JP5938395B2 - Polyolefin resin foam and polyolefin resin foam dustproof material using the same - Google Patents

Description

  The present invention relates to a polyolefin resin foam and a polyolefin resin foam dustproof material using the same.

  At present, resin foams containing polystyrene resins and polyolefin resins as resin components are widely used as cushioning materials for packaging, structural members for automobiles, and the like because of their various characteristics.

  Among them, a dustproof material made of a resin foam containing a polyolefin-based resin as a resin component has attracted much attention because of its excellent cushioning properties, dustproof properties, moldability, and the like.

For example, Patent Document 1 discloses a thermoplastic polymer that is a mixture of an olefin elastomer and an olefin polymer other than the olefin elastomer, and the mixing ratio (weight basis) is 20/80 to 80/20 in the former / the latter. Further, after impregnating a high-pressure inert gas of 6 to 100 MPa at an impregnation temperature of 10 to 350 ° C., the step of reducing the pressure, the average cell diameter is 10 to 90 μm, and the repulsive load when compressed by 50% is 0. A dustproof material made of a foam having properties of 0.1 to 3.0 N / cm ² and an apparent density of 0.01 to 0.10 g / cm ³ is disclosed.

Patent Document 2 discloses a dust-proof material composed of a foam having a thickness of 0.1 to 1.0 mm, the foam having a fine cell structure having an average cell diameter of 10 to 65 μm, a 0.1 mm There is disclosed a foam dustproof material having a characteristic that a repulsive load when compressed to a thickness of 0.010 to 0.100 MPa and an apparent density of 0.01 to 0.050 g / cm ³ .

JP 2005-097566 A JP 2009-091556 A

However, the dustproof material disclosed in Patent Document 1 is too soft to be inferior in handling property (handling property), in addition to being inferior in followability to fine gaps and steps, and has the ability to prevent intrusion of dust and water. There is a problem of being insufficient.
Moreover, since the dustproof material currently disclosed by patent document 2 is a foaming dustproof material which has a fine cell structure, it is too soft and handling property is inferior. In addition, there is a problem that the repulsive load when compressed to a high degree is large, the followability is insufficient, and the followability to fine gaps and steps is inferior.

Moreover, even when these foamed dustproof materials are crushed in the thickness direction and used in order to further improve the followability to fine gaps and steps, the foamed dustproof materials described in Patent Documents 1 and 2 can be easily used. It cannot be crushed and the followability is insufficient, and even if the followability is sufficient, the foam dustproof material tries to restore in the thickness direction after long-term use, and there is a problem that long-term reliability is lacking. It was.
Therefore, the present inventors can easily crush with low load (followability) by using a resin foam having specific physical properties, and prevent entry of dust, water, etc. from fine gaps and steps, In addition, the inventors have found that a dustproof material that maintains the shape and dustproof / waterproof performance can be obtained even after long-term use, and have completed the present invention.

As a result of intensive studies to solve the above problems, the thickness was 0.1 to 3.0 mm, the average bubble diameter was 0.02 to 0.2 mm, and the apparent density was 30 to 100 kg / m ³ .
The compression stress when compressed by 50% is 15 KPa or more,
A polyolefin resin foam having a compressive stress of 400 KPa or less when compressed by 80% is excellent in handling property (handling property) when used as a dustproof material, and easily crushed (following property) with a low load. It has been found that it becomes a dustproof material capable of preventing entry of dust, water, etc. from fine gaps and steps for a long period of time.

  In particular, when the foamed structure of the polyolefin resin foam of the present invention is an open-cell structure, a dustproof material further excellent in followability, dimensional stability, and long-term stability can be provided.

That is, the present invention has a thickness of 0.1 to 3.0 mm, an average bubble diameter of 0.02 to 0.2 mm, an apparent density of 30 to 100 kg / m ³ ,
The compression stress when compressed by 50% is 15 KPa or more,
A polyolefin-based resin foam characterized by having a compressive stress of 400 KPa or less when compressed by 80%.
Moreover, it is a foaming dustproof material using the said polyolefin resin foam.

The polyolefin-based resin foam of the present invention has a small average bubble diameter and an appropriate strength due to the above-described configuration, so when used as a dustproof material, it has excellent handling properties, such as dust and water from fine gaps and steps. It becomes a foamed dustproof material with excellent followability that prevents intrusion and easily crushes at low loads.
In addition, the polyolefin resin foam of the present invention has little change over time (high dimensional accuracy) even when highly compressed, and thus has long-term dust resistance when used as a dustproof material, for example. It will be a thing.

When the foamed structure of the polyolefin resin foam of the present invention is an open-cell structure, it can be more easily crushed with a low load, and the apparent magnification can be made more non-foamed.
Therefore, while maintaining high dust resistance, there is little shape change over time, and the dimensional stability is more excellent.

The present invention has a thickness of 0.1 to 3.0 mm, an average cell diameter of 0.02 to 0.2 mm, an apparent density of 30 to 100 kg / m ³ ,
The compression stress when compressed by 50% is 15 KPa or more,
A polyolefin-based resin foam characterized by having a compressive stress of 400 KPa or less when compressed by 80%.

The polyolefin resin foam of the present invention has a lower limit of thickness of 0.1 mm and an upper limit of 3.0 mm. When the thickness is less than 0.1 mm, the strength of the polyolefin-based resin foam is insufficient, and handling properties are deteriorated. When the thickness exceeds 3.0 mm, the compressive stress of the polyolefin resin foam becomes too large, resulting in poor followability, and intrusion of dust, water, etc. from minute gaps or steps when used as a dustproof material. It cannot be prevented. The preferable lower limit of the thickness is 0.2 mm, and the preferable upper limit is 1.5 mm.
In addition, in order to adjust to the said thickness range, you may give the process by a slice etc. suitably.

  In the polyolefin resin foam of the present invention, the lower limit of the average cell diameter is 0.02 mm, and the upper limit is 0.2 mm. When the average cell diameter is less than 0.02 mm, the strength of the polyolefin-based resin foam is insufficient, and handling properties are deteriorated. When the average bubble diameter exceeds 0.2 mm, the followability deteriorates, and when used as a dustproof material, it becomes impossible to prevent the entry of dust, water, etc. from fine gaps or steps. The preferable lower limit of the average cell diameter is 0.04 mm, and the preferable upper limit is 0.15 mm.

The polyolefin resin foam of the present invention has an apparent density lower limit of 30 kg / m ³ and an upper limit of 100 kg / m ³ . When the apparent density is less than 30 kg / m ³ , the strength of the polyolefin-based resin foam is insufficient, and handling properties are deteriorated. When the apparent density exceeds 100 kg / m ³ , the compressive stress of the polyolefin resin foam becomes too large, resulting in poor followability. When used as a dustproof material, dust or water from fine gaps or steps Intrusion cannot be prevented. The preferable lower limit of the apparent density is 35 kg / m ³ , the preferable upper limit is 90 kg / m ³ , the more preferable lower limit is 40 kg / m ³ , and the more preferable upper limit is 70 kg / m ³ .

The polyolefin resin foam of the present invention has a lower limit of compressive stress of 15 KPa when compressed by 50%. When the compressive stress when compressed by 50% is less than 15 KPa, the strength of the polyolefin resin foam is insufficient, and the handling property is deteriorated. The preferable lower limit of the compressive stress when compressed by 50% is 35 KPa, and the more preferable lower limit is 40 KPa.
Further, the upper limit of the compressive stress when compressed by 50% is not particularly limited, but is preferably 100 KPa or less, more preferably 90 KPa or less, and further preferably 80 KPa or less from the viewpoint of followability. .

Moreover, the upper limit of the compressive stress when the polyolefin resin foam of the present invention is compressed by 80% is 400 KPa. When the compressive stress when compressed by 80% exceeds 400 KPa, it cannot be easily compressed, the repulsive force becomes stronger and the followability becomes worse. When used as a dustproof material, It becomes impossible to prevent intrusion of dust or water from the step. A preferable upper limit of the compressive stress when compressed by 80% is 380 KPa, and a more preferable upper limit is 350 KPa.
Further, the lower limit of the compressive stress when compressed by 80% is not particularly limited, but is preferably 100 KPa or more, more preferably 150 KPa or more, and further preferably 180 KPa or more from the viewpoint of sealing properties. .

  The foam structure of the polyolefin resin foam of the present invention is preferably an open cell structure. Here, the open cell structure means that the open cell rate measured by the measurement method described later is 60% or more. Since the open cell ratio is 60% or more, it can be easily crushed with a low load, and the shape can be maintained with little dimensional change even after long-term use. Etc. can be prevented. Preferably it is 65% or more, more preferably 70% or more.

  The surface hardness of the polyolefin resin foam of the present invention is not particularly limited, but the preferred lower limit is 50 and the preferred upper limit is 100. If the surface hardness is less than 50, followability cannot be maintained, and when used as a dustproof material, it may not be possible to prevent entry of dust, water, and the like from fine gaps and steps over time. If the surface hardness exceeds 100, it cannot be easily compressed, the repulsive force becomes strong and the followability becomes poor, and when used as a dustproof material, it prevents the entry of dust, water, etc. from minute gaps or steps. It may not be possible. The more preferable lower limit of the surface hardness is 55, the more preferable upper limit is 95, the still more preferable lower limit is 60, and the still more preferable upper limit is 90.

The polyolefin resin foam of the present invention having the above physical properties is, for example, a polyolefin resin having a melting point in the range of 140 to 180 ° C. and a deflection temperature under load of 80 to 140 ° C., a melting point in the range of 140 to 180 ° C. and It can be produced by extrusion foaming a mixed resin composition containing a thermoplastic elastomer having a softening point of 45 to 160 ° C.
Hereinafter, although this manufacturing method is explained in full detail, this invention is not limited to this manufacturing method.

(Polyolefin resin)
The preferable lower limit of the melting point of the polyolefin resin is 140 ° C., and the preferable upper limit is 180 ° C. When the melting point of the polyolefin-based resin is less than 140 ° C., the dimensional stability may be inferior when used in a high temperature environment. Specifically, when used as a dustproof material, the foam may be deformed by a high temperature and followability to fine clearance may be inferior. If the melting point of the polyolefin resin exceeds 180 ° C., it is necessary to knead the resin at a high temperature, so that in addition to causing thermal deterioration of the polyolefin resin, the physical properties of other additive resins may be significantly reduced. The minimum with more preferable melting | fusing point of polyolefin resin is 155 degreeC, and a more preferable upper limit is 170 degreeC.

The preferable lower limit of the deflection temperature under load of the polyolefin resin is 80 ° C., and the preferable upper limit is 140 ° C. If the deflection temperature under load of the polyolefin resin is less than 80 ° C., the dimensional stability may be inferior when used in a high temperature environment. Specifically, when used as a dustproof material, the foam may be deformed by a high temperature and followability to fine clearance may be inferior. When the deflection temperature under load of the polyolefin resin exceeds 140 ° C, it is necessary to knead the resin at a high temperature. In addition to causing thermal degradation of the polyolefin resin itself, the physical properties of other additive resins must be significantly reduced. There is. The more preferable lower limit of the deflection temperature under load of the polyolefin resin is 90 ° C., and the more preferable upper limit is 130 ° C.

Although it does not specifically limit as a melt flow rate (MFR) of the said polyolefin resin, A preferable minimum is 0.2 g / 10min and a preferable upper limit is 5 g / 10min. When the MFR of the polyolefin resin is less than 0.2 g / 10 min, the load on the extruder increases and the productivity decreases, or the melted polyolefin resin containing a foaming agent smoothly flows in the mold. It may become impossible to flow and unevenness may occur on the surface of the resulting polyolefin resin foam, resulting in a decrease in appearance. If the MFR of the polyolefin resin exceeds 5 g / 10 min, the resin pressure in front of the ring die will decrease, and the resin pressure in the ring die bubble generation section will also decrease, so bubbles will be generated in front of the bubble generation section. If the foam formation part suddenly causes foam breakage, the foaming property is lowered, and the appearance of the resulting polyolefin resin foam may be lowered, or the polyolefin resin foam may not be obtained. The more preferable lower limit of MFR of the polyolefin resin is 0.25 g / 10 min, the more preferable upper limit is 4 g / 10 min, the still more preferable lower limit is 0.3 g / 10 min, and the more preferable upper limit is 3.5 g / 10 min.

In addition, in this specification, MFR of polyolefin resin means what was measured by the test temperature of 230 degreeC and the test load of 21.18N based on B method of JISK7210: 1999.
Moreover, MFR of polyolefin resin means what measured MFR of the resin by the said method, when the polyolefin resin was used individually by 1 type. When two or more types of polyolefin resins are mixed and used, the MFR of each polyolefin resin is measured by the above measuring method, and the value calculated from the respective MFR values as follows: .
That is, when the polyolefin resin is a mixture of n types of polyolefin resins, MFR of polyolefin resin 1 is MFR ₁ , MFR of polyolefin resin 2 is MFR ₂ ,... MFR of polyolefin resin n Is MFR _n , the content of the polyolefin resin 1 is C1, the content of the polyolefin resin 2 is C2,... The content of the polyolefin resin n is Cn. In addition, content of polyolefin resin n shall remove | divide the weight of polyolefin resin n by the weight of the whole polyolefin resin. And MFR of polyolefin resin is computed by a following formula.
Melt flow rate (g / 10min) = (MFR ₁ ) ^C1 x (MFR ₂ ) ^C2 x ... x (MFR _n ) ^Cn

The polyolefin resin is not particularly limited as long as it has the above physical properties, and specific examples thereof include homopolypropylene, copolymers of propylene and other olefins, and the like.
The copolymer of propylene and another olefin may be either a random copolymer or a block copolymer, but a block copolymer is preferred because of excellent heat resistance.
Examples of other olefins copolymerized with propylene include, in addition to ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, and the like. An α-olefin having 4 to 10 carbon atoms.
Among these, homopolypropylene and block copolymer polypropylene which are excellent in foamability and heat resistance are preferable, and homopolypropylene which is further excellent in heat resistance is more preferable.

Moreover, as said polyolefin resin, since it is excellent in foamability, it is preferable to use a high melt tension polypropylene resin. High melt tension polypropylene resins include high melt tension polypropylene (HMS-PP) that has free-end long-chain branching in the molecular structure, such as electron beam cross-linking, and high molecular weight components to increase melt tension. There are things. Commercially available products can be used as the high melt tension polypropylene, and specific examples thereof include trade name “Newstrain SH9000” manufactured by Nippon Polypro Co., Ltd. and trade name “DaployWB135HMS” manufactured by Borealis.
The said polyolefin resin may be used independently and 2 or more types may be used together.

(Thermoplastic elastomer)
The minimum with preferable melting | fusing point of the said thermoplastic elastomer is 140 degreeC, and a preferable upper limit is 180 degreeC. If the melting point of the thermoplastic elastomer is less than 140 ° C., the dimensional stability may be inferior when used in a high temperature environment. Specifically, when used as a dustproof material, the foam may be deformed by a high temperature and followability to fine clearance may be inferior. If the melting point of the thermoplastic elastomer exceeds 180 ° C., it is necessary to knead the resin at a high temperature. In addition to causing thermal degradation of the thermoplastic elastomer itself, the physical properties of other polyolefin resins or additive resins are significantly reduced. There are things to do. A more preferable lower limit of the melting point of the thermoplastic elastomer is 150 ° C., and a more preferable upper limit is 170 ° C.

The preferable lower limit of the softening point of the thermoplastic elastomer is 45 ° C, and the preferable upper limit is 160 ° C. When the softening point of the thermoplastic elastomer is less than 45 ° C., the dimensional stability may be inferior when used in a high temperature environment. Specifically, when used as a dustproof material, the foam may be deformed by a high temperature and followability to fine clearance may be inferior. When the softening point of the thermoplastic elastomer exceeds 160 ° C., it is necessary to knead the resin at a high temperature. In addition to causing thermal deterioration of the thermoplastic elastomer itself, the physical properties of other polyolefin resins or additive resins are remarkably increased. May decrease. A more preferable lower limit of the softening point of the thermoplastic elastomer is 70 ° C, and a more preferable upper limit is 150 ° C.

The melt flow rate (MFR) of the thermoplastic elastomer is not particularly limited, but the preferable lower limit is 0.1 g / 10 min, and the preferable upper limit is 20 g / 10 min. When the MFR of the thermoplastic elastomer is less than 0.1 g / 10 min, the load on the extruder increases and the productivity decreases, or the molten thermoplastic elastomer containing the foaming agent smoothly flows in the mold. It may become impossible to flow and unevenness may occur on the surface of the resulting polyolefin resin foam, resulting in a decrease in appearance. If the MFR of the thermoplastic elastomer exceeds 20 g / 10 min, the resin pressure in front of the ring die will decrease, and the resin pressure in the ring die bubble generation section will also decrease, so bubbles will be generated in front of the bubble generation section. If the foam formation part suddenly causes foam breakage, the foaming property is lowered, and the appearance of the resulting polyolefin resin foam may be lowered, or the polyolefin resin foam may not be obtained. The more preferable lower limit of MFR of the thermoplastic elastomer is 0.2 g / 10 min, and the more preferable upper limit is 15 g / 10 min.

Although it does not specifically limit as hardness of the said thermoplastic elastomer, From the point from which the polyolefin-type resin foam which has the outstanding softness | flexibility is obtained, it is preferable that it is 90 or less by the duro A hardness prescribed | regulated by JISK6253. More preferably, it is about 80.

The thermoplastic elastomer has a structure in which a hard segment and a soft segment are combined, exhibits rubber elasticity at room temperature, and has a property that it can be plasticized and molded at a high temperature in the same manner as a thermoplastic resin. Generally, the hard segment is a polyolefin resin such as polypropylene or polyethylene, and the soft segment is a rubber component such as an ethylene-propylene-diene copolymer or an ethylene-propylene copolymer or amorphous polyethylene.
The thermoplastic elastomer is a polymerization type elastomer that is produced directly in a polymerization reaction vessel by polymerizing a monomer that becomes a hard segment and a monomer that becomes a soft segment; kneading such as a Banbury mixer or a twin screw extruder Blend type elastomer produced by physically dispersing polyolefin resin as hard segment and rubber component as soft segment using a machine; hard using kneader such as Banbury mixer and twin screw extruder By adding a crosslinking agent when physically dispersing the polyolefin resin that becomes the segment and the rubber component that becomes the soft segment, the rubber component is completely or partially crosslinked and microdispersed in the polyolefin resin matrix. The resulting dynamically crosslinked elastomer And the like.

In the present invention, both a non-crosslinked elastomer and a crosslinked elastomer can be used. When a non-crosslinked elastomer produced by physically dispersing a rubber component that becomes a soft segment is used, the produced product is recycled. In consideration of the properties, it is possible to easily manufacture with an extruder similar to the case of extrusion foam molding of a normal polyolefin resin, and further, the foam molded product is recycled and supplied to the extruder again to perform the same foam molding. Even in this case, poor foaming due to the crosslinked rubber can be suppressed. On the other hand, when a crosslinked elastomer obtained by physically dispersing the rubber component serving as the soft segment and simultaneously partially or dynamically crosslinking the rubber component is used, it has excellent compatibility with the polyolefin-based resin, and can be obtained. It is preferable because the heat resistance of the foam is increased.
Examples of the diene component constituting the ethylene-propylene-diene copolymer elastomer include ethylidene norbornene, 1,4-hexadiene, dicyclopentadiene, and the like.
Here, the ethylene-propylene-diene copolymer elastomer may be used singly or in combination of two or more, and by using such an ethylene-propylene-diene copolymer elastomer, a normal polyolefin is used. Manufacture with an extruder similar to the case of extrusion foam molding of a resin is facilitated.

(Mixed resin composition)
Although it does not specifically limit as a melt flow rate (MFR) of the said mixed resin composition, A preferable minimum is 0.1 g / 10min and a preferable upper limit is 3 g / 10min. When the MFR of the mixed resin composition is less than 0.1 g / 10 min, the load on the extruder increases, the productivity decreases, and the molten polyolefin resin containing the foaming agent smoothly flows in the mold. It may not be able to flow, and corrugate may be generated on the surface of the resulting polyolefin resin foam to deteriorate the appearance. When the MFR of the mixed resin composition exceeds 3 g / 10 min, when an annular die is used as the mold, the resin pressure in front of the annular die is lowered, and the resin pressure in the annular die bubble generating part is also lowered. Therefore, bubbles are generated in front of the bubble generation part, and foaming is suddenly generated in the foam forming part, resulting in a decrease in foaming property, and the appearance of the resulting polyolefin resin foam is reduced. There is a possibility that a foam cannot be obtained. The more preferable lower limit of MFR of the mixed resin composition is 0.2 g / 10 min, and the more preferable upper limit is 2.5 g / 10 min.

Although it does not specifically limit as a ratio of the said polyolefin resin and thermoplastic elastomer in the said mixed resin composition, It is preferable that it is the range of 20: 80-80: 20 by mass ratio. If the content of the thermoplastic elastomer is less than this range, the resulting polyolefin resin foam may have poor buffering properties and flexibility. If the content of the thermoplastic elastomer is more than this range, the rubber elasticity of the mixed resin composition becomes too strong and the foamability may be lowered, or the shrinkage of the resulting polyolefin resin foam may be increased. A more preferable range of the ratio between the polyolefin resin and the thermoplastic elastomer is 40:60 to 60:40.

(Bubble nucleating agent)
When producing the polyolefin resin foam of the present invention, it is preferable to use a cell nucleating agent. The cell nucleating agent promotes the generation of cell nuclei when the polyolefin-based resin foaming composition forms cells, and has an effect on the refinement and uniformity of the cells.
Examples of the cell nucleating agent include talc, mica, silica, diatomaceous earth, alumina, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, and sulfuric acid. Inorganic compounds such as potassium, barium sulfate, sodium hydrogen carbonate and glass beads; organic compounds such as polytetrafluoroethylene, azodicarbonamide, a mixture of sodium hydrogen carbonate and citric acid, and inert gases such as nitrogen. Of these, talc is preferable for inorganic compounds and polytetrafluoroethylene is preferable for organic compounds because it is highly effective in reducing bubbles. Further, it is particularly preferable that the polytetrafluoroethylene becomes a fibril when dispersed to increase the melt tension of the resin.

The amount of the cell nucleating agent is not particularly limited, but a preferable lower limit is 0.01 parts by weight and a preferable upper limit is 15 parts by weight with respect to 100 parts by weight of the mixed resin composition. When the amount of the cell nucleating agent is less than 0.01 parts by weight, it is difficult to increase the number of bubbles of the obtained polyolefin resin foam, and the surface smoothness of the resulting polyolefin resin foam is lowered. There is. When the amount of the cell nucleating agent exceeds 15 parts by weight, secondary aggregation is likely to occur, and the surface smoothness of the foam due to poor extrusion foaming may be deteriorated. A more preferable lower limit of the amount of the cell nucleating agent is 0.1 parts by weight, and a more preferable upper limit is 12 parts by weight.

The cell nucleating agent used in the present invention may be mixed with the mixed resin composition in its own form, or may be individually supplied into the extruder. Moreover, you may mix with a mixed resin composition as a masterbatch, and may supply separately in an extruder.
The base resin of the master batch is not particularly limited as long as it has excellent compatibility with the mixed resin composition. For example, homopolypropylene, block polypropylene, random polypropylene, low density polyethylene, high density polyethylene, etc. are preferably used. can do.

In the polyolefin resin foaming composition used in the present invention, various additives usually used for foam molding can be blended as optional components in addition to the polyolefin resin and the cell nucleating agent. Examples of the additive include a weather resistance stabilizer, a light stabilizer, a pigment, a dye, a flame retardant, a crystal nucleating agent, a plasticizer, a lubricant, a surfactant, a dispersant, an ultraviolet absorber, an antioxidant, and a filler. , Reinforcing agents, antistatic agents and the like. Of these, the surfactant imparts slipperiness and anti-blocking property. Moreover, a dispersing agent improves the dispersibility of an inorganic filler, for example, higher fatty acid, higher fatty acid ester, higher fatty acid amide etc. are mentioned.
The addition amount of the additive can be appropriately selected within a range not impairing the formation of bubbles and the physical properties of the resulting foam, and the addition amount used for molding a normal thermoplastic resin can be adopted.
The additive can also be used as a masterbatch for ease of handling, prevention of contamination of the production environment due to powder scattering, and improvement of dispersibility in the thermoplastic resin.
The masterbatch can be usually performed by kneading an additive or the like in a thermoplastic base resin at a high concentration to form a pellet. The base resin is not particularly limited as long as it has excellent compatibility with the mixed resin composition. For example, homopolypropylene, block polypropylene, random polypropylene, low density polyethylene, high density polyethylene, and the like are preferably used. Can do.

(Foaming agent)
As the foaming agent, a known foaming agent that can be used for extrusion foaming can be used. Since it is easy to adjust the expansion ratio, a physical foaming agent supplied by being press-fitted into the extruder is preferable. In the present invention, it is particularly preferable to use carbon dioxide. By using carbon dioxide in the supercritical state, subcritical state, or liquefied carbon dioxide, fine bubbles can be formed more than conventional foams, and the surface smoothness of the resulting polyolefin resin foam And flexibility can be improved. The amount of the foaming agent that is press-fitted into the extruder may be adjusted as appropriate according to the expansion ratio of the polyolefin resin foam. However, if the amount is small, the expansion ratio of the polyolefin resin foam is reduced, and the weight and On the other hand, heat insulation may decrease, but if it is large, foaming may occur in the mold, resulting in bubble breakage or large voids in the polyolefin resin foam. The amount is preferably about 1 to 10 parts by weight, more preferably about 2 to 8 parts by weight, and particularly preferably about 3 to 6 parts by weight with respect to 100 parts by weight of the composition.

(Extruder)
In the method for producing a polyolefin resin foam of the present invention, any of a single screw extruder, a twin screw extruder, and a tandem type extruder can be used as the extruder. Among these, a tandem type extruder is preferable because it is easy to adjust the extrusion conditions.

  The mold used in the above manufacturing method has an annular ring having a bubble generation part formed by constricting the resin flow path and a foam molding part for growing the generated bubbles and smoothing the foam surface. Consists of dies. Since the polyolefin resin foam of the present invention has finer bubbles than the conventional one, when foamed using a conventional annular die, a large number of corrugates are generated on the surface of the foam and obtained. The surface smoothness of the foam deteriorates. However, the annular die of the foam forming part can suppress the generation of corrugation in the bubble generating part and obtain a foam with a smooth surface by an appropriate slip resistance in the foam molded part. Here, the corrugated means a large number of ridges and valleys formed by undulation of the foam from the annular die so as to absorb the linear expansion in the circumferential direction due to volume expansion.

In the said manufacturing method, it is preferable that the resin discharge speed V in a bubble production | generation part is 50-300 kg / cm < ² > / hr, and the resin pressure in front of an annular die shall be 7 Mpa or more.
Discharge speed V is more preferably about 70~250kg / ^cm 2 · hr, and more preferably about 100~200kg / ^cm 2 · hr. The resin pressure before the ring die is preferably 7 MPa or more, and more preferably 8 MPa or more and 20 MPa or less. In addition to improving the foamability of the polyolefin-based resin by extrusion foaming under the above conditions, the bubbles can be refined and the strength of the cell membrane can be further increased. Under these conditions, the obtained foam is improved in workability in the case of secondary processing, and a sheet-like foam obtained by slicing is excellent in surface smoothness. When the discharge speed V is less than about 50 kg / cm ² · hr, it may be difficult to obtain finer bubbles or a foam with a high expansion ratio. On the other hand, when it is larger than about 300 kg / cm ² · hr, the resin generates heat at the mold bubble generation part, causing bubble breakage, and the foaming ratio is likely to be lowered, and a corrugated corrugate is likely to be generated. This is not preferable because the diameter becomes uneven and the surface smoothness of the foam decreases. The discharge speed V is appropriately adjusted according to the cross-sectional area of the annular die bubble generating unit and the extrusion discharge amount.

  The method of adjusting the cross-sectional area of the bubble generating part includes changing the length of the bubble generating part of the mold (in the case of a flat mold) and the diameter (in the case of an annular die) and the interval between the bubble generating parts of the mold. There are two methods including a method of changing (in the case of a flat die or an annular die).

If the resin pressure in front of the annular die is lower than 7 MPa, bubble generation starts before the annular die bubble generation part and a good foam cannot be obtained, which is not preferable. On the other hand, if the pressure is higher than 20 MPa, the load on the extruder becomes too high, or the injection pressure of the foaming agent becomes too high, so that it is not possible to press-fit.
The resin pressure in front of the annular die is appropriately adjusted by the molten resin viscosity, the extrusion discharge amount, and the sectional area of the annular die bubble generating part. Furthermore, the molten resin viscosity is appropriately adjusted depending on the viscosity of the blended resin composition, the amount of foaming agent added, and the molten resin temperature. In this specification, the molten resin temperature refers to the temperature measured by a thermocouple attached in a direct contact with the molten resin in a straight pipe mold for measuring the resin pressure before the annular die. say.

(Foam dustproof material)
The foaming dustproof material (foaming sealing material) of this invention is comprised from the polyolefin resin foam which has the above specific characteristics. Although the foam dustproof material effectively exhibits its function even in the form of a foam alone, a foam dustproof material in which an adhesive layer is provided on one or both surfaces of the foam is easy to use and is preferred. For example, if the foamed dustproof material has an adhesive layer on one or both sides of the foam, it can be fixed or temporarily fixed to an adherend that requires dustproofing.

The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and examples thereof include acrylic pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives (natural rubber-based pressure-sensitive adhesives, synthetic rubber-based pressure-sensitive adhesives), silicone-based pressure-sensitive adhesives, and polyester-based pressure-sensitive adhesives. , Urethane pressure-sensitive adhesives, polyamide-based pressure-sensitive adhesives, epoxy-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, fluorine-based pressure-sensitive adhesives, and the like can be appropriately selected and used. An adhesive may be used independently and may be used in combination of 2 or more type. The pressure-sensitive adhesive may be any form of pressure-sensitive adhesive such as an emulsion-based pressure-sensitive adhesive, a solvent-based pressure-sensitive adhesive, an oligomer-based pressure-sensitive adhesive, or a solid-type pressure-sensitive adhesive.
As the pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive is suitable from the viewpoint of preventing contamination of the adherend.

  The pressure-sensitive adhesive layer can be formed using a known formation method. For example, a method of applying a pressure-sensitive adhesive on a predetermined part or surface (coating method), a pressure-sensitive adhesive is formed on a release film such as a release liner to form a pressure-sensitive adhesive layer, and then the pressure-sensitive adhesive layer is Alternatively, a method of transferring onto the surface (transfer method) and the like can be mentioned. In forming the adhesive layer, a known coating method (casting method, roll coater method, reverse coater method, doctor blade method, etc.) can be appropriately used.

  The thickness of the adhesive layer is usually about 5 to 100 μm. The thinner the adhesive layer, the higher the effect of preventing the adhesion of dust and dirt at the end, and thus the thinner the adhesive layer, the better.

  Furthermore, when the adhesive layer is formed only on one side (one side) of the foam, another layer may be formed on the other side of the foam, for example, other types of adhesives. Layer and the like.

  The shape, thickness and the like of the foam dustproof material of the present invention are not particularly limited, and can be appropriately selected depending on the application. For example, the thickness of the foam dustproof material can be selected from a range of about 0.1 to 3 mm (preferably 0.3 to 2 mm).

  Moreover, as foaming dust-proof materials, processes, such as a punching process, are usually made into various shapes according to the apparatus used, and are commercialized.

  Since the foamed dustproof material of the present invention has the characteristics as described above, it is easy to construct, has almost no change in thickness over time, and has excellent sealing properties, dimensional accuracy, and dimensional stability.

(Measuring method)
The measurement method is described below.
<Average bubble diameter>
In the present specification, the average cell diameter of the polyolefin resin foam is measured as follows in accordance with the test method of ASTM D2842-69.
Specifically, the foamed sheet is cut along the MD direction (extrusion direction) and the TD direction (direction perpendicular to the extrusion direction), and the center of each cut surface is scanned by an electron microscope (manufactured by Hitachi, Ltd.). S-3000N) and enlarged.
Next, the photographed image is printed on A4 paper, and a straight line having a length of 60 mm is drawn on the image. The cut surface cut in the MD direction is parallel to the MD direction, the cut surface cut in the TD direction is parallel to the TD direction, and the VD direction (thickness direction) is perpendicular to the MD direction and the TD direction (sheet). Draw a straight line (perpendicular to). At this time, the magnification in the electron microscope was adjusted so that about 10 to 20 bubbles were formed on a straight line of 60 mm.
The average chord length (t) of the bubbles was calculated from the number of bubbles present on the straight line by the following formula, and the average chord length was defined as the average bubble diameter in each direction (MD direction, TD direction, and VD direction).
Average string length t = 60 / (number of bubbles × photo magnification)
When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. Also, if some of the bubbles come into point contact with a straight line, this bubble is included in the number of bubbles, and if both ends of the straight line are located in the bubble without penetrating the bubbles Includes the bubbles in which both ends of the straight line are located in the number of bubbles.
Based on the average chord length t calculated by the above formula, the bubble diameter is calculated by the following formula.
Bubble diameter (mm) D = t / 0.616
The arithmetic average value of the obtained bubble diameter in the MD direction (DMD), the bubble diameter in the TD direction (DTD), and the bubble diameter in the VD direction (DVD) is defined as the average bubble diameter of the polyolefin resin foam.
Average bubble diameter (mm) = (DMD + DTD + DVD) / 3

<Apparent density>
In the present specification, the apparent density of the polyolefin resin foam is measured by a method based on the method described in JIS K 7222-1999. Specifically, a test piece of 10 cm ³ or more (100 cm ³ or more in the case of semi-rigid and soft materials) is cut from the sample so as not to change the original cell structure of the sample, and its mass is measured. calculate.
Density (kg / m ³ ) = test piece mass (g) / test piece volume (cm ³ ) × 10 ³

<Compressive stress>
In this specification, the compressive stress of the polyolefin resin foam is measured by a method based on the method described in JIS K6767 Foamed Plastic-Polyethylene Test Method. Specifically, the compression stress is measured when a sample cut to 50 mm × 50 mm is compressed at 1 mm / min. As a measuring device, Tensilon universal testing machine UCT-10T manufactured by Orientec Corporation can be used. The tested thickness is about 2 mm.

<Open cell ratio>
In the present specification, the measurement of the open cell ratio of the polyolefin resin foam refers to that measured as follows. Specifically, a sample cut to a 25 mm square is superimposed on a thickness of 5 cm, an apparent volume is calculated, and the following formula is calculated.
Open cell ratio (%) = {apparent volume−actual volume (measured value)} ÷ apparent volume × 100
As the measuring device, a Mictomerix dry automatic density meter Accupic II 1340 (V1.0) manufactured by Shimadzu Corporation can be used.

<Surface hardness>
In the present specification, the measurement of the surface hardness of the polyolefin resin foam refers to the value measured as follows. Specifically, a sample with a smooth surface cut to 50 mm square is superimposed on a thickness of about 6 mm or more, and the pressure surface of the instrument is pressed against the surface of the sample placed horizontally, and the memory after loading a 1 kg weight is read. It was. As a measuring device, an Asker rubber hardness meter CSC2 manufactured by Kobunshi Keiki Co., Ltd. is used.

<Melting point>
The melting point refers to a value measured as described below in accordance with the method for measuring the transition temperature of JIS K7121 plastic.
Specifically, heating / cooling rate: 10
C./min., Measurement start / end temperature: -40.degree. A differential scanning calorimeter (DSC) of model number DSC6220 manufactured by SII Nano Technology is used as the measuring device.

<MFR>
MFR refers to a value measured as follows in accordance with the flow test method of JIS K7210 thermoplastics.
Specifically, the measurement is performed at a test temperature of 230 ° C., a test load of 21.18 N, and a preheating time of 5 minutes. A semi-auto melt indexer manufactured by Toyo Seiki Seisakusho is used for the measuring device.

<Load deflection temperature>
The deflection temperature under load refers to a value measured according to JIS K7191 B method.

<Softening point>
The softening point refers to a value measured as follows in accordance with a softening temperature measurement method by thermomechanical analysis (TMA) of JIS K7196 thermoplastic film and sheet.
Specifically, measurement is performed with test piece size: Φ10 × 1 (mm), heating rate: 5 ° C./min, measurement mode: test mode with needle (tip Φ1 mm), load: 500 mN. As the measuring device, EXSTAR TMA / SS6100, which is a heat / stress / strain measuring device manufactured by SII Nano Technology, is used.

<IP code>
The IP code is a value measured in the following manner in accordance with an IP code measuring method based on a protection grade (IP code) by an outer shell of JIS C0920 electric machine equipment.
Specifically, IP43 having a diameter of 1.0 mm or more that is protected against the invasion of foreign solids having a diameter of 1.0 mm or more and that is not adversely affected by spray water within 60 degrees from the vertical. IP44 that is protected against intrusion of foreign solids and is not adversely affected by splashes from any direction. IP57 was designated as IP57 which did not hinder normal operation even if there was a slight intrusion of dust and was not adversely affected even when immersed in water for a specified pressure and time.

<Concavity and convexity followability>
An acrylic plate having a size of 200 mm × 200 mm square and a thickness of 10 mm and having unevenness with a height of 1 mm uniformly on one side at intervals of 5 mm was used. Two acrylic plates were used and overlapped so that the concavo-convex surfaces overlapped, and a 100 mm × 100 mm square foam was sandwiched between them in a uniform manner, and the four corners were fixed. Thereafter, the foam was compressed by 50% with respect to the thickness, and the followability with respect to the unevenness of 1 mm height in the compressed state was visually observed.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited by these. In each example, parts and% are based on weight in principle.
[Example 1]
A tandem extruder was prepared by connecting a second extruder having a diameter of 75 mm to the tip of a first extruder having a diameter of 65 mm.
In the first extruder of this tandem type extruder, 60 parts by weight of polyolefin resin (E110G manufactured by Prime Polymer Co., Ltd., melting point: 161 ° C., deflection temperature under load: 115 ° C., MFR: 0.3 g / 10 min) was added to non-crosslinked ethylene. -100 wt. Of mixed resin composition to which 40 parts by weight of thermoplastic elastomer (Propylene-diene copolymer elastomer, Thermoran Z101N, melting point: 170 ° C., softening point: 142 ° C., MFR: 11 g / 10 min) manufactured by Mitsubishi Chemical Corporation was added. A polyolefin-based resin foaming composition in which 10 parts by weight of a master batch containing 70% by weight of talc having an average particle diameter of 12 μm as a cell nucleating agent was mixed into the first extruder was melt-kneaded. 4.2 parts by weight of carbon dioxide in a supercritical state as a blowing agent is injected from the middle of the first extruder, and the foamed polyolefin resin foaming composition and carbon dioxide are uniformly mixed and kneaded. The molten resin composition containing the agent was continuously supplied to the second extruder and melted and kneaded while cooling to a resin temperature suitable for foaming. Then, the bubble generating part diameter φ36 mm of the mold attached to the tip of the second extruder, the bubble generating part interval of the mold 0.25 mm (cross-sectional area of the bubble generating part: 0.275 cm ² ), the interval of the foam molding part Discharge rate 30 kg / hr (discharge speed V = 109 kg / cm ² · hr), resin temperature 175 ° C., resin pressure in front of the annular die Extruded and foamed under the condition of 8 MPa, and the cylindrical foam molded in the foam molding part of the annular die is attached onto the cooled mandrel, and the outer surface is cooled by blowing air from the air ring. At one point on the mandrel, the cylindrical foam was cut with a cutter to obtain a sheet-like polyolefin resin foam listed in Table 1. The polyolefin resin foam obtained by the above method does not generate corrugation and has excellent surface smoothness, and therefore has excellent secondary processability such as slicing.
In addition, 100 mass parts of the mixed resin composition obtained by mixing the polyolefin resin and the thermoplastic elastomer at the above ratio was melt-kneaded at 200 ° C. with an extruder and maintained at 200 ° C. (extruder, mold temperature). The mixed resin composition (extruded foaming resin composition) molded into a cylindrical pellet was obtained after extrusion into a strand at 200 ° C.). It was 0.7 g / 10min as a result of measuring a melt flow rate about the obtained mixed resin composition.

[Example 2]
Both sides of the polyolefin resin foam obtained in Example 1 were sliced with a splitting machine to remove the epidermis, and the sheet-like polyolefin resin foam described in Table 1 was obtained.

[Example 3]
Supercritical dioxide in the same manner as in Example 1, except that the polyolefin resin was changed to Prime Polymer E-100GV (melting point: 161 ° C., deflection temperature under load: 120 ° C., MFR: 0.5 g / 10 min). Carbon (4.2 parts by weight) was press-fitted and extruded and foamed under the conditions of a resin temperature of 175 ° C. and a resin pressure of 10.2 MPa in front of the annular die to obtain a sheet-like polyolefin resin foam described in Table 1.
The melt flow rate of the mixed resin composition was measured in the same manner as in Example 1. As a result, it was 1.3 g / 10 min.

[Example 4]
Both sides of the polyolefin resin foam obtained in Example 3 were sliced with a splitting machine to remove the skin, and a sheet-like polyolefin resin foam described in Table 1 was obtained.

[Example 5]
Supercritical carbon dioxide was changed to 4.2 in the same manner as in Example 1 except that the thermoplastic elastomer was changed to Notio (melting point: 154 ° C., softening point: 100 ° C., MFR: 7 g / 10 min) manufactured by Mitsui Chemicals. Part weight injection was performed, and extrusion foaming was performed under the conditions of a resin temperature of 180 ° C. and a resin pressure of 10.0 MPa in front of the annular die to obtain a sheet-like polyolefin resin foam described in Table 1.
The melt flow rate of the mixed resin composition was measured in the same manner as in Example 1. As a result, it was 0.5 g / 10 min.

[Comparative Example 1]
A sheet-like foamed body of modified polyphenylene oxide, which is a commercially available engineering plastic, described in Table 1 (“Heat Cell” manufactured by Sekisui Plastics Co., Ltd.) was used.

[Comparative Example 2]
A sheet-like closed-cell foam ("Softlon" manufactured by Sekisui Chemical Co., Ltd.) shown in Table 1 obtained by irradiating commercially available polyethylene with an electron beam was used.

[Comparative Example 3]
A commercially available urethane foam in the form of a sheet shown in Table 1 (“Polon SR-S15P” manufactured by INOAC) was used.

[Comparative Example 4]
A commercially available sheet-like foam (Pef, manufactured by Toray Industries, Inc.), which is a semi-rigid, closed-cell polyolefin foam formed by electron beam crosslinking, was used.

[Comparative Example 5]
SH9000 manufactured by Nippon Polypro Co., Ltd. (melting point: 164 ° C., deflection temperature under load: 116 ° C., MFR: 0.3 g / 10 min), and thermoplastic elastomer EXCELLINK 3300B (melting point: 148 ° C., deflection temperature under load) : 98 ° C., MFR: 0.9 g / 10 min) In the same manner as in Example 1, 4.2 parts by weight of carbon dioxide in a supercritical state was injected, and the resin temperature was 172 ° C. before the ring die. Extrusion foaming was performed under the condition of a resin pressure of 10.8 MPa to obtain a sheet-like polyolefin resin foam described in Table 1.
The melt flow rate of the mixed resin composition was measured in the same manner as in Example 1. As a result, it was 0.5 g / 10 min.

  According to Table 1, an example of an open cell structure having a thickness, an average cell diameter and an apparent density within a predetermined range, a compressive stress when compressed by 50% is 15 KPa or more, and a compressive stress when compressed by 80% is 400 KPa or less. If it is a sheet-like polyolefin resin foam, it is excellent in handling property (handleability), easily crushed (followability) with a low load, has good dimensional accuracy, and excellent long-term stability of the seal.

  The polyolefin resin foam of the present invention is suitably used in the field of dustproof materials. In addition, the polyolefin resin foam of the present invention can be suitably used in fields where flexibility and followability are required, electronic devices where electrical sealability and dust resistance are required, household appliances, housing, automobiles, and the like. The foamed dustproof material of the present invention can be suitably used in electronic devices, home appliances, houses, automobiles, and the like that require sealing properties, dustproof properties, and dimensional accuracy.

Claims (4)

The mixed resin composition has a melt flow rate of 0.1 when it contains a polyolefin-based resin and a thermoplastic elastomer in a mass ratio of 20:80 to 80:20 and is measured under a load of 230 ° C. and 21.18 N. -3 g / 10 min, the obtained polyolefin resin foam has a thickness of 0.1-3.0 mm, an average cell diameter of 0.02-0.2 mm, an apparent density of 30-100 kg / m3,
The compression stress when compressed by 50% is 15 KPa or more,
The compressive stress when compressed by 80% is 400 KPa or less,
The open cell rate is 60% or more ,
The polyolefin resin having a melting point in the range of 140 to 180 ° C. and a deflection temperature under load of 80 to 140 ° C .;
A polyolefin-based resin foam comprising the mixed resin composition containing the thermoplastic elastomer having a melting point in the range of 140 to 180C and a softening point of 45 to 160C. . The polyolefin resin foam according to claim 1, wherein the polyolefin resin has a melt flow rate of 0.2 to 5 g / 10 min . The polyolefin resin foam according to claim 1 or 2, wherein the surface of the polyolefin resin foam is removed and sliced. The foaming dust-proof material which used the polyolefin-type resin foam of Claim 1, 2, or 3 for the dust-proof material.