JP6012566B2 - Polyolefin resin thin-layer foamed sheet, method for producing the same, and use thereof - Google Patents

Description

  The present invention relates to a polyolefin-based resin thin-layer foam sheet, a production method thereof, and an application thereof. More specifically, the present invention relates to a polyolefin-based resin thin-layer foamed sheet that is optimal as a sealing material for electronic devices that have been reduced in thickness, weight, and size, a method for producing the same, and a use thereof.

Polyolefin resin foams are widely used as cushioning materials (sealing materials), packaging materials, packing materials and the like because of their high strength and excellent flexibility.
In recent years, as electronic devices such as smartphones and tablet terminals are made thinner, lighter, and smaller, members used are also required to be thinner, lighter, and smaller. Among them, the sealing material is also required to be thinner and lighter, and a thin layer sheet of 0.5 mm or less is desired.

Conventionally, as a sealing material, a thin film obtained by slicing a foam or a film has been used.
However, in the slicing process, it is difficult to stably process to 0.5 mm or less, and it is difficult to process a thinner 0.4 mm or less.
In addition, the film can be thinned, but since it does not have a bubble layer, it is inferior in flexibility and shock-absorbing properties, inferior in sealing and dust-proofing effects compared to foam, and non-foamed. However, there is a problem that the weight increases.

  For example, in Japanese Patent Application Laid-Open No. 2003-94378 (Patent Document 1), after a resin film is bonded to one side of a polyolefin resin foam to form a laminate, the resin film side of the laminate has a predetermined thickness. A method for producing a polyolefin-based resin foam laminated sheet to be sliced has been proposed. According to this method, it is said that there is no trouble such as the resin foam being cut, and the polyolefin resin foam laminated sheet can be continuously produced with high accuracy even when the thickness is 0.7 mm or less.

  Japanese Patent Application Laid-Open No. 2012-107161 (Patent Document 2) discloses a closed cell cross-linked polyolefin resin foam having a specific product of tensile strength and average number of cells (cells) in a different direction under specific conditions. There has been proposed a method for producing an open-cell crosslinked polyolefin resin foam by allowing bubbles to communicate with each other by repeatedly performing a compression process of passing through and rotating between two rotating rolls a plurality of times. According to this method, it is said that an open-cell crosslinked polyolefin resin foam excellent in low compressive strain and sealing properties can be obtained.

JP 2003-94378 A JP 2012-107161 A

  In the technique of Patent Document 1, since the foam and the film are bonded and sliced to form a thin layer, the obtained foam is a foamed laminated sheet with a film. Moreover, although it is said that even if it is 0.7 mm or less in thickness, a foaming lamination sheet can be continuously produced with sufficient precision, the thickness of the foam actually obtained is larger than 0.5 mm. Thus, it is difficult to reduce the thickness of the foam to a thickness of 0.5 mm or less, and when the thickness is 0.4 mm or less, the variation further increases.

  In the technique of Patent Document 2, since a closed cell foam sheet is passed through a roll to form continuous cells, the obtained foam is hard and heavy, and further weight reduction is a problem. Moreover, there exists a subject that the energy of a heating and pressurization is required in the roll passage for making closed cells into continuous cells.

  Accordingly, it is an object of the present invention to provide a polyolefin resin thin-layer foamed sheet that is optimal as a sealing material for electronic devices that have been reduced in thickness, weight, and size, a manufacturing method thereof, and an application thereof.

  The inventors of the present invention have conventionally disclosed a polyolefin resin foam sheet having a plurality of bubbles partitioned by a wall containing a polyolefin resin and having a specific thickness, a foaming ratio, an open cell rate, and a bubble breaking rate. It has been found to be thinner, lighter, and smaller than other foam sheets, and it is superior in flexibility and lightness compared to films, and is optimal as a sealing material for electronic devices that are thinner, lighter, and smaller. The present invention has been reached.

  Further, the inventors of the present invention have a plurality of bubbles partitioned by a wall containing a polyolefin-based resin and have a specific thickness, a foaming ratio, an open cell rate, a bubble breaking rate, and an average cell diameter. It was found that a thin sheet that could not be obtained by slicing can be easily manufactured by heating at least one surface of a resin foam sheet and pressing the molten sheet surface to a specific thickness to achieve the present invention. It was. That is, in the present invention, a flexible sheet having a high open cell ratio can be hot-pressed to leave a bubble layer and easily obtain a thin-layer sheet including only a foam sheet.

  Thus, according to the present invention, a polyolefin resin thin-layer foamed sheet having a plurality of bubbles partitioned by a wall containing a polyolefin resin, having a thickness of 0.05 to 0.5 mm and an expansion ratio of 2 to 15 times A polyolefin-based resin thin-layer foamed sheet having an open cell ratio of 30 to 95% and a bubble breakage ratio of 1 to 30% is provided.

Moreover, according to the present invention, there is provided a method for producing the above polyolefin resin thin layer foam sheet,
It has a plurality of bubbles partitioned by a wall containing a polyolefin resin, has a thickness of 0.2 to 3.0 mm, an expansion ratio of 10 to 25 times, an open cell ratio of 75 to 95%, and a bubble breakage ratio of 5 to 30 %, A step of obtaining a polyolefin resin foam sheet having an average cell diameter of 0.02 to 0.2 mm, and heating at least one surface of the obtained polyolefin resin foam sheet, and pressing while melting the foam sheet surface There is provided a method for producing a polyolefin resin thin-layer foamed sheet comprising a step of obtaining a polyolefin resin thin-layer foamed sheet obtained by compressing the foamed sheet at a compression rate of 20 to 95%.

  Furthermore, according to this invention, the sealing material for electronic devices containing the said polyolefin resin thin layer foam sheet and the base material for adhesive tapes are provided.

  According to the present invention, it is possible to provide a polyolefin-based resin thin-layer foamed sheet that is optimal as a sealing material for electronic devices that are reduced in thickness, weight, and size, a manufacturing method thereof, and an application thereof.

The polyolefin resin thin-layer foam sheet of the present invention is
(1) A first cut surface including a straight line parallel to the thickness direction of the polyolefin-based resin thin-layer foam sheet, a second cut surface perpendicular to the first cut surface, and a third perpendicular to the first cut surface and the second cut surface The average bubble diameter of the bubbles at the cut surface is 0.01 to 0.18 mm.
(2) The direction perpendicular to the thickness direction of the polyolefin-based resin thin-layer foamed sheet on the first cut surface including a straight line parallel to the thickness direction of the polyolefin-based resin thin-layer foamed sheet and the second cut surface perpendicular to the first cut surface Tear strengths of 30 to 450 N / cm and 15 to 200 N / cm, respectively.
(3) The polyolefin-based resin thin layer foamed sheet has a non-foamed layer having a thickness of 1 to 30 μm on at least one surface layer (having a non-foamed layer in the range of 1 to 30 μm on at least one surface layer). ), And (4) The above-described effects are further exhibited when the polyolefin-based resin thin-layer foamed sheet satisfies any one condition of having at least one or more bubbles in the thickness direction (VD direction).

The method for producing a polyolefin-based resin thin-layer foam sheet of the present invention is as follows.
(5) The heating temperature is 5 to 100 ° C. lower than the melting point mp of the polyolefin resin, and the press pressure is 0.1 to 1.0 MPa.
(6) Carbon dioxide gas is used as a foaming agent in the step of obtaining a polyolefin-based resin foamed sheet, and (7) The molded part where the polyolefin-based resin foamed sheet grows bubbles and grows the generated bubbles and forms the sheet. The above-described effect is further exhibited when any one of the conditions is produced by using a mold ring die constituted by:

It is a figure explaining the binarization of the cross-sectional image for measuring the bubble tear rate of a foam sheet. 2 is an electron micrograph of a cut surface of a polyolefin resin foam sheet in Example 1. FIG. It is the electron micrograph of MD direction and TD direction of the cut surface of the polyolefin-type resin thin layer foam sheet in Example 1. FIG. It is the electron micrograph of MD direction and TD direction of the cut surface of the polyolefin-type resin thin layer foam sheet in Example 2. FIG. It is the electron micrograph of MD direction and TD direction of the cut surface of the polyolefin-type resin thin layer foam sheet in Example 3. FIG. It is a figure which shows the measuring method of the average bubble diameter of a foam sheet.

(Polyolefin resin thin-layer foam sheet)
The polyolefin-based resin thin-layer foamed sheet of the present invention (hereinafter also referred to as “thin-layer foamed sheet”) is a polyolefin-based resin thin-layer foamed sheet having a plurality of bubbles partitioned by a wall containing a polyolefin-based resin and having a thickness. Is 0.05 to 0.5 mm, the expansion ratio is 2 to 15 times, the open cell rate is 30 to 95%, and the bubble breaking rate is 1 to 30%.

The thin layer foam sheet of the present invention has a thickness of 0.05 to 0.5 mm.
When the thickness of the thin-layer foamed sheet is less than 0.05 mm, the mechanical strength is lowered, and winding with a roll may be difficult. On the other hand, if the thickness of the thin-layer foamed sheet exceeds 0.5 mm, it is not preferable because it is not suitable as a sealing material for electronic devices that are thin, light, and miniaturized.
A preferred thickness is in the range of 0.05 to 0.4 mm, and a more preferred range is 0.05 to 0.35 mm.
The thickness variation is preferably about ± 0.05 mm.

Moreover, the thin-layer foamed sheet of the present invention has a foaming ratio of 2 to 15 times.
The expansion ratio of the thin-layer foamed sheet is a value calculated from the apparent density and the polyolefin resin density measured according to the method described in JIS K 7222-1999. I will explain it.
When the expansion ratio of the thin-layer foamed sheet is less than 2, the flexibility may be inferior and the lightness may be inferior. On the other hand, when the expansion ratio of the thin-layer foamed sheet exceeds 15 times, the mechanical strength may be inferior.
A preferable foaming ratio is in a range of 2 to 14 times, and a more preferable range is 2 to 13 times.

Furthermore, the thin-layer foamed sheet of the present invention has an open cell ratio of 30 to 95%.
A specific method for measuring the open cell ratio of the thin-layer foamed sheet will be described in the Examples section.
When the open cell ratio of the thin-layer foamed sheet is less than 30%, the stress when compressed may be high. On the other hand, when the open cell ratio of the thin-layer foamed sheet exceeds 95%, the mechanical strength of the sheet may be lowered.
A preferable open cell ratio is in the range of 35 to 95%, and a more preferable range is 40 to 90%.

Moreover, the thin layer foamed sheet of the present invention has a bubble breaking rate of 1 to 30%.
The bubble breakage rate is obtained by binarizing a scanning electron micrograph of the cross section of the thin-layer foamed sheet so that the torn part and the other part 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.
When the cell tearing rate of the thin-layer foamed sheet is less than 1%, the stress when compressed may increase. On the other hand, if the cell tearing rate of the thin-layer foamed sheet exceeds 30%, the mechanical strength of the sheet may decrease.
A preferable bubble breaking rate is in the range of 1 to 25%, and a more preferable range is 1 to 20%.

The thin-layer foamed sheet of the present invention includes a first cut surface including a straight line parallel to the thickness direction of the thin-layer foamed sheet, a second cut surface perpendicular to the first cut surface, and a first cut surface and a perpendicular to the second cut surface. It is preferable that the average bubble diameter of the bubble in a 3rd cut surface is 0.01-0.18 mm.
When the thin-layer foam sheet obtained by hot pressing is derived from a foam sheet obtained by extrusion foam molding, the first cut surface is a surface parallel to the sheet flow direction (MD direction) during molding of the foam sheet, It is good also considering a cut surface as a surface parallel to the sheet | seat width direction (TD direction) at the time of shaping | molding of a foam sheet.
A specific method for measuring the average cell diameter of the bubbles at each cut surface of the thin-layer foamed sheet will be described in the Examples section.

If the average cell diameter of the bubbles on the first cut surface is less than 0.01 mm, it may be difficult to obtain a foam sheet having sufficient cushioning properties and cushioning properties. On the other hand, if the average bubble diameter of the bubbles on the first cut surface exceeds 0.18 mm, followability to fine irregularities may be inferior.
A preferable average cell diameter of the bubbles on the first cut surface is in the range of 0.01 to 0.17 mm, and a more preferable range is 0.01 to 0.16 mm.

  When the average cell diameter of the bubbles on the second cut surface is less than 0.01 mm, it may be difficult to obtain a foam sheet having sufficient cushioning properties and cushioning properties. On the other hand, when the average bubble diameter of the bubbles on the second cut surface exceeds 0.18 mm, followability to fine irregularities may be inferior. A preferable average cell diameter of the bubbles on the second cut surface is in the range of 0.01 to 0.17 mm, and a more preferable range is 0.01 to 0.16 mm.

  If the average cell diameter of the bubbles on the third cut surface is less than 0.01 mm, it may be difficult to obtain a foam sheet having sufficient cushioning properties and cushioning properties. On the other hand, if the average bubble diameter of the bubbles on the third cut surface exceeds 0.18 mm, followability to fine irregularities may be inferior. The average bubble diameter of the bubbles on the preferred third cut surface is in the range of 0.01 to 0.17 mm, and the more preferred range is 0.01 to 0.16 mm.

Moreover, the thin-layer foam sheet of this invention is perpendicular | vertical to the thickness direction of the thin-layer foam sheet in the 1st cut surface containing the straight line parallel to the thickness direction of a thin-layer foam sheet, and the 2nd cut surface perpendicular | vertical to a 1st cut surface. It is preferable that the tear strengths in different directions are 30 to 450 N / cm and 15 to 200 N / cm, respectively.
When the thin-layer foamed sheet obtained by hot pressing is derived from the foamed sheet formed by extrusion foaming, the sheet flow during molding of the foamed sheet is in the direction perpendicular to the thickness direction of the thin-layer foamed sheet at the first cut surface. The direction perpendicular to the thickness direction of the thin-layer foamed sheet in the direction (MD direction) and the second cut surface may be the sheet width direction (TD direction) when the foamed sheet is formed.
The tear strength of the thin-layer foamed sheet refers to a value measured according to the method described in JIS K 6767-1999 Foamed Plastics-Polyethylene Test Method, and a specific measurement method will be described in the column of Examples.

If the tear strength in the direction perpendicular to the thickness direction of the thin-layer foamed sheet at the first cut surface is less than 30 N / cm, the mechanical strength may decrease and winding may be difficult. On the other hand, when the tear strength in the direction perpendicular to the thickness direction of the thin-layer foamed sheet at the first cut surface exceeds 450 N / cm, secondary workability may be inferior.
The tear strength in the direction perpendicular to the thickness direction of the thin-layer foamed sheet at the preferred first cut surface is in the range of 30 to 430 N / cm, and more preferably in the range of 30 to 400 N / cm.
When the tear strength in the direction perpendicular to the thickness direction of the thin-layer foamed sheet at the second cut surface is less than 15 N / cm, the mechanical strength may decrease and winding may be difficult. On the other hand, if the tear strength in the direction perpendicular to the thickness direction of the thin-layer foam sheet at the second cut surface exceeds 200 N / cm, the secondary workability may be inferior.
The tear strength in the direction perpendicular to the thickness direction of the thin-layer foamed sheet at the preferred second cut surface is in the range of 15 to 180 N / cm, and more preferably in the range of 15 to 160 N / cm.

The thin-layer foamed sheet of the present invention preferably has a non-foamed layer having a thickness of 1 to 30 μm on at least one surface layer.
If the thickness of the non-foamed layer is less than 1 μm, the mechanical strength may be insufficient and winding may be difficult. On the other hand, when the thickness of the non-foamed layer exceeds 30 μm, the stress at the time of compression may increase.
A preferable thickness of the non-foamed layer is in the range of 1 to 25 μm, and a more preferable range is 1 to 20 μm.
Although described in detail in the method for producing a thin-layer foamed sheet, the non-foamed layer can be formed by heating and melting the foamed sheet.

Moreover, it is preferable that the thin-layer foam sheet of this invention has at least 1 or more bubble in the thickness direction (VD direction).
If the number of bubbles is 0, the buffer property of the thin-layer foamed sheet is impaired, which is not preferable. On the other hand, as the number of bubbles increases, the buffer property of the thin-layer foamed sheet can be obtained, but it is not preferable because the strength of the thin-layer foamed sheet is insufficient. The number of bubbles is preferably about 1 to 20 although it depends on the bubble diameter.

The polyolefin resin constituting the thin layer foamed sheet of the present invention is not particularly limited as long as the various physical properties can be imparted to the thin layer foamed sheet. Specific examples include homopolyethylene, homopolypropylene, ethylene or a copolymer of propylene and other olefins. The copolymer may be either a random copolymer or a block copolymer. Polyolefin resins may be used singly or in appropriate combination of two or more.
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.
Among these, homopolypropylene excellent in foamability and heat resistance and a block copolymer of polypropylene are preferable. In particular, homopolypropylene having excellent heat resistance is preferable.

  The polyolefin resin is preferably a resin having a melt flow rate (MFR) of 0.2 to 5 g / 10 min. If the MFR is low, the load on the extruder increases and the productivity is reduced, or the raw material mixture of the molten foam sheet containing the foaming agent cannot flow smoothly in the mold, and the resulting foam sheet is obtained. The surface may be uneven and the appearance may deteriorate. On the other hand, if it is high, the resin pressure in front of the mold ring die will decrease, and the resin pressure in the ring die bubble generation unit will also decrease, so bubbles will be generated in front of the bubble generation unit and in the foam sheet molding unit When foam breakage occurs abruptly, foamability is lowered, and the appearance of the resulting foamed sheet may be deteriorated or a foamed sheet may not be obtained. A more preferable MFR is 0.2 to 4 g / 10 min, and a more preferable MFR is 0.2 to 3.5 g / 10 min.

  The polypropylene resin is preferably a high melt tension polypropylene resin having excellent foamability. Examples of the high melt tension polypropylene resin 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. Specific examples of commercially available products include the trade name “Newstrain SH9000” manufactured by Nippon Polypro Co., Ltd. and the product name “DaployWB135HMS” manufactured by Borealis. It is done.

The thin layer foamed sheet of the present invention may contain other components in addition to the polyolefin resin. For example, a thermoplastic elastomer is mentioned.
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 manufactured by physically dispersing polyolefin resin that becomes hard segment and rubber component that becomes soft segment using a kneading machine; using kneading machines 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 micro-dispersed in the polyolefin resin matrix. Dynamically cross-linked Elastomer, and the like.

Among the above-mentioned thermoplastic elastomers, 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 thin-layer foamed sheet is recycled and supplied to the extruder again for foam molding, it is possible to suppress foaming failure due to the crosslinked rubber, which becomes a problem when the crosslinked elastomer is used.

  If the content of the thermoplastic elastomer is small, the cushioning property and flexibility of the thin-layer foamed sheet may be poor. On the other hand, if the amount is too large, the foam elasticity may decrease due to the rubber elasticity of the thermoplastic resin composition becoming too strong, and the shrinkage of the thin-layer foamed sheet may increase. The content is preferably about 10 to 300 parts by weight, more preferably about 15 to 150 parts by weight, still more preferably about 20 to 100 parts by weight, and more preferably 25 to 70 parts by weight with respect to 100 parts by weight of the polyolefin resin. The degree is particularly preferred.

Thin-layer foamed sheets include surfactants, dispersants, weathering stabilizers, light stabilizers, pigments, dyes, flame retardants, plasticizers, lubricants, UV absorbers, antioxidants, fillers in addition to thermoplastic elastomers. , 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 other additives can be appropriately selected within a range that does not impair the formation of bubbles and the physical properties of the thin-layer foamed sheet, and the content contained in a normal thin-layer foamed sheet can be adopted.

(Manufacturing method of polyolefin resin thin layer foam sheet)
The method for producing a polyolefin-based resin thin-layer foam sheet of the present invention is as follows.
It has a plurality of bubbles partitioned by a wall containing a polyolefin resin, has a thickness of 0.2 to 3.0 mm, an expansion ratio of 10 to 25 times, an open cell ratio of 75 to 95%, and a bubble breakage ratio of 5 to 30 %, A step of obtaining a polyolefin resin foam sheet having an average cell diameter of 0.02 to 0.2 mm (step A), and heating at least one surface of the obtained polyolefin resin foam sheet to melt the foam sheet surface A step of obtaining a polyolefin-based resin thin-layer foamed sheet that is pressed at a compression rate of 20 to 95% of that of the foamed sheet (Step B)
It is characterized by including.

  For example, FIG. 2 is an electron micrograph of the cut surface of the foam sheet obtained in step A, and FIGS. 3 to 5 are electron micrographs of the MD and TD directions of the cut surface of the thin resin layer foam sheet obtained in step B. It is.

(Process A)
In step A, it has a plurality of bubbles partitioned by a wall containing a polyolefin-based resin, has a thickness of 0.2 to 3.0 mm, a foaming ratio of 10 to 25 times, an open cell ratio of 75 to 95%, and a bubble breakage rate Of 5 to 30% and an average cell diameter of 0.02 to 0.2 mm is obtained.

The foam sheet of the present invention 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 type extruder. Among these, a tandem type extruder is preferable because the extrusion conditions can be easily adjusted.
The raw material of the foam sheet is kneaded in the extruder, extruded from the extruder, and foamed to become a foam sheet. A die is usually installed at a portion where the raw material of the foam sheet is extruded from the extruder. An example of such a die is an annular die (sizing die).

An annular die is a foam sheet molding that is formed at the aperture of the foaming agent-containing kneaded molten resin flow path section, and the foam sheet molding that is continuous with the bubble generation section and grows the foam and smoothes the foam sheet surface. Part.
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 sheet using an annular die as described above, even if the bubbles forming the foam sheet are finer than before, the occurrence of numerous corrugated sheets that reduce surface smoothness on the sheet surface is suppressed. it can. The inventors believe 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 foamed sheet molding part. The corrugated here means a large number of ridges and valleys formed by undulation of the foam sheet coming out of the annular die so as to absorb the linear expansion in the circumferential direction due to volume expansion.
Here, it is preferable to perform extrusion foaming under conditions where the resin discharge speed V in the bubble generating portion of the annular die is 50 to 300 kg / cm ² · hr and the resin pressure before the annular die is 7 MPa or more. .

When the discharge speed V is less than about 50 kg / cm ² · hr, it becomes difficult to obtain finer bubbles and a foam sheet having a high expansion ratio. On the other hand, when it is larger than about 300 kg / cm ² · hr, the resin generates heat in the mold bubble generation part and the bubbles are broken, and the expansion ratio is liable to decrease. In addition, a corrugated corrugate is likely to occur, and the cell diameter may be non-uniform and the surface smoothness of the foam sheet 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 · hr) 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 / hr).

Preferably ejection velocity V is approximately 70~250kg / cm ² · hr, and more preferably about 100~200kg / cm ² · hr. The resin pressure in front of the annular die is preferably 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 foamed sheet is improved. For example, a sheet-like foamed sheet obtained by slicing can be obtained with excellent 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 sheet 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.

  As described above, in the process A, the foam sheet is manufactured by using a mold annular die constituted of a bubble generation portion and a formation portion for growing the generated bubble and forming the sheet. Is preferred.

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 adjust the bubble breaking rate with the resin pressure, the resin pressure in front of the annular die is 10 to 30% lower than the extrusion conditions for obtaining a closed cell foamed sheet or a foamed sheet with a small bubble breaking rate. do it.
In order to adjust the bubble breakage rate with the resin temperature, the resin temperature may be increased by 1 to 3 ° C. than the extrusion conditions under which a closed cell foamed sheet or a foamed sheet with a low bubble breakage rate is obtained.

The raw material of the foam sheet 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, and methyl ethyl ether, and inorganic gases such as carbon dioxide, nitrogen, and ammonia. These foaming agents may be used alone or in combination of two or more.

  Among the foaming agents, inorganic gas is preferable, and carbon dioxide is particularly preferable. Carbon dioxide is a foam having finer bubbles than the conventional foam sheet obtained by using carbon dioxide in other forms by using carbon dioxide in a supercritical state, subcritical state, or liquefied carbon dioxide. A sheet can be obtained. The foam sheet having fine bubbles can improve the surface smoothness and flexibility.

  The amount of the foaming agent press-fitted into the extruder can be adjusted as appropriate according to the apparent density of the foamed sheet. However, when the amount is small, the apparent density of the thin-layer foamed sheet is increased, and the lightness and flexibility may be lowered. On the other hand, if it is large, bubbles may be broken in the mold, and a large gap may be formed in the foamed sheet. Therefore, the amount of the foaming agent is preferably 1 to 10 parts by weight, more preferably 2 to 8 parts by weight, and 3 to 6 parts by weight with respect to 100 parts by weight of the raw material of the foam sheet. Particularly preferred.

The raw material of the foamed sheet 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 hydrogen carbonate, glass beads, and organic compounds such as polytetrafluoroethylene, azodicarbonamide, and a mixture of sodium hydrogen carbonate and citric acid. Among them, talc is preferable for inorganic compounds, and polytetrafluoroethylene is preferable for organic compounds because it has a high effect on bubble miniaturization. Further, it is particularly preferable that the polytetrafluoroethylene becomes a fibril when dispersed to increase the melt tension of the resin.

  If the amount of the bubble nucleating agent is small, it is difficult to increase the number of bubbles in the foam sheet, and the average bubble diameter cannot be reduced, and the bubble breakage rate may not be increased. On the other hand, if the amount is large, secondary aggregation may occur, resulting in poor extrusion foaming. Therefore, the amount of the cell nucleating agent is preferably 0.01 to 15 parts by weight, and more preferably 0.1 to 12 parts by weight with respect to 100 parts by weight of the raw material of the foam sheet.

  The cell nucleating agent may be supplied into the extruder as a raw material mixture of the foamed sheet by mixing itself with other components of the foamed sheet or individually. In addition, the bubble nucleating agent is mixed with the base resin in advance as a masterbatch for easy handling and prevention of contamination of the production environment due to powder scattering and for improving dispersibility in the thermoplastic resin. It is preferable to supply. The masterbatch can be usually obtained by kneading an additive or the like in a thermoplastic base resin at a high concentration to form a pellet.

  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.

(Process B)
In Step B, a polyolefin resin thin layer obtained by heating at least one surface of the obtained polyolefin resin foam sheet, pressing the foam sheet surface while melting, and compressing the foam sheet at a compression rate of 20 to 95%. A foam sheet is obtained.

The thin-layer foamed sheet of the present invention can be obtained by heat-pressing a polyolefin resin foamed sheet using a known apparatus such as a dielectric heating roll or a press.
The conditions of the heating press may be set as appropriate depending on the apparatus used, the raw material of the thin-layer foamed sheet, particularly the thermal physical properties of the resin, and the heating temperature is 5 to 100 ° C. lower than the melting point mp of the polyolefin resin, And it is preferable that the pressure of the said press is 0.1-1.0 MPa.
When the polyolefin resin is a polypropylene resin, the heating temperature is preferably in the range of 60 to 160 ° C. because it has a melting point mp in the range of 140 to 180 ° C.
Further, if the pressing pressure is less than 0.1 MPa, it may be difficult to accurately press the foamed sheet. On the other hand, when the pressure of the press exceeds 1.0 MPa, the foamed sheet may be crushed too much.
The pressing speed may be appropriately set depending on conditions such as heating temperature and pressing pressure, the following compression ratio, etc., but is about 0.1 to 20 m / min.
Moreover, a spacer etc. can be used suitably for a dielectric heating roll and a press so that it may become target thickness.

In the process B, it heat-presses to the thickness of 20 to 95% of a foam sheet (compression rate).
When the thickness of the hot press is less than 20% of the foamed sheet, a thin layer sheet having a sufficient thickness may not be obtained. On the other hand, if the heating press exceeds 95% of the thickness of the foamed sheet, the number of bubbles in the thin-layer foamed sheet is reduced, and the flexibility may be inferior.
A preferable hot press is in the range of 20 to 90% of the foamed sheet, and a more preferable range is 20 to 85%.

  When a foam is heated and pressed using a dielectric heating roll or a press, another material may be in contact between the surface of the foam and the heating roll or press. For example, PET film, aluminum foil, non-woven fabric, etc. These materials may be separated from the foamed sheet after pressing, or may remain bonded.

(Use of polyolefin resin thin-layer foam sheet)
The thin-layer foamed sheet of the present invention is thinner and lighter than conventional sliced foamed sheets, lighter than resin sheets (non-foamed films), and has a cushioning property. It can be used as a sealing material for downsized electronic devices and a base material for adhesive tape.
ADVANTAGE OF THE INVENTION According to this invention, the sealing material for electronic devices containing the thin layer foam sheet of this invention and the base material for adhesive tapes can be provided.

  The application of the sealing material for electronic equipment of the present invention is not particularly limited, and can be used for fixing electronic components inside various electronic equipment packages. Electronic devices include mobile phones (smartphones), digital cameras, portable game consoles, personal computers, tablet terminals, portable DVD players, etc. Microphones, speakers, flashes, viewfinders, motors, LEDs for these electronic devices Examples include around display devices, speakers, key cushions, battery cushions, substrates, and liquid crystal displays. Among these, because it has excellent buffering (shock absorption) properties, it closes portable electronic devices such as tablet terminals, digital cameras, portable game machines, mobile phones, portable DVD players, and notebook computers. It can be preferably used in the inside.

The application of the adhesive tape substrate of the present invention is not particularly limited, and can be used for applications that smoothly absorb the impact applied to various electronic devices and prevent the entire electronic device from being subjected to a large impact. Moreover, it can be used suitably also as a dustproof material and waterproofing material which prevent penetration | invasion to apparatuses, such as dust and water. Examples of the electronic device include those exemplified for the use of a sealing material for electronic devices.
The base material for adhesive tapes of this invention can be used in combination with well-known adhesive agents and adhesives, such as a double-sided tape.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, the following examples are only illustrations of this invention and this invention is not limited only to the following examples.
In Examples and Comparative Examples, the obtained polyolefin-based resin foam sheet and polyolefin-based resin thin-layer foam sheet (these are also referred to as “foam sheets”, but when divided, the former is referred to as “foam sheet” and the latter (Hereinafter referred to as “thin layer foam sheet”) was evaluated as follows.
In addition, the apparatus used in the following evaluation is not specifically limited, You may use the apparatus in which an equivalent measurement is possible.

(Thickness and its variation)
The thicknesses of the foamed sheet and the thin-layer foamed sheet are measured at 12 points at 30 mm intervals in the sheet width direction (TD direction), and the average value is calculated. The thickness measuring device measures the thickness of the polyolefin resin foam sheet with a size of φ10 mm and no load. A thickness gauge (model number “NO. 547-301”) manufactured by Mitutoyo Corporation can be used as a measuring device used for measuring the thickness of the foam sheet and the thin-layer foam sheet.
The thickness variation between the foam sheet and the thin-layer foam sheet refers to the difference (mm) between the maximum value and the minimum value of the thicknesses measured at the above 12 points.

(Foaming ratio)
The expansion ratio of the foam sheet and the thin-layer foam sheet refers to a value calculated from the apparent density and the polyolefin resin density measured according to the method described in JIS K 7222-1999.
Specifically, a specimen 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 (bubble) structure of the sample, and the mass and volume thereof are determined. Measure and calculate the apparent density by the following formula.
Apparent density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
Using the density of the polyolefin resin (polypropylene and thermoplastic elastomer) and the apparent density, the expansion ratio is calculated by the following formula.
Foaming ratio (times) = polyolefin resin density (g / cm ³ ) / apparent density (g / cm ³ )

(Open cell ratio)
The open cell ratio of the foam sheet and the thin layer foam sheet is a value measured as follows.
Specifically, an actual volume V of a sample piece obtained by superposing a sample cut into a 25 mm square to a thickness of about 5 cm is used as a micrometric automatic dry density meter (manufactured by Shimadzu Corporation, model: Accupic II 1340 (V1.0 )) To measure. The test pieces are stacked so that there is as little gap as possible between the test pieces to a thickness of about 5 cm. Further, the apparent volume V0 of the test piece is calculated from the outer shape of the test piece. From the obtained value, the open cell ratio (%) is calculated by the following formula.
Open cell ratio (%) = (V0−V) / V0 × 100

(Average cell diameter of foam sheet)
The average cell diameter of the foam sheet refers to a value measured by the following test method.
The foamed sheet was cut out perpendicularly to the sheet surface along the MD direction (extrusion direction: arrow 1 in FIG. 6) and TD direction (width direction perpendicular to the extrusion direction: arrow 2 in FIG. 6) from the center in the width direction. The cross section is photographed at a magnification of 20 to 100 times with a scanning electron microscope (manufactured by Hitachi, Ltd., model: S-3000N or Hitachi High-Technologies Corporation, model: S-3400N). At this time, the magnification of the electron microscope is adjusted so that the number of bubbles present on a 60 mm straight line drawn on the printed photograph is about 10 to 20.
Four images are printed on the A4 sheet, and the average chord length (t) of the bubbles is calculated from the number of bubbles on an arbitrary straight line (length 60 mm) parallel and perpendicular to each direction by the following equation. .
Average chord length t (mm) = 60 / (number of bubbles × photo magnification)
However, when the thickness of the test piece is thin and the number of bubbles for 60 mm length cannot be counted in the VD direction (sheet thickness direction: arrow 3 in FIG. 6), the number of bubbles for 30 mm or 20 mm is counted for 60 mm. Convert to the number of bubbles. Arbitrary straight lines are included so that bubbles do not touch only at the contact points as much as possible. Measurement is performed at 3 locations, 2 locations, using 2 images per direction.

The magnification of the photograph is obtained by the following equation by measuring the scale bar on the photograph up to 1/100 mm with “Digimatic Caliper” manufactured by Mitutoyo Corporation.
Photo magnification = Scale bar measured value (mm) / Scale bar display value (mm)
And the bubble diameter in each direction is calculated by the following formula.
D (mm) = t / 0.616
Furthermore, let the cube root of those products be an average bubble diameter.
Average bubble diameter (mm) = (D _MD × D _TD × D _VD ) ^1/3
D _MD : Bubble diameter in the MD direction (mm)
D _TD : Bubble diameter in TD direction (mm)
D _VD : Bubble diameter in the VD direction (mm)

(Average cell diameter of thin layer foam sheet)
The average cell diameter of the thin-layer foamed sheet is measured in the same manner as the measurement of the average cell diameter of the foamed sheet except that the enlargement ratio is 500 times.

(Heating dimensional change rate)
The heating dimensional change rate of the foamed sheet refers to a value measured as follows in accordance with the method described in JIS K 6767-1999 Foamed Plastics-Polyethylene Test Method.
Specifically, a square of 100 mm × 100 mm is similarly drawn along the flow direction of the sheet at the time of manufacture inside the test piece cut into 150 mm × 150 mm along the flow direction of the sheet at the time of manufacture. The lengths L _MD0 and L _TD0 in the sheet flow direction (MD direction) and the sheet width direction (TD direction) are accurately measured.
Then, the test piece was heated for 22 hours at 140 ° C., standard conditions (temperature 23 ± 2 ° C., a relative humidity of 50 ± 5%) after standing 1 hour at in each direction length L _MD and L _TD Measure accurately.
The resulting respective dimension change rate in the following equation from the value (%) was calculated [Delta] L _MD and [Delta] L _TD, the high number of variation rate (absolute value) and the dimensional change rate [Delta] L (%) of the specimen .
Dimensional change rate ΔL _MD (%) = (L _MD −L _MD0 ) / L _MD0 × 100
Dimensional change rate ΔL _TD (%) = (L _TD −L _TD0 ) / L _TD0 × 100

(50% compressive stress)
The compressive stress of the foam sheet is measured using a Tensilon universal testing machine UCT-10T (Orientec Co., Ltd.) and universal testing machine data processing software UTPS-STD (Soft Brain Co., Ltd.).
The specimen size is 50 × 50 × 2 mm, the origin of displacement is the initial load point (sample initial stress 1.6 kPa setting), and the compression speed is 1 mm / min. When the thickness of the test piece is 2 mm or more, measurement is performed using the test piece as it is, and when the thickness of the test piece is less than 2 mm, the test pieces are stacked to have a thickness of about 2 mm.

The stress at the time of 50% compression of the initial thickness (measured value of the digital linear gauge) is defined as a compressive stress. The number of test pieces shall be three. The sample dimensions were measured with Mitsutoyo's “Digimatic Caliper” for width and length up to 1/100 mm, with Peacock's “Digital Linear Gauge” measuring area of 10 cm ² and a weight of 50 gf (total 1.0 kPa). Is measured to 1/100 mm. The test piece is conditioned for 16 hours or more in an environment of temperature 23 ± 2 ° C. and humidity 50 ± 5%, and then measured in an environment of temperature 23 ± 2 ° C. and humidity 50 ± 5%. The compressive stress is calculated by the following formula.
σ ₅₀ = F ₅₀ / A ₀ × 10 ³
σ ₅₀ : compressive stress (kPa)
F ₅₀ : Load at the time of 50% deformation (N)
A ₀ : Initial cross-sectional area of the test piece (mm ² )

(Bubble breaking rate)
The bubble breakage rate of the foam sheet and the thin-layer foam sheet is a value measured as follows.
Specifically, the sample is cut by an arbitrary surface including a straight line parallel to the thickness direction, and the cut surface is enlarged to 20 times magnification with a scanning electron microscope (manufactured by Hitachi, Ltd., model: S-3000N). To shoot.
Next, the image of the cut surface is taken into 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, and the set range is binarized. In binarization, black and white are reversed at threshold = 50. For example, binarization is performed as shown in FIG. 1A (before binarization) and FIG. 1B (after binarization). In addition, the sample of FIG. 1 is a foamed sheet before a heat press.
In the binarized image, the white part is deleted, the area of the part is measured, and the ratio of the area of the white part to the whole area is defined as the bubble breakage rate A (%) of the cut surface.
Further, the foam sheet is cut along a plane perpendicular to the cut surface, and the cut surface is measured in the same manner as described above to obtain the bubble breakage rate B (%). The average value is defined as the bubble breaking rate (%) of the foam sheet.

(Number of bubbles in the thickness direction)
The number of bubbles in the thin-layer foamed sheet refers to a value measured as follows.
Specifically, the number of bubbles (pieces) in the thickness direction is visually measured from the image of the scanning electron microscope used in the measurement of the average bubble diameter. The minimum number n is measured to be n or more.

(Tear strength)
According to JIS K 6767-1999 “Foamed plastic-polyethylene test method”, Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), universal testing machine data processing software UTPS-STD (manufactured by Softbrain Co., Ltd.) , Using a test piece defined in JIS K 6767. The test speed was 500 mm / min, and the chuck interval was 50 mm. Test specimens were punched out in the flow direction (MD direction) and the width direction (TD direction), respectively, and conditioned for 16 hours or more in an environment of temperature 23 ± 2 ° C. and humidity 50 ± 5%. Measurement is performed in an environment of 23 ± 2 ° C. and humidity of 50 ± 5%.
The tear strength is calculated by the following formula.
Tear strength (N / cm) = Maximum load (N) / Test specimen thickness (cm)

Example 1
Polypropylene resin as a polyolefin resin (high melt tension polypropylene, MFR: 0.3 g / 10 min, melting point 164 ° C., manufactured by Nippon Polypro Co., Ltd., product name: NEWTRAIN SH9000), 40 parts by mass of thermoplastic elastomer (non-crosslinked) Ethylene-propylene-diene copolymer elastomer, MFR: 11 g / 10 min, melting point 170 ° C., manufactured by Mitsubishi Chemical Corporation, product name: Thermolan Z101N) 60 parts by mass was added to prepare 100 parts by mass of the compounded resin composition.
10 parts by mass of master batch (product name: Talpet 70P, manufactured by Nitto Flour Chemical Co., Ltd.) containing 70% by mass of talc (average particle size 13 μm) as a cell nucleating agent in 100 parts by mass of the obtained blended resin composition And 10 parts by mass of a pigment (manufactured by Toyochem Co., Ltd., product name: PPM OYA164 BLK-FD) were mixed to prepare a polyolefin resin foaming composition.

  A tandem type extruder having a diameter of 65 mm and a second extruder having a diameter of 75 mm connected to the tip of the first extruder is prepared, and the resulting polyolefin resin foaming composition is used in the tandem type extruder. It supplied to the 1st extruder and melt-kneaded. In the middle of the first extruder, 4.2 parts by mass of supercritical carbon dioxide is injected as a blowing agent, and the molten polyolefin resin foaming composition and carbon dioxide are mixed and kneaded uniformly. The molten resin composition containing was continuously supplied to the second extruder and cooled to a resin temperature suitable for foaming while being melt-kneaded.

Thereafter, an annular die of a mold attached to the tip of the second extruder (bubble generating part diameter φ 36 mm, mold bubble generating part interval 0.25 mm (cross-sectional area of the bubble generating part: 0.275 cm ² ), foam From the molded part interval 3.4 mm, the foam molded part outlet diameter φ70), discharge rate 30 kg / hr (discharge rate V = 109 kg / cm ² · hr), melt temperature 176 ° C., melting in front of the ring die Cylindrical foam was obtained by extrusion foaming under conditions of an object pressure of 9.8 MPa. The cylindrical foam molded in the foam molding part of the annular die was put on a cooled mandrel, and the outer surface was cooled by blowing air from the air ring. The cooled cylindrical foam was cut with a cutter at one point on the mandrel to obtain a sheet-like polyolefin resin foam sheet having a thickness of 2.0 mm.
The electron micrograph of MD direction and TD direction of the cut surface of a foam sheet is shown in FIG.

Next, a dielectric heating roll is prepared, and one surface of the obtained polyolefin-based resin foam sheet is placed between the dielectric heating roll and the nip roll under the conditions of a heating temperature of 140 ° C., a nip roll pressure of 0.5 MPa, and a speed of 1.0 m / min. A 0.47 mm thick polyolefin-based resin thin-layer foamed sheet that was passed through and heated and pressed was obtained.
The obtained polyolefin-based resin thin-layer foam sheet can be easily crushed at a compression rate of 77% compared to the original thickness, and the thickness after 24 hours at room temperature was observed. The shape was maintained.
The electron micrograph of MD direction and TD direction of the cut surface of a thin layer foam sheet is shown in FIG.

(Example 2)
The foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1 except that a 1.5 mm thick foamed sheet obtained by slicing one side of the polyolefin resin foamed sheet obtained in Example 1 was used. Thus, a polyolefin-based resin thin-layer foam sheet having a thickness of 0.23 mm was obtained.
FIG. 4 shows electron micrographs in the MD direction and TD direction of the cut surface of the thin-layer foamed sheet.
The obtained polyolefin-based resin thin-layer foamed sheet was easily crushed at a compression rate of 85% compared to the original thickness, was not restored over time, and maintained its shape.

(Example 3)
The foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1 except that a 0.5 mm thick foamed sheet obtained by slicing both surfaces of the polyolefin resin foamed sheet obtained in Example 1 was used. Thus, a polyolefin resin thin-layer foamed sheet having a thickness of 0.14 mm was obtained.
The obtained polyolefin-based resin thin-layer foamed sheet was easily crushed at a compression rate of 72% compared to the original thickness, was not restored over time, and maintained its shape.
FIG. 5 shows electron micrographs in the MD direction and TD direction of the cut surface of the thin layer foam sheet.

Example 4
The foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1 except that a 1.0 mm thick foamed sheet obtained by slicing both surfaces of the polyolefin resin foamed sheet obtained in Example 1 was used. Thus, a polyolefin-based resin thin layer foam sheet having a thickness of 0.18 mm was obtained.
The obtained polyolefin-based resin thin-layer foamed sheet was easily crushed at a compression rate of 82% compared to the original thickness, was not restored over time, and maintained its shape.

(Example 5)
Using a 0.5 mm thick foam sheet obtained by slicing both sides of the polyolefin resin foam sheet obtained in Example 1 (similar to Example 3), the heating temperature 140 ° C. of the dielectric heating roll was changed to 80 ° C. The foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1 to obtain a polyolefin-based resin thin-layer foamed sheet having a thickness of 0.39 mm.
The obtained polyolefin-based resin thin-layer foamed sheet could be easily crushed at a compression rate of 22% compared to the original thickness, was not restored over time, and maintained its shape.

(Example 6)
Using a foamed sheet having a thickness of 0.5 mm obtained by slicing both surfaces of the polyolefin-based resin foam sheet obtained in Example 1 (similar to Example 3), the heating temperature 140 ° C. of the dielectric heating roll was changed to 120 ° C. The foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1 to obtain a polyolefin-based resin thin-layer foamed sheet having a thickness of 0.32 mm.
The obtained polyolefin-based resin thin-layer foamed sheet was easily crushed at a compression rate of 36% compared to the original thickness, was not restored over time, and maintained its shape.

(Example 7)
Using a foam sheet having a thickness of 0.5 mm obtained by slicing both surfaces of the polyolefin resin foam sheet obtained in Example 1 (similar to Example 3), the speed of the dielectric heating roll was set to 5.0 m / min. Except for changing to min, the foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1 to obtain a polyolefin-based resin thin-layer foamed sheet having a thickness of 0.18 mm.
The obtained polyolefin-based resin thin-layer foamed sheet could be easily crushed at a compression rate of 64% compared to the original thickness, was not restored over time, and maintained its shape.

(Example 8)
Using a foam sheet having a thickness of 0.5 mm obtained by slicing both surfaces of the polyolefin resin foam sheet obtained in Example 1 (similar to Example 3), the nip roll pressure 0.5 MPa of the dielectric heating roll is set to 0.1 MPa, Except that the speed 1.0 m / min was changed to 5.0 m / min, the foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1, and a 0.29 mm thick polyolefin resin thin layer foamed A sheet was obtained.
The obtained polyolefin-based resin thin-layer foamed sheet was easily crushed at a compression rate of 42% compared to the original thickness, was not restored over time, and maintained its shape.

(Comparative Example 1)
Using a foamed sheet of 0.5 mm thickness obtained by slicing both surfaces of the polyolefin resin foamed sheet obtained in Example 1 (similar to Example 3), the heating temperature 140 ° C. of the dielectric heating roll was set to 170 ° C., and the speed 1 Except for changing 0.0 m / min to 5.0 m / min, the foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1, but the foamed sheet was melted and could not be heated, A polyolefin resin thin-layer foam sheet could not be obtained.

(Comparative Example 2)
Using a 0.5 mm thick foam sheet (similar to Example 3) obtained by slicing both sides of the polyolefin resin foam sheet obtained in Example 1, and changing the heating temperature of the dielectric heating roll from 140 ° C. to 50 ° C. Except for the above, the foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1. However, the foamed sheet had excellent resilience and could not be crushed, and had a compression rate of 4% compared to the original thickness. Only a resin thin layer foam sheet was obtained.

(Comparative Example 3)
Heating of a dielectric heating roll using a commercially available semi-rigid, closed-cell polyolefin (polyethylene) long sheet-like foam sheet (product name: Toraypef, general-purpose grade, 15020AA00, thickness 1.9 mm) by electron beam crosslinking Except that the temperature was changed from 140 ° C. to 100 ° C., the foamed sheet was heated and pressed using a dielectric heating roll in the same manner as in Example 1. A layer foam sheet could not be obtained.

(Comparative Example 4)
Except for using a commercially available closed-cell polyolefin (polyethylene) sheet-like foamed sheet (Sekisui Chemical Co., Ltd., product name: Softlon, grade # 0503, thickness 2.9 mm) irradiated with an electron beam, Example 1 and Similarly, the foamed sheet was heated and pressed using a dielectric heating roll. However, the foamed sheet had high hardness and could not be crushed, and only a polyolefin resin thin-layer foamed sheet having a compressibility of 1% compared to the original thickness was obtained. There wasn't.

The thickness, foaming ratio, open cell ratio, average cell diameter, heating dimensional change rate, 50% compression stress and bubble breakage rate of the foamed sheets obtained in each Example and Comparative Example, and heating temperature, press pressure and press speed Table 1 shows the heating press conditions.
Further, the thickness of the thin-layer foamed sheet obtained in each Example and Comparative Example, thickness variation, compression ratio from the original thickness, foaming ratio, open cell rate, bubble breakage rate, number of cells in the thickness direction, and sheet flow Table 2 shows the tear strength in the direction (MD direction) and the sheet width direction (TD direction).

From the results of Tables 1 and 2, the polyolefin of the present invention having a thickness of 0.05 to 0.5 mm, an expansion ratio of 2 to 15 times, an open cell ratio of 30 to 95%, and a bubble breakage ratio of 1 to 30% -Based resin thin-layer foam sheets (Examples 1 to 8) are thinner than conventional ones as in the comparative examples, and have excellent mechanical properties (tear strength), and are thinner, lighter, and smaller for electronic devices. It can be seen that this is an optimum thin-layer foam sheet as a sealing material.
Moreover, it turns out that the polyolefin-type resin thin layer foam sheet (Examples 1-8) of this invention can be easily manufactured with the heat press at comparatively low temperature.

Claims (11)

  A polyolefin-based resin thin-layer foamed sheet having a plurality of bubbles partitioned by a wall containing a polyolefin-based resin, having a thickness of 0.05 to 0.5 mm, an expansion ratio of 2 to 15 times, and an open cell ratio of 30 to A polyolefin-based resin thin-layer foamed sheet characterized by 95% and a bubble breaking rate of 1 to 30%.   A first cut surface including a straight line parallel to the thickness direction of the polyolefin-based resin thin-layer foamed sheet, a second cut surface perpendicular to the first cut surface, and a third perpendicular to the first cut surface and the second cut surface. The polyolefin-based resin thin-layer foamed sheet according to claim 1, wherein the average cell diameter of the cells on the cut surface is 0.01 to 0.18 mm.   A direction perpendicular to the thickness direction of the polyolefin-based resin thin-layer foam sheet on a first cut surface including a straight line parallel to the thickness direction of the polyolefin-based resin thin-layer foam sheet and a second cut surface perpendicular to the first cut surface The polyolefin-based resin thin-layer foamed sheet according to claim 1 or 2, wherein the tear strength is 30 to 450 N / cm and 15 to 200 N / cm, respectively.   The polyolefin-based resin thin-layer foamed sheet according to any one of claims 1 to 3, wherein the polyolefin-based resin thin-layer foamed sheet has a non-foamed layer having a thickness of 1 to 30 µm on at least one surface layer thereof.   The polyolefin-based resin thin-layer foamed sheet according to any one of claims 1 to 4, wherein the polyolefin-based resin thin-layer foamed sheet has at least one or more bubbles in the thickness direction (VD direction). It is a manufacturing method of the polyolefin resin thin layer foam sheet according to any one of claims 1 to 5,
It has a plurality of bubbles partitioned by a wall containing a polyolefin resin, has a thickness of 0.2 to 3.0 mm, an expansion ratio of 10 to 25 times, an open cell ratio of 75 to 95%, and a bubble breakage ratio of 5 to 30 %, A step of obtaining a polyolefin resin foam sheet having an average cell diameter of 0.02 to 0.2 mm, and heating at least one surface of the obtained polyolefin resin foam sheet, and pressing while melting the foam sheet surface A method for producing a polyolefin resin thin-layer foamed sheet comprising a step of obtaining a polyolefin resin thin-layer foamed sheet obtained by compressing the foamed sheet at a compression rate of 20 to 95%.   The polyolefin resin thin-layer foamed sheet according to claim 6, wherein the heating temperature is 5 to 100 ° C lower than the melting point mp of the polyolefin resin, and the pressure of the press is 0.1 to 1.0 MPa. Manufacturing method.   The method for producing a polyolefin resin thin-layer foam sheet according to claim 6 or 7, wherein carbon dioxide gas is used as a foaming agent in the step of obtaining the polyolefin resin foam sheet.   The polyolefin resin foamed sheet is produced by using a mold ring die composed of a foamed part and a molded part for growing the produced foam and molding the sheet. The manufacturing method of the polyolefin-type resin thin layer foam sheet as described in any one.   The sealing material for electronic devices containing the polyolefin-type resin thin layer foam sheet as described in any one of Claims 1-5.   The base material for adhesive tapes containing the polyolefin-type resin thin-layer foam sheet as described in any one of Claims 1-5.