KR102339566B1 - PLA composite and method of heat shrinkable blown film - Google Patents

Abstract

The present invention relates to a biodegradable polylactic acid (PLA) composite material, particularly a PLA composite material, which substitutes for a petrochemical synthesis system generating environmental pollution and carbon dioxide and can be decomposed at a ratio of 90% or more within 6 months at a temperature of 60℃ under a humidity of 80% in the presence of activated microorganisms, when being discarded, and has an excellent light transmission, and a method for manufacturing a heat shrinkable blown film. The biodegradable PLA composite material includes 96.7-93.3 wt% of PLA, 3-6 wt% of polycaprolactone (PCL), and 0.3-0.7 wt% of any one crosslinking agent selected from calcium stearate and magnesium stearate. The biodegradable PLA composite material having an excellent light transmission and the method for manufacturing a heat shrinkable blown film according to the present invention use a coextrusion blowing process to avoid a need for T die-based heat sealing or adhesion treatment, thereby providing improved cost efficiency and productivity.

Description

Biodegradable PLA composite material with excellent light transmittance and method of manufacturing heat shrinkable blown film {PLA composite and method of heat shrinkable blown film}

The present invention relates to a biodegradable PLA composite material, and more particularly, it replaces the petrochemical synthesis system that generates environmental pollution and carbon dioxide and decomposes more than 90% within 6 months under a temperature of 60 ℃, a humidity of 80%, and an activated microorganism at the time of disposal It relates to a biodegradable PLA composite material with excellent light transmittance and a method for manufacturing a heat-shrinkable blown film.

In general, for heat shrinkable films, petrochemical synthetic systems such as PP, PE, PVC, and PET were used. These petrochemical synthetic materials are decomposed after 100 years or more when discarded, so social issues such as generation of microplastics, environmental pollution, and increase in greenhouse gases are being issued. In particular, in the packaging field, packaging, and labels, etc., most of them are destroyed before use, increasing environmental pollution, and there is a problem in that recycling is difficult due to printing.

In addition, the conventional biodegradable heat-shrinkable film production method was produced through secondary stretching in the longitudinal and transverse directions after producing the primary sheet paper and film by a casting method using a T-die. In this method, productivity and cost may increase, and it is difficult to produce various types of heat-shrinkable films due to the limitations of manufacturing and production facilities, and there is a problem that heat sealing or adhesive treatment must be accompanied when used.

In addition, biodegradable PLA material is inflexible, has brittle characteristics, and crystallization proceeds at 60℃ or higher, so transparency may be lost during logistics and transport. Issues may arise, and in the case of frozen food packaging, the packaging may be damaged due to its brittle characteristics.

In addition, the T-die casting heat-shrink film made from a material branded with PBS, PBAT, PBSA, PCL, PGA, etc. on the existing PLA material requires a high melt flow index (MI) during production for good productivity, but the co-extrusion method For heat-shrink blown films, if a conventional branded material is used, productivity may be difficult due to high MI, and light transmittance may decrease due to high glass transition temperature (Tg).

And there are inorganic mineral systems such as talc, calcium carbonate, silica, titanium dioxide, zeolite, and alumina used as conventional plasticizers, crosslinking agents, emulsifiers, lubricants, etc., and organic types such as palm oil and stearic acid, but inorganic mineral systems can reduce transparency, The organic type has strong incompatibility characteristics due to the nature of PLA, so it can escape to the film surface and cause contamination when applied to the product.

KR Registered Patent Publication No. 10-2029207 (2019.09.30)

The present invention was devised to solve the same problems as in the prior art, and replaces the petrochemical synthesis system that generates environmental pollution and carbon dioxide, and can be decomposed more than 90% within 6 months under a temperature of 60 ℃, a humidity of 80%, and an activated microorganism at the time of disposal. It is an object of the present invention to provide a biodegradable PLA composite material having excellent light transmittance and a method for manufacturing a heat-shrinkable blown film.

The biodegradable PLA composite material with excellent light transmittance according to the present invention for achieving the above object is a crosslinking agent of one type selected from among 96.7 to 93.3% by weight of PLA, 3 to 6% by weight of PCL, and calcium stearate or magnesium stearate. It is characterized in that it contains 0.7% by weight.

In addition, the PLA material has a molecular weight (Mw) of 100,000 to 120,000 g/mol, a glass transition temperature (Tg) of 58°C, a melting temperature (Tm) of 166°C, and the PCL material has a molecular weight (Mw) of 80,000g/mol, a glass transition temperature (Tg) -68 ℃, melting temperature (Tm) 60 ℃, it is characterized in that the melt flow index (MI) is 12g/10min or less at 170℃, 2160g by branding a crosslinking agent.

In addition, the method for manufacturing a biodegradable PLA composite material with excellent light transmittance according to the present invention mixes and kneads a PCL (Polycaprolactone) material, a crosslinking agent of one of calcium stearate and magnesium stearate, and then heats and presses a kneader at a temperature of 60 to 80 ° C. a first step of pulverizing after kneading with a furnace; A second step of mixing the material of the first step and the PLA material and extruding it using a twin extruder to produce a resin; It is characterized in that it includes.

In addition, the heat-shrink blown film manufacturing method using a biodegradable PLA composite material with excellent light transmittance according to the present invention is a PCL (Polycaprolactone) material, calcium stearate, and magnesium stearate, mixed and kneaded with a crosslinking agent, followed by heating and pressure kneading. A first step of pulverizing after kneading at a temperature of 60 ~ 80 ℃; A second step of mixing the material of the first step and the PLA material and extruding it using a twin extruder to produce a resin; a third step of producing a film by controlling the amount of air injected in the form of a tube by co-extrusion with the resin of the second step; a fourth step of cooling the film of the third step through an air ring; It is characterized in that it includes.

The biodegradable PLA composite material and heat-shrink blown film manufacturing method with excellent light transmittance according to the present invention is manufactured by applying the co-extrusion blow method to omit the T-die type heat sealing or bonding process, so that economic efficiency and productivity can be improved. can have an effect.

In addition, 100% biodegradable material can solve social issues such as carbon dioxide reduction and environmental pollution reduction, and has the effect of being used as an alternative to disposable packaging material.

1 is a process diagram showing a method of manufacturing a biodegradable PLA composite material according to the present invention.
Figure 2 is a process diagram showing a method for manufacturing a heat-shrinkable blown film using a biodegradable PLA composite material according to the present invention.

Hereinafter, a biodegradable PLA composite material having excellent light transmittance and a method for manufacturing a heat-shrinkable blown film according to the present invention will be described in detail.

1 is a process diagram illustrating a method for manufacturing a biodegradable PLA composite material according to the present invention, a first step of pulverizing a PCL (Polycaprolactone) material and a crosslinking agent after mixing and kneading as shown in the figure; a second step of mixing and extruding the material of the first step and the PLA material to produce a resin; includes

In the first step, after mixing the PCL material, calcium stearate, and magnesium stearate, one kind of powder crosslinking agent is mixed, and then kneaded at a temperature of 60 to 80 ° C. This is the resin production stage.

Inorganic mineral systems such as talc, calcium carbonate, silica, titanium dioxide, zeolite, and alumina, which are used as conventional plasticizers, crosslinking agents, emulsifiers, and lubricants, etc., can reduce transparency, and organic systems such as palm oil and stearic acid are incompatible due to the nature of PLA. It is strong and it leaks out to the film surface and can cause contamination when applying the product. This is improved by using a salt mixture powder such as calcium stearate and magnesium stearate that is insoluble in water, ethanol, and ether.

At this time, the molecular weight (Mw) of the PCL material used is preferably 80,000 g/mol or more, and if the molecular weight (Mw) is 80,000 g/mol or less, the melt flow index (MI) may increase due to the PCL melting point (Tm) of 60 ° C. and coextrusion blown film production may become difficult.

The second step is a step of producing the resin using a twin extruder after mixing the material of the first step and the PLA material.

The screw temperature of the twin extruder used here is 160~180℃, and the resin is extruded and cut to produce resin with a size of around 4mm.

The cutting method is produced with a cooling belt system using air, and a mesh belt with a metal mesh size of 3 to 5 mm in width and length is used. The melt flow index of the resin produced under these conditions is less than 12g/10min at 170℃/2,160g, and it can be produced without any special issue in the mesh size.

If water cooling or water cutting method is used, a dehumidifying and drying step is required at 60°C for 4 to 6 hours to remove moisture. By using the system, the inconvenience of water cooling and water cutting methods can be solved.

In the first step and the second step, the content of each material is made in a ratio of 0.3 to 0.7 wt% of a crosslinking agent selected from among 96.7 to 93.3 wt% of PLA, 3 to 6 wt% of PCL, and calcium stearate or magnesium stearate As a result, the light transmittance of the film produced by this content can ensure transparency of 80 to 90% (555 nm wavelength).

If the PCL content is 3 wt% or less, the crystallinity of the PLA material may increase and the light transmittance may decrease. there may be

If the content of the crosslinking agent of calcium stearate or magnesium stearate is 0.3 wt% or less, crosslinking and slip properties are lowered, and when producing a tube-shaped blown heat-shrink blown film, the inside of the film is adhered by two pressing rolls. If it is 0.7% by weight or more, the releasability inside the film tube may be improved, but the melt flow index may be increased, so there may be difficulties in producing a heat-shrinkable blown film.

After mixing the PLA, PCL, and the crosslinking agent, the resin may be produced in a twin extruder at a time, but mixing at a certain ratio may be difficult due to the slip property of the crosslinking agent.

And the PLA material is molecular weight (Mw) 100,000 ~ 120,000 g / mol, glass transition temperature (Tg) 58 ℃, melting temperature (Tm) 166 ℃, PCL material molecular weight (Mw) 80,000 g / mol, glass transition temperature ( Tg) −68° C., melting temperature (Tm) 60° C., and blending calcium stearate as a crosslinking agent and lubricant so that the melt flow index (MI) is 12 g/10min or less at 170° C. and 2160 g.

Although PBS and PBAT materials can be used to solve the transparency and flexibility of PLA materials, PBS has a glass transition temperature (Tg) of -32 °C and PBAT is -28 °C, which is advantageous in terms of amorphous and flexibility. PCL with a transition temperature of -68°C is effective.

2 is a process diagram illustrating a method for manufacturing a heat-shrinkable blown film using a biodegradable PLA composite material according to the present invention.

A method for manufacturing a heat-shrinkable blown film using a biodegradable PLA composite material according to the present invention comprises: a first step of pulverizing a PCL material and a crosslinking agent after mixing and kneading; a second step of mixing and extruding the material of the first step and the PLA material to produce a resin; A third step of producing a film in the form of a tube by a co-extrusion method with the resin of the second step; a fourth step of cooling the film of the third step; includes

The first and second steps are omitted because they are the same as the above-described biodegradable PLA composite material manufacturing method.

The third step is a step of producing a film by controlling the amount of air injected in the form of a tube by a co-extrusion method with the resin of the second step.

At this time, the extruder screw temperature is 160 ~ 180 ℃, the die temperature is 170 ℃, to produce a film in the form of a tube in the bottom up. Here, if the die temperature is 170° C. or higher, the melt flow index (MI) increases, which may cause difficulties in film formation.

The coextrusion packaging film production method follows the existing production method, but controls the amount of air injected into the tube-shaped film through the die to control the expansion rate in the transverse and longitudinal directions to produce the film.

The tube-type film should be produced so that orientation and stretching does not occur in the longitudinal direction depending on the speed of the two rubber compression rolls and the winding machine. It is produced by adjusting it so that it becomes a film.

The fourth step is a step of cooling the third step tube-shaped film through an air ring.

The air temperature of the air ring is cooled to 15~25℃. Here, if the air temperature is 25° C. or higher, there may be a problem in that the film and the film are adhered when passing through two rubber compression rolls inside the tube-shaped film, and when the air temperature is 15° C. or lower, expansion in the transverse or longitudinal direction may be difficult.

In the present invention, a heat-shrinkable film was produced in a tube type with the material in the same manner as above, and it was verified through experiments with the following ratios.

<Example 1>

When the melt cloudiness index for each material (MI: 170℃, 2160g)

Condition result
A PLA 93.3 wt%
PCL 6 wt%
0.7 wt% calcium stearate
11.8g/10min
B PLA 95.5 wt%
PCL 4 wt%
0.5 wt% calcium stearate
7.6g/10min
C PLA 96.7 wt%
PCL 3 wt%
0.3 wt% calcium stearate
3.7g/10min

The above data are average values after 5 measurements according to ISO 1133 method.

<Example 2>

A 25 micrometer thick film was produced according to the data ratio of A, B, and C of Example 1, and heat shrinkage, haze, tensile strength, and light transmittance were tested. The size of the film was 250 mm in the longitudinal direction and 250 mm in the transverse direction.

A B C unit heat shrinkage
(80℃ hot air 5 minutes) longitudinal 66 62 59 % transverse 38 36 35 % haze 0.7 0.9 1.1 % The tensile strength longitudinal 286 271 259 kgf/cm2 transverse 229 217 210 kgf/cm2 light transmittance 97.1 95.9 94.8 %

The measurement method is as follows.

Heat Shrinkage:

Haze: ASTM D 1003

Tensile strength: ASTM D 638

Light transmittance: ASTM D 1003 (555nm wavelength)

<Comparative Example 1>

In the present invention, calcium stearate and light transmittance were compared by adding CaCO3 (size: 4-6㎛) among inorganic mineral Talc, CaCO3, and TiO2 according to the composition ratio below. The film is a 25 μm thick film produced by the same method.

composition ratio result unit Exam conditions
One PLA 93.3 wt%
PCL 6 wt%
0.7 wt% calcium stearate
97.1
%

ASTM D 1003
(555nm wavelength)
2 PLA 93.3 wt%
PCL 6 wt%
0.7 wt% calcium stearate
89.6
%

The present invention obtained a result of a 100% biodegradable heat-shrinkable film with excellent light transmittance as a tube-type film of the co-extrusion method as described above. In addition, as a result of Comparative Example 1, the light transmittance of the film to which calcium stearate was added was better than that of the inorganic mineral CaCO3.

Claims (4)

A first step of mixing and kneading 3 to 6% by weight of PCL (Polycaprolactone) material and 0.3 to 0.7% by weight of a crosslinking agent of one of calcium stearate and magnesium stearate, kneading it in a heated and pressurized kneader at a temperature of 60 to 80 ℃, followed by pulverization;
A second step of mixing the material of the first step and the PLA material 96.7~93.3% by weight and then extruding using a twin extruder to produce a resin;
A third step of producing a non-stretched film by controlling the amount of air injected in the form of a tube by a co-extrusion method with the resin of the second step;
a fourth step of cooling the film of the third step through an air ring; includes,
The PLA material has a molecular weight (Mw) of 100,000 to 120,000 g/mol, a glass transition temperature (Tg) of 58°C, and a melting temperature (Tm) of 166°C, and the PCL material has a molecular weight (Mw) of 80,000 g/mol, a glass transition temperature (Tg) ) A biodegradable PLA composite material with excellent light transmittance, characterized in that it is minus 68 ° C, melting temperature (Tm) 60 ° C, and melt flow index (MI) is 12 g/10 min or less at 170 ° C and 2160 g by branding a crosslinking agent. A method for manufacturing a heat-shrinkable blown film using
According to claim 1, wherein the extruder screw temperature of the third step is 160 ~ 180 ℃, the die temperature is 170 ℃,
A method for manufacturing a heat-shrinkable blown film using a biodegradable PLA composite material with excellent light transmittance, characterized in that the airing air temperature of the fourth step is 15 to 25°C. delete delete

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