JP2013203793A - Damping material - Google Patents

Abstract

An object of the present invention is to provide a vibration damping material that can absorb intermittent impact, has excellent vibration damping properties, heat resistance, and cleanness, and can be used easily.
It is composed of a polyolefin resin foam having an apparent density of ^{30 to} 100 kg / m ³ and an open cell ratio of 20 to 70%, and has a coefficient of static friction with respect to a stainless steel plate of 0.5 or more. The above-mentioned problem is solved by the damping material.
[Selection] Figure 1

Description

  The present invention relates to a vibration damping material. The vibration damping material of the present invention can absorb intermittent impacts, is excellent in vibration damping properties, heat resistance and cleanliness, and can be used easily.

  Polyolefin resin foams are widely used as cushioning materials, packaging materials, packing materials and the like because of their high strength and excellent flexibility. One of the uses of the polyolefin resin foam as described above is a use as an impact absorbing material for electronic members. Various precision parts are used in electronic devices. Since these parts are very sensitive to impacts, shock absorbers that reduce external shocks are used. In recent years, with the miniaturization and thinning of electronic devices, the thinning of internal members has progressed, and the foam that absorbs impact is also required to be thin. In addition, since the electronic device is downsized, the interval between the internal members is further narrowed, and there is a problem that the members come into contact with each other with a slight vibration, and the member is damaged or malfunctions due to the impact. Therefore, there has been a demand for a vibration damping material that suppresses vibration of the electronic member and suppresses backlash of the member.

  Surface frictional resistance is very important as one of the indexes for evaluating vibration damping. This is because if the frictional resistance against the substrate, the member, the housing, etc. is large, the deviation between the vibration damping material and the member is suppressed, and the vibration can be efficiently suppressed, so that rattling is suppressed. Furthermore, if it is the damping material which is easy to compress, a damping material and a member can be stuck more closely. Therefore, flexibility to cope with a minute clearance such as a gap between members inside the electronic device is also important.

Japanese Patent Application Laid-Open No. 2011-215805 (Patent Document 1) discloses an impact-absorbing material that has excellent flexibility and excellent impact-absorbing property even if it is thin, and can follow even a minute clearance. Have been described.
Japanese Patent Laid-Open No. 2010-84798 (Patent Document 2) is characterized in that an impact absorbing material including an adhesive foam is disposed between an electronic component and a protective member that protects the electronic component. A shock absorbing structure is described.
Japanese Patent Application Laid-Open No. 2011-213924 (Patent Document 3) describes a foamed polyurethane sheet that has good impact absorbability and recoverability, excellent mechanical strength, and low water absorption.

JP 2011-215805 A JP 2010-84798 A JP 2011-213924 A

  However, the shock absorbing material described in Patent Document 1 is only evaluated for the shock absorbing property with respect to the instantaneous shock absorbing property when the device is dropped. This document does not describe anything about evaluating whether or not the above-mentioned shock absorbing material can absorb intermittent vibration and suppress rattling from the viewpoint of evaluating damping performance. .

In addition, if a plurality of members are bonded using a foam as described in Patent Document 2, there is a problem that they cannot be easily peeled off. For example, it is not easy to use as a vibration damping material used for a member such as a battery pack that needs to be replaced.
Furthermore, the internal temperature of electronic equipment can be very high due to miniaturization. Therefore, vibration damping materials for electronic devices are required to have vibration damping properties equivalent to those at room temperature even at high temperatures. However, this document does not describe anything about vibration damping at high temperatures.

  In addition, the urethane foam used in Patent Document 3 is extremely inferior in cleanliness because a foaming agent remains.

  Therefore, an object of the present invention is to provide a vibration damping material that can absorb intermittent vibration, has excellent vibration damping properties, heat resistance, and cleanness, and can be used easily.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors use a polyolefin resin foam having a specific apparent density and open cell ratio, and further having a specific static friction coefficient with respect to a stainless steel plate. As a result, the inventors have found that the above problems can be solved, and have completed the present invention.

Thus, according to the present invention,
It is composed of a polyolefin resin foam having an apparent density of ^{30 to} 100 kg / m ³ and an open cell ratio of 20 to 80%, and has a static friction coefficient with respect to a stainless steel plate of 0.5 or more. Material is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the vibration damping material which can absorb intermittent vibration, is excellent in vibration damping property, heat resistance, and clean property, and can be used easily can be provided.

  The vibration damping material of the present invention exhibits more excellent vibration damping performance when the polyolefin resin foam has a loss coefficient tan δ of 0.05 or more in the measurement of solid viscoelasticity at 25 to 120 ° C.

  When the polyolefin resin foam has a compressive stress of 400 kPa or less when the polyolefin resin foam is compressed 80% at a compression rate of 1 mm / min, the vibration damping material of the present invention can cope with a finer clearance.

  When the polyolefin resin foam has a compressive stress of 1500 kPa or less when the polyolefin resin foam is compressed by 90% at a compression rate of 1 mm / min, the vibration damping material of the present invention can cope with a finer clearance.

  When the vibration damping material of the present invention further contains an elastomer and / or a plastomer, it exhibits better vibration damping performance.

It is a schematic diagram which illustrates the general usage method of a damping material. It is a schematic sectional drawing of the annular die which shows one Embodiment of this invention.

(Polyolefin resin foam)
The polyolefin resin foam (hereinafter also simply referred to as “foam”) used in the vibration damping material of the present invention has an apparent density of ^{30 to} 100 kg / m ³ . By having an apparent density in this range, a vibration damping material having high strength and excellent flexibility can be provided. When the apparent density is less than 30 kg / m ³ , the mechanical strength of the foam may be lowered. On the other hand, when the apparent density exceeds 100 kg / m ³ , the flexibility of the damping material may be lowered. A more preferable range of the apparent density is 30 to 90 kg / m ³ , and a more preferable range is 35 to 70 kg / m ³ .

  The foam has a plurality of bubbles and a wall containing a polyolefin resin that partitions the plurality of bubbles for each bubble. The foam has an open cell ratio of 20 to 70%. When the open cell ratio is less than 20%, the flexibility of the foam is inferior, and energy generated by vibration cannot be efficiently dissipated, resulting in inferior vibration damping. On the other hand, if the open cell ratio exceeds 70%, sufficient strength of the foam cannot be obtained. A preferable range of the open cell ratio is 20 to 60%, and a more preferable range is 20 to 55%. A specific measurement method will be described in the following example section.

  The foam has a coefficient of static friction with respect to a stainless plate of 0.5 or more. When the static friction coefficient is 0.5 or more, deviation between the member and the vibration damping material is suppressed, and rattling of the member can be prevented. A preferable range of the coefficient of static friction with respect to the stainless steel plate is 0.6 or more. A specific measurement method will be described in the following example section.

  It is preferable that the foam always has a loss coefficient tan δ of 0.05 or more in solid viscoelasticity measurement at 25 to 120 ° C. The loss coefficient tan δ is an evaluation index of the damping characteristics of the damping material. A loss factor tan δ of 0.05 or more is preferable because vibration can be easily released as thermal energy and can be efficiently damped. A more preferable range of the loss coefficient tan δ is 0.06 or more, and a more preferable range is 0.07 or more. In order to increase the loss coefficient tan δ, the open cell ratio of the polyolefin resin foam to be used may be increased so that the energy escape field in the foam increases. A specific method for measuring the loss factor tan δ will be described in the following example section.

  The foam can be used after being compressed. By compressing, the adhesion between the member and the damping material is improved, and rattling of the member can be further suppressed. When a foam is used after being compressed, its availability as a damping material can be evaluated using compression stress as an index. A specific measurement method will be described in the Examples section.

  The foam preferably has a compressive stress of 400 kPa or less when compressed 80% at a compression rate of 1 mm / min. When the compressive stress exceeds 400 kPa, the flexibility is inferior, and the device may be damaged when compressed. A more preferable range of the compressive stress of the foam under these conditions is 350 kPa or less.

  The foam preferably has a compressive stress of 1500 kPa or less when compressed 90% at a compression rate of 1 mm / min. When the compressive stress exceeds 1500 kPa, the stress may be strong when highly compressed and the device may be damaged. A more preferable range of the compressive stress of the foam under these conditions is 1000 kPa or less, and a more preferable range is 800 kPa or less.

  The foam preferably has an average cell diameter of 0.02 to 0.20 mm. When the average cell diameter is less than 0.02 mm, the apparent density of the foam increases, and the flexibility of the foam may decrease. On the other hand, if the average cell diameter exceeds 0.20 mm, physical properties such as flexibility of the foam may be deteriorated. A more preferable range of the average cell diameter is 0.05 to 0.18 mm, and a more preferable range is 0.07 to 0.15 mm.

  The foam preferably has a thickness of 0.1 to 3 mm. When the thickness is less than 0.1 mm, the thickness becomes thinner than the bubble diameter, and physical properties such as flexibility may be deteriorated. On the other hand, if the thickness exceeds 3 mm, the stress at the time of compression may increase. A more preferable range of the thickness is 0.2 to 3 mm, and a further preferable range is 0.3 to 2 mm. Moreover, the thickness is preferably 1.0 times or more of the average bubble diameter, and more preferably in the range of 2.0 to 30 times.

Moreover, the said foam may have that many walls which divide each bubble have a tear, ie, it may have a bubble tear. The degree of bubble breakage is defined by the bubble breakage rate, and the range is preferably 1 to 30%. If the bubble breakage rate is less than 1%, it is not easily deformed and the adhesion to the member may be poor. On the other hand, if the bubble breaking rate exceeds 30%, sufficient strength of the foam may not be obtained. A more preferable range of the bubble breaking rate is 5 to 20%, and a more preferable range is 5 to 15%.
The bubble breakage rate is obtained by binarizing a scanning electron micrograph of the cross section of the foam so that the torn portion and the other portion are black and white, and the area of the photograph obtained from the binarized photograph Means the percentage of the area torn. A specific measurement method will be described in the Examples section.

The polyolefin resin constituting the foam preferably has a melting point in the range of 120 to 180 ° C. When the temperature inside the electronic device is high, the resin may melt out if the melting point of the polyolefin resin is less than 120 ° C. When the melting point of the polyolefin resin exceeds 180 ° C., it is necessary to knead the resin at a high temperature, which may cause thermal degradation of the polyolefin resin. A more preferable range of the melting point is 155 to 170 ° C.
As described above, the polyolefin resin foam used in the vibration damping material of the present invention is a mixed resin containing a specific amount of a polyolefin resin having a specific melting point and a thermoplastic elastomer, a cell nucleating agent, and a foaming agent. It is obtained by extruding a melt of a resin composition containing carbon dioxide. This polyolefin resin foam does not melt or deform even under a high temperature environment such as 140 ° C., and the loss coefficient tan δ can always be maintained at 0.05 or more.

The type of polyolefin resin constituting the foam is not particularly limited as long as the various physical properties can be imparted to the foam. Specific examples include homopolyethylene, homopolypropylene, ethylene, or a copolymer of propylene and another olefin. The copolymer may be either a random copolymer or a block copolymer. Polyolefin resin may be used individually by 1 type, and may be used in combination of 2 or more types as appropriate.
Examples of other olefins include, in addition to ethylene and propylene, carbon numbers such as 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, and 1-decene. The alpha olefin whose is 4-10 is mentioned.
Of these, homopolypropylene having excellent foamability and heat resistance and a block copolymer of polypropylene are preferable. Among these, homopolypropylene having excellent heat resistance is more preferable.

  In addition, it is preferable to use a resin having a melt flow rate (MFR) of 0.2 to 5 g / 10 min as the polypropylene resin. When the MFR is low, the load on the extruder increases and the productivity decreases, or the raw material mixture of the molten foam containing the foaming agent cannot flow smoothly in the mold, and the resulting foam The surface may be uneven and the appearance may deteriorate. On the other hand, if the MFR is high, the resin pressure in front of the annular die is reduced, and the resin pressure in the annular die bubble generating part is also reduced, so that bubbles are generated in front of the bubble generating part and the foam molding part. When foam breakage occurs abruptly, foamability is lowered, and the appearance of the resulting foam may be deteriorated or the foam may not be obtained. A more preferable range of MFR is 0.2 to 4 g / 10 minutes, and a further preferable range is 0.2 to 3.5 g / 10 minutes.

  The polypropylene resin is preferably a high melt tension polypropylene resin having excellent foamability. Examples of high melt tension polypropylene resins include those having free-end long-chain branching in the molecular structure by electron beam crosslinking (HMS-PP), and those having increased melt tension by including a high molecular weight component. is there. Commercially available products can be used as the high melt tension polypropylene-based resin, and specific examples of the commercially available products include trade name “New Train SH9000” manufactured by Nippon Polypro Co., Ltd., and trade name “DaployWB135HMS” manufactured by Borealis.

  The foam may contain other components in addition to the polyolefin resin. Examples include elastomers such as thermoplastic elastomers and plastomers such as polyethylene-based plastomers.

  A thermoplastic elastomer has a structure in which a hard segment and a soft segment are combined, has rubber elasticity at room temperature, and has the property of being 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.

  As the thermoplastic elastomer, for example, 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; 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 kneader; using kneader such as Banbury mixer and twin screw extruder By adding a crosslinking agent when physically dispersing the polyolefin resin that becomes the hard 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. Dynamically cross-linked Eras Ma and the like.

Of the thermoplastic elastomers described above, it is particularly preferable to use a non-crosslinked elastomer produced by physically dispersing a polyolefin resin and a rubber component in view of the recyclability of the produced product.
Examples of the diene component constituting the non-crosslinked ethylene-propylene-diene copolymer include ethylidene norbornene, 1,4-hexadiene, dicyclopentadiene, and the like. Here, the non-crosslinked ethylene-propylene-diene copolymer elastomer may be used alone or in combination of two or more. By using such a non-crosslinked ethylene-propylene-diene copolymer elastomer, it becomes possible to manufacture with an extruder similar to the case of extrusion foam molding of a normal polypropylene resin. Furthermore, even when the foam is recycled and supplied again to the extruder for foam molding, foaming failure due to the crosslinked rubber, which is a problem when using a crosslinked elastomer, can be suppressed.

  The thermoplastic elastomer preferably has a durometer A hardness of 90 or less as defined in JIS K6253. By having this hardness, the foam which has the outstanding softness | flexibility and grip property can be provided. A more preferable duro A hardness is about 80 to 20.

  If the content of the thermoplastic elastomer is small, the cushioning property and flexibility of the foam may be poor. Moreover, the grip property of a foam falls and a favorable static friction coefficient cannot be obtained. On the other hand, when the content of the thermoplastic elastomer is large, the rubber elasticity of the thermoplastic resin composition becomes too strong, and the foamability may be lowered, and the open cell ratio may be lowered. In addition, shrinkage of the foam may increase. A preferable range of the content of the thermoplastic elastomer is about 10 to 300 parts by weight with respect to 100 parts by weight of the polyolefin-based resin, a more preferable range is 20 to 150 parts by weight, and a further preferable range is 30 to 100 parts by weight. A particularly preferred range is 40 to 70 parts by weight.

  Examples of the polyethylene plastomer include a polyethylene polymer containing a copolymer component such as an ethylene homopolymer or an α-olefin. In the present invention, since the desired flexibility and strength can be easily obtained, the polyethylene plastomer is preferably a copolymer of ethylene and an α-olefin.

As the α-olefin, those having 4 to 8 carbon atoms are preferable, and 1-butene, 1-hexene, 1-octene and combinations thereof are more preferable.
Examples of the copolymer of ethylene and α-olefin include, for example, trade name Esprene NO416 (ethylene-1-butene copolymer) manufactured by Sumitomo Chemical Co., Ltd., and trade name kernel KS240 (ethylene-1-hexene manufactured by Nippon Polychem Co., Ltd.). Copolymer) and trade name Affinity EG8100 (ethylene-1-octene copolymer) manufactured by Dow Chemical.

  If the content of plastomer is low, the cushioning property and flexibility of the foam may be poor. Moreover, the grip property of a foam falls and a favorable static friction coefficient cannot be obtained. On the other hand, when the content of plastomer is large, the elasticity of the thermoplastic resin composition becomes too strong, and the foamability may be lowered, and the open cell ratio may be lowered. In addition, shrinkage of the foam may increase. A preferable range of the content of the thermoplastic elastomer is about 10 to 300 parts by weight with respect to 100 parts by weight of the polyolefin-based resin, a more preferable range is 20 to 150 parts by weight, and a further preferable range is 30 to 100 parts by weight. A particularly preferred range is 40 to 70 parts by weight.

In addition to elastomers and / or plastomers, foams are surfactants, dispersants, weathering stabilizers, light stabilizers, pigments, dyes, flame retardants, plasticizers, lubricants, UV absorbers, antioxidants, fillers , Other additives such as reinforcing agents and antistatic agents may be included.
The surfactant imparts slipperiness and antiblocking property. Moreover, a dispersing agent improves the dispersibility of an inorganic filler. Examples of the dispersant include higher fatty acids, higher fatty acid esters, higher fatty acid amides, and the like.
The content of the other additives can be appropriately selected within a range that does not impair the formation of bubbles and the physical properties of the foam, and the content contained in a normal foam can be employed.

  The foam may be removed by slicing the epidermis. The foam of the present invention is excellent in slice processability. By removing the skin of the foam, it is possible to suppress the occurrence of creases when the foam is bent. In addition, it is possible to provide a foam superior in air permeability, moisture permeability, flexibility and buffering property. As the slicing machine, a known machine such as a type in which a blade rotates can be used.

(Manufacturing method of polyolefin resin foam)
The foam can be produced by an extrusion foam molding method. Examples of the extruder that can be used in this method include a single-screw extruder, a twin-screw extruder, and a tandem extruder. Among these, a tandem type extruder is preferable because the extrusion conditions can be easily adjusted.

  The raw material of the foam is kneaded in the extruder, extruded from the extruder, and foamed to become a foam. A die is usually installed at a portion where the foam material is extruded from the extruder. An example of such a die is an annular die shown in the schematic cross-sectional view of FIG.

  An annular die D shown in FIG. 2 includes a bubble generation unit 2 formed at the throttle of the foaming agent-containing kneaded molten resin flow channel unit 3, and the bubble generation unit 2. It has the foam molding part 1 which smoothes. In FIG. 2, 4 is an annular die-in side mold, and 5 is an annular die-out side mold.

  The resin pressure in front of the annular die is a pressure measured by a measuring instrument such as a strain gauge in the flow path from the tip of the extruder to the annular die. Specifically, it can be measured with a strain gauge attached to the end flange of the extruder, a straight pipe mold having flanges on both sides, and a straight pipe mold part connected in order to the ring die.

By forming a foam using an annular die as described above, it is possible to suppress the occurrence of a large number of corrugated surfaces that reduce surface smoothness even if the bubbles constituting the foam are finer than before. . The inventors consider that this is because the annular die can suppress the generation of corrugation in the bubble generation part by an appropriate slip resistance in the foam molding part. The corrugated here means a large number of ridges and valleys formed by undulation of the foam from the annular die to absorb the linear expansion in the circumferential direction due to volume expansion.
Here, extrusion foaming is performed under the condition that the resin discharge speed V in the bubble generating portion 2 of the annular die D is 50 to 300 kg / cm ² · hour and the resin pressure before the annular die D is 7 MPa or more. It is preferable to make it.

When the discharge speed V is smaller than about 50 kg / cm ² · hour, it becomes difficult to obtain finer bubbles and a foam with a high expansion ratio. On the other hand, when the discharge speed V is higher than about 300 kg / cm ² · hour, the resin generates heat at the mold bubble generation portion, and the bubbles are broken, and the expansion ratio is likely to decrease. In addition, a corrugated corrugate is likely to occur, and the bubble diameter may be non-uniform and the surface smoothness of the foam may be reduced. The discharge speed V can be appropriately adjusted according to the cross-sectional area of the annular die bubble generating part and the extrusion discharge amount.

Here, the resin discharge speed V (kg / cm ² · hour) is a value defined by the following equation.
V = extruded resin weight / mould bubble generating section cross-sectional area / time Extruded resin weight refers to the total weight extruded from the mold. Therefore, the weight of the extruded resin is the total amount of the thermoplastic resin composition and the foaming agent. Further, the weight of the extruded resin can be expressed by the discharge amount per hour (kg / hour).

A more preferable range of the discharge speed V is about 70 to 250 kg / cm ² · hour, and a more preferable range is about 100 to 200 kg / cm ² · hour. A preferable range of the resin pressure in front of the ring die is 8 MPa or more and 20 MPa or less. By extrusion foaming under the above conditions, the foamability of the polypropylene resin can be improved, the bubbles can be refined, and the strength of the cell membrane can be increased. Under these conditions, the workability in the case of secondary processing of the obtained foam is improved. For example, a sheet-like foam obtained by slicing can have a superior surface smoothness.

  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, bubbles may be generated before the annular die bubble generating part, and a good foam may not be obtained. Moreover, when it becomes higher than 20 MPa, the load on the extruder may become too high. In addition, the injection pressure may be too high to allow the foaming agent to be injected.

  The resin pressure in front of the annular die can be appropriately adjusted according to the molten resin viscosity, the extrusion discharge amount, and the sectional area of the annular die bubble generating portion. Furthermore, the molten resin viscosity can be appropriately adjusted depending on the viscosity of the blended resin composition, the amount of foaming agent added, and the molten resin temperature. Note that the molten resin temperature means a temperature measured by a thermocouple attached so as to be in direct contact with the molten resin in a straight pipe mold for measuring the resin pressure before the annular die.

  The resin temperature is preferably in the range of about 10 ° C. to 20 ° C. higher than the melting point of the polypropylene resin in order to improve foamability. When the resin temperature approaches the melting point, crystallization of polypropylene starts, the viscosity increases rapidly, the extrusion conditions may become unstable, and the load on the extruder may increase. On the other hand, if it is too high, the solidification of the resin after foaming may not catch up with the foaming speed, and the foaming ratio may not increase.

In order to control the flexibility by the resin pressure and improve the adhesion to the member, the resin pressure in front of the annular die may be lowered by 10 to 30%.
In order to control the flexibility by the resin temperature and improve the adhesion to the member and the vibration damping performance, the resin temperature may be increased by 1 to 3 ° C.

  The raw material of the foam includes a foaming agent. The foaming agent is not particularly limited, and various known foaming agents can be used. For example, hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, n-hexane, petroleum ether, ketones such as acetone and methyl ethyl ketone, methanol, ethanol, isopropyl alcohol, etc. Alcohols, low boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, halogen-containing hydrocarbons such as trichloromonofluoromethane, dichlorodifluoromethane, inorganic gases such as carbon dioxide, nitrogen, ammonia, etc. Is mentioned. One of these foaming agents may be used alone, or two or more thereof may be appropriately combined and used in combination.

  Of the foaming agents, inorganic gas is preferable, and carbon dioxide is particularly preferable. Carbon dioxide is a foam having finer bubbles than conventional foams obtained by using carbon dioxide in other forms by using supercritical, subcritical, or liquefied carbon dioxide. You can get a body. The foam having fine bubbles can improve the surface smoothness and flexibility.

  The amount of the foaming agent that is press-fitted into the extruder can be appropriately adjusted according to the apparent density of the foam. However, when the amount of the foaming agent to be press-fitted into the extruder is small, the apparent density of the foam is increased, and the lightness and flexibility may be lowered. On the other hand, if the amount of the foaming agent that is press-fitted into the extruder is large, foaming may occur in the mold, and large voids may be generated in the foam. Therefore, a more preferable range of the amount of the foaming agent that is press-fitted into the extruder is 1 to 10 parts by weight with respect to 100 parts by weight of the foam raw material, and a more preferable range is 2 to 8 parts by weight, which is particularly preferable. The range is 3-6 parts by weight.

  The foam material may contain a cell nucleating agent. The cell nucleating agent promotes the generation of cell nuclei at the time of foaming and affects the refinement and uniformity of the cells and the bubble breaking rate. 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, potassium sulfate, Examples thereof include inorganic compounds such as barium sulfate, sodium hydrogencarbonate, and glass beads, and organic compounds such as polytetrafluoroethylene.

If the amount of the cell nucleating agent is small, it is difficult to increase the number of bubbles in the foam, and the average cell diameter may not be reduced.
On the other hand, if the amount of the cell nucleating agent is large, secondary agglomeration may occur, resulting in poor extrusion foaming. Therefore, a more preferable range of the amount of the cell nucleating agent is 0.1 to 10 parts by weight with respect to 100 parts by weight of the foam raw material, and a more preferable range is 0.5 to 6 parts by weight.

  The cell nucleating agent may be supplied as a raw material mixture of the foam by mixing itself with other components of the foam, or without mixing the cell core and other components of the foam. These may be individually fed into the extruder. In addition, the cell nucleating agent is mixed with the base resin in advance in order to facilitate handling, to prevent contamination of the production environment due to powder scattering, and to improve dispersibility in the thermoplastic resin. Therefore, it is preferable to supply as a master batch.

  The base resin for the masterbatch is preferably a resin having excellent compatibility with the polyolefin resin. Examples thereof include homopolypropylene, block polypropylene, random polypropylene, low density polyethylene, and high density polyethylene.

  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. Various measurement methods will be described below.

(Melt flow rate)
The melt flow rate (MFR) of a polypropylene resin refers to that measured at a test temperature of 230 ° C. and a test load of 21.18 N in accordance with the method B of JIS K7210: 1999.
The MFR of the polypropylene resin refers to the MFR of the resin measured by the above method when one polypropylene resin is used alone.
In addition, when two or more types of polypropylene resins are used in combination, the MFR of each polypropylene resin is measured by the above measuring method, and calculated from the respective MFR values as follows. Say.
That is, when the polypropylene resin is a mixture of n types of polypropylene resins, MFR of polypropylene resin 1 is MFR ₁ , MFR of polypropylene resin 2 is MFR ₂ ,... MFR of polypropylene resin n together with the MFR _n, the content of the polypropylene resin 1 C1, the content of the content of the polypropylene resin 2 C2 · · · polypropylene resin n and Cn. In addition, content of polypropylene resin n shall remove | divide the weight of polypropylene resin n by the weight of the whole polypropylene resin. And MFR of polypropylene resin is computed by a following formula.
MFR (g / 10 min) = (MFR ₁ ) ^C1 × (MFR ₂ ) ^C2 ×... × (MFR _n ) ^Cn

(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 (D _MD ), the bubble diameter in the TD direction (D _TD ), and the bubble diameter in the VD direction (D _VD ) is the average of the recycled resin-containing polyolefin resin foam. The bubble diameter.
Average bubble diameter (mm) = (D _MD + D _TD + D _VD ) / 3

(Apparent density)
In this specification, the apparent density of the polyolefin resin foam having tearing in the bubbles 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 without changing the original cell structure of the sample, its mass is measured, and calculate.
Density (kg / m ³ ) = Test piece mass (g) / Test piece volume (cm ³ ) × 10 ³

(Open cell ratio)
First, a foam sheet is cut into 10 cm x 10 cm, and the weight (Wd) is measured. The porosity of the foam is calculated from the weight and the density of the foam, and the volume (V) of the bubbles contained in the foam is calculated. Next, the sheet is submerged in a container filled with water so that the sheet is completely submerged. The whole container is placed in a commercially available decompression device, the pressure is reduced to -0.05 MPa, the decompression operation is stopped, and after waiting for 3 minutes, the sheet is returned to normal pressure. Was taken out of the water, the surface adhering water was wiped off, the weight was measured, and the water absorption (Ww) was calculated by subtracting Wd. The value of the amount of water absorption when it is assumed that all the bubbles of the foam are filled with water is equal to V, and the actual amount of water absorption is related to the communication rate of the bubbles for that value. What was calculated | required by was made into the open cell rate.
Open cell ratio (%) = Ww / V × 100

(Bubble breaking rate)
In the present specification, the bubble breaking rate of the polyolefin resin foam is measured as follows.
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 magnified 20 times.
Next, the image of the cut surface cut along the TD direction is taken into the foam evaluation software (Nano Hunter NS2K-Pro manufactured by Nano System Co., Ltd.), the measurement range is a square with a coordinate width of 370 × 370, Binarization was performed. In binarization, black and white were reversed with a threshold = 50.
In the binarized image, the part where the bubbles are not broken and completely communicated is deleted, the area is measured, and the ratio of the area of the white part to the area occupied in the MD direction The bubble breaking rate was taken as. This measurement was performed a total of three times in different ranges in the captured image, and the average value of each result was taken as the overall bubble breakage rate.

(Loss factor tan δ)
Using a viscoelastic spectrometer (manufactured by SII Nano Technology, model: EXSTAR DMS6100), a measurement is performed on a foam sheet having a length of 25 mm (MD direction), a width of 10 mm (TD direction), and a thickness of about 0.5 mm. Measured under conditions of 25-120 ° C, temperature rising rate 2 ° C / min, frequency 1 Hz, chuck interval 10 mm, strain amplitude 5 μm, minimum tension / compression force 50 mN, tension / compression gain 1.8, and force amplitude initial value 50 mN. The storage elastic modulus (E ′) at each temperature was read, and the ratio (E ″ / E ′) of loss elastic modulus (E ″) and storage elastic modulus (E ′) was calculated. .

(Static friction coefficient)
The static friction coefficient in the present invention is specified by the following measuring method. That is, the coefficient of static friction was measured according to the tilt method defined in JIS K7125.
A 40 mm × 65 mm sample cut out from the foam sheet to be measured is fixed with double-sided tape under a 500 g weight having a bottom surface of 40 mm × 65 mm. This is placed on a flat stainless steel plate having a smooth surface (SUS304, surface roughness Ry = 0.lμm or less), and the stainless steel plate is inclined once per second to increase the inclination angle. First, the inclination angle (θ) when moving 10 mm is read from the position where the weight to which the sample is fixed is placed. The static friction coefficient (μ0) is calculated by the following formula.
Coefficient of static friction (μ0) ≧ tan θ (Formula 1)
This was measured three times, and the average value was taken as the coefficient of static friction. The static friction coefficient (μ0) is determined for each of the front and back sides of the foam sheet.
In this test, the test piece is left in a room at a room temperature of 23 ° C. and a relative humidity of 50% for 24 hours, and then measured by the above-described static friction coefficient measuring apparatus placed in the room.

(Compressive stress)
The compressive stress refers to a value measured as described below in accordance with the method described in JIS K6767 Foamed Plastics-Polyethylene-Test Method. Specifically, the compression stress is measured when a test piece cut to 50 mm × 50 mm is compressed 80% or 90% at a compression rate of 1 mm / min. As the measuring device, Tensilon universal testing machine UCT-10T manufactured by Orientec Corporation can be used. When the thickness of the test piece is 2 mm or more, the measurement is performed as it is, and when the thickness of the test piece is less than 2 mm, the measurement is performed so that the thickness is about 2 mm.

(Damping performance test)
Damping performance is measured by the following method.
A double-sided tape is attached to one side of a foam cut to 10 mm × 10 mm, and two of them are attached to a stainless steel plate with an interval of 20 mm. An acrylic plate having a thickness of 2 mm and 50 mm × 50 mm is placed thereon. They were fixed on a vibrator set at a frequency of 5 Hz and an amplitude of 20 mm, given a constant vibration, and the time when the acrylic plate placed on the top shifted from the start was measured.

[Example 1]
(Manufacture of polyolefin resin foam)
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, 100 parts by weight of polypropylene resin (Newstrain SH9000 MFR: 0.2 g / 10 min manufactured by Nippon Polypro Co., Ltd.) is a non-crosslinked ethylene-propylene-diene copolymer elastomer. 67 parts by weight of a thermoplastic elastomer (Thermolan Z101N manufactured by Mitsubishi Chemical Corporation, MFR: 14 g / 10 min) was added to obtain a compounded resin composition. A thermoplastic resin composition is prepared by mixing 10 parts by weight of a master batch (“Talpet 70P” manufactured by Nitto Flour & Chemical Co., Ltd.) containing 70% by weight of talc having an average particle size of 12 μm as a cell nucleating agent with 100 parts by weight of this blended resin composition I got a thing. The thermoplastic resin composition was supplied to the first extruder and melt kneaded. From the middle of the first extruder, 4.2 parts by weight of carbon dioxide in a supercritical state was injected as a blowing agent. After the press-fitting, the molten thermoplastic resin composition and carbon dioxide are uniformly mixed and kneaded, and then the molten resin composition containing the foaming agent is continuously supplied to the second extruder for foaming while being melt-kneaded. Cooled to a suitable resin temperature. Then, the bubble generating part diameter φ34 mm of the mold attached to the tip of the second extruder, the bubble generating part interval of the mold 0.3 mm (cross-sectional area of the bubble generating part: 0.275 cm ² ), the interval of the foam molding part Discharge rate 30 kg / hour (discharge speed V = 109 kg / cm ² · hour), resin temperature 178 ° C., resin pressure 7 to before the annular die Extrusion foaming was performed under the condition of 8 MPa. The cylindrical foam formed in the foam molding part of the annular die is attached to the cooled mandrel, and the outer surface is cooled by blowing air from the air ring to cool the cylindrical foam. Was molded. Next, at one point on the mandrel, a cylindrical foam was cut by a cutter to obtain a sheet-like polypropylene resin foam. The obtained foam was sliced with a splitting machine (“AB-320D” manufactured by Fortuna) to remove the epidermis, thereby obtaining a sheet-like foam having a thickness of 0.5 mm in which both main surfaces were sliced. .

[Example 2]
Except for using a polypropylene resin (Prime Polypro E110G manufactured by Prime Polymer Co., Ltd.) having an MFR of 0.3 g / 10 min, and a metallocene plastomer (Kernel KS240T manufactured by Nippon Polytech Co., Ltd.) having an MFR of 2.2 g / 10 min In the same manner as in Example 1, a sheet-like foam having a thickness of 0.5 mm was obtained.

[Example 3]
A sheet-like foam having a thickness of 0.5 mm was obtained in the same manner as in Example 2 except that a metallocene plastomer having an MFR of 12 g / 10 min (kernel KS571 manufactured by Nippon Polyethylene Co., Ltd.) was used.

[Example 4]
A sheet-like foam having a thickness of 0.5 mm was obtained in the same manner as in Example 2 except that a metallocene plastomer having an MFR of 2.2 g / 10 min (kernel KF282 manufactured by Japan Polytechnic Co., Ltd.) was used.

[Comparative Example 1]
A polypropylene resin foam was obtained in the same manner as in Example 1 except that the thermoplastic elastomer was changed to 90 parts by weight and the amount of the cell nucleating agent was changed to 5 parts by weight.

[Comparative Example 2]
Inoac Polon L-32 was used as it was.

1: Foam molding part 2: Bubble generation part 3: Blowing agent-containing kneaded molten resin flow path part 4: Ring die-in side mold 5: Ring die-out side mold

Claims (5)

It is composed of a polyolefin resin foam having an apparent density of ^{30 to} 100 kg / m ³ and an open cell ratio of 20 to 70%, and has a static friction coefficient with respect to a stainless steel plate of 0.5 or more. Wood.   The vibration damping material according to claim 1, wherein the polyolefin resin foam has a loss coefficient tan δ of 0.05 or more in solid viscoelasticity measurement at 25 to 120 ° C.   The vibration damping material according to claim 1 or 2, wherein the polyolefin resin foam has a compressive stress of 400 kPa or less when compressed by 80% at a compression speed of 1 mm / min.   The damping material according to any one of claims 1 to 3, wherein the polyolefin resin foam has a compressive stress of 1500 kPa or less when compressed by 90% at a compression rate of 1 mm / min.   The vibration damping material according to any one of claims 1 to 4, further comprising an elastomer and / or a plastomer.