JPH07133364A - Production of thick crosslinked expanded sheet - Google Patents

Abstract

PURPOSE:To form the title sheet which is highly inorganic-filled, has a high expansion ratio, is thick-walled, is freed from crazings, etc., and has a beautiful appearance. CONSTITUTION:The production process comprises extruding a resin mixture prepared by mixing 100 pts.wt. base resin comprising an ethylene/vinyl acetate copolymer of a vinyl acetate content of 5-90wt.% or mixture thereof with at least one polyolefin resin selected from the group consisting of polyethylene, polypropylene and an ethylene copolymer with 50-500 pts.wt. inorganic powder, 5-50 pts.wt. flame retardant, 2-20 pts.wt. flame retardant aid, and 5-50 pts.wt. blowing agent and mixing this composition with a crosslinking agent comprising dicumyl peroxide and a crosslinking aid comprising a polyfunctional monomer in amounts satisfying the relationships: X+Y=0.8-1.3, X>=0.3, and Y>=0.1 (X is the amount (pts.wt.) of the crosslinking agent used, and Y is the amount (pts. wt.) of the crosslinking aid used) and expanding the extrudate by heating to the decomposition temperature of the crosslinking agent or above.

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 thick crosslinked foamed sheet comprising a mixture obtained by adding a large amount of inorganic powder to a polyolefin resin, which has a large expansion ratio, is thick, has no cracks and has a beautiful appearance. .

[0002]

2. Description of the Related Art Polyolefin-based resin foam sheets such as polyethylene, polypropylene, and ethylene-based copolymers are
Since it is lightweight and has excellent properties such as heat insulation, cushioning, and sound absorption, it is widely used in a very wide range of fields such as construction materials, packaging materials, and buoyancy materials. However, this polyolefin resin foamed sheet has a major drawback that it is extremely flammable, and various flame retardants or inorganic substances are filled to make the foamed sheet flame-retardant.

As a base resin for such an inorganic-filled foamed sheet, Japanese Patent Publication Nos. 62-16217 and 6-6 are available.
No. 3-1976, Japanese Examined Patent Publication No. 63-20858, and Japanese Examined Fairness 4
An ethylene-vinyl acetate copolymer, which has a small decrease in mechanical strength even when it is filled with an inorganic substance and is capable of achieving a high expansion ratio, as disclosed in JP-A-56057, is preferably used.

By the way, as a method for producing a crosslinked foamed sheet, a resin composition containing a foaming agent is molded by an extruder or the like, then irradiated with ionizing radiation to be crosslinked and then heated for foaming. There is a method of molding a resin composition containing an agent and a cross-linking agent with an extruder, then heating it to cross-link it and then foaming it.In the former method, if the sheet is thick, ionizing radiation reaches the center of the sheet. Since it cannot be performed, it has a fatal defect that crosslinking in the thickness direction is not performed uniformly, and it is the present situation that it cannot be used for producing a relatively thick foam sheet.

On the other hand, in the latter method, the organic peroxide is decomposed by heating and cross-links, so that the degree of cross-linking in the thickness direction becomes relatively uniform, which is suitable for producing a thick foam sheet. The above-mentioned high-expansion-ratio inorganic-filled foamed sheet also uses the latter crosslinking method.

In the production of the foamed sheet, in consideration of productivity, a sheet having a thickness twice the desired sheet thickness is produced, and the sheet is sliced into a half thickness and two sheets are simultaneously cut. The method of obtaining the foamed sheet is used. For example,
When producing a 6 mm foam sheet, two 6 mm foam sheets were obtained simultaneously by producing a 12 mm sheet and slicing.

In recent years, mainly in cold regions, the temperature difference between indoors and outdoors becomes large in the severe winter season, so that conventional thin foam sheets cannot maintain sufficient heat insulation performance, and dew condensation causes water drops to be stored indoors. There is a problem that it may affect existing products, and a thicker foam sheet has been desired.

However, there is a limit in increasing the thickness of the foamed sheet using the organic peroxide as a crosslinking agent.
To further thicken the conventional product, it is necessary to thicken the sheet before foaming, but the thicker the sheet before foaming, the more the difference in heat conduction between the edge and center of the sheet, or the surface of the sheet and the inside. Since the end part is foamed, the center part is not foamed because the foamed sheet is extremely deformed and stress is generated, cracking is likely to occur, significantly reducing the value as a product. However, there has been a problem that the foamed sheet is made thicker.

[0009]

Therefore, the inventors of the present invention have earnestly studied for the purpose of providing a method for producing a thick crosslinked foamed sheet having a large expansion ratio, a thick wall, and a beautiful appearance without cracks or the like. As a result, the present invention has been completed.

[0010]

That is, the present invention is a method for producing a thick crosslinked foamed sheet having a high expansion ratio and a high inorganic content, which comprises an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 90% by weight. Inorganic powder 5 per 100 parts by weight of the resin, which is composed of the homopolymer or a mixture of the copolymer and one or more ethylene-based polymers selected from the group of polyethylene, polypropylene and ethylene copolymer.
0 to 500 parts by weight, flame retardant 5 to 40 parts by weight, flame retardant aid 2
˜20 parts by weight and 5 to 50 parts by weight of a foaming agent are added to the composition, and X parts by weight of dicumyl peroxide as a cross-linking agent is further added to the composition. When Y parts by weight,

[0011]

## EQU2 ## X + Y = 0.8 to 1.3 However, after extruding a resin composition compounded so that X ≧ 0.3 and Y ≧ 0.1,
It is characterized by heating above the decomposition temperature of the crosslinking agent to foam.

The ethylene-vinyl acetate copolymer used as the base resin of the thick crosslinked foamed sheet in the present invention is intended for those having a wide range of vinyl acetate content of 5 to 90% by weight.

Usually, in the ethylene-vinyl acetate copolymer, the lower the content of vinyl acetate, the higher the crystallinity of the polymer, and the polymer having a content of 5 to 40% by weight corresponds to that. Further, those having 40 to 90% by weight have extremely low crystallinity.

In any case, the melt index is 0.
A wide molecular weight of 1 to 300 can be used, but a crystalline polymer having a molecular weight of 0.5 to 10 and an amorphous polymer having a molecular weight of 10 to 100 are preferably used.

As the polyolefin resin, an ethylene polymer is preferable in terms of compatibility and molding processability. Among them, polyethylene, ethylene-α-olefin copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-propylene copolymer, ethylene-vinyl acetate-vinyl chloride copolymer are more preferable. , Ethylene-methacrylic acid copolymer, ethylene-
Examples thereof include a methyl methacrylate copolymer, an ethylene-n-butyl acrylate copolymer, an ethylene-t-butyl acrylate copolymer and the like. In the present invention, the vinyl acetate content is 5
Blending up to 30% crystalline ethylene-vinyl acetate copolymer or polyethylene with non-crystalline ethylene-vinyl acetate copolymer gives the best foamed sheet.

In the present invention, the inorganic powder is not particularly limited. For example, hydrated metal compounds such as magnesium hydroxide, aluminum hydroxide and basic magnesium carbonate, metal oxides such as alumina and titania, calcium carbonate. , Carbonates and bicarbonates such as magnesium carbonate and sodium bicarbonate, borate salts such as zinc borate, borax and barium borate, phosphate salts such as calcium phosphate, potassium metaphosphate, silicates such as talc and clay, silicic acid, gypsum Sulfates and sulfites, etc., blast furnace slag, and residual waste such as red mud.

When it is desired to obtain a highly flame-retardant foamed sheet, a hydrated metal oxide is used, and the above magnesium hydroxide,
Aluminum hydroxide and basic magnesium carbonate are preferable.

The particle size of the inorganic powder is usually 0.01 to 30 μm.
m, preferably 0.05 to 10 μm, especially 0.1 to 2 μm
A range of m is desirable. If the particle size exceeds this upper limit, the extruded sheet will become rough and the expansion ratio will decrease. If it is less than this lower limit, it is difficult to reproduce a uniformly dispersed state, and the expansion ratio is reduced.

The amount of the inorganic powder added is 50 to 500 parts by weight, preferably 80 to 250 parts by weight, particularly preferably 100 to 200 parts by weight. The reason is that if it is less than the lower limit, the effect of adding the inorganic powder cannot be exhibited, and if it is more than the upper limit, it becomes difficult to achieve high foaming.

In the present invention, the foamed sheet having particularly excellent flame retardancy uses a hydrated metal compound such as magnesium hydroxide, aluminum hydroxide or basic calcium carbonate as an inorganic substance and a so-called halogen flame retardant together.
As the halogen-based flame retardant, decabromodiphenyl ether, brombenzene and the like are commonly used.

The amount added is 5 to 40 parts by weight, preferably 5 to 30 parts by weight, more preferably 15 to 30 parts by weight. Further, in this case, a general-purpose flame retardant aid such as antimony trioxide is added in an amount of 2 to 20 parts by weight, preferably 10 to 20 parts by weight.

If the amount of the halogen-based flame retardant added is less than the lower limit of the above-mentioned amount, the effect cannot be exhibited, and if it is more than the upper limit, the foamability is impaired.

In the present invention, a foamed sheet having particularly excellent flame retardancy has an oxygen index (OI) of more than 30 obtained by a test method according to JIS-D1201-1977 "Combustion test method for organic materials for automobile interior". In addition, it also has an excellent low smoke emission property, in which the maximum extinction coefficient (C _S · max) which is an index of smoke emission is 2.7 or less.

Further, in the method of the present invention, since a large amount of the inorganic powder is contained, a surface treating agent such as a silane surface treating agent or a titanate surface treating agent is used for the purpose of improving the compatibility between the inorganic powder and the resin. May be used, especially preferred are isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate, isopropyl distearoyl methacryl titanate, monoalkoxy titanate compounds such as isopropyl diisostearoyl acrylic chicnate, maleated polybutadiene, stearic acid, stearin. It is a carboxylic acid such as vinyl acid or zinc stearate, or a metal salt or ester thereof.

Further, as the foaming agent to be blended in the present invention, various organic and inorganic pyrolyzable foaming agents can be used. Examples of the organic foaming agent include azodicarbonamide, N,
N'-dinitrosopentamethylenetetramine, P, P '
-Oxybisbenzenesulfonyl hydrazide and the like.
Examples of the inorganic foaming agent include sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide and the like.

The reason why the addition amount is limited to 5 to 50 parts by weight is that if it is less than 5 parts by weight, a high expansion ratio and a thick foam sheet cannot be obtained, and if it exceeds 50 parts by weight. This is because it does not contribute to the improvement of the foaming ratio or the wall thickness, and the efficiency remarkably deteriorates.

Further, it is indispensable that the polyolefin resin foam sheet in the present invention is crosslinked,
Without a crosslinked structure, it is impossible to increase the expansion ratio and increase the wall thickness. As the crosslinking means, crosslinking by thermal decomposition of organic peroxide is preferable, and among them, the crosslinking agent preferably used is dicumyl peroxide.

Further, in the crosslinking by the organic peroxide, the radical generated by thermal decomposition causes a hydrogen abstraction reaction from the polymer, so that the radical generated by the organic peroxide is recombined and the radical disappears, or with other substances. If the reaction is carried out, the crosslinking efficiency is extremely lowered, a good crosslinked structure cannot be obtained, and it becomes difficult to increase the expansion ratio and increase the thickness.

Therefore, it is necessary to stabilize the generated radicals and increase the crosslinking efficiency by reacting with the additive such as a crosslinking assistant faster than the generated radicals cause a recombination reaction.

As the type of such a crosslinking aid, oxime / nitroso compounds, maleimide compounds and the like are known, in addition to compounds having sulfur or a monofunctional or polyfunctional double bond, but preferably trifunctional. Most preferred are monomers, especially trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl cyanurate, triallyl isocyanurate and the like.

In the present invention, the addition amount of the cross-linking agent and the cross-linking aid is in the range of 0.8 to 1.3, and the blending parts of both are 0.3 or more and 0.1 or more, respectively. It is desirable to mix them as follows.

The reason for the above limitation is that when the sum of the compounding parts of both is less than 0.8 or the compounding parts of both are 0.3 or less and 0.1 or less, respectively, the crosslinking does not proceed sufficiently. Not only a high expansion ratio and a thick foamed sheet cannot be obtained, but also the foamed sheet adheres to a roll or the like of a manufacturing machine during the production of the foamed sheet, resulting in markedly poor productivity.

When the sum of the blending parts of both exceeds 1.3, the cross-linking proceeds too much in the course of foaming and cracks are generated in the foamed sheet, resulting in a foamed sheet having an extremely poor appearance, which makes the product valuable. It will be significantly impaired.

The mixing parts of both can be appropriately selected within the range of the above-mentioned mixing parts depending on the kinds of the base resin, the inorganic powder, the crosslinking aid, etc. to be used, whereby the wall thickness is 13 to 30 mm. It is possible to obtain a thick foamed sheet within the range.

Next, a specific example of the manufacturing process of the foamed sheet in the method of the present invention will be described. The necessary components such as the base resin, the inorganic powder, the foaming agent, the flame retardant, the flame retardant auxiliary agent, the crosslinking agent, and the crosslinking auxiliary agent are weighed and then kneaded. Banbury mixer or 2 roll mill, 2 in some cases
A shaft extruder is used. Usually, the mixture is kneaded, pelletized, and then formed into a sheet by an extruder, but a sheet may be directly extruded from a twin-screw extruder or the like to obtain a formed body.

Then, it is introduced into a heating device for foaming such as a hot air oven, an infrared heating furnace, a molten salt bath, etc., and a foamed sheet is continuously obtained. Although it depends on the size of the device and the composition of the raw materials, the foamed sheet has a thickness of 13 to 30 mm and a width of 500 to 1500 mm.

The thickness of the foamed sheet can be easily adjusted by changing the thickness of the molded sheet before foaming, but it can also be adjusted by appropriately selecting the number of blending parts of the foaming agent. However, in this case, the expansion ratio also changes.

[0038]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. In the following, “parts” means “parts by weight” and the measurement is carried out by the following method.

Thickness: The thickness of foam was measured with a dial gauge.

Density: A cube of 100 mm square was cut out from the foam, and the volume and mass were measured and calculated.

Magnification: The volume of the foamed resin sheet was a, the volume of foamed after foaming was b, and b / a was calculated as the foaming magnification.

Appearance: The presence or absence of cracks, adhesion, etc. was visually confirmed.

Oxygen index (OI): JIS D-1201-
It was measured by 1977.

Maximum extinction coefficient (C _S · max): JISD
It was measured by -1201-1977 and measured by a smoke density measuring device (manufactured by Suga Test Instruments Co., Ltd.).

Examples 1 to 7 Vinyl acetate content 19 to
87% ethylene-vinyl acetate copolymer (product of Mitsui Polychemical Co., Ltd., Evaflex 460, 360, 4
0, Dainippon Ink Co., Ltd. product, Ebaslen 450P,
310FH) 100 parts, magnesium hydroxide powder (Kyowa Chemical Co., Ltd. product, Kisuma 5B) 120 parts, isopropyl triisostearoyl titanate as a surface treatment agent (Kenrich Petrochemical Company, USA, KEN-REAT TTS) 3 parts, deca as a flame retardant. 25 parts of bromodiphenyl ether (hereinafter abbreviated as DBDE), 12 parts of antimony trioxide as a flame retardant aid,
Azodicarbonamide as a foaming agent (product of Eiwa Chemical Co., Ltd., Vinyl Hall AC # 1L, abbreviated as ADCA in the table) 2
7 parts, as a cross-linking agent, dicumyl peroxide (Mitsui Petrochemical Co., Ltd. product hereinafter, abbreviated as DCP) 0.3-0.
8 parts, a composition comprising 0.1 to 0.6 part of trimethylolpropane trimethacrylate (hereinafter abbreviated as TMPT) as a cross-linking aid was sufficiently kneaded at a temperature of 110 ° C. in a small laboratory Banbury mixer. Pelletized. Then, using a 40 mm extruder, it was formed into a sheet having a thickness of 9 mm.

This sheet was placed in a constant temperature bath at 220 ° C. for about 16 minutes.
After leaving for a minute, it was taken out to obtain a foamed sheet.

Example 8 60 parts of ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (Mitsui Polychemical Co., Ltd., Evaflex 360), medium density polyethylene (Mitsui Petrochemical Co., Ltd., Neozec 200)
6H) 40 parts, DCP 0.8 parts, TMPT 0.5 parts The same experiment as in Example 1 was performed.

(Example 9) 50 parts of ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (Evaflex 360 manufactured by Mitsui Polychemical Co., Ltd.), ethylene-ethyl acrylate copolymer having an ethyl acrylate content of 19% Coalescence (Nippon Unicar Co., Ltd. product, A-702) 50
Parts, DCP 0.9 parts, and TMPT 0.4 parts, the same experiment as in Example 1 was performed.

Example 10 100 parts of ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (Mitsui Polychemical Co., Ltd., Evaflex 360), aluminum hydroxide powder (Showa Denko Co., Ltd., Hijilite) H-42M) 120 parts, DCP 0.7 part, TMPT0.
The same experiment as in Example 1 was carried out except that the amount was 2 parts.

Example 11 100 parts of ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (Mitsui Polychemical Co., Ltd., Evaflex 360), aluminum hydroxide powder (Showa Denko Co., Ltd., Hijilite) H-42M) 60 parts, magnesium hydroxide powder (Kyowa Chemical Co., Ltd. product, Kisuma 5B) 60 parts, DCP 0.7
Part and TMPT 0.3 part, the same experiment as in Example 1 was performed.

(Example 12) 100 parts of ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (Evaflex 360, a product of Mitsui Polychemical Co., Ltd.), DCP
Example 1 except that 0.8 part and 0.5 part of triallyl isocyanurate (abbreviated as TAIC in the table) as a crosslinking aid were used.
The same experiment was performed.

(Comparative Examples 1 to 6) Medium-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., Neozec 2006H) or ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (manufactured by Mitsui Polychemical Co., Ltd., Evaflex 360). ) 100 parts, DCP 0.8-0.9 parts, TMPT
0.6 parts and a thickness of 2 to 9 m using a 40 mm extruder
The same experiment as in Example 1 was performed except that the sheet was molded into a sheet of m.

Comparative Examples 7 to 9 Vinyl acetate content 25%
100 parts of ethylene-vinyl acetate copolymer (product of Mitsui Polychemical Co., Ltd., Evaflex 360), DCP
The same experiment as in Example 1 was carried out except that the sheet was molded into a sheet having a thickness of 9 mm by using a 40 mm extruder with 0 to 1.3 parts and TMPT from 0 to 1.3 parts.

Comparative Example 10 100 parts of ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% (Evaflex 360, a product of Mitsui Polychemical Co., Ltd.), DCP
The same experiment as in Example 1 was conducted except that 1.0 part was used and 0.8 part of divinylbenzene, which is a bifunctional monomer, was used as the crosslinking aid.

The results of Examples 1 to 12 are shown in Table 1 and Comparative Example 1
The results of Nos. 10 to 10 are shown in Table 2.

[0056]

[Table 1]

[0057]

[Table 2]

From the results shown in Tables 1 and 2, when the contents of the cross-linking agent X and the cross-linking aid Y are out of the range of X + Y = 0.8 to 1.3, the foamed sheet obtained has cracks or sticking. It turns out that it causes a defect of quality.

The compositions used in Comparative Examples 1 to 3 contained 0.8 parts of the cross-linking agent in the same amount as in Examples 2, 3, 8, and 12, but the content of the cross-linking aid was large and the composition was suitable. Quantity X + Y = 0.8 ~
Since it exceeds the range of 1.3, crosslinking proceeds excessively during foaming, and when the thickness of the sheet before foaming is large, the thickness of the obtained foamed sheet is sufficient, but cracks occur,
When the thickness was small, the appearance of the foamed sheet was good, but the thickness was insufficient.

The compositions used in Comparative Examples 4-6 were the same as in Example 9.
Although it contains 0.9 parts of the same amount of the cross-linking agent as above, but the content of the cross-linking aid is large, and the appropriate content exceeds the range of X + Y = 0.8 to 1.3. Too much,
If the thickness of the sheet before foaming is large, the thickness of the obtained foamed sheet is sufficient but cracks occur, and if the thickness is small, the appearance of the foamed sheet is good but the thickness is insufficient. Met.

The compositions used in Comparative Examples 7 and 8 contained no cross-linking agent or co-agent, so that cross-linking did not proceed sufficiently, and the resulting foamed sheets were tacky, thick, and
The magnification was not enough.

The composition used in Comparative Example 9 contained the same amount of the cross-linking agent as in Example 6, but the content of the cross-linking aid was small. Therefore, the appropriate content of X + Y = 0.8 to 1.3. And the cross-linking did not proceed sufficiently, and the resulting foamed sheet was tacky, and neither the thickness nor the magnification was sufficient.

Since the composition used in Comparative Example 10 exceeds the appropriate content range of X + Y = 0.8 to 1.3, the obtained foamed sheet has a sticky appearance, thickness and magnification. It wasn't enough.

[0064]

According to the manufacturing method of the present invention, it is possible to form a thick crosslinked foamed sheet having a high expansion ratio, a thick wall, a crack and the like and a beautiful appearance. It can contribute to the improvement of heat insulation performance in cold regions,
Its industrial value is extremely large.

Claims (3)

[Claims] 1. A method for producing a thick crosslinked foamed sheet having a high expansion ratio and a high inorganic content, wherein the vinyl acetate content is 5 to 9.
Base consisting of 0% by weight of ethylene-vinyl acetate copolymer alone or a mixture of the copolymer and one or more polyolefin resins selected from the group consisting of polyethylene, polypropylene and ethylene copolymers. 50 to 500 parts by weight of inorganic powder, 5 to 50 parts by weight of flame retardant, 2 to 20 parts by weight of flame retardant aid, with respect to 100 parts by weight of resin,
When 5 to 50 parts by weight of the foaming agent is mixed, and X parts by weight of the dicumyl peroxide as a crosslinking agent and Y parts by weight of the crosslinking aid composed of the polyfunctional monomer are used, X + Y = 0.8 to 1.3 However, a resin composition containing a cross-linking agent and a cross-linking aid so that X ≧ 0.3 and Y ≧ 0.1 is extruded and molded, and then the cross-linking agent is added. A method for producing a thick crosslinked foamed sheet, which comprises foaming by heating above the decomposition temperature of. 2. The crosslinking aid is one or more trifunctional monomers selected from the group consisting of trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl cyanurate and triallyl isocyanurate. The method for producing a thick crosslinked foamed sheet according to claim 1. 3. The method for producing a thick crosslinked foamed sheet according to claim 1, wherein the thickness is in the range of 13 to 30 mm.