JPH04348122A - Production of molded product and metallic mold for reaction molding - Google Patents

Abstract

PURPOSE:To obtain a molded product in which occurrence of voids is prevented or remarkably reduced by injecting a reaction solution containing a norbornene- based monomer and a metathetic catalyst system into a metallic mold kept under a pressure at a specific level or above and carrying out bulk polymerization. CONSTITUTION:A reaction solution containing a norbornene-based monomer such as norbornene or dicyclopentadiene and a metathetic catalyst system such as tungsten or molybdenum is injected into a metallic mold and bulk polymerization is then carried out. In the process, the reaction solution in at least the latter period of injection is injected into the metallic mold kept under >=1.2kg/ cm<2>abs (absolute pressure) internal pressure. In the reaction process, the internal pressure is kept at >=1.2kg/cm<2>abs to afford the objective molded product. The aforementioned metallic mold has an injection port, a cavity and a liquid reservoir having an air vent equipped with a pressure holding mechanism.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molded articles by reaction molding using norbornene monomers. The present invention also relates to a mold for reaction molding.

0002

[Prior Art] In recent years, reaction molding methods (RIM, LIM, RTM, etc.), technological development is progressing. The norbornene polymer molded article obtained by this method has excellent heat resistance, dimensional stability, water absorption resistance, etc., and is also lightweight.

[0003] In reaction molding using norbornene monomers, generally a reaction liquid (liquid A) containing the monomer and a metathesis catalyst, and a reaction liquid (liquid B) containing the monomer and an activator are used.
After mixing the liquid (liquid) in a mixing unit such as a mixing head, the mixed liquid is injected into a mold and reacted. These operations are usually performed in an inert gas atmosphere. Bubbles (gas) mixed in the mixing section and gas inside the mold are discharged to the outside through an air vent provided at the last place in the mold where gas accumulates when the reaction liquid is injected.

However, when a molded article is manufactured by a reaction molding method using a reaction solution containing a norbornene monomer,
Many voids (bubbles and pores) occur inside and on the surface of the molded product. This is particularly noticeable in thick-walled molded products or molded products with uneven thickness. This is due to the entrainment of bubbles in the reaction solution and incomplete filling of the closed portion within the mold.

[0005] Conventionally, therefore, a reaction solution containing a norbornene monomer and a metathesis catalyst system was injected into a mold at a temperature higher than the temperature of the mold (mold), and after being injected into the mold,
A method of pressurizing the inside of the mold has been proposed (Japanese Patent Application Laid-open No. 2-2
No. 39915). A method of introducing an inert gas is used to pressurize the inside of the mold. According to this method, a thick-walled molded product substantially free of pores can be obtained.

However, in the method described in this publication, pressure is applied after the reaction liquid is injected into the mold, and therefore a good molded product cannot be obtained unless pressure is applied at the right time just before the reaction liquid hardens. In other words, if the pressure is applied too early, it will not be possible to apply uniform pressure, and the molded product will be easily deformed due to the sudden pressure applied.On the other hand, if the pressure is applied too late, voids will occur due to the pressure. Prevention effect cannot be obtained. Therefore, in this method, it is necessary to precisely control the timing of pressurization, but it is extremely difficult to start the reaction uniformly, especially in the case of thick-walled molded products with complex shapes or uneven thickness molded products. Therefore, it is difficult to obtain good molded products by applying this method.

On the other hand, voids are often caused by entrainment of bubbles due to non-uniform flow of the reaction liquid within the mold. In particular, when molding thick-walled products, the flow of the reaction liquid in the mold is not only uniform in the injection direction, but also flows in the thickness direction, resulting in non-uniform flow and the formation of bubbles. It is easy to get caught and create voids.

[0008] In addition, in areas where the wall thickness of the molded product changes significantly, when the reaction liquid is injected, a pressure drop occurs in the thick wall area due to the volume change, and gases (nitrogen and oxygen) and low boiling point components dissolved in the reaction liquid occur. causes gasification. Moreover, the flow of the reaction liquid in this part tends to be non-uniform, and bubbles are entrained due to turbulent flow. As a result, in a molded product with uneven thickness, a large number of voids are likely to occur inside the molded product or on the surface of the molded product. Therefore, there is a need for an improved method and apparatus that can produce void-free molded products even if they are thick-walled molded products or uneven-walled molded products.

[0009]

[Problems to be Solved by the Invention] An object of the present invention is to produce a molded article in which the generation of voids is prevented or significantly reduced by a reaction molding method using a reaction liquid containing a norbornene monomer and a metathesis catalyst system. The purpose is to provide a method. Another object of the present invention is to provide a reaction molding die suitable for producing a molded article in which the occurrence of voids is prevented or significantly reduced.

As a result of intensive research in order to overcome the problems of the prior art, the present inventors injected the reaction liquid while maintaining the pressure inside the mold above a certain level, and
When bulk polymerization is carried out with the internal pressure maintained at a certain level or higher during the reaction process, (1) the resistance to the flow of the reaction liquid in the mold is kept constant, so the flow is made uniform; ) Even when molding a molded product with uneven thickness, a constant pressure is maintained throughout the mold, so pressure fluctuations due to volume changes are alleviated or eliminated. Because the pressure is applied, there are no sudden pressure fluctuations, and even pressure can be applied even after the injection of the reaction liquid is finished.As a result, not only thin-walled molded products but also
Even when manufacturing thick-walled molded products or molded products with uneven thickness, there are extremely few voids inside or on the surface of the molded product, and because no sudden pressure is applied, the molded product does not deform, and its appearance remains unchanged. It has been found that a molded article with excellent properties and physical properties can be obtained.

Furthermore, it has been found that it is effective to provide a pressure holding mechanism in the air vent of the mold in order to maintain the pressure inside the mold above a certain level. The present invention has been completed based on these findings.

0012

[Means for Solving the Problems] Thus, according to the present invention, when a reaction solution containing a norbornene monomer and a metathesis catalyst system is injected into a mold for bulk polymerization, the reaction solution at least in the latter stage of injection is maintained at an internal pressure of 1. Provided is a method for producing a molded article, which comprises injecting into a mold maintained at 2 kg/cm2 (absolute pressure) or higher, and maintaining the internal pressure at 1.2 kg/cm2 (absolute pressure) or higher during the reaction process. .

Further, according to the present invention, there is provided a mold for reaction molding having a liquid reservoir equipped with an injection port, a cavity, and an air vent, characterized in that the air vent is provided with a pressure holding mechanism. A mold for reaction molding is provided.

The present invention will be explained in detail below. (Reaction liquid) In the present invention, a reaction liquid containing a norbornene monomer and a metathesis catalyst system is used.

Norbornene Monomer The norbornene monomer used in the present invention may be any one having a norbornene ring, but if a tricyclic or higher polycyclic norbornene monomer is used, the polymer will have a high heat distortion temperature. can get. Further, in order to make the ring-opened polymer produced thermosetting, at least 10% by weight, preferably 30% by weight or more of the crosslinking monomer based on the total monomers may be used.

Specific examples of norbornene monomers include bicyclics such as norbornene and norbornadiene, tricyclics such as dicyclopentadiene and dihydrodicyclopentadiene, tetracyclics such as tetracyclododecene, and tricyclics such as tricyclopentadiene. Pentacyclics, heptacyclics such as tetracyclopentadiene, alkyl substituted products thereof (e.g. methyl, ethyl, propyl, butyl substituted products, etc.), alkenyl substituted products (e.g. vinyl substituted products, etc.), alkylidene substituted products (e.g. , ethylidene substituted products, etc.), aryl substituted products (
For example, substituents having polar groups such as phenyl, tolyl, naphthyl substituents), ester groups, ether groups, cyano groups, and halogen atoms are exemplified. These monomers may be used in combination of one or more types. Among them,
From the viewpoint of ease of availability, reactivity, heat resistance, etc., tricyclics to pentacyclics are preferred.

[0017] The crosslinking monomer has two reactive double bonds.
It is a polycyclic norbornene monomer having at least 1 ring, and specific examples thereof include dicyclopentadiene, tricyclopentadiene, and tetracyclopentadiene. When the norbornene monomer and the crosslinking monomer are the same, it is not necessary to use any other crosslinking monomer.

[0018] Furthermore, monocyclic cycloolefins such as cyclobutene, cyclopentene, cyclopentadiene, cyclooctene, and cyclododecene, which can undergo ring-opening polymerization together with one or more of the above norbornene monomers, may be used in combination to the extent that the object of the present invention is not impaired. be able to.

Metathesis Catalyst System In the present invention, a metathesis catalyst system comprising a known metathesis catalyst and an activator can be used as a catalyst for ring-opening polymerization of norbornene monomers. Specific examples of metathesis catalysts include halides, oxyhalides, oxides, and organic ammonium salts of tungsten, molybdenum, tantalum, and the like. Specific examples of the activator (cocatalyst) include alkyl aluminum halides, alkoxyalkylaluminum halides, aryloxyalkylaluminum halides, organotin compounds, and the like.

[0020] The metathesis catalyst is usually used in an amount of about 0.01 to 50 mmol per mol of the norbornene monomer.
It is preferably used in a range of 0.1 to 20 mmol. The activator is preferably 1% relative to the metathesis catalyst component.
-10 (molar ratio) is used. Both the metathesis catalyst and the activator are preferably used after being dissolved in a monomer, but they may also be used after being suspended or dissolved in a small amount of a solvent as long as the properties of the product are not essentially impaired.

Additives such as antioxidants, fillers, reinforcing materials, pigments, colorants, and elastomers can be added to the norbornene polymer. These additives are blended by being dissolved or dispersed in the reaction solution, but may also be placed in the mold.

[0022] The elastomer to be added to the reaction solution is as follows:
For example, natural rubber, polybutadiene, polyisoprene,
Styrene-butadiene copolymer (SBR), styrene-
Butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), ethylene-propylene-diene terpolymer (EPDM)
, ethylene-vinyl acetate copolymer (EVA), and hydrides thereof. Addition of these elastomers to the reaction solution not only imparts impact resistance to the resulting polymer, but also makes it possible to adjust the viscosity of the reaction solution.

(Bulk polymerization) In a preferred method for producing norbornene-based polymers, the norbornene-based monomer is generally divided into two parts and placed in separate containers, a metathesis catalyst is added to one part, and an activator is added to the other. Prepare various stable reaction solutions. These two types of reaction solutions are mixed and then poured into a mold of a predetermined shape, where ring-opening polymerization is carried out in bulk.

In the present invention, reaction injection (RI) has conventionally been used.
M) Impingement mixers, known as molding devices, can be used to mix the two reaction stock solutions. In this case, the vessels containing the two reaction stock solutions become sources of separate streams. The two streams are instantaneously mixed in the mixing head of the RIM machine and then injected into the mold, where they undergo immediate bulk polymerization to obtain the molded article.

In addition to the impingement mixer, low pressure injection machines such as dynamic mixers and static mixers can be used. In cases where the pot life at room temperature is as long as one hour, the two reaction solutions may be injected or poured several times into a preheated mold after mixing is completed in a mixer; , may be injected continuously. This method has the advantage that it can be made more compact than an impingement mixer, and can be operated at low pressure. By slowing down the speed, it becomes possible to uniformly impregnate the reaction solution into the system.

Furthermore, the present invention is not limited to the method using two types of reaction stock solutions. As will be readily apparent to those skilled in the art, various variations are possible, such as using a third vessel containing the monomer and desired additives as a third stream. Note that the reaction solution is usually stored and operated under an inert gas atmosphere such as nitrogen gas.

In the present invention, at least the reaction liquid in the latter stage of injection is injected into a mold maintained at an internal pressure of 1.2 kg/cm2abs (absolute pressure) or higher, and the internal pressure during the reaction process is kept at 1.2 kg/cm2abs (absolute pressure).
Bulk polymerization is carried out while maintaining the g/cm2abs or higher. Here, the reaction solution in the late injection period refers to the last 3 injected amount.
0% by volume, preferably 50% by volume. Applying internal pressure from the beginning of injection can provide a greater effect of preventing generation of voids. If the holding pressure level in the mold is too low, the effect of preventing void generation will be reduced, and conversely, if the holding pressure level is too high, large molded products will require a large amount of mold clamping pressure, making it impractical. do not have. The range of internal pressure is usually 1.
2-10kg/cm2abs, preferably 1.5-7k
g/cm2abs.

From the beginning of injection of the reaction solution, the internal pressure of the mold was set at 1.2
In order to maintain the pressure at kg/cm2abs or higher, a method of introducing an inert gas such as nitrogen, argon, or carbon dioxide gas into the mold and pressurizing the mold can be mentioned.

The mold temperature is usually above room temperature, preferably 40 to 200°C, particularly preferably 50 to 130°C. The components used in the polymerization reaction are preferably stored and operated under an inert gas atmosphere such as nitrogen gas. Polymerization time is usually less than 20 minutes, preferably less than 5 minutes.

(Mold for reaction molding) In the present invention, the injection port,
A reaction molding mold having a cavity and a liquid reservoir equipped with an air vent is used, and the reaction molding mold is provided with a pressurized gas introduction means and a pressure holding mechanism in the air vent. FIG. 1 is a partial sectional view of a reaction molding mold of the present invention.

The mold of the present invention usually has a split mold structure and consists of a cavity mold 1 and a core mold 2. When the mold is completely tightened, a space 10 (cavity ) can be done. The diagonal lines in the cavity 10 in FIG. 1 indicate a reaction solution or a molded product.

A reaction solution containing a monomer and a metathesis catalyst (
After mixing a reaction liquid (Liquid A) containing a monomer and an activator in a mixing section such as a mixing head, the mixed liquid (reaction liquid) is injected into a mold and reacted. The reaction solution enters cavity 1 from an injection port (not shown) with a narrow cross-sectional area.
0 and fills the cavity while expelling the gas inside.

[0033] When mixing the liquids A and B, many bubbles (
To avoid this, the cavity mold 1 is provided with a liquid reservoir 3, and the reaction liquid at the initial stage of mixing is removed through a narrow passage 9 provided at the seam between the two molds. The liquid reservoir 3 is installed at a location (at the top) where the reaction solution in the cavity does not easily fill up when the reaction solution is injected, and where the gas accumulates last. The shape and size of the liquid reservoir 3 can be determined as appropriate depending on the size and shape of the molded product.

Gas is exhausted from the liquid reservoir 3 to the atmosphere through the opening 12 through the line 4 constituting the air vent. In the mold of the present invention, this air vent is provided with a pressure holding mechanism. FIG. 1 shows an example in which the air vent is provided with a pressurized gas introduction means as well as a pressure holding mechanism.

The pressurized gas introduction means is constructed by connecting a pressurized gas introduction line 11 to the air vent line 4 at a position outside the mold via a three-way valve 5. As the pressurized gas, an inert gas such as nitrogen or argon is used. This three-way valve is operated to maintain a constant pressure inside the mold before injecting the reaction solution. The internal pressure of the mold is confirmed with a pressure gauge 7 provided on the air vent line 4. The pressurized gas introduction line is
Instead of being provided in the air vent line, it may be provided in the core mold, or it may be provided at the inlet as shown in FIG. In FIG. 2, the reaction liquid is injected from a gate (injection port) 13, and a check valve 14 having a spring 15 is disposed at a position facing the gate of the core mold 2. The pressurized gas 16 is introduced into the mold through a solenoid valve 18, a pressurized gas introduction line 17, and a check valve 14 in order, and the inside of the mold is maintained at a constant pressure by the action of the check valve.

In the mold shown in FIG. 1, a pressure holding mechanism is provided in front of the exhaust port 12 of the air vent line 4. FIG. 1 shows a pressure holding valve 6 as a pressure holding mechanism. There are no restrictions on the pressure holding method of the pressure holding valve 6, and generally a spring adjustment method or an accumulation method is adopted. As mentioned above, the level of holding pressure is 1.2 to 1.
The range is 0 kg/cm2abs. As another method for maintaining the internal pressure above a certain level, an orifice with a certain diameter can be used instead of a pressure-holding valve. The diameter of the orifice is usually about 0.1 to 5 mm, preferably about 0.3 to 3 mm. When using an orifice, it is not possible to increase the internal pressure at the beginning of injection of the reaction solution, but the internal pressure increases immediately after injection and easily reaches 1.2 kg/cm.
Can maintain a level of 2abs. Further, instead of the pressure holding valve, a valve whose opening degree can be controlled may be used. The specific means to be adopted as the pressure holding mechanism is determined by the injection rate of the reaction liquid, reaction activity, etc.

[0037] The mold is preferably sealed with a sealing material to maintain internal pressure. Specifically, a sealing groove 8 is provided in the periphery of the cavity portion and the liquid reservoir portion of the cavity mold 1, and a sealing material is placed in this groove. Oil-resistant rubber is usually used as the sealing material. From the viewpoint of cost and required hardness, natural rubber (NR) or acrylonitrile-butadiene copolymer rubber (NBR) is preferred. The hardness of the rubber is selected depending on the degree of holding pressure in the mold, but is usually 50 to 80 degrees, preferably 60 to 7 degrees.
Preferably, the angle is 0°. If the hardness of the rubber is too low, the durability will be poor, and if the hardness is too high, the sealing performance will decrease and it will be difficult to maintain pressure. The shape of the sealing material is not particularly limited, but it is generally a square shape, an O-ring, or a hollow seal. Forming double seal grooves further improves sealing performance.

[0038] There are no particular restrictions on the shape, material, and size of the mold. Since a low-viscosity reaction liquid is used, not only those made of metal but also those made of various materials such as various synthetic resins and low-melting point alloys can be used.

(Molded product) According to the manufacturing method of the present invention, the generation of voids is suppressed not only in thin-walled molded products but also in thick-walled molded products and molded products with uneven thickness, and the appearance and physical properties are good. A molded product can be obtained.

[0040] Here, the thick-walled molded product is a molded product with a wall thickness of 5 mm or more. Generally, in the production of thick-walled molded products, when the reaction liquid is injected, the flow of the reaction liquid in the thickness direction within the mold cannot be ignored, and the flow becomes uneven in this direction, making it easy to entrain bubbles. . This tendency is particularly remarkable in the late stage of injection. However, if a pressure above a certain level is applied and maintained inside the mold at least in the later stages of injection, resistance will occur to the flow of the reaction liquid in the injection direction, thereby suppressing the occurrence of turbulent flow. The flow becomes uniform.

In addition, a molded product with uneven thickness is a molded product that has a part where the wall thickness of the molded product changes rapidly (uneven thickness part) as shown in FIG. 3, and usually the thickness of the uneven thickness part is It refers to something that changes by 1.5 times or more compared to other parts. When the reaction liquid is injected, the pressure of the reaction liquid changes in proportion to the change in wall thickness at the uneven thickness portion. Therefore, gas and low boiling point components dissolved in the reaction liquid are gasified. Moreover, in areas with uneven thickness, the flow becomes non-uniform and tends to trap bubbles. In this case as well, this tendency is greater in the later stages of injection. However, if the pressure inside the mold is maintained at a certain level or higher, the fluctuation in pressure at uneven thickness portions will be reduced and the flow will be uniform.

As described above, it is possible to obtain a norbornene-based polymer molded article in which the generation of voids inside the molded article and on the surface of the molded article is suppressed. Furthermore, compared to the method of applying pressure after injecting the reaction liquid, the present invention maintains the internal pressure of the mold above a certain level before injecting the reaction liquid and during the reaction process. Since sudden pressure is not applied to the product, deformation of the molded product due to pressure fluctuations is prevented.

[0043]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. In addition, in the following examples, unless otherwise specified, parts and percentages are based on weight.

[Example 1] (Preparation of reaction solution) Dicyclopentadiene (DCP) and methyltetracyclododecene (MTD) containing 2% of phenolic antioxidant (manufactured by Ciba Geigy, trade name Irganox 259) monomer mixture (DCP/MT
D = 85/15) into two containers, one containing diethylaluminum chloride (DEAC) for the monomer.
) was added at a concentration of 33 mmolar, n-propanol at a concentration of 34.6 mmolar, and silicon tetrachloride at a concentration of 20 mmolar. On the other hand, tri(tridecyl)ammonium molybdate was added to the monomer at a concentration of 4 mmol. The pot life of the reaction solution was 1 minute at 25°C.

(Molded product manufacturing experiment) A molded product manufacturing experiment was conducted using a reaction molding mold having an air vent equipped with pressurized gas introduction means and a pressure holding mechanism (pressure holding valve) as shown in FIG. Ta.

[0046] Both the cavity type and the core type of the mold are made of aluminum, and the shape of the cavity (therefore, the molded product) is 50 cm x 50 cm, and the average wall thickness is 7 mm.
, the weight is approximately 1.8 kg. Using nitrogen gas as a pressurized gas and changing the internal pressure of the mold as shown in Table 1, the reaction solution was injected and subjected to bulk polymerization to obtain each molded product.

[0047] As the reaction solution, both of the above reaction solutions were used as a mixture. That is, both reaction solutions were mixed at a ratio of 1:1 using a gear pump and a power mixer, and injected into a mold heated to 70° C. for the cavity and 50° C. for the core through the injection port. The bulk polymerization reaction time was about 20 seconds. After the reaction was completed, the molded product was removed from the mold and the number of voids was examined.

The number of voids in the molded product was counted by the following method. <Number of voids> The number of holes with a diameter of 0.5 mm or more was counted by passing the molded product through a 200 W light bulb and counting the number in a predetermined 10 cm x 10 cm square. The results are shown in Table 1.

[0049]

[Table 1] (*1) Internal pressure is from 0.0kg/cm2G to 0.5kg/
It rose to cm2G.

As is clear from the results in Table 1, the reaction solution was injected into the pressurized mold, and the internal pressure during the reaction process was reduced to 1.
．． It can be seen that the number of voids can be significantly reduced by carrying out bulk polymerization while maintaining the weight at 2 kg/cm2abs or more.

[Example 2] A mold having a cavity with one uneven thickness portion shown in FIG. 3 (the overall shape is box-like, and the weight of the molded product is 1.6 kg) was used. A molded article was produced in the same manner as in Example 1 using the same reaction solution as in Example 1, except that the internal pressure was maintained at the internal pressure shown in . The results are shown in Table 2. Note that the unit of numerical values in FIG. 3 is mm.

The number of voids was measured in the same manner as in Example 1. The number of bubbles on the surface of the molded product was determined by counting the number of small bubbles with a diameter of 0.01 mm or more on the surface of the uneven thickness portion (5 cm x 3 cm) using a 10x microscope.

[0053]

[Table 2]

From the results in Table 2, it can be seen that by applying internal pressure to the mold in advance, pressure fluctuations at uneven thickness areas when injecting the reaction liquid can be reduced, the flow can be made uniform, and voids and fine surfaces can be eliminated. It can be seen that bubble formation is prevented.

[0055]

[Effects of the Invention] According to the present invention, there is provided a method for producing a molded article in which the generation of voids is prevented or significantly reduced by a reaction molding method using a reaction liquid containing a norbornene monomer and a metathesis catalyst system. Ru. Further, according to the present invention, there is provided a reaction molding die suitable for producing a molded article in which the occurrence of voids is prevented or significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of a reaction molding mold of the present invention.

FIG. 2 is a partial sectional view of the reaction molding mold of the present invention.

FIG. 3 is a schematic cross-sectional view showing an uneven thickness part of a molded product (the unit of numerical values is mm).

[Explanation of sign]

1 Cavity type 2 Core type 3 Liquid reservoir 4 Air vent line 5 Three-way valve 6 Pressure holding valve 7 Pressure gauge 8 Seal groove 9 Passage from cavity to liquid reservoir 10 Cavity 11 Pressurized gas introduction line 12 Exhaust port 13 Gate 14 Check valve 15 Spring 16 Pressurized gas 17 Pressurized gas introduction line 18 Solenoid valve 19 Reaction liquid injection direction

Claims (2)

[Claims] Claim 1: When bulk polymerizing a reaction solution containing a norbornene monomer and a metathesis catalyst system by injecting it into a mold, the reaction solution at least in the latter half of the injection is kept at an internal pressure of 1.2 kg/mold.
A method for manufacturing a molded article, which comprises injecting the mixture into a mold maintained at a pressure of 1.2 kg/cm2 (absolute pressure) or higher, and maintaining the internal pressure during the reaction process at 1.2 kg/cm2 (absolute pressure) or higher. 2. A reaction molding mold having a liquid reservoir equipped with an injection port, a cavity, and an air vent, the mold comprising:
A mold for reaction molding characterized by a pressure holding mechanism installed in the air vent.