JP2023102780A - Resin composition for foam sheet and foam sheet - Google Patents

Abstract

To provide a resin composition capable of obtaining a foam sheet that has excellent handleability and can be used adjacent to various materials such as metal.SOLUTION: A resin composition for a foam sheet is in a liquid form and contains a resol-type phenol resin and a thermally expandable microcapsule.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a foam sheet resin composition and a foam sheet.

Patent Document 1 (International Publication No. 2018/074316) describes a technique related to a resin composition that foams when heated. This document describes a curable resin composition containing a film-forming resin, an epoxy resin, a specific organic solvent, heat-expandable particles, and a curing agent component for the epoxy resin (claim 1), the film-forming resin containing a phenoxy resin (claim 4), the curing agent component for the epoxy resin containing one or more selected from imidazole derivatives and dicyandiamide (claim 5), and using a novolac resin such as phenol novolac or cresol novolac as the curing agent component for the epoxy resin. (Paragraph 0035).

WO2018/074316

However, when the present inventor examined the technique described in Patent Document 1 above, there was room for improvement in terms of whether the foam sheet can be used adjacent to various materials such as metals, and in terms of handleability of the resin composition.

INDUSTRIAL APPLICABILITY The present invention provides a resin composition that is excellent in handleability and provides a foamed sheet that can be used adjacent to various materials such as metals.

According to the present invention, the following foam sheet resin composition and foam sheet are provided.
[1] a resol-type phenolic resin;
a thermally expandable microcapsule;
A resin composition for a foamed sheet, which comprises and is in a liquid state.
[2] The resin composition for foam sheets according to [1], further comprising a solvent.
[3] The resin composition for a foamed sheet according to [1] or [2], wherein the resin composition has a viscosity of 0.1 Pa·s or more and 2000 Pa·s or less measured at 25°C using an E-type viscometer.
[4] The resin composition for foamed sheets according to any one of [1] to [3], which is used by coating on a substrate.
[5] The resin composition for foamed sheets according to any one of [1] to [3], which is used by impregnating a substrate.
[6] a resol-type phenolic resin;
a thermally expandable microcapsule;
A resin composition for a foamed sheet, comprising:
[7] The resin composition for foam sheets according to [6], which is laminated on a base material.
[8] The resin composition for foam sheets according to [7], which is a wound body.
[9] The resin composition for foam sheets according to any one of [1] to [8], further comprising an inorganic filler.
[10] The resin composition for foamed sheets according to [9], wherein the inorganic filler is barium sulfate.
[11] The resin composition for foam sheets according to any one of [1] to [10], further comprising polyvinyl acetal.
[12] The resin composition for a foamed sheet according to [11], wherein the polyvinyl acetal is polyvinyl butyral.
[13] A foamed sheet, which is a heat-cured product of the resin composition for foamed sheets according to any one of [1] to [12].

ADVANTAGE OF THE INVENTION According to this invention, it is excellent in handleability, and can provide the resin composition from which a foam sheet|seat which can be used adjacently to various materials, such as a metal, is obtained.

FIG. 2 is a diagram showing the relationship between the ratio of thermally expandable microcapsules to the total solid content and the expansion ratio in Examples. FIG. 2 is a cross-sectional view schematically showing the structure of a laminate of steel plates and foam sheets in Examples.

Embodiments of the present invention will be described below. In each embodiment, the composition can contain each component alone or in combination of two or more.
Further, in this specification, "-" indicating a numerical range represents above and below, and includes both numerical values at both ends.

(Resin composition for foam sheet)
(First embodiment)
In the present embodiment, the resin composition for foamed sheets (hereinafter also simply referred to as "resin composition") is a liquid composition containing a resol-type phenolic resin and thermally expandable microcapsules. Moreover, the resin composition may further contain a solvent.
Specifically, the resin composition in the present embodiment has a property of foaming by heat curing.

Since the resin composition in the present embodiment is liquid, it can be used by being applied onto a desired substrate, for example.
Specifically, the resin composition may be used by coating it on a substrate. The substrate can be, for example, sheet-like.
As the sheet-like substrate, for example, one that can withstand the heat drying conditions when the resin composition is heat-cured to obtain a foamed sheet can be used. Specific examples of sheet-like substrates include polyester films, polypropylene films, polyimide films, polyamide films, polysulfone films, and polyetherketone films.

Moreover, the resin composition may be used, for example, by impregnating a substrate. The substrate can be, for example, sheet-like.
The sheet-like substrate impregnated with the resin composition takes the form of, for example, woven fabric, non-woven fabric, or paper. Specific examples of raw materials for the sheet-like substrate include inorganic fibers such as glass fibers and carbon fibers; and organic fibers such as aramid fibers and cellulose.
Here, specifically, the sheet-like resin composition obtained by impregnating the sheet-like base material with the liquid resin composition is different from the expandable paper product.
Further, the sheet-shaped resin composition will be described later in the second embodiment.
Next, the constituent components of the resin composition will be described.

(Resol type phenolic resin)
A resol-type phenolic resin is a phenolic resin obtained by reacting a phenolic resin and an aldehyde in the presence of a basic catalyst.

Examples of phenols used for synthesizing resol-type phenolic resins include phenol; cresols such as o-cresol, m-cresol and p-cresol; ethylphenols such as o-ethylphenol, m-ethylphenol and p-ethylphenol; butylphenols such as isopropylphenol, butylphenol and p-tert-butylphenol; alkylphenols such as p-tert-amylphenol, p-octylphenol, p-nonylphenol and p-cumylphenol; monohydric phenols such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol, and trinitrophenol; monohydric phenols such as 1-naphthol and 2-naphthol; These can be used alone or in combination of two or more.

Aldehydes used for the synthesis of resol-type phenolic resins include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde, and the like. These may be used alone or in combination of two or more. Precursors of these aldehydes or solutions of these aldehydes can also be used. Among them, it is preferable to use an aqueous formaldehyde solution from the viewpoint of production cost.

Basic catalysts used for the synthesis of resol-type phenolic resins include, for example, hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide and calcium hydroxide; carbonates such as sodium carbonate and calcium carbonate; oxides such as lime; sulfites such as sodium sulfite; phosphates such as sodium phosphate;

Water is generally used as a reaction solvent for synthesizing the resol-type phenolic resin, but an organic solvent may also be used. Specific examples of such organic solvents include alcohols, ketones, aromatics and the like. Specific examples of alcohols include propyl alcohols such as methanol, ethanol and isopropanol (IPA), ethylene glycol, diethylene glycol, triethylene glycol, glycerin and the like. Specific examples of ketones include acetone and methyl ethyl ketone. Specific examples of aromatics include toluene and xylene.

In the resin composition, the resol-type phenolic resin may contain a polyacetal-modified phenolic resin, preferably a polyvinyl butyral-modified phenolic resin.

The content of the resol-type phenolic resin in the resin composition is preferably 50% by mass or more, more preferably 55% by mass or more, and still more preferably 60% by mass or more relative to the total solid content other than the thermally expandable microcapsules in the resin composition, from the viewpoint of suppressing excessive increase in viscosity when melted when the resin composition is formed into a sheet, and from the viewpoint of improving the heat resistance and mechanical strength of the foamed sheet.
In addition, from the viewpoint of making the foamability of the resin composition more preferable, the content of the resol-type phenolic resin in the resin composition is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less, relative to the total solid content other than the thermally expandable microcapsules in the resin composition.

(Thermal expandable microcapsules)
Thermally expandable microcapsules (hereinafter also simply referred to as “thermally expandable capsules”) are microcapsules that have the property of expanding and foaming when heated. Specifically, they are particles obtained by microencapsulating a volatile liquid foaming material with a thermoplastic shell polymer having gas barrier properties.
A thermally expandable microcapsule functions as a foaming material through the following mechanism. That is, the heating softens the outer shell of the capsule, while vaporizing the liquid foam contained in the capsule and increasing the pressure. As a result, the particles expand to form hollow spherical particles (expanded particles of thermally expandable microcapsules).

Examples of the liquid foaming material include low-boiling hydrocarbons such as normal pentane, isopentane, isobutane, and isopropane.
Examples of the thermoplastic shell polymer include one or more selected from the group consisting of polyacrylonitrile, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-methyl methacrylate copolymer, vinylidene chloride-ethyl methacrylate, acrylonitrile-methyl methacrylate copolymer and acrylonitrile-ethyl methacrylate.

Commercially available examples of thermally expandable microcapsules include Expancel series (manufactured by Nippon Philite Co., Ltd.); Microsphere F series such as Matsumoto Microsphere F-65D (dry type, average particle size 12 to 18 μm); Microsphere FN series such as Matsumoto Microsphere FN-100SSD (dry type, average particle size 6 to 11 μm); Advancel series (made by Sekisui Chemical Co., Ltd.); Kureha Microsphere series (made by Kureha Co., Ltd.).

The average particle size of the thermally expandable microcapsules is, for example, 3 μm or more, preferably 5 μm or more, and more preferably 10 μm or more, from the viewpoint of improving the expandability of the resin composition.
Moreover, from the viewpoint of improving the strength of the foamed sheet, the average particle size of the thermally expandable microcapsules is, for example, 30 μm or less, preferably 25 μm or less, and preferably 20 μm or less.

The content of the thermally expandable microcapsules in the resin composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and even more preferably 3% by mass or more, relative to the total solid content in the resin composition, from the viewpoint of lowering the density of the foamed sheet.
In addition, from the viewpoint of improving the strength of the foam sheet, the content of the thermally expandable microcapsules in the resin composition is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 35% by mass or less, relative to the total solid content in the resin composition.

(other ingredients)
In this embodiment, the resin composition may further contain components other than the resol-type phenolic resin and the thermally expandable microcapsules.
Moreover, the resin composition may further contain a resin other than the resol-type phenolic resin.
For example, the resin composition may further contain a thermosetting resin other than the resol-type phenolic resin.
The resin composition preferably does not contain an epoxy resin from the viewpoint of preventing the sheet obtained using the resin composition from being tacky and allowing the sheet to be inserted more smoothly into, for example, a hole.
In addition, the resin composition preferably does not contain a novolak-type phenolic resin, from the viewpoint of increasing the degree of freedom in selecting the material of the member adjacent to the foamed sheet obtained using the resin composition, and from the viewpoint that it can be used more stably adjacent to a metal material such as Cu.

Moreover, the resin composition may further contain a thermoplastic resin. From the viewpoint of obtaining a sheet-shaped resin composition more stably using the resin composition of the present embodiment, and from the viewpoint of improving the mechanical strength and flexibility of the resulting sheet-shaped resin composition, the resin composition preferably further contains polyvinyl acetal, more preferably polyvinyl butyral (PVB).

From the viewpoint of improving the mechanical strength and flexibility of the foamed sheet, the content of the thermoplastic resin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and even more preferably 20% by mass or more relative to the total solid content other than the thermally expandable microcapsules in the resin composition.
In addition, from the viewpoint of improving the heat resistance of the foam sheet, the content of the thermoplastic resin in the resin composition is preferably 40% by mass or less, more preferably 35% by mass or less, relative to the total solid content other than the thermally expandable microcapsules in the resin composition.

Moreover, the resin composition may further contain an inorganic filler.
Examples of inorganic fillers include one or more selected from the group consisting of barium sulfate, calcium carbonate, talc, silica and mica. From the viewpoint of improving the peelability of the foam sheet at high temperatures, the inorganic filler is preferably barium sulfate.

From the viewpoint of improving foamability of the resin composition, the specific gravity of the inorganic filler is preferably 3 or more and preferably 6 or less.

The average particle size of the inorganic filler is preferably 10 µm or less, more preferably 3 µm or less, still more preferably 2 µm or less, from the viewpoint of improving foamability of the resin composition, and may be, for example, 0.1 µm or more.

The content of the inorganic filler in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass or more, relative to the total solid content in the resin composition, from the viewpoint of improving the peelability of the foam sheet at high temperatures.
In addition, from the viewpoint of improving the foamability of the resin composition, the content of the inorganic filler in the resin composition is preferably 45% by mass or less, more preferably 40% by mass or less, and still more preferably 35% by mass or less, relative to the total solid content in the resin composition.

(solvent)
Moreover, the resin composition preferably further contains a solvent.
Specific examples of solvents include water, organic solvents, and mixed solvents of water and organic solvents. Examples of organic solvents include alcohols such as methanol, ethanol, isopropanol (IPA) and butanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, aromatic hydrocarbons such as toluene and ethylbenzene, and mixtures thereof. From the viewpoint of improving the solubility of polyvinyl acetal such as polyvinyl butyral in the resin composition, and from the viewpoint of improving the resistance of the microcapsules to solvents, the solvent preferably contains alcohols, more preferably isopropanol.

The content of the solvent in the resin composition is, for example, the balance after removing components other than the solvent in the resin composition.
In addition, the content of the solvent in the resin composition is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more with respect to the entire resin composition, from the viewpoint of obtaining an appropriate viscosity by film formation.
In addition, from the viewpoint of suppressing the occurrence of air bubbles on the surface and the failure to obtain a smooth surface due to excessive volatilization during coating, the content of the solvent in the resin composition is preferably 70% by mass or less, more preferably 60% by mass or less, and further preferably 50% by mass or less.

In addition, the viscosity of the resin composition at 25° C. is preferably 0.1 Pa s or more, more preferably 1 Pa s or more, and still more preferably 5 Pa s or more, from the viewpoint of improving production stability when obtaining a sheet-like resin composition.
In addition, from the viewpoint of enhancing the ease of handling of the resin composition, the viscosity of the resin composition at 25° C. is preferably 2000 Pa s or less, more preferably 1000 Pa s or less, still more preferably 500 Pa s or less, and even more preferably 100 Pa s or less.

Here, the viscosity of the resin composition is measured using an E-type viscometer (eg RE85U manufactured by Toki Sangyo Co., Ltd.) at 25° C., 50 or 20 rpm, cone plate type 3°×R12.

The resin composition in the present embodiment is obtained, for example, by stirring and mixing a resol-type phenolic resin, thermally expandable microcapsules and other ingredients in a stirring vessel.

Since the resin composition in the present embodiment contains a combination of a resol-type phenolic resin and a thermally expandable microcapsule, generation of amine gas or the like during foaming can be suppressed compared to a resin composition obtained by directly blending a chemical foaming agent such as N,N'-dinitrosopentamethylenetetramine. Therefore, the base material to which the resin composition is applied can be selected from various materials such as metals, and the degree of freedom in selecting the material of the adjacent member is excellent.
In addition, since the B-stage can be obtained when forming into a sheet, the handling is easy, and for example, it is possible to suppress the occurrence of tack on the surface.

(Second embodiment)
In the present embodiment, the resin composition for a foamed sheet is a sheet-like composition containing a resol-type phenolic resin and thermally expandable microcapsules. Moreover, the resin composition may be obtained by molding the liquid resin composition described above in the first embodiment into a sheet. The resin composition is preferably in a semi-cured (B stage) state.
Also in the present embodiment, the resin composition specifically has a property of foaming by heat curing.

The resin composition may be laminated on a substrate, for example. Moreover, the resin composition may be elongated or wound.
As the substrate, for example, those described in the first embodiment can be used.

Here, specifically, the resin composition in the present embodiment is different from the foamable paper product. At this time, the foamed paper product as a whole including the fibers is foamed, whereas the fiber layer in the sheet-like composition of the present embodiment does not swell and only the surface layer swells, which is preferable because the strength of the base material is maintained.
When the resin composition is impregnated into a base material, the content of fibers in the resin composition is preferably 80% by mass or less, more preferably 50% by mass or less, based on the entire resin composition, from the viewpoint of improving the flexibility of the resin composition, and from the viewpoint that the fiber layer in the sheet-like composition in the present embodiment does not swell and only the surface layer swells, so that the base strength is maintained, whereas the entire foamed paper product including the fibers is foamed.
Moreover, from the viewpoint of improving the strength of the resin composition, the content of fibers in the resin composition may be, for example, 3% by mass or more with respect to the entire resin composition.

Moreover, the resin composition may be arranged in a laminate having, for example, the following laminate structure. At this time, the resin composition may be, for example, an adhesive layer.
Laminate 1: Sheet substrate/resin composition Laminate 2: substrate/resin composition/release sheet In the laminate 2, the release sheet is preferably provided in contact with the surface of the resin composition opposite to the substrate. As the release sheet, for example, the same sheet-like substrate as described above in the first embodiment can be used.

Next, the constituent components of the resin composition will be described.
As the resol-type phenolic resin and the thermally expandable microcapsules, for example, those described above in the first embodiment can be used. In addition, the contents of these components with respect to the total solid content can also be the aspects described above in the first embodiment, for example.

Moreover, the resin composition may further contain components other than the resol-type phenolic resin and the thermally expandable microcapsules.
The resin composition may further contain a resin other than the resol-type phenolic resin, and the resin other than the resol-type phenolic resin and its content can be, for example, the above-described aspects in the first embodiment.
In addition, the resin composition may further contain an inorganic filler, for example, and the above-described aspect of the first embodiment can also be adopted for the inorganic filler.
Also, the resin composition is preferably solvent-free.

The resin composition in the present embodiment is obtained by applying a varnish-like resin composition containing, for example, a resol-type phenolic resin and thermally expandable microcapsules onto a substrate and molding it into a sheet.
More specifically, a varnish-like resin composition containing a resol-type phenolic resin, a thermally expandable microcapsule, and a solvent is applied to a sheet or the like, the solvent is removed by heat treatment, the sheet is formed, and then the B-stage state (semi-cured state) is produced by heat treatment.
As the solvent and the sheet-shaped substrate, for example, those described above in the first embodiment can be used.

The thickness of the resin composition is preferably 5 µm or more, more preferably 10 µm or more, still more preferably 20 µm or more, and even more preferably 30 µm or more, from the viewpoint of improving the strength of the foamed sheet.
In addition, from the viewpoint of improving the applicability of the resin composition in a state before foaming to a narrow space, the thickness of the resin composition is preferably 500 µm or less, more preferably 200 µm or less, and still more preferably 100 µm or less.
Moreover, when the resin composition is elongated, the width may be, for example, 10 mm or more and 2000 mm or less.

Also in this embodiment, the same effects as in the first embodiment can be obtained. Moreover, since the resin composition in this embodiment is in the form of a sheet, it can be cut into a desired shape before use, and a foamed sheet can be obtained more easily.

(foam sheet)
The foamed sheet is a heat-cured resin composition for foamed sheets, more specifically, a completely cured resin composition for foamed sheets (C-stage state). The foam sheet has a cell structure in which cells formed by foaming thermally expandable microcapsules are dispersed in the cured product.

The foamed sheet is obtained, for example, by heat-curing the resin composition for foamed sheet described above. Specifically, the heat curing can be performed under the condition that the resin composition is completely cured, and more specifically, it can be performed by heating at a temperature of about 100 to 200 ° C. for about 3 minutes to 3 hours.

The thickness of the foamed sheet is preferably 10 µm or more, more preferably 50 µm or more, still more preferably 100 µm or more, and even more preferably 200 µm or more, from the viewpoint of strength improvement.
Moreover, from the viewpoint of weight reduction of the foamed sheet, the thickness of the resin composition is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less.

In the present embodiment, the foam sheet is a heat-cured product of the first or second resin composition, so it is excellent in handling the resin composition, has a preferable foam structure, and can be used adjacent to various materials such as metal.
The foam sheet can be suitably used, for example, as a member for fixing members such as magnets and coils to predetermined positions such as corresponding holes in rotors and stators that constitute electric motors such as motors.

Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than those described above can also be adopted.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
In this embodiment, a liquid resin composition was prepared.
Phenol (P: 100 parts by mass), 37% formalin aqueous solution (F: 121 parts by mass) (F/P molar ratio = 1.4), 27% ammonia aqueous solution 3.3 parts by mass Triethylamine 3 parts by mass were added to a reaction apparatus equipped with a stirrer, a reflux condenser and a thermometer, and reacted for 40 minutes under reflux conditions. After that, isopropanol (42 parts by mass) was added when the temperature in the system reached 70°C while dehydration was performed under a reduced pressure condition of 91 kPa, and the mixture was reacted at 80°C for 2 hours to obtain a resol-type phenolic resin (in Table 1, "phenolic resin").
To this, isopropanol (120 parts by mass) and polyvinyl butyral resin (“PVB” in Table 1, calculated molecular weight 40,000, Sekisui Chemical Co., Ltd., S-LEC BM-1) (22 parts by mass) were added, dissolved and mixed to obtain a polyvinyl butyral-modified phenolic resin varnish. Thermally expandable microcapsules: ADVANCEL EML101 manufactured by SEKISUI CHEMICAL CO., LTD.
As described above, a liquid resin composition of this example was obtained. Table 1 shows the formulation and viscosity of the resin composition. In Table 1, "solid content RC in resin varnish" is the solid content in the resin varnish, that is, the total (parts by mass) of components other than the solvent in the resin varnish.

(Method for measuring viscosity)
The viscosity of the resin composition was measured using an E-type viscometer (RE85U manufactured by Toki Sangyo Co., Ltd.) at 25° C., 50 rpm, cone plate type 3°×R12.

(Example 2)
In this example, the liquid resin composition obtained in Example 1 was used to produce a sheet-like resin composition.
A release film (product name: Sepanium 20M2S-S, manufactured by Toyo Aluminum Co., Ltd.) was coated with the resin varnish obtained in Example 1 with a thickness of 1 mil (25.4 μm) using a squeegee and dried at 80° C. in a dryer for 10 minutes to obtain a sheet-shaped resin composition having a thickness of 53 μm after drying.
Further, when an iron plate heated to 90° C. was pressed against the obtained resin composition and cooled, the resin composition could be transferred to the iron plate and the release film could be peeled off.

(Example 3)
In this example, the sheet-shaped resin composition obtained in Example 2 was cured by heating to obtain a foamed sheet.
That is, the iron plate to which the resin composition was transferred was preheated at 80 ° C. for 10 minutes in a dryer, then heated to 130 ° C. at a temperature increase rate of 5 ° C./min, and held at 130 ° C. for 30 minutes to obtain a foamed sheet. The resulting foamed sheet had a thickness of 209 µm.

(Example 4)
In this example, various thermally expandable microcapsules were used to prepare liquid resin compositions, and the foaming ratios of foamed sheets were measured.
A polyvinyl butyral-modified phenolic resin varnish was obtained by the method described above in Example 1. To this, one of the following thermally expandable microcapsules A to C was added and stirred to obtain a resin composition. The amount of thermally expandable microcapsules added was 3, 5, 10, 20 or 30% by mass based on the solid content of the resol-type phenolic resin.
Thermally expandable microcapsules A (“EML-101” in FIG. 1): ADVANCEL EML-101 (manufactured by Sekisui Chemical Co., Ltd., average particle size 12 to 18 μm)
Thermally expandable microcapsules B (“F-65D” in FIG. 1): Matsumoto Microsphere F-65D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., dry type, average particle size 12 to 18 μm)
Thermally expandable microcapsules C (“FN-100SSD” in FIG. 1): Matsumoto Microsphere FN-100SSD (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., dry type, average particle size 6 to 11 μm)

The obtained resin composition was coated in a sheet having a thickness of 35 μm to 45 μm. Then, it was heated under the following conditions to obtain a foamed sheet.
Preheating conditions: 80°C, 10 minutes Temperature rise: 5°C/min (at 140°C and 150°C), 7.5°C/min (at 170°C)
Holding temperature: 140°C, 150°C or 170°C
Holding time: 30 minutes The thickness of the resulting foamed sheet was measured to calculate the expansion ratio. FIG. 1 shows the relationship between the blending ratio of the thermally expandable microcapsules to the total solid content and the expansion ratio.

From FIG. 1, all the resin compositions containing thermally expandable microcapsules A to C exhibited sufficient expansion ratios.

Moreover, the breaking strength of the foam sheet was measured for some of the resin compositions shown in FIG.
First, a release film (product name: TV212, manufactured by Toyobo Co., Ltd.) was coated with a resin composition with a thickness of 80 μm to 150 μm using a squeegee, dried in a dryer at 70° C. for 10 minutes, and after drying, a sheet-like resin composition having a thickness of 40 μm was obtained.
A 2.5 cm wide, 10 cm long steel plate (steel plate 101 in FIG. 2, which will be described later) is spaced 10.0 mm in the length direction from one end, and the obtained sheet-like resin composition (2.5 cm wide, 10.0 mm long) was placed three times. Adjacent to the sheet-like resin composition, a SUS spacer having a length of 1 cm and a thickness of 200 μm was arranged on the other end side. Another steel plate (steel plate 103 in FIG. 2, which will be described later) was placed on the spacer, shifted in the longitudinal direction from the end of the spacer so as to cover the entire spacer and resin composition, and was fixed.
The obtained laminate was preheated at 80° C. for 10 minutes in a dryer, then heated to 150° C. at a heating rate of 5° C./min and held at 150° C. for 30 minutes to obtain a foamed sheet (foamed sheet 105 in FIG. 2 described later). It was confirmed that the space between the two steel plates was filled with the foam sheet.
FIG. 2 is a cross-sectional view schematically showing the configuration of a laminate of steel plates and foam sheets after the spacers have been pulled out.

The spacers were pulled out and both ends of the thick steel plate were held, and a tensile test was performed to measure the strength at break (MPa) (room temperature 25° C., test speed: 0.5 mm/min).

From Table 2, all of the obtained foamed sheets had sufficient tensile strength.

(Example 5)
In this example, resin compositions containing an inorganic filler (Examples 5-1 to 5-7) were prepared and coated in a sheet to obtain a foamed sheet. Formulations and evaluation results are shown in Tables 3 and 4.
The following components were used in the resin compositions shown in Tables 3 and 4. Resin 1 and Resin 2 below are obtained by adjusting the polyvinyl butyral-modified phenol resin varnish produced by the method described above in Example 1 to each of the following RCs using a solvent (IPA).
Resin 1: Solid content in resin varnish RC = 50%
Resin 2: Solid content in resin varnish RC = 45%
Barium sulfate: The following was used.
・ B-30: manufactured by Sakai Chemical Industry Co., Ltd., surface treatment grade, average particle size 0.3 μm
・ B-34: manufactured by Sakai Chemical Industry Co., Ltd., surface treatment grade, average particle size 0.3 μm
・ B-55: manufactured by Sakai Chemical Industry Co., Ltd., high whiteness grade, average particle size 0.6 μm
・Sedimentation 100: Standard product manufactured by Sakai Chemical Industry Co., Ltd., average particle size 0.6 μm
Thermally expandable microcapsules C: Matsumoto Microsphere FN-100SSD (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., dry type, average particle size 6 to 11 μm)

(coating)
First, a release film (product name: TV212, manufactured by Toyobo Co., Ltd.), which is a substrate, was coated with a resin composition in a thickness of 80 μm to 150 μm using a squeegee, dried in a dryer at 70° C. for 10 minutes, and after drying, a sheet-like resin composition having a thickness of 40 μm was obtained. A release film (product name: TV212, manufactured by Toyobo Co., Ltd.) was laminated as a release sheet to obtain a laminate.
At this time, if the release film (product name: TV212, manufactured by Toyobo Co., Ltd.), which is the base material, can be coated without repelling, it is evaluated as "good" (good).

(tackiness)
When touched with a hand after coating, the resin was not adhered, but had stickiness (tackiness), and the case where the release sheet could be overlaid was rated as "low".

(Peelability of release film as substrate)
An iron plate heated to 80° C. was pressed against the resin composition side of the laminate described above in the “Coating” section, and the resin composition was transferred to the iron plate. After that, the releasability of the release film as the substrate was evaluated. Evaluation criteria are shown below.
○: The release film can be peeled off without removing the resin composition from the iron plate △: The resin composition is peeled off from the iron plate and adheres to the release film side

(viscosity)
It was measured according to Example 1 at the number of revolutions shown in Table 4.

From Tables 3 and 4, the resin compositions and sheets of Examples 5-1 to 5-7 all had favorable coatability and tackiness, and exhibited sufficient expansion ratios.
In addition, the sheet-like resin compositions obtained in Examples 5-1 to 5-7 all had excellent peelability of the release film, which is the base material, at 25°C, and had sufficient practicality. Further, in Examples 5-2 to 5-7, even at a high temperature (40° C.), the peelability of the release film as the substrate was excellent.

100 Laminate 101 Steel plate 103 Steel plate 105 Foam sheet

Claims (13)

a resol-type phenolic resin;
a thermally expandable microcapsule;
A resin composition for a foamed sheet, which comprises and is in a liquid state. The foam sheet resin composition according to claim 1, further comprising a solvent. The resin composition for a foamed sheet according to claim 1, wherein the viscosity of the resin composition measured at 25°C using an E-type viscometer is 0.1 Pa·s or more and 2000 Pa·s or less. The resin composition for a foamed sheet according to claim 1, which is used by coating it on a substrate. The resin composition for a foam sheet according to claim 1, which is used by impregnating a base material. a resol-type phenolic resin;
a thermally expandable microcapsule;
A resin composition for a foamed sheet, comprising: The foam sheet resin composition according to claim 6, which is laminated on a substrate. The resin composition for foam sheets according to claim 7, which is a wound body. The resin composition for foam sheets according to any one of claims 1 to 8, further comprising an inorganic filler. The resin composition for a foamed sheet according to claim 9, wherein the inorganic filler is barium sulfate. The resin composition for a foamed sheet according to any one of claims 1 to 8, further comprising polyvinyl acetal. The resin composition for a foamed sheet according to claim 11, wherein said polyvinyl acetal is polyvinyl butyral. A foamed sheet, which is a heat-cured product of the resin composition for a foamed sheet according to any one of claims 1 to 8.

Images