JP5957221B2 - Vinylidene chloride copolymer - Google Patents

Description

  The present invention relates to a vinylidene chloride copolymer and a film using the same.

  Since vinylidene chloride polymer has high crystallinity, it has excellent gas barrier properties and water vapor barrier properties when formed into a film. However, since it is inferior in flexibility and thermal stability, it is produced by copolymerizing with other monomers to enhance internal plasticization.

  A vinylidene chloride copolymer for extrusion molding is generally produced by copolymerizing vinylidene chloride and vinyl chloride using a suspension polymerization method, and adding a plasticizer and a heat stabilizer necessary for extrusion molding. ing. Vinylidene chloride copolymers are mainly used as barrier films.

  Copolymers of vinylidene chloride and methyl acrylate are excellent in internal plasticization performance by copolymerizing methyl acrylate, and the amount of plasticizer added for extrusion can be reduced to a very small amount. An excellent film can be produced.

  The resulting film is laminated on the surface with aluminum foil, paper, other types of synthetic resin films, etc., taking advantage of high gas barrier properties, for example, pharmaceuticals, retort food, microwave food, frozen food, candy candy, It is used as a packaging material for foods such as processed meat, fishery processed foods, and seasoned boiled processed foods.

  On the other hand, vinylidene chloride copolymers are easily pyrolyzed during extrusion processing, and carbides flow out due to pyrolysis, and the resulting film turns yellow, resulting in a decrease in film quality and film productivity. It tends to be easy to do. In Patent Documents 1 and 2, a vinylidene chloride copolymer is blended with a copolymer of ethylene and vinyl acetate (hereinafter abbreviated as EVA) in order to improve the thermal stability of the vinylidene chloride copolymer. Thus, a copolymer with improved thermal stability during extrusion and a film obtained from the copolymer are described.

  Patent Documents 3 and 4 describe that the extrudability of the copolymer is improved by blending another copolymer with the vinylidene chloride copolymer.

JP-A-55-108442 JP-A-1-131268 JP-A-53-16753 Japanese Patent No. 2947931

  However, the vinylidene chloride copolymers described in Patent Documents 1 and 2 have insufficient thermal stability, and the vinylidene chloride copolymers described in Patent Documents 3 and 4 have thermal stability. Although satisfied, characteristics such as suitability for food packaging and filling machines and gas barrier properties tend to be lowered. In addition, in the case of conventional vinylidene chloride copolymers, when extrusion processing is carried out continuously, thermally deteriorated products generated inside the extruder may adhere to the screw or die and adversely affect the resulting film. .

  The present invention provides a vinylidene chloride copolymer having a crystal melting point lower than that of a conventional vinylidene chloride and methyl acrylate copolymer having the same composition while maintaining stable extrudability. The purpose is to do.

  As a result of repeated studies to improve the thermal stability during extrusion molding of the vinylidene chloride copolymer and improve the productivity, the present inventors have found that the crystalline melting point of the vinylidene chloride copolymer and the chloride It has been found that a vinylidene chloride copolymer having stable extrudability can be provided when the copolymerization ratio of methyl acrylate constituting the vinylidene copolymer satisfies a specific condition, and the present invention has been made. .

That is, the present invention is as follows.
[1] A vinylidene chloride copolymer having 90 to 97% by mass of vinylidene chloride and 3 to 10% by mass of methyl acrylate as monomer units,
The relationship represented by the following formula (1) between the crystalline melting point Y (° C.) of the vinylidene chloride copolymer in differential scanning calorimetry and the content x (mass%) of the monomer unit based on the methyl acrylate. A vinylidene chloride copolymer satisfying the above requirements.
Y ≦ 175-3x (1)
[2] The vinylidene chloride copolymer according to [1], which has a weight average molecular weight of 70000 to 90000 as determined by gel permeation chromatography.
[3] The vinylidene chloride copolymer according to [1] or [2], which has a molecular weight distribution by a gel permeation chromatography method of 2.5 to 5.
[4] A film comprising the vinylidene chloride copolymer according to any one of [1] to [3].

  The present invention provides a vinylidene chloride copolymer having a crystal melting point lower than that of a conventional copolymer of vinylidene chloride and methyl acrylate having the same composition while maintaining stable extrudability. it can.

It is a schematic diagram of a single layer film manufacturing apparatus.

  A preferred embodiment of the present invention will be described. The following embodiment is an example for explaining the present invention, and is not intended to limit the present invention only to this embodiment. The present invention can be implemented in various forms without departing from the gist thereof.

(Vinylidene chloride copolymer)
The vinylidene chloride copolymer of this embodiment has 90 to 97% by mass of vinylidene chloride and 3 to 10% by mass of methyl acrylate as monomer units. When the vinylidene chloride copolymer has 90% by mass or more of monomer units based on vinylidene chloride, a film having high barrier properties can be obtained. On the other hand, if the monomer unit based on vinylidene chloride exceeds 97% by mass, the vinylidene chloride copolymer tends to be thermally deteriorated in the extruder during extrusion molding.

The vinylidene chloride copolymer of the present embodiment has a crystalline melting point Y (° C.) of the vinylidene chloride copolymer when measured under a temperature rising condition of 5 ° C./min using a differential scanning calorimeter, It is necessary that the content x (mass%) of the monomer units based on methyl acrylate constituting the vinylidene chloride copolymer satisfy the following formula (1).
Y ≦ 175-3x (1)

  By satisfying the above formula (1), when the extrusion process of the vinylidene chloride copolymer is carried out continuously for a long time, it suppresses that the thermally deteriorated product generated in the extruder adheres to the screw or die. it can.

  When the content x (% by mass) of the monomer unit based on methyl acrylate is increased, the crystal melting point Y (° C.) can be decreased. However, as x is increased, the copolymer is extruded with the copolymer. The gas barrier properties of the obtained film tend to be reduced. When compared with a copolymer having the same composition, the vinylidene chloride copolymer obtained in the present embodiment can reduce thermal deterioration during extrusion while maintaining the gas barrier properties of the film in the composition. .

  The vinylidene chloride copolymer weight average molecular weight (Mw) measured by gel permeation chromatography is preferably 70000-90000. When the Mw of the vinylidene chloride copolymer is in the above range, the stability of the bubbles can be maintained during the inflation of the extrusion, and the thermal deterioration can be prevented from occurring in the extruder.

  The molecular weight distribution (Mw / Mn), which is the ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the vinylidene chloride copolymer measured by gel permeation chromatography, is 2.5-5. 0 is preferred. If the molecular weight distribution of the vinylidene chloride copolymer is 2.5 or more, the thermal stability is good, and if it is 5.0 or less, the required film strength can be maintained. Mw and Mn are values converted from polystyrene as a standard sample.

  The shape of the vinylidene chloride copolymer is particulate, and the weight average particle diameter is preferably 100 μm to 1 mm, more preferably 150 μm to 300 μm. When the weight average particle diameter is within this range, the extrusion load during production of the film becomes constant, and stable extrusion processing becomes possible. As a result, the film thickness of the obtained film can be made uniform.

  The particle size of the vinylidene chloride copolymer can be obtained by adjusting the number of rotations of the stirrer and the amount of suspending agent during polymerization.

(Method for producing vinylidene chloride copolymer)
As a method for improving the thermal stability at the time of extrusion molding of a vinylidene chloride copolymer, a method of lowering the extrusion molding temperature can be considered, but a copolymer of vinylidene chloride and methyl acrylate is included in the crystal. When extrusion molding is performed at a temperature lower than the melting point, a portion that does not completely melt is generated in the extruder, which becomes an unmelted foreign matter and is mixed in the film, which may significantly hinder the film quality. In order to lower the extrusion temperature, it is necessary to lower the crystal melting point of the copolymer.

  As a result of repeated studies to improve the thermal stability during extrusion molding of vinylidene chloride copolymers and improve productivity, the present inventors have found that vinylidene chloride having a specific copolymerization ratio and methyl acrylate When the copolymer is a solvent that does not dissolve and an organic solvent other than a hydrocarbon solvent is added before polymerization or during polymerization, the crystalline melting point of the resulting vinylidene chloride copolymer decreases, It has been found that the extrusion temperature can be lowered.

  That is, the vinylidene chloride copolymer of the present embodiment can be produced as follows.

  First, water, a polymerization initiator and an aqueous suspending agent solution are added to a monomer mixture of 90 to 97% by weight of vinylidene chloride and 3 to 10% by weight of methyl acrylate with respect to the total amount of monomers constituting the vinylidene chloride copolymer. Further, a small amount of organic solvent other than hydrocarbon is added and dissolved to prepare a mixed solution. The organic solvent is a solvent that does not dissolve the obtained vinylidene chloride copolymer. Next, when the temperature of the mixed liquid is increased and a predetermined polymerization temperature is reached, polymerization is performed for a predetermined time, and after cooling, the resulting polymer slurry is recovered and dehydrated, and then the residual monomer is removed to remove the vinylidene chloride copolymer. A polymer is obtained. The organic solvent may be added during the polymerization.

  By using an organic solvent that does not melt the obtained vinylidene chloride copolymer, a copolymer satisfying the formula (1) can be obtained. Although it does not specifically limit as an organic solvent, Alcohol, ketones, or esters which are organic solvents other than a hydrocarbon type solvent can be used. Examples of alcohols include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol and the like. Examples of ketones include acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of esters include methyl acetate and ethyl acetate.

  When an organic solvent having a high solubility in water is added alone, a part of the added organic solvent moves to the aqueous phase, and the effect of lowering the melting point is reduced. In order to prevent this, it is advisable to add them after mixing in advance with monomers having the same composition as the polymer composition to be obtained.

  If the boiling point of the organic solvent is too high, the organic solvent remains in the residual monomer removal step after polymerization, so it is necessary to increase the processing temperature or extend the processing time, which increases the thermal stability and productivity. In order to worsen, it is preferable to use an organic solvent having a boiling point of 100 ° C. or lower under normal pressure.

  The addition amount of the organic solvent is preferably 1 to 10% by mass and more preferably 3 to 5% by mass with respect to the total amount of vinylidene chloride monomer and methyl acrylate monomer. If the amount of the organic solvent added is too small, the effect of lowering the crystal melting point becomes small, and if it is too large, the load of the removal step increases.

  The addition amount of the polymerization initiator is preferably 0.1 to 5% by mass, more preferably 0.5 to 3.0% by mass with respect to the total amount of vinylidene chloride and methyl acrylate.

  The polymerization temperature is preferably in the range of 5 to 150 ° C., the polymerization may be performed at a constant temperature, or the polymerization may be performed by changing the temperature during the polymerization. When the temperature is changed during the polymerization, the polymerization is preferably performed at the initial temperature for at least 1 hour. If the polymerization temperature is too low, it is necessary to lower the half-life temperature of the polymerization initiator used or to increase the amount of polymerization initiator added in order to maintain the molecular weight. Lowering the half-life temperature of the polymerization initiator makes it difficult to handle safely due to low temperature activity, and if the polymerization initiator is added too much, the molecular weight becomes too small, and bubble stability during inflation of extrusion molding is reduced. It tends to get worse.

  A radical polymerization initiator can be used as the polymerization initiator. As the radical polymerization initiator, an organic peroxide having a 10-hour half-life temperature of 80 ° C. or less can be used. Specifically, lauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy- 2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyneodecanoate, stearoyl peroxide, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t -Butyl peroxypivalate, diisopropyl peroxydicarbonate, etc., preferably 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, diisopropyl peroxy Examples thereof include oxydicarbonate and t-butyl peroxyneodecanoate.

  The half-life temperature of the radical polymerization initiator is an index representing the decomposition rate of the organic peroxide at a constant temperature, until the original organic peroxide decomposes and the amount of active oxygen becomes 1/2. It is indicated by the time required for. The 10-hour half-life temperature means a temperature at which the time required for the amount of active oxygen to be halved is 10 hours. The 10-hour half-life temperature is a relatively inert solution with respect to radicals, such as benzene, and an organic peroxide solution having a concentration of 0.1 mol / L is sealed in a glass tube subjected to nitrogen substitution. Measured by soaking in a thermostatic bath and pyrolyzing.

  In the method for producing the vinylidene chloride copolymer, deionized water is preferably used as water. The amount of water added is preferably equal to or more than 3 times the total amount of monomers. By making the amount of water added equal to or greater than the total amount of monomers, the mixed monomer can be dispersed in water in a discontinuous phase.

  As the suspending agent, cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, partially saponified products of polyvinyl alcohol and polyvinyl acetate, and the like can be used.

  The addition amount of the suspending agent is preferably 0.03 to 1.0% by mass with respect to the total amount of the monomers, and if it is 0.03% by mass or more, the suspension stability is good, and the particles during If the comrades are difficult to adhere to each other and are 1.0% by mass or less, it becomes easy to make the mixed monomer disperse in a discontinuous phase in water.

  The suspending agent can be added under stirring after dissolving the required amount in a predetermined amount of water used for the polymerization to prepare an aqueous suspending agent solution, and adding vinylidene chloride and methyl acrylate to the polymerization machine. .

  The polymerization rate of the vinylidene chloride copolymer obtained in the production method of the present embodiment is preferably 90% or more, more preferably 95% or more. Productivity can be achieved.

  In the manufacturing method of the said vinylidene chloride type-copolymer, you may add a plasticizer in the ratio of 1 mass% or less with respect to the copolymer obtained.

  Examples of the plasticizer include phthalic acid esters, adipic acid esters, sebacic acid esters, and citrate esters.

  The plasticizer may be added at any step in the production process. For example, the plasticizer can be charged at the same time when the monomer is charged into the polymerization machine, charged into the slurry after the polymerization, or dry blended into the vinylidene chloride copolymer after the residual monomer is removed. .

  In the method for producing the vinylidene chloride copolymer, various additives may be added as necessary.

  Additives include epoxidized soybean oil, epoxidized linseed oil, bisphenol A diglycidyl ether, epoxidized polybutadiene, epoxidized octyl stearate, vitamin E, butylhydroxytoluene (BHT), alkyl thiodipropionate Antioxidants such as esters, sodium pyrophosphate, sodium tripolyphosphate, disodium ethylenediaminetetraacetate (EDTA-2Na), magnesium oxide and other heat stabilization aids, various light stabilizers, various lubricants, various colorants, etc. be able to.

  The additive can be added in each step in the same manner as the plasticizer, but it is desirable to dry blend the additive of the inorganic powder into the vinylidene chloride copolymer after the residual monomer is removed.

(Film made of vinylidene chloride copolymer)
The present invention provides a film containing the vinylidene chloride copolymer. The film obtained from the vinylidene chloride copolymer of the present invention can be produced mainly by an extrusion method, particularly an inflation method or a T-die method. The inflation method was extruded from a circular die of a screw extruder, and the tubular extrudate was passed through a first cooling bath below room temperature, then passed through a second preheating bath, and air was inflated between two pairs of pinch rollers. This is a method of forming a film by forming bubbles. The T-die method is a method of making a film by extrusion cooling from a T-die.

  FIG. 1 is a diagram schematically illustrating an example of an apparatus for producing a single layer film using the vinylidene chloride copolymer of the present embodiment. The vinylidene chloride copolymer produced in the present embodiment is charged from a hopper 2 attached to an extruder 1, becomes a melt kneaded by a screw 3, and is extruded in a cylindrical shape from a slit portion of a circular die 4. It becomes a cylindrical parison 5. The cylindrical parison 5 is cooled by the cooling tank 6 filled with the cooling water 7 and the refrigerant 8 in the parison, and guided to the pinch rolls 20 and 21. Next, the cylindrical parison 5 is preheated through the hot water tank 9, and then is inflated by inserting air between the pinch rolls 22 and 23 and the pinch rolls 24 and 25 by an inflation method to form a cylindrical film. At this time, the stretching ratios in the circumferential direction and the longitudinal direction of the cylinder are determined by the amount of air introduced and the rotational speed ratio between 22 and 23 and the pinch rollers 24 and 25. The obtained film is folded into two flat sheets and wound on a winding bobbin 30 or 31.

  Moreover, the obtained monolayer film can be subjected to post-processing such as corona discharge treatment, if necessary. The monolayer film thus obtained is excellent in gas barrier properties, non-extractability by oily foods, mechanical properties, and high-frequency sealing properties, and requires barrier properties such as ham, sausage, cheese, sugar beet, and other foods. It can be used as a packaging material. In addition, the obtained monolayer film can be laminated with aluminum foil, paper, and other types of synthetic resin films on the surface thereof, taking advantage of high gas barrier properties, for example, pharmaceuticals, retort foods, microwave foods It can be used as a packaging material for foods such as frozen foods, candy confectionery, processed meat and fishery products, and seasoned boiled processed foods.

Hereinafter, the contents of the present invention will be specifically described with reference to Examples , Reference Examples and Comparative Examples. In addition, this invention is not limited to the following Example.

[Example 1]
A mixture of 237 g of vinylidene chloride and 13 g of methyl acrylate, 7.5 g of methanol added, and 1.5 g of t-butylperoxy-2-ethylhexanoate dissolved as a radical initiator were purged with nitrogen. The inner surface was put into a polymerization machine made of stainless steel, and stirring was started to bring the inside of the machine to 25 ° C. Then, 0.2 g of hydroxypropylmethylcellulose dissolved in 300 g of deionized water was put into the apparatus, and the temperature was raised to 76 ° C. over 1 hour to initiate polymerization. After 9 hours, the inside of the apparatus was cooled to 25 ° C. over 1 hour, opened to the atmosphere, and the slurry was taken out. Next, the obtained slurry was filtered to separate water, and the obtained undried copolymer was placed in a hot air dryer at 80 ° C. and dried for 24 hours. The polymerization rate was 92.0%.

[Example 2]
A copolymer was obtained in the same manner as in Example 1 except that 12.5 g of methanol was added to a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate. The polymerization rate was 96.4%.

[ Reference Example 3]
A copolymer was obtained by performing the same operation as in Example 1 except that 7.5 g of acetone was added to a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate, and the polymerization temperature was 83 ° C. . The polymerization rate was 95.1%.

[Example 4]
A copolymer was obtained in the same manner as in Example 1 except that 12.5 g of methanol was added to a mixture of 230 g of vinylidene chloride and 20 g of methyl acrylate. The polymerization rate was 94.6%.

[ Reference Example 5]
A copolymer was obtained in the same manner as in Example 1 except that 7.5 g of acetone was added to a mixture of 230 g of vinylidene chloride and 20 g of methyl acrylate, and the polymerization temperature was 83 ° C. The polymerization rate was 96.0%.

[Example 6]
A copolymer was obtained in the same manner as in Example 1 except that 2.57.5 g of ethyl acetate was added to a mixture of 237.5 g of vinylidene chloride and 12.5 g of methyl acrylate. The polymerization rate was 93.6%.

[Example 7]
A copolymer was obtained in the same manner as in Example 1, except that 2.5 g of ethyl acetate was added to a mixture of 235 g of vinylidene chloride and 15 g of methyl acrylate. The polymerization rate was 94.0%.

[Example 8]
A copolymer was obtained in the same manner as in Example 1 except that 12.5 g of acetone was added to a mixture of 235 g of vinylidene chloride and 15 g of methyl acrylate. The polymerization rate was 95.4%.
[Example 9]
A copolymer was obtained in the same manner as in Example 1 except that 12.5 g of ethanol was added to a mixture of 227.5 g of vinylidene chloride and 22.5 g of methyl acrylate. The polymerization rate was 95.8%.

[Example 10]
A copolymer was obtained in the same manner as in Example 1 except that 12.5 g of methyl ethyl ketone was added to a mixture of 225 g of vinylidene chloride and 25 g of methyl acrylate. The polymerization rate was 93.9%.

[ Reference Example 11]
A copolymer was obtained in the same manner as in Example 1 except that 12.5 g of methanol was added to a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate, and the polymerization temperature was 60 ° C. The polymerization rate was 96.0%.

[ Reference Example 12]
A copolymer was obtained in the same manner as in Example 1 except that 7.52.5 g of acetone was added to a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate. The polymerization rate was 95.5%.

[Comparative Example 1]
A polymerizer in which 237 g of vinylidene chloride and 13 g of methyl acrylate are mixed with 1.5 g of t-butylperoxy-2-ethylhexanoate dissolved as a radical initiator, and the inner surface purged with nitrogen is made of stainless steel The stirring was started and the inside of the apparatus was brought to 25 ° C. Then, 0.2 g of hydroxypropylmethylcellulose dissolved in 300 g of deionized water was put into the apparatus, and the temperature was raised to 76 ° C. over 1 hour to initiate polymerization. After 9 hours, the inside of the apparatus was cooled to 25 ° C. over 1 hour, opened to the atmosphere, and the slurry was taken out. Next, the obtained slurry was filtered to separate water, and the obtained undried copolymer was placed in a hot air dryer at 80 ° C. and dried for 24 hours. The polymerization rate was 96.1%.

[Comparative Example 2]
A copolymer was obtained in the same manner as in Comparative Example 1 except that a mixture of 235 g of vinylidene chloride and 15 g of methyl acrylate was used. The polymerization rate was 94.7%.

[Comparative Example 3]
A copolymer was obtained in the same manner as in Comparative Example 1, except that a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate was used. The polymerization rate was 95.7%.

[Comparative Example 4]
A copolymer was obtained in the same manner as in Comparative Example 1 except that 230 g of vinylidene chloride and 20 g of methyl acrylate were used. The polymerization rate was 95.3%.

[Comparative Example 5]
A copolymer was obtained in the same manner as in Comparative Example 1 except that a mixture of 225 g of vinylidene chloride and 25 g of methyl acrylate was used. The polymerization rate was 94.0%.

[Comparative Example 6]
A copolymer was obtained by performing the same operation as in Comparative Example 1 except that 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate were used and the polymerization temperature was 70 ° C. The polymerization rate was 94.6%.

[Comparative Example 7]
A copolymer was obtained by performing the same operation as in Comparative Example 1 except that 1.25 g of methanol was added to a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate, and the polymerization temperature was 50 ° C. Obtained. The polymerization rate was 95.0%.

[Comparative Example 8]
A copolymer was obtained by performing the same operation as in Comparative Example 1 except that 22.5 g of methanol was added to a mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate, and the polymerization temperature was 70 ° C. The polymerization rate was 95.6%.

[Comparative Example 9]
A mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate was used, the polymerization temperature was raised to 70 ° C., and the temperature was raised to 80 ° C. after 2 hours. A polymer was obtained. The polymerization rate was 94.4%.

[Comparative Example 10]
A mixture of 232.5 g of vinylidene chloride and 17.5 g of methyl acrylate was used, the polymerization temperature was set to 76 ° C., and the temperature was raised to 80 ° C. after 2 hours. A polymer was obtained. The polymerization rate was 95.9%.

About the copolymer obtained by the Example , the reference example, and the comparative example, crystal | crystallization melting | fusing point, a weight average molecular weight, molecular weight distribution, and extrusion processability were calculated | required with the following method. The results are shown in Tables 1 and 2.

(Crystal melting point)
The crystal melting point was measured using a differential scanning calorimeter (trade name “DSC-50”) manufactured by Shimadzu Corporation. A sample was weighed 10 to 15 mg in an aluminum pan, sealed with an aluminum lid, placed on the sample stage of the main body, and measured in a nitrogen atmosphere (nitrogen gas flow rate: about 50 mL / min). The mixture was heated from room temperature to 186 ° C. at a heating rate of 5 ° C./min, held at that temperature for 1 minute, and then cooled to 40 ° C. at a cooling rate of 5 ° C./min. When a plurality of crystal melting points exist, the lowest crystal melting point is defined as the crystal melting point Y of the vinylidene chloride copolymer.

(Weight average molecular weight and molecular weight distribution)
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the vinylidene chloride copolymer were measured by the gel permeation chromatography method (GPC method) under the following conditions, and the molecular weight distribution was calculated.
・ Equipment: Shimadzu GPC system ・ Column: GS series packed column (Showa Denko)
・ Detector: Differential refractometer ・ Set temperature: 40 ℃
・ Developing solvent: THF (tetrahydrofuran)
・ Concentration of measurement sample: 0.5 mass%
Standard molecular weight of polystyrene: 580, 3050, 11300, 66000, 552,500, 3150,000

(Extrudability)
A vinylidene chloride copolymer film was produced using the single-layer film production apparatus shown in FIG. 1, and the extrusion processability at that time was evaluated. At this time, the cylindrical parison 5 is rapidly cooled to about 10 ° C. by the cooling water 7 in the cooling tank 6 and the refrigerant 8 in the parison, and preheated to about 40 ° C. by the hot water tank 9, and the amount of air introduced and the pinch rolls 22 and 23 And the pinch rolls 24 and 25 were adjusted to have a rotational speed ratio, and were stretched about 3 times in the circumferential direction and longitudinal direction of the cylinder and oriented.

Extrudability was judged by visual observation, and the results were expressed as follows.
A: Stable operation time exceeds 10 hours.
B: Stable operation time is 5 hours or more and less than 10 hours.
C: Stable operation time is 3 hours or more and less than 5 hours.
D: Inflation is impossible or stable operation time is less than 3 hours.

  As shown in Table 1, it can be confirmed that the vinylidene chloride copolymers produced in the examples have a lower crystal melting point of the produced copolymer and have improved extrudability when compared with the same composition. It was.

  According to the present invention, it is possible to provide a vinylidene chloride copolymer having a low crystalline melting point while maintaining stable extrusion moldability, and it is possible to improve productivity during extrusion molding.

DESCRIPTION OF SYMBOLS 1 ... Extruder, 2 ... Hopper, 3 ... Screw, 4 ... Circular die, 5 ... Cylindrical parison, 6 ... Cooling tank, 7 ... Cooling water, 8 ... Refrigerant in parison, 9 ... Hot water tank, 20, 21, 22 , 23, 24, 25 ... pinch rolls, 30, 31 ... winding bobbins.

Claims (2)

A vinylidene chloride copolymer having 90 to 97% by mass of vinylidene chloride and 3 to 10% by mass of methyl acrylate as monomer units,
The weight average molecular weight by gel permeation chromatography method is 70000-90000, and the molecular weight distribution is 2.5-5.0,
The relationship represented by the following formula (1) between the crystalline melting point Y (° C.) of the vinylidene chloride copolymer in differential scanning calorimetry and the content x (mass%) of the monomer unit based on the methyl acrylate. A vinylidene chloride copolymer satisfying the above requirements.
Y ≦ 175-3x (1) A film comprising the vinylidene chloride copolymer according to claim 1 .

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