JPH02173131A - Production of formed phenolic resin - Google Patents

Abstract

PURPOSE:To produce a foamed phenolic resin containing uniformly dispersed fibers and having high strength by dissolving a novolak phenolic resin in a solvent, impregnating the solution in a nonwoven fiber sheet and foaming the product after drying. CONSTITUTION:The objective foamed phenolic resin is produced by dissolving (A) a novolak phenolic resin produced by reacting phenols with formaldehyde in the presence of an acid catalyst in (B) a volatile polar organic solvent having a boiling point of <=120 deg.C and capable of dissolving the component A (e.g. methanol, acetone or acetonitrile), adding (C) a curing agent (e.g. hexamethylenetetramine) to the solution, adding and uniformly mixing (B) a foaming agent (preferably a decomposition-type organic foaming agent) and (E) a foam stabilizer (preferably a silicone compound), impregnating the obtained solution in a nonwoven fiber sheet (e.g. glass mat), drying at normal temperature in air for about 48hr and foaming the product.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing phenolic resin foams useful for applications such as heat insulating materials, cushioning materials, panels, boards, and the like.

More specifically, in the present invention, a novolac type phenolic resin is dissolved in a solvent or mixed uniformly, and the solution is impregnated into a sheet-like nonwoven fiber base material and foamed. The present invention relates to a method for producing a high-strength phenolic resin foam, which is characterized in that phenolic resin is uniformly dispersed within the foam.

(Prior Art) Conventionally, in order to improve the mechanical strength of phenolic resin foam, it has been considered to mix various reinforcing fiber materials into the foam, and the first one is shredded glass fiber. and a foamable resin composition powder (raw material for phenolic resin foam) containing an initial charge of phenolic resin, which is then foamed and cured in a mold. After scattering between a large number of laminated cotton-like sheet materials, these are preformed using hot rolls, hot presses, etc. at a temperature that allows the initial charge of phenolic resin to melt for each corresponding resin composition, and the inside of each cotton-like sheet is preformed. A method of impregnating and retaining a resin composition and heating and foaming the multilayer body to harden it (Special Publications Publication No. 4
No. 7-8945), No. 3, No. 1 is a cotton-like sheet impregnated with a powdered foamable resin composition solution, which is made of two sheets or laminated in large numbers. A method of impregnating and retaining a resin composition inside each cotton-like sheet and heating and foaming and curing this multilayer body (Japanese Patent Laid-Open No. 61-23
3526) is known.

(Problems to be Solved by the Invention) However, in the first method, it is difficult to mix the fibers and the resin composition uniformly, and it is difficult to obtain a foam molded product in which the phenol resin foam layer and the fibers are uniformly mixed. It was difficult. In the second method, the sheet is impregnated at the lowest possible temperature at which the resin melts without causing foaming hardening, but because this temperature range is narrow, foaming hardening tends to occur locally, and the adhesion between the sheet and the resin is poor. The third method also improves the above points, but since it uses a powdered resin composition, it is difficult to mix the foam stabilizer, resulting in poor foaming state and poor plasticity. There were problems such as difficulty in adding additives such as agents.

This invention was made in view of the above problems, and provides a method for easily producing a composite molded article in which fibers and a phenolic resin foam layer are evenly mixed, and for easily modifying it with additives, etc. It is.

(Means for Solving the Problems) The present inventor has developed a sheet-like non*i#! The fiber base material is impregnated with a resin dissolved in a solvent, and the solvent is almost completely removed by drying at low temperatures for a long time.

We found a scale that minimizes the effect of solvent on foam,
Furthermore, it was discovered that the fibers of the base material are dispersed during foaming and are uniformly mixed within the foam, and this invention has been achieved.

That is, the present invention is characterized in that a sheet-like nonwoven fiber base material is impregnated with a liquid mixture containing a solvent in which novolak and novolak are soluble, a foaming agent, a hardening agent, and a foam stabilizer, and then foamed. This is a method for producing a phenolic resin foam, and a volatile polar organic solvent with a boiling point of 120° C. or less is used as a solvent in which novolak is soluble.

(Function) The phenol resin used in the present invention is a novolac type phenol resin, which is produced by reacting phenols and formaldehyde using an acid catalyst using a conventional method, and is soluble or emulsifiable in the solvents described below. Almost all novolac resins can be used as long as they can be mixed uniformly.

Therefore, in addition to phenol, phenols include alkylphenols such as cresols, xylenols, and octylphenols, phenols with a structure similar to alkylphenols such as bisphenol A, phenylphenol, and styrenated phenol, P-vinylphenol, isopropylphenol, etc. Alkenylphenols and the like may be used alone or in combination of two or more, and as the aldehyde, formaldehyde, paraformaldehyde, acel-aldehyde, furfural, etc. can be used. A novolac type phenol resin is produced by carrying out a normal reaction using an acidic catalyst as a catalyst.

The solvent is one that dissolves the above-mentioned phenolic resin and is inert, and furthermore, it has a boiling point of 120°C, which easily vaporizes at room temperature.
Below, a polar organic solvent is used. As such solvents, lower alcohols such as methanol and ethanol, ketones such as acetone, nitriles such as acetonitrile, ethers, esters, amines, and aromatic compounds having polar groups can be used. be. Negligible hydrocarbons and many aromatic compounds do not dissolve phenolic resins, and carboxylic acids cannot be used because blowing agents tend to decompose.

As blowing agents, N,N'-dinitrosopentamethylenetetramine, benzenesulfonyl hydrazide,
Organic decomposition type blowing agents such as azobisisobutyronitrile,
Inorganic decomposition type blowing agents such as sodium bicarbonate and ammonium nitrite are used, but organic decomposition type blowing agents are preferred from the viewpoint of miscibility with solvents.

As a curing agent, common hexamethylenetetramine is used. As the foam stabilizer, common silicone-based, metal soap-based, and polymer-based foam stabilizers are used, but silicone-based foam stabilizers that are resistant to high temperatures are preferred. Other modifiers include rubbers,
It is possible to add polyvinyl alcohols, polyamides, etc.

As a method for producing a foam, first, novolak is dissolved in a solvent, and a curing agent, a foaming agent, a foam stabilizer, and other additives are added and mixed uniformly. At this time, it is easier to mix the foaming agent and foam stabilizer if they are added last.

The concentration of the novolak resin may be arbitrary, but from the viewpoint of workability, it is desirable that the viscosity of the novolac solution be 100 to 10 QQOcps. At this viscosity, even substances that are poorly soluble in the solvent can be mixed uniformly, and it is also easy to impregnate the base material.

The appropriate amount of blowing agent is added depending on the expansion ratio and the adhesion density of the blowing agent to the base material. If the amount of foaming agent is small, sufficient foaming will not occur and the shape and physical properties of the foam will be adversely affected.
On the other hand, if the amount of foaming agent is too large, the pressure inside the mold becomes too high during foaming, which may cause blowing out of the mold, which is dangerous. Usually, when the foaming ratio is 2 to 10 times, the amount of blowing agent is 5 to 50 g.
/ m. A curing agent and a foam stabilizer are also added as appropriate, and the amounts thereof are preferably 3 to 20 parts for the curing agent and 1 to 10 parts for the foam stabilizer per 100 parts of the novolak.

This mixed solution is impregnated into a sheet-like nonwoven fiber base material, and conventional methods such as impregnation and coating may be used, but it is necessary to impregnate the resin into the base material. At this time, the ratio of the mixed liquid and the base material is desirably such that the novolak resin:base material=2:8 to 9:1.

For drying, it is best to air dry at room temperature for about 48 hours; drying by applying heat is also possible, but applying heat causes decomposition of the foaming agent, which is not preferable. For air drying, hang the impregnator Wt fiber base material in a shaded and well-ventilated place or dry it on release paper to form a clean sheet. When applying heat, heat at 40-70℃.
Let dry for 2 hours.

The nonwoven fiber base material used in the present invention is a nonwoven fabric formed into a sheet of inorganic nonwoven fibers such as glass fiber, metal fiber, and carbon fiber, and organic nonwoven fibers such as cotton, recycled fiber, and synthetic fiber. A typical example is glass mat. The thickness and weight can be set arbitrarily.

Foaming of this sheet-like base material is carried out by loading the base material cut into an appropriate size into a mold and heating it. Although it is possible to use one or more base materials, the thickness of the base material may be limited by the heating device when the base material is made into multiple layers. The heating method may be a generally known method such as a heating press,
Anything can be used, such as infrared rays and a dryer. However, it is difficult to make molded products with a thickness of 30 mm or more using a press that heats the surface of the mold. The optimal heating temperature is 120-180°C, and foaming and curing is performed in several minutes to several tens of minutes.

In the method of the present invention, since the resin is dissolved in the liquid substance, additives can be easily mixed, and foam stabilizers and plasticizers can be easily added, making it possible to obtain more useful foams. In addition, since the non-woven fiber base material is impregnated with resin, the binder of the non-woven fiber base material is peeled off due to the foaming pressure during foaming, and the fibers are uniformly dispersed within the foam. This results in high strength.

(Example) Example 1 5 parts by weight of hexamethylenetetramine as a curing agent and 5 parts by weight of hexamethylenetetramine as a blowing agent were added to 100 parts by weight of a 50% by weight methanol solution of novolac resin prepared in a conventional manner using phenol and formaldehyde as an acid catalyst. , 5 parts by weight of N'-dinitrosopentamethylene diamine (Celmic A, manufactured by Sankyo Kasei Co., Ltd.), and 2 parts by weight of silicone oil (L-7002 manufactured by Nippon Unica Co., Ltd.) as a foam stabilizer were stirred with a mixer. 25CIIIX25dll of Shiko mixed liquid
Glass mat (MC450A: Nittobo Co., Ltd. 1!II
) Nitobuzuke was impregnated, lightly squeezed and air-dried in the shade. The amount of impregnation after drying is Novolac resin: Matte = 1
=1, and the thickness was 1.511n. One to three of these sheets were placed in a mold of 25 mm x 25 mm x 0.6-2 G and heated at 150° C. for 10 minutes to foam, thereby obtaining a glass fiber-containing foam having the same shape as the mold. The glass fibers in this foam were almost uniformly dispersed. Strength etc. are as described in Table 1.

Example 2 A mixed solution prepared in the same manner as in Example 1 was mixed with 25anX25
A nylon nonwoven fabric of AN was impregnated with a roller and air-dried in the shade. The amount of resin after drying is: Novolac resin: Nonwoven fabric = 6
: 4, and the thickness was 1 pus. Put 3 of these sheets into a mold of 25 an x 25 x 2 x 1
When heated and foamed at 50° C. for 10 minutes, a foam having the same shape as the mold was formed.

Example 3 70Lllt% methanol solution of novolak resin 100
The weight parts include 8 parts by weight of the curing agent used in Example 1, 6 parts by weight of the foaming agent, 3 parts by weight of the foam stabilizer, and polyvinyl alcohol (
5 parts by weight of PVA 202 (manufactured by Kuraray ■) were mixed and impregnated into an aluminum fiber nonwoven fabric (25anX25(2)) by a hand lay-up method. The amount of resin after air drying was novolac resin:nonwoven fabric=2:1.

This was placed in a mold of 25 aIIX 25 an

Comparative Example 1 For 100 parts by weight of the novolak resin used in Example 1,
Similarly, the foaming agent used in Example 1 was 10% heavy base, and the hardening agent 10%
Parts by weight were added, kneaded using heated rolls, and then pulverized to obtain a powdered resin composition. 30g of this powder was sprinkled on the mat used in Example 1, and then another layer of mat was placed on top of the mat, and the two layers were put into a 25cm x 250Xlan mold with a size of 150'.
A foam was obtained by foaming and curing for CIO. However, this foam is difficult to handle because the powder moves when the resin composition is loaded.
Furthermore, the foam itself was non-uniform as it had cavities that were not filled with the phenol foam layer.

Comparative Example 2 To 100 parts by weight of the same novolac resin as in Comparative Example 1, 10 parts by weight of a foaming agent and 10 parts by weight of a curing agent were added, and the mixture was kneaded with a heated roll. Thereafter, it was pulverized to obtain a powdered resin composition.

Next, as a binder, a mixture of methyl alcohol (special grade reagent) and trichlorotrifluoroethane in a volume ratio of 1:5 was used, and 5 g of the mixture was sprayed onto the cloak used in Example 1 in the form of a mist using a nozzle.

The foamable resin composition 3 is placed on the mat that has absorbed this binder.
0g was sprinkled on top of the mat, which had been similarly absorbed with the binder, and preformed under a pressure of about 1kg, and then heated at 60°C.
It was dried for 100 minutes in a hot air circulating high temperature bath. Next, put this sheet into a 25cm x 25cm x 1cm mold15
A foam was formed by heating and foaming at 0°C for 10 minutes. This foam had a poor foaming condition, no resin was attached to the glass layer on the surface, and the surface was uneven.

Table 1 shows the physical properties of the foams produced in Examples 1 to 3.

(Effects of the Invention) According to the present invention, a composite in which fibers and phenol resin are uniformly mixed can be efficiently and stably obtained. Since this sheet-like foamable composite does not use heat during production, it is easily manufactured, and various additives can be mixed in, allowing various combinations to be used depending on the use of the composite.

Claims (2)

[Claims] (1) A phenolic resin characterized by impregnating a sheet-shaped nonwoven fiber base material with a liquid mixture containing novolak and a novolac-soluble solvent, a foaming agent, a hardening agent, and a foam stabilizer, drying it, and then foaming it. Method of manufacturing foam. (2) The method for producing a phenolic resin foam according to claim 1, characterized in that a volatile polar organic solvent with a boiling point of 120° C. or less is used as the novolac-soluble solvent.