform, glossy surface. In addition, when using it as a model, 1. Since no molding agent is required,
It has the characteristic that the surface of the model is faithfully transferred to the epoxy resin. If the model is a wooden model, a mold release agent will be required, and the transferability to the epoxy resin will be poor. Acrylite (trade name, Mitsubishi Rayon) is used as the methacrylic resin.

However, the inventors of the present invention have found that it is not possible to obtain an injection molded product with sufficient gloss by satisfying only the conditions of the epoxy resin of the injection mold and the material of the model as described above.

That is, 1. In order to achieve the content of the present invention, after casting or gel coating the model with epoxy resin, the model is evacuated under reduced pressure.17. It is necessary to flow the resin by blowing gas and stirring. This effect not only removes the air bubbles that were already present in the resin, but also removes the macroscopic and microscopic air pockets that occur due to the complex shape of the model and replaces them with resin. It's about doing the same thing. In addition, it removes the air layer that is physically adsorbed on the surface of the model, promotes wetting of the resin to the model, and faithfully reverses the uniformity of the model surface.

In addition, it is believed that by fluidizing the resin, it is effective to even out the dispersion of microgels generated at an early stage when the epoxy resin starts to harden, and to suppress segregation. Generally, when epoxy resin is cast, the resin is allowed to stand and cure without stirring in order to prevent air from entering, but since curing is an exothermic reaction, the center of the cast material is at the highest temperature. Therefore, the curing rate is highest at the center.

In other words, the length of the molecules and the crosslinking density should be different between the inside and outside of the cast material. When resin is actually cast into a model, the curing rate of the resin on the surface that comes into contact with the model is low, but when used as a 1m resin mold, this is the most important part because it becomes the surface that comes into contact with the injection molded product. As a means of increasing the hardening rate of the part that comes into contact with the model, it is sometimes heated by heating it, but in order to prevent dimensional changes in the mold, it is necessary to heat it with the model attached and the cavity and core set.

Usually, it is heated by placing it in a dryer, but since resin molds do not have good thermal conductivity, a temperature gradient occurs in the cast material, and the surface that comes into contact with the model has the lowest temperature.

Flowing by casting or evacuation of the gel coat resin reduces the temperature gradient of the resin up to the macroscopic gelation stage, making the molecular weight distribution and crosslinking density uniform in each part of the resin at the early stage of curing. As the resin mold comes into contact with the model, the trowel also contributes to increasing the mechanical strength of important parts.

Therefore, cracks in the 1M mold and chips at the edges are reduced. In addition, it is thought to have the effect of improving the gloss of the molded product.

One drawback of resin molds is that they have poor thermal conductivity. For this reason, the resin mold accumulates heat during injection molding, reducing the durability of the mold and generally prolonging the molding cycle. In order to minimize these drawbacks, it is preferable to include a filler with good thermal conductivity in the resin. Furthermore, by adding a filler, the shrinkage rate when the resin is cured can be reduced.

In the present invention, the fillers used are:

Examples include aluminum powder, iron powder, gold powder such as copper powder and brass powder, metal oxides such as aluminum oxide and titanium oxide, and inorganic fillers such as talc and calcium carbonate, but are not particularly limited.

When the resin is fluidized by exhaust gas, the filler in the resin is suspended, forming a very thin layer of filler-free resin at the interface with the model. This is effective in eliminating microscopic irregularities that occur on the surface of the resin mold due to the presence of the filler. When resin is poured into a model and left to stand still, some of the filler settles and comes into contact with the monaural surface. Therefore, the very thin layer of the mold that comes into contact with the model has a shape in which the filler protrudes from within the resin layer, resulting in microscopic unevenness on the resin surface. The existence of this unevenness.

This reduces the gloss of the surface of the molded product during injection molding. Furthermore, as the number of molding shots increases, the surface of the mold tends to become rougher.

As described above, the resin molded by the resin mold manufactured by the method of the present invention is not limited to @.

ABS, methacrylic resin, nylon 6.6. It is possible to obtain molded products with excellent gloss from resins such as polyacetal, polycarbonate, and polyurethane.

The procedure for manufacturing a resin mold for injection molding according to the present invention will be explained below with reference to the drawings.

The drawing is an example of a cross-sectional view of a resin mold for injection molding according to the present invention. Place a wooden frame on the parting board and set it in it without applying a mold release agent like the original model made of methacrylic resin. The cooling pipe 17 is also set in an appropriate position. An uncured epoxy resin containing a reactive diluent and a curing agent are mixed and cast or gel coated. Immediately place the entire wooden frame in the vacuum system and begin evacuation. The air bubbles contained in the resin and the air that was physically adsorbed on the surface of the model rise, causing the resin to flow considerably up and down.

The filler in the resin should also float and be a little far from the interface with the model. If you continue evacuation for a while, the generation of bubbles will decrease, so at that point return the evacuation system to normal pressure and wait to see if it gels. If the evacuation is prolonged, the remaining bubbles will gel, so evacuation for about 10 to 30 minutes is usually best.

When applying gel coat, when the gel coat layer is in a tack state, further resin is cast, resin is laminated with glass cloth, carbon cloth, high heat resistant fiber, etc., or backing is done with powdered aluminum or silica sand. choose which one to do. When the parting board and wooden mold are removed from the mold in this way, a cavity 16 is generally obtained.

The core 20 is manufactured by applying a mold release agent to the surfaces of the model and the cavity 16 without releasing the model 1-.

Set it in a wooden frame and also set the cooling pipe 21. In this case, the release agent is applied to the model when gloss is not required on the back side of the molded product. The operations after resin casting or gel coating are the same as those for producing the cavity 16.

If necessary, it is heated and cured, but in that case, the cavity 16 and core 20 are heated without being released from the model. The heating temperature is desirably 110° C. or lower, which is enough to prevent the model from deforming. When the production of the cavities 16 and cores 20 is completed, the models are released and each is fixed to a metal mold using room temperature curing epoxy resin 12 to complete the resin mold for injection molding.

The contents of the present invention will be explained in more detail below with reference to Examples.

Examples 1 to 7 440 parts of liquid epoxy resin (trade name Epicote 828. Shell Chemical) was added with 55 parts of aluminum powder having an average particle size of about 44μ.
0 parts, 5 parts of an anti-sedimentation agent (trade name Thyroid AL-1, Fuji Devine Chemical), and predetermined amounts of reactive diluents as shown in Table IK were added and stirred for 2 hours using a Disilver. A predetermined curing agent at a predetermined PHR was added to these resins to obtain a casting resin. Separately, a methacrylic model (150 pieces in diameter, a disc with a speed of 2 feet) was set on top of a methacrylic parting board, and surrounded by a wooden frame with an inner diameter of 190 mm. Outer diameter 6
Approximately 101 #I from the surface of the 1M1 cooling pipe 21 model
After setting it at a distance of I+, a casting resin with a hardening agent added thereto was cast to a thickness of 30!1IIIK. The casting resin powder was approximately 1.7 Kf. Further, the resin temperature immediately before casting was in the range of 27 to 29°C in all Examples 1 to 71. Place the entire wooden frame in a vacuum system and exhaust information g 50 Z/ll#
It was evacuated using a + vacuum pump. The pressure was reduced to about 1 wHg in about 1 minute. Evacuation was continued for an additional 20 minutes. During this time +Q
I added 1 fluid amount of r fat. After completing the evacuation, the system was returned to normal pressure and opened at about 12:00 to further advance curing. After curing, the model was removed from the mold and the wooden frame and parting board were removed to produce Core 20. Next, a mold release agent Lc was applied to the parting surface of the core 200 except for the part coated with model Kf51.

After placing the core 20 in a wooden frame of the same size as the spear made by Ko-Aku 0 and setting the cooling pipe 17, apply the same resin to a thickness of about 3 mm.
0+mlC was cast. Exhaust l under the same conditions as core 20 production.
-1 Cured. Further, the model was heated at 80° C. for 6 hours to proceed with curing without demolding. After cooling, the cavity 16 and the core 20 are separated. Cavity 16 is 8 in width and 5 in depth.
Room-temperature curing epoxy resin was injected into the fixed side template 4 with the groove 18 and the fixed 1' HII mounting plate 3 [7] and fixed with adhesive. Similarly, the core 20 is attached to the movable 111+1 template 5 with the groove 22.
It was confirmed that it was adhered to the receiving plate 6. Methacrylic resin (Acrivet M, Mitsubishi Rayon) was used as the molding material, and an injection molding machine (JSW-N 200BIl, Japan Steel Works) was used at an injection temperature of 240°C, an injection gauge pressure of 53 kg/l-4, and an injection time of 15 seconds. Molding was performed under conditions of cooling time of 30 seconds. The gloss of the injection molded product was evaluated by measuring the haze value in accordance with JIS K 6714K.

Separately, each resin after mixing was used to prepare a sample scent strip according to ASTM D 648.1. After heat curing at 80C for 6 hours, the heat distortion temperature was measured at a fiber stress of 18.6 K9/crl. The results are shown in Table IK.

Table 1 Influence of reactive diluent and curing agent on haze value of molded product after 20 f/,, becomes. Furthermore, even if a reactive diluent and curing agent with low vapor pressure are used as in Example 7, the haze value will be high if the heat distortion temperature is low.

Examples 8 to 9 The same resin as in Examples 2 and 6 was used, and resin molds were manufactured in the same manner as in Examples 2 and 6, except that evacuation under reduced pressure was not performed. The surfaces of the resin mold cavity 16 and the core 20 had a beautiful luster, but in Examples 1-
When injection molding was carried out under the same conditions as in Example 7, the haze value of the molded product after 20 shots was 83% for the molded product corresponding to Example 2Vc and 85% for the molded product corresponding to Example 6Vc, and the visual gloss was very good in both cases. There wasn't.

Examples 10 to 13 Liquid epoxy resin (trade name Evo) -) YD-127
260 parts of reactive diluent o-) luidine glycidylamine (trade name GOT, Nippon Kayaku),
690 parts of aluminum powder with an average particle size of about 62 μm and 6 parts of Olben (trade name, Shiraishi Kogyo) as an anti-settling agent were added, and the mixture was stirred with a Disilver for 2 hours. 100 parts of the mixed resin were taken, and 9 parts of a curing agent mixed in a ratio of 30 parts of triethylenetetramine and 70 parts of polyamide amine (trade name: Tomide 235S, manufactured by Fuji Kasei) were added and thoroughly mixed.

A methacrylic model was set on a methacrylic partition board and surrounded by a 240+W square wooden frame.

What is the shape of the model? 00III++ corner, height 10-, wall thickness 2.

The edge part has a box shape with a minimum radius of 1.5.

The cooling pipe 17 was set at a position approximately 10+++ meters away from the surface of the model, and the mixed resin was cast to a thickness of 40 cm. Place one section in a vacuum system and exhaust 950 L/=
The mixture was evacuated for 15 minutes using a vacuum pump. The degree of reduced pressure is lmmH
It reached 17 g. After the evacuation was completed, the vacuum system was returned to normal pressure. Approximately 1 hour after the start of reduced pressure, the resin turned into a gel, and was left in that state for about 12 hours. Apply silicone mold release agent to the entire surface of the model without releasing it from the cavity 16 created after removing the wooden frame? After that, the core 20 was manufactured in exactly the same way as the cavity 16 was manufactured.

After mold release, the model cavity 16 was adhesively fixed to the fixed side mounting plate 3 and the fixed side template 4, and to the movable 11111 mold plate 5 and the receiving plate 6, which were the core 20, with room temperature curing epoxy resin (Example 1)
0). Separately, a wooden model with the exact same shape as the methacrylic model was manufactured. When epoxy resin is poured into a wooden model, air bubbles will come out from the porous surface of the model.
The model was sealed in advance with an amino alkyd resin (trade name: Melbicoat≠20 Clear, Nagataka Chemical Industry). After applying a thin layer of silicone mold release agent, mold cavity 16 and core 2 using the same procedure as for the Metafurirumi model.
0 was manufactured (Example 11). In addition, Examples 10 and II
Do not exhaust the resin after casting.

Resin molds were manufactured under all other conditions (Examples 12 and 13).

Injection molding machine (FS-150, 6 Seishin Kogyo), injection temperature 240℃, injection gauge pressure 40Kq/ln! ABS resin (Cycolac AM, Ube Cycon) was injection molded under the conditions of 15 seconds for injection time and 50 seconds for cooling time. Table 2v shows the results of visual inspection of the resin mold condition and the surface condition of the molded product.
c showed.

Table 2 Relationship between the manufacturing conditions of KIllll11 and the A note resistance and gloss of the molded product

[Brief explanation of the drawing]

The drawing is a sectional view of an example of a resin plate for injection molding according to the present invention. In the figure, 1... Spool pusher, 2... Four cater rings, 3... Fixed side mounting plate, 4... Fixed side template, 5
・I. Movable side template, 6... Receiving plate, 7... Spencer block. 8.9... Ejector plate, 10... Movable side mounting plate. 11... Spool lock pin, 12... Machining turbine. 13... Ejector rod hole, 14... Movable side spool lock part reinforcing metal, 15... Fixed side adhesive fixing layer, 16... Cavity, 17... Fixed side cooling pipe. 18... Fixed side groove, 19... Movable side adhesive fixed layer, 2
0...Core, 21...Movable side cooling pipe, 22...
- Movable gutter. Patent applicant: Nippon Devcon Co., Ltd. Agent: Yuzo Kodama

Claims (1)

[Claims] 1. When manufacturing an injection molding resin mold in which the basic structure of the injection molding mold is made of epoxy resin, it is necessary to use a low viscosity resin mold that has at least one epoxy group in one molecule among the components that make up the epoxy resin. contains a reactive diluent of
A method for manufacturing a resin mold for injection molding, characterized by casting or gel coating an epoxy resin at a temperature of ℃ or above onto a prototype model made of methacrylic resin, and then exhausting the resin under reduced pressure to cause the resin to flow.