JPS61266146A - Master pattern material for casting - Google Patents

Abstract

PURPOSE:To form a master pattern for casting so as to have adequate workability and compressive strength and to provide a smooth surface having low water absorptivity thereto by putting the prefoamed particles of a crosslinked PP resin having a specific gel fraction into a mold and heating the same to expand to the specific density and average cell size. CONSTITUTION:Adequate amts. of water, antisticking agent talc, org. peroxide crosslinking agent such as 1,1-bis(t-butyl peroxy)3,3,5-trimethyl cyclohexane and crosslinking assistant divinyl benzene are added to the PP resin such as ethylene/propylene random copolymer having <=40% residue of n-heptane extraction and the mixture is heated in an autoclave to form the crosslinked resin particles. Suitable amts. of water and volatile org. foaming agent such as dichlorofluoromethane are added thereto and the particles are released after the pressurizing and heating up to form the prefoamed and crosslinked particles having 0.01-50% gel fraction. Such particles are put into a metallic mold and are heated to expand, then the foamed molding having 0.2-0.02g/cm<3> density and 70-1,000mum average cell size is obtd. The good master pattern for casting having the adequate cutting workability, compressive strength, smooth surface and low water absorptivity is thus obtd.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a molding material for casting that is mainly made of an in-mold foamed product of crosslinked polypropylene resin pre-expanded particles, and more specifically, it relates to a mold material for casting that is made mainly from an in-mold foamed product of cross-linked polypropylene resin pre-expanded particles. The present invention relates to a casting material whose main raw material is an in-mold foamed product of pre-expanded crosslinked polypropylene resin particles having surface hardness.

[Prior art]

Traditionally, wood has been used as the main material for casting molds, and even today, wood such as cedar is commonly used. Wood has characteristics such as high surface hardness and excellent dimensional stability during molding, but on the other hand, it is expensive, requires drying, and has knots and grain, making it extremely difficult to process and mold. It has drawbacks such as requiring skill, being inconvenient to transport as the wooden original is heavy, and if deformed during storage, it must be corrected each time it is used.

Due to the above-mentioned drawbacks of wood, attempts have been made in recent years to use in-mold foam molded products of polystyrene as a casting material. However, although polystyrene foam moldings solve the above-mentioned drawbacks of wood, they also have the disadvantage of being brittle due to the inherent nature of foamed polystyrene, so they are easily scratched when processed with woodworking tools. It has processing problems.

Japanese Patent Publication No. 47-43404 discloses a product which is crosslinked and foamed by a specific method and has a gel fraction of 30 to 90% and a bulk density of 0.5 to 0.
．． 05g/am3. A casting master material made of a crosslinked crystalline polyolefin resin foam having an average cell diameter of 400 μm or less is shown. However, since this casting material uses pyrolytic amides as a blowing agent, it cannot be used to produce precision castings, and it still has the disadvantage of high water absorption. The reality is that it has poor releasability from sand and is not actually used.

〔the purpose〕

An object of the present invention is to provide a foam molding material for casting that overcomes the above-mentioned drawbacks found in conventional foam molding materials for U-adjustment and has a low water absorption rate and provides castings with good one-dimensional accuracy.

[Configuration] The present invention has a gel fraction of 0. Density 0 made by integrally molding 50% cross-linked polypropylene resin pre-expanded particles in a mold
．． 2~0.02g/co? , average bubble diameter 70-1000
The gist of this article is a molding material for casting, which is a cross-linked polypropylene resin in-mold foamed molded product having a micrometer diameter.

The casting mold of the present invention is made of a foam formed by foam-molding crosslinked polypropylene resin pre-expanded particles having a gel fraction of 0.01 to 50% in a mold. In this case, the gel fraction indicates the proportion of insoluble matter obtained after immersing the crosslinked pre-expanded particles in boiling xylene for 8 hours, and is expressed by the following formula.

P (%) = -X100 P gel fraction (%) ■: Weight of cross-linked pre-expanded particles M: Weight of insoluble matter When the gel fraction exceeds 50%, void formation increases in the molded product. In addition, the water absorption rate also increases, which is not preferable, and the gel fraction of the crosslinked resin pre-expanded particles is set to the above-mentioned 0.
It is preferable to set the range to 0.01 to 50%, preferably 5 to 45%.

Further, in the in-mold foamed product of the pre-expanded particles used as a casting material in the present invention, the density (bulk density) is 0.02 to 0.2 g/cm3. Preferably 0.03
~0.15 g/cm', and the average bubble diameter is 70 to 1000 μm, preferably 80 to 900 μm.
It is defined in the μm range. If the density of the foam is larger than the above range, the mechanical strength will be high and the dimensional stability will increase, but workability will deteriorate and the weight will also increase, which is undesirable. On the other hand, if the density is smaller than the above range, the weight will increase Although this method is excellent in terms of flexibility, it is not preferable because the foam becomes flexible and has poor one-dimensional stability. In the case of the present invention, the compression hardness (JTS K-6767) of the foam is generally preferably set to 0.7 kg/al or more -F.

In addition, if the average cell diameter of the foam is smaller than the above range, it becomes difficult to cut the foam and the surface condition of the cut product deteriorates due to tearing of the cell membrane, which is undesirable. In this case as well, problems such as roughness of the cut surface and increased water absorption occur, which is not preferable.

The polypropylene resins used as the mold material resin for casting of the present invention include ethylene-propylene random copolymer, ethylene-propylene blow 4=tsuk copolymer, propylene i1 homopolymer, and propylene-1-butene random copolymer. Examples include merging. In particular, among these polymers, 0.5% by weight of ethylene
Preference is given to using an ethylene-propylene random copolymer of up to 10% by weight, preferably between 11% and 5% by weight. Further, it is preferable to use a polypropylene resin having an n-hebutane extraction residue ratio of 40% or less because a rigid foam can be obtained. In this case, the n-heptane extraction residue ratio means stereoregularity and is expressed by the following formula.

■, R (%) = -X100 Ran-heptane extraction residue ratio (%) L: Weight of insoluble matter after 8 hours of n-heptane extraction M: n-
Weight before hebutane extraction In the present invention, the above-mentioned polypropylene resins may be used alone or in combination, and in the case of a blend, the blending ratio is arbitrary.

The molding material for casting of the present invention is an in-mold crosslinked foam molded product formed from so-called crosslinked pre-expanded particles formed by crosslinking the resin particles and foaming the obtained crosslinked particles. In this case, crosslinked particles are prepared by mixing resin particles, water, an anti-fusing agent, and a crosslinking agent in an autoclave, raising the temperature to the softening temperature of the resin while stirring, impregnating the resin with the crosslinking agent, and then increasing the temperature to the crosslinking temperature. It can be obtained by raising and holding the temperature at . Examples of the crosslinking include dicumyl peroxide, 1,1-bis(butylperoxy)3,3.5
-trimethylcyclohexane, n-butyl-4,4-bis(1,-butylperoxy)valerate, thi-butylcumyl peroxide, 2,5-dimethyl-2,5-di(thi-butylperoxy)hexane, etc. of organic peroxides are used. Further, it is preferable to use divinylbenzene as a crosslinking aid in combination with these crosslinking agents. The amount of the crosslinking agent used is 0.05 parts per 100 parts of resin.
The amount of divinylbenzene used is 0.05 to 5 parts by weight per 100 parts by weight of the resin. In addition, for pre-foaming of cross-linked particles, the cross-linked particles, water, anti-fusing agent, and blowing agent are mixed in an autoclave, the temperature is raised to the foaming temperature under pressure, and one end of the container is opened to transfer the contents to a low-pressure zone. This can be done by releasing it. In this case, examples of the anti-fusing agent include aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, zinc carbonate, etc.
Examples of the blowing agent include volatile organic blowing agents such as propane, butane, pentane, trichlorofluoromethane, and dichlorodifluoromethane, as well as inorganic gases such as carbon dioxide, nitrogen, and air.

The pre-expanded particles obtained as described above are pressurized with air in a pressure-resistant container, and 0.5 to 3 kg/cJ is added into the particles.
After giving the particles an internal pressure of about G, put them into a mold for molding,
By heating and foaming, the product is integrally molded into a foam molded product, which is then cooled and taken out from the mold.

The crosslinked polyethylene resin in-mold foamed molded product thus obtained is dried and used as a mold material for casting.

〔effect〕

The mold material for casting of the present invention is made of the above-mentioned specific foam and can be used in the same way as conventional materials made of wood or foam. Because of its excellent compressibility, it has the advantage that the tools used in conventional wooden model manufacturing can be used as is, and it also has a smooth surface and high compression hardness, and is even more advantageous.
Since it has extremely low water absorption, it provides a casting material with excellent dimensional stability. Further, the casting mold material of the present invention has high compressive hardness and low water absorption, so it has extremely excellent mold releasability.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 5, Comparative Examples 1 to 5 In an autoclave, 100 parts by weight of the ethylene-propylene random copolymer particles shown in Table 1, 300 parts by weight of water, and 0.3 parts by weight of finely divided aluminum oxide as an anti-fusing agent were added. A crosslinking agent and a crosslinking aid shown in Table 1 were blended, the temperature was raised to 100° C. while stirring, and the temperature was maintained for 1 hour. Thereafter, the temperature was raised to 150°C and held for 1 hour to perform a crosslinking reaction, and then the container was once cooled and the crosslinked resin particles were taken out.

Next, 100 parts by weight of the crosslinked resin particles, 300 parts by weight of water, and a volatile blowing agent shown in Table 1 as a blowing agent were added to the autoclave again, and the temperature was raised to the foaming temperature shown in Table 1 while stirring. After holding at this temperature for 15 minutes, one end of the container was opened while pressurizing the inside of the container to 40 kg/cl #G, and the crosslinked particles and water were released under atmospheric pressure to perform foaming and pre-foaming. Crosslinked particles were obtained.

Next, the pre-expanded cross-linked particles were placed in a pressure-resistant container and pressurized with air, so that 1.5 kg/DIt was added to the pre-expanded cross-linked particles.
The particle had an internal pressure of G. The particles were placed in a mold, heated and foamed at a steam pressure of 3.2 kg/c+#G, and then cooled to obtain a foamed molded article in which the particles were fused, that is, a casting material.

Next, each of the in-mold foam molded products obtained above was evaluated in terms of the difficulty of cutting, the surface condition of the cut product, the compression roughness, and the water absorption rate, and the results were evaluated using the following criteria. Shown in the table.

The difficulty of cutting is evaluated by cutting the in-mold foam molded product into a thickness of 10 mm using a hand saw, and the surface condition of the cut product is evaluated by the difficulty of cutting at that time. The surface condition of the product was evaluated by visual observation.

〔Evaluation criteria〕

(1) Difficulty of cutting process: O: Smooth cutting with no resistance during cutting.

Δ...There is some resistance when cutting, but it is possible to cut.

×...The resistance is large and vibrations occur during cutting.

(2) Surface condition of cut product: O...Surface is smooth.

Δ...The surface is slightly rough.

×: Some particles have rough and peeling surfaces.

(3) Compression Katasa (compliant with TTS-6767):
O...0.7kg/cJ or more Δ...-0.7kg/crl-0.4J/cIIT×・
・・0.4 kg/cJ or less (4) Water absorption rate (JIS-6767B method): 0-0.
003g/cn? Less than Δ...0.03 to 0.003g/rJ×...0.0
3 g/cJ or more 18 Kaisho Gl-266146 (5) 18 Kai BHGI-266146 (6) beokigogo gastric mass cloud pi

Claims (2)

[Claims] (1) Pre-expanded crosslinked polypropylene resin particles with a gel fraction of 0.01 to 50% are integrally molded in a mold with a density of 0.
．． 2~0.02g/cm^3, average bubble diameter 70~100
A molding material for casting consisting of a 0μm crosslinked polypropylene resin in-mold foam molding. (2) The mold material for casting according to claim 1, wherein the pre-expanded crosslinked polypropylene resin particles are obtained using a volatile blowing agent.