CN116178917A - Biodegradable film, packaging material and adhesive tape - Google Patents

Abstract

The present invention provides a biodegradable film having a structure of one or more layers, comprising a polyhydroxyalkanoate resin A and a biodegradable resin B having a glass transition temperature of 20 ℃ or higher, wherein the polyhydroxyalkanoate resin A is contained in an amount of 76% by weight or more in the biodegradable film, and the biodegradable film is subjected to cross-sectional observation by a transmission electron microscope, and wherein at least one layer of the biodegradable resin B is dispersed in the polyhydroxyalkanoate resin A in the form of a dispersed phase having an average length of 0.1 to 20 [ mu ] m and a ZD direction thickness of 0.01 to 3 [ mu ] m. The biodegradable film has the characteristics of high biodegradation speed and stable storage, has good mechanical property, optical property and barrier property, can be suitable for various aspects including packaging, express delivery and transportation, and can be quickly biodegraded into small molecules such as carbon dioxide, water and the like after the service life is finished, and the environment is not polluted.

Description

Biodegradable film, packaging material and adhesive tape

Technical Field

The invention belongs to the field of high polymer materials, and relates to a biodegradable film, a packaging material containing the biodegradable film and an adhesive tape.

Background

Plastic film is an important material and is widely used in various aspects of human production and life. Food packaging, adhesive tape, plastic bags, etc. are common applications of plastic films. The common plastic film is difficult to degrade in nature and can be left in nature for a long time. The product has short service cycle, light weight and difficult recycling, but has large usage amount and is easy to cause environmental pollution.

Biodegradable plastics can be decomposed by bacteria, and the use of such materials can effectively improve the above-mentioned problems. Currently, the more common biodegradable plastics on the market include: polylactic acid, polybutylene terephthalate adipate, polyhydroxyalkanoate, polybutylene succinate, polyglycolic acid, polycaprolactone, polypropylene carbonate, and the like. Polylactic acid is one of the largest-used biodegradable plastics at present because of its excellent processability and comprehensive performance of mechanical properties. However, polylactic acid has a slow biodegradation rate, especially in environments with low bacterial content and low ambient temperature. That is, polylactic acid, although it can be considered compostable by standard methods of industrial composting (typically at 58 ℃), is often difficult to identify by standard methods of home composting (typically at 28 ℃) and soil burial, meaning that it does not degrade rapidly under home composting conditions or after burial by soil, but remains in compost or soil for a longer period of time.

In addition, polyhydroxyalkanoate (PHA) is a polyhydroxyalkanoate containing-O-CHR- (CH) ₂ ) _m -polymers of CO-repeat units, wherein R is alkyl and m is an integer greater than or equal to 1. Which are generally chain polyesters produced from the bacterial fermentation of sugars or lipids. Polyhydroxyalkanoates are polymers that are capable of relatively rapid biodegradation, which can be achieved by industrial composting, household composting, soil-borne degradation, and even seawater degradation. However, the glass transition temperature is near 0 ℃, the crystallization speed is slow, the melt Cheng Kuan, the thermal stability of the melt is poor, the viscosity is low, and the like, so that the processability of PHA is poor, and the PHA is difficult to prepare into high-quality plastic films: particularly, problems such as unstable production, low production efficiency, uneven thickness, appearance, performance and the like are presented. Second, PHA articles have poor performance characteristics, particularly heat resistance. For example, plastic films are often used as packaging films, tapes, etc., and the films are often subjected to coating, vapor deposition, heat sealing, etc., and heated. The film of PHA undergoes significant dimensional shrinkage (heat shrinkage) upon heating, resulting in an articlePoor appearance, even processing failure, and the like.

For this reason, there is a need for a biodegradable film that has both a rapid degradation capability and a sufficient low heat shrinkage rate and other service properties.

Disclosure of Invention

In order to solve the above problems, the present invention provides a biodegradable film having a structure of one or more layers, comprising a polyhydroxyalkanoate resin A and a biodegradable resin B having a glass transition temperature of 20 ℃ or higher, wherein the polyhydroxyalkanoate resin A is contained in an amount of 76% by weight or more in the biodegradable film, and the biodegradable film is subjected to cross-sectional observation by a transmission electron microscope, wherein at least one layer of the biodegradable resin B is dispersed in the polyhydroxyalkanoate resin A in the form of a dispersed phase having an average length of 0.1 to 20 μm and a ZD direction thickness of 0.01 to 3 μm.

The biodegradable film of the present invention may be a single layer or a plurality of layers. The multilayer film has two or more layers. Since different layers may have different functions, multilayer films can provide a wide variety of needs as compared to single layer films.

The polyhydroxyalkanoate resin A may contain a homopolymer or copolymer of the following monomer units: 2-hydroxybutyric acid, 3-hydroxyvaleric acid, 3-hydroxycaproic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxydodecanoic acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, and the like. Specifically, the polyhydroxyalkanoate resin A contains one or more of polyhydroxybutyrate, polyhydroxyvalerate, polyhydroxycaproate, polyhydroxycaprylate, polyhydroxypelargonate, polyhydroxylaurate, polyhydroxyvalerate, polyhydroxybutyrate hydroxycaproate, polyhydroxybutyrate hydroxypelargonate and polyhydroxybutyrate hydroxylaurate.

In the above polyhydroxyalkanoate resin a such as polyhydroxybutyrate hydroxyvalerate, polyhydroxybutyrate hydroxycaproate, the ratio of the copolymerization components may be selected according to actual needs, and the copolymerization structure may be random, block or both.

From the standpoint of high production efficiency and good comprehensive properties, the polyhydroxyalkanoate resin A is preferably one or more of polyhydroxybutyrate, polyhydroxybutyrate hydroxyvalerate and polyhydroxybutyrate hydroxycaproate. Wherein, in the polyhydroxybutyrate hydroxyvalerate, the content of the hydroxyvalerate copolymerized units can be selected according to actual needs, such as below 10 weight percent; the content of the hydroxycaproic acid copolymerized units in the polyhydroxybutyrate hydroxycaproate may be selected according to practical requirements, for example, from 5 to 15% by weight.

The polyhydroxyalkanoate resin A provides the biodegradable film with good biodegradability. The biodegradable resin B is matched with the polyhydroxyalkanoate resin A, so that the biodegradability of the biodegradable film is not greatly reduced, and meanwhile, the processability, the use performances such as thermal performance and mechanical performance are improved.

The biodegradable resin B is a polymer having a glass transition temperature of 20 ℃ or higher and is generally considered to have biodegradability, and particularly, is a polymer composition having a relative biodegradation rate of 90% or higher within 6 months when evaluated for biodegradability under the conditions specified in GB/T19277.1-2011. Wherein the relative biodegradation rate is a percentage of the sample's biodegradation rate and the reference material's biodegradation rate. The biodegradable resin B may contain one or more of aliphatic polyesters, aliphatic aromatic polyesters, aliphatic polycarbonates, and further, may contain one or more of polylactic acid, polyglycolic acid, cellulose, or copolymers of these polymers, under the conditions conforming to the above definition.

The polylactic acid (PLA) is one or more of a homopolymer or a copolymer of lactic acid. Polylactic acid can be obtained by dehydration polycondensation of lactic acid or other substances as a raw material; can also be obtained from lactide and other substances through ring-opening polymerization. Among them, as lactide, there may be mentioned L-lactide which is a cyclic dimer of L-lactic acid, D-lactide which is a cyclic dimer of D-lactic acid, meso-lactide obtained by cyclic dimerization of D-lactic acid and L-lactic acid, or DL-lactide which is a racemic mixture of D-lactide and L-lactide. Any of the aforementioned lactides may be used in the present invention. For copolymers of lactic acid, the copolymerized units include lactic acid copolymerized units and non-lactic acid copolymerized units, preferably containing 85 to 99mol% of L-lactic acid and/or D-lactic acid copolymerized units; the non-lactic acid copolymerization unit is preferably one or more of hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxyoctanoic acid, glycolide and caprolactone.

The polyglycolic acid (PGA) is a polyglycolic acid-containing-CH ₂ COO-repeat unit polymers, which are usually synthesized from glycolic acid or glycolide, also known as polyglycolic acid, polyglycolide.

The cellulose is macromolecular polysaccharide composed of glucose, and comprises methyl cellulose, carboxymethyl cellulose, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cyanoethyl cellulose, benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose, phenyl cellulose and the like.

Further, from the viewpoint of improving processability, mechanical properties, use properties such as thermal properties, and storage stability, it is preferable that the biodegradable resin B contains polylactic acid.

Preferably, the polylactic acid has a number average molecular weight of 5 ten thousand or more. Further, it is preferably 8 ten thousand or more, and most preferably 10 ten thousand or more.

Further, from the viewpoint of improving the biodegradability, processability, mechanical properties and the like, it is preferable that the polylactic acid contains at least two kinds of optical purities, and the weight ratio of the polylactic acid having an optical purity of 97% or more to the polylactic acid having an optical purity of 96% or less is 40: 60-90: 10. the optical purity is the percentage of the compound stereoisomer accounting for the total amount, and the percentage of the polylactic acid, namely the L-lactic acid accounting for the total lactic acid amount. The optical purity can be measured by polarimeter with an accuracy of 1%.

In the biodegradable film of the present invention, the polyhydroxyalkanoate resin A is contained in an amount of 76 wt% or more, preferably 80 wt% to 95 wt%. If the content of the polyhydroxyalkanoate resin A is too small, the biodegradable film has better processability and usability, but the biodegradability may be reduced; if the content of the polyhydroxyalkanoate resin a is too large, the processability and the usability of the biodegradable film are poor.

In the biodegradable film of the present invention, one or more additives such as a filler, a plasticizer, a compatibilizer, a capping agent, a chain extender, a flame retardant, a hydrolysis aid, a nucleating agent, an antioxidant, a lubricant, an antistatic agent, an antifogging agent, a light stabilizer, an ultraviolet absorber, a pigment, a mold inhibitor, an antibacterial agent, or a foaming agent may be used within a range that does not hinder achievement of the object of the present invention.

The filler has the effects of improving processability, increasing weight, improving surface roughness and the like. Fibrous, platelet, granular, or powder fillers commonly used in the rubber and plastic industry, including inorganic or organic fillers, may be used. The inorganic filler may be specifically one or more of fibrous inorganic fillers such as glass fibers, asbestos fibers, carbon fibers, graphite fibers, metal fibers, potassium titanate whiskers, aluminum borate whiskers, magnesium whiskers, silicon whiskers, wollastonite, sepiolite, asbestos, slag fibers, xonotlite, silica apatite, gypsum fibers, silica/alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, or boron fibers, or one or more of flaky or particulate inorganic fillers such as glass flakes, non-swellable mica, graphite, metal foil, ceramic beads, talc, clay, mica, sericite, zeolite, bentonite, vermiculite, montmorillonite, dolomite, kaolin, fine silicic acid, feldspar powder, potassium titanate, fine hollow glass spheres, calcium carbonate, magnesium carbonate, calcium sulfate, titanium dioxide, boehmite, alumina, silica, gypsum, samite, dawsonite, or clay. The organic filler is specifically one or more of vegetable fibers such as starch, cellulose, sisal fibers, bamboo fibers, animal fibers such as wool fibers, organic synthetic fibers such as aramid fibers, and aromatic polyester fibers. The filler may be subjected to any form of surface treatment to enhance interfacial adhesion with the resin.

The plasticizer has the purpose of improving the toughness, the elongation and the processability of the film. Examples of the acid ester include, but are not limited to, hydroxybenzoates such as 2-ethylhexyl hydroxybenzoate, polyhydric alcohol esters such as acetic acid esters of ethylene oxide adducts of glycerol, phthalic acid esters such as di-2-ethylhexyl phthalate, adipic acid esters such as dioctyl adipate, maleic acid esters such as di-n-butyl maleate, citric acid esters such as tributyl acetylcitrate, alkyl phosphoric acid esters such as tricresyl phosphate, tricarboxylic acid esters such as trioctyl trimellitate, esters of succinic acid and triethylene glycol monomethyl ether, esters of adipic acid and diethylene glycol monomethyl ether, alkyl ether esters of polycarboxylic acids such as esters of 1,3, 6-hexanetrioic acid and polyethylene glycol monomethyl ether, acetylated polyoxyethylene alkyl (alkyl carbon number of 2-15) ethers such as acetylated polyoxyethylene hexyl ether, polyethylene glycol diacetate having an addition mole number of ethylene oxide of 3 to 20, polyethylene oxide-1, 4-butanediol ether diacetate, polyethylene glycol, polypropylene glycol, polyether such as polyethylene glycol, polyethylene glycol or polyethylene-polypropylene glycol copolymer, soybean oil, or copolymer of the chemical structure of the same. Preferably one or more of dioctyl phthalate, dibutyl phthalate, butyl benzyl phthalate, dioctyl sebacate, dibutyl sebacate, tributyl citrate, triethyl citrate, acetyl tributyl citrate, glyceryl triacetate, polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol copolymer, polylactic acid-ethylene glycol copolymer, polylactic acid-propylene glycol copolymer, soybean oil, or epoxidized soybean oil. The above plasticizers may be used alone or in combination of two or more.

The compatibilizer has the effects of reducing the phase size of two incompatible (or partially compatible) polymers, changing the phase dispersion structure and improving various properties of the material. Examples of the compound include a compound containing one or more of an epoxy functional group, an isocyanate functional group, a carbodiimide functional group, an acid anhydride functional group, a silane functional group, an oxazoline functional group, and a phosphite functional group, and the total number of the functional groups contained in the compound is two or more. Specifically, the compatibilizer may be one or more of toluene diisocyanate, diphenylmethane diisocyanate, p-xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, lysine triisocyanate, gamma-glycidoxypropyl trimethoxysilane, polycarbodiimide, ethylene-acrylate-maleic anhydride terpolymer, and acrylate polymer having an epoxy functional group, and non-reactive compatibilizers such as block copolymers, graft copolymers, random copolymers, and homopolymers may be mentioned.

Examples of the blocking agent include a compound containing one of an epoxy functional group, an isocyanate functional group, a carbodiimide functional group, an acid anhydride functional group, a silane functional group, an oxazoline functional group, and a phosphite functional group, and the total number of the functional groups contained in the compound is one.

The chain extender plays a role in increasing the molecular weight of the polymer, and the chemical structure of the chain extender is similar to that of the reactive compatibilizer.

The hydrolysis auxiliary agent plays a role in promoting the hydrolysis of the polymer. Examples of the compound include compounds containing at least one of a carboxyl group, an acid anhydride group, a sulfonic acid group, a hydroxyl group, and an amine group. Carboxylic acids are organic compounds containing a carboxyl group. Examples thereof include monoacids such as acetic acid, butyric acid and stearic acid, dibasic acids such as succinic acid, adipic acid and sebacic acid, and polybasic acids such as citric acid. Examples of the carboxylic acid include saturated carboxylic acids such as lauric acid, myristic acid and palmitic acid, and unsaturated carboxylic acids such as oleic acid, docosahexaenoic acid and maleic acid. Anhydrides are organic compounds containing anhydride groups. Examples thereof include saturated carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride and n-hexane anhydride, and unsaturated carboxylic acid anhydrides such as butene anhydride and maleic anhydride. Preferably, the number of carbon atoms of the carboxylic acid and/or carboxylic anhydride is 4 or more. More preferably, the carboxylic acid is one or more of succinic acid, 2-methyl-2-hydroxysuccinic acid, propylsuccinic acid, glutaric acid, 2-methyl-glutaric acid, 3-methyl-glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, galactaric acid, citric acid, cyclohexane carboxylic acid, benzoic acid, naphthoic acid, tetrahydrosuccinic acid, tetramethylsuccinic acid, aminopentanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, aminocaprylic acid, isooctanoic acid, nonanoic acid, aminononanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, docosylic acid, tetracosanoic acid, hexacosanoic acid, triacontanoic acid, erucic acid, linoleic acid, linolenic acid, cinnamic acid, isocinnamic acid, eleonic acid, eleostearic acid, ricinoleic acid, and the carboxylic anhydride is one or more of maleic anhydride, phenoxyacetic anhydride, phthalic anhydride, polyanhydride, and maleic anhydride. Further preferably, the carboxylic acid is one or more of succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, cyclohexane carboxylic acid, benzoic acid, naphthalene carboxylic acid, and the carboxylic anhydride is one or more of succinic anhydride, glutaric anhydride, benzoic anhydride, maleic anhydride, phenoxyacetic anhydride, phthalic anhydride, polysebacic anhydride, and maleic anhydride-containing copolymers.

The biodegradable film of the present invention is obtained by dispersing a biodegradable resin B in a polyhydroxyalkanoate resin A in the form of a dispersed phase having an average length of 0.1 to 20 μm and a thickness in the ZD direction of 0.01 to 3 μm in at least one layer when observed by a transmission electron microscope in a cross-section. The biodegradable film having the above structure is less susceptible to the biodegradability of the biodegradable resin B, maintains the biodegradability of the polyhydroxyalkanoate resin a to the maximum extent, and has significantly improved processability and service performance compared with the polyhydroxyalkanoate resin a. Wherein the ZD direction refers to the thickness direction of the film. Preferably, at least in one layer, the biodegradable resin B is dispersed in the polyhydroxyalkanoate resin A in the form of a dispersed phase having an average length of 0.5 to 10. Mu.m, more preferably 1 to 5. Mu.m, and a thickness in the ZD direction of 0.1 to 2. Mu.m.

Further, the biodegradable film of the present invention has a relative biodegradation rate of 90% or more within 12 months when evaluated for home compost degradability at 28℃under the conditions specified in ASTM D5338-15. Namely, the biodegradable film has the property of degrading household compost, is easy to degrade in the environment, and does not cause environmental pollution.

Further, the biodegradable film of the present invention has excellent heat resistance, and preferably has a heat shrinkage of 10% or less in at least one direction after 30 minutes treatment at 120 ℃. When plastic films are formed into packaging films, tapes, and the like, it is often necessary to apply, vapor-deposit, heat-seal, and the like to the films, and it is necessary to heat the films. The heat shrinkage refers to the shrinkage of the film in a certain direction after treatment at a certain temperature and time. If the heat shrinkage rate is large, obvious dimensional change can occur in the processing process of the film, so that the appearance of the product is poor, even the processing cannot be finished, and the like. Since the length and width of a film are much larger than the thickness, the heat shrinkage in a certain direction in a plane composed of the length and width is often measured. In fact, the heat shrinkage of the film tends to be different in different directions, the difference depending on the composition of the film, the production method, and the like. The biodegradable film of the present invention preferably has a heat shrinkage of 8% or less in at least one direction after 30 minutes at 120 ℃. Further preferably, the heat shrinkage in at least one direction is 8% or less, and the heat shrinkage in a direction perpendicular to the direction is 6% or less. Preferably, the heat shrinkage in at least one direction is 6% or less. Further preferably, the heat shrinkage in at least one direction is 6% or less, and the heat shrinkage in a direction perpendicular to the direction is 4% or less.

It is common to use the film travelling direction during the film making process as the Machine Direction (MD) and the direction perpendicular to the machine direction as the Transverse Direction (TD).

The thickness of the biodegradable film is not particularly limited, and may be generally 1 μm to 1mm, preferably 5 μm to 100. Mu.m.

Further, in order to improve uniformity of use properties such as mechanical properties, the thickness variation coefficient of the biodegradable film is 10% or less, preferably 5% or less. The thickness variation coefficient is the ratio of the standard deviation of the thickness to the average thickness.

Further, in order to improve the use performance, the biodegradable film has a tensile strength of 50MPa or more, an elongation at break of 20% or more, and a tensile elastic modulus of 4500MPa or less in at least one direction. Preferably, the elongation at break is 100% or more and the tensile elastic modulus is 3000MPa or less.

Further, it is preferable that the biodegradable film has good transparency. The biodegradable film has a total light transmittance of 90% or more, and/or a haze of 40% or less, and/or an internal haze of 10% or less. Preferably, the biodegradable film has a haze of 10% or less, and/or an internal haze of 8% or less. Most preferably, the biodegradable film has a haze of 6% or less, and/or an internal haze of 6% or less.

Further, in order to improve the heat resistance of the biodegradable film, it is preferable that at least one direction of the biodegradable film has a heat deformation rate of-10% to +10%, preferably-5% to +5%, when the temperature is raised from 25 ℃ to 150 ℃ at 5 ℃/min under a load of 9.8 mN/(3 mm×20 μm). In the present invention, the 120℃heat distortion rate was measured by a thermo-mechanical analyzer (TMA).

Further, in order to improve the heat resistance of the biodegradable film, it is preferable that the biodegradable film has a shrinkage stress of not more than 2.5 mN/. Mu.m at 120℃when the temperature is raised from 25℃to 150℃at 5℃per minute in at least one direction. In the present invention, the 120℃shrinkage stress was measured by a thermo-mechanical analyzer (TMA).

Further, in order to improve the smooth feeling during use and to improve the barrier property in cooperation with the vapor deposition layer when used as a barrier packaging material, the biodegradable film has at least one surface with a roughness Ra of 0.4 μm or less. Preferably, the roughness of both surfaces is 0.4 μm or less.

Further, in order to improve the processability of the film during coating, winding and the like, the dynamic friction coefficient of at least one surface of the biodegradable film is 0.2 to 0.8.

The biodegradable film of the present invention may be produced by known molding methods such as extrusion, casting, molding, blow molding, calendaring, unidirectional stretching, biaxial stretching, etc., and may be produced by further heat treatment.

Preferably by extrusion, casting, biaxially oriented processes. For example, extruding single-layer melt through one extruder or carrying out multi-layer coextrusion through a plurality of extruders to obtain multi-layer melt, casting the multi-layer melt on a casting roller to form an unoriented casting film, and then carrying out unidirectional or bidirectional stretching and heat treatment to form the biodegradable film.

The casting is carried out by using a casting roller with lower temperature, but for certain film formulations, the too low temperature can lead to adhesion between the film and the casting roller, and the next process cannot be carried out smoothly. And too high a temperature of the casting roll may reduce the cooling efficiency of the melt, so that the film is crystallized and the next process cannot be smoothly performed. Preferably, the surface temperature of the casting roll is 25 ℃ or less, preferably 5 to 20 ℃.

Unidirectional stretching is typically accomplished by stretching the film in the direction of travel (i.e., MD) by rollers having different rotational speeds at a temperature.

Biaxial stretching generally includes stretching in the MD and TD directions. Stretching in the MD direction is the same as that in the unidirectional stretching. The TD stretching is accomplished by heating and advancing the film in the drying tunnel while holding the edge of the film to expand the width. The biodegradable film of the present invention is preferably prepared by biaxial stretching from the viewpoint of improving the performance and production efficiency thereof.

The temperature, speed and multiplying power of unidirectional or bidirectional stretching have important influence on the service performance of the film.

For the biodegradable film of the present invention, if the stretching temperature is too low, the film is difficult to achieve the required multiplying power, and breakage may occur; when the stretching temperature is too high, the film is more likely to crystallize during stretching, resulting in a decrease in properties such as elongation at break. The stretching temperature is preferably 60℃to 75 ℃.

For the biodegradable film of the present invention, uniformity of stretching temperature in the width direction has a great influence on thickness uniformity of the film. Generally, the better the temperature uniformity, the better the thickness uniformity.

If the stretching ratio is too low, the film is insufficiently oriented, the stretching strength and elongation at break are reduced, the stretching ratio is too high, the film is at risk of being damaged, the stretching strength and elongation at break are also reduced, and the heat shrinkage is increased. In addition, in the biaxially stretched film, in order to balance the performances in the MD and TD directions, the difference in stretch ratio in the MD and TD directions is preferably between-100% and +200%, and more preferably between-50% and +100%.

After unidirectional or bidirectional stretching is finished, heat treatment is often needed to be carried out on the film so as to reduce defects in the film, reduce the heat shrinkage rate and balance the performances of the film in the MD direction and the TD direction. The heat treatment is carried out at a higher temperature and can be accompanied by a certain degree of relaxation in the width direction, so that the defects in the film are further reduced and the heat shrinkage is reduced. The heat treatment may be performed in a plurality of regions at the same or different temperatures. When the heat treatment temperature is too high, the preparation process of the film is unstable, so that the thickness uniformity is reduced, and the production efficiency is reduced; when the heat treatment temperature is too high, the heat shrinkage of the film will be high. Preferably, the heat treatment is performed in 2 or more zones, and the temperature is 120 to 135 ℃, preferably 125 to 130 ℃, respectively. The relaxation rate is generally 1% to 20%, preferably 5% to 15%. The relaxation rate is too high, the preparation process of the film is unstable, the relaxation rate is too low, and the effect of reducing the heat shrinkage rate cannot be achieved.

In view of the need to balance the biodegradability with the usability such as mechanical properties, surface properties, heat shrinkability, etc., when the biodegradable film has a multilayer structure, it is preferable to have a thicker intermediate layer and thinner 2 surface layers. The middle layer is the main body of the film, and the mechanical property and the thermal property of the film are determined to a great extent. The surface layer mainly provides the film with surface properties. The components of the two surface layers can be the same or different; the intermediate layer and any one of the surface layers may have the same composition or may have different compositions.

The thickness of the intermediate layer and the surface layer can be changed according to actual needs, and in general, the thickness of the surface layer is 0.5 μm to 5 μm.

The biodegradable film of the present invention may be subjected to various surface treatments for the purpose of improving printability, laminating suitability, coating suitability, and the like. Examples of the surface treatment include corona discharge treatment, plasma treatment, flame treatment, acid treatment, and release treatment.

The invention also provides a packaging material containing the biodegradable film. The packaging material specifically comprises a film for foods, medical products and other articles.

The thickness of the packaging material is not particularly limited, and may be generally 1 μm to 1mm, preferably 5 μm to 100 μm.

Further, the packaging material of the present invention may contain one or more of a vapor deposition layer, a heat sealing layer, an adhesive layer, and an adhesive layer, in addition to the biodegradable film of the present invention.

The vapor deposition layer is formed of at least 1 vapor deposition material selected from the group consisting of metal, metal oxide, and silica, and thus, the presence of such a vapor deposition layer can suppress ingress and egress of moisture, oxygen, carbon dioxide, or other gases, and can improve barrier properties, mechanical properties, and appearance of the base film.

The heat sealing layer is a film layer containing thermoplastic or thermosetting resin, and the film layer is connected with the opposite film layer in a melting and solidifying mode under the condition of low heating and pressurizing so as to form a sealing structure.

The adhesive layer is a solid, semi-solid or liquid layered material containing an adhesive that can be easily separated again after bonding, such as acrylic, rubber, polyurethane adhesives, etc., for connecting different layers of the multilayer film or connecting the multilayer film with other articles.

The adhesive layer is made of a solid, semi-solid or liquid layered material which can be cured by heating or other means, and is different from the adhesive layer in that the adhesive layer cannot be easily separated after being cured, and the adhesive layer comprises one or more of a curing adhesive, a thermosetting resin and a thermoplastic resin, and is used for connecting different layers of the multilayer film.

The invention also provides an adhesive tape containing the biodegradable film. The adhesive tape comprises at least one substrate layer, the biodegradable film provided by the invention and at least one adhesive layer. The adhesive tape can be used in the fields of packaging, express delivery, automobile manufacturing, electronic and electric product manufacturing, building decoration, office stationery, medical and sanitary products and the like.

The biodegradable film has the advantages of high biodegradation speed and good usability, particularly has good heat resistance and low heat shrinkage, can meet the requirement on dimensional stability during processing such as coating, evaporation, heat sealing and the like, and can be suitable for various fields including packaging, express delivery, transportation and the like.

Detailed Description

The present invention will be further understood from the following specific examples of the present invention and comparative examples, but the scope of the present invention is not limited thereby.

The materials used in the examples and comparative examples are as follows:

a: polyhydroxybutyrate hydroxycaproate (PHBH), manufactured by Beijing blue Crystal microorganism technology Co., ltd., glass transition temperature of 0 ℃, melting point of 116 ℃, 135 ℃, hydroxycaproic acid structural unit content of 9mol%, biomass material.

B1: polylactic acid, manufactured by Nature orks, U.S.A., specification: 4032D, number average molecular weight 11 ten thousand, biomass material, optical purity: 98% and glass transition temperature 62 ℃.

B2: polylactic acid, manufactured by Nature orks, U.S.A., specification: 4060D, number average molecular weight 11 ten thousand, biomass material, optical purity: 78% and a glass transition temperature of 59 ℃.

C1: sebacic acid, manufactured by chinese national reagent company, specification: AR, biomass material, is used as a hydrolysis aid.

C2: zinc stearate, manufactured by ala Ding Shiji company, china, specification: AR, a non-biomass material, is used as a catalyst.

And C3: epoxy compound, manufactured by BASF corporation, germany, specification: joncryl ADR 4468, a non-biomass material, is used as a chain extender, compatibilizer.

The raw materials and samples used in the examples and comparative examples were tested according to the following experimental methods. Unless specifically indicated, the test conditions were uniformly 23 ℃.

Number average molecular weight: the measurement was performed using Agilent 1260 Gel Permeation Chromatography (GPC) using methylene chloride as the mobile phase, 3 times, and the average was taken.

Optical purity: the polylactic acid in the sample was extracted, and the average value of the specific rotation of the polylactic acid in the extracted sample was obtained by measuring 6 times using SAC-i type full-automatic polarimeter of ATAGO Co., japan with methylene chloride as a solvent. The optical purity was calculated as follows, with the specific rotation of the PLLA standard being-156 °.

Optical purity = 100% x average of sample specific rotations/specific rotations of PLLA standard

Morphology observation: ultrathin sheets having a thickness of about 70nm or less were prepared along the MD/ZD direction or TD/ZD direction of the film sample using an ultrathin microtome, and then observed by a Transmission Electron Microscope (TEM). Using image processing software, 100 biodegradable resin B dispersed phases were counted. The maximum value of the distance in the ZD direction of each disperse phase is taken as the thickness in the ZD direction of each disperse phase, and the maximum value of the distance in the MD direction or the TD direction is taken as the length in the MD direction or the TD direction of each disperse phase. And calculating the average value of the ZD direction thickness, the MD direction length and the TD direction length of all the disperse phases.

Film processability: preparing a biaxially oriented film by the method described in the example, wherein the biaxially oriented film can be prepared, and the film has good processability and is marked as O; otherwise, the film processability was poor, which was marked as X.

Degradability of household compost: the composting temperature was 28.+ -. 2 ℃ and the remaining conditions were evaluated for biodegradability according to the conditions specified in ASTM D5338-15. The relative biodegradation rate reaches more than 90% within 12 months, which is marked as O, and the household compost degradability is realized; otherwise, the composition was marked as X without home compost degradability.

Heat shrinkage rate: and (3) taking a film sample with the MD multiplied by TD size not smaller than 300mm multiplied by 300mm, selecting a position without obvious defects at the center of the film, and cutting test bars with the length of 150mm and the width of 10mm, wherein the lengths are respectively along the MD direction or the TD direction. Two points 10 cm.+ -. 0.5cm away were marked on each test bar and the exact distance between the two points was measured with a Nikon PROFILE PROJECTORV-12B universal projection tester with an accuracy of 0.1mm. The sample bar is hung in a blast oven by a dovetail clamp, a weight with the weight of 3g is added and held at the other end of the sample bar, and the holding part is arranged at the outer sides of the two marking points. After heating the sample at 120℃for 30min, it was cooled to room temperature, and the exact distance between the two mark points was again measured with a universal projection tester with an accuracy of 0.1mm. The test was repeated for 5 bars, and the heat shrinkage was calculated as follows: heat shrinkage= (distance before heating-distance after heating)/distance before heating×100%.

Heat distortion rate at 120 ℃): a film sample with MD X TD dimension not less than 300mm X300 mm is taken, a defect-free part is selected in the center of the film, and test bars with length more than 10mm and width 3mm are cut, wherein the length direction is MD direction or TD direction. The thermo-mechanical analyzer of the TMA-SS7100 type was used to test under the following conditions: the initial temperature was 25℃and the final temperature was 155℃at a heating rate of 5℃per minute, the initial holding length was 10mm (in the longitudinal direction of the sample), and the stretching force was 9.8 mN/(3 mm. Times.20 μm) remained unchanged. Shrinkage stress = shrinkage force/thickness. The length direction is MD direction, and is marked as MD thermal deformation rate; the length direction was the TD direction, and was noted as the TD heat distortion rate. The test was repeated 3 times for each direction and the average was plotted. The heat distortion rate at 120℃was read and was set to +in terms of dimensional shrinkage.

Shrinkage stress at 120 ℃): a film sample with MD X TD dimension not less than 300mm X300 mm is taken, a defect-free part is selected in the center of the film, and test bars with length more than 10mm and width 3mm are cut, wherein the length direction is MD direction or TD direction. The following conditions were used for testing using a thermo-mechanical analyzer (TMA) model TMA-SS 7100: the initial temperature is 25 ℃, the end temperature is 155 ℃, the heating speed is 5 ℃/min, and the holding length (the length direction of the sample) is 10 mm. The length direction is MD direction and is marked as MD shrinkage stress; the length direction is the TD direction and is denoted as TD shrinkage stress. The test was repeated 3 times for each direction and the average was plotted. The shrinkage stress at 120℃was read and the stress in the shrinkage direction was +A.

Thickness and thickness coefficient of variation: the thickness of each of the 9 positions was measured using a model 7050 thickness meter of Sanyo instruments, and the average value was used as the thickness of the sample. And calculating the thickness variation coefficient according to the following steps:

thickness coefficient of variation = standard deviation of thickness/thickness x 100%

Transparency: the haze and light transmittance of a 5 cm. Times.5 cm sample were measured using a Japanese SUGA haze meter HZ-V3 with D65 as a light source. A sample of 3cm by 5cm was placed in a cuvette containing absolute ethanol, and the haze was measured as the internal haze using D65 as a light source.

Surface roughness: a sample of 5cm by 5cm was taken, and the arithmetic average height Ra of both surfaces of the film sample was measured as surface roughness using a non-contact surface measuring machine VertScan-R5300 of Ryoka corporation, japan.

Coefficient of dynamic friction: HEIDON surface Performance tester TYPE was used: 14 measurement. The coefficient of dynamic friction between the same surface and surface of the sample was measured using an ASTM flat die attachment and a 200g load weight, with the number of parallel samples n=5, taking the average value as the coefficient of dynamic friction of the sample. The dynamic friction coefficients of the two surfaces were tested separately.

Tensile strength, elongation at break, tensile elastic modulus: test pieces 150mm by 10mm in size were manufactured from DUMBBELL SD-100 test piece manufacturing machine. The tensile strength, elongation at break and elastic modulus of the test piece were measured by a tensile tester AG-IS 1KN manufactured by Shimadzu corporation, the intercept was 50mm, and the tensile speed was 100mm/min. The test was repeated 5 times and the average was taken.

Water content: 0.5g of the sample was placed in a sample compartment of a solid moisture tester (HT 3 type, manufactured by Aboni Corp., germany) and tested for moisture content at 130 ℃. Moisture content = weight of water detected/weight of resin. The test was repeated 3 times and the average was taken.

Examples 1 to 11, comparative example 1

The proportions and preparation conditions are shown in Table 1.

< preparation of raw materials >

If only one raw material is contained, the subsequent process is directly carried out.

If two or more raw materials are contained, all the raw materials are dried by a dryer until the water content is below 200ppm (weight ratio), and then blended by an extruder and pelletized to obtain the blended resin raw material.

< preparation of cast film >

The raw material prepared in the previous step is dried to a water content of 200ppm by weight or less by using a dryer. The melt was extruded under the conditions shown in the table, cast on a casting roll, and cooled to give an unoriented cast film.

< MD stretching >

The unoriented cast film was first stretched in the MD direction according to the conditions shown in the table.

< TD stretching >

The MD stretched film was heated in the drying tunnel under the conditions shown in the table and then subjected to TD stretching.

< Heat treatment >

And (3) carrying out heat treatment on the TD stretched film, wherein the heat treatment is divided into 3 areas, so that the temperature can be independently controlled, and meanwhile, the relaxation rate in the TD direction can be controlled. And finally, rolling to obtain a film sample.

The surface of the film contacting the casting roll is the A surface, and the reverse surface is the B surface. The average thickness of the prepared film was made 25 μm by controlling the output of the extruder and the line speed of the casting and stretching equipment.

The biodegradable films of each example and comparative example were subjected to performance test, and the results are shown in Table 2.

Example 6 is a better technical scheme, and has the advantages of high biodegradation speed and good service performance, and particularly has good heat resistance, low heat shrinkage and good transparency.

On the basis of example 6, examples 1 to 4 changed the contents of A, B1 and B2, and it can be seen that the biodegradation time of the film increases, the transparency decreases, and the mechanical properties are also affected as the contents of B1 and B2 increase.

On the basis of example 6, example 5 did not use C1 to C3, resulting in an increase in the size of the dispersed phase, an increase in the heat shrinkage, and a decrease in transparency and mechanical properties.

In examples 7 and 8, the heat treatment temperature was lowered in addition to example 6, and the mechanical properties were improved, but the heat shrinkage was also greatly improved.

On the basis of example 6, example 9 increased the heat treatment temperature, and although the heat shrinkage was somewhat reduced, the preparation process was unstable, the thickness uniformity was deteriorated, and the mechanical properties were also greatly reduced.

On the basis of example 6, examples 10 and 11 increased the casting roll temperature, resulting in a significant decrease in transparency and mechanical properties.

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Claims (14)

1. A biodegradable film comprising a polyhydroxyalkanoate resin A and a biodegradable resin B having a glass transition temperature of 20 ℃ or higher, wherein the polyhydroxyalkanoate resin A is contained in an amount of 76 wt.% or more in the biodegradable film, and the biodegradable film is subjected to cross-sectional observation by a transmission electron microscope, and wherein the biodegradable resin B is dispersed in the polyhydroxyalkanoate resin A in the form of a dispersed phase having an average length of 0.1 to 20 [ mu ] m and a ZD-direction thickness of 0.01 to 3 [ mu ] m in at least one layer.

2. The biodegradable film according to claim 1, characterized in that said polyhydroxyalkanoate resin a contains one or more of polyhydroxybutyrate, polyhydroxyvalerate, polyhydroxycaproate, polyhydroxycaprylate, polyhydroxypelargonate, polyhydroxydodecanoate, polyhydroxybutyrate hydroxyvalerate, polyhydroxybutyrate hydroxycaproate, polyhydroxybutyrate hydroxypelargonate, polyhydroxybutyrate hydroxydodecanoate.

3. The biodegradable film according to claim 1, characterized in that said biodegradable resin B is one or more of polylactic acid, polyglycolic acid, cellulose or copolymers of these polymers.

4. The biodegradable film according to claim 1, characterized in that when evaluated for degradability in home compost at 28 ℃ according to the conditions specified in ASTM D5338-15, the relative biodegradation rate reaches 90% or more within 12 months.

5. The biodegradable film according to claim 1, characterized in that it has a thermal shrinkage of 10% or less in at least one direction after being treated at 120 ℃ for 30 minutes.

6. The biodegradable film according to claim 1, characterized in that the thickness variation coefficient is 10% or less.

7. The biodegradable film according to claim 1, characterized in that at least one direction has a tensile strength of 50MPa or more, an elongation at break of 20% or more and a tensile elastic modulus of 4500MPa or less.

8. The biodegradable film according to claim 1, characterized in that it has a haze of 10% or less.

9. The biodegradable film according to claim 1, characterized in that at least one direction has a heat distortion rate of-10% to +10% at 120 ℃ when the film is heated from 25 ℃ to 150 ℃ at 5 ℃/min under a load of 9.8 mN/(3 mm x 20 μm).

10. The biodegradable film according to claim 1, characterized in that the shrinkage stress at 120 ℃ is 2.5mN/μm or less when the temperature is raised from 25 ℃ to 150 ℃ at 5 ℃/min in at least one direction.

11. The biodegradable film according to claim 1, characterized in that at least one surface has a roughness Ra of 0.4 μm or less.

12. The biodegradable film according to claim 1, characterized in that at least one surface has a dynamic friction coefficient comprised between 0.2 and 0.8.

13. A packaging material comprising the biodegradable film according to any one of claims 1 to 12.

14. An adhesive tape comprising the biodegradable film according to any one of claims 1 to 12.