JP2004027239A - Foam manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a foam having excellent toughness and compression resistance and being useful as e.g. a foam for insulating folded plates having excellent insulation and moldability in a machine for formation of folded plates. <P>SOLUTION: The method has the first process of molding a foaming resin composition based on a resin composition essentially consisting of (A) a low-density polyethylene of a density of 0.930 g/cm<SP>3</SP>or lower, (B) a high-density polyethylene of a density of 0.940-0.960 g/cm<SP>3</SP>and (C) a copolymer of ethylene with one or more monomers selected from vinyl acetate, acrylic acid and ethyl acrylate, in a ratio of (A) to (B) plus (C) of 60-80 wt.% to 40-20 wt.% and a (B) to (C) weight ratio of 0.3-1.0:1.0, and a heat-decomposable foaming agent into a sheet to obtain a molding; the second process of irradiating a radiation onto the molding to cross-link the composition; and the third process of heating the cross-linked product to foam. <P>COPYRIGHT: (C)2004,JPO

Description

The invention described in claim 1 (hereinafter, the invention described in the claim 1 is referred to as the present invention 1) and the invention described in the claim 2 (hereinafter, the invention described in the claim 2 is referred to as the present invention 2) include a heat-insulating folded plate. The present invention relates to a method for producing a foam useful as a foam for use.

(4) A foam formed on a metal plate and formed into a folded plate shape by a folded plate forming machine is widely used as a roofing material. Such a foam for a heat-insulated folded plate is required to have heat insulation properties, moldability in a folded plate forming machine, performance of retaining dew water, and good appearance. Conventionally, crosslinked polyethylene foam sheets have been used as foams for heat insulation folded plates because of their closed cells and high heat insulation properties, but conventional crosslinked polyethylene foam sheets are compressed by forming rolls of a folding plate forming machine. They could not withstand the stresses and shear stresses, resulting in tears and significant reductions in thickness. In order to solve such a drawback, a polyethylene crosslinked foam for folded plates composed of low-density polyethylene and a specific linear low-density polyethylene has been proposed (for example, see Patent Document 1). However, it was not enough for tearing and reduction in thickness at the time of forming a folded plate.

Also, in order to increase the water retention of the crosslinked polyethylene foam sheet surface, the foam sheet is sliced to expose air bubbles on the slice surface, and the slice surface is attached to a metal plate with the slice surface facing the indoor side and folded Has also been manufactured. However, since the cell diameter of the conventional ordinary crosslinked polyethylene foam sheet is as small as less than 0.4 mm, even if sliced, the water retention of the surface was not sufficient. In order to improve this drawback, it has been proposed that the number of bubbles on a surface located within a distance of 1 mm or less from the slice surface be 300 / m ² (for example, see Patent Document 2). However, this has a drawback that the appearance is poor when construction is performed in which the attic is very large and air bubbles are visible.
JP-A-60-188430 JP-A-3-231937

The present invention has been made in view of the above problems, and an object of the present inventions 1 and 2 is to provide a heat insulating material having excellent toughness and compression resistance, for example, excellent heat insulating properties and excellent formability in a folding plate forming machine. An object of the present invention is to provide a method for producing a foam useful as a foam for a folded plate.

The method for producing a foam of the present invention 1 comprises a low-density polyethylene (A) having a density of 0.930 g / cm ³ or less, a high-density polyethylene (B) having a density of 0.940 to 0.960 g / cm ³ , and vinyl acetate and acrylic. It comprises a copolymer (C) of at least one monomer selected from the group consisting of acid and ethyl acrylate and ethylene, and the ratio of (A) to (B) + (C) is 60 to 80. % By weight and a resin composition having a weight ratio of (B) to (C) of 0.3 to 1.0: 1.0 (hereinafter referred to simply as “resin composition”). The first step of molding a foamable resin composition containing a pyrolytic foaming agent as a main component into a sheet to obtain a molded body, and irradiating the obtained molded body with radiation. The second step of crosslinking the resin composition, and then heating and foaming the crosslinked molded body And a third step.
The method for producing a foam of the present invention 2 comprises a low-density polyethylene (A) having a density of 0.930 g / cm ³ or less, a high-density polyethylene (B) having a density of 0.940 to 0.960 g / cm ³ , and vinyl acetate and acrylic. It comprises a copolymer (C) of at least one monomer selected from the group consisting of acid and ethyl acrylate and ethylene, and the ratio of (A) to (B) + (C) is 60 to 80. % By weight and a resin composition having a weight ratio of (B) to (C) of 0.3 to 1.0: 1.0 (hereinafter referred to simply as “resin composition”). And a first step of forming a crosslinkable foamable resin composition containing a thermal decomposition type foaming agent and a chemical crosslinking agent as main components into a sheet shape to obtain a molded body, and heating the obtained molded body. And a second step of crosslinking the resin composition, and then heating the crosslinked molded body It comprises a third step of foaming.

{Circle around (1)} The first step of the present invention 1 is a step of forming a foamable resin composition containing the above “resin composition” and a pyrolytic foaming agent as main components into a sheet to obtain a molded body.

In the resin composition used in the first aspect of the invention, the density of the low-density polyethylene (A) is limited to 0.930 g / cm ³ or less. Since the force becomes insufficient, the sheet may be broken or the thickness may be reduced at the time of forming the folded plate, 60 to 80% by weight based on the total amount of (A), (B) and (C) Limited to.

As the low-density polyethylene (A), those having a melt flow rate of 0.5 to 20 g / 10 minutes are preferable from the viewpoint of easy sheet forming. Preferably, the particle size passes through a 10-mesh wire mesh.

In the resin composition used in the first aspect of the present invention, when the density of the high-density polyethylene (B) decreases, the compression resistance becomes insufficient when the density is low, and the thickness tends to decrease when the folded plate is formed. since easily torn brittle, limited to 0.940~0.960g / cm ^3, preferably 0.940~0.955g / cm ^3.

As the high-density polyethylene (B), those having a melt flow rate of 2 to 20 g / 10 minutes are preferable from the viewpoint of easy sheet forming. Preferably, the particle size passes through a 10-mesh wire mesh.

In the resin composition used in the present invention 1, the copolymer (C) is a copolymer of ethylene and at least one monomer selected from the group consisting of vinyl acetate, acrylic acid, and ethyl acrylate. . In the composition of the copolymer (C), when the content of at least one monomer selected from the group consisting of vinyl acetate, acrylic acid, and ethyl acrylate is reduced, the composition is easily torn, and even in forming a folded plate, the composition is easily broken. When the content is increased and the content increases, the foam becomes too soft, the compression resistance is weakened, and the thickness is significantly reduced in forming the folded plate. Therefore, the content is preferably 5 to 25% by weight.

As the copolymer (C), those having a melt flow rate of 0.5 to 20 g / 10 minutes are preferable from the viewpoint of easy sheet forming. Preferably, the particle size passes through a 10-mesh wire mesh.

In the resin composition used in the present invention 1, the weight ratio of the high-density polyethylene (B) to the copolymer (C) is such that when the amount of the high-density polyethylene (B) decreases, the compression resistance of the foam becomes lower. Since the toughness of the foam decreases as the size decreases and increases, the content is limited to 0.3 to 1.0: 1.0.

樹脂 Additives such as an ultraviolet absorber, a flame retardant, a colorant, and an antioxidant may be added to the resin composition used in the present invention 1 as needed.

熱 The pyrolytic blowing agent used in the present invention 1 is not particularly limited, and examples thereof include azodicarbonamide, dinitrosopentamethylenetetramine, oxybisbenzenesulfonylhydrazide, metal carbonate, and metal bicarbonate.

使用 The amount of the pyrolytic foaming agent varies depending on the desired expansion ratio, but is preferably 5 to 30 parts by weight based on 100 parts by weight of the resin composition.

方法 As a method of obtaining a molded article by forming the sheet into a sheet, the method of molding with an extruder and the like can be mentioned.

と し て As the extruder, a single screw extruder or a multi-screw extruder having two or more screws is used by connecting one or more screws.

第 The second step of the present invention 1 is a step of irradiating the molded body obtained in the first step with radiation to crosslink the resin composition.

放射線 Examples of the radiation include ionizing radiation such as electron beam, α-ray, β-ray, and γ-ray. From the viewpoint of easy handling, electron beam is preferable.

程度 The degree of the cross-linking varies depending on the resin used, but for foaming in the third step described below, the gel fraction is preferably set to 30 to 60% by weight.

第 The third step of the present invention 1 is a step of heating and foaming the molded article crosslinked in the second step.

The foaming device is not particularly limited, and examples thereof include a hot blast stove; an electric heating stove; a high-frequency heating stove; and a liquid bath of a liquid or a molten salt.

In the first step of the second aspect of the present invention, the crosslinkable foamable resin composition containing the above-mentioned “resin composition”, the thermal decomposition type foaming agent and the chemical crosslinking agent as main components is molded into a sheet to obtain a molded article. It is a process.

樹脂 The resin composition used in the present invention 2 is the same as the resin composition according to claim 1.

種類 The type and amount of the thermal decomposition type foaming agent used in the present invention 2 are the same as those of the thermal decomposition type foaming agent according to claim 1.

化学 The chemical crosslinking agent used in the present invention 2 is not particularly limited, and examples thereof include an organic peroxide and an azide compound.

{Examples of the organic peroxide include dicumyl peroxide, 2,5-dimethyl-2,5-ditertiary peroxyhexane, ditertiary butyl peroxyphthalate, methyl ethyl ketone peroxide and the like.

使用 The amount of the organic peroxide to be used varies depending on the resin used, but is usually preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the resin composition. In addition, for foaming in the third step described below, it is preferable to blend the resin crosslinked by the decomposition of the organic peroxide such that the gel fraction becomes 30 to 70% by weight.

方法 As a method of obtaining a molded article by forming the sheet into a sheet, the method of molding with an extruder and the like can be mentioned.

と し て As the extruder, a single screw extruder or a multi-screw extruder having two or more screws is used by connecting one or more screws.

{Circle around (2)} The second step of the present invention 2 is a step of heating the molded body extruded in the first step and decomposing a part or all of the chemical crosslinking agent to crosslink the resin.

第 The third step of the present invention 2 is a step of heating and foaming the molded article crosslinked in the second step.

In the present invention 2, in the foaming step, the resin may be foamed by heating while being crosslinked.

Examples of the foaming device include a foaming device similar to the foaming device described in the first aspect of the invention.
(Action)

In the method for producing a foam according to the first and second aspects of the present invention, a molded article is obtained from a resin composition in which the above-mentioned specific polymer substance is mixed in the above-mentioned specific composition and a pyrolysis type foaming agent. Then, since it is crosslinked and foamed, it is possible to produce a foam which is excellent in toughness and compression resistance, and which is useful as a foam for heat-insulating folded plates, for example, having excellent heat insulating properties and excellent moldability in a folding plate forming machine.

The configuration of the method for producing a foam of the present inventions 1 and 2 is as described above, and is excellent in toughness and compression resistance, for example, a foam for a heat-insulated folded plate excellent in heat insulation and moldability in a folded plate forming machine. Can be produced as a useful foam.

Hereinafter, embodiments of the present invention will be described.
(Examples 1 to 3, Comparative Examples 1 and 2)
A low-density polyethylene (A) having a density of 0.923 g / cm ³ , a melt flow rate of 3.5 g / 10 min, and passing through a 20-mesh wire netting, and a high-density polyethylene (B) having a density of 0.945 g / cm ³ , A copolymer having a melt flow rate of 4.0 g / 10 min and passing through a 20-mesh wire gauze was used as a copolymer (C) as an ethylene-vinyl acetate copolymer having a vinyl acetate content of 12% by weight and a melt flow rate of 2.0 g / 10 min. One that passed through a 20 mesh wire mesh was used.
The weight ratio of (B) and (C) was 0.4: 1.0, and the weight ratio of (A) and (B) + (C) was as shown in Table 1. A resin composition obtained by mixing 20 parts by weight of azodicarbonamide as a pyrolytic foaming agent with respect to a total of 100 parts by weight of (A) + (B) + (C) was used. And extruded to obtain a sheet having a thickness of 3.8 mm.

(4) The obtained sheet was irradiated with an electron beam to crosslink it so as to have a gel fraction of 38% by weight, and then heated and foamed in a hot air oven at 300 ° C. to obtain a foam sheet having a thickness of 8 mm.

An acrylic adhesive was applied to one surface of the foam sheet, bonded to a steel plate having a thickness of 0.6 mm, and formed into a folded plate of nominal size 2033 according to JIS A 6514 by a folded plate forming machine. The tear during the forming of the folded plate and the thickness (mm) of the foam after the forming of the folded plate were observed and measured. Further, the appearance of the obtained folded plate on the foam side was observed and evaluated according to the following criteria. Table 1 shows the above results.
Tear at the time of forming a folded plate ○: No tear. ×: Torn.
Appearance of folded plate on foam side の: Good appearance.
Δ: There were irregularities.
×: The appearance was poor due to the tear.

(Examples 4 to 6, Comparative Examples 3 and 4)
The same low-density polyethylene (A), high-density polyethylene (B) and copolymer (C) as in Example 1 were used.
The weight ratio of (B) and (C) was 0.6: 1.0, and the weight ratio of (A) and (B) + (C) was as shown in Table 2. A resin composition obtained by mixing 20 parts by weight of azodicarbonamide as a pyrolytic foaming agent with respect to a total of 100 parts by weight of (A) + (B) + (C) was used. And extruded to obtain a sheet having a thickness of 3.8 mm.

架橋 The obtained sheet was crosslinked and foamed in the same manner as in Example 1, and the obtained foam sheet was evaluated in the same manner as in Example 1. The results are shown in Table 2.

(Examples 7 to 9, Comparative Examples 5 and 6)
The same low-density polyethylene (A), high-density polyethylene (B) and copolymer (C) as in Example 1 were used. The weight ratio of (B) and (C) was 0.9: 1.0, and the weight ratio of (A) and (B) + (C) was as shown in Table 3. A resin composition obtained by mixing 20 parts by weight of azodicarbonamide as a pyrolytic foaming agent with respect to a total of 100 parts by weight of (A) + (B) + (C) was used. And extruded to obtain a sheet having a thickness of 3.8 mm.

架橋 The obtained sheet was crosslinked and foamed in the same manner as in Example 1, and the obtained foam sheet was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Examples 7 to 9)
The same low-density polyethylene (A), high-density polyethylene (B) and copolymer (C) as in Example 1 were used. The weight ratio between (B) and (C) was set to 0.2: 1.0. The weight ratio of (A) and (B) + (C) was changed as shown in Table 4. A resin composition obtained by mixing 20 parts by weight of azodicarbonamide as a pyrolytic foaming agent with respect to a total of 100 parts by weight of (A) + (B) + (C) was used. And extruded to obtain a sheet having a thickness of 3.8 mm.

架橋 The obtained sheet was crosslinked and foamed in the same manner as in Example 1, and the obtained foam sheet was evaluated in the same manner as in Example 1. The results are shown in Table 4.

(Comparative Examples 10 to 12)
The same low-density polyethylene (A), high-density polyethylene (B) and copolymer (C) as in Example 1 were used. The weight ratio between (B) and (C) was 1.2: 1.0. The weight ratio of (A) and (B) + (C) was changed as shown in Table 9. A resin composition obtained by mixing 20 parts by weight of azodicarbonamide as a pyrolytic foaming agent with respect to a total of 100 parts by weight of (A) + (B) + (C) was used. And extruded to obtain a sheet having a thickness of 3.8 mm.

架橋 The obtained sheet was crosslinked and foamed in the same manner as in Example 1, and the obtained foam sheet was evaluated in the same manner as in Example 1. The results are shown in Table 4.

(Examples 10 to 12, Comparative Examples 13 and 14)
The same low density polyethylene (A) and high density polyethylene (B) as in Example 1 were used.
As the copolymer (C), an ethylene-ethyl acrylate copolymer having an ethyl acrylate content of 10% by weight and having a melt flow rate of 4.0 g / 10 minutes and passing through a 20-mesh wire mesh was used.
The weight ratio of (B) and (C) was 0.8: 1.0, and the weight ratio of (A) and (B) + (C) was as shown in Table 5.
A resin composition obtained by mixing 20 parts by weight of azodicarbonamide as a pyrolytic foaming agent with respect to a total of 100 parts by weight of (A) + (B) + (C) was used. And extruded to obtain a sheet having a thickness of 3.8 mm.

(4) The obtained sheet was irradiated with an electron beam to crosslink it so as to have a gel fraction of 36% by weight, and then heated and foamed in a hot air oven at 300 ° C. to obtain a foam sheet having a thickness of 8 mm.

An acrylic adhesive was applied to one surface of the foam sheet, bonded to a 0.8 mm-thick steel plate, and formed into a folded plate of nominal size 2033 according to JIS A 6514 by a folded plate forming machine. The tear during the forming of the folded plate and the thickness (mm) of the foam after the forming of the folded plate were observed and measured. Further, the appearance of the obtained folded plate on the foam side was observed and evaluated according to the following criteria. Table 5 shows the above results.
Tear at the time of forming a folded plate ○: No tear. ×: Torn.
Appearance of folded plate on foam side の: Good appearance.
Δ: There were irregularities.
×: The appearance was poor due to the tear.

Claims (2)

It is selected from the group consisting of low-density polyethylene (A) having a density of 0.930 g / cm ³ or less, high-density polyethylene (B) having a density of 0.940 to 0.960 g / cm ³ and vinyl acetate, acrylic acid, and ethyl acrylate. A copolymer (C) of at least one monomer and ethylene, wherein the proportion of (A) and (B) + (C) is 60 to 80% by weight and 40 to 20% by weight, A resin composition having a weight ratio of (B) to (C) of 0.3 to 1.0: 1.0 and a foamable resin composition containing a pyrolytic foaming agent as a main component are formed into a sheet. A first step of molding into a molded body,
A second step of irradiating the obtained molded body with radiation to crosslink the resin composition;
Next, a method for producing a foam comprising a third step of heating and foaming the crosslinked molded body. It is selected from the group consisting of low-density polyethylene (A) having a density of 0.930 g / cm ³ or less, high-density polyethylene (B) having a density of 0.940 to 0.960 g / cm ³ and vinyl acetate, acrylic acid, and ethyl acrylate. A copolymer (C) of at least one monomer and ethylene, wherein the proportion of (A) and (B) + (C) is 60 to 80% by weight and 40 to 20% by weight, A resin composition in which the weight ratio between (B) and (C) is 0.3 to 1.0: 1.0, and a crosslinkable foamable resin mainly composed of a pyrolytic foaming agent and a chemical crosslinking agent A first step of forming the composition into a sheet to obtain a molded body;
A second step of heating the obtained molded body to crosslink the resin composition,
Next, a method for producing a foam comprising a third step of heating and foaming the crosslinked molded body.