JPS6284853A - Material for casting pattern - Google Patents

Abstract

PURPOSE:To obtain a material having excellent cutting workability and parting characteristic for a casting pattern by foam molding a crosslinked PE resin particles which is formed of a HDPE resin and having a limited gel fraction in a mold integrally. CONSTITUTION:The material for the casting pattern consists of the foamed material formed by foam molding the crosslinked PE resin particles having <=50% gel fraction in the mold and the density thereof is limited to 0.2-0.022g/cm<3> and the average cell size to a 70-1,000mum range. The workability is deteriorated if the density exceeds the above-mentioned range and the dimensional stability is deteriorated if the range is below the range. The crosslinked PE resin particles used as the material for the casting pattern is formed of the HDPE resin.

Description

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

[Prior art]

Traditionally, wood has been used as the main material for casting models, and even now, 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. Wood for casting has disadvantages such as requiring skill, being heavy and inconvenient to transport, and needing to be modified each time it is used if it becomes deformed during storage. Due to the above-mentioned drawbacks, attempts have been made in recent years to use in-mold foam molded products of polystyrene as materials for casting models. 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 material with a gel fraction of 30 to 90% and a bulk density of 0.5 to 0, which is obtained by cross-linking and foaming using a specific method, as a material that eliminates the defects found in the above-mentioned wood.
．． 05g/c+J, and a casting pattern material made of a crystalline polyolefin resin crosslinked foam having an average cell diameter of 400 μm or less. However, this foam uses a pyrolytic amide as one blowing agent, so if you try to reduce the density, you have to use a lot of blowing agent, and it cannot be used to produce precision castings. However, the reality is that it still has the disadvantage of high water absorption and therefore poor releasability from sand, so it is not actually used.

〔the purpose〕

An object of the present invention is to overcome the above-mentioned drawbacks of conventional foams for casting models, and to provide a foam for casting models that has a low water absorption rate and does not deform when the model is stored, which provides castings with good one-dimensional accuracy. shall be.

〔composition〕

The present invention consists of a cross-linked polyethylene resin in-mold foam molded product in which cross-linked polyethylene resin particles with a gel fraction of 20 to 40% are integrally foam-molded in a mold, and the density is 0.2 to 0.02.
2 g/crl and an average cell diameter of 70 to 1000 μm.

The crosslinked polyethylene resin particles are made of a high density polyethylene resin.

The casting model material of the present invention is made of a foam formed by foam-molding crosslinked polyethylene resin pre-expanded particles having a gel fraction of 50% or less in a mold. In this case, the gel fraction is 8% when the cross-linked pre-expanded particles are placed in boiling xylene.
This indicates the percentage of insoluble matter obtained after soaking for a period of time.
It is expressed by the following formula.

P (%) = -X100 P gel fraction (%) L: Weight of crosslinked pre-expanded particles M: Weight of insoluble matter If the gel fraction exceeds 50%, void formation will increase in the molded body, Moreover, it is not preferable because the water absorption rate increases, and the gel fraction of the crosslinked resin pre-expanded particles is preferably set to 20 to 40%.

Further, in the in-mold foamed product of the pre-expanded particles used as the casting model material of the present invention, its density (bulk density) is 0.2 to 0.022 g/aJ, preferably 0.14 g/aJ.
-0.03g/cj, and the average bubble diameter is 70-1000μm, preferably 80-900μm.
It is defined in the scope of the garden. 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 it 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 of the foam (JIS K-6767) is generally preferably set to 0.7 kg/cj or more. Furthermore, 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 polyethylene resin used as the casting model material of the present invention has a density of 0.945 g/cj or more, preferably a density of 0.
．． It is a high density polyethylene resin with a weight of 950 to 0.970 g/aJ. With low-density polyethylene resin, if you try to obtain a foam with the same strength, it will be heavier;
This is not preferable because it increases the cost.

The cast model material of the present invention is an in-mold crosslinked foamed molded product formed from so-called crosslinked pre-expanded particles, which are formed by crosslinking the resin particles and foaming the obtained crosslinked particles. If the crosslinked particles are autoclaved,
Mix resin particles, water, an anti-fusing agent, and a cross-linking agent, raise the temperature to the softening temperature of the resin while stirring, and impregnate the resin with the cross-linking agent.
Thereafter, it is obtained by raising and maintaining the temperature at the crosslinking temperature.

The crosslinking includes 1, for example, dicumyl peroxide,
1,1-bis(t-butylperoxy)3,3.5-trimethylcyclohexane, n-butyl-4,4-bis(
7-butylperoxy)valerate, 7-butylcumyl peroxide, 2,5-dimethyl-2,5-di(7-butylperoxy)valerate, 2,5-dimethyl-2,5-di(7-butylperoxy)valerate
Organic peroxides such as butylperoxy)hexane are used. Moreover, divinylbenzene can also be used together with these crosslinking agents as a crosslinking aid. The amount of the crosslinking agent used is 0.05 to 5 parts by weight per 100 parts by weight of the resin, and the amount of divinylbenzene used is per 100 parts by weight of the resin.

The proportion is 0.05 to 5 parts by weight. In addition, to pre-foam the crosslinked particles, mix the crosslinked particles, water, anti-fusing agent, and blowing agent in an autoclave, raise the temperature to the foaming temperature under pressure, open one end of the container, and 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 to give a concentration of 0.5 to 3 kg/cn per particle.
After giving the particles an internal pressure of about T, put them into a forming mold,
By heating and foaming, the product is molded into a single foam molded product, which is then cooled and taken out from the mold.

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

〔effect〕

The casting model material of the present invention is made of the above-mentioned specific foam, and can be used in the same way as conventional wood or foam. It has the advantage of being able to use the tools used to produce conventional wood patterns as is, and has a smooth surface and high compressive hardness, and even more advantageously, has extremely low water absorption. Because it is a material, it provides a mold for casting with excellent dimensional stability. Furthermore, the casting model 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.

〔Evaluation criteria〕

(1) Female quality of cutting process: 0: Smooth cutting with no resistance during cutting.

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

X: The resistance is large and vibrations occur during cutting.

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

△...The surface is slightly rough.

X: There are particles that are rough and peeling on the surface.

(3) Compression flatness (based on JIS-6767): 0
=-0.1kg/a! More than X...0.7g10 (less than (4) Water absorption rate (JIS-K-6767B method):○・
・-0,003g/cn? Less than △---0.03-0.003g/cn (X...0.
03 g/cd or more Examples and Comparative Examples The autoclave had the density shown in Table 1, 100 parts by weight of MI high-density polyethylene particles, 300 parts by weight of water, 0.3 parts by weight of finely divided aluminum oxide, and dicumyl per as a crosslinking agent. The amount of oxide shown in Table 1 was added, and in Comparative Example 1, 0.4 part by weight of divinylbenzene was added, the temperature was raised to 100° C. with stirring, and the temperature was maintained at this temperature for 1 hour. Thereafter, the temperature was raised to 150°C and held for 90 minutes, and then the container was cooled and the crosslinked resin particles were taken out.

Next, 100 parts by weight of crosslinked resin particles were added to the autoclave again.
300 parts by weight of water, 0.3 parts by weight of finely divided aluminum oxide, and dichlorodifluoromethane were blended in the amounts shown in Table 1,
The temperature was raised while stirring, and the temperature was increased to 9! shown in Table 1. Hold at foam temperature for 15 minutes. After that, the inside of the container is filled with air at 40kg/cnfG.
While pressurizing the container, one end of the container was opened, and the crosslinked resin particles and water were released under atmospheric pressure to perform foaming, thereby obtaining pre-foamed crosslinked particles.

Next, the obtained pre-expanded particles were placed in a pressure container and pressurized with air to give the particles an internal pressure of 1.5 kg/cJG. Put these particles into a forming mold and weigh 3.2kg/c+JG
Heated with steam pressure of 1g! After foaming, the mixture was cooled to obtain a foam molded product in which the particles were fused to each other, that is, a material for a casting model.

Claims (1)

[Claims] (1) Consists of a cross-linked polyethylene resin in-mold foam molded product made by integrally foam-molding cross-linked polyethylene resin particles with a gel fraction of 50% or less in a mold, and has a density of 0.2 to 0.02 g/
cm^3 and an average cell diameter of 70 to 1000 μm, and the crosslinked polyethylene resin particles are made of high-density polyethylene resin.