JP3308584B2 - Method for producing highly filled inorganic resin foam and foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin foam highly filled with an inorganic substance.

[0002]

2. Description of the Related Art Conventionally, there has been widely known a method in which a polyolefin resin foam is highly filled with an inorganic substance to achieve flame retardancy.

In general, when the inorganic material is highly filled, the cell membrane of air bubbles does not elongate and the air bubbles are easily broken. Therefore, as a polyolefin resin, ethylene-vinyl acetate (EVA) copolymer having a high vinyl acetate content (50% by weight or more) is used. Methods using the coalescence are disclosed, for example, in JP-B-62-16216 and JP-B-62-16217.

However, the vinyl acetate content is high (40
When the EVA copolymer is used, there is a problem that mechanical strength is low and heat resistance is reduced. Therefore,
Using an EVA copolymer having a low vinyl acetate content (less than 40% by weight), using an organic peroxide as a cross-linking agent to crosslink after heating and foaming, in order to obtain an EVA copolymer in which cell membranes of cells are hardly broken. The method of improving the elongation of the cell membrane by making
It is disclosed in Japanese Patent Publication No. Sho 60-26500.

However, in the method using an organic peroxide as the crosslinking agent, the organic peroxide contained in the surface portion of the foamable resin sheet reacts with oxygen in the air, so that the crosslinking of the resin sheet surface is insufficient. It becomes something. When such a resin sheet is foamed by heating, air bubbles are generated, but the generated air bubbles are easily broken, and the obtained foam has many pores on the surface due to the broken air bubbles.

In particular, when the inorganic material is highly filled, a large number of holes are easily formed on the surface. Therefore, when another material is adhered to the foam surface in such a state, there is a problem that the adhesiveness is impaired or a large amount of adhesive is required.

[0007] In order to solve the above problem, it is conceivable to perform cross-linking by an electron beam before the foaming step. However, if cross-linking is performed before the foaming step, the foaming property may be reduced, or the difference in electron beam permeability may cause a problem. There are problems such as uneven crosslinking.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide an electronic resin sheet comprising a composition of an EVA copolymer highly filled with an inorganic substance, on both surfaces of which an electronic material is provided. By irradiating a line and cross-linking uniformly, by heating and foaming, it has excellent mechanical properties,
An object of the present invention is to provide a method for producing a highly-filled inorganic foam having a smooth surface without pores.

[0009]

The present invention comprises the following two aspects. The process according to claim 1 inorganic high filling resin foam according an ethylene vinyl acetate content is less than 40 wt% - vinyl acetate copolymer 1 00 parts by weight, inorganic powders 50-3
After irradiating the foamable resin sheet of the composition containing 00 parts by weight with an electron beam, in the method for producing an inorganic high-filled resin foam to be heated and foamed, irradiating both sides of the foamable resin sheet with an electron beam, The inorganic high-filled resin foam is formed so that the gel fraction in the thickness direction is 15 to 50%, and the difference between the maximum value and the minimum value of the gel fraction in the thickness direction is 20% or less. I do.

[0010] A foam according to a second aspect is produced by the method for producing a highly-filled inorganic resin foam according to the first aspect. As described above, the above object is achieved.

Hereinafter, the present invention will be described in detail. As a resin component used in the composition of the present invention, ethylene-vinyl acetate having an ethylene content of 40% by weight or less (EV
A) is a copolymer, other thermoplastic resins, for example, low density polyethylene, high density polyethylene, linear low density polyethylene, even polypropylene, etc. have been mixed
No.

When the vinyl acetate content of the EVA copolymer increases, the foaming property deteriorates and the heat resistance of the obtained foam decreases, so that the vinyl acetate content is reduced to 40% by weight or less, preferably It is 10 to 30% by weight.

The inorganic powder used in the above composition includes, for example, aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, calcium hydroxide and the like. One or a mixture of two or more of these may be used. Is done.

Further, the above-mentioned inorganic powder may be, if necessary,
It may be treated with a silane-based or titanate-based coupling agent. The average particle size of the inorganic powder is 0.01 to
A range of 50 μm is preferred.

If the amount of the inorganic powder is too small, the flame retardant effect is not exerted on the foam, and if the amount is too large, the foam is not formed. Therefore, 50 to 300 parts by weight with respect to 100 parts by weight of the resin component. Is limited to the range.

In order to impart foamability and flame retardancy to the above composition, a flame retardant, a flame retardant auxiliary, a pyrolytic foaming agent, and other additives, if necessary, are further compounded. Examples of the flame retardant include decabromodiphenyl ether, bis (bromoethyl ether) tetrabromobisphenol A,
Organic halogen compounds such as hexabromocyclododecane are preferred, and triphenyl phosphate, tricresyl phosphate, tris (2,3-dibromopropyl) phosphate and the like are also included.

Examples of the thermal decomposition type blowing agent include one or more of azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, and 4,4'-oxybis (benzenesulfonyl hydrazide). Is a mixture of

The amounts of these substances are as follows.
10 to 30 parts by weight of an organic halogen-based flame retardant, 3 to 10 parts by weight of a flame retardant auxiliary, 5 to 25 parts by weight of a thermal decomposition type foaming agent with respect to parts by weight.
Parts by weight are preferred.

The above components are kneaded using a kneading device such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer, or a roll at a temperature lower than the decomposition temperature of the thermal decomposition type foaming agent to form a sheet. To obtain a foamable resin sheet.

Next, the foamable resin sheet is irradiated with an electron beam to be crosslinked, and then heated and foamed at a temperature higher than the decomposition temperature of the foaming agent in a foaming step to obtain a highly-filled inorganic foam. In the electron beam irradiating step, in order to obtain a uniform thing without unevenness of the crosslink density in the thickness direction and the width direction of the foamable resin sheet, both sides of the resin sheet are irradiated with the same output electron beam from the irradiation device. .

Further, in order to reduce variations in the crosslink density in the thickness direction and the width direction, it is preferable to perform irradiation while scanning the irradiation source in the width direction. Also,
Since the transmission power of the electron beam in the thickness direction of the foamable resin sheet varies depending on the thickness, specific gravity, etc. of the resin sheet, the acceleration voltage and irradiation amount of the electron beam are appropriately adjusted according to the thickness, specific gravity, etc. of the resin sheet. Is preferred.

In the present invention, even if the electron beam irradiation is uniform in the thickness direction and the width direction of the foamable resin sheet, if the irradiation dose is insufficient, no bubbles are generated, and if the irradiation dose is excessive, the cell film of the bubbles is generated. Since the elongation of the foam is insufficient and a foam having a high expansion ratio cannot be obtained, the gel fraction (index of the crosslink density) of the foam in the thickness direction of the foam is 15 to
It is applied to be in the range of 50%.

Further, if the electron beam irradiation on the foamable resin sheet causes excess or deficiency in the width direction or the thickness direction, the foamability is adversely affected, and the smoothness of the foam surface is lost, and the foam has a hole. Therefore, the electron beam irradiation is performed so that the difference between the maximum value and the minimum value of the gel fraction in the thickness direction of the foam is 20% or less.

When the foamable resin sheet contains a large amount of a filler, the resin sheet has a large specific gravity and is brittle, and when the resin sheet is heated and foamed in a vertically suspended state, Since the sheet may be stretched and broken by its own weight, a method in which the resin sheet is floated by, for example, hot air and foamed while being kept horizontal is preferable.

[0025]

According to the present invention, by irradiating both surfaces of a foamable resin sheet highly filled with an inorganic substance with an electron beam, it is possible to form a resin foam highly filled with an inorganic substance having a uniform crosslinking density.

Further, the gel fraction in the thickness direction of the resin foam highly filled with an inorganic substance is 15 to 50%, and the difference between the maximum value and the minimum value of the gel fraction in the thickness direction is 20% or less. Irradiation with an electron beam provides a highly-inorganic resin-filled foam having excellent mechanical strength, no pores on the surface due to breakage of bubble cells, and a smooth surface.

[0027]

Embodiments of the present invention will be described below. (Example 1) 1) Production of highly-filled inorganic foam EVA copolymer ("Evaflex 360" manufactured by Du Pont-Mitsui Polychemicals, vinyl acetate content 25% by weight) 1
With respect to 00 parts by weight, 200 parts by weight of magnesium hydroxide ("Kisuma 5B" manufactured by Kyowa Chemical Industry Co., Ltd.) as inorganic powder, 20 parts by weight of decabromodiphenyl ether as a flame retardant, 30 parts by weight of azodicarbonamide as a foaming agent, and as a lubricant A composition comprising 0.5 part by weight of a fatty acid amide was added to 1
After sufficiently kneading with two rolls heated to 20 ° C, 1
It was formed into a sheet by hot pressing at 20 ° C. to produce a foamable resin sheet having a thickness of 2.0 mm.

An accelerating voltage of 700 is applied to the foamable resin sheet.
After adjusting the irradiation dose with KV to be 3.0 Mrad and irradiating both sides of the foamable resin sheet with an electron beam, the resin sheet was heated in a 220 ° C. gear oven for 5 minutes to foam the resin sheet. A highly filled foam (9 mm thick) was produced. 2) Evaluation of appearance of highly-filled inorganic foam The appearance of the highly-filled inorganic foam produced in 1) was visually observed, and the appearance was evaluated according to the following criteria. The results are shown in Table 1.

(A) Good appearance: ○ (b) An unfoamed layer is present at the center of the surface: Δ (Electron beam does not penetrate sufficiently to the center and no bubbles are formed because no air bubbles are generated. (C) There is an abnormal foam layer on the surface: × (Excessive cross-linking breaks air bubbles to generate huge air bubbles.) 3) Measurement of gel fraction of highly-filled inorganic foam was prepared in 1). Inorganic high-filled foam (thickness 9 mm)
Nine samples were sliced from the inorganic high-filled foam by slicing each 1 mm in the thickness direction.

Approximately 50 mg was taken out from the center of each sample to obtain a sample. Each sample was immersed in a xylene solution at 120 ° C. for 24 hours. The solution was filtered through a 200-mesh filter paper, and the filter residue was separated and dried. .

Next, the filtration residue is put in a crucible and put into a crucible for 500 minutes.
The mixture was heated at a temperature of 12 ° C. for 12 hours, and the organic matter was incinerated to make only inorganic substances. The gel fraction was calculated from the weight ratio between the sample and the undissolved portion in the sample based on the following equation.

Gel fraction (%) = [(W ₁ −W ₂ ) /
W ₀ ] × 100 where W ₀ is the weight of the sample, W ₁ is the weight of the filtration residue, W ₂
Indicates the weight of the inorganic substance. (1) Difference between maximum value and minimum value of gel fraction Based on the above gel fraction measurement method, nine values obtained from nine samples are compared, and the difference between the maximum value and the minimum value is determined. The results are shown in Table 1.

Nine numerical values (gel fraction) are compared in the upper part, the central part, and the lower part in the thickness direction, and the central part is larger than the upper part and the lower part. In Table 1, the difference between the maximum value and the minimum value is indicated by +, and conversely, when the central portion is smaller than the upper and lower portions, the difference between the maximum value and the minimum value is indicated by-. (Comparative Examples 1 to 3) After the appearance evaluation and the gel fraction were measured in the same manner as in Example 1 except that the thickness of the foamable resin sheet was changed as shown in Table 1, the appearance evaluation results were obtained. Table 1 shows the difference between the maximum value and the minimum value of the gel fraction. (Examples 2 and 3, Comparative Examples 4 and 5) Acceleration voltage of 800 KV
After the appearance evaluation and the measurement of the gel fraction were performed in the same manner as in Example 1 except that the thickness of the foamable resin sheet was changed as shown in Table 1, the appearance evaluation result and the maximum gel fraction were obtained. Table 1 shows the difference between the value and the minimum value. (Examples 4 and 5, Comparative Examples 6 and 7) 900 KV of acceleration voltage
After the appearance evaluation and the measurement of the gel fraction were performed in the same manner as in Example 1 except that the thickness of the foamable resin sheet was changed as shown in Table 1, the appearance evaluation result and the maximum gel fraction were obtained. Table 1 shows the difference between the value and the minimum value.

The surface state and cross-sectional state of the highly-filled inorganic foam obtained in Example 5 were observed with a microscope, and a surface photograph and a sectional photograph are shown in FIGS. 1 and 2, respectively. (Examples 6 and 7, Comparative Examples 8 and 9) Acceleration voltage of 1,000
KV and the appearance evaluation and gel fraction were measured in the same manner as in Example 1 except that the thickness of the foamable resin sheet was changed as shown in Table 1. Table 1 shows the difference between the maximum value and the minimum value.

[0035]

[Table 1] (Examples 8 to 11 and Comparative Examples 10 to 12) On both surfaces of a foamable resin sheet having a thickness of 2 mm, an acceleration voltage of 700 KV was applied as shown in Table 2.
After irradiating the electron dose shown in the above, in the same manner as in Example 1,
A 9-mm-thick highly-filled inorganic foam was produced, and its appearance was evaluated. The results are shown in Table 2.

The gel fraction of the highly-filled inorganic foam was measured in the same manner as in Example 1, and the measurement results are shown in Table 2. (Examples 12 to 15, Comparative Examples 13 to 15) 2.5 m thick
m accelerating voltage of 800 KV on both sides of the foamable resin sheet
After irradiation with the electron dose shown in Table 2, a 9-mm thick highly-filled inorganic foam was produced in the same manner as in Example 1, and the appearance was evaluated. The results are shown in Table 2.

The gel fraction of the highly-filled inorganic foam was measured in the same manner as in Example 1, and the measurement results are shown in Table 2. (Examples 16-18, Comparative Examples 16-19) After irradiating both surfaces of a foamable resin sheet having a thickness of 3 mm with an electron dose shown in Table 2 at an acceleration voltage of 900 KV, a thickness of 9 mm was obtained in the same manner as in Example 1. Was prepared and the appearance was evaluated. The results are shown in Table 2.

Further, the gel fraction of the highly-filled inorganic foam was measured in the same manner as in Example 1, and the measurement results are shown in Table 2. (Examples 19 to 23, Comparative Examples 20 to 21) After irradiating both sides of a foamable resin sheet having a thickness of 3 mm with an electron dose shown in Table 2 at an acceleration voltage of 900 KV, a thickness of 9 mm was obtained in the same manner as in Example 1. Was prepared and the appearance was evaluated. The results are shown in Table 2.

Further, the gel fraction of the highly-filled inorganic foam was measured in the same manner as in Example 1, and the measurement results are shown in Table 2.

[0040]

[Table 2] (Comparative Example 22) A foamable resin sheet having a thickness of 3 mm was prepared in the same manner as in Example 1 except that 0.5 part by weight of dicumyl peroxide was added as a crosslinking agent. Heating was performed in a gear oven at 220 ° C. without irradiation with an electron beam to produce a highly-filled inorganic foam.

Micrographs were taken of the foam in the same manner as in Example 5, and surface photographs and cross-sectional photographs were shown in FIGS. 3 and 4, respectively.

[0042]

According to the present invention, there is provided an inorganic material-filled resin foam having excellent mechanical properties, having no pores on the surface due to breakage of foam cells, and having a smooth surface.

[Brief description of the drawings]

FIG. 1 is a photomicrograph showing the surface condition of a highly-filled inorganic foam obtained in Example 5.

FIG. 2 is a micrograph showing a cross-sectional state of the highly-filled inorganic material foam shown in FIG.

FIG. 3 is a micrograph showing the surface state of the highly-filled inorganic foam obtained in Comparative Example 22.

FIG. 4 is a photomicrograph showing a cross-sectional state of the highly inorganic foam shown in FIG.

Claims (2)

(57) [Claims] An electron beam is irradiated on a foamable resin sheet of a composition containing 100 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of less than 40% by weight and 50 to 300 parts by weight of an inorganic powder. after, in the manufacturing method of the heat foamed to inorganic high filling resin foam, wherein by irradiating an electron beam on both sides of the foamed resin sheet, the inorganic high filling resin foam
The gel fraction in the thickness direction is 15 to 50%, and the thickness is
The difference between the maximum value and the minimum value of the gel fraction in the direction 20%
A method for producing a highly-filled inorganic resin foam, which is formed as follows. 2. A foam which is produced by the method for producing a highly-filled inorganic resin foam according to claim 1.