JP2014189658A - Light-shielding polyolefin resin foam sheet and production method and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-shielding polyolefin resin foam sheet which can achieve both light shielding performance and flexibility required in thinned and miniaturized electronic apparatuses, and to provide a production method and use of the polyolefin resin foam sheet.SOLUTION: A light-shielding polyolefin resin foam sheet comprises a polyolefin resin including a pigment, and has a 90% compressive stress of 400 to 1,000 kPa, and a total light transmittance τt of 0 to 1%.

Description

  The present invention relates to a polyolefin-based resin foam sheet for light shielding, a method for producing the same, and a use thereof. More specifically, the present invention relates to a polyolefin-based resin foam sheet that is optimal as a light-shielding sheet 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 or sheet 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.

As one application of the electronic device member, there is a light shielding sheet for preventing light leakage from around the liquid crystal or around the LED. As electronic devices become thinner and smaller, the distance between the light source and the frame becomes thinner, so there are many demands for light shielding from minute gaps. In addition, in order to prevent light leakage from a minute gap, the followability of the sheet to a minute clearance is also important.
Conventional light-shielding sheets are multilayer sheets of at least two layers, or non-foamed sheets such as films. Further, even in the case of a foam sheet, the light-shielding property is maintained by laminating a reflective layer on one side to form two layers.

For example, Japanese Patent Application Laid-Open No. 2010-190950 (Patent Document 1) is an adhesive tape that is used by being stuck between an LCD panel of an LCD module and a backlight housing, and includes a base material layer, a light reflection layer, and It has a support having a light-shielding layer and an adhesive layer provided on at least one side of the support, has a total light transmittance Tt of 0.1% or less on the light-shielding layer side, and total reflection on the light-reflecting layer side A light-shielding reflective tape having a rate Rt of 20 to 50% has been proposed.
According to this light-shielding / reflecting tape, it is said that light unevenness at the edge of the image display portion of the LCD module can be suppressed and high average luminance can be realized.

Japanese Patent Laid-Open No. 2008-250309 (Patent Document 2) proposes a light-shielding structure having a light-shielding layer made of black foam and a white or silver reflective layer, and a liquid crystal display device having the same. ing.
According to this reflection / light-shielding structure, when used between the liquid crystal display module unit and the backlight unit, it has excellent backlight reflection and light-shielding properties, thus improving the visibility of the liquid crystal display and reducing power consumption. Further, it is excellent in impact resistance, and when used as a touch panel, “bleeding” due to pressing is unlikely to occur.

JP 2010-190950 A JP 2008-250309 A

However, the conventional light-shielding sheet requires at least two layers, which makes the manufacturing complicated, and because it is non-foamed, the light-shielding property can be maintained, but there is no flexibility, so the clearance becomes minute. There is a problem that the light-shielding property is not sufficient in an electronic device which is inferior in follow-up property and has been thinned.
Specifically, in the technique of Patent Document 1, in order to coat white ink for making one side of the base film a reflective layer and black ink for making the other side a light shielding layer, respectively, There is a problem that the corona treatment of the material film is required and the production becomes complicated. Moreover, since a base film is a non-foamed sheet, there exists a subject that it is inferior to followability with respect to fine clearance.
Moreover, in the technique of patent document 2, it is necessary to affix a reflective layer to a foam, and there exists a subject that manufacture becomes complicated. Moreover, this reflective light-shielding structure has improved the light-shielding property by sticking a reflective layer, and the light-shielding performance of only a foam is unknown.

  Accordingly, it is an object of the present invention to provide a polyolefin-based resin foam sheet for light shielding that satisfies both light shielding properties and flexibility required for electronic devices that are becoming thinner and smaller, a method for producing the same, and a use thereof. .

  The inventors of the present invention have found that a polyolefin resin foam sheet composed of a polyolefin resin containing a pigment is optimal for shading as a result of intensive studies to achieve the above-mentioned problems. It came.

  Thus, according to the present invention, a polyolefin-based resin foam for light shielding, which is composed of a polyolefin-based resin containing a pigment, has a 90% compressive stress of 400 to 1000 kPa and a total light transmittance τt of 0 to 1%. A sheet is provided.

Moreover, according to the present invention, there is provided a method for producing the light shielding polyolefin resin foam sheet,
Using a mold annular die composed of a foamed part and a molded part that grows the foam and forms a sheet while melt-kneading a polyolefin-based resin foaming composition containing a pigment and a foaming agent There is provided a method for producing a polyolefin resin foam sheet for light shielding, which is obtained by foam molding to obtain a polyolefin resin foam sheet for light shielding.

  Furthermore, according to this invention, the light-shielding sheet for electronic devices containing said polyolefin resin foam sheet for light shielding is provided.

ADVANTAGE OF THE INVENTION According to this invention, the polyolefin-type resin foam sheet for light shielding which was compatible with the light-shielding property and the softness | flexibility requested | required by the electronic device which was thinned and reduced in size, its manufacturing method, and its use can be provided.
That is, the polyolefin-based resin foam sheet for light shielding of the present invention has a high light shielding property by suppressing the total light transmittance only with the foamed sheet, and has a low stress even when compressed to a high compression (90%). The foamed sheet follows the fine clearance between the substrates (the gap between the plastic and the metal), especially when used in electronic equipment. And the light leakage from the unevenness between the substrates can be prevented.
Moreover, the polyolefin resin foam sheet for light shielding of the present invention can maintain high light shielding properties even when a reflective sheet or the like is pasted.

  Since the polyolefin-based resin foam sheet for light shielding of the present invention has high light shielding properties only by the foam sheet, it is not necessary to apply ink for forming a reflective layer or a light shielding layer and corona treatment for its base treatment. It can be easily produced only by molding.

The polyolefin-based resin foam sheet for shading of the present invention is
(1) having an average cell diameter of 0.02 to 0.17 mm, an apparent density of 0.030 to 0.100 g / cm ³ and an open cell ratio of 60 to 99%;
(2) Polyolefin resin is a polypropylene resin having a melt flow rate of 0.2 to 5 g / 10 min, a thermoplastic elastomer having a melt flow rate of 0.2 to 15 g / 10 min, and a melt flow rate of 0. At least one polyethylene-based plastomer that is 3-15 g / 10 min.
(3) When the pigment is a black pigment and the content ratio is 1 to 20% by mass of the polyolefin resin, and (4) When any one condition of having an adhesive layer on at least one surface is satisfied The above effects are further exhibited.

  The manufacturing method of the polyolefin-type resin foam sheet for light shielding of this invention further exhibits said effect, when a foaming agent is a carbon dioxide gas.

It is a figure explaining the binarization of the cross-sectional image for measuring the bubble tear rate of a foam sheet. It is an electron micrograph of the cut surface which shows an example of the polyolefin-type resin foam sheet for light shielding of this invention. It is a figure for demonstrating the measuring method of an average bubble diameter. It is a figure for demonstrating the evaluation method of light-shielding property.

(Light-shielding polyolefin resin foam sheet)
The polyolefin-based resin foam sheet for light shielding (hereinafter also referred to as “foamed sheet”) of the present invention is composed of a polyolefin-based resin containing a pigment, 90% compressive stress is 400 to 1000 kPa, and total light transmittance τt is 0 to 1%. It is characterized by being.
FIG. 2 is an electron micrograph of a cut surface showing an example of the foamed sheet of the present invention.

The foamed sheet of the present invention has a 90% compressive stress of 400 to 1000 kPa.
A specific method for measuring the 90% compressive stress of the foam sheet will be described in the Examples section.
If the 90% compressive stress of the foam sheet is less than 400 kPa, the strength of the foam sheet is insufficient, the handling property is deteriorated, and the followability to fine irregularities is deteriorated when vibration is applied, and light leakage from the gaps is prevented. May occur. On the other hand, if the 90% compressive stress of the foam sheet exceeds 1000 kPa, it cannot be easily compressed, the repulsive force becomes strong, the followability to fine irregularities is deteriorated, and light leakage from the gap may occur. is there.
A preferable 90% compressive stress is in the range of 400 to 900 kPa, and a more preferable range is 400 to 800 kPa.

The foamed sheet of the present invention has a total light transmittance τt of 0 to 1%.
The total light transmittance τt of the foamed sheet is a value measured according to the method described in JIS K7361-1: 1997 Test method for total light transmittance of plastic-transparent material. This is explained in the example column.
The total light transmittance τt of the foam sheet is most preferably 0%. On the other hand, if the total light transmittance τt of the foamed sheet exceeds 1%, light leakage may occur locally in the dark, and it may be difficult to maintain the light shielding property.
A preferable total light transmittance τt is in the range of 0 to 0.9%, and a more preferable range is 0 to 0.8%.

The foam sheet of the present invention preferably has an average cell diameter of 0.02 to 0.17 mm.
The average cell diameter of the foam sheet refers to a value measured according to the test method of ASTM D2842-69, and a specific measurement method will be described in the column of the examples.
When the average cell diameter of the foamed sheet is less than 0.02 mm, it may be difficult to obtain a foamed sheet having sufficient cushioning and buffering properties. On the other hand, when the average cell diameter of the foamed sheet exceeds 0.17 mm, followability to fine irregularities may be inferior.
A more preferable average bubble diameter is in the range of 0.04 to 0.17 mm, and a further preferable range is 0.06 to 0.16 mm.

The foamed sheet of the present invention preferably has an apparent density of 0.030 to 0.100 g / cm ³ .
The apparent density of the foamed sheet refers to a value measured according to the method described in JIS K7222: 2005, and a specific measuring method will be described in the column of Examples.
If the apparent density of the foamed sheet is less than 0.030 g / cm ³ , the foamed sheet may have insufficient strength and handling properties may deteriorate. On the other hand, when the apparent density of the foamed sheet exceeds 0.100 g / cm ³ , the flexibility of the foamed sheet is lowered, and the followability to fine irregularities may be insufficient.
A more preferable apparent density is in the range of 0.030 to 0.090 g / cm ³ , and a further preferable range is 0.035 to 0.075 kg / cm ³ .

The foam sheet of the present invention preferably has an open cell ratio of 60 to 99%.
The open cell ratio of the foamed sheet refers to a value measured according to the method described in ASTM D2856-87, and a specific measuring method will be described in the column of Examples.
When the open cell ratio of the foamed sheet is less than 60%, the stress when compressed may be high. On the other hand, when the open cell ratio of the foamed sheet exceeds 99%, the mechanical strength of the sheet may decrease.
A more preferable open cell ratio is in the range of 70 to 99%, and a further preferable range is 75 to 99%.

The foamed sheet of the present invention preferably has a thickness of 0.1 to 3.0 mm.
When the thickness of the foamed sheet is less than 0.1 mm, the mechanical strength is lowered, and winding with a roll may be difficult. On the other hand, if the thickness of the foamed sheet exceeds 3.0 mm, it is not preferable because it is not suitable as a sealing material for electronic devices that are thinned, lightened, or downsized.
A more preferable thickness is in the range of 0.1 to 2.5 mm, and a more preferable range is 0.1 to 2.0 mm.

The foamed sheet of the present invention preferably has a bubble breakage rate of 5 to 30%.
The bubble breakage rate is obtained by binarizing the scanning electron micrograph of the cross section of the foam sheet so that the torn part and the other part are black and white, and the torn area of the photograph obtained from the binarized photograph This means the area ratio (see FIG. 1). A specific measurement method will be described in the Examples section.
When the bubble breaking rate of the foamed sheet is less than 5%, there is no air escape when compressed, and the rebound stress may increase. On the other hand, when the bubble breaking rate of the foamed sheet exceeds 30%, the mechanical strength of the foamed sheet may be lowered.
A more preferable bubble breaking rate is in the range of 5 to 25%, and a more preferable range is 5 to 20%.

The polyolefin resin constituting the foamed sheet of the present invention contains a pigment as a colorant.
The pigment is not particularly limited as long as it can impart light-shielding properties to the foamed sheet of the present invention and does not impair the effects of the present invention, and examples include pigments known in the art.
Examples of the pigment include black pigments such as a trade name “PPM OYA164 BLK-FD” manufactured by Toyochem Co., Ltd. and a trade name “PEX 999018 Black” manufactured by Tokyo Ink Co., Ltd. A combination of the above can be used.
Among these pigments, a black pigment having a trade name “PPM OYA164 BLK-FD” manufactured by Toyochem Co., Ltd. is particularly preferable.

The content ratio of the pigment in the polyolefin-based resin is preferably 1 to 20% by mass.
When the content ratio of the black pigment is less than 1% by mass, the blackness may be insufficient. On the other hand, when the content ratio of the black pigment exceeds 20% by mass, the magnification of the foamed sheet may be difficult to increase.
A more preferable content ratio of the black pigment is in the range of 1 to 15% by mass, and a more preferable range is 5 to 15% by mass.

The type of polyolefin resin constituting the foamed sheet of the present invention is not particularly limited as long as the various physical properties can be imparted to the foamed sheet. Specific examples include a homopolymer of ethylene or propylene, a copolymer of ethylene or propylene and another olefin, and the like. 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. When the MFR is less than 0.2 g / 10 min, the load on the extruder increases and the productivity decreases, or the raw material mixture of the molten foam sheet containing the foaming agent cannot flow smoothly in the mold. As a result, unevenness may occur on the surface of the obtained foamed sheet and the appearance may deteriorate. On the other hand, if the MFR exceeds 5 g / 10 minutes, the resin pressure in front of the die 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. If the foamed sheet is rapidly broken in the foamed sheet molding part, foamability is lowered, and the appearance of the resulting foamed sheet may be deteriorated or the foamed sheet may not be obtained. A more preferable MFR is 0.2 to 4 g / 10 min, and a further 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 product name “Newstrain SH9000” manufactured by Nippon Polypro Co., Ltd. and the product name “DaployWB135HMS” manufactured by Borealis. It is done.

The 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 foamed sheet is recycled and supplied again to the extruder for foam molding, poor foaming due to the crosslinked rubber, which becomes a problem when the crosslinked elastomer is used, can be suppressed.

The thermoplastic elastomer is preferably a resin having a melt flow rate (MFR) of 0.2 to 15 g / 10 min. If the MFR is less than 0.2 g / 10 min, the load on the extruder increases, the productivity decreases, or the molten polyolefin resin containing the foaming agent cannot flow smoothly in the mold, Unevenness may occur on the surface of the resulting foamed sheet and the appearance may deteriorate. On the other hand, if the MFR exceeds 15 g / 10 min, the resin pressure in front of the die 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. If the foam formation portion suddenly breaks down, the foamability is lowered, and the appearance of the resulting foamed sheet may be deteriorated or the foamed sheet may not be obtained.
A more preferable MFR is 0.5 to 15 g / 10 min, and an even more preferable MFR is 1.0 to 15 g / 10 min.

Examples of the polyethylene plastomer include a polyethylene polymer containing a polyethylene resin and a copolymer component such as an α-olefin.
As an alpha olefin, a C4-C8 thing is preferable and it is more preferable that it is at least 1 sort (s) selected from 1-butene, 1-hexene, and 1-octene.
Examples of the ethylene / α-olefin copolymer include a product name manufactured by Sumitomo Chemical Co., Ltd .: Esprene NO416 (ethylene-1-butene copolymer), a product name manufactured by Nippon Polyethylene Co., Ltd .: Kernel KS240T (ethylene-1) -Hexene copolymer) and product name: affinity EG8100 (ethylene-1-octene copolymer) manufactured by Dow Chemical Co., etc.

The polyethylene plastomer is preferably a resin having a melt flow rate (MFR) of 0.3 to 15 g / 10 min. If the MFR is less than 0.3 g / 10 min, the load on the extruder increases, the productivity decreases, or the molten polyolefin resin containing the foaming agent cannot flow smoothly in the mold, Unevenness may occur on the surface of the resulting foamed sheet and the appearance may deteriorate. On the other hand, if the MFR exceeds 15 g / 10 min, the resin pressure in front of the die 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. If the foam formation portion suddenly breaks down, the foamability is lowered, and the appearance of the resulting foamed sheet may be deteriorated or the foamed sheet may not be obtained.
More preferable MFR is 0.5 to 15 g / 10 min, and further preferable MFR is 0.5 to 13 g / 10 min.

If the content of the thermoplastic elastomer and the polyethylene plastomer is small, the cushioning property and flexibility of the foamed sheet may be poor. On the other hand, when the content is large, the foaming property may be lowered due to the rubber elasticity of the thermoplastic resin composition becoming too strong, or the shrinkage of the foamed sheet may be increased.
The content thereof is preferably about 10 to 90% by mass, more preferably about 10 to 80% by mass, and further preferably about 10 to 70% by mass with respect to 100% by mass of the polyolefin resin.
When both the thermoplastic elastomer and the polyethylene plastomer are contained, the total content is preferably about 10 to 90% by mass, and about 10 to 80% by mass, with respect to 100% by mass of the polyolefin resin. Is more preferable, and about 10-70 mass% is further more preferable.

  Accordingly, the foamed sheet of the present invention comprises a polypropylene resin having a melt flow rate in the range of 0.2 to 5 g / 10 minutes and a thermoplastic elastomer having a melt flow rate in the range of 0.2 to 15 g / 10 minutes. And at least one polyethylene plastomer having a melt flow rate in the range of 0.3 to 15 g / 10 min.

In addition to the above resin components, the foam sheet is a surfactant, a dispersant, a weather resistance stabilizer, a light stabilizer, a pigment, a dye, a flame retardant, a plasticizer, a lubricant, an ultraviolet absorber, an antioxidant, a filler, Other additives such as a reinforcing agent and an antistatic agent may be contained.
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, the physical properties of the foamed sheet, and the like, and the content contained in a normal foamed sheet can be adopted.

(Method for producing foam sheet)
The method for producing a polyolefin resin foam sheet of the present invention includes:
Using a mold annular die composed of a foamed part and a molded part that grows the foam and forms a sheet while melt-kneading a polyolefin-based resin foaming composition containing a pigment and a foaming agent A polyolefin resin foam sheet for light shielding is obtained by foam molding.
Examples of the polyolefin resin foaming composition that is a raw material of the foamed sheet include the resin materials and additives exemplified in the above foamed sheet.

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 mass / mold bubble generation section cross-sectional area / time Extruded resin mass refers to the total mass extruded from the mold. Therefore, the mass of the extruded resin is the total amount of the thermoplastic resin composition and the foaming agent. Further, the mass of the extruded resin can be expressed as a discharge amount per hour (kg / hr).

The discharge speed V is preferably about 70 to 250 kg / cm ² · hr,
More preferably, it is about 00 kg / cm ² · hr. Resin pressure in front of ring die is 8
It is preferable that it is 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, it is preferable that the foam sheet is manufactured by using a mold annular die constituted by a bubble generation portion and a formation portion for growing the generated bubble and forming the sheet.

The resin temperature is preferably in the range of about 10 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. Conversely, if it is too high, the resin solidification after foaming may not catch up with the foaming speed, and the foaming ratio may not be increased.
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 (carbon dioxide gas) 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, if the amount is small, the apparent density of the 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 mass, more preferably 2 to 8 parts by mass, and 3 to 6 parts by mass with respect to 100 parts by mass 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 mass and more preferably 0.1 to 12 parts by mass with respect to 100 parts by mass 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 cell nucleating agent is used as a masterbatch by mixing with the base resin in advance to facilitate handling and prevent contamination of the production environment due to powder scattering, and to improve 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.

  One side or both sides of the foamed sheet obtained as described above may be sliced to a desired thickness using a known apparatus such as a splitting machine.

(Use of foam sheet)
The foamed sheet of the present invention is superior in light shielding properties and flexibility as compared with conventional foamed sheets, and is useful as a light shielding sheet for electronic devices that have been made thinner and smaller.
According to the present invention, a foam sheet having an adhesive layer on at least one surface can be provided.
The pressure-sensitive adhesive layer is not particularly limited as long as it is a known pressure-sensitive adhesive layer used in the technical field. For example, a trade name “IMT-30C” manufactured by NHIEI KAKO CO., LTD., A trade name “# 8612DFT” manufactured by DIC Corporation. ", Trade name" CT-6348 "manufactured by Sumitomo 3M Limited.

The use of the foam sheet having the pressure-sensitive adhesive layer of the present invention is not particularly limited, and can be used for the purpose of smoothly absorbing a shock applied to various electronic devices and preventing a large shock from being applied to the entire electronic device. . 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. As an electronic device, what was illustrated for the use of the light shielding sheet for electronic devices as follows is mentioned.
Further, the foamed sheet of the present invention can maintain high light shielding properties even when a reflective sheet or the like is pasted.

Moreover, according to this invention, the light shielding sheet for electronic devices containing the polyolefin-type resin foam sheet for light shielding of this invention is provided.
The use of the light-shielding sheet for electronic devices of the present invention is not particularly limited, and can be used for fixing electronic components while shielding light inside various electronic device packages. Examples of electronic devices include digital cameras, portable game machines, personal computers, and tablet terminals such as microphones, speakers, flashes, viewfinders, motors, LED display devices, speakers, key cushions, battery cushions, boards, and liquid crystal devices. Is mentioned. Among these, since it has very good light-shielding properties, it is used for portable electronic devices such as LED display devices, tablet terminals, digital cameras, portable game machines, mobile phones, portable DVD players, and notebook computers. It can be preferably used in a closed interior.

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 foamed sheets were 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)
For the thickness of the foam sheet, the thickness of 12 points is measured 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 foamed sheet with no load at a size of φ10 mm. As a measuring device used for measuring the thickness of the foam sheet, a Mitsutoyo Corporation thickness gauge (model number “NO. 547-301”) can be used.

(Apparent density)
The apparent density of the foamed sheet is measured by the method described in JIS K7222: 2005 “Foamed Plastics and Rubber—How to Obtain the Apparent Density”.
That is, a test piece having a volume of 100 cm ³ or more is cut so as not to change the original cell structure of the material, the mass of the cut test piece is measured, and the apparent density is calculated by the following equation.
Apparent density (g / m ³ ) = (Mass of test piece (g) / Volume of test piece (cm ³ ))
A test specimen for measurement was cut from a 35 cm × 100 cm piece from a sample (foamed sheet) that had passed 72 hours or more after molding, and the piece was subjected to atmospheric conditions of temperature 23 ± 2 ° C. and humidity 50 ± 5% for 16 hours or more. The condition is adjusted by leaving it alone.

(magnification)
Using the density of polyolefin resin (polypropylene and thermoplastic elastomer) and the apparent density, the magnification is calculated by the following formula.
Magnification (times) = Polyolefin resin density (g / cm ³ ) / apparent density (g / cm ³ )

(Average bubble diameter)
The average cell diameter of the foam sheet is measured by the following test method.
That is, the foamed sheet was cut perpendicularly to the sheet surface from the center in the width direction along the MD direction (extrusion direction: arrow A in FIG. 3) and TD direction (width direction perpendicular to the extrusion direction: arrow B in FIG. 3). The cross section was 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), and the photographed image was printed. To do. At this time, the magnification in the scanning electron microscope is adjusted so that the number of bubbles present on a straight line of 60 mm drawn on the printed image (photograph) is about 10-20. Four images are printed on A4 paper, 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 the length of 60 mm in the VD direction (sheet thickness direction: arrow C in FIG. 3) cannot be counted, the number of bubbles for 30 mm or 20 mm is counted. Convert to the number of bubbles. In any given line, bubbles should be avoided only at the contact points. If a bubble comes in contact only at a contact, it is included in the number of bubbles. Measurement is performed at 3 locations, 2 locations, using 2 images per direction.

The magnification of a photograph is obtained by the following equation by measuring the scale bar on the photograph with a “Digimatic Caliper” manufactured by Mitutoyo Corporation to the nearest 1/100 mm.
Photo magnification = Scale bar measured value (mm) / Scale bar display value (mm)
And the bubble diameter D 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)

(Open cell ratio)
The open cell ratio of the polyolefin resin foam sheet is measured in accordance with ASTM D2856-87.
Specifically, the volume V of the test piece ( length 50 mm × width 50 mm × thickness 100 mm) is measured using a cyclic automatic densimeter manufactured by Shimadzu Corporation. Further, the apparent volume V0 of the test piece is calculated from the outer shape of the test piece. The open cell ratio is calculated by substituting the volumes V and V ₀ into the following equation.
Open cell ratio (%) = (V ₀ −V) / V ₀ × 100

(Bubble breaking rate)
The bubble tear rate of the foam sheet refers to a value measured as follows.
Specifically, the foamed sheet is cut along an arbitrary surface including a straight line parallel to the thickness direction, and the cut surface is magnified 20 times with a scanning electron microscope (manufactured by Hitachi, Ltd., model: S-3000N). Magnify and 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 the binarized image, the white part where the bubbles are not torn and completely communicated is deleted, the area of the part is measured, and the ratio of the area of the white part to the total area is the bubble of the cut surface. The tear rate A (%).
Further, the foam sheet is cut along a plane perpendicular to the cut surface, and the cut surface is also measured in the same manner as described above to obtain the bubble breaking rate B (%). Let bubble break rate (%).

(90% compressive stress)
The compressive stress is measured using a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.) and a universal testing machine data processing software UTPS-STD (manufactured by Softbrain Corporation).
The specimen size is 50 × 50 × 2 mm (20 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 compressive stress is defined as the stress at the time of 90% compression of the initial thickness (digital linear gauge measurement value). The number of test pieces shall be three. The sample dimensions were measured with Mitsutoyo's “Digimatic Caliper” up to 1/100 mm in width and length, with “Digital Linear Gauge” manufactured by Ozaki Seisakusho Co., Ltd., measuring area 10 cm ² , load (weight) 50 gf. As an additional (total 1.0 kPa), the thickness 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 ₉₀ = F ₉₀ / A ₀ × 10 ³
σ ₉₀ : compressive stress (kPa)
F ₉₀ : Load at 90% deformation (N)
A ₀ : Initial cross-sectional area of the test piece (mm ² )

(Total light transmittance τt)
The total light transmittance τt of the foamed sheet is measured according to the method described in JIS K7361-1: 1997 “Plastics—Test method for total light transmittance of transparent material—Part 1: Single beam method”.
That is, after stabilization of the apparatus light source using a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd., model: HM-150 type), a square sample with a side of 50 mm is measured by the double beam method with a light source (D65). . The stabilization time is measured after 30 minutes and confirmed to be stable.
The number of tests is three times, and the average is the value of total light transmittance τt.
However, after the test piece is conditioned at a temperature of 20 ± 2 ° C. and a humidity of 65 ± 5% for 24 hours or more, the test environment is measured at a temperature of 20 ± 2 ° C. and a humidity of 65 ± 5%. The thickness of the measurement sample conforms to the thickness of each sample (Table 1).

(Light shielding)
The light shielding property of the foam sheet refers to a result evaluated as follows.
Specifically, as shown in FIG. 4, a sample (foamed sheet) 1 having a width of 2 mm and cut into a 100 mm square is uniformly sandwiched between black polypropylene plastic (resin case) 2 so as to be 10% compressed, and the inside The light leakage from the gap between the polypropylene resin plastics is visually confirmed by illuminating with the LED of the light source 3 (high luminance 5 mm white LED 60 ° OSW54K5B61A, luminance: 10000 mcd). A visual position is confirmed from two places (viewing direction 4) of two surfaces which contact | abut among four surfaces. FIG. 4 shows a state in which the lower resin case 2, the foam sheet 1, and the upper resin case 2 are lifted in an oblique direction.
The light shielding property is evaluated according to the following criteria.
○: No light leakage △: Light leakage from a part ×: Light leakage from the whole

(Melt Mass Flow Rate (MFR))
Melt mass flow rate (MFR) is a semi-auto melt indexer 2A manufactured by Toyo Seiki Seisakusyo Co., Ltd., JIS K7210: 1999 “Plastic-thermoplastic melt mass flow rate (MFR) and melt volume flow rate I (MVR) test” Method "Measured by the method described in Method B.
Measurement conditions are 3 to 8 g of sample, preheating 270 seconds, load hold 30 seconds, and test load 21.18N. The test temperature is 230 ° C. for polypropylene resin, thermoplastic elastomer, and 190 ° C. for polyethylene resin. The number of test of the sample is 3, and the average is the value of melt mass flow rate (g / 10 min).

Example 1
Polypropylene resin (manufactured by Prime Polymer Co., Ltd., product name: Prime Polypro E110G, MFR: 0.3 g / 10 min) as a polyolefin resin, 60 parts by mass of polyethylene resin (manufactured by Nippon Polyethylene Co., Ltd.) which is a metallocene plastomer , Product name: kernel KS240T, MFR: 2.2 g / 10 min) and thermoplastic elastomer which is an olefin elastomer (manufactured by Prime Polymer Co., Ltd., product name: Prime TPO R110E, MFR: 1.5 g / 10) Min) 10 parts by mass of a masterbatch (manufactured by Nitto Flour Chemical Co., Ltd., product) containing 70 parts by mass of talc (average particle size 13 μm) as a cell nucleating agent in 100 parts by mass of the compounded resin composition added with 20 parts by mass Name: Talpet 70P) and pigment (manufactured by Toyochem Co., Ltd.) Name: PPM OYA164 BLK-FD) were mixed with 10 parts by weight, to obtain a polyolefin resin foam compositions.

  A tandem type extruder in which a second extruder with a diameter of 75 mm is connected to the tip of a first extruder with a diameter of 65 mm is prepared, and the obtained polyolefin resin foaming composition is used as the first of the tandem type extruder. The mixture was supplied to an extruder and melt kneaded. 4.2 parts by mass of carbon dioxide in a supercritical state as a blowing agent is injected from the middle of the first extruder, and the foamed polyolefin resin foaming composition and carbon dioxide are mixed and kneaded uniformly. The molten resin composition containing the agent was continuously supplied to the second extruder and melted and kneaded while cooling to a resin temperature suitable for foaming.

Thereafter, a die ring 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 molding Discharge amount 30 kg / hr (discharge speed V = 109 kg / cm ² · hr), resin (melt) temperature 179 ° C., before ring die Extrusion foaming was performed under the condition of a resin pressure of 11 MPa to obtain a cylindrical foam. The cylindrical foam molded in the foam molding part of the annular die was allowed to run along the 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 obtained polyolefin resin foam sheet was free of corrugation and excellent in surface smoothness.
Here, the “corrugated” means a large number of ridges and valleys formed by undulation of the foam discharged from the annular die to absorb the linear expansion in the circumferential direction due to volume expansion.

(Example 2)
The polyolefin resin foam sheet obtained in Example 1 was sliced with a splitting machine (manufactured by Fortuner, model: AB-320D) to remove the epidermis, and both sides were sliced to give a polyolefin system having a thickness of 1.0 mm. A resin foam sheet was obtained.

(Example 3)
The polyolefin resin foam sheet obtained in Example 1 was sliced with a splitting machine to remove the epidermis, and a polyolefin resin foam sheet having a thickness of 0.5 mm with both surfaces sliced was obtained.

Example 4
The polyolefin resin foam sheet obtained in Example 1 was sliced with a splitting machine to remove the epidermis, and a polyolefin resin foam sheet having a thickness of 0.2 mm with both surfaces sliced was obtained.

(Example 5)
In the preparation of the polyolefin resin foaming composition, 10 parts by mass of the master batch containing 70% by mass of talc (average particle diameter 13 μm) as a cell nucleating agent was changed to 7 parts by mass, and the resin (melt) temperature was 178 ° C. A sheet-like polyolefin-based resin foam sheet having a thickness of 2.0 mm was obtained in the same manner as in Example 1 except that extrusion foaming was performed under the condition of a resin pressure of 8 MPa in front of the annular die.
The obtained polyolefin resin foam sheet was free from corrugation and excellent in surface smoothness.

(Example 6)
The polyolefin resin foam sheet obtained in Example 5 was sliced with a splitting machine to remove the epidermis, and a polyolefin resin foam sheet having a thickness of 1.0 mm with both surfaces sliced was obtained.

(Example 7)
In preparation of the polyolefin resin foaming composition, 10 parts by mass of the master batch containing 70% by mass of talc (average particle diameter 13 μm) as a cell nucleating agent was changed to 5 parts by mass, and the resin (melt) temperature was 178 ° C. A sheet-like polyolefin-based resin foam sheet having a thickness of 2.0 mm was obtained in the same manner as in Example 1 except that extrusion foaming was performed under the condition of a resin pressure of 8 MPa in front of the annular die.
The obtained polyolefin resin foam sheet was free from corrugation and excellent in surface smoothness.

(Example 8)
The polyolefin resin foam sheet obtained in Example 7 was sliced with a splitting machine to remove the epidermis, and a polyolefin resin foam sheet having a thickness of 1.0 mm with both surfaces sliced was obtained.

Example 9
Polypropylene resin as a polyolefin resin (manufactured by Nippon Polypro Co., Ltd., product name: NEWTRAIN SH9000, MFR: 0.3 g / 10 min) and 60 parts by mass of thermoplastic elastomer (manufactured by JSR Corporation, product name: EXELINK) 3300B, MFR: 3.5 g / 10 min) A master batch (product made by Mitsubishi Rayon Co., Ltd.) containing 20% by mass of polytetrafluoroethylene as a cell nucleating agent in 100 parts by mass of the compounded resin composition added with 40 parts by mass Name: MZX-4) 5 parts by mass and pigment (manufactured by Toyochem Co., Ltd., product name: PPM OYA164 BLK-FD) were mixed to obtain a polyolefin resin foaming composition, resin (melt) Example except that extrusion foaming was performed under the conditions of a temperature of 176 ° C. and a resin pressure of 9.8 MPa in front of the annular die. In the same manner as in Example 1, a sheet-like polyolefin resin foam sheet having a thickness of 2.0 mm was obtained.
The obtained polyolefin resin foam sheet was free from corrugation and excellent in surface smoothness.

(Example 10)
The polyolefin resin foam sheet obtained in Example 9 was sliced with a splitting machine to remove the epidermis, and a polyolefin resin foam sheet having a thickness of 1.0 mm with both surfaces sliced was obtained.

(Comparative Example 1)
The same as in Example 1 except that no pigment was used in the preparation of the polyolefin resin foaming composition, the resin (melt) temperature was 178 ° C., and the resin pressure was 8 MPa in front of the ring die. Thus, a 2.0 mm thick sheet-like polyolefin resin foam sheet was obtained.

(Comparative Example 2)
The polyolefin resin foam sheet obtained in Comparative Example 1 was sliced with a splitting machine to remove the skin, and a 1.0 mm thick polyolefin resin foam sheet with both sides sliced was obtained.

(Comparative Example 3)
The polyolefin resin foamed sheet obtained in Comparative Example 1 was sliced with a splitting machine to remove the skin, and a polyolefin resin foamed sheet having a thickness of 0.5 mm with both sides sliced was obtained.

(Comparative Example 4)
Polypropylene resin as polyolefin resin (manufactured by Nippon Polypro Co., Ltd., product name: NEWTRAIN SH9000, MFR: 0.3 g / 10 min) and thermoplastic elastomer (manufactured by Mitsubishi Chemical Co., Ltd., product name: Zelas) MC745, MFR: 2.8 g / 10 min) 100 parts by mass of a compounded resin composition to which 40 parts by mass was added, and 10 parts by mass of a master batch containing 70% by mass of talc (average particle size 13 μm) as a cell nucleating agent In the same manner as in Example 1 except that a polyolefin-based resin foaming composition was obtained, and the resin (melt) temperature was 176 ° C., and the resin pressure was 9.8 MPa in front of the annular die. Thus, a sheet-like polyolefin resin foam sheet having a thickness of 2.0 mm was obtained.

(Comparative Example 5)
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) manufactured by Toray Industries, Inc. was used.

(Comparative Example 6)
A commercially available cushioning material (manufactured by Mitomo Sangyo Co., Ltd., trade name: air foam sheet HR-752, thickness 1.0 mm) was used.

(Comparative Example 7)
A commercially available cushioning material (manufactured by Konan Shoji Co., Ltd., trade name: petit foam, thickness 2.0 mm) was used.

  Table 1 shows the measurement and evaluation results of the foamed sheets obtained in each Example and Comparative Example.

  From the results in Table 1, the polyolefin-based resin foam sheets of Examples 1 to 10 are superior in light shielding properties and flexibility as compared with those of Comparative Examples 1 to 7, and for electronic devices whose thickness and size have been reduced. It turns out that it is useful as a light-shielding sheet.

A MD direction (extrusion direction)
B TD direction (width direction perpendicular to extrusion direction)
C VD direction (sheet thickness direction)
1 Sample (foamed sheet)
2 Resin case (black polypropylene resin plastic)
3 Light source (LED)
4 Visual direction

Claims (8)

  A polyolefin resin foam sheet for light shielding, comprising a polyolefin resin containing a pigment, having a 90% compression stress of 400 to 1000 kPa and a total light transmittance τt of 0 to 1%. The polyolefin resin foam sheet for light shielding has an average cell diameter of 0.02 to 0.17 mm, an apparent density of 0.030 to 0.100 g / cm ³ , and an open cell rate of 60 to 99%. The polyolefin resin foam sheet for light shielding as described.   The polyolefin resin includes a polypropylene resin having a melt flow rate of 0.2 to 5 g / 10 min, a thermoplastic elastomer having a melt flow rate of 0.2 to 15 g / 10 min, and a melt flow rate of 0.1. The polyolefin-based resin foam sheet for light shielding according to claim 1 or 2, comprising at least one polyethylene-based plastomer that is 3 to 15 g / 10 min.   The polyolefin resin foam sheet for light shielding according to any one of claims 1 to 3, wherein the pigment is a black pigment and the content ratio thereof is 1 to 20% by mass of the polyolefin resin.   The polyolefin resin foam sheet for light shielding according to any one of claims 1 to 4, wherein the polyolefin resin foam sheet for light shielding has an adhesive layer on at least one surface thereof. It is a manufacturing method of the polyolefin-type resin foam sheet for light shielding as described in any one of Claims 1-5,
Using a mold annular die composed of a foamed part and a molded part that grows the foam and forms a sheet while melt-kneading a polyolefin-based resin foaming composition containing a pigment and a foaming agent A method for producing a light-blocking polyolefin resin foam sheet, which is obtained by foam molding to obtain a light-blocking polyolefin resin foam sheet.   The method for producing a light shielding polyolefin resin foam sheet according to claim 6, wherein the foaming agent is carbon dioxide gas.   The light shielding sheet for electronic devices containing the polyolefin-type resin foam sheet for light shielding as described in any one of Claims 1-5.