JPH03189048A - Mold material for foundry sand molds - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a mold material used in the production of foundry sand molds used in the production of metal casting products, and in particular to a silicate mold material using a novel silicate polyol. - Concerning mold materials containing urethane binders.

<Prior art> Generally, foundry sand molds (hereinafter simply referred to as sand molds) used to manufacture cast products of various metals are made by hardening foundry sand such as silica sand or zircon sand with an organic binder. The former method uses an organic binder, such as the shell mold method, OJ process, dinocure method,
Examples include the Pepset method, the cold box method, the method using furan resin, and the method using acid-curing phenol resin.

Among these, a method using a urethane resin-based binder is the Pepset method, which utilizes a urethanization reaction between an alkali-curing phenol resin and a polyisocyanate.
This method is used for a wide variety of small quantities of large or complex mechanical castings.

On the other hand, polyether-based urethane resin binders have poor heat resistance, so they were not used as binders for iron castings that require high temperatures, except for low-temperature applications such as aluminum castings. . Therefore, as organic binders for iron, phenol urethane resins using phenol polyols with good heat resistance and carbonizability, and furan resin binders have been used.

<Problems to be Solved by the Invention> However, with phenol-urethane resin, the liquid phenol resin has a high viscosity and requires a diluent, which causes the odor of the diluent and formalin odor peculiar to phenol resin to be produced during sand mold manufacturing. Furthermore, furan resins have problems in the working environment, such as a pungent mediocre acid odor from sulfonic acid, which is a curing agent for furan resins.

The present invention provides a new foundry sand mold material using a polyether-based urethane resin binder that has sufficient heat resistance as a binder for iron foundry sand molds.

An object of the present invention is to use (a) tetraalkoxysilane or its hydrolyzed and dehydrated polycondensate (silicate oligomer) with a hydrolysis rate of 50% or less as a binder, with a functional group number of 2.
A hydroxyl value of 200 obtained by modifying with a polyol of
~1500 silicate polyol, (5) urethanization catalyst, and (c) polyisocyanate, and the ratio of silicate polyol (a) to polyisocyanate (c) is 0.8 to 1.5% in terms of N G Olo H equivalent ratio. This is achieved by using a range of 5.

Hereinafter, the present invention will be explained in detail.

The tetraalkoxysilane used in the present invention is represented by the following formula.

OR.

R40Si ORz OR.

(Here, R, -R, may be the same or different (
It is an alkyl group such as methyl group, ethyl group, butyl group.

) The hydrolysis dehydration polycondensation reaction of tetraalkoxysilane is as shown below (N formula).In other words, silicate oligomers are produced by adding the required amount of acidic, neutral or alkaline water to the tetraalkoxysilane monomer and carrying out the reaction. This is done by removing the resulting alcohol (which yields twice as many moles of water as added).

m (S i (OR) a ) +mnHz O−
(S i (OR) 4-211011) ea
+2mnROH (1) (In the formula, R represents an alkyl group, and n represents a number of 0 to 2. m is an integer, preferably 2 to 3o.) The hydrolysis rate of a silicate oligomer is (I[ ) is a value calculated according to the formula, and the amount of water to be added is determined by the desired hydrolysis rate.

That is, a tetraalkoxysilane in which all alkoxy groups have been decomposed is expressed as a hydrolysis rate of 100%, and a tetraalkoxysilane in which two alkoxy groups have been decomposed is expressed as a hydrolysis rate of 50%. In the present invention, a tetraalkoxysilane (referred to as an oligomer with a hydrolysis rate of O) or a silicate oligomer with a hydrolysis rate of up to 50%, preferably a silicate oligomer with a hydrolysis rate of 0 to 30%, more preferably 0 to 20%, is used. Ru.

Polyols having two functional groups used in the present invention include polyfunctional alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butanediol, and hexanediol; Examples include those to which alkylene oxide is added, such as oxide and propylene oxide.

All of these polyols are flammable and are thermally decomposed by molten iron. Therefore, the molecular weight of these polyols is preferably small, preferably 62-300, more preferably 62-150.

The reaction of tetraalkoxysilane or its hydrolyzed and dehydrated polycondensate with a polyol is carried out by a conventional transesterification reaction. That is, a predetermined amount of tetraalkoxysilane or its hydrolyzed and dehydrated polycondensate and a predetermined amount of polyol are placed in a reaction vessel, and heated at approximately 60 to 200 degrees while stirring.
It is obtained by reacting at C and distilling off the alcohol. The reaction may be carried out under a nitrogen stream, under reduced pressure, or at room temperature and atmospheric pressure, and may be carried out with or without a catalyst. , magnesium acetate, titanate ester, etc. can be used.

The reaction ratio of the tetraalkoxysilane or its hydrolyzed and dehydrated polycondensate with the polyol is preferably 1=1 to 15 in equivalent ratio of the alkoxy group of the tetraalkoxysilane or its hydrolyzed and dehydrated polycondensate to the polyol. , more preferably 1:1 to 8. Excess polyol reacts with polyisocyanate and improves standing strength, but it is thermally decomposed during pouring, so it is better to have less polyol. Further, if necessary, an organic solvent, other organic foundry binder, urethane ether polyol, ester polyol, etc. may be added to the silicate polyol.

The proportion of the silicate polyol used in the present invention is preferably 0.4 to 3% based on the sand. If it is less than 0.4%, sufficient sand mold strength cannot be obtained, and if it exceeds 3%, the collapsibility of the sand mold becomes poor. Note that "%" means "% by weight" unless otherwise specified.

As the urethanization catalyst used in the present invention, all catalysts commonly used in the production of urethane resins can be used. For example, amine catalysts such as N, N, N', N'-tetramethyl/hexamethylene diamine, pentamethyldiethylenetriamine, triethylamine, N, N, N', N'-tetramethyl-1,3=butanediamine, dibutyltin There are organometallic catalysts such as dilaurate. Generally, the amount of these urethanization catalysts added to the total resin is 0.
If it is less than 1%, the strength of the sand mold will not be sufficient, and if it exceeds 3%, the curing speed will be too fast and the modeling work will not be able to be carried out smoothly. It is preferable that it is 3%.

The polyisocyanate used in the present invention includes:
- Organic compounds having two or more isocyanates M in the molecule, including aliphatic and aromatic polyisocyanate compounds, as well as modified products thereof. Examples of aliphatic polyisocyanates include hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and methylcyclohexane diisocyanate. Examples of aromatic polyisocyanates include toluene diisocyanate, diphenylmethane diisocyanate, and polymeric diphenylmethane diisocyanate. Examples of modified products include carbodiimide modified products and prepolymer modified products.

Preferred polyisocyanates in the present invention are aromatic polyisocyanates or modified products of aromatic polyisocyanates, and particularly preferred are diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, and modified products thereof. These isocyanates are specifically shown below.

Diphenylmethane diisocyanate has the structure shown below.

Polymeric diphenylmethane diisocyanate is a polymer of the above diphenylmethane diisocyanate, and N
GO (%) is 29-35, viscosity 2500cps
(25°C) or less.

Examples of these modified products include carbodiimide modified products and prepolymer modified products. Carbodiimide-modified products are those in which carbodiimide bonds are introduced using a known phosphorus-based catalyst, and prepolymer-modified products are those in which isocyanate and polyol are reacted to leave isocyanate groups at the ends. As polyols, all polyols for polyurethane resins can be used. Further, it is also possible to use a mixture of isocyanate and an organic solvent.

In the present invention, the ratio of silicate polyol (a) and polyisocyanate (c) is 0 in terms of NC010H equivalent ratio.
．． It needs to be 8 to 1.5, preferably 1.
It is 0 to 1.2. If the equivalence ratio is less than 0.8, a sand mold with sufficient strength cannot be obtained, and if it exceeds 1.5, the strength will not improve and the cost will increase.

The method of manufacturing a foundry sand mold using the mold material of the present invention is not particularly limited, and the sand mold can be manufactured according to a general sand mold manufacturing method. That is, it is manufactured by sequentially adding and mixing a silicate polyol, a urethanization catalyst, and a polyisocyanate to foundry sand in any order, and then pouring the mixture into a mold or the like and leaving it to stand.

In addition to the above-mentioned silicate polyol, urethanization catalyst, and polyisocyanate, when producing the mold, -C
In addition, various additives used in mold manufacturing, such as refractory fine powder such as silica alumina, various stabilizers, etc. can be used in combination.

The mold material of the present invention obtained in this way is a new mold material that is completely different from conventional mold materials.It has excellent flame retardancy and heat resistance, has no problems such as odor, and the properties of castings manufactured using it are also excellent. You can get what you want.

<Example> The mold material of the present invention will be specifically explained using examples.
The present invention is not limited to these specific examples.

Company Materials a) Silicate polyol: ■ 1 mol of tetraethyl silicate and 4 mol of diethylene glycol were placed in a reaction vessel and heated to 140°C.
By removing the ethanol produced, the hydroxyl value is 550 and the viscosity is 3.
A silicate polyol of 50 c p s / 25 °C is obtained.

■ 1 mole of tetraethyl silicate and 4 moles of propylene glycol were reacted in the same manner as in (■), and the hydroxyl value was 650.
A silicate polyol with a viscosity of 500 cps/25°C is obtained.

■React 1 equivalent of 40% hydrolyzed product of tetramethylsilicate and 1 equivalent of diethylene glycol in the same manner as in ■,
Calculate the amount of methanol flowing out at 40% of the calculated amount.)7
A mixture of 0.4 equivalents of diethylene glycol reacted with 1 equivalent of silicate oligomer and 0.6 equivalents of unreacted diethylene glycol, a silicate polyol with a hydroxyl value of 630 and a viscosity of 410 cps/25°C. get.

b) Urethane catalyst: tin octylate C) Isocyanate: polymeric diphenylmethane diisocyanate, viscosity 53 cps/25°C, NCO%
32.0% d) Foundry sand: Freemantle, average particle size 49 μm Foundry sand molds were manufactured using the above materials in the following manner, and after 24 hours had passed, sand molds made by George Fisher Co. The standing strength was measured using an impact penetration tester (scale 3). Table 1 shows the measurement results of standing strength and the contents of each prescription.

Take 300 g of foundry sand into a sand mixer, add the required amount of silicate polyol and urethanization catalyst while stirring, stir for 30 seconds, then add isocyanate, stir for 30 seconds, and mix this sand to a diameter Fill a 5cm by 5cm high mold and allow to harden.

As described above, the strength of the sand mold obtained using the mold material of the present invention was equivalent to or higher than that of conventional mold materials, and was sufficient for casting, and there was no problem of bad odor.

<Effects of the Invention> The template material of the present invention contains silicon oxide (Si
Since it contains 100 oz (Oz), it has better heat resistance than ordinary polyether polyols, and also has no problems in the working environment such as odor.

Applicant M.D. Kasei Co., Ltd. Mitsubishi Kasei Corporation

Claims (1)

[Claims] (1) A mold material containing foundry sand and a binder thereof, wherein the binder is (a) a tetraalkoxysilane or a hydrolysis rate of 50
% or less of the hydrolyzed and dehydrated polycondensate (silicate oligomer) with a polyol having a functional group of 2, a silicate polyol having a hydroxyl value of 200 to 1500, (b) a urethanization catalyst, and (c) a polyisocyanate. and the ratio of silicate polyol (a) and polyisocyanate (c) is 0.8 in terms of NCO/OH equivalent ratio.
A molding material for a foundry sand mold, characterized in that the temperature is in the range of 1.5 to 1.5.