JP2005350571A - Thermoplastic resin foam sheet and method for producing thermoplastic resin foam sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic resin composition, a thermoplastic resin foam sheet, and a method for producing a thermoplastic resin foam sheet that are excellent in flexibility and can realize high water-stopping properties.
SOLUTION: A thermoplastic resin foam sheet containing an ethylene-propylene-diene copolymer rubber, having closed cell layers having a closed cell ratio of 80% or more on both surfaces, and having a thickness direction. A thermoplastic resin foam sheet having an open cell layer with a closed cell ratio of 10% or less at the center.
[Selection figure] None

Description

The present invention relates to a thermoplastic resin foam sheet that can be suitably used for various sealing materials in the fields of architecture, civil engineering, electricity, electronics, vehicles, and the like, and a method for producing a thermoplastic resin foam sheet.

Currently, foam is widely used as a sealing material in various fields such as architecture, civil engineering, electricity, electronics, and vehicles. As a foam used for such a sealing material, for example,
Rubber foams made of synthetic rubber or natural rubber such as ethylene-propylene-diene copolymer rubber (EPDM), polyurethane rubber, ethylene-propylene copolymer rubber (EPR), chloroprene rubber, polyethylene resin, polypropylene resin And the like, and the like. In particular, foams using EPDM are excellent in flexibility, and are widely used as sealing materials around air and watertight sealing materials for houses, automobiles, etc., and display panels around plasma displays, liquid crystal displays, mobile phones and the like. .

However, since foams using conventional EPDM usually have an open cell structure, they are excellent in flexibility, but it is difficult to ensure high water tightness unless the foams are compressed. The watertight seal material could not function sufficiently.
In particular, in recent years, dry foams tend to be used in place of wet sealing materials such as caulking for the purpose of improving workability in exteriors of houses, and EPDM is used as such dry foams. In some cases, it was necessary to have better water tightness. In addition, with regard to sealing materials used around automobile lamps, etc., high water tightness is required with the spread of high-pressure car wash machines, etc., but foams using conventional EPDM cause water leakage and the like. There was a thing.

In order to solve such problems, Patent Document 1 improves the followability and adhesion when used for a sealed member having irregularities on the surface by increasing the hydrophobicity and the closed cell ratio. A foamed sealing material for the purpose of realizing a water-stopping property is disclosed.
However, in such foamed sealing materials, the water-stopping property is improved by increasing the hydrophobicity, but the repulsive force is increased by increasing the closed cell ratio. There has been a problem that the member is deformed.

Further, Patent Document 2 discloses a fixed seal material in which a foam film is made of a foam structure having both closed cells and open cells, and the cell membrane is water-swellable and the number of cells per 1 cm length is 8 or more. Is disclosed. By having both cell structure of closed cell structure and open cell structure,
By taking in each advantage and making the cell membrane swellable with water, the initial sealing property can be secured and the sealing effect can be satisfactorily exhibited. However, the fixed sealing material disclosed in Patent Document 2 requires the use of a water-absorbing swelling polymer such as a polyacrylic acid type or a starch graft type, and thus it is difficult to manufacture with high industrial productivity. In addition, there is a problem that it is difficult to cope with sealed portions of various shapes lacking in formability. Moreover, although the sealing material used for a wide use needs to be comparatively cheap, there also existed a problem that a raw material became a cost increase factor.
Furthermore, by providing layers made of acrylic adhesive tape or butyl resin on both surfaces of the foam using EPDM, water tightness is also improved, but in this case, there is a problem that it leads to cost increase. there were.
Accordingly, there has been a strong demand for a foam having excellent flexibility and high water stopping properties.

JP 2001-288453 A JP-A-9-111899

In view of the above-described present situation, an object of the present invention is to provide a thermoplastic resin foam sheet and a method for producing a thermoplastic resin foam sheet that are excellent in flexibility and can realize high water-stopping properties.

The present invention is a thermoplastic resin foam sheet containing ethylene-propylene-diene copolymer rubber, having closed cell layers with a closed cell ratio of 80% or more on both surfaces, and having a thickness direction. It is a thermoplastic resin foam sheet having an open cell layer with a closed cell ratio of 10% or less at the center.
Hereinafter, the present invention will be described in more detail.

As a result of intensive studies, the inventors of the present invention have made both surfaces of the thermoplastic resin foam sheet into a layer having a high closed cell ratio and a central portion in the thickness direction as a layer having a low closed cell ratio. The inventors have found that deformation, water leakage, etc. can be prevented, and that high flexibility and excellent water stopping properties can be realized, and the present invention has been completed.

The thermoplastic resin foam sheet of the present invention comprises an ethylene-propylene-diene copolymer rubber (E
PDM).
By containing the EPDM, it is possible to produce a thermoplastic resin foam sheet that is excellent in flexibility and excellent in moldability.

The thermoplastic resin foam sheet of the present invention has closed cell layers having a closed cell ratio of 80% or more on both surfaces. When the closed cell ratio of the closed cell layer is less than 80%, the water-stopping property of the thermoplastic resin foam sheet may be lowered. In the present specification, the closed cell ratio means a volume ratio of bubbles (closed cells) not connected to other bubbles with respect to the total bubble volume, for example, an air hydrometer (1-1 / 2 to 1 atm). Method) (trade name “1000 type”, manufactured by Tokyo Science Co., Ltd.).

The preferable lower limit of the thickness of the closed cell layer is 10% of the entire thermoplastic resin foam sheet, and the preferable upper limit is 60%. If it is less than 10%, the water stoppage may be insufficient.
If it exceeds 0%, the flexibility may be insufficient.

The thermoplastic resin foam sheet of the present invention has an open cell layer having a closed cell ratio of 10% or less at the central portion in the thickness direction. When the closed cell ratio of the open cell layer exceeds 10%, the thermoplastic resin foam sheet becomes insufficiently flexible, the repulsive force during compression increases, and the sealed member when used as a sealing material The problem that it deform | transforms or the clearance gap of a to-be-sealed part expands by deformation | transformation of a to-be-sealed member becomes easy to arise.

The preferable lower limit of the thickness of the open cell layer is 40% of the entire thermoplastic resin foam sheet, and the preferable upper limit is 90%. If it is less than 40%, the flexibility may be insufficient.
If it exceeds 0%, the water-stopping property may be insufficient.

In the thermoplastic resin foam sheet of the present invention, the preferred lower limit of the expansion ratio is 10 L / kg.
The upper limit is 40 L / kg. When it is less than 10 L / kg, the compression flexibility decreases,
The repulsive force at the time of compression may increase, and the member to be sealed may be deformed when used as a sealing material, or the gap in the portion to be sealed may be expanded due to deformation of the member to be sealed. 40L /
If it exceeds kg, the compression set becomes large, so that the long-term water stoppage may be lowered.

In the thermoplastic resin foam sheet of the present invention, the preferable upper limit of the 25% compressive strength in the thickness direction is 10 kPa. If it exceeds 10 kPa, the water stoppage decreases when there is unevenness such as steps.

In the thermoplastic resin foam sheet of the present invention, the preferable lower limit of the 50% compressive strength in the thickness direction is 10 kPa, and the upper limit is 200 kPa. If the pressure is less than 10 kPa, it may be necessary to increase the compression rate in order to obtain sufficient water stopping properties. If the pressure exceeds 200 kPa, the member to be sealed may be deformed due to the repulsive force.

Moreover, the thermoplastic resin foam sheet of the present invention according to another aspect is a thermoplastic resin foam sheet containing ethylene-propylene-diene copolymer rubber, and has a closed cell ratio of 80% on one surface. It has the above closed cell layer and an open cell layer with a closed cell rate of 10% or less on the other surface.
The thermoplastic resin foam sheet of the present invention according to such another aspect is extremely flexible because the open cell layer is exposed on the surface, and the sealed member is deformed when used as a sealing material. It is possible to prevent the gap of the sealed portion from being enlarged due to deformation of the sealed member.

The thermoplastic resin foam sheet according to another embodiment of the present invention has a closed cell ratio of 80% on one surface.
It has the above closed cell layer. When the closed cell ratio of the closed cell layer is less than 80%, the water-stopping property of the thermoplastic resin foam sheet may be lowered.

The preferable lower limit of the thickness of the closed cell layer is 10% of the entire thermoplastic resin foam sheet, and the preferable upper limit is 60%. If it is less than 10%, the water stoppage may be insufficient.
If it exceeds 0%, the flexibility may be insufficient.

The thermoplastic resin foam sheet according to another embodiment of the present invention has a closed cell ratio of 10% on the other surface.
It has the following open cell layer. When the closed cell ratio of the open cell layer exceeds 10%, the thermoplastic resin foam sheet becomes insufficiently flexible, the repulsive force during compression increases, and the sealed member when used as a sealing material The problem that it deform | transforms or the clearance gap of a to-be-sealed part expands by deformation | transformation of a to-be-sealed member becomes easy to arise.

The preferable lower limit of the thickness of the open cell layer is 40% of the entire thermoplastic resin foam sheet, and the preferable upper limit is 90%. If it is less than 40%, the flexibility may be insufficient.
If it exceeds 0%, the water-stopping property may be insufficient.

In the thermoplastic resin foam sheet of the present invention according to another aspect, a preferable lower limit of the expansion ratio is 10 L / kg, and an upper limit is 40 L / kg. When it is less than 10 L / kg, the compression flexibility is reduced, the repulsive force at the time of compression is increased, the sealed member is deformed when used as a sealing material, or the gap of the sealed portion is deformed by the deformation of the sealed member. May expand. If it exceeds 40 L / kg, the compression set becomes large, so that the long-term water stoppage may be lowered.

In the thermoplastic resin foam sheet of the present invention according to another aspect, the preferable upper limit of the 25% compressive strength in the thickness direction is 10 kPa. If it exceeds 10 kPa, there is unevenness such as steps,
Water stoppage decreases.

In the thermoplastic resin foam sheet of the present invention according to another aspect, a preferable lower limit of 50% compressive strength in the thickness direction is 10 kPa, and an upper limit is 200 kPa. If the pressure is less than 10 kPa, it may be necessary to increase the compression rate in order to obtain sufficient water stopping properties.
If it exceeds 0 kPa, deformation of the sealed member may occur due to repulsive force.

In the thermoplastic resin foam sheet of the present invention, an adhesive layer may be formed on one side or both sides.
By having an adhesive layer, workability and water stoppage are improved.
The method for forming the pressure-sensitive adhesive layer is not particularly limited, and examples thereof include a method for attaching a double-sided pressure-sensitive adhesive tape, a method for applying an acrylic pressure-sensitive adhesive or a rubber-based pressure-sensitive adhesive to the surface, and the like.
In addition, when forming the said adhesion layer, it is preferable to give a corona treatment to the surface in which the said adhesion layer is formed previously. Thereby, the adhesive force of a thermoplastic resin foam sheet and an adhesion layer can be improved.

Although it does not specifically limit as a manufacturing method of the thermoplastic resin foam sheet of this invention, For example, Mooney viscosity (ML1 _{+ 4} 125 degreeC) is 4 or more and less than 30, and diene content is 2.0- 20% of ethylene-propylene-diene copolymer rubber of 5.0%
Thermoplastic containing 90 to 80% by weight of crystalline thermoplastic resin having a melt flow rate (190 ° C.) of 2 to 20 g / 10 min, 10 to 80% by weight, an organic peroxide, a pyrolytic foaming agent and zinc oxide A step of preparing a resin composition, a step of forming a foamable sheet by molding the thermoplastic resin composition into a sheet, a step of irradiating and crosslinking the surface of the foamable sheet, and a step of irradiating the radiation A method having a step of heating and foaming the foamable sheet to produce a sheet-like foam is suitable. Such a manufacturing method is also one aspect of the present invention.

According to the method for producing a thermoplastic resin foam sheet of the present invention, a closed cell layer having a high closed cell ratio and excellent water blocking properties is obtained by performing a crosslinking and foaming step after molding a predetermined thermoplastic resin composition. Can be produced on both surfaces, and has an open cell layer with a low closed cell ratio and excellent flexibility at the center in the thickness direction. As a result, it is not necessary to prepare a closed cell layer and an open cell layer separately, or to perform an open cell process separately, and a series of thermoplastic resin foam sheets having both high flexibility and excellent water stopping properties. It can be manufactured efficiently in the process.
In addition, the degree of cross-linking on both surfaces of the thermoplastic resin foam sheet is easily adjusted by changing the physical properties of the thermoplastic resin composition within a predetermined range or changing the dose of radiation to be irradiated. Therefore, a thermoplastic resin foam sheet having desired flexibility and water-stopping property can be produced.

In the method for producing a thermoplastic resin foam sheet of the present invention, first, Mooney viscosity (ML _1
+4 125 ° C) is 4 or more and less than 30, and 20 to 90% by weight of ethylene-propylene-diene copolymer rubber (EDPM) having a diene content of 2.0 to 5.0%, melt flow Thermoplastic resin composition containing 10 to 80% by weight of a crystalline thermoplastic resin having a rate (MFR) (190 ° C.) of 2 to 20 g / 10 min, an organic peroxide, a pyrolytic foaming agent and zinc oxide To prepare.

The above EPDM has a Mooney viscosity (ML _{1 + 4} 125 ° C.) of 4 or more and less than 30.
If it is less than 4, the crosslinkability is lowered and the foamability is lowered, so that the obtained thermoplastic resin foam sheet is inferior in flexibility. If it is 30 or more, the crosslinkability becomes too high, and therefore the closed cell ratio of the obtained thermoplastic resin foam sheet is increased, and the flexibility is lowered. The Mooney viscosity is a measure of viscosity by a Mooney viscometer such as raw rubber or rubber compound.

In the EPDM, the lower limit of the diene component content is 2.0%, and the upper limit is 5.0%.
If it is less than 2.0%, the crosslinkability is lowered and the foamability is lowered, so that the flexibility is inferior. If it exceeds 5.0%, the weather resistance of the resulting thermoplastic resin foam sheet is lowered.

The diene component used in the above EPDM is not particularly limited. For example, 5-ethylidene-2-norbornene, 5-propylidene-5-norbornene, dicyclopentadiene, 5
-Cyclic dienes such as vinyl-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, norbornadiene; 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl- 1,4-hexadiene, 5-methyl-1,5
-Chain non-conjugated dienes such as heptadiene, 6-methyl-1,5-heptadiene, 6-methyl-1,7-octadiene and the like.

The crystalline thermoplastic resin has an MFR (190 ° C.) of 2 to 20 g / 10 minutes.
If it is less than 2 g / 10 minutes, the crosslinkability becomes too high, so that the closed cell ratio of the obtained thermoplastic resin foam sheet is increased and the flexibility is lowered. When it exceeds 20 g / 10 minutes, the crosslinkability of the crystalline thermoplastic resin is lowered and the foamability is lowered, so that the flexibility of the obtained thermoplastic resin foam sheet is lowered.

As the crystalline thermoplastic resin having an MFR (190 ° C.) of 2 to 20 g / 10 min, EP
It is not particularly limited as long as it can be melt kneaded with DM and can form and maintain a cell structure by foaming. For example, linear low density polyethylene, high pressure method low density polyethylene, medium density polyethylene, high density polyethylene, Polyethylenes such as ethylene-propylene copolymer, ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid ester copolymer Resins; Polypropylene resins such as polypropylene and propylene-α-olefin copolymers; Thermoplastic elastomers such as polyolefin elastomers, polystyrene elastomers, polyamide elastomers, and polyester elastomers; and vinyl chloride resins. These crystalline thermoplastic resins may be used alone or in combination of two or more.
The α-olefin is not particularly limited, and examples thereof include butene, 4-methyl-1-pentene, pentene, hexene, heptene, octene and the like. These α-olefins may be used alone or in combination of two or more.
Among these crystalline thermoplastic resins, thermoplastic elastomers, polyethylene resins, and polypropylene resins are preferable because of excellent moldability.

In the above thermoplastic resin composition, the mixing ratio of EPDM and crystalline thermoplastic resin is EPDM.
The range is from 80 to 10% by weight of the crystalline thermoplastic resin with respect to 20 to 90% by weight. E above
When the proportion of PDM is less than 20% by weight and the proportion of the crystalline thermoplastic resin exceeds 80% by weight, the production stability of the resulting thermoplastic resin foam sheet is lowered.
Further, when the ratio of the EPDM exceeds 90% by weight and the ratio of the crystalline thermoplastic resin is less than 10% by weight, the rubber elasticity of the obtained thermoplastic resin foam sheet becomes too strong, The foam shape cannot be maintained.

The thermoplastic resin composition contains an organic peroxide. The organic peroxide has a role as a crosslinking agent for crosslinking the thermoplastic resin.
Examples of the organic peroxide include 1,1-bis (t-butylperoxy) 3, 3, 5
-Trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane,
2,2-bis (t-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dicumylper Oxide, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane,
2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, benzoyl peroxide, cumylperoxyneodecanate, t-butylperoxybenzoate, 2
, 5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate, and the like.
These organic peroxides may be used alone or in combination of two or more.

The content of the organic peroxide is determined by the degree of crosslinking required in the thermoplastic resin foam sheet, but the preferred lower limit is 0.01 parts by weight with respect to 100 parts by weight of EPDM, and the upper limit is 5 Parts by weight. If it is less than 0.01 part by weight, gelation may not occur due to crosslinking, and if it exceeds 5 parts by weight, a sufficient foaming ratio may not be obtained. A more preferred lower limit is 0.1 parts by weight, and an upper limit is 3 parts by weight.

The thermoplastic resin composition contains a pyrolytic foaming agent.
Examples of the pyrolytic foaming agent include azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, 4,4.
-Oxybis (benzenesulfonyl hydrazide) etc. are mentioned. These may be used independently and may use 2 or more types together.
The minimum with preferable content of the said pyrolyzable foaming agent is 1 weight part with respect to 100 weight part of the mixture of EPDM and a crystalline thermoplastic resin, and an upper limit is 30 weight part. If it is less than 1 part by weight, foaming may be insufficient, and if it exceeds 30 parts by weight, bubbles may break during foaming.

The thermoplastic resin composition contains zinc oxide. The zinc oxide has a role as a foaming aid that promotes foaming and lowers the foaming temperature.
It does not specifically limit as said zinc oxide, A conventionally well-known thing can be used.
The preferred lower limit of the zinc oxide content is a mixture 10 of EPDM and a crystalline thermoplastic resin.
It is 0.1 weight part with respect to 0 weight part, and a preferable upper limit is 2.0 weight part. When the foaming temperature is less than 0.1 part by weight, the foaming temperature becomes a high temperature of 200 ° C. or higher, the organic peroxide is excessively decomposed during foaming, and the crosslinking proceeds too much. The closed cell ratio increases and flexibility decreases. If it exceeds 2.0 parts by weight, the foaming temperature becomes low, and foaming occurs before the crosslinking due to the decomposition of the organic peroxide proceeds sufficiently, and foaming failure due to outgassing may occur.

The thermoplastic resin composition may contain conventionally known additives such as a crosslinking aid, an antioxidant, a filler, a stabilizer, a pigment, a flame retardant, an antistatic agent, and a plasticizer, if necessary. Good.

The method for preparing the thermoplastic resin composition is not particularly limited. For example, using a kneader such as a Banbury mixer or a kneader, EPDM, crystalline thermoplastic resin, organic peroxide, pyrolytic foaming agent And a method of mixing and kneading zinc oxide at a temperature not higher than the decomposition temperature of the pyrolytic foaming agent.

In the method for producing a thermoplastic resin foam sheet of the present invention, the above thermoplastic resin composition is then formed into a sheet shape to produce a foamable sheet. It does not specifically limit as a method to shape | mold into a sheet form, For example, T-die shaping | molding, calendar | calender shaping | molding, hot press molding etc. are mentioned.

In the method for producing a thermoplastic resin foam sheet of the present invention, next, radiation is applied to both surfaces of the foamable sheet to crosslink the surface layer portion. Examples of the method of crosslinking only the surface layer portion of the foamable sheet as described above include a method of irradiating low-energy ionizing radiation and crosslinking only the surface layer portion of the foamable sheet by energy attenuation. .
Moreover, it does not specifically limit as said radiation, For example, an alpha ray, a beta ray, a gamma ray, an electron beam etc. are mentioned.

In the method for producing a thermoplastic resin foam sheet of the present invention, the foamable sheet irradiated with the radiation is then heated and foamed to produce a sheet-like foam, which is used as a thermoplastic resin foam sheet. Examples of the method of heating and foaming the foamable sheet irradiated with the radiation include a method of heating to a temperature higher than the decomposition temperature of the pyrolyzable foaming agent contained in the thermoplastic resin composition of the present invention.

After producing a sheet-like foam by the method for producing a thermoplastic resin foam sheet of the present invention, a step of cutting in a direction perpendicular to the thickness direction at the center in the thickness direction of the sheet-like foam. A thermoplastic resin foam sheet can also be manufactured by performing. Such a method for producing a thermoplastic resin foam sheet is also one aspect of the present invention.

According to such a production method, a closed cell layer having a high closed cell ratio on one surface and an excellent water-stopping property, and an open cell layer having a low closed cell rate and excellent flexibility on the other surface are provided. The thermoplastic resin foam sheet can be efficiently produced by a simple method.
In addition, since two thermoplastic resin foam sheets having the above-described configuration can be produced at the same time, high productivity can be realized, which is economically advantageous.

ADVANTAGE OF THE INVENTION According to this invention, while being excellent in a softness | flexibility, the manufacturing method of the thermoplastic resin foam sheet and thermoplastic resin foam sheet which can implement | achieve high water-stopping property can be provided.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited only to these examples.

(Example 1)
EPD with Mooney viscosity (ML _{1 + 4} 125 ° C) of 8 and diene content of 3.5%
M (Mitsui Chemicals, EPT3012P) 60 parts by weight, MFR (190 ° C., 2.16 kg)
Is 1.0 g / 10 min, and the density is 0.902 g / cm ³ crystalline polyethylene resin (Dow Chemical Co., affinity PL1880G) 40 parts by weight, organic peroxide is 1.0 part by weight dicumyl peroxide, heat As a decomposable foaming agent, 10 parts by weight of azodicarbonamide and 0.5 parts by weight of zinc oxide were kneaded with a pressure kneader to prepare a thermoplastic resin composition.

After pelletizing the obtained thermoplastic resin composition, the thickness was 3.3 m using a T-die extruder.
m foamable sheets were prepared.
Next, both surfaces of the foamable sheet are irradiated with an electron beam with an acceleration voltage of 500 kV for 5 Mrad to crosslink from the surface of the foamable sheet to a portion having a depth of 1 mm, and then heated to 240 ° C. in a heating foaming furnace to foam. As a result, a thermoplastic resin foam sheet having a thickness of 10 mm was obtained.
The closed cell ratio of the surface layer 3 mm of the obtained thermoplastic resin foam sheet was 88%, and the closed cell ratio of the central portion 3 mm in the thickness direction was 0%.

(Example 2)
2. Mooney viscosity (ML _{1 + 4} 125 ° C.) 20, diene content 4.9% EPDM (Dow Elastomer, Nodel 4720) 40 parts by weight, MFR (190 ° C., 2.16 kg)
60 parts by weight of crystalline polyethylene resin (engaged 8450, manufactured by Dow Elastomer Co., Ltd.) having a density of 0.902 g / cm ³ at 0 g / 10 min, dicumyl peroxide 1 as an organic peroxide
. 0 parts by weight, 10 parts by weight of azodicarbonamide as a pyrolytic foaming agent, and 0 parts of zinc oxide
. 5 parts by weight were kneaded with a pressure kneader to prepare a thermoplastic resin composition.

After pelletizing the obtained thermoplastic resin composition, the thickness was 3.3 m using a T-die extruder.
m foamable sheets were prepared.
Next, both surfaces of the foamable sheet are irradiated with an electron beam with an acceleration voltage of 500 kV for 5 Mrad to crosslink from the surface of the foamable sheet to a portion having a depth of 1 mm, and then heated to 240 ° C. in a heating foaming furnace to foam. As a result, a thermoplastic resin foam sheet having a thickness of 10 mm was obtained.
The closed cell ratio of the surface layer 3 mm of the obtained thermoplastic resin foam sheet was 83%, and the closed cell ratio of the central portion 3 mm in the thickness direction was 5%.

(Example 3)
A thermoplastic resin foam sheet having a thickness of 5 mm was obtained by slicing the thermoplastic resin foam sheet prepared in Example 1 in the direction perpendicular to the thickness direction at the center in the thickness direction.

(Comparative Example 1)
After producing a foamable sheet in the same manner as in Example 1, a thermoplastic resin foam sheet is obtained by heating to 240 ° C. in a heating foaming furnace and foaming without irradiating the surface of the electron beam. It was. However, outgassing of the foaming agent occurred during foaming, and foaming was not sufficiently performed.

(Comparative Example 2)
2. Mooney viscosity (ML _{1 + 4} 125 ° C.) 40, diene content 4.9% EPDM (Dow Elastomer, Nodel 4640) 30 parts by weight, MFR (190 ° C., 2.16 kg)
A thickness of 10 mm in the same manner as in Example 1 except that 70 parts by weight of crystalline polyethylene resin (engage 8450 manufactured by Dow Elastomer Co., Ltd.) having a density of 0.902 g / cm ³ was used at 0 g / 10 min.
A thermoplastic resin foam sheet was prepared.
The closed cell ratio of the surface layer 3 mm of the obtained thermoplastic resin foam sheet was 85%, and the closed cell ratio of the central portion 3 mm in the thickness direction was 64%.

(Comparative Example 3)
A foamable sheet was produced in the same manner as in Example 1 except that 0.3 parts by weight of zinc stearate was used instead of zinc oxide.
Both surfaces of the obtained foamable sheet were irradiated with 5 Mrad of an electron beam with an acceleration voltage of 500 kV to crosslink from the surface of the foamable sheet to a portion having a depth of 1 mm, and then heated to 240 ° C. in a heating foaming furnace. By foaming, a thermoplastic resin foam sheet having a thickness of 7 mm was obtained.
In addition, it was thought that it was because gas outgassing generate | occur | produced in the center part of the thickness direction in foaming, compared with the thermoplastic resin foam sheet obtained in Example 1.
The closed cell ratio of the surface layer 3 mm of the obtained thermoplastic resin foam sheet was 88%, and the closed cell ratio of the central portion 3 mm in the thickness direction was 15%.

(Comparative Example 4)
A commercially available foam made of EPDM (Epto Sealer 1010, manufactured by Nitto Denko Corporation, thickness 10 mm) was used as the thermoplastic resin foam sheet. The closed cell ratio was 0% for both the surface layer 3 mm and the central portion 3 mm in the thickness direction.

(Evaluation)
The thermoplastic resin foam sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated by the following methods. The results are shown in Table 1. Table 1 also shows the expansion ratio of the produced thermoplastic resin foam sheet.

(1) Compression flexibility 25% and 50% compression strengths were measured by a method based on JIS K6767.

(2) Water-stop test (leakage time)
A test piece cut out into a U-shape with a width of 10 mm is prepared from a thermoplastic resin foam sheet, and the test piece is sandwiched between two acrylic resin plates so as to maintain the U-shape. Two acrylic resins The gap between the plates was narrowed so that the compressibility of the test piece was 50% and 75%. Next, stand up so that the U-shaped opening of the test piece cut out in the U-shape is on top, put water of 100 mm height inside the U-shape, and wait until the water leakage is confirmed by visual inspection. Measured.

(3) Workability test Effectiveness when sealing a sealed portion with a gap of 1.0 mm and a length of 10 mm using a thermoplastic resin foam sheet (by repulsive force when compressing a thermoplastic resin foam sheet) The deformation of the member to be sealed was evaluated by the following method.
Two stainless steel plates with a thickness of 1 mm, a width of 20 mm, and a length of 100 mm are prepared, and a test piece of 10 mm thickness, 20 mm width, 100 mm length (Example 3 is 5 mm thickness) is formed from a thermoplastic resin foam sheet. Cut out. First, one stainless steel plate is placed on a horizontal table, and then placed on it with the width direction and length direction aligned, and the remaining one stainless steel plate is placed on the test piece in the width direction. And placed in the same length direction. Next, length direction both ends of the upper stainless steel plate,
The upper and lower stainless steel plates were compressed from the upper side until the distance between them became 1/2 of the foam thickness (compression rate 50%). At this time, the gap T (mm) between the upper stainless steel plate and the lower stainless steel plate at the center in the length direction of the stainless steel plate was measured, and the deflection amount (mm) of the stainless steel plate was calculated by the following equation.
Deflection amount of stainless steel plate (mm) = T (mm)-1/2 (mm) of foam thickness
In the above case, if the amount of deflection exceeds 0.5 mm, it is considered that there will be a problem in construction.

ADVANTAGE OF THE INVENTION According to this invention, while being excellent in a softness | flexibility, the manufacturing method of the thermoplastic resin foam sheet and thermoplastic resin foam sheet which can implement | achieve high water-stopping property can be provided.

Claims (4)

A thermoplastic resin foam sheet containing an ethylene-propylene-diene copolymer rubber, which has a closed cell layer with a closed cell ratio of 80% or more on both surfaces, and is independent at the center in the thickness direction. A thermoplastic resin foam sheet characterized by having an open cell layer having a cell ratio of 10% or less. A thermoplastic resin foam sheet containing ethylene-propylene-diene copolymer rubber, having a closed cell layer with a closed cell ratio of 80% or more on one surface, and a closed cell ratio on the other surface A thermoplastic resin foam sheet characterized by having an open cell layer of 10% or less. 20 ethylene-propylene-diene copolymer rubbers having a Mooney viscosity (ML _{1 + 4} 125 ° C.) of 4 or more and less than 30 and a diene content of 2.0 to 5.0%.
Heat containing 10 to 80% by weight of a crystalline thermoplastic resin having a melt flow rate (190 ° C.) of 2 to 20 g / 10 min, an organic peroxide, a thermally decomposable blowing agent and zinc oxide. A step of preparing a plastic resin composition;
Forming the foamable sheet by molding the thermoplastic resin composition into a sheet,
Irradiating the surface of the foamable sheet with radiation and crosslinking; and
A method for producing a thermoplastic resin foam sheet, comprising a step of heating and foaming a foamable sheet irradiated with radiation to produce a sheet-like foam. The method for producing a thermoplastic resin foam sheet according to claim 3, further comprising a step of cutting in a direction perpendicular to the thickness direction at a central portion in the thickness direction of the sheet-like foam.