KR102274956B1 - Manufacturing method of foamed film - Google Patents

Abstract

The present invention relates to a manufacturing method of a foamed film having buffering properties, in which a resin composition of an ethylene-propylene-diene terpolymer except an ethylene vinyl acetate copolymer is used to be molded into a blown bubble film, and thus, it is possible to reduce the density of the foamed film, and a state of a foam cell becomes uniform and mechanical properties and heat resistance of the film become balanced. According to the present invention, since melt viscosity and viscoelasticity of the composition are improved by the ethylene-propylene-diene terpolymer, even if the blown bubble is slowly cooled, the molding stability of the foamed film and blocking resistance are improved.

Description

Manufacturing method of foamed film {Manufacturing method of foamed film}

The present invention relates to a method for producing a foamed film, using ethylene vinyl acetate copolymer (EVA) as a main raw material, and generating foam bubbles in the film by a foaming agent so that the film exhibits cushioning properties.

A foamed film is a film produced by generally foaming a synthetic resin with a foaming agent added thereto in the molding process of the film. Compared with a film that does not contain foamed cells, the foamed film provides light weight, heat insulation, insulation, elasticity, and cushioning properties due to the foamed pores formed. , flexibility, and buffering properties are improved, and by using these characteristics, it is used for various purposes such as various packaging materials, food containers, insulation materials, interleaving papers, and gaskets.

As a base resin constituting the foam film, a thermoplastic resin such as polyolefin, polyurethane, or vinyl chloride resin is used, and the foam film is manufactured using the characteristics of each resin.

As an example of the foamed film, there is a foamed film using an ethylene vinyl acetate copolymer (EVA) as a base resin.

EVA foam film is applied as a cushioning material due to its excellent elasticity, cushioning properties, and flexibility, but its application as an internal cushioning material for electronic products is limited because durability, weather resistance, heat resistance and flammability are lowered.

On the other hand, the EVA foam film is generally prepared by a cross-linking foaming method to facilitate film molding and to control foam cells and improve mechanical strength.

The cross-linked EVA foam film by the cross-linked foaming method can change the viscoelastic behavior by first cross-linking the resin under specific conditions, so that the temperature range with viscoelasticity suitable for the production of low-density (high-foaming) foam can be broadened.

In addition, heat resistance and mechanical properties can be improved by crosslinking.

However, since crosslinking is required for molding, the manufacturing process is complicated, and there is a problem in that it is not easy to select suitable molding conditions for controlling mechanical properties and foaming cells.

EVA's viscoelasticity decreases rapidly at temperatures above its melting point, and since the temperature range of the appropriate processing region is very narrow, only a high-density (low-foaming) foam can be obtained without crosslinking, and a low-density film cannot be obtained, resulting in poor buffering properties. And there is a problem that the mechanical properties are deteriorated.

That is, the film molding method by the non-crosslinked foaming method is not easy to control foaming and improve mechanical and thermal properties. In particular, compared to the T-die method, the blown bubble film molding method has superior productivity and facilitates the production of thin films. There is a problem that is not easier when using .

Republic of Korea Patent Publication No. 2003-0084849 (EVA film for crosslinking foaming)

In order to solve the above problems, the present invention improves workability and foamability even if the blown bubble film molding method is used without crosslinking the EVA resin, and the foamed film has a balanced mechanical and thermal properties. An object of the present invention is to provide a method for producing a film.

In order to solve the above problems, the present invention, 30-50 parts by weight of low-density polyethylene, 10-30 parts by weight of high-density polyethylene, 30-50 parts by weight of ethylene-propylene-diene ternary copolymer relative to 100 parts by weight of ethylene vinyl acetate copolymer Mixing a resin composition containing 2 to 6 parts by weight of talc, 0.02 to 1.0 parts by weight of stearic acid amide, 0.05 to 5 parts by weight of a blowing agent, and 90 to 110% by weight of activated alumina compared to the blowing agent; and molding the blown bubble film by melting the resin composition using a blown bubble film molding machine and extruding the resin composition through a circular die.

According to the present invention, since the melt viscosity and viscoelasticity of the composition are improved by the ethylene-propylene-diene terpolymer, the molding stability of the foamed film can be improved even when the blown bubble is slowly cooled.

In addition, since activated alumina adsorbs moisture and gas in the extruder and discharges it when forming a blown bubble film, sufficient foaming occurs while foaming is gradually made, and the foaming ratio increases, so that the density can be reduced, and the foam cell Since the small size is uniformly distributed, the formation state of the foam cell is improved.

1 is a diagram showing an example of a blown bubble film forming machine for producing a foamed film according to an embodiment of the present invention.

The present invention, using a blown bubble film molding machine, relative to 100 parts by weight of the ethylene vinyl acetate copolymer, 30-50 parts by weight of low-density polyethylene, 10-30 parts by weight of high-density polyethylene, 30-50 parts by weight of ethylene-propylene-diene ternary copolymer parts, talc 2-6 parts by weight, stearic acid amide 0.02-1.0 parts by weight, blowing agent 0.05-5 parts by weight, and a resin composition containing activated alumina in an amount of 90-110% by weight compared to the blowing agent is melted and extruded through a circular die. It is a manufacturing method of a foamed film for forming a fresh bubble film.

Ethylene-vinyl acetate copolymer (EVA) is a copolymer of ethylene and vinyl acetate obtained by radical polymerization of ethylene and vinyl acetate in the presence of a catalyst in a reactor. characteristics are very good.

The content of vinyl acetate in the EVA of the present invention is 5 to 25% by weight, but when it is less than 5% by weight, elasticity is lowered, and the blown bubble foam film has insufficient extensibility, flexibility, feel, appearance, and heat seal strength, and is 25% by weight. %, the MI exceeds 5 g/10 min, and the tensile strength, tear strength, impact strength, etc. are lowered, and the adhesiveness is strong and the film formability is lowered.

In addition, it is preferable that the density of the EVA is 0.930 to 0.950 g/cm 3 , and if it is less than 0.930 g/cm 3 , the tensile strength, tear strength, impact strength, extensibility, flexibility, feel, and appearance characteristics of the blown bubble foam film This decreases, and when it exceeds 0.950 g/cm 3 , tensile strength, tear strength, impact strength, and the like are reduced.

In addition, it is preferable that the melt index (MI) of the EVA is 0.5 to 5 g/10 min. If it is less than 0.5 g/10 min, the moldability of the blown bubble foam film deteriorates and productivity decreases, as well as flexibility and feel. If it exceeds 5 g/10 min, the tensile strength, tear strength, impact strength, etc. of the blown bubble foam film are deteriorated.

The EVA foam film foamed using the EVA copolymer has excellent elasticity, so it is used as a cushioning material and a sealing material.

However, when EVA is not crosslinked in the foam film, EVA has a low melting point (especially as the content of VA increases, the melting point decreases), so there is a problem in applying it to applications requiring continuous use heat resistance of 80~110℃ and low mechanical properties. Strength is also an issue.

In addition, since foaming of the foaming agent is not easy, there is a problem in that it is difficult to increase the foaming ratio (lower density) and to make the foamed cell size uniform.

In addition, there is a problem that the molding of the film is not easy due to low viscoelasticity.

In the present invention, in order to solve this problem, low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ethylene-propylene-diene terpolymer (EPDM) may be used in the resin composition together with EVA.

In the resin composition, LDPE suppresses the blown bubble foam film from increasing in adhesion due to EVA and increases the melt viscosity of the resin composition so that the blown bubble is stably molded into a film shape without settling during the film forming process. do.

In this case, the LDPE preferably has a melt index (MI) of 0.5 to 5 g/10 min. If it is less than 0.5 g/10 min, the moldability of the blown bubble foam film is deteriorated, and if the MI exceeds 5 g/10 min, blown bubble foaming The mechanical properties of the film are lowered.

LDPE preferably has a density of 0.910 to 0.940 g/cm 3 . If it is less than 0.910 g/cm 3 , the mechanical properties of the blown bubble foam film decrease, and if it exceeds 0.940 g/cm 3 , elasticity, flexibility, extensibility, and impact resistance decrease. will do

If the LDPE content in the resin composition of the present invention is less than 30 parts by weight, it is not easy to form the blown bubble foam film under the molding conditions of the present invention, and the produced blown bubble foam film has non-uniform size and distribution of foam cells and is sticky. And, when the LDPE content exceeds 50 parts by weight, the impact resistance is deteriorated.

EVA and LDPE have a low melting point, so heat resistance is lowered, so adding HDPE and EPDM can improve the heat resistance of the foamed film.

By adding HDPE to the resin composition, the melt strength of the composition is increased, suppressing the sagging of the bubbles even when the bubbles are slowly cooled, thereby improving the moldability of the blown bubble foam film and improving the gas barrier properties and heat resistance in the foamed film.

For this purpose, it is preferable that HDPE has a melting point of 130 to 135° C. and a melt index (M.I.) of 0.5 to 5.0 g/10 min (ASTM D1238, 190° C./2.16 kg).

If the HDPE content in the resin composition of the present invention is less than 10 parts by weight, it is not easy to form the blown bubble foam film under the molding conditions of the present invention, the heat resistance, gas barrier properties, and tensile strength of the foam film are lowered, and the HDPE content is 30 parts by weight If the ratio is exceeded, the foaming rate is lowered, making it difficult to reduce the density, and the size and distribution of the foamed cells in the film formed by blown bubble film molding become non-uniform.

EPDM is an ethylene-propylene-diene ternary copolymer having a Mooney viscosity of 50 to 150 (ML ₁₊₄ ) and a density of 0.89 g/cm 3 or less.

In the resin composition of the present invention, EPDM improves the melt viscosity of the composition when molding the foamed film, so that the bubble stability is improved even when the blown tube bubble is slowly cooled. By this slow cooling, the film can be easily stretched biaxially, so that the foam film is less deformed in MD (Machine direction) and TD (Transverse direction) and heat shrinkage resistance can be improved.

In addition, elasticity, heat resistance, and dimensional stability of the foamed film may be improved.

If the EPDM content in the resin composition of the present invention is less than 30 parts by weight, it is not easy to form the blown bubble foam film under the molding conditions of the present invention, the heat resistance and elasticity of the foamed film decrease, and when the EPDM content exceeds 50 parts by weight, foaming The low density makes it difficult to achieve low density, and the size and distribution of foam cells in the film formed by blown bubble film molding become non-uniform.

As the foaming agent in the resin composition, an organic or inorganic thermal decomposition foaming agent, water, hydrocarbon-based and Freon-based solvents, nitrogen, carbon dioxide, propane, gas such as butane may be used.

Among them, examples of the thermally decomposable foaming agent include inorganic foaming agents such as sodium bicarbonate, sodium carbonate, ammonium hydrogen carbonate, ammonium carbonate and sodium nitrite.

Examples of other blowing agents used in the present invention include azo compounds such as azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile and azodiaminobenzene, N,N'dimethyl-N,N' Nitroso compounds such as dinitrosoterephthalamide and N,N'dinitrosopentamethylenetetramine, sulfonylhydrazide compounds such as benzenesulfonylhydrazide and p,p'-oxybisbenzenesulfonylhydrazide, calcium and azide compounds such as azide and 4,4'-diphenyldisulfonylazide.

The amount of the foaming agent used in the resin composition of the present invention may be 0.05 to 5 parts by weight. If the foaming agent content is small, the amount of gas for foaming is small, and a low-density foamed film cannot be obtained. and the foamed cells are not uniform, and the tensile strength, tear strength, and surface smoothness are lowered.

Although you may add a foaming agent to the resin composition of this invention as it is, it can also add as a masterbatch previously added to the resin component, and can also improve dispersibility.

The blowing agent is decomposed by heating in the extruder to generate gas. However, there is a problem in that the decomposition residue of the foaming agent powder generated by this decomposition accumulates in the filter of the extruder and blocks the filter, making continuous operation difficult for a long time and making the size of the foam cell in the film non-uniform.

In order to solve this problem, in the present invention, it is possible to make the foam cells in the film fine and uniformly formed by using a particle size of 0.1 to 3 μm in which the foaming agent powder is refined.

However, when a foaming agent of fine powder having a small particle size is used as described above, moisture adsorption may occur easily and the foaming state may be deteriorated.

In order to solve this problem, in the present invention, activated alumina having a particle diameter of 0.1 to 3 μm may be used together with a foaming agent.

In the extruder, the blowing agent generates cracked gas and the generated gas is accumulated inside the extruder. At this time, activated alumina, which is a porous adsorbent, adsorbs and stores the gas at high temperature and high pressure inside the extruder. Thereafter, when the resin composition is discharged out of the extruder through the die, activated alumina is adsorbed and the stored gas is released, thereby promoting foaming.

The present invention suppresses foaming before the die of the extruder, and from the time it is discharged from the die to before the frost line of the blown bubble film formed, the gas retained by the activated alumina is released to continue foaming, thereby reducing the size of the foaming cell and The foaming rate can be improved while the distribution of the foamed cells is uniform.

To this end, the temperature of the extruder and the cooling rate of the blown bubble film can be adjusted.

The activated alumina can be used in an amount of 90 to 110% by weight compared to the foaming agent. If it is out of the above range, the ratio of the foaming agent or activated alumina is relatively large, so the extruder filter replacement cycle does not lengthen or the density of the foaming cells is formed too fine. may be difficult to lower.

In the present invention, talc is added as an inorganic filler to improve blocking resistance and heat resistance in the film.

The talc is a chemical composition, and SiO ₂ and MgO components are in the range of 58 to 63 wt%, 30 to 33 wt%, and it is preferable from the viewpoint of heat resistance and gas barrier properties to use high purity talc in which other components are 10 wt% or less .

The talc having an average particle diameter of 5 to 15 μm can suppress film appearance defects due to aggregation of talc, suppress clogging of the filter mesh when extruding the composition, and suppress the formation of resin impurities during film molding. It is preferable to be able to

In the talc, when the sum of the volumes of particles having a particle diameter of 20 μm or more is 5% by volume or less of the total volume of the total particles, the generation of resin impurities during film molding is suppressed, the foamed cells are uniformly distributed, and the blocking resistance is improved. It can be improved and it is preferable.

If the content of talc is less than 2 parts by weight, the improvement in blocking resistance, heat resistance, gas barrier properties, and suppression of resin impurity generation is insignificant, and if it exceeds 6 parts by weight, the filter mesh is clogged during extrusion and the film formability is deteriorated. do.

Stearic acid amide is used together with inorganic materials so as not to deteriorate the formability and physical properties of the film, and in particular, it can prevent resin impurities from occurring in the circular die during extrusion.

If the content of the stearic acid amide is less than 0.05 parts by weight, the improvement in blocking resistance is insignificant, and when it exceeds 0.5 parts by weight, a migration phenomenon may occur and transparency may decrease due to whitening.

The talc of the present invention may be treated with a cationic surfactant and then treated with an anionic surfactant.

Since the resin composition of the present invention has low polarity, it is preferable to hydrophobize the talc by cation exchange with a cationic surfactant. The affinity between the silicate talc and the resin composition is improved, so that the fine particles of talc can be uniformly finely dispersed in the resin composition.

In this case, the cationic surfactant may include a quaternary phosphonium salt.

Examples of the quaternary phosphonium salt include dodecyltriphenylphosphonium salt, methyltriphenylphosphonium salt, lauryltrimethylphosphonium salt, stearyltrimethylphosphonium salt, and trioctylphosphonium salt.

Among them, it is more preferable to have an alkyl chain having 6 or more carbon atoms capable of sufficiently making talc non-polar.

It can then be treated with an anionic surfactant.

As the anionic surfactant, a compound having at least one functional group having high chemical affinity at the molecular terminal may be used even if chemically bonding or not chemically bonding with the hydroxyl group present in the talc.

Due to this, the dispersibility of talc, which is a fine particle, may be further improved.

As the anionic surfactant, sodium laurate, sodium stearate, sodium oleate and the like may be used.

On the other hand, in the present invention, 0.5 to 1 part by weight of a polyhydric alcohol fatty acid ester and an amide compound together with the stearic acid amide may be further added to the composition of the present invention.

The polyhydric alcohol fatty acid ester can be obtained from an aliphatic alcohol having 2 to 6 carbon atoms and a fatty acid having 8 to 22 carbon atoms, and all or part of the hydroxyl groups of the aliphatic alcohol are completely esterified or partially esterified with a fatty acid.

Examples of the polyhydric alcohol fatty acid ester include propylene glycol laurate, diethylene glycol oleate, glycerin laurate, glycerin stearate, glycerin behenate, and the like.

Examples of the amide compound include N,N-bis(hydroxyethyl) fatty acid amide, N-hydroxyethyl-N-polyoxyethylene fatty acid amide, and N,N-bis(polyoxyethylene) fatty acid amide.

Examples of the amide compound include N,N-bis(hydroxyethyl)octanoic acid amide, N,N-bis(hydroxyethyl)stearic acidamide, N,N-bis(hydroxyethyl)lauric acid amide, N , N-bis (hydroxyethyl) behenic acid amide, N, N-bis (polyoxyethylene) stearic acid amide, and the like.

By further using the compound, the miscibility between the components in the composition of the present invention is improved, so that the appearance of the foamed film becomes uniform, the function by the components is sufficiently exhibited, and in particular, the smoothness and blocking resistance of the film are expressed in a balanced way. become possible

In this case, the ratio of the polyhydric alcohol fatty acid ester to the amide compound is preferably 60:40 to 40:60 because it can represent a balanced characteristic.

A method for preparing the resin composition of the present invention may use a known method without any particular limitation.

For example, a resin and various additives including inorganic substances, stearic acid amide and foaming agents are mixed in a mixer such as a tumbler blender or Henschel mixer and melted by an extruder, a Banbury mixer or a kneader and granulated, or inorganic substances, stearic acid and various A method of preparing a masterbatch having an increased content of additives and mixing the masterbatch with a resin in a predetermined ratio may be used.

In the present invention, as other additives, a heat stabilizer, an ultraviolet absorber, an antistatic agent, an antioxidant, a colorant, and the like may be blended.

The foamed film of the present invention is produced by a blown bubble film molding method.

In the blown bubble film forming method, the molten thermoplastic resin is extruded in the form of a tube bubble, the pressure of the air in the tube is slightly increased, and the pressure is applied while stretching while stretching, and the tube-shaped film is folded by sandwiching it between a pair of rolls. It is a method of manufacturing a film by continuously winding a sealed and folded tube.

An example of a blown bubble film forming machine is shown in FIG. 1 below.

A resin component, a foaming agent, and an additive constituting the resin composition of the present invention are mixed, and the mixed resin composition is supplied to an extruder of a blown bubble film molding machine and melted.

Then, the tube of the resin composition extruded through the circular die is expanded by injection of air and cooled to prepare a blown film form.

At this time, it is preferable that the circular die gap width is 0.4 to 1.2 mm. If it is less than 0.4 mm, the melt pressure rises and melt fracture occurs, so the stability of the bubble is poor and high-discharge extrusion processing is difficult, 1.2 If it exceeds mm, the discharge is excessive, so it is difficult to control cooling, it is difficult to form bubbles, and since the film is oriented only in the longitudinal direction, it becomes a foamed film that is easy to tear only in the longitudinal direction.

In the injection of air, cooling air is blown by an air ring device installed on the die surface to cool the bubbles.

In the present invention, the temperature of the resin composition in the die is 170° C. or higher, the length of the neck of the blown bubble is 1 to 4 times the diameter of the die, and the temperature of the film at the end of the neck is controlled in cooling the blown bubble. The temperature of the film of the blown bubble was set to 40 °C or lower by the first cooling ring, the temperature of the film in the frost line (the end of the expansion part) was set to 50 °C or lower, and the temperature of the film of the blown bubble was 40 by the second cooling ring installed above the frost line. ℃ or less, and the third cooling ring installed above the second cooling ring can be manufactured in a way that the temperature of the film of the blown bubble is 35 ℃ or less.

By cooling of the present invention, the neck portion and the expanded portion of the blown bubble are cooled slowly while crystallization is delayed, but since the resin composition of the present invention has increased viscoelasticity, the molding and biaxial stretching of the film are facilitated.

By slowly cooling the temperature of the outer surface of the bubble including the neck portion and the expansion portion to the above temperature, it is possible to prevent the foaming agent from rapidly foaming at the initial stage of film forming. This makes it possible to maximize the release of the foaming gas, so that the foaming ratio is high and the foaming is slow, so that the size of the foamed cells can be miniaturized and the distribution can be made uniform.

In addition, since the expanded portion is in an amorphous state, it is not stretched only in the longitudinal direction, which is the longitudinal direction, due to the melt tension of the resin composition, but is stretched biaxially in both the longitudinal and transverse directions at the same time. Due to this, the mechanical strength of the foamed film is improved, foaming occurs a lot, and the resulting foamed cells are uniformly distributed in the film, and in particular, the foamed cells are small in size and uniform in shape.

In this way, when the molten resin is slowly cooled, the crystallization of the resin continues, so that the degree of crystallinity is increased. As a result, peeling from the foaming nucleating agent easily occurs during stretching due to the increased stretching stress, so that a large number of foamed cells are generated.

In addition, since the resin is maintained at a high temperature by slow cooling, foaming occurs uniformly, and thus the size of the foamed cells becomes uniform.

It is preferable that the blow-up ratio due to expansion is in the range of 2.0 to 5.0 because it can be uniformly stretched in both the longitudinal and transverse directions of the bubble at the same time. If it is less than 2.0, the shape of the foamed cells is not uniform and sufficient orientation is not achieved. The anisotropy is large, the improvement in tensile strength is insignificant, and when it exceeds 5.0, the bubble becomes unstable, making it difficult to process a stable foamed film.

When molding the blown bubble film of the present invention, the take-up speed is preferably in the range of 5 to 30 m/min. If it is less than 5 m/min, the orientation does not occur in the longitudinal direction of the film and productivity decreases, and if it exceeds 30 m/min, The cooling of the bubble becomes non-uniform, and the heat resistance, gas barrier properties, and blocking resistance of the film deteriorate.

The foamed film of the present invention has a density of 0.60 to 0.80 g/cm 3 and a thickness of 20 to 300 μm prepared by the method of the present invention.

At this time, if the density is less than 0.60g/cm3, the buffering property is rather reduced, mechanical properties such as impact resistance and durability are lowered, the feel is bad and the sense of quality of the film is reduced, and when it exceeds 0.80g/cm3, elasticity, buffering property, sealing sex is lowered

The manufacturing process of the foamed film of the present invention will be described with reference to FIG. 1 below.

The tubular film extruded from the circular die mounted on the extruder is rapidly expanded into a film of a predetermined width by supplying air from the air injection tube to the inside, and taken up by being pinched by a nip roll, and using a take-up reel to wind up

A circular die has a circular die head and a weld portion.

In the present invention, there is no particular limitation on the configuration of the air injection means for supplying the air injected into the tubular film, for example, the air injection tube may be connected to a blower or the air injection tube may be connected to a compressed air cylinder. have.

The molten resin composition is extruded from the circular orifice of the die to form tube bubbles, and in the neck portion formed by the blown bubbles immediately after extrusion, the bubbles are mainly elongated in the longitudinal direction (MD).

Thereafter, the bubble is rapidly expanded so that the bubble has a defined diameter. In this expansion, the bubble is drawn simultaneously in MD and TD. There is a frost line in the vicinity of the upper part of the expansion part, where the resin is cooled and solidified.

Above the frost line, the tube bubble cools more slowly.

Since the resin composition of the present invention has an increase in melt viscosity and viscoelasticity compared to the EVA copolymer, the film does not sink or fluctuate even if the molding (cooling) temperature changes after melt extrusion. heat resistance, elasticity, gas barrier properties, and blocking resistance can be improved.

Hereinafter, the present invention will be described in more detail based on the following Examples and Comparative Examples.

However, the following examples are only for illustrating the present invention, and the present invention is not limited by the following examples, and can be substituted and changed to other equivalent examples without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which the present invention pertains.

[Example 1]

35 parts by weight of low-density polyethylene (density 0.924 g/cm3, MI=2.0 g/10 min) relative to 100 parts by weight of EVA copolymer (vinyl acetate content 9.5%, density 0.929 g/cm 3 , MI=0.8 g/10 min), high density 20 parts by weight of polyethylene (density 0.954 g/cm 3 , MI=1.1 g/10 min), 40 parts by weight of ethylene-propylene-diene terpolymer (EPDM) (KEP070P, Kumho Polychem), talc having an average particle size of 15 μm 3 parts by weight, 0.15 parts by weight of stearic acid amide as a lubricant, 1.5 parts by weight of sodium bicarbonate having an average particle diameter of 2 μm as a foaming agent, and 1.5 parts by weight of activated alumina having an average particle diameter of 2 μm were mixed in a ribbon mixer to prepare a resin composition.

The resin composition was put into an extruder of a blown bubble film molding machine as shown in FIG. 1, and a foamed film having a thickness of 60 μm was prepared under the following conditions.

<Film forming conditions>

Extrusion cylinder temperature: 220℃, die temperature: 190℃, extrusion amount: 50kg/hour,

Round die: φ200mm, die gap width: 0.7mm,

Blow-up ratio: 3.5, take-up speed: 25 m/min.

At this time, in cooling the blown bubble, the temperature of the end of the neck portion is 105°C by the first cooling ring, the temperature of the frost line formed at the end of the expansion portion is 45°C, and the temperature of the blown bubble above the frost line is the second The temperature of the film of the blown bubble was adjusted to 30° C. or less by the cooling ring at 35° C., and by the third cooling ring provided above the second cooling ring.

A foamed film having a density of 0.68 g/cm 3 was prepared according to Example 1.

[Example 2]

A foamed film was prepared in the same manner as in Example 1, except that in Example 1, fine particle talc according to the following manufacturing method was used for the talc.

(Method for producing fine talc)

Talc having an average particle diameter (D50) of 15 μm and the sum of the volumes of particles having a particle diameter of 20 μm or more accounts for 27.5% of the total volume of all particles, using a sieve of 700 mesh (open 21 μm), the average Particulate talc was prepared having a particle diameter (D50) of 13 μm and the sum of the volumes of particles having a particle diameter of 20 μm or more to 1% of the total volume of all particles.

[Example 3]

In Example 2, a solution in which the particulate talc was dispersed in distilled water was added to a dodecyltriphenylphosphonium chloride solution, treated for 3 hours, and the resulting precipitate was filtered to obtain talc treated with a cationic surfactant, and the talc was again prepared A foamed film was prepared in the same manner as in Example 1, except that organic talc treated with sodium laurate was used.

[Example 4]

In Example 3, the same as in Example 2, except that 0.8 parts by weight of an additive in which glycerin lauryl acid to N,N-bis(hydroxyethyl) lauryl amide was 50 to 50 by weight was added. A foamed film was prepared using the same method.

[Comparative Examples 1 to 5]

A foamed film was prepared in the same manner as in Example 1, except that the resin composition and the temperature of the outer surface of the blown bubble in Example 1 were changed as shown in Table 1 below.

division Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 EVA 100 100 100 100 100 100 100 100 100 LDPE 35 35 35 35 35 35 35 35 35 HDPE 20 20 20 20 20 20 20 20 20 EPDM 40 40 40 40 0 60 40 40 40 blowing agent 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Activated Alumina 1.5 1.5 1.5 1.5 1.5 1.5 0 2.0 1.5 talc 3 3 3 3 3 3 3 3 3 slush 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 additive - - - 0.8 - - - - - 1) Example 2: Use of particulate talc
2) Example 3: Use of organic talc
3) Comparative Example 5: The cooling temperature of the blown bubble was adjusted to 90°C at the end of the neck part, 35°C at the end of the expansion part, and 30°C at the top of the frost line

Film formability and physical properties in Examples and Comparative Examples were evaluated using the following method, and the results are shown in Table 2 below.

<Evaluation method>

1. Blown bubble stability

The state of the tube bubble (settling, shaking, breakage, etc. of the bubble) is visually observed and evaluated as good or bad.

2. Formation of foam cells in the film

For the evaluation of the state of the foamed cells, the foamed films prepared by the methods of Examples and Comparative Examples are randomly cut into pieces of 1cm in width and 1cm in length, and then placed on an optical microscope, the degree of formation of the foamed cells, the size with the naked eye. The distribution and uniformity of formation are observed and evaluated as good, normal, or poor.

3. Blocking resistance

Blocking resistance is evaluated based on the following criteria by winding the molded film 60m under the condition of winding force of 100 N and leaving it for 7 days in a constant temperature and humidity room with a temperature of 23°C and a humidity of 50%RH, and observing the state of the film while unwinding the film. do.

(double-circle) : Blocking phenomenon does not occur at all, and it loosens well without resistance.

(circle): A blocking phenomenon does not generate|occur|produce and it loosens easily.

△: There is some crimping, but it is possible to loosen it.

X: Blocking occurs frequently, and whitening or rupture of the film occurs during unwinding.

4. Heat resistance

The sample film is immersed in hot water at 90° C. for 30 minutes, taken out, and the state of the film is visually observed and evaluated according to the following criteria.

◎: There is no abnormality at all and the shape of the film is good

○: There is no damage to the film, but slight deformation occurs

×: damage to the film was observed

division Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Extruder filter replacement cycle 7 days 7 days 7 days 7 days 7 days 5 days 1 day 5 days 7 days Blown Bubble Stability Good Good Good Good bad Good Good Good bad foam cell state Good Good Good Good usually bad bad bad bad blocking resistance ○ ◎ ◎ ◎ ○ △ ○ ○ ○ heat resistance ○ ○ ○ ○ △ ◎ ○ ○ ○ Foam film tensile strength
(kg/cm2) 347 354 356 353 297 358 346 334 272 foam film elongation
(%) 172 186 189 185 161 189 181 166 225

From Table 2, it can be seen that the workability (filter replacement cycle, bubble stability) of the blown bubble film according to the Example and the properties of the foam film prepared thereby are excellent when compared with the comparative example from Table 2 above. From this, it is confirmed that when the composition according to the present invention and the blown bubble film molding method are used, the functions of the composition components are sufficiently expressed and the properties of the foamed film are improved while balancing.

Claims (5)

Based on 100 parts by weight of the ethylene vinyl acetate copolymer, 30-50 parts by weight of low-density polyethylene, 10-30 parts by weight of high-density polyethylene, 30-50 parts by weight of ethylene-propylene-diene ternary copolymer, 2-6 parts by weight of talc, 0.02 parts by weight of stearic acid amide -1.0 parts by weight, 0.05-5 parts by weight of a foaming agent, and mixing a resin composition comprising activated alumina in an amount of 90-110% by weight compared to the foaming agent; and
A method for producing a foamed film, including a step of melting the resin composition using a blown bubble film molding machine and extruding the resin composition through a circular die to form a blown bubble film. The method of claim 1,
The ethylene-vinyl acetate copolymer is a radical polymerization of ethylene and vinyl acetate, the content of vinyl acetate is 5 to 25% by weight, the density is 0.930 to 0.950 g/cm 3 , and the melt index (MI) is 0.5 to 5 g/10 Method for producing a foamed film, characterized in that the minute. The method of claim 1,
The ethylene-propylene-diene terpolymer has a Mooney viscosity of 50 to 150 (ML ₁₊₄ ) and a density of 0.89 g/cm 3 or less. The method of claim 1,
The talc is a method for producing a foamed film, characterized in that the average particle diameter is 5 ~ 15㎛. The method of claim 1,
In the step of forming the blown bubble film,
The temperature in the die is 170°C or higher,
Make sure that the length of the neck of the blown bubble is 1 to 4 times the diameter of the die,
In cooling the blown bubble, the temperature of the film at the end of the neck is set to 110° C. or lower by the first cooling ring, and the temperature of the film at the frost line (end of the expansion section) is set to 50° C. or lower, and is higher than the frost line. The temperature of the blown bubble film is set to 40°C or lower by the second cooling ring provided, and the temperature of the blown bubble film is set to 35°C or lower by the third cooling ring provided above the second cooling ring. Method for producing a foamed film, characterized in that.

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