JP2007056195A - Vinyl chloride-based resin composition and stretch film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vinyl chloride-based resin composition having both excellent molding processability and mechanical strength, and to provide a stretch film. <P>SOLUTION: The polyvinyl chloride-based resin composition is obtained by using a polyvinyl chloride-based resin, wherein the polyvinyl chloride-based resin composition is obtained by adding (A) 10-20 parts by weight of adipic acid-based polyester plasticizer having 1,000-3,000 weight-average molecular weight, (B) 10-20 parts by weight of a mixed adipic acid ester-based plasticizer obtained by the reaction of ≥2 kinds of aliphatic alcohols having a ≤10C alkyl with adipic acid, and (C) 5-15 parts by weight of epoxidized plant oil to 100 parts by weight of the polyvinyl chloride-based resin, in which the resin has a weight average molecular weight (MW) expressed in terms of a polystyrene and measured by gel permeation chromatography (GPC) is 1.2×10<SP>5</SP>-2.2×10<SP>5</SP>and a ratio (MW/MN) of the weight average molecular weight (MW) to the number average molecular weight (MN) of 2.05-2.20, and the ratio of the contents of the plasticizer (A) and plasticizer (B), (A)/(B), is 0.5-1.6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polyvinyl chloride composition and a stretch film, and in particular, has excellent properties for food packaging despite the thin thickness of the film. Furthermore, it is specified in Ministry of Health and Welfare Notification No. 20 in 1982. The present invention relates to a polyvinyl chloride composition and a stretch film that are suitably used for stretch packaging with a small amount of n-heptane extract measured by the evaporation residue test method, and therefore, a low migration of plasticizers to fatty foods.

Many stretch films excellent in transparency, flexibility, and heat sealability have been developed and widely used as food packaging films for food packaging, particularly for fresh foods such as meat, fresh fish, and fruits and vegetables. Stretch film packaging methods include manual packaging using a handler upper, automatic packaging using a push-up type automatic packaging machine and a pillow type automatic packaging machine.
Due to the recent increase in interest in environmental problems, a film having a thinner film thickness and a smaller n-heptane extraction amount is required. In other words, with vinyl chloride resins conventionally used in stretch films, the mechanical strength of the film decreases when it is thinned, so the amount of plasticizer is reduced, but when the amount of plasticizer is reduced, the melt viscosity during molding increases. Heat generation occurs, coloring of the film occurs, and further progress causes a problem of decomposition in the molding machine. Therefore, there is a limit to reducing the plasticizer.
On the other hand, in order to improve the mechanical strength, a method of increasing the molecular weight (polymerization degree) of the vinyl chloride resin is generally known, but this method increases the melt viscosity of the material and stabilizes it. Therefore, a larger amount of plasticizer is required for the molding process, and even if the thickness can be reduced, the effect of low elution is reduced. On the other hand, in order to improve the fluidity at the time of molding, generally, a technique for lowering the molecular weight (polymerization degree) of vinyl chloride resin is known, but this method reduces the mechanical strength of the film. More generally, as the molecular weight of vinyl chloride resin decreases, the porosity (porosity) in the particles decreases, and the transportability of the raw material powder often decreases due to the decrease in the plasticizer absorbability during compounding. May cause unmelted spots.

  As a method for improving the mechanical strength and fluidity of vinyl chloride resin, for example, a method disclosed in Patent Document 1 has been proposed. This is a method of creating a vinyl chloride resin by a two-stage polymerization method in which repolymerization is performed by suspension polymerization using a vinyl chloride resin polymerized by a normal method as a seed resin. A method for producing a highly productive vinyl chloride polymer is provided. However, in this method, the morphological change of the vinyl chloride resin occurs during repolymerization, and the porosity (porosity) becomes small. For example, in a soft (transparent) formulation using a plasticizer, uneven absorption of the plasticizer is caused. When the resulting blend is molded, bumps and fish eyes are generated, which may cause poor appearance and reduced physical properties.

JP-A-11-349761

  Therefore, the present inventors have made extensive studies in view of the present situation, and as a result, have an average molecular weight in a specific range, and the ratio MW / MN of the weight average molecular weight (MW) and the number average molecular weight (MN) is It is found that the above problem can be solved by adding a specific plasticizer to a polyvinyl chloride resin that is in a specific range and further has a molecular weight distribution as described above, which is manipulated by use of a chain transfer agent and temperature control, The present invention has been completed.

The gist of the present invention is as follows.
1 In a composition consisting of a polyvinyl chloride resin, the weight average molecular weight (MW) measured by gel permeation chromatography (GPC) by a polystyrene conversion method is 1.2 × 10 ^{5 to} 2.2 × 10 ⁵ . The weight average molecular weight (MW) and the number average molecular weight (MN) ratio MW / MN is 100 to 3 parts by weight with respect to 100 parts by weight of the polyvinyl chloride resin. , Adipic acid type polyester plasticizer (A) 10-20 parts by weight, mixed adipic acid ester plasticizer obtained by reaction of two or more aliphatic alcohols having an alkyl group having 10 or less carbon atoms with adipic acid (B) 10 to 20 parts by weight, 5 to 15 parts by weight of epoxidized vegetable oil (C) are added, and the ratio (A) / (B of the addition amount of the plasticizer (A) and the plasticizer (B). There polyvinyl chloride resin composition, characterized in that in the range of 0.5 to 1.6.
2. A vinyl chloride resin composition having a broad polymerization degree distribution by use of a chain transfer agent and temperature control.
(3) The above 1 or 3, wherein the thickness of the film is 8 μm or less, and the n-heptane extraction amount measured by the evaporation residue test method stipulated in Ministry of Health and Welfare Notification No. 20 in 1982 is 40 mass ppm or less A stretch film comprising the polyvinyl chloride resin composition according to 2.

  The stretch film made of the polyvinyl chloride composition obtained by the present invention is suitably used for food container packaging, and in particular, is excellent in food packaging characteristics despite being thin, and also has the Ministry of Health, Labor and Welfare Notification No. 20 It is possible to obtain a polyvinyl chloride stretch film that has a small n-heptane extraction amount as defined in 1), and therefore has a low migration of plasticizers to fatty foods.

Hereinafter, the present invention will be described in detail, but the scope of the present invention is not limited to the embodiments described below.
The vinyl chloride resin in the present invention is a vinyl chloride homopolymer, a copolymer with a monomer copolymerizable with vinyl chloride (hereinafter referred to as vinyl chloride copolymer), and this vinyl chloride copolymer. Examples include graft copolymers obtained by graft copolymerization of vinyl chloride with other polymers, and these copolymers have lower mechanical properties when the content of constituent units other than vinyl chloride in the copolymer increases. Therefore, it is preferable to contain 60% by weight or more of vinyl chloride. Each polymer may be obtained by any polymerization method such as emulsion polymerization method, suspension polymerization method, solution polymerization method, bulk polymerization method, etc., each used alone or in combination of two or more polymers. Is done. As the monomer copolymerizable with vinyl chloride, any monomer having a reactive double bond in the molecule may be used. For example, α-olefins such as ethylene, propylene, butylene; vinyl acetate, propionic acid Vinyl esters such as vinyl; vinyl ethers such as butyl vinyl ether and cetyl vinyl ether; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; esters of acrylic acid or methacrylic acid such as methyl acrylate, ethyl methacrylate, and phenyl methacrylate Aromatic vinyls such as styrene and α-methylstyrene; vinyl halides such as vinylidene chloride and vinyl fluoride; N-substituted maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; Is a single type or a combination of two or more types Used in combination.

  The polymer other than the vinyl chloride copolymer may be any polymer that can be graft copolymerized with vinyl chloride, such as an ethylene-vinyl acetate copolymer, an ethylene-vinyl acetate / carbon monoxide copolymer, Ethylene-ethyl acrylate copolymer, ethylene-ethyl acrylate / carbon monoxide copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, acrylonitrile-butadiene copolymer, polyurethane, chlorinated polyethylene, chlorinated Polypropylene etc. are mentioned, These are used individually by 1 type or in combination of 2 or more types.

As the dispersant, general partially saponified polyvinyl acetate, water-soluble partially saponified polyvinyl acetate, cellulose derivative, gelatin, nonionic surfactant, anionic surfactant, etc. are usually used for suspension polymerization of vinyl chloride. A dispersant can be used.
As the polymerization initiator, an oil-soluble polymerization initiator generally used for suspension polymerization of vinyl chloride, such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxypivalate, dioctyl peroxydicarbonate, diisopropyl peroxydicarbonate, t-butyl. Organic peroxides such as peroxyneodecanoate and α-cumylperoxyneodecanoate, azo compounds such as azobis (dimethylpareronitrile), and the like are used. These polymerization initiators are generally used in an amount of 0.01 to 0.50% by weight based on the vinyl chloride monomer.

The vinyl chloride monomer alone or a mixture of copolymerizable monomers mainly composed of the vinyl chloride monomer may be charged all at once before starting the polymerization, or a part of the vinyl chloride monomer. Can be charged before the start of polymerization, and the remainder can be charged continuously or intermittently after the start of polymerization.
The polymerization temperature varies depending on the type of polymerization initiator to be used, the polymerization method, and the target degree of polymerization (molecular weight), but is generally in the range of 0 to 90 ° C, particularly 40 to 70 ° C.
In the reaction, a normal constant temperature polymerization method may be employed, or a continuous temperature elevation polymerization method may be employed. The operations such as dehydration and drying of the generated vinyl chloride polymer slurry employ conventional means such as centrifugal dehydration and fluidized drying, and can easily handle a vinyl chloride heavy polymer having a water content of 0.1% or less. Coalescence can be obtained.

The vinyl chloride resin in the present invention has a weight average molecular weight (MW) measured by gel permeation chromatography (GPC) by a polystyrene conversion method of 1.2 × 10 ^{5 to} 2.2 × 10 ⁵ and has a weight. The ratio MW / MN of the average molecular weight (MW) to the number average molecular weight (MN) needs to be in the range of 2.05 to 2.20. When the molecular weight is less than 1.2 × 10 ⁵ , mechanical properties such as tensile strength and elongation are not sufficient, and when the molecular weight exceeds 2.2 × 10 ⁵ , the melt viscosity becomes high and shear heat is generated during processing. It is easy to decompose and inferior in continuous productivity.
Also, by way MW / MN is less than 2.0 ^5, the spread of the polymerization degree distribution is sufficiently (broad)
However, when the MW / MN exceeds 2.20, mechanical properties such as tensile strength and elongation are not sufficiently exhibited and there is no significant difference from ordinary vinyl chloride resin. Cause. A more preferable MW / MN is 2.08 to 2.15. Incidentally, since the MW / MN of a commercially available vinyl chloride resin that does not manipulate the normal molecular weight distribution is about 2.00 ± 0.02, the spread of the molecular weight distribution can be determined from this index.

There are various methods for obtaining such a vinyl chloride resin, but in order to achieve this object, it is more preferable to start polymerization at a low temperature to polymerize a high polymerization degree component and to add a chain transfer agent. This is a method of increasing the low molecular weight component. Conversely, in the method of starting polymerization at a high temperature, polymerizing a low polymerization degree component, and adding a crosslinking agent to increase the high polymerization degree component, the shape of the obtained polymerization degree distribution is the same as that using the above chain transfer agent. A polymer can be obtained, but if a transparent molded product is produced using this polymer, bumps and fish eyes are generated, and the mechanical strength is also lowered.
The chain transfer agent that can be suitably used in the present invention may be those usually used at the time of polymerization of the vinyl chloride resin, and examples thereof include halogenated hydrocarbons, aldehydes, 2-mercaptoethanol, thioglycolic acid and the like. From the viewpoint of property and quality, 2-mercaptoethanol can be preferably used. Furthermore, antioxidants etc. can be used arbitrarily.
The polymerization mode may be bulk polymerization, suspension polymerization, emulsion polymerization, and the like, and may be appropriately selected according to the purpose such as productivity and quality.

  An adipic acid polyester plasticizer having an average molecular weight of 1,000 to 3,000 is used to improve solvent extraction resistance by increasing the entanglement with the polyvinyl chloride resin in the resin composition. Although it is a particularly effective component in the stretch film of the present invention, on the other hand, since it has a high molecular weight, it has a contradicting action such as low plasticization efficiency, low fluidity, and excellent extrudability. Also have. For this reason, it is preferable to use this polyester plasticizer in the minimum necessary addition amount, and the addition amount is 10 to 20 parts by weight with respect to 100 parts by weight of the polyvinyl chloride resin. If the amount is less than 10 parts by weight, the extraction resistance, which is the purpose of adding a polyester plasticizer, is not improved. If the amount exceeds 20 parts by weight, the plasticization efficiency is lowered, so that the transparency of the film is lowered. Since the fluidity of the product is lowered, extrusion molding with a uniform film thickness becomes difficult.

  Adipic acid-based polyester plasticizer is a reaction product of adipic acid and dihydric alcohol, and dihydric alcohol includes ethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, and adipic acid and one kind or Reaction products with two or more dihydric alcohols, specifically poly (propylene glycol, adipic acid) ester, poly (butanediol, adipic acid) ester, poly (ethylene glycol, adipic acid) ester, poly (1,6-hexanediol, butanediol, adipic acid) ester, poly (butanediol, ethylene glycol, adipic acid) ester, poly (ethylene glycol, propylene glycol, butanediol, adipic acid) ester, and the like. An average molecular weight of 1000 to 3000 is effectively used. However, if the average molecular weight is less than 1000, physical properties cannot be improved. On the other hand, when the average molecular weight exceeds 3000, the extrusion moldability is significantly lowered, and furthermore, the cold resistance of the stretch film is lowered. Furthermore, those having an average molecular weight of about 2000 are preferably used in terms of improvement in physical properties and extrusion moldability.

The adipic acid plasticizer as the third component is a mixed adipic ester plasticizer of two or more aliphatic alcohols having 10 or less alkyl groups and adipic acid, and the mixed adipic ester plasticizer is A reaction product of two or more aliphatic alcohols having an alkyl group having 10 or less carbon atoms and adipic acid, which includes C8,10 adipate (mixed ester of alcohol having 8 to 10 carbon atoms and an alkyl group) ), C7,9 adipate (7,9), C6,8,10 adipate (6,8,10), and the like, and similarly used alone or in combination of two or more. .
Among them, diisononyl adipate as an adipate plasticizer and C6,8,10 adipate and C7,9 adipate as mixed adipate plasticizers have the extrudability and stretchability of the stretch film, respectively. It is easy to give and is used suitably. This addition amount is 10 to 20 parts by weight with respect to 100 parts by weight of the polyvinyl chloride resin. If this is less than 10 parts by weight, the stretchability of the stretch film is lowered, and the extrudability of the stretch film becomes insufficient. On the other hand, when this addition amount exceeds 20 parts by weight, the n-heptane extraction amount increases.

  The fourth component, epoxidized vegetable oil, is added in order to improve the extrudability of the stretch film, particularly the thermal stability during extrusion. Examples of the epoxidized vegetable oil include epoxidized soybean oil and epoxidized linseed oil. Among these, epoxidized soybean oil is preferably used in view of the above-described effects. This addition amount is 5 to 15 parts by weight with respect to 100 parts by weight of the polyvinyl chloride resin. If it is less than 5 parts by weight, the thermal stability during extrusion molding is poor, and if it exceeds 15 parts by weight, the film is strongly colored, which is not preferable.

  In the film of the present invention, in addition to the first to fourth components described above, an antifogging agent, a stabilizer, a lubricant and the like can be appropriately selected and blended as necessary. Examples of the antifogging agent include monoglycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, and polyoxyethylene alkyl ether. The monoglycerin fatty acid ester is preferably a monoglycerin ester of a saturated or unsaturated fatty acid having 12 to 18 carbon atoms. Specific examples include monoglycerol laurate, monoglycerol myristate, monoglycerol palmitate, monoglycerol stearate, monoglycerol oleate, and monoglycerol linoleate. As the polyglycerol fatty acid ester, a polyglycerol ester of a saturated or unsaturated fatty acid having 12 to 18 carbon atoms is preferable. Specific examples include polyglycerol laurate, polyglycerol myristate, polyglycerol palmitate, polyglycerol stearate, polyglycerol oleate, and polyglycerol linoleate. The sorbitan fatty acid ester is preferably a sorbitan ester of a saturated or unsaturated fatty acid having 12 to 18 carbon atoms. Specific examples include sorbitan laurate, sorbitan myristate, sorbitan palmitate, sorbitan stearate, sorbitan oleate, sorbitan renolate and the like. The polyoxyethylene alkyl ether is preferably a saturated alcohol polyoxyethylene alkyl ether having 12 to 18 carbon atoms, more preferably a polyoxyethylene alkyl ether having 3 to 7 added moles of ethylene oxide. Specific examples include polyoxyethylene lauryl ether, polyoxyethylene myristyl ether, polyoxyethylene palmityl ether, and polyoxyethylene stearyl ether.

Among the above, monoglycerol laurate, monoglycerol oleate, monoglycerol linoleate, polyglycerol laurate, polyglycerol oleate, polyglycerol linoleate, sorbitan laurate, sorbitan oleate, sorbitan linoleate, polyoxyethylene lauryl ether These may be used alone or in combination of two or more.
Stabilizers include 2-ethylhexyl acid, higher fatty acids having 8 to 22 carbon atoms, citric acid, gluconic acid, sorbic acid, benzoic acid, isodecanoic acid, neodecanoic acid and other calcium salts, and 2-ethylhexyl acid, carbon number 8 Examples include Ca—Zn salts composed of zinc salts such as ˜22 higher fatty acids, isodecanoic acid and neodecanoic acid, and these are used alone or in combination of two or more. In addition, with respect to the above stabilizer, tris (nonylphenyl) phosphite, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), dipropylene glycol, synthesis, Isoparaffin petroleum hydrocarbon, tridecyl alcohol, dehydroacetic acid and the like may be used in combination. Each of these addition amounts is preferably 1 part by weight or less with respect to 100 parts by weight of the polyvinyl chloride resin.
Examples of the lubricant include higher fatty acids having 8 to 22 carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, and isostearic acid; 1,2-dihydroxy stearic acid; lauric acid amide, stearic acid amide, and the like. 8 to 22 higher fatty acid amides; aliphatic hydrocarbons such as liquid paraffin and synthetic paraffin; monoglycols such as glycerin and propylene glycol; and polyglycols such as polyethylene glycol and polypropylene glycol. Used in combination. Each of these addition amounts is preferably 1 part by weight or less with respect to 100 parts by weight of the polyvinyl chloride resin.

  The stretch film in the present invention is formed by mixing the above-described composition with a Henschel mixer or the like, and then forming the film by a commonly used T-die method or inflation method. Moreover, the thickness of this film is 5-8 micrometers or less. If it is a film obtained by molding the above composition to a thickness of 8 μm or less, the elution amount of n-heptane can be 40 ppm or less, which is less than the regulated value of 150 ppm, and a film with low elution and excellent packaging properties Obtainable.

Hereinafter, although the effect of the present invention is explained in detail based on an example, the present invention is not limited to the following examples.
Poly (butanediol, adipic acid) ester having a mean molecular weight of 2300 (made by Dainippon Ink & Chemicals, Inc.) as a polyester plasticizer with respect to 100 parts by weight of the polyvinyl chloride resin having the contents shown in Tables 1 and 2. W-360EL "), C6,8,10 adipate (C6,8,10A) (" D-610A "manufactured by Taoka Chemical Co.) as a mixed adipate plasticizer, epoxidized soybean oil (ESBO) (Asahi Denka Kogyo) Co., Ltd. “O-130P”) and each resin added in the amounts (parts by weight) shown in Tables 1 and 2, respectively, were further added to Ca—Zn stabilizers (“SC-24” manufactured by Asahi Denka Kogyo K.K. "): 0.5 parts by weight, diglycerin fatty acid ester (" DO-100 "manufactured by Riken Vitamin Co., Ltd.): 2.5 parts by weight were blended and extruded by the T-die method to produce a stretch film. Filmed. The thickness of each stretch film was measured and listed in Table 1. The obtained film was evaluated by the following method, and the results are shown in Tables 1 and 2.
(1) Molecular weight measurement

  The gel permeation chromatography “HLC-8120GPC” manufactured by Tosoh Corporation is equipped with a chromatographic column “KF-807L” manufactured by Showa Denko KK, the solvent is tetrahydrofuran (THF), and the solvent is 4 ml. 10 mg of a vinyl chloride resin sample was dissolved, and the obtained solution was measured at a solvent flow rate of 1.0 ml / min and a solvent temperature of 40 ° C., and the weight average molecular weight of the vinyl chloride resin was calculated in terms of polystyrene. The weight average molecular weight of the standard polystyrene used is 2 million, 670,000, 110,000, 20,000, and 4,000.

Here, when there were Ni polymers having a molecular weight Mi, the number average molecular weight (MN) and the weight average molecular weight (MW) were determined by calculation using the following formulas to calculate MW / MN.
Number average molecular weight (MN) = ΣMiNi / ΣNi
Weight average molecular weight (MW) = ΣMi2Ni / ΣMiNi

[Appearance evaluation]
-The film obtained above was observed and visually judged according to the following criteria.
○ …… No transparency, no discoloration, and good transparency. △ …… Slightly there is coloration, but there is no problem in practical use. × …… Sometimes it has been decomposed, or has been broken during film formation.

[Food hygiene test]
N-Heptane dissolution test: The dissolution volume (ppm) was measured by the dissolution test method defined in Ministry of Health, Labor and Welfare Notification No. 20.

[Packaging suitability]
-Automatic packaging machine suitability: 500 g of contents were put into a PP tray, and the automatic packaging suitability of the film was evaluated at a packaging speed of 40 packs / minute using "A-18K" manufactured by Fujikikai.
○ …… Wrapable without wrinkles or tears △ …… Slightly lacking but able to be wrapped × …… Wrinkles, torn and unsuitable for packaging

From Tables 1 and 2, it can be seen that Examples 1 to 13, which are the scope of the present invention, are excellent in evaluating any item. On the other hand, it can be seen that Comparative Examples 1 to 4, Comparative Example 6, and Comparative Example 8 are inferior in characteristics such as packaging suitability.
In Comparative Example 5, Comparative Example 7, and Comparative Example 9 to Comparative Example 13, decomposition and generation of flaws and tearing failed to form a film, and a sample for evaluation could not be obtained.

Claims (3)

In a composition comprising a polyvinyl chloride resin, the weight average molecular weight (MW) measured by gel permeation chromatography (GPC) by a polystyrene conversion method is 1.2 × 10 ^{5 to} 2.2 × 10 ⁵ . And an average molecular weight of 1,000 to 3, based on 100 parts by weight of a polyvinyl chloride resin having a ratio MW / MN of 2.05 to 2.20 of the weight average molecular weight (MW) and the number average molecular weight (MN). 10 to 20 parts by weight of adipic acid polyester plasticizer (A) of 000, a mixed adipic acid ester plasticizer obtained by reaction of two or more aliphatic alcohols having an alkyl group having 10 or less carbon atoms with adipic acid ( B) 10 to 20 parts by weight, 5 to 15 parts by weight of epoxidized vegetable oil (C) are added, and the ratio (A) / (B) of the added amount of the plasticizer (A) and the plasticizer (B) is A polyvinyl chloride resin composition characterized by being in the range of 0.5 to 1.6. A vinyl chloride resin composition characterized by using a vinyl chloride resin having a broad polymerization degree distribution by use of a chain transfer agent and temperature control. The n-heptane extraction amount measured by the evaporation residue test method stipulated in the Ministry of Health and Welfare Notification No. 20 in 1982 is 40 ppm by mass or less, wherein the film has a thickness of 8 μm or less. A stretch film comprising the polyvinyl chloride resin composition according to 2.