KR101363862B1 - Manufacturing method of foam with integrated conductive outer skins - Google Patents

Abstract

According to the present invention, a non-conductive resin composition for an inner layer containing a polyolefin resin and a foaming agent and a conductive resin composition for the skin containing a polyolefin resin and a conductive additive are coextruded, and the skin layer is integrally laminated on both sides of the inner layer, and the skin layer is laminated. After the surface crosslinking, there is provided a conductive skin integral foam produced by foaming the inner layer and thereby expanding and stretching the skin layer, and the conductive foam of the present invention can be manufactured at a uniform and excellent cost and at a cost that is both physical and electrical. It is particularly useful for protecting electronics from impact.

Description

Manufacturing method of foamed body integral foam foam {Manufacturing method of foam with integrated conductive outer skins}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates primarily to conductive foams used to protect electronics from physical and electrical shocks. In particular, the present invention relates to a panel for loading or packaging a liquid crystal display panel (PANEL), a board assay, a module, and the like. The present invention relates to a conductive skin integrated foam and a method of manufacturing the same, which are useful for preventing the liquid crystal display from being damaged by physical and electrical shocks.

Since the display panel is weak to shock and sensitive to static electricity, the shock must not be transmitted to the display panel during transport, and if static electricity is generated on the surface of the display panel, the cell of the display panel is damaged by static electricity. As a result, defects such as color blur and color bleeding appear.

In order to solve this problem, a method of inserting an antistatic foam sheet between display panels is proposed (Domestic Patent Publication No. 10-2007-006060) to cushion the shock applied to the display panel and prevent static electricity from occurring. The above method is to produce a crosslinked or crosslinked non-crosslinked polyolefin foam by adding a liquid antistatic agent or conductive carbon, and coating an antistatic agent and a conductive carbon on one or both surfaces of the crosslinked or uncrosslinked polyolefin foam. A method (domestic patent application 10-2007-0086151) having a cushioning property and an antistatic function has been proposed.

In addition, the prior art as described above is macroscopically, an internal additive method for producing a conductive material such as an antistatic agent and a conductive carbon, etc. in the production of crosslinked or crosslinked polyolefin foam, and one or both sides of the crosslinked or crosslinked polyolefin foam. There is an external method for coating the antistatic agent and the conductive material, the product produced by the external method will cause a defect of the electronic product due to the separation or blooming of the antistatic agent and the conductive material.

In connection with the above, Korean Patent Application Publication No. 10-2008-0112008 of the present applicant relates to an antistatic foam sheet for protecting an LCD panel, and includes an antistatic foam sheet including a polyolefin resin, which is a basic resin, carbon black, a foam, and the like. By presenting the composition of the foaming material for the interleave between the packaging materials and products for electronic products sensitive to static electricity, LCD panels and glass substrates, etc. was achieved. However, foam gap according to the known technology has a problem that the surface resistance is somewhat reduced, there is a problem that the foam foam (foam foam) is easily worn by the physical force applied to the carbon black embedded in the surface.

Korean Patent Registration No. 10-1004426 of the present applicant is composed of a polyethylene copolymer resin foam and a conductive polyethylene copolymer resin film attached to both sides of the polyethylene copolymer resin foam; The conductive polyethylene copolymer resin film is composed of a conductive film layer and a non-conductive film layer are integrated, and a cushioning material for display panel lamination in which the non-conductive film layer is attached to the polyethylene copolymer resin foam is described. Preparation of a mixture for preparing a conductive film mixture comprising a conductive polyethylene copolymer resin and a permanent antistatic polymer (IDP) and a non-conductive film mixture comprising only a polyethylene copolymer resin to form a non-conductive film layer Process; The conductive film mixture and the non-conductive film mixture prepared by the mixture preparation process are molded into a conductive polyethylene copolymer resin film in which the conductive film layer and the non-conductive film layer are integrated by using a blown-film extrusion system. Conductive film forming step; A method for producing a cushioning material for display panel lamination including a laminating step of binding the conductive polyethylene copolymer resin film subjected to the conductive film forming step to both sides of the polyethylene copolymer resin foam is described.

Despite the similar structure of the skin layer and the foam, it has been technically limited to impart antistatic and conductive performance to the skin layer. The technical limitation is that when foaming a coextruded sheet in which the conductive material is a skin layer and the foam layer is made of an inner layer, the expansion ratio of the skin layer and the inner layer of the conductive material is different, resulting in process instability such as cracking and bursting in a high temperature foaming furnace. There is a real problem. In particular, carbon black or the like is used as the skin layer of the conductive material. However, when it reacts with the polymer material, the viscoelasticity is very low, and the elongation is lowered.

The existing method of imparting conductivity to this problem is first of all the method of embedding the conductive material in the entire extrusion sheet and foaming, and second of the method of laminating the antistatic or conductive film on the general foam, and third of the general foam It is a situation that uses a method of coating a general film on the coating with a conductive material.

It is therefore an object of the present invention to provide a conductive foam of more improved quality.

Another object of the present invention is to provide a conductive foam which can be produced at a more economical cost.

It is a further object of the present invention to provide a conductive foam which can be produced in a more simplified process.

Another object of the present invention is to provide a conductive foam that can be produced in a more improved manufacturing environment.

According to the present invention achieving the above object,

(a) Coextruded non-conductive resin composition for inner layer containing polyolefin resin and blowing agent, and conductive resin composition for skin containing polyolefin resin and melting additive (MI) of 15.0g / 10min or less and coextruded Manufacturing a sheet in which a conductive skin layer is integrally laminated on the sheet;

(b) surface crosslinking the skin layer of the coextruded sheet; And

(c) heating the surface-cross-coextruded sheet to foam the inner layer, thereby expanding and stretching the skin layer, thereby providing a method for manufacturing a conductive skin integral foam.

Preferably, according to the present invention, there is provided a method for producing a conductive skin-integrated foam, wherein the polyolefin-based resin which is the base resin of the conductive resin composition for the skin is a polyolefin-based resin having a melt index (MI) of 0.3 to 10.0 g / 10 min.

Preferably, according to the present invention, in step (b), the degree of surface crosslinking of the epidermal layer is provided with a method for producing a conductive skin integral foam, wherein the gel fraction is 3 to 25%.

Preferably, according to the present invention, in step (b), a polyolefin resin, which is a base resin of the inner layer non-conductive resin composition, is also crosslinked together.

Preferably, according to the present invention, there is provided a method for producing a conductive skin integral foam, wherein the crosslinking in step (b) is crosslinking by electron beam irradiation.

Preferably the present invention provides a method for producing a conductive skin integrated foam characterized in that the step (a) in the co-extrusion so that the thickness of the skin layer is 0.1 ~ 1.0mm and the thickness of the inner layer is 0.2 ~ 10.0mm.

According to the present invention preferably provides a method for producing a conductive skin-integral foam, characterized in that the step (c) is expanded and stretched so that the thickness of the skin layer film is 10 ~ 70㎛.

According to the present invention, there is provided a method for producing a conductive skin-integral foam, wherein the inner layer polyolefin resin and the outer layer polyolefin resin are the same or different polyolefin resins.

Preferably, according to the present invention, the polyolefin resin is low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene polyethylene, α-olefin copolymer, medium density polyethylene (MDPE), high density polyethylene (HDPE), polypropylene One, two or more selected from the group consisting of resins, ethylene propylene copolymers, ethylene vinyl acetate copolymers, ethylene acrylic acid copolymers, ethylene methacrylic acid copolymers, ethylene acrylic acid ester copolymers and ethylene methacrylic acid ester copolymers Provided is a method for producing a conductive skin integral foam, which is a mixture.

According to the present invention, there is provided a method for producing a conductive skin-integral foam, wherein the non-conductive resin composition for inner layer and the conductive resin composition for skin layer contain or do not contain a crosslinking agent.

Preferably, according to the present invention, there is provided a method for producing a conductive skin integrated foam, wherein the crosslinking agent is an organic peroxide.

According to the present invention, there is provided a method for producing a conductive skin integral foam, wherein the blowing agent is a thermal decomposition chemical blowing agent.

Preferably, according to the present invention, the conductive additive is a carbon nanotube, permanent antistatic polymer (IDP), graphene and carbon black of the conductive skin integrated foam, characterized in that at least one mixture selected from the group consisting of carbon black. A manufacturing method is provided.

According to the present invention, there is also provided a conductive skin integral foam produced by the above method.

Conductive skin integral foam produced according to the present invention is a monolithic foam with only the outer skin layer can solve the peeling problem caused by the conventional method of laminating the foam and the film, the conductive skin is expanded and stretched according to the foam of the inner layer is thin As the cell form of inner foam is transferred to the epidermis, fine surface irregularities are formed to facilitate the transfer of LCD products when used as LCD protective sheet, and the elongation of the epidermal layer and inner layer is cross-linked by electron beam irradiation. It can be modified to produce products without breaking or bursting that may occur during foaming, and have excellent properties such as tensile strength, scratch resistance, chemical resistance, and volatile organic compounds (VOCs) in the manufacturing process. Can effectively block the release of the product, making the working environment safer, A can be simplified more, it is possible to minimize the expensive conductive skin thickness it has the advantage of greatly reducing the production cost.

1 is a cross-sectional view schematically showing the pre-expanded state of the conductive skin integral foam co-extruded in accordance with the present invention,
2 is a cross-sectional view schematically showing a state after foaming of the cushioning material of FIG. 1.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 2, the polyolefin-based conductive skin-integrated foam according to the present invention is a polyolefin-based resin foam as the inner layer 10 and a conductive non-foaming polyolefin-based resin laminated on both sides of the polyolefin-based resin foam layer as the skin layer 20. With a film.

The polyolefin-based conductive skin integral foam according to the invention can be prepared by the following steps:

(a) Co-extruded non-conductive resin composition for inner layer containing polyolefin resin, crosslinking agent and foaming agent and conductive resin composition for skin containing polyolefin resin, crosslinking agent and conductive additive and integrally laminated skin layer on both sides of inner layer Manufacturing a sheet;

(b) surface crosslinking the skin layer of the coextruded sheet;

(c) heating the surface crosslinked coextrusion sheet to foam the inner layer and thereby expand and stretch the skin layer.

In the present invention, the material constituting the inner layer is a polyolefin resin composition containing a polyolefin resin and a crosslinking agent, and the material constituting the skin layer is a polyolefin resin composition containing a polyolefin resin and a conductive additive.

The polyolefin resin constituting the inner layer and the polyolefin resin constituting the skin layer may be the same or different polyolefin resins. Preferred examples of the polyolefin resin used in the present invention are low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene polyethylene, α-olefin copolymer, medium density polyethylene (MDPE), high density polyethylene (HDPE), poly One or two selected from the group consisting of propylene resin, ethylene propylene copolymer, ethylene vinyl acetate copolymer, ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer, ethylene acrylic acid ester copolymer and ethylene methacrylic acid ester copolymer There is a mixture of the above.

The blowing agent contained in the inner layer polyolefin resin composition may be a conventional one well known in the art, and particularly preferred is a thermal decomposition chemical blowing agent. The content of the blowing agent can be appropriately adjusted according to the desired degree of foaming of the inner layer. It is preferable to mix | blend a blowing agent to the extent that foaming magnification can be made 5 to 50 times.

In addition, the resin composition for the inner layer and the skin layer may or may not contain a crosslinking agent. When it contains, the crosslinking agent can use a conventional thing well known in the art, Especially, an organic peroxide is especially preferable. Of course, other conventional additives such as lubricants, plasticizers, surfactants, antioxidants, ultraviolet stabilizers, etc. may be blended into the resin compositions for the inner and skin layers according to the present invention.

In the step (b), if the surface of the polyolefin resin for the skin layer is cross-linked and controlled to the desired physical properties, it is possible to effectively prevent breakage or bursting of the skin that may occur during foaming. When the surface crosslinking of the polyolefin resin for the skin layer is made in step (b), it is also possible to make crosslinking of the polyolefin resin for the inner layer together. For example, the electron beam may be irradiated only to the epidermal layer so that only surface crosslinking may be performed. The electron beam may also be irradiated to the inner layer of the coextruded sheet to crosslink the polyolefin resin for the inner layer together. The crosslinking of the inner layer may be performed in step (b) as described above, but may be performed in step (c). In the present production method, in addition to the crosslinking method using an electron beam, a crosslinking method using a chemical crosslinking method or a combination of electron beam crosslinking and chemical crosslinking can be used.

As the conductive additive contained in the resin composition for the skin layer, one or two or more mixtures selected from the group consisting of carbon nanotubes (CNT), permanent antistatic polymer (IDP), graphene and carbon black are preferable. It can be adjusted appropriately to the desired surface resistance. The surface resistance is preferably selected within the following ranges depending on the application: 10 ² to 10 ^{5 5} / sq (conductivity), 10 ⁶ to 10 ⁹ Ω / sq (anti-discharge), 10 ¹⁰ to 10 ¹² Ω / sq (Antistatic).

In the conductive skin integrated foam according to the present invention, both the inner layer and the skin layer are integrally laminated by co-extrusion since both are made of polyolefin resin. The polyolefin resin used in the resin composition for the skin layer is 15 g / 10 min or less of melt index (MI), preferably 0.3 to 10.0 g / 10 min, and more preferably 0.5 to 4.0 g / 10 min. If the melt index of the polyolefin resin for the skin layer is higher than 15.0 g / 10 min, there is a problem that it is difficult to manufacture the coextruded sheet due to the large bank flow in the coextruder such as extrusion die-die (T-DIE). When the inner layer 10 is foamed, the degree of expansion and elongation of the epidermal layer is low, so that it is difficult to form a thin epidermal layer, so that the surface irregularities are not easily exposed, and it is not preferable because it causes a price increase.

In step (b), the degree of crosslinking of the polyolefin resin for the epidermal layer is preferably 3 to 25% of a gel fraction. The reason for crosslinking with 3 ~ 25% crosslinking degree expressed as gel fraction before foaming the inner layer is that when the crosslinking degree is lower than 3%, skin layer sticks to mesh when foaming in foaming furnace such as horizontal foaming furnace etc. This causes the skin layer to burst and the non-conductive foam is easily exposed. If the crosslinking degree is higher than 25%, the expansion and contraction degree of the skin layer is low during foaming of the inner layer 10, making it difficult to form a thin skin layer. There is a problem. More preferred crosslinking degree of the polyolefin resin for the skin layer is 5 ~ 10% Gel Fraction.

In order to minimize the thickness of the skin layer, there is a method of minimizing the thickness of the coextrusion, and the method of maximizing the foaming ratio of the inner layer in the foaming, which is linked to the cost reduction. In the final product, the thickness of the conductive skin layer is preferably 10 to 70 μm. The reason is that the thickness of the conductive skin layer is less than 10 μm, so that the skin is easily damaged during the manufacturing process. When the thickness is made thicker than 70㎛, it is easy to cause partial quality defects due to bending or wrinkles.

In step (c), the skin layer 20 is expanded and stretched by the foaming of the inner layer 10 so that the thickness thereof becomes thinner by 1/5 to 1/20 of the thickness of the skin layer in the coextruded sheet formed in step (a). . Therefore, the thickness of the epidermal layer in step (a) is preferably 0.1 ~ 1.0mm. In addition, it is preferable that the thickness of the inner layer is 0.2 to 10.0 mm in step (a), and the foaming of the inner layer in step (c) is preferably performed by heating to a temperature at which the foaming agent of the inner layer is decomposable.

In the conductive skin-integral foam produced by the above-described method, the conductive skin is expanded and stretched in all directions by the foaming of the inner layer, so that the surface physical properties are uniform and good in all directions, and the inner layer foam becomes thinner and thinner. The cell (CELL) form is transferred to the epidermis and surface irregularities are formed. When the surface irregularities are used as LCD protective sheet, it forms an air layer on the contact surface with the LCD and provides the effect of convenient transportation of LCD products. In addition, there is an advantage that can solve the problem of peeling, which is one of the problems of the conventional method of laminating the conductive skin on the foam or coating the conductive coating.

The features and other advantages of the present invention as described above will become more apparent from the following embodiments.

Example 1

Single-screw polyolefin-based resin composition for inner layer containing 10.0 parts by weight of azodicarbonamide as a chemical foaming agent and 1 part by weight of dicumyl peroxide as a crosslinking agent based on 100 parts by weight of a polyethylene copolymer (MI 0.8 g / 10 minutes, manufactured by H Company) Melt kneading with an extruder.

On the other hand, the polyolefin-based resin composition for the skin layer in which 3 parts by weight of carbon nanotubes was blended as a conductive additive with respect to 100 parts by weight of a high density polyethylene resin (MI 3.5, manufactured by H Company) was melt kneaded with a single screw extruder.

Next, the skin layer, the inner layer, and the skin layer were laminated in three layers on the feed block, and then coextruded from a T-die to prepare a coextrusion sheet having a total thickness of 1.3 mm having a thickness of 250 µm and an inner layer of 800 µm, respectively. .

The surface of the prepared coextruded sheet was irradiated with an electron beam to surface crosslink with a gel fraction of 7%.

The surface-crosslinked coextrusion sheet was heated in a foaming furnace to prepare a polyolefin-based conductive skin integral foam.

The properties of the conductive foams produced are shown in Table 1.

[Examples 2 to 4 and Comparative Examples 1 to 4]

The same procedure as in Example 1 was repeated except that the production conditions were changed as shown in Table 1.

division Example Comparative Example One 2 3 4 5 6 One 2 MI of epidermal layer resin
(g / 10 min) 0.8 0.8 3.0 3.0 3.5 0.3 15.5 17.0 Epidermal layer crosslinking degree (%) 7.5 7.5 7.5 7.5 27 25.0 - - Of conductive additive
Type and content
(Parts by weight) CNT
3 Carbon black
12 CNT
2 Carbon black
12 Carbon black
12 Carbon black
12 Carbon black
12 Carbon black
12 In coextrusion sheet
Thickness of epidermal layer (㎛) 250 250 250 250 250 250 - - In foam
Thickness of epidermal layer (㎛) 35 35 32 32 95 90 - - Coextrusion Sheet Formability Good Good Good Good Good Good Molding
Impossible Molding
Impossible Foam Surface Exposure none none none none none none - - In coextrusion sheet
Surface condition of the epidermis Smooth Smooth Smooth Smooth Smooth Smooth In foam
Surface condition of the epidermis clear
Fine iron clear
Fine iron clear
Fine iron clear
Fine iron Weak
Unevenness Weak
Unevenness - - Inner foam state Very good Very good Very good Very good usually usually - -

Claims (15)

In preparing conductive foams,
(a) Coextruded non-conductive resin composition for inner layer containing polyolefin resin and foaming agent and conductive resin composition for skin containing polyolefin-based resin and conductive additive of melt index (MI) 0.3-10.0 g / 10 min. Manufacturing a sheet in which conductive skin layers are integrally laminated on both surfaces; (b) surface crosslinking the skin layer of the coextruded sheet; And (c) heating the surface crosslinked coextrusion sheet to expand the inner layer and thereby expand and stretch the skin layer.
In the step (b), the degree of surface crosslinking of the epidermal layer is 3 to 25% of gel fraction;
In the step (b) or step (c) is configured to cross-link the polyolefin resin which is a base resin of the non-conductive resin composition for the inner layer;
In step (a) the thickness of the epidermal layer is configured to be 0.1 ~ 1.0mm and the thickness of the inner layer is 0.2 ~ 10.0mm;
In step (c), the thickness of the skin layer film is configured to expand and stretch to 10 ~ 70㎛;
The polyolefin resin is low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene polyethylene, α-olefin copolymer, medium density polyethylene (MDPE), high density polyethylene (HDPE), polypropylene resin, ethylene propylene copolymer , An ethylene vinyl acetate copolymer, an ethylene acrylic acid copolymer, an ethylene methacrylic acid copolymer, an ethylene acrylic acid ester copolymer and an ethylene methacrylic acid ester copolymer;
The non-conductive resin composition for the inner layer and the conductive resin composition for the skin layer are configured to further include an organic peroxide as a crosslinking agent;
The blowing agent consists of a pyrolytic chemical blowing agent;
The conductive additive is composed of one or two or more kinds selected from the group consisting of carbon nanotubes, permanent antistatic polymer (IDP), graphene and carbon black;
The epidermal treated by the step of expanding and extending the epidermal layer is a cell (CELL) form of the inner layer foam is formed to transfer to the epidermis is a method of producing a conductive skin integral foam, characterized in that the surface is configured to be formed.
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