JPH0380417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention first forms a film by extrusion using a polyolefin resin composition containing a specific carbon black and having a low melt index (MI). The first film formed in this manner is wound around a heated calendar roll to form a film having many convex portions (hereinafter also referred to as embossed film), and then a second film (which becomes the back film) is formed. is wrapped around the embossed film, and both films are thermally fused on a calendar roll to create a cushioning sheet made of polyolefin film having a large number of convex protrusions forming independent air chambers. (hereinafter also referred to as air cushioning sheet)
and a cushioning sheet formed by laminating an embossed film and a back film obtained by using a polyolefin film extruded from the above-mentioned specific polyolefin resin composition as a raw material film. .

Conventionally, packaging containers for transporting and storing expensive electronic component materials such as ICs, FPCs, and LSIs, or their products, have been unable to shield electromagnetic waves that have a negative impact on the packaged items. Moreover, it was desired that the material be made of a buffering material that is conductive and has no chargeability, but packaging materials that have all of the various performances mentioned above are
There were almost no practical products that could be produced industrially, and there were only those that were difficult to produce industrially and had poor basic physical properties as packaging materials.

In particular, as a conductive cushioning material, "a cushioning material made of plastic film having many convex protrusions forming independent air chambers" made of plastic resin containing carbon black is used.
Although it has been proposed, the productivity of the buffering material is poor and the basic physical properties of the obtained buffering material are poor, so it has not been able to be industrially produced or put to practical use.

As a result of intensive research into an industrial production method for cushioning materials that solved the above-mentioned problems, the inventors found that a raw material film molded using a polyolefin resin composition containing a specific carbon black can be produced efficiently. The present invention was completed based on the discovery that it is possible to produce a cushioning sheet (air cushioning sheet) having the shape described above, and that the resulting cushioning sheet has excellent performance.

That is, in this invention, carbon black having an oil furnace type pore structure with a porosity (described in detail later) of 40% or more is blended in a polyolefin resin at a ratio of about 5 to 20% by weight, The melt index (MI) of the composition is
A raw material film of about 20 to 300μ is formed by extrusion using a polyolefin composition with a yield of 0.2g/10 minutes or less, and the first film formed in this way is
A film (embossed film) that has many convex projections on its entire surface when heated by being wound around a heated calendar roll that has many recesses on its circumference.
A second flat film (to be a back film) of the same type as the first film is further wrapped around the embossed film having the protrusions in a heated state, and then rolled onto a calendar roll. The film is characterized by thermally fusing both films together to form a cushioning sheet (air cushioning sheet) made of polyolefin film that has many convex protrusions on its entire surface that form independent air chambers. A method for producing an antistatic cushioning material, and an air cushioning material constructed by laminating an embossed film and a backing film obtained by using a polyolefin film extruded from the above-mentioned specific polyolefin composition as a raw material film. Regarding the seat.

The manufacturing method of this invention uses a specific polyolefin composition containing a relatively low proportion of a special carbon black with a highly porous pore structure, and the composition has a considerably low melt index (MI). Therefore, first, it is possible to sufficiently shape the raw material film, and it is also possible to stably mold an air cushioning sheet from the molded raw material film with good reproducibility. The manufacturing method of this invention takes into account the possibility of thermal damage to the protrusions during molding of the embossed film in which convex protrusions are formed, and the heat fusion properties of the embossed film and the back film. Using a polyolefin composition with a high MI value of about 1 to 10 g/10 min (common in film molding), which is blended with a high proportion of other common carbon blacks, Compared to the case of molding a plastic sheet, the productivity is about 2 times or more, especially 3 to 10 times higher, and the by-product production rate of off-grade that cannot be used as a product is about 20% or less, especially Ten
% or less.

In addition, the air cushioning sheet of this invention has many convex protrusions on its entire surface that form independent air chambers, so it is extremely lightweight and extremely soft due to the cushioning properties of the sealed air. It has cushioning properties and is suitable as a packaging material for precision electronic materials. Furthermore, it is made of polyolefin film molded from a polyolefin composition containing an appropriate amount of special carbon black, so it exhibits electrical conductivity. The surface specific electrical resistance is approximately
It has a low 10 ² to 10 ⁸ ohm, especially 10 ³ to 10 ⁷ ohm, and as a result, it has a non-static property that makes it difficult for dust and fine dust to adhere to its surface, and it also has a non-static property that makes it difficult for dust and fine particles to adhere to its surface. Electronic materials will not be damaged by static electricity.

Hereinafter, this invention will be explained in more detail with reference to the drawings.

FIG. 1 is a flow diagram schematically showing an example of the manufacturing method of the present invention.

FIG. 2 is a perspective view showing an example of the cushioning sheet of the present invention and a cross-sectional view showing an enlarged part of the sheet.

In the manufacturing method of the present invention, the raw material film is carbon black having an oil furnace type pore structure (or hollow shell structure) with a porosity of 40% or more, particularly 50 to 90%, more preferably 60 to 80%. It is blended into the polyolefin resin in a proportion of about 5 to 20% by weight, especially 7 to 15% by weight, and the melt index (MI) of the composition is 0.2g/10
By using a polyolefin resin composition having a yield of about 20 to 300μ, especially about 0.005 to 0.1g/10 minutes, various extrusion methods such as T-die extrusion and inflation extrusion can be used. 30〜
It was obtained by molding a 200μ film.

The above-mentioned porosity P of carbon black is defined as the ratio (A/B) of the total volume B of pores (hollow parts) built in or opened in the particles to the apparent particle volume A of carbon black (A/B). It is a value expressed in percent), and is generally calculated from the following formula from each volume measured with a soap tomato measuring machine manufactured by Carlo Erba.

P=(A/B)×100 (%) The oil furnace type carbon black with a pore structure has a particle size of about 1000 angstroms (Å) or less, particularly about 100 to 500 angstroms, and It is preferable to have pores (hollow parts) of various shapes built-in or open therein.

In this invention, if the blending ratio of the carbon black is too large, it may be impossible to mold the raw material film from such a resin composition by extrusion molding, or it may be difficult to mold stably, or Even if the raw material film can be formed, it may not be possible to further form a cushioning sheet from the raw material film with good productivity, so it is not appropriate. Also, if the blending ratio is too low, the moldability will be poor. This is not appropriate because the conductivity of the obtained raw material film (that is, the surface specific electrical resistance of the film) deteriorates.

Other common carbon blacks require a high proportion of about 20% by weight or more in the resin composition in order to obtain appropriate conductivity, and a resin composition with such a high carbon black content is used. When a cushioning sheet is formed using a resin composition, the moldability of the raw material film and the cushioning sheet are poor, resulting in poor productivity.In order to improve this, various modifiers are added to the resin composition. However, in this invention, the above-mentioned special carbon black is blended into the polyolefin resin composition and its blending ratio is improved. can be relatively low at 5 to 20% by weight, and there is no need to add various extra modifiers, so the film formability is improved.
The basic physical properties do not deteriorate, and the productivity of the cushioning sheet is dramatically improved.

Examples of the polyolefin include low density polyethylene (LDPE, LLDPE, etc.), high density polyethylene (HDPE), polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-acrylonitrile copolymer. In particular, in the present invention, low density polyethylene having a melt index (MI) of about 0.3 to 20 g/10 minutes is most suitable.

In addition, in this invention, when the melt index (MI) of the polyolefin resin composition used for molding the raw material film becomes too high than 0.2 g/10 minutes, a cushioning sheet is molded from the obtained raw material film. Problems may arise in the formation of protrusions on the embossed film and in the heat fusion of the films.
This is not appropriate because it becomes impossible to manufacture a cushioning sheet of stable quality with good reproducibility.

The polyolefin resin composition used in the present invention is generally a polyolefin resin composition containing a high proportion of carbon black, which can only be formed into a film by T-die extrusion method, and by inflation extrusion molding. It is also advantageous that films can be formed using both the T-die extrusion method and the inflation extrusion method, whereas it is impossible or extremely difficult to form a film using this method.

In the manufacturing method of the present invention, the raw material film formed as described above is used. For example, as shown in FIG. is wound around a heated calender roll 3 having a large number of concave portions 2 on the entire circumferential surface to form a film (embossed film) 4 having a large number of convex protrusions 6 on the entire surface in a heated state, and further 2, a flat second film 5 (made of the same material as the first film, with a cushioning sheet backing The film 7) is further wound in a heated state, and both films 1 and 7 are wrapped around the calender roll 3.
5 or 7 are thermally fused to form the cushioning sheet 8 of the present invention in which the embossed film 4 and the backing film 7 are joined, and the cushioning sheet 8 is wound up as a roll-shaped cushioning sheet 11.

In FIG. 1, roll 12 and roll 13
It is appropriate that the roll 14 has the function of pressing the first film 1 or the second film 5 against the peripheral surface of the calendar roll 3 and the function of heating each film.Furthermore, the roll 14 is an embossing roll. It is preferable that the cooling roll is for peeling off the cushioning sheet 8 formed by heat-sealing the embossed film 4 and the backing film 7 on the embossing roll 3 and cooling it.

The above-mentioned cushioning sheet can be molded using a conventionally known molding method for this kind of cushioning material (for example, the molding method described in Japanese Patent Publication No. 37-13782, Japanese Patent Publication No. 38-330, etc.). It can be performed under similar molding conditions.

Note that the first film 1 described above is rolled using a heated embossing roll 3 having a large number of recesses 2 on the entire circumference.
In order to form an embossed film 4 having a large number of convex protrusions 6 over the entire surface, for example,
When the first film 1 is wound around the embossing roll 3, the inner space of the recess 2 of the embossing roll 3 is depressurized and each part of the first film 1, which is heated and softened, is wrapped around the inner surface of the recess 2. It can be formed by suctioning toward the surface and deforming it into a convex projection.

In the manufacturing method of the present invention, the above-mentioned embossed film can be well formed using a raw material film made of a polyolefin composition with an extremely low MI value, which is blended with a high proportion of a specific carbon black. With a raw material film made of a polyolefin composition with a high MI value that contains a high proportion of carbon black (or further contains a modifier), it is difficult to form the protrusions during molding of the embossed film mentioned above. be.

The conductive cushioning sheet of the present invention includes, for example,
Embossed film 4 manufactured by the above-mentioned manufacturing method and obtained using a polyolefin film extruded from the above-mentioned specific polyolefin composition as a raw material film, as shown in FIG. and a flat back film 7 are laminated and integrally formed,
This is a cushioning sheet 8 made of polyolefin film having a large number of convex protrusions 6 forming independent air chambers.

The cushioning sheet of this invention is extremely lightweight and flexible because it is made of a raw material film with a thickness of about 20 to 300μ, and has air cushioning properties due to the convex protrusions forming independent air chambers. It is a cushioning material that continuously exhibits soft cushioning properties and has excellent basic physical properties.
Due to the above-mentioned special carbon black, which is blended at a ratio of 20% by weight, the surface specific electrical resistance of the cushioning sheet is 10 ² to 10 ⁸ ohms, which shows sufficient conductivity. It also has non-static properties.

The convex projections of the cushioning sheet may be of any shape as long as they form air chambers having a shape such as a prism, a cylinder, an elliptical cylinder, a hemisphere, or a combination thereof. In particular, the height of the convex projection is about 1 to 20 mm, particularly preferably about 2 to 18 mm, and the base area is about 0.1 to 15 cm ² , particularly preferably 0.2 to 18 mm.
Preferably, the air chamber has a columnar air chamber, such as a columnar shape or an elliptical columnar shape, with a size of about 10 cm ² .

This cushioning sheet has a spacing between convex protrusions.
It is preferable to have a large number of convex protrusions arranged over the entire surface so as to have a diameter of 0.5 to 20 mm and 1 to 15 mm.

Example 1 A polyethylene composition (manufactured by Lion Corporation, having a pore structure of particle size: 370 Å and porosity: 68%) is blended with low density polyethylene at a blending ratio of about 12% by weight. 100μ and 75μ raw films were molded by inflation extrusion using MI: 0.05g/10min). The 100μ raw material film is used as the first raw material film for forming an embossed film, and is wound around a heated calendar roll that has many concave portions on the circumference, and is heated to approximately 120°C to form a convex shape. An embossed film having a large number of protrusions is formed, and the raw material film of 75 μm is wrapped in a heated state on the embossed film having the protrusions, and both films are thermally fused on a calendar roll to form an independent film. The convex protrusions (height: about 5 mm, diameter: 11 cylindrical protrusions) forming the air chamber are arranged as shown in Figure 2 with a distance of about 1.5 mm between each protrusion. A large number of cushioning sheets were formed.

The cushioning sheet thus obtained had extremely flexible and soft cushioning properties, and the durability of its cushioning performance was sufficiently high.

Furthermore, when the surface electrical resistivity of this cushioning sheet was measured, it was found to be 10 ⁵ ohms.

Comparative Example 1 The same procedure as in Example 1 was carried out, except that the ketone black was changed to acetylene black (a carbon black with an insufficient pore structure, with a particle size of about 410 Å and a porosity of about 14%). A cushioning sheet was manufactured.

The surface electrical resistivity of the cushioning sheet obtained as described above was about ¹⁰¹⁰ ohms, and it could not be said to have electrical conductivity.

Comparative Example 2 A polyethylene composition was prepared in the same manner as in Example 1, except that the amount of acetylene black used was changed to 25% by weight, and the composition was used to form a raw material film and to form a cushioning sheet. Manufacturing Example 1
However, in the manufacturing process of the raw material film and the manufacturing process of the cushioning sheet, the quality of the film was uneven, and the embossing and bonding of the cushioning sheet were not done properly, resulting in defective products. The production rate was as high as approximately 50% or more, and product productivity was extremely low.

[Brief explanation of drawings]

Hereinafter, this invention will be explained in more detail with reference to the drawings. FIG. 1 is a flow diagram schematically showing an example of the manufacturing method of the present invention. FIG. 2 is a perspective view showing an example of the cushioning sheet of the present invention and a cross-sectional view showing an enlarged part of the sheet. 1...First film, 2...Concave portion of embossing roll, 3...Emboss roll, 4...Embossed film, 5...Second film, 6...Convex projection, 7... Back film, 8...Buffer film.

Claims (1)

[Claims] 1. Carbon black having an oil furnace type pore structure with a porosity of 40% or more is blended with polyolefin in a proportion of about 5 to 20% by weight,
The melt index (MI) of the composition is
A raw material film of about 20 to 300μ is formed by extrusion using a polyolefin composition with a yield of 0.2g/10 minutes or less, and the first film formed in this way is
A film having a large number of convex protrusions is formed in a heated state by being wound around a heated calendar roll having a large number of concave portions on the circumferential surface, and then the first film and the first film are placed on top of the film having the protrusions. A second sheet of the same type of flat film is further wrapped in a heated state, and both films are thermally fused on a calender roll, creating a number of convex protrusions that form independent air chambers. 1. A method for producing a conductive cushioning material, comprising forming a cushioning sheet made of a polyolefin film comprising: 2. Carbon black with an oil furnace type pore structure with a porosity of 40% or more is blended with the polyolefin at a ratio of about 5 to 20% by weight,
The melt index (MI) of the composition is 0.2
An independent air chamber is formed by laminating an embossed film and a backing film obtained by using a polyolefin film extruded from a polyolefin composition having a yield of less than 100 g/10 minutes as a raw material film. 1. A conductive cushioning material characterized by being a cushioning sheet made of polyolefin film having a large number of convex projections.