KR102296146B1 - Flexible polylactic acid-based heat sealing film - Google Patents

Abstract

The present invention relates to a thermal adhesive film having excellent thermal adhesion even at a relatively low temperature, excellent flexibility, mechanical properties, storage stability, and overall physical properties such as blocking resistance, and excellent eco-friendliness and biodegradability. The thermal adhesive film is a block copolymer comprising a hard segment including a polylactic acid repeating unit, and a soft segment including a polyurethane polyol repeating unit in which polyether-based polyol repeating units are linearly connected via a urethane bond. In this case, the soft segment is included in an amount of 5 to 35% by weight based on the weight of the block copolymer, and the polylactic acid repeating unit contains 94 poly-L-lactic acid repeating units and 94 poly-D-lactic acid repeating units. : included in a molar ratio of 6 to 88:12.

Description

Flexible polylactic acid-based thermal adhesive film {FLEXIBLE POLYLACTIC ACID-BASED HEAT SEALING FILM}

The present invention relates to a thermal adhesive film. More specifically, the present invention relates to a flexible polylactic acid-based thermal adhesive film having excellent thermal adhesion, excellent flexibility, mechanical properties, storage stability, blocking resistance, etc., and excellent eco-friendliness and biodegradability. .

Crude oil-based resins such as polyethylene terephthalate (PET), nylon, polyolefin or soft polyvinyl chloride (PVC) are still widely used as materials for various uses, such as packaging materials. However, these crude oil-based resins do not have biodegradability, so there is a problem of causing environmental pollution, such as disposing of a large amount of carbon dioxide, which is a global warming gas, when discarded. In addition, as petroleum resources are gradually depleted, the use of biomass-based resins, typically polylactic acid resins, has been widely reviewed.

In particular, the development of functional composite films for food packaging using biodegradable films is being made in accordance with the recent trend of thinning and functionalization of films. Accordingly, customers' interest in biodegradable thermal adhesive films is increasing, and for this purpose, an amorphous polylactic acid resin in which optical isomers of D-lactide and L-lactide monomers are combined is used.

However, in the case of the amorphous polylactic acid resin used as the raw material resin of the heat-adhesive film as described above, blocking occurs above the glass transition temperature, and there is a problem in processability during film extrusion. In addition, in the case of polylactic acid resin, due to the unique low cohesive attraction (cohesive attraction), the adhesive strength during thermal bonding is not high, and storage conditions are limited, so there is a problem in storage stability. Therefore, the polylactic acid resin, compared to the linear low-density polyethylene (LLDPE) resin used as a conventional heat-adhesive resin, has poor adhesive strength, processability and storage stability, and is used only for limited applications.

In addition, polylactic acid resin has insufficient mechanical properties, etc. compared to crude oil-based resin, and has a low flexibility when molding into a film. To overcome this, a low molecular weight softener or plasticizer is added to the polylactic acid resin, or polylactic acid resin There has been proposed a method of introducing a plasticizer obtained by addition polymerization of polyether-based or aliphatic polyester-based polyol to the like. However, even if a packaging film including a polylactic acid resin is obtained according to these methods, it is true that there is a limit to improving the flexibility in most cases. Moreover, the plasticizer and the like are not only bleed out over time, but there is a disadvantage in that the haze of the packaging film is increased and the transparency is lowered. Therefore, recently, in order to solve the above problems, a method of obtaining a block copolymer by introducing a polyurethane polyol repeating unit into a polylactic acid resin has been proposed (refer to Korean Patent Application Laid-Open No. 2013-0135758).

However, the conventional polylactic acid resin has properties such as glass transition temperature, melting temperature, and crystallization required during film processing, and is still improved to have the thermal adhesive strength, flexibility and mechanical strength required as a thermal adhesive film. There are many things to be

Republic of Korea Patent Publication No. 2013-0135758 (2013.12.11) SK Chemicals

An object of the present invention is to have excellent thermal adhesion even at a relatively low temperature, and excellent overall physical properties such as flexibility, mechanical properties, storage stability, and blocking resistance,

An object of the present invention is to provide a thermal adhesive film having excellent eco-friendliness and biodegradability.

According to the above object, the present invention provides a polyurethane polyol repeating unit in which a hard segment comprising a polylactic acid repeating unit of the following formula (1), and a polyether-based polyol repeating unit of the following formula (2) are linearly connected via a urethane bond A polylactic acid resin comprising a soft segment containing Provided is a heat sealing film, wherein the repeating unit comprises a poly-L-lactic acid repeating unit and a poly-D-lactic acid repeating unit in a molar ratio of 94:6 to 88:12:

[Formula 1]

[Formula 2]

In Formula 1, n is an integer of 700 to 5000;

In Formula 2, A is a linear or branched alkylene group having 2 to 5 carbon atoms, and m is an integer of 10 to 100.

The thermal adhesive film according to the present invention has excellent thermal adhesive properties even at a relatively low temperature, and excellent overall physical properties such as flexibility, mechanical properties, storage stability, and blocking resistance, and has excellent eco-friendliness and biodegradability.

Hereinafter, a thermal adhesive film according to a specific embodiment of the present invention will be described.

Composition and properties of thermal adhesive film

The thermal adhesive film has the following polylactic acid resin as a main component.

polylactic acid resin

The polylactic acid resin is a hard segment comprising the polylactic acid repeating unit of Formula 1, and the polyether-based polyol repeating units of Formula 2 are linearly formed through a urethane bond (-C(=O)-NH-) It includes a soft segment including linked polyurethane polyol repeating units.

Preferably, the polylactic acid resin is a block copolymer including the hard segment and the soft segment.

In the polylactic acid resin according to an embodiment of the present invention, the polylactic acid repeating unit of Formula 1 contained in the hard segment is a poly-L-lactic acid repeating unit (see Chemical Formula 1a below) and a poly-D-lactic acid repeating unit ( Formula 1b) is a repeating unit copolymerized in a certain molar ratio.

[Formula 1a]

[Formula 1b]

In Formulas 1a and 1b, p and q are integers greater than or equal to 1 representing the number of repeating units.

The poly-L-lactic acid repeating unit may be derived from L-lactide or L-lactic acid of Formula 3a below, and the poly-D-lactic acid repeating unit is represented by the following formula It may be derived from D-lactide or D-lactic acid of 3b.

[Formula 3a]

[Formula 3b]

The polylactic acid repeating unit copolymerized with these poly-L-lactic acid repeating units and poly-D-lactic acid repeating units is, for example, atactic or heterotactic without special stereoregularity (tacticity). may be a copolymerized repeating unit of Accordingly, the hard segment may be non-crystalline.

In the polylactic acid repeating unit, the molar ratio of the poly-L-lactic acid repeating unit and the poly-D-lactic acid repeating unit is 94:6 to 88:12. When the molar ratio is within the above range, better thermal bonding properties can be exhibited at the thermal bonding process temperature, for example, 100° C. to 130° C., during molding into a film, and problems such as fusion in the inlet during extrusion are prevented And it is possible to reduce the thickness variation during film forming and further improve the blocking resistance.

In the case of a general polylactic acid resin, when the stereoisomers (poly-L-lactic acid and poly-D-lactic acid repeating units) are copolymerized in the molar ratio as described above, it is difficult to achieve crystallization due to the fluidity problem of the polylactic acid chain, but the Since the polylactic acid resin has a block-copolymerized structure with a soft segment in which the hard segment secures the fluidity of the polymer chain, the crystallization process is possible. Accordingly, the polylactic acid resin of the present invention has excellent processability and high storage stability by preventing blocking at Tg or higher during the extrusion process or storage.

In addition, in the case of general polylactic acid resin, the adhesive strength is not high at the time of thermal bonding after film molding due to the unique low cohesive attraction, but the polylactic acid resin of the present invention is a molecule that exhibits cohesiveness with amorphous hard segments By including the block copolymer of the soft segment having a structure, it is useful as a thermal adhesive film because it has excellent adhesion at 100°C to 130°C while having crystallinity.

In addition, the polylactic acid resin of the present invention basically contains a polylactic acid repeating unit as a hard segment, so it can exhibit biomass-based resin-specific biodegradability, and has excellent mechanical properties during film molding, and at the same time, a soft segment By providing it, flexibility can also be improved at the time of film forming. In addition, as these hard segments and soft segments are combined with the block copolymer, bleed out of the soft segments can be minimized, and moisture resistance, mechanical properties, heat resistance, and transparency of the film by the addition of these soft segments Alternatively, deterioration in haze characteristics and the like can be greatly reduced.

The polylactic acid resin according to an embodiment of the present invention comprises, based on the weight thereof, in an amount of 65 to 95% by weight of the hard segment and 5 to 35% by weight of the soft segment, preferably 80 to 95% by weight of the hard segment. and 5 to 20% by weight of the soft segment, more preferably 82 to 94% by weight of the hard segment, and 6 to 18% by weight of the soft segment. When the hard segment content is within the above range, the molecular weight properties may be more excellent (for example, it may have a relatively high molecular weight and a narrow molecular weight distribution), and thus mechanical properties such as film strength during film molding are better can be done At the same time, when the content of the soft segment is within the above range, flexibility of the film can be secured during film forming, and the polyurethane polyol repeating unit can sufficiently perform a role as an initiator to exhibit excellent molecular weight properties.

The polyurethane polyol repeating unit included in the soft segment has a structure in which the polyether polyol repeating units of Formula 2 are linearly connected via a urethane bond (-C(=O)-NH-). More specifically, the polyether-based polyol repeating units are obtained by ring-opening (co)polymerization of a monomer such as alkylene oxide, and have a hydroxyl group at the terminal thereof. The terminal hydroxyl group reacts with a diisocyanate compound to form the urethane bond (- C(=O)-NH-) may be formed, and the polyether-based polyol repeating units may be linearly connected to each other through the urethane bond to form the polyurethane polyol repeating unit. By including such a polyurethane polyol repeating unit as a soft segment, the flexibility of the film including the polylactic acid resin can be greatly improved. In addition, the polyurethane polyol repeating unit does not reduce the heat resistance, blocking resistance, mechanical properties or transparency of the polylactic acid resin or a film containing the same, and enables the provision of a film exhibiting excellent physical properties.

As such, the polylactic acid resin of one embodiment of the present invention includes a polyurethane polyol repeating unit and a polylactic acid repeating unit in which a plurality of polyether polyol repeating units are linearly linked through a urethane bond, While it is possible to provide a film exhibiting flexibility, it has a small molecular weight distribution, which satisfies excellent molecular weight characteristics, and includes a polylactic acid repeating unit in a large segment size, so that the film can exhibit excellent mechanical properties, heat resistance and blocking resistance. In contrast, the conventional polylactic acid-based copolymer has problems such as a decrease in film transparency and a high haze value due to the low compatibility between the polyester polyol and polylactic acid, and also has a wide molecular weight distribution and poor melt properties. Therefore, the film extrusion state was not good, and the mechanical properties, heat resistance and blocking resistance of the film were not sufficient. In addition, conventionally, using a trifunctional or more isocyanate compound, the polyether polyol repeating unit is branched with the polylactic acid repeating unit, or after copolymerizing the polyether polyol repeating unit and the polylactic acid repeating unit, the chain is extended by urethane reaction The polylactic acid-based copolymer of this type has a small block size of the polylactic acid repeating unit corresponding to the hard segment, so the heat resistance, mechanical properties and blocking resistance of the film are not sufficient, and the molecular weight distribution is wide and the melting property is poor. This may indicate problems such as poor film extrusion state.

The polyether-based polyol repeating unit and the diisocyanate compound are reacted so that the molar ratio of the terminal hydroxyl group of the polyether-based polyol repeating unit and the isocyanate group of the diisocyanate compound is 1: 0.50 to 1: 0.99, and the polyurethane polyol repeats units can be formed. Preferably, the molar ratio may be 1:0.60 to 1:0.90, more preferably 1:0.70 to 1:0.85. As the polyurethane polyol repeating unit has a hydroxyl group at its terminal, it may act as an initiator in the polymerization process for the formation of the polylactic acid repeating unit. However, if the reaction molar ratio of the isocyanate group to the hydroxyl group (NCO/OH) exceeds 0.99, the number of terminal hydroxyl groups of the polyurethane polyol repeating unit becomes insufficient (OHV < 3), and thus it cannot function properly as an initiator. can This may make it difficult to prepare a polylactic acid resin having excellent molecular weight characteristics and the like, and the polymerization yield may also be greatly reduced. Conversely, when the reaction molar ratio (NCO/OH) of the isocyanate group to the hydroxyl group is too low, the number of terminal hydroxyl groups of the polyurethane polyol repeating unit is too large (OHV > 21), so a high molecular weight polylactic acid repeating unit and excellent molecular weight It may be difficult to obtain a polylactic acid resin having properties.

Meanwhile, the polyether-based polyol repeating unit may be, for example, a repeating unit of a polyether-based polyol (co)polymer obtained by ring-opening (co)polymerizing at least one alkylene oxide. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran. Examples of the polyether-based polyol repeating unit obtained therefrom include a repeating unit of polyethylene glycol (PEG); repeating unit of poly(1,2-propylene glycol); a repeating unit of poly(1,3-propanediol); repeating unit of polytetramethylene glycol; repeating unit of polybutylene glycol; repeating units of polyols, which are copolymers of propylene oxide and tetrahydrofuran; repeating units of polyols, which are copolymers of ethylene oxide and tetrahydrofuran; Or the repeating unit of polyol which is a copolymer of ethylene oxide and propylene oxide, etc. are mentioned. Given flexibility to the polylactic acid resin film, affinity with the polylactic acid repeating unit, and moisture content characteristics, the polyether-based polyol repeating unit is a repeating unit of poly(1,3-propanediol) or polytetramethylene glycol It is preferable to use a repeating unit of

In addition, the polyether-based polyol repeating unit may have a number average molecular weight of 1,000 to 100,000, preferably 10,000 to 50,000. If the molecular weight of such a polyether-based polyol repeating unit is too large or small, the flexibility or mechanical properties of the film obtained from the polylactic acid resin of one embodiment may not be sufficient. In addition, the molecular weight characteristics of the polylactic acid resin, for example, a weight average molecular weight and molecular weight distribution in a predetermined range may not be implemented, and the processability of the polylactic acid resin may be reduced or the mechanical properties of the film may be reduced.

Further, the diisocyanate compound capable of forming a urethane bond by bonding with a terminal hydroxyl group of the polyether-based polyol repeating unit may be any compound having two isocyanate groups in the molecule. Examples of such diisocyanate compounds include 1,6-hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 1 ,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-bisphenylene diisocyanate, and hexamethylene diisocyanate, isophorone diisocyanate or hydrogenated diphenylmethane diisocyanate. In addition, various diisocyanate compounds well known to those skilled in the art may be used without particular limitation. However, it is preferable to use 1,6-hexamethylene diisocyanate in terms of imparting flexibility to the polylactic acid resin film.

The polylactic acid resin according to an embodiment of the present invention may include a block copolymer in which the polylactic acid repeating unit of the hard segment is combined with the polyurethane polyol repeating unit of the soft segment, and the end of the polylactic acid repeating unit A carboxyl group may form an ester bond with a terminal hydroxyl group of the repeating unit of the polyurethane polyol. For example, the chemical structure of such a block copolymer may be represented by the following general formula 1:

[General formula 1]

Polylactic acid repeating unit (L) -Ester- Polyurethane polyol repeating unit (E-U-E-U-E) -Ester- Polylactic acid repeating unit (L)

In the above formula, E represents a polyether-based polyol repeating unit, U represents a urethane bond, and Ester represents an ester bond.

The thermal adhesive film of the present invention may include the polylactic acid resin in an amount of 1% by weight or more, more specifically 30% by weight or more.

additional ingredients

It is not necessary that all of the polylactic acid repeating units included in the thermal adhesive film have the form of a block copolymer combined with the polyurethane polyol repeating unit, and at least some of the polylactic acid repeating units are the polyurethane polyol repeating unit and It may have a form of unbonded polylactic acid resin. In this case, the thermal adhesive film may include the above-described block copolymer, and a single polylactic acid resin not bonded to the polyurethane polyol repeating unit. In addition, the polylactic acid single resin may include a poly-L-lactic acid repeating unit and a poly-D-lactic acid repeating unit in a molar ratio of 94:6 to 88:12. The polylactic acid single resin may be included in an amount of 1 to 30% by weight based on the total weight of the thermal adhesive film of the present invention.

The thermal adhesive film may further include a phosphorus-based stabilizer and/or antioxidant in order to suppress oxidation or thermal decomposition of the soft segment or the like during the manufacturing process thereof. Examples of the antioxidant include hindered phenol-based antioxidants, amine-based antioxidants, thio-based antioxidants, or phosphite-based antioxidants. The types of each of these stabilizers and antioxidants are known to those skilled in the art.

In addition to these stabilizers and antioxidants, the thermal adhesive film contains known various plasticizers, ultraviolet stabilizers, color inhibitors, matting agents, deodorants, flame retardants, weathering agents, antistatic agents, mold release agents, antioxidants, Various additives such as ion exchangers, coloring pigments, inorganic or organic particles may be further included.

Examples of the plasticizer include phthalic acid ester plasticizers such as diethyl phthalate, dioctyl phthalate, and dicyclohexyl phthalate; aliphatic dibasic acid ester plasticizers such as di-1-butyl adipate, di-n-octyl adipate, di-n-butyl sebacate, and di-2-ethylhexyl azerate; phosphate ester plasticizers such as diphenyl 2-ethylhexyl phosphate and diphenyl octyl phosphate; hydroxypolycarboxylic acid ester plasticizers such as tributyl acetyl citrate, tri-2-ethylhexyl acetyl citrate, and tributyl citrate; fatty acid ester-based plasticizers such as methyl acetyl ricinoleate and amyl stearate; polyhydric alcohol ester plasticizers such as glycerin triacetate; and epoxy plasticizers such as epoxidized soybean oil, epoxidized linseed oil fatty acid butyl ester, and octyl epoxy stearate.

Moreover, as an example of a color pigment, Inorganic pigments, such as carbon black, a titanium oxide, zinc oxide, and iron oxide; Organic pigments, such as a cyanine type, a phosphorus type, a quinone type, a relinone type, an isoindolinone type, and a thioindigo type, etc. are mentioned.

Other inorganic or organic particles may be further included to improve the blocking resistance of the film, for example, silica, colloidal silica, alumina, alumina sol, talc, mica, calcium carbonate, polystyrene, polymethyl methacrylate, Silicone etc. are mentioned.

In addition, various additives known to be used in the polylactic acid resin or its film may be included, and specific types or methods of obtaining them are known to those skilled in the art.

Properties

As described above, the heat-adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, reacts a polyether polyol repeating unit with a diisocyanate compound so that a plurality of polyether polyol repeating units are linear with a urethane bond. After forming a linked polyurethane polyol repeating unit, as it includes a block copolymer copolymerized with a polylactic acid repeating unit, it has a relatively narrow molecular weight distribution compared to previously known similar polylactic acid-based copolymers with a relatively large molecular weight. can have

The heat-adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, may have a number average molecular weight (Mn) of 50,000 to 200,000, preferably 50,000 to 150,000, and its weight average molecular weight (Mw) This may be 100,000 to 400,000, preferably 100,000 to 320,000. When the number average molecular weight and the weight average molecular weight are within the above ranges, the processability from the raw resin to a film may be more excellent, and mechanical properties such as strength of the obtained film may be more excellent.

The thermal adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, has a molecular weight distribution (Mw / Mn) defined as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is, for example, It may have a value of 1.60 to 2.30, preferably 1.80 to 2.20. When the molecular weight distribution is within the above range, when the raw resin is melt-processed by a method such as extrusion, it exhibits appropriate melt viscosity and melt characteristics, thereby exhibiting excellent film extrusion state and processability, and the obtained film has excellent mechanical strength, etc. properties can be shown. On the other hand, when the molecular weight becomes too large or the molecular weight distribution becomes too narrow (smaller), the melt viscosity at the processing temperature for extrusion of the raw resin, etc. When the distribution is too wide (larger), the mechanical properties such as the strength of the film are lowered or the melt viscosity is too small, and the melt properties are poor, making it difficult to form into a film, or the film extrusion state may be poor.

The thermal adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, may have a glass transition temperature (Tg) of 30 ℃ to 50 ℃, more preferably 40 ℃ to 50 ℃. As the glass transition temperature range is indicated, the flexibility or stiffness of the film including the polylactic acid resin is optimized, and it can be used very preferably as a packaging film. If the glass transition temperature is too low, the flexibility of the film can be improved, but as the stiffness is too low, the slipping, handling, shape maintaining properties or blocking resistance of the film may be poor. have. Conversely, if the glass transition temperature is too high, the flexibility of the film is low and the stiffness is too high, so that the film is easily folded so that the marks do not disappear or the adhesion may be poor, and noise may occur severely.

In addition, the thermal adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, the melting temperature (Tm) may be from 100 ℃ to 130 ℃, more preferably from 110 ℃ to 120 ℃. When the melting temperature is within the above range, processing properties of the raw resin into a film and heat resistance of the film may be more excellent.

In addition, the heat-adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, may have a melting enthalpy (ΔHm) of 5 to 30 J/g, more preferably 10 to 20 J/g. . When the melting enthalpy is within the above range, there is an advantage of securing extrusion stability due to crystallization of the resin and thermal bonding strength at a thermal bonding temperature (100 to 130°C).

In addition, as the thermal adhesive film is manufactured to have predetermined molecular weight characteristics, that is, a specific weight average molecular weight and molecular weight distribution range, the raw resin exhibits excellent processability that can be easily molded into a film by melt processing such as extrusion. , mechanical properties such as film strength can also be maintained excellently.

For example, the thermal adhesive film, for example, the polylactic acid resin (block copolymer) contained therein, may be melt-processed by a method such as extrusion, under a processing temperature of 150 ℃ to 190 ℃, under such processing temperature It may exhibit a melt viscosity of 1500 to 3500 Pa·s, preferably 1700 to 3000 Pa·s. Therefore, the heat-adhesive film can be very easily processed into a film having excellent physical properties and excellent film extrusion from the raw resin, and its productivity can also be greatly improved.

The thermal adhesive film may have a thickness variation within about ±20%, preferably within about ±10%, and more preferably within about ±5%. When the thickness deviation is within the above range, there is an advantage of ensuring uniformity of quality during production.

The heat-adhesive film may have a sum of Young's modulus in the longitudinal and width directions of about 350 to 750 kgf / mm 2 , preferably about 400 to 650 kgf / mm 2 , more preferably about 500 to 600 kgf / mm 2 have. For example, the sum of the Young's modulus may be measured according to ASTM D638, and more specifically, under the conditions of a temperature of 20°C and a relative humidity of 65%, an elongation speed of 300 mm/min using a universal tester, and a distance between grips of 100 mm, the width It may be the sum of Young's modulus under test conditions using a specimen of 10 mm and 150 mm in length. The sum of Young's modulus may reflect the optimized flexibility and strength of the polylactic acid resin film, and such flexibility and strength may be due to structural characteristics and glass transition temperature of the polylactic acid resin. When the sum of Young's modulus is too low, spreading or slack may occur during film forming and processing processes of the film, and handling properties, process permeability, slit processability, or shape retention characteristics may be deteriorated. In addition, due to the lack of slip property of the film, the releasability may be insufficient or the film may be deformed prior to thermal bonding. Conversely, when the sum of the Young's modulus is excessively high, when the film is folded, the folding line remains as it is, and the appearance is not good, or it is not easily deformed according to the shape of the film, which may cause difficulties in use.

The thermal adhesive film has an initial tensile strength of about 8 kgf / mm 2 or more in both the longitudinal direction and the width direction, preferably about 10 kgf / mm 2 or more, more preferably about 12 kgf / mm 2 or more, more preferably about 15 kgf / mm 2 It may be more than, it may be a maximum of 30kgf / mm2 or less. In this case, the test condition may be the same as the Young's modulus. When the initial tensile strength is within the above range, the handleability of the film becomes easier and the fracture rate is very low.

The thermal adhesive film may have an elongation of about 50% or more, preferably about 70% or more, more preferably about 100% or more, and a maximum of 200% or less with respect to the width direction (MD) of the film.

The heat-adhesive film has excellent blocking resistance, and thus has excellent processability and is very easy for users to handle.

The thermal adhesive film has very good thermal adhesive properties, and exhibits excellent thermal adhesive properties at a process temperature of the thermal adhesive film, for example, 100° C. to 130° C.

In addition, it may exhibit an adhesive strength of 600 gf/15 mm or more at a temperature of 100° C., and more preferably, an adhesive strength of 800 gf/15 mm or more at a temperature of 100° C.

In addition, it may exhibit an adhesive strength of 1000gf/15mm or more at a temperature of 130°C, and more preferably, an adhesive strength of 1500gf/15mm or more at a temperature of 130°C.

As described above, the thermal adhesive film of the present invention has excellent thermal adhesion even at a relatively low thermal bonding process temperature as it contains the optical isomer of the polylactic acid repeating unit in a specific ratio in the polylactic acid resin as the main raw material. In addition, by including the polyurethane polyol repeating unit of a specific content as the soft segment, the flexibility of the film prepared using the polylactic acid resin can be greatly improved. It exhibits a large molecular weight and a narrow molecular weight distribution and includes a polylactic acid repeating unit as a block unit hard segment, so that a film prepared using the same can exhibit excellent mechanical properties, heat resistance and blocking resistance. The thermal adhesive film may exhibit excellent flexibility and transparency even when stored for a long period of time, as well as mechanical properties such as sufficient strength and anti-bleed out characteristics. In addition, it can exhibit the unique eco-friendly characteristics and biodegradability of polylactic acid resin.

The thermal adhesive film may be provided with properties required as a food packaging material such as gas barrier properties such as water vapor, oxygen or carbon dioxide gas, releasability, printability, etc., if necessary in a range that does not impair the effect thereof. To this end, a compound having these properties may be blended into the film, or a thermoplastic resin such as an acrylic resin, a polyester resin, or a silicone-based resin, an antistatic agent, a surfactant, a mold release agent, or the like may be applied to at least one surface of the film. In addition, as another method, other films having a function such as a polyolefin-based sealant may be co-extruded to form a multilayer film. It may be manufactured in the form of a multilayer film by other methods such as adhesion or lamination.

Manufacturing method

The thermal adhesive film according to an embodiment of the present invention may be prepared by first preparing a polylactic acid resin composition as follows, and then processing it into a film.

Method for producing polylactic acid resin composition

The polylactic acid resin composition comprises the steps of: ring-opening (co)polymerizing a monomer such as at least one alkylene oxide to form a (co)polymer having a polyether-based polyol repeating unit; reacting the (co)polymer with a diisocyanate compound in the presence of a catalyst to form a (co)polymer having a polyurethane polyol repeating unit; and polycondensation of D-lactic acid and L-lactic acid in a predetermined molar ratio or ring-opening polymerization of D-lactide and L-lactide in a predetermined molar ratio in the presence of a (co)polymer having the polyurethane polyol repeating unit. It can be prepared by a manufacturing method comprising

In this case, L-lactic acid and D-lactic acid are used as monomers in a molar ratio of 94:6 to 88:12, or L-lactide and D-lactide are used in a molar ratio of 94:6 to 88:12. In addition, it is preferable to copolymerize the polylactic acid repeating unit (hard segment) and the polyurethane polyol repeating unit (soft segment) in a ratio of 65 to 95% by weight and 5 to 35% by weight of the soft segment.

In addition, according to a preferred example, a (co)polymer having a polyether-based polyol repeating unit and a diisocyanate compound are subjected to a urethane reaction in the presence of a catalyst, and the polyether-based polyol repeating units are linearly linked via a urethane bond. After obtaining a (co)polymer having a repeating unit, by polymerizing it with lactic acid (D- and L-lactic acid) or lactide (D- and L-lactide) in the presence of a catalyst, excellent physical properties such as the molecular weight properties described above A polylactic acid-based resin or a block copolymer included therein of one embodiment having a can be prepared.

In addition, having a polyurethane polyol repeating unit corresponding to the reaction molar ratio of the (co)polymer having the polyether-based polyol repeating unit and the diisocyanate compound, the molecular weight of the polyether-based polyol (co)polymer, or the content of the soft segment Adequate control of the amount of (co)polymer, etc. is also a major factor enabling the polylactic acid resin of the above-described embodiment to be prepared. Appropriate ranges such as the reaction molar ratio and the molecular weight of the polyether-based polyol (co)polymer are as described above.

Hereinafter, the manufacturing method of the polylactic acid resin composition of the present invention will be described in more detail.

First, a (co)polymer having a polyether-based polyol repeating unit is formed by ring-opening (co)polymerizing one or more monomers such as alkylene oxide, which is a conventional method for producing a polyether-based polyol (co)polymer. can proceed accordingly.

Thereafter, the (co)polymer having the polyether-based polyol repeating unit, the diisocyanate compound, and the urethane reaction catalyst are charged in a reactor, and the urethane reaction is performed by heating and stirring. By this reaction, two isocyanate groups of the diisocyanate compound and a terminal hydroxyl group of the (co)polymer combine to form a urethane bond. As a result, a (co)polymer having a polyurethane polyol repeating unit in a form in which the polyether polyol repeating units are linearly linked via the urethane bond can be formed, which is included as a soft segment of the polylactic acid resin composition described above. . At this time, in the polyurethane polyol (co)polymer, polyether-based polyol repeating units (E) are linearly bonded in EUEUE form via a urethane bond (U) to have polyether-based polyol repeating units at both ends. can

The urethane reaction is a conventional tin (Sn)-based catalyst, for example, stannous octoate (tin(II) 2-ethylhexanoate), dibutyltin dilaurate, dioctyltin dilaurate ( It can proceed in the presence of dioctyltin dilaurate). In addition, the urethane reaction may be performed under reaction conditions for the production of conventional polyurethane resins. For example, after adding a diisocyanate compound and a polyether-based polyol (co)polymer under a nitrogen atmosphere, the urethane reaction catalyst is added and reacted at a reaction temperature of 70° C. to 80° C. for 1 to 5 hours to form a polyurethane polyol repeating unit It is possible to prepare a (co)polymer having

Subsequently, in the presence of a (co)polymer having a repeating unit of the polyurethane polyol, lactic acid (D- and L-lactic acid) is polycondensed, or lactide (D- and L-lactide) is ring-opened by polymerization. The polylactic acid resin composition according to the embodiment, in particular, a block copolymer included therein can be prepared.

When subjected to such a polymerization reaction, the polylactic acid repeating unit included as a hard segment is formed, and the polylactic acid resin is prepared. can be formed.

As a result, a polylactic acid-based copolymer in which a prepolymer in which a polyether polyol and a polylactic acid are first combined is prepared, and then these prepolymers are chain-extended with a diisocyanate compound, or in the prior art, the prepolymers are trifunctional The block copolymer of an embodiment showing different structure and molecular weight characteristics and the like from the branched copolymer reacted with the above isocyanate compound may be formed.

In particular, since the block copolymer of this embodiment may include blocks (hard segments) in which the polylactic acid repeating units are relatively large units (molecular weight), the film formed of the polylactic acid resin composition including them has a narrow molecular weight distribution and Appropriate Tg and thus excellent mechanical properties and heat resistance may be exhibited.

On the other hand, the lactide ring-opening polymerization reaction includes alkaline earth metal, rare earth metal, transition metal, aluminum, germanium, tin or antimony. It can proceed in the presence of a metal catalyst. More specifically, these metal catalysts may be in the form of carboxylates, alkoxides, halides, oxides or carbonates of these metals. Preferably, as the metal catalyst, tin octoate, titanium tetraisopropoxide or aluminum triisopropoxide may be used.

Method for manufacturing thermal adhesive film

Using the polylactic acid resin composition prepared above as a raw material, it can be processed into the thermal adhesive film of the present invention.

The thermal adhesive film may be prepared according to a conventional film processing method. For example, after forming in the form of a stretched film by applying an inflation method, a sequential biaxial stretching method, a simultaneous biaxial stretching method, etc. to the above-described polylactic acid resin composition, it may be heat-set. At this time, the stretched film forming process is performed by melt-extruding the polylactic acid resin into a sheet with an extruder equipped with a T-die, cooling and solidifying the sheet-like molten extrudate to obtain an unstretched film, and then forming the unstretched film It can proceed by a method of stretching in the longitudinal direction and the width direction.

The stretching conditions of the film may be appropriately adjusted according to heat shrinkage characteristics, dimensional stability, strength, Young's modulus, and the like. For example, in terms of strength and flexibility of the finally manufactured thermal adhesive film, the stretching temperature is preferably controlled to be above the glass transition temperature of the polylactic acid resin and below the crystallization temperature. In addition, the stretching ratio may be in the range of about 1.5 to 10 times in the length and width directions, respectively, and of course, the stretching ratio in the length and width directions may be adjusted differently from each other.

After forming the stretched film in this way, a heat-adhesive film is finally manufactured through heat setting, and this heat setting is preferably performed at 100° C. or higher for about 10 seconds or more for strength and dimensional stability of the film.

Specific Examples and Test Examples

Hereinafter, the operation and effect of the invention will be described in more detail through specific examples of the invention. However, these embodiments are merely presented as an example of the invention, and the scope of the invention is not defined thereby.

Property definition and measurement method

Definitions and measuring methods of each physical property in Examples to be described later are as summarized below.

(1) NCO/OH: Reaction of "isocyanate group of diisocyanate compound (such as hexamethylene diisocyanate)/terminal hydroxyl group of polyether-based polyol repeating unit (or (co)polymer)" for formation of polyurethane polyol repeating unit Molar ratio was shown.

(2) OHV (KOHmg/g): A polyurethane polyol repeating unit (or (co)polymer) was dissolved in dichloromethane, acetylated, and hydrolyzed. It was measured by titrating the resulting acetic acid with 0.1N KOH methanol solution. . This corresponds to the number of hydroxyl groups present at the end of the polyurethane polyol repeating unit (or (co)polymer).

(3) molecular weight (Mw, Mn) and molecular weight distribution (MWD): polylactic acid resin was dissolved in chloroform at a concentration of 0.25% by weight, and gel permeation chromatography (manufactured by Viscotek TDA 305, column: Shodex LF804 * 2ea) was used. was measured, and a weight average molecular weight (Mw) and a number average molecular weight (Mn) were calculated using polystyrene as a standard material, respectively. A molecular weight distribution value (Mw/Mn) was calculated from the calculated Mw and Mn.

(4) Glass transition temperature (Tg, °C): Using a differential scanning calorimeter (TA Instruments), the sample was melted and quenched, and then the temperature was raised to 10 °C/min for measurement. The mid value of the baseline and each tangent line in the vicinity of the endothermic curve was taken as Tg.

(5) Melting temperature (Tm, °C): Using a differential scanning calorimeter (TA Instruments), the sample was melted and quenched, and then the temperature was raised to 10 °C/min for measurement. The maximum temperature of the melting endothermic peak of the crystal was defined as Tm.

(6) Content of polyurethane polyol repeating unit (wt%): Using a 600MHz nuclear magnetic resonance (NMR) spectrometer, the content of the polyurethane polyol repeating unit contained in each prepared polylactic acid resin was quantified.

(7) Melting enthalpy (ΔHm, J/g): Using a differential scanning calorimeter (TA Instruments), the sample was melt quenched and then heated to 10° C./min. It was calculated by measuring the integral of the melting endothermic peak of the crystal and the baseline near the curve.

(8) Melt Viscosity and Extrusion State: For the production of a biaxially oriented film, the polylactic acid resin is extruded into a sheet at an extrusion temperature of 200 to 250 ° C in a 30 mm diameter single screw extruder equipped with a T die and cooled to 5 ° C. Electrostatically applied and cast on one drum. At this time, the melt viscosity of the sheet-like discharge was measured using a rheometer (Rheometer, Physica, USA). Specifically, through a 25 mm parallel plate type shearing tool, the melt viscosity of the molten resin (complex viscosity, Pa· s) was measured with a rheometer.

In addition, the extrusion state was evaluated according to the following criteria.

◎: Good melt viscosity and constant discharge pressure.

Δ: The melting point is also slightly insufficient, but the discharge pressure is constant.

×: The ejection pressure is not constant, and the sheet extrusion state is poor.

(9) Film thickness deviation (%): The thickness of the produced film after stretching was measured using a digital thickness gauge (Mitutoyo, Japan).

(10) Initial tensile strength (kgf/㎟) MD, TD: A film sample having a length of 150mm and a width of 10mm was aged for 24 hours in an atmosphere of a temperature of 20°C and a humidity of 65%RH, and a universal tester (UTM, INSTRON), the tensile strength was measured under the conditions of a stretching speed of 300 mm/min and a distance between grips of 100 mm. The average value of a total of 5 tests was expressed as a result value. The longitudinal direction of the film was indicated by MD and the width direction by TD.

(11) Elongation (%) MD, TD: Elongation until the film breaks under the same conditions as the tensile test of (9) above, and the average value of the total 5 tests was expressed as the result. The longitudinal direction of the film was indicated by MD and the width direction by TD.

(12) Young's modulus (kgf/㎟) MD, TD: The same specimen as the tensile test in (9) above, using a universal testing machine (UTM, INSTRON) according to ASTM D638, elongation speed 300mm/min and distance between grips 100mm The Young's modulus was measured with The average value of a total of 5 tests was expressed as a result value. These Young's modulus values, particularly, the sum of Young's modulus measured in the length and width directions correspond to the flexibility of the film, and the greater the flexibility, the lower the Young's modulus sum value. The longitudinal direction of the film was indicated by MD and the width direction by TD.

(13) Blocking resistance: Using the COLORIT P type of stamping foil (Coolz), match the antistatic side and the printed side of the film sample, and leave it for 24 hours under ^{a temperature of 40° C. and a pressure of 1 kg/cm 2 ,} The blocking state of the antistatic layer and the printing surface was observed. Based on these observation results, the blocking resistance between the antistatic layer and the printing surface of the in-mold transfer foil was evaluated according to the following criteria. It satisfies practicality when it is at a level of ○ or higher in the following categories.

◎: No change,

○: there is a slight surface change (5% or less),

×: more than 5% peeling

(14) Evaluation of thermal adhesion properties: The thermal adhesion film to be tested was thermally bonded at a temperature of 100 to 130 ° C under the conditions of a pressure of 2 kgf / cm ² and an adhesion time of 2 seconds, and the adhesive strength (gf / 15 mm) was measured while peeling it. , and also the phenomenon observed during peeling was evaluated according to the following criteria.

◎: Adhesive, and delamination does not occur at the bonding site during peeling.

Δ: Adhesive, but delamination occurred in the adhesive portion.

x: It does not adhere|attach.

raw material

The raw materials used in the following Examples and Comparative Examples are as follows:

(1) Polyolefin-based polyol repeating units and their counterparts

- PPDO 2.0: poly(1,3-propanediol); Number average molecular weight 2,000

- PPDO 2.4: poly(1,3-propanediol); Number average molecular weight 2,400

- dodecanol

(2) diisocyanate compound - HDI: hexamethylene diisocyanate

(3) Lactide monomers - L-lactide and D-lactide: manufactured by Purac

(4) antioxidants, etc.

- TNPP: tris (nonylphenyl) phosphite

- U626: bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite

- PEPQ: (1,1'-biphenyl)-4,4'-diylbisphosphonic acid tetrakis[2,4-bis(1,1-dimethylethyl)phenyl]ester

- S412: tetrakis [methane-3- (laurylthio) propionate] methane

- I-1076: octadecyl 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate

- O3: bis[3,3-bis-(4'-hydroxy-3'-tert-butyl-phenyl)butanoic acid]glycol ester

Examples A to E: Preparation of polylactic acid resins A to E

In an 8L reactor equipped with a nitrogen gas inlet tube, stirrer, catalyst inlet, outlet condenser and vacuum system, the reactants having the components and contents shown in Table 1 below were charged together with the catalyst. As a catalyst, dibutyltin dilaurate at a concentration of 80 ppm relative to the total reactant content was used. A urethane reaction was performed for 2 hours at a reactor temperature of 70° C. under a nitrogen stream, and a total of 4 kg of L-lactide and D-lactide were added in the amounts and ratios according to Table 1 below, followed by nitrogen flushing 5 times. was carried out.

Thereafter, the temperature was raised to 150° C. to completely dissolve L-lactide and D-lactide, and through the catalyst inlet, the catalyst tin 2-ethylhexylate was diluted with 100 mL of toluene so as to have a concentration of 100 ppm relative to the total reactant content in the reaction vessel. added in. The reaction was carried out at 185° C. under pressure of 1 kg nitrogen for 2 hours, and 200 ppm of phosphoric acid was added through the catalyst inlet and mixed for 15 minutes to inactivate the residual catalyst. Then, unreacted L- or D-lactide (about 5% by weight of the initial input amount) was removed through a vacuum reaction until 0.5 torr was reached. The physical properties of the obtained resin were measured and shown in Table 1 below.

Examples F to J: Preparation of polylactic acid resins F to J

Except that D-lactide was not added to the reactant or added in an amount outside the scope of the present invention as shown in Table 1, the polylactic acid resins A to J were prepared in the same manner as in Preparation Examples. The molecular weight, Tg and Tm, ΔHm, and the like of the obtained resin were measured and shown in Table 1 below.

Examples 1 to 5 and Comparative Examples 1 to 7: Preparation of thermal adhesive film

After drying one or more of the prepared polylactic acid resins A to J under reduced pressure under vacuum of 1 torr at 80 ° C. for 6 hours, in a 30 mm diameter single screw extruder equipped with a T die, the extrusion temperature conditions shown in Table 2 It was extruded into a sheet form. This was electrostatically cast on a drum cooled to 5° C. to prepare an unstretched film.

The prepared unstretched film was stretched 3 times in the longitudinal direction between heating rolls under the stretching conditions shown in Table 2, and then the stretched film in the longitudinal direction was fixed with a clip, led into a tenter, and stretched 4 times in the width direction, Heat treatment was performed at 120° C. for 60 seconds while being fixed in the width direction. Through this, a biaxially stretched polylactic acid resin film having each thickness and thickness deviation shown in Table 2 was obtained. Tables 2 and 3 show the evaluation results of the obtained films.

Resins A to E according to the scope of the present invention (L-/D-lactide = 92/8 to 90/10, soft segment 5 to 35 wt%), as shown in Table 1 above, have a glass transition temperature (Tg) is 50 ° C or less, the melting temperature (Tm) is 130 ° C or less, the melting enthalpy (ΔHm) was measured to be 20 J/g or less, and the molecular weight properties were also very excellent, and as shown in Table 2 above, fusion at the inlet during extrusion It was found that crystallization was possible under commercially meaningful process conditions because the extrusion state was uniform because there was no

On the other hand, resins F to J outside the scope of the present invention, as shown in Table 1 above, most have a melting temperature (Tm) of 130° C. or higher and a melting enthalpy (ΔHm) of more than 20 J/g, or as shown in Table 2, It was found that the extrusion state was poor due to fusion at the inlet during extrusion.

In addition, in the case of the films of Examples 1 to 5 prepared with the resin according to the scope of the present invention, as shown in Table 2, the thickness deviation was excellent within ±5% and the blocking resistance was excellent, and other tensile strength, elongation, Film properties such as Young's modulus were excellent, and as shown in Table 3, at the same time, thermal adhesion properties at 100 to 130° C. were excellent.

On the other hand, in the case of the films of Comparative Examples 1 and 2 using the resins F and G outside the scope of the present invention, the thermal adhesion properties were very poor, and in the case of the films of Comparative Examples 3 and 4 using the resins H and I, the thickness deviation and resistance to The blocking property was poor. In addition, in the case of the film of Comparative Example 5 in which the resins I and J were blended, the thermal adhesive properties were poor. In addition, even if the resin (A or E) according to the scope of the present invention was used, in Comparative Examples 6 and 7 blended with an excess of the resin (G) outside the scope of the present invention, thermal adhesion properties were poorly displayed.

Claims (12)

A hard segment containing a polylactic acid repeating unit of Formula 1, and a soft segment containing a polyurethane polyol repeating unit in which the polyether-based polyol repeating units of the following Chemical Formula 2 are linearly connected via a urethane bond. It is a heat sealing film (heat sealing film) containing a lactic acid resin,
In this case, the polylactic acid resin comprises 65 to 95% by weight of the hard segment and 5 to 35% by weight of the soft segment based on the weight thereof,
The polylactic acid repeating unit comprises a poly-L-lactic acid repeating unit and a poly-D-lactic acid repeating unit in a molar ratio of 94:6 to 88:12,
The polylactic acid resin has a melting temperature (Tm) of 100 ℃ to 130 ℃,
wherein the thermal adhesive film has an adhesive strength of 1500 gf/15 mm or more at a temperature of 130° C., a thermal adhesive film:
[Formula 1]

[Formula 2]

In Formula 1, n is an integer of 700 to 5000; In Formula 2, A is a linear or branched alkylene group having 2 to 5 carbon atoms, and m is an integer of 10 to 100.
The method of claim 1,
The polylactic acid resin, comprising 80 to 95% by weight of the hard segment and 5 to 20% by weight of the soft segment, a thermal adhesive film.
The method of claim 1,
Wherein the poly-L-lactic acid repeating unit and the poly-D-lactic acid repeating unit are derived from L-lactide and D-lactide, respectively.
The method of claim 1,
The polyurethane polyol repeating unit is linearly connected via a urethane bond formed by the reaction of the hydroxyl group at the end of the polyether-based polyol repeating unit with the isocyanate group of the diisocyanate compound, the thermal adhesive film.
5. The method of claim 4,
The reaction molar ratio of the terminal hydroxyl group of the polyether-based polyol repeating unit and the isocyanate group of the diisocyanate compound is 1: 0.50 to 1: 0.99, the thermal adhesive film.
The method of claim 1,
The polyether-based polyol repeating unit has a number average molecular weight of 1,000 to 100,000, a thermal adhesive film.
The method of claim 1,
The polylactic acid resin is a block copolymer comprising the hard segment and the soft segment, a thermal adhesive film.
8. The method of claim 7,
The polylactic acid resin is a block copolymer in which the terminal carboxyl group of the polylactic acid repeating unit included in the hard segment and the terminal hydroxyl group of the polyurethane polyol repeating unit are linked by an ester bond, a thermal adhesive film.
The method of claim 1,
The thermal adhesive film, the polyurethane polyol repeating unit and the non-bonded polylactic acid repeating unit comprising 1 to 30% by weight, the thermal adhesive film.
The method of claim 1,
The polylactic acid resin has a number average molecular weight of 50,000 to 200,000, and a weight average molecular weight of 100,000 to 400,000, a thermal adhesive film.
The method of claim 1,
The thermal adhesive film having a thickness deviation within ±5%, thermal adhesive film.
The method of claim 1,
The thermal adhesive film exhibits an adhesive strength of 800 gf/15 mm or more under thermal bonding conditions at a temperature of 100° C., the thermal adhesive film.