JPS5826370B2 - Method for producing urea-formaldehyde resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a urea-formaldehyde resin foam (hereinafter UF
It is abbreviated as form.

), and specifically relates to an improved method for producing UF foam with a slight formaldehyde odor.

Aqueous solution of urea-formaldehyde initial reactant (hereinafter abbreviated as resin liquid).

), a curing agent, and a foaming agent (hereinafter abbreviated as curing liquid).

) is used as a raw material, brought into a foamed state by a mechanical method or the like, and then mixed and cured to produce UF foam.

UF foam has the characteristics of being inexpensive, non-combustible, capable of foaming on-site, and having good water absorption properties, and has been used as an energy-saving insulation material for homes for an era.
Demand is expected to increase for use as filler material for coal mines, agricultural materials, and other uses.

In producing UF foams by known methods, the biggest problem encountered is the formaldehyde odor that remains after foaming.

Various attempts have been made to reduce the formaldehyde odor of urea formaldehyde resins, but no effective method has been found.

There are known methods for reducing the amount of free formaldehyde in resin liquids by adding various formaldehyde scavengers during the manufacturing process of resin liquids and treating them. However, it is difficult to reduce the formaldehyde content generated in the process after reacting the resin liquid and the curing liquid to form a foam.

That is, the formaldehyde scavenger added during the manufacturing process of the resin liquid reacts with unreacted formaldehyde and methylol groups in the resin liquid, so it is extremely difficult to stably contain the formaldehyde scavenger in the resin liquid. .

However, in order to effectively collect formaldehyde generated during the process of reacting the resin liquid and the curing liquid to form a foam and the curing process after forming the form,
Based on the idea that it is necessary for the formaldehyde scavenger to stably exist in the yarn until after it is formed into a foam, the present inventors have created a formaldehyde scavenger that exists in the yarn until the point of forming the yarn. As a result of various studies on methods for making it exist stably, it was found that a method of including a formaldehyde scavenger in the curing liquid is effective.

The present inventor had previously invented a method of incorporating urea into the curing liquid as a formaldehyde scavenger, but as a result of continued intensive studies on the effects of various formaldehyde scavengers, the inventor discovered that urea can be incorporated into the curing liquid as a formaldehyde scavenger. The present invention was completed based on the discovery that the effect of reducing formaldehyde odor can be further increased by replacing part or all of thiourea with thiourea.

As already stated, the object of the present invention is to provide a method for producing a UF foam that has a slight formaldehyde odor after foaming.

The present invention is an improved method for producing UF foam, which is characterized in that the curing solution contains thiourea or thiourea and urea in a method of producing UF foam by reacting a resin liquid and a curing liquid according to a known method. It is.

In the past, a known method for manufacturing UF foam was to foam a resin liquid and then spray a curing liquid.
This method causes many problems such as clogging of the resin in the foaming gun, and the current method is to foam the curing liquid and then spray the resin liquid.

That is, by blowing air into the curing liquid to create fine bubbles, and then spraying the resin liquid onto the bubbles, a UF foam having a uniform cell structure can be obtained.

Specifically, West German Sharamhemy, UK B, 1. Using a foaming gun for UF foam commercially available from P. Co., Ltd., etc., spray the resin liquid from a spray nozzle to the hardening liquid that has been foamed by blowing air into it, mix it, and spray this into the space of the construction area. , or introduce.

The obtained foam is usually left to harden and dry.

Note that it is of course possible to use a gas such as nitrogen or carbon dioxide instead of air, or to use various foaming agents.

The resin liquid is manufactured, for example, in the following manner.

Water is added to urea and formalin as needed, and the mixture is initially reacted at 80 to 95°C near neutrality.

When the reaction has progressed to a certain extent, the pH is adjusted to continue the reaction, and at the end of the reaction, a small amount of urea is added to reduce unreacted formaldehyde.

Dilute with water as necessary to adjust solids content.

Of course, modified products obtained by replacing a portion of urea with melamine, phenol, etc. can also be used.

Further, as the curing liquid, an aqueous solution containing a curing agent, a foaming agent, an auxiliary agent, and thiourea or thiourea and urea is used.

All known hardeners, foaming agents and auxiliaries can be used; examples of hardeners include phosphoric acid, sulfuric acid, acetic acid,
Examples of foaming agents include alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyldiphenyl ether sulfonates, higher fatty acid salts, and higher alcohol sulfate ester salts. , polyoxyethylene alkyl sulfate salts, alkylphenol/ethylene oxide adducts, etc., or a mixture of two or more thereof.

Examples of auxiliary agents include polyethylene glycol, polypropylene glycol, polyvinyl alcohol, etc. as hydrophilicity imparting agents, and salts such as calcium and magnesium as water quality conditioners.

Thiourea or thiourea and urea (hereinafter simply referred to as thiourea, etc.).

) and the amount of formaldehyde generated after foaming is affected by the manufacturing conditions of the resin solution, especially the amount of unreacted formaldehyde in the resin solution, as well as the mechanical conditions of foaming. Although it is difficult to unambiguously determine the amount of urea to be added, it is usually appropriate to use it in an amount of 1 to 20% by weight based on the solid content of the resin liquid.

If the amount of thiourea etc. added is small, the effect of reducing the amount of formaldehyde generated will be insufficient, and if the amount added is too large, the density of the foam will increase, the compressive strength will decrease, etc., both of which are undesirable.

Addition of thiourea, etc. is a curing agent, foaming agent,
It may be added together with auxiliary agents, stirred and dissolved to form an aqueous solution.

Of course, it can also be added when the curing liquid is used.

Curing liquids containing thiourea, etc. are usually stable at temperatures below 50°C for more than a month, but at high temperatures, thiourea, etc. may decompose due to the effect of the curing agent, so store it at as low a temperature as possible and cure it as soon as possible. Better to use on eyes.

In this respect, it is safest if an aqueous solution of thiourea or the like is mixed immediately before foaming.

According to the present invention, by simply adding thiourea or the like to the curing solution, U.
F form is obtained, which brings about remarkable effects especially in applications such as insulation materials for houses and fillers for coal mines.

The method of the present invention will be explained below with reference to Examples.

Parts in the examples represent parts by weight.

Example 1 36.7 parts of urea, 75.4 parts of 37% formalin, 30 parts of water
1 part and 0.3 part of 24% aqueous ammonia were stirred and mixed at around 90°C for 30 minutes to 1 hour.

The pH was adjusted to 4 to 5 by adding 40% formic acid, and after further reaction for 1 hour, the pH was adjusted to 8 with 20% caustic soda.

After adding 4.2 parts of urea and reacting at 65°C for 30 minutes, the reaction product obtained by immediately cooling was diluted with the same volume of water.
A resin liquid was prepared.

After stirring and mixing 13.4 parts of 85% phosphoric acid, 8.3 parts of sodium branched dodecylbenzenesulfonate, and 3.3 parts of a stabilizer, 29.4 parts of thiourea was added to 45.7 parts of water.
After stirring and mixing, the mixture was diluted with water to a volume ratio of 10 to prepare a hardening solution.

Using the above resin liquid and curing liquid at a volume ratio of 1:1, English B, 1. Using a foaming gun for UP foam commercially available from P. Co., Ltd., air was blown into the foam, followed by curing and drying to obtain the UP foam of the present invention.

The density of this foam is 11.8 kg/m', the compressive strength is 0.299/cyrt-, and the amount of formaldehyde generated during 24 hours from 1 hour after foaming was measured according to JISA-5908, and the result was 13.8 ppm. Yes, and the formaldehyde odor was extremely slight.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the use of thiourea was omitted when preparing the hardening solution.

The density of the obtained UF foam is 10.1 kg/m'
, compressive strength is 0.35 kg/cyi, JIS
According to A-5908, the amount of formaldehyde generated during 24 hours from 1 hour after foaming was measured and the result was 86.4.
ppm, and the formaldehyde odor was noticeable.

Comparative Example 2 The same procedure as in Example 1 was carried out except that 29.4 parts of urea was used instead of 29.4 parts of thiourea when preparing the curing agent.

The density of the obtained UF foam is 10.9 kg/m'
The compressive strength was 0.30 kg/cyrY, and the amount of formaldehyde generated was 18.5 ppm.

Examples 2 to 4 Examples 2 to 4 were carried out in the same manner as in Example 1, except that the amount of thiourea etc. added during the preparation of the curing agent was changed, and the results were as shown in the following table.

Claims (1)

[Claims] 1. In a method for producing a urea-formaldehyde resin foam by reacting an aqueous solution of a urea-formaldehyde initial reactant with an aqueous solution containing a curing agent and a foaming agent, thiourea or thiourea is added to the aqueous solution containing a curing agent and a foaming agent. A method for producing a urea-formaldehyde resin foam, characterized by containing urea and urea.