JP7042032B2 - Melamine resin foam - Google Patents

Description

The present invention relates to a melamine resin foam.

By reacting the melamine monomer and formaldehyde in the presence of a catalyst, methylol melamine, which is a precondensate, is obtained, and when the reaction is further advanced, the precondensate is crosslinked in a network to form a melamine resin. Can be manufactured. Melamine resin has high strength and hardness, and is excellent in water resistance and weather resistance, and is therefore preferably used as an adhesive for woodworking and daily necessities such as tableware.

Further, by adding a foaming agent and heating immediately after obtaining methylol melamine which is a precondensate, it is possible to generate a melamine resin foam having a porous shape by generating fine bubbles. Since this foam is lightweight and highly flexible, it is used as a cleaner sponge for cleaning dishes and the like, as well as cushions and mats for bedding.

Conventionally, a wide range of research has been conducted on melamine resin foams. Specifically, a melamine-based resin foam having a characteristic of foaming a resin composition containing a melamine formaldehyde condensate, a foaming agent and an isocyanate is known (Patent Document 1). This foam solves the problem of brittleness without impairing the flame retardancy and thermal conductivity inherent in the melamine resin foam.

Japanese Unexamined Patent Publication No. 7-157590

However, the precondensate trimethylolmelamine tends to be inferior in storage stability because it rapidly thickens after being left at room temperature for about 1 hour, and further affects the internal shape of the final foam. There was a possibility of giving.

Further, since the melamine resin foam has excellent sound absorption performance, it may be used as a building material such as a wall material or a ceiling material. Generally, as the density of the resin foam increases, the sound absorption performance tends to improve, but this is contrary to the weight reduction, so there is room for further improvement.

An object to be solved by the present invention is to provide a melamine resin foam which is lightweight, has a porous internal shape, and has remarkably excellent sound absorption performance.

The present invention is characterized in that a mixed solution containing a methyleneated melamine-formaldehyde initial condensate (A), a hydrofluorocarbon (B), an emulsifier (C), and a curing agent (D) is foamed. It is a melamine resin foam.

The melamine resin foam according to the present invention has the effects of being lightweight, having a porous internal shape, and having remarkably excellent sound absorption performance.

<Methyleneated melamine-formaldehyde initial condensate>
In the present invention, the methyleneated melamine-formaldehyde initial condensate (A) is used. The component (A) can be synthesized by a two-step reaction. The primary reaction is the synthesis of methylol melamine, which is a precondensate, and can be obtained by adding a basic catalyst to an aqueous solution containing a melamine monomer and formaldehyde and no alcohol, and heating the mixture. Formaldehyde is preferably blended as formalin in order to improve workability.

Further, other aldehydes may be blended as long as the effect of the present invention is not impaired. Examples of other aldehydes include paraformaldehyde, acetaldehyde, terephthalaldehyde, propionaldehyde, acrolein, benzaldehyde, trioxane, dicyclopentadiene, furfural and the like.

The mixing ratio of the melamine monomer and the aldehydes containing formaldehyde is preferably 1: 1 to 5 in terms of molar ratio, and particularly preferably 1: 2 to 4. By blending within this range, the molecular structure of the finally produced melamine resin becomes a three-dimensional network, so that mechanical properties such as flexibility and strength tend to be significantly improved.

Examples of the basic catalyst include metal hydroxides and ammonia. Before the reaction of the primary reaction, a basic catalyst is added to adjust the pH of the aqueous solution, and the pH at that time is preferably 8 or more and less than 11, and particularly preferably 8.5 or more and less than 10. .. Within this range, methylol melamine can be efficiently synthesized.

The reaction temperature of the primary reaction is preferably 80 ° C. or higher and lower than 110 ° C., and particularly preferably 85 ° C. or higher and lower than 105 ° C. Further, the reaction time is preferably 0.5 hours or more and less than 4 hours, and particularly preferably 1 hour or more and less than 3 hours. By synthesizing under these reaction conditions, storage stability tends to be improved.

Water is usually used as the reaction solvent, but other solvents may be used as long as the effects of the present invention are not impaired. However, if alcohol such as methanol or ethanol is used, it cannot be used because the flexibility and elasticity of the final foam tend to be inferior. However, if it is contained in a small amount as a stabilizer in general formalin, it does not have such an effect.

Next, as a secondary reaction, the methylol melamine synthesized by the primary reaction is further subjected to a methyleneation reaction to synthesize a methyleneated melamine-formaldehyde initial condensate. Specifically, after completion of the primary reaction, it can be obtained by adding an acidic catalyst to a basic aqueous solution containing methylol melamine and heating it.

Examples of the acidic catalyst include hydrochloric acid, sulfuric acid, nitric acid, formic acid, oxalic acid, p-toluenesulfonic acid amide and the like. Before the reaction of the secondary reaction, an acidic catalyst is added to adjust the pH of the aqueous solution, and the pH at that time is preferably 6 or more and less than 8, and preferably 6.5 or more and less than 7.5. Especially preferable. Within this range, the methyleneated melamine-formaldehyde initial condensate can be efficiently synthesized.

The reaction temperature of the secondary reaction is preferably 50 ° C. or higher and lower than 80 ° C., and particularly preferably 55 ° C. or higher and lower than 75 ° C. Further, the reaction time is preferably 0.3 hours or more and less than 3 hours, and particularly preferably 0.5 hours or more and less than 2 hours. By synthesizing under these reaction conditions, storage stability tends to be improved.

After completion of the secondary reaction, a basic catalyst can be added as needed. In that case, the pH is preferably 8 or more and less than 11. In the present invention, after synthesizing the component (A), various additives can be further added to produce a foam. Examples of the additive include a foaming agent (B), an emulsifier (C), and a curing agent (D).

<Effervescent agent>
In the present invention, hydrofluorocarbon (B) is used as a foaming agent. The foaming agent is a chemical substance that generates fine bubbles by heating, and a foam can be produced by dispersing it in the component (A).

The boiling point of the component (B) is preferably 50 to 150 ° C, more preferably 60 to 140 ° C, and particularly preferably 65 to 130 ° C. Within this range, there is a tendency that a porous and highly flexible foam can be efficiently produced.

Further, the surface tension of the component (B) at 25 ° C. is preferably 8 to 30 mN / m, more preferably 10 to 25 mN / m, and particularly preferably 12 to 20 mN / m. .. When the physical property value is within this range, the flexibility and elasticity of the foam tend to be further improved.

Specific examples of the component (B) include CF ₃ (CF ₂ ) ₅ H (boiling point 71 ° C., surface tension 13.4 mN / m), CF ₃ (CF ₂ ) ₅ CH ₂ CH ₃ (boiling point 114 ° C., surface). Tension 15.5 mN / m), CF ₃ (CHF) ₂ CF ₂ CF ₃ (boiling point 55 ° C, surface tension 14.1 mN / m), CH ₂ CHFCF ₂ CF ₂ CF ₂ (annular structure, boiling point 83 ° C, surface tension) 19.6 mN / m) and the like.

As for the blending ratio of the component (B), it is preferable to blend 1 to 100 parts by weight with respect to 100 parts by weight of the component (A), and it is particularly preferable to blend 5 to 50 parts by weight. .. By blending within this range, the weight of the foam can be reduced, and the cell shape of the foam tends to be uniform.

In addition, various organic foaming agents and inorganic foaming agents can be blended as the foaming agent. Examples of the organic foaming agent include amide compounds such as azodicarbonamide and hydrazodicarbonamide, and examples of the inorganic foaming agent include carbonate compounds such as sodium hydrogencarbonate and ammonium carbonate.

Further, in addition to the foaming agent, a hydrocarbon may be blended as a foaming aid. When a hydrocarbon is added, the flexibility and elasticity of the foam tend to be improved. The hydrocarbon may be linear, branched, or cyclic as long as it is a saturated hydrocarbon having 5 to 18 carbon atoms.

The hydrocarbon preferably has a boiling point of 0 to 100 ° C, and particularly preferably 10 to 90 ° C. Specific examples of the chemical substance include various isomers of pentane and various isomers of hexane.

When a hydrocarbon is used, the mixing ratio is preferably 0.1 to 100 parts by weight, and 0.5 to 50 parts by weight, based on 100 parts by weight of the component (A). It is particularly preferable to do so.

<Emulsifier>
In the present invention, the emulsifier (C) is used. Examples of the component (C) include those which are anionic, cationic or amphoteric, and those which are nonionic. Among these, it is preferable to use an anionic surfactant. Specific examples thereof include esterified alkyl sulfonic acid, alkyl benzene sulfonic acid, phenol sulfonic acid, sulfuric acid and the like.

As for the blending ratio of the component (C), it is preferable to blend 1 to 30 parts by weight with respect to 100 parts by weight of the component (A), and it is particularly preferable to blend 3 to 20 parts by weight. .. By blending within this range, the cell diameter of the foam can be kept within a certain range, so that it is possible to suppress the bias of the cavity and to impart flexibility.

<Curing agent>
In the present invention, the curing agent (D) is used. By blending the component (D), the curing reaction of the component (A) after synthesis can be promoted. As the component (D), it is preferable to use an acidic aqueous solution. Specific examples thereof include formic acid, sulfuric acid, phosphoric acid, oxalic acid, hydrochloric acid and acetic acid.

As for the blending ratio of the component (D), it is preferable to blend 0.1 to 20 parts by weight with respect to 100 parts by weight of the component (A) in terms of solid content, and 1 to 10 parts by weight is preferably blended. Especially preferable. By blending within this range, the component (A) can be efficiently cured.

As a method for producing a foam, a known method can be used. Examples thereof include a method in which the components (A) to (D) are stirred to obtain a mixed solution, then poured into an appropriate mold, heated, or irradiated with microwaves to cause foaming.

In addition, in the present invention, various additives such as antioxidants, preservatives, tackifiers, and plasticizers may be contained in the production of the melamine resin foam.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but only specific examples thereof are shown, and the present invention is not particularly limited thereto.

<Synthesis of melamine methyleneated-formaldehyde initial condensate>
120 parts by weight of melamine monomer and 210 parts by weight of 37% formalin were placed in a separable flask equipped with a stirrer, a reflux condenser and a thermometer, and a 48% sodium hydroxide aqueous solution having a pH of 9 was used as a basic catalyst. The mixture was added so as to be 0.0, and the reaction was carried out at 95 ° C. for 90 minutes. Then, paratoluenesulfonic acid amide was added so that the pH became 7.2, and the reaction was carried out at 70 ° C. for 45 minutes. After the reaction is completed, the mixture is naturally cooled, and when the temperature drops to 60 ° C., a 48% aqueous sodium hydroxide solution is added again so that the pH becomes 9.0, and excess water is added until the solid content becomes 75%. After removal and natural cooling again, the mixture was placed in a plastic bottle with a lid and stored at 30 ° C. for 1 hour to obtain a methyleneated melamine-formaldehyde initial condensate (hereinafter referred to as compound 1).

A melamine resin foam was produced using the compound 1 obtained above. Hereinafter, all the blending amounts are converted into solid content.

<Manufacturing of melamine resin foam>
(Example 1)
As the component (A), 75 parts by weight of the compound 1 was added.
As a component (B), CF ₃ (CF ₂ ) ₅ H (boiling point 71 ° C., surface tension 13.4 mN / m, hereinafter referred to as HFC 1) was added to 23 parts by weight.
As a component (C), 8 parts by weight of sodium dodecylbenzene sulfonate was added.
As a component (D), formic acid is added to 2 parts by weight.
As other components (foaming aid), 6 parts by weight of n-hexane was mixed, put into a disc turbine type mixer, and stirred at a rotation speed of 3000 rpm for 30 seconds to obtain a mixed solution. Then, 35 g of the mixed solution was poured into a 2 L polycup, heated at 160 ° C. for 10 minutes to foam, then demolded, and further heated at 200 ° C. for 30 minutes to completely cure the melamine resin of Example 1. A foam was obtained.

(Examples 2 to 4 and Comparative Example 1)
A melamine resin foam was obtained in the same manner as in Example 1 by the formulation shown in Table 1. In that case, as the component (B), CF ₃ (CF ₂ ) ₅ CH ₂ CH ₃ (boiling point 114 ° C., surface tension 15.5 mN / m, hereinafter referred to as HFC2) is used as another component (foaming aid). As n-pentane was used.

For the melamine resin foams obtained in Examples and Comparative Examples, test pieces were prepared and their physical properties were evaluated. The results are shown in Table 2.

<Preparation of test piece>
The inside of the foam was cut out so as not to include the surface of the obtained melamine resin foam, and the size was adjusted to 50 mm × 50 mm × 25 mmt to prepare a test piece.

<Density>
The weight of the test piece was measured and the density (g / cm ³ ) was calculated.

<Cell diameter>
Using a microscope (KEYENCE Co., Ltd.), each test piece was observed at 750 times, 5 cells were randomly selected for each field of view, and images of a total of 30 cells in a total of 6 fields were output. .. Then, the maximum value of the diameter in the cell of each sample was defined as the cell diameter of each sample, and the average value of the cell diameters of 30 samples was defined as the cell diameter (μm) of the test piece.

<Sound absorption rate>
The obtained test piece is further adjusted to a size of φ28.6 mm × 25 mmt, and the sound absorption coefficient at 315 to 5000 Hz by the transfer function method (JIS A1405) using WinZac MTX (Nitto Boseki Acoustic Engineering Co., Ltd.). Was measured. Of these, the sound absorption coefficient (%) at 500 Hz, 1000 Hz, 1250 Hz, 1600 Hz, 2500 Hz, and 5000 Hz was used as an index of sound absorption performance.

The results were obtained that the melamine resin foam produced in the examples was lightweight, had a porous internal shape, and had remarkably excellent sound absorption performance. On the other hand, it was obtained that the melamine resin foam produced in the comparative example was inferior in sound absorption performance.

Claims (3)

Melamine resin foaming characterized by foaming a mixed solution containing a methyleneated melamine-formaldehyde initial condensate (A), a hydrofluorocarbon (B), an emulsifier (C), and a curing agent (D). body. The melamine resin foam according to claim 1 , wherein the hydrofluorocarbon (B) has a surface tension of 8 to 30 mN / m at 25 ° C. A methyleneated melamine-formaldehyde initial condensate (A) obtained by blending a melamine monomer and formaldehyde, adding a basic catalyst and heating to cause a primary reaction, and then adding an acidic catalyst and heating to perform a secondary reaction. A method for producing a melamine resin foam, which comprises foaming a mixed solution containing hydrofluorocarbon (B), an emulsifier (C), and a curing agent (D).