JP2016055635A - Method for producing water-soluble film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a water-soluble film, which enables preparation of the water-soluble film having excellent appearance even when a water content thereof is low immediately after being extruded from a mold.SOLUTION: The method for producing a water-soluble film comprises: a step (A) of obtaining a sheet-like composition by extruding a raw material composition comprising a water-soluble resin and water from a mold; and a step (B) of transporting the sheet-like composition by a casting roller. In the step (A), a water content of the sheet-like composition at a mold exit is 20 to 55 wt%. When the mold exit is denoted by x, and a point of contact of the sheet-like composition and the casting roller is denoted by y, a linear distance between x and y is 10 mm or more. In the step (B), a surface temperature of the casting roller is higher than a dew point temperature of an atmosphere around the casting roller.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a water-soluble film used for packaging medicine such as detergents and agricultural chemicals.

As a general method for producing a water-soluble film, a water-soluble resin such as polyvinyl alcohol is dissolved in a solvent such as water, kneaded and defoamed to prepare a stock solution, and then cast into a drum-type roll or endless belt by a casting method. A method of coating, drying, and forming a film is known.
In such a method, the content of moisture and the like after discharging from the mold is considered to affect the film shape after film formation.

For example, Patent Document 1 describes a manufacturing method for obtaining a film by discharging a water-soluble resin such as polyvinyl alcohol from a mold onto a casting roller or a belt traveling on a belt-type film forming machine and drying the film. In this case, it is described that the concentration of volatile components such as water is 55 to 80% by weight.
Patent Document 2 describes a production method for obtaining a film by drying a water-soluble resin such as polyvinyl alcohol on a metal surface. At that time, the content of a solvent such as water is 40 to 99% by weight. It is described that.

On the other hand, these methods are known to increase the energy cost required for drying since the moisture concentration of the film immediately after the mold is discharged is high, and a reduction in the moisture concentration of the film immediately after the mold is discharged is required. ing.
However, simply lowering the moisture concentration immediately after discharging the mold has a problem that the film sticks to the mold and film formation becomes difficult.

On the other hand, the distance between the mold outlet and the casting roller or the distance between the mold outlet and the endless belt is increased.
However, in particular, if the distance between the mold outlet and the casting roller is increased, water vapor due to volatilization of the water in the film is likely to be caught in the gap between the film and the casting roller immediately after the mold is discharged, and the film oozes out the water. There has been a problem that dents are generated on the surface of the film.

JP 2002-79530 A JP 2001-329130 A

In view of the above situation, the present invention provides a method for producing a water-soluble film capable of producing a water-soluble film having an excellent appearance even when the moisture content immediately after being extruded from a mold is low. Objective.

The present invention includes a step (A) of extruding a raw material composition containing a water-soluble resin and water from a mold to form a sheet-like composition, and a step (B) of conveying the sheet-like composition with a casting roller. In the step (A), when the moisture content of the sheet-shaped composition at the mold outlet is 20 to 55% by weight, the mold outlet is x, and the contact between the sheet-shaped composition and the casting roller is y. This is a method for producing a water-soluble film in which the linear distance between x and y is 10 mm or more, and in the step (B), the casting roller surface temperature is higher than the dew point temperature in the atmosphere around the casting roller.
Hereinafter, the present invention will be described in detail.

In the present invention, first, the step (A) of extruding a raw material composition containing a water-soluble resin and water from a mold to form a sheet-like composition is performed.

The step (A) is usually performed using a multi-screw extruder.
As the multi-screw extruder, a twin-screw extruder or a twin-screw extruder may be used in addition to a twin-screw extruder, but a twin-screw extruder is preferably used from the viewpoint of cost.

When performing the said process (A), it is preferable to perform the process of supplying the raw material composition containing water-soluble resin and water, and the process of mixing the said raw material composition prior to that.
Examples of the method of charging the raw material composition include a method of charging from a raw material supply port installed in the barrel of the multi-screw extruder.
One place may be sufficient as the place which throws the said raw material composition into a multi-screw extruder, and two or more places may be sufficient as it. Moreover, the water-soluble resin and water may be added simultaneously or separately.

The step of mixing the raw material composition is preferably performed by rotating a screw installed inside the barrel of the multi-screw extruder.
Although it does not specifically limit as a structure of the screw of the said multi-screw extruder, It is preferable that the screw element of a full flight and a kneading disk is included at least.
The full flight has the ability to transport the raw material composition, and the kneading disc has the ability to mix and dissolve the raw material composition in a shorter time, thereby increasing the production rate. .

In the said process (A), it does not specifically limit as a kind of metal mold | die used, Conventionally well-known metal mold | dies, such as a circular die and a T die, can be used, A T die is especially preferable.

Examples of the water-soluble resin include polyvinyl alcohol resins, polyethylene glycol resins, carboxymethyl cellulose resins, pullulans, sodium acrylate resins, gelatin, and the like. Especially, what contains a polyvinyl alcohol-type resin is preferable.
Moreover, only 1 type may be used for the said water-soluble resin, or 2 or more types of resin may be used together.

The polyvinyl alcohol resin preferably has a hydroxyl group content of 40 mol% or more.
When the amount of the hydroxyl group is less than 40 mol%, water solubility is insufficient, and kneading with the liquid becomes insufficient in a multi-screw extruder, so that a desired film may not be obtained. The amount of the hydroxyl group is more preferably 60 mol% or more, and further preferably 70 mol% or more. Moreover, it is preferable that the said hydroxyl amount is 99.5 mol% or less.
In addition, the said hydroxyl amount means content of the structural unit shown in following formula (1).

The polyvinyl alcohol resin can be obtained by saponifying a polymer of a vinyl ester monomer.
For the saponification, an alkali or an acid is generally used, but an alkali is preferably used.

Examples of the vinyl ester monomers include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, and the like.
Among these, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate are preferably used.

The vinyl ester monomer polymer may be a copolymer of the vinyl ester monomer and a monomer other than the vinyl ester monomer.
Examples of other monomers, that is, comonomers to be copolymerized, include olefins, (meth) acrylic acid and salts thereof, (meth) acrylic acid esters, (meth) acrylamide derivatives, N-vinylamides, N-vinylimidazole. , Vinyl ethers, nitriles, vinyl halides, allyl compounds, maleic acid and its salts, maleic acid esters, itaconic acid and its salts, itaconic acid esters, crotonic acid and its salts, vinyl sulfonate, vinylsilyl compounds, acetic acid And isopropynyl.
As for the other monomer, only one kind may be used, or two or more kinds may be used in combination.

Examples of the olefins include ethylene, propylene, 1-butene, and isobutene.
Examples of the (meth) acrylic acid esters include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, and (meth) acrylic acid. Examples thereof include n-butyl and 2-ethylhexyl (meth) acrylate.
Examples of the (meth) acrylamide derivative include acrylamide, n-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, 3-dimethylaminopropylmethacrylamide, (meth) acrylamidepropanesulfonic acid and salts thereof. Can be mentioned.

Examples of the N-vinylamides include N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, and the like.
Examples of the N-vinylimidazoles include N-vinylimidazole.
Examples of the vinyl ethers include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl ether.
Examples of the nitriles include (meth) acrylonitrile.
Examples of the vinyl halides include vinyl chloride and vinylidene chloride.
Examples of the allyl compound include allyl alcohol, hydroxypolyethoxyallyl ether, sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, allyl acetate, and allyl chloride.
As said vinyl silyl compound, vinyl trimethoxysilane etc. are mentioned, for example.

When the polyvinyl alcohol resin is a copolymer of the vinyl ester monomer and another monomer, the preferred lower limit of the content of the other monomer is 0.5 mol%, and the preferred upper limit is 25 mol%. The more preferred lower limit is 1 mol%, and the more preferred upper limit is 10 mol%.

The polyvinyl alcohol-based resin may be subjected to a modification treatment by adding a predetermined functional group.
Although it does not specifically limit as a functional group provided as a result of the said modification | denaturation process, A formal group, an acetoacetal group, a butyral group, an amino group, an amide group, a carboxyl group, a sulfo group etc. are mentioned.

Although the polymerization degree of the said polyvinyl alcohol-type resin is not specifically limited, It is preferable that it is 300-4000. If the degree of polymerization is less than 300, the strength of the resulting film may be insufficient, and it may not be possible to form the film uniformly. When the degree of polymerization exceeds 4000, the viscosity increases, the mold back pressure increases, and extrusion with an extruder or a gear pump may be insufficient.
The more preferable lower limit of the polymerization degree is 500, and the more preferable upper limit is 3000.

The shape of the water-soluble resin is not particularly limited, and a wet cake-like water-soluble resin containing pellets, powder, and water to be charged into a multi-screw extruder later may be used.

The raw material composition contains water in addition to the water-soluble resin.
Moreover, the said raw material composition may contain the other liquid in addition to water.

Examples of the other liquid include ethanol, methanol, propanol, isopropanol, acetone, methyl ethyl ketone, acetic acid, methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, glycerin, ethylene glycol, propylene glycol, butylene glycol, diglycerin, Examples include polyethylene glycol.
The other liquids may be used alone or in combination of two or more.

The raw material composition may further contain a conventionally known plasticizer, surfactant, and preservative.
Examples of the plasticizer include glycerin, diglycerin, triglycerin, polyglycerin, ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, trimethylolpropane, triethylene glycol, polyethylene glycol, polypropylene glycol, pentaerythritol, and mannitol. , Polyhydric alcohol plasticizers such as sorbitol, fructose and glucose, and mixtures thereof.

The raw material composition may contain a conventionally known surfactant. By including the surfactant, the film surface during film formation can be smooth, and the peelability of the film containing liquid from the substrate can be improved.

The water-soluble resin content in the raw material composition is preferably 50 to 80% by weight.
When the content of the water-soluble resin is more than 80% by weight, the water-soluble resin is not sufficiently dissolved in water and a non-uniform film can be obtained, or the viscosity of the raw material composition is increased, so that the multiaxial extrusion is performed. The pressure inside the machine may rise too much, making it impossible to form a film. Further, when the content of the water-soluble resin is less than 50% by weight, the cost and efficiency of the step of removing the liquid may be deteriorated. Preferably it is 55 to 70% by weight.
The water-soluble resin content can be calculated from the amount of raw material composition charged into the multi-screw extruder per unit time.

In the said process (A), the moisture content of the sheet-like composition in a metal mold | die exit is 20 to 55 weight%.
By making the water content of the sheet-like composition at the mold outlet 20% by weight or more, the solubility of the water-soluble resin in water increases, and a sheet-like composition is obtained without clogging in the mold. Can do. When the water content of the sheet-like composition at the mold outlet exceeds 55% by weight, the viscosity of the sheet-like composition extruded from the mold decreases, the neck-in amount increases, and the thickness is uniform in the width direction. A film cannot be obtained. In addition, the preferable minimum of the moisture content of the sheet-like composition in the said mold exit is 25 weight%, a more preferable minimum is 30 weight%, a preferable upper limit is 50 weight%, and a more preferable upper limit is 45 weight%.
The “moisture content of the sheet-like composition at the mold outlet” refers to the moisture content of the sheet-like raw material composition immediately after being extruded from the mold.

In the said process (A), it is preferable that the thickness of the sheet-like composition in the said metal mold exit is 300 micrometers or more. By setting the thickness of the sheet-shaped composition within the above-mentioned range, a film having a uniform thickness and less influence of disturbance can be obtained.

In the present invention, next, the step (B) of conveying the sheet-like composition with a casting roller is performed. A water-soluble film can be obtained by drying and film-forming the sheet-like raw material composition extruded from the metal mold | die through the said process (B).
The water-soluble film as used herein refers to a film in which 90% by weight of the total weight is dissolved by being immersed in water at a temperature of 20 ° C. and left as it is for 24 hours.

FIG. 1 is a diagram schematically showing a part of the step (B).
As shown in FIG. 1, the sheet-like composition 5 extruded from the mold 4 is conveyed by being wound around a rotating casting roller 6.
Here, in the present invention, the surface temperature of the casting roller 6 is higher than the dew point temperature D of the ambient atmosphere of the casting roller 6, the mold outlet of the mold 4 is x, the sheet-like composition 5, the casting roller 6, When the contact point of y is y, the linear distance between x and y is 10 mm or more. In addition, when z is the axial center of the casting roller 6, it is preferable that the angle of the minor angle (∠xyz) formed by x, y, and z is 100 ° or more and less than 180 °.
In addition, “the minor angle formed by x, y, and z” refers to the smaller one of the angles formed from the three points x, y, and z with y as the vertex.

The casting roller may be a single roller or a plurality of rollers.

In the present invention, in the step (B), the casting roller surface temperature (roller surface temperature) is higher than the dew point temperature (atmosphere dew point temperature) of the surrounding atmosphere of the casting roller.
The difference between the surface temperature and the atmospheric dew point temperature [roller surface temperature−atmospheric dew point temperature] is preferably 3 to 20 ° C.
When the roller surface temperature is higher than the atmospheric dew point temperature, it is possible to prevent the film surface from being dissolved and the formation of a dent due to the dew condensation on the roller surface. As a result, a water-soluble film excellent in appearance can be produced.
In the present invention, the “dew point temperature in the ambient atmosphere of the casting roller” refers to a dew point temperature that is present in the same space as the casting roller and measured air at a position of 10 mm or more and less than 100 mm from the surface of the casting roller.
The dew point temperature can be measured using a commercially available dew point meter.

In the step (B), the surface temperature of the casting roller is preferably 60 ° C. or higher.
When the surface temperature of the casting roller is less than 60 ° C., the sheet-like raw material composition immediately after being extruded from the mold may not be sufficiently dried and may not be uniformly peeled off from the casting roller. The surface temperature of the casting roller is more preferably 70 to 100 ° C.
Moreover, it is preferable that atmospheric dew point temperature is 10-70 degreeC.

In the step (B), when the die exit is x, the contact between the sheet-like composition and the casting roller is y, and the axial center of the casting roller is z, the linear distance between x and y is 10 mm or more. By setting the linear distance between the mold outlet and the casting roller contact to be 10 mm or more, the amount of the water-soluble resin and water-containing raw material mixture adhering to the mold outlet top surface can be reduced. It is possible to obtain a water-soluble film free from water.
The linear distance between x and y is preferably 250 mm or less. When the linear distance between x and y exceeds 250 mm, the influence of disturbance on the sheet-like raw material composition extruded from the mold outlet becomes large, and a film having a uniform thickness may not be obtained. The linear distance between x and y is more preferably 20 to 150 mm.

In the step (B), the linear distance between y and z (roller radius of the casting roller) is preferably 300 mm or more. By setting the roller radius within the above range, the sheet-like composition immediately after discharging the mold can be sufficiently dried.

In addition, when the exit of the mold is x, the contact between the sheet-like composition and the casting roller is y, and the axial center of the casting roller is z, the minor angle (∠xyz) formed by x, y and z is It is preferably 100 ° or more and less than 180 °. By setting the angle of the minor angle (∠xyz) within the above-mentioned range, the amount of water vapor entrapped in the gap between the sheet-like composition immediately after the mold is discharged and the casting roller is reduced, so that there is no poor appearance. Can be obtained.

If the angle of minor angle (∠xyz) is less than 100 °, the amount of water vapor entrained in the gap between the sheet-like composition immediately after the mold discharge and the casting roller increases, and the surface of the water-soluble film is indented. May occur. In addition, the time during which the sheet-like composition contacts the casting roller is shortened, and the sheet-like composition immediately after discharging the mold may not be sufficiently dried and may not be uniformly peeled off from the casting roller. Note that the angle of the inferior angle (∠xyz) is more preferably 110 ° or more and 150 ° or less.

In order to set the angle of the minor angle (∠xyz) to 100 ° or more and less than 180 °, for example, a method of pressing the touch roller from the outside at the contact point between the sheet-like composition and the casting roller, It is preferable to use a method of blowing air from the outside at the contact point with the casting roller and a method of sucking air from the inside at the contact point of the sheet-like composition and the casting roller.
Examples of the method for blowing air from the outside include a method using an air knife.
As a method of sucking air from the inside, a method using a vacuum chamber can be mentioned.

The touch roller is preferably one that sandwiches the entering sheet-like composition to prevent air from entering and can uniformly nip the sheet-like composition. By preventing the intrusion of air and causing the sheet-like composition to be uniformly nipped, the sheet-like composition can be conveyed stably without any defects.

The air knife is preferably one that blows air from the tip of the air knife head to the entering sheet-like composition and uniformly blows it in the width direction by a gas flow such as a blade. By uniformly spraying in the width direction, air between the sheet-like composition and the casting roller can be eliminated, and a film having a uniform thickness can be obtained.
The vacuum chamber is preferably capable of sucking air from the vacuum chamber suction portion to the sheet-like composition that enters, generating negative pressure, and sucking it uniformly in the width direction. By uniformly sucking in the width direction, air between the sheet-like composition and the casting roller can be eliminated, and a film having a uniform thickness can be obtained. The air knife and the vacuum chamber may be used alone or in combination.

By using the method for producing a film of the present invention, the amount of water vapor entrapped in the gap between the sheet-like composition immediately after discharging the mold and the casting roller is reduced, so that a water-soluble film having no appearance defect can be obtained. .
Examples of the use of the water-soluble film include water-soluble films used for packaging medicines such as detergents and agricultural chemicals.

According to the present invention, since the moisture content of the sheet-like composition at the mold outlet is low, the drying process can be simplified and the productivity can be improved. Moreover, since the amount of water vapor entrained in the gap between the sheet-like composition immediately after the mold is discharged and the casting roller is reduced, a water-soluble film having no appearance defect can be obtained.

It is the figure which showed typically a part of process (B) of this invention. It is an example of the multi-screw extruder used by this invention. FIG. 4 is a diagram schematically showing a part of the process in Example 1. It is the figure which showed typically a part of process in Example 2. FIG. It is the figure which showed typically a part of process in Example 3 grade | etc.,.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
A film was produced by extrusion molding using a multi-screw extruder (a twin-screw extruder (screw diameter φ25 mm, L / D = 45)) in which the screw is composed of a full flight and a kneading disk as shown in FIG. The biaxial extruder 1 was connected to the mold 4 via the gear pump 3, and the mold outlet 41 had a width of 400 mm and a clearance of 0.4 mm. The specific procedure is as follows.

A polyvinyl alcohol resin (SELVOL 518, manufactured by SEKISUI SPECIALTY CHEMICALS AMERICA, degree of polymerization 1300, hydroxyl amount 88 mol%) was charged at 1.00 kg / Hr from the raw material supply port 21 (hopper).
At the same time, water and glycerin were charged from two liquid inlets. Water was supplied to the inside of the barrel 2 at 0.48 kg / Hr from the liquid inlet 22a and glycerin was supplied from the liquid inlet 22b at 0.08 kg / Hr. The liquid was supplied at a position where water touched the resin before glycerin.
The screw speed of the twin screw extruder 1 was set to 350 rpm, and the barrel temperature and the mold temperature were both set to 90 ° C.
As shown in FIG. 3, the sheet pushed out from the mold exit is rotated at 1 m / min by rotating a casting roller of φ1000 mm and a surface temperature of 60 ° C. while pressing the touch roller 61 from the outside to dry the sheet. A film having a water content of 6.2% by weight and a thickness of 50 μm was obtained. As a result of measuring the temperature and humidity of air at a position 40 mm from the surface of the casting roller at this time, the dew point temperature (atmosphere dew point temperature) was 49 ° C.
In addition, it was 45 weight% when the moisture content of the sheet | seat immediately after extruded from the metal mold | die exit was measured with the heat drying type moisture meter (MX-50, A & D product make).
Further, when the die exit is x, the contact between the sheet and the casting roller is y, and the axial center of the casting roller is z, the linear distance between x and y (= hereinafter also referred to as an air gap) is 100 mm. Furthermore, the angle of the minor angle (∠xyz) formed by x, y and z was 130 °.

(Examples 2-11, Comparative Examples 1-5)
A film was obtained by using the same method as in Example 1 except that the production conditions were changed as shown in Table 1.
In Examples 2, 4 to 8, the casting roller was rotated while air was blown from the outside using an air knife 62 as shown in FIG.
Further, in Example 3, as shown in FIG. 5, the sheet was dried by rotating the casting roller while sucking air from the inside using the vacuum chamber 63.
Furthermore, in Examples 9 to 11, the sheet was dried by rotating the casting roller at 1 m / min without using the touch roller 61. Thereafter, the film was peeled off from the casting roller and dried on a φ1000 mm casting roller (second casting roller) heated to a surface temperature of 60 ° C. rotating at 1 m / min to obtain a film.
In Comparative Example 2, since the pressure loss in the extruder was high and the resin was hardly extruded from the mold, no film was obtained.

<Evaluation>
The following evaluation was performed about the film obtained by the Example and the comparative example. The results are shown in Table 1.
In addition, since the film was not obtained about the comparative example 2, the following evaluation was not performed.

(Film appearance: hollow)
The surface (length 2 m, width 300 mm) of the obtained film was observed using a digital microscope (Dinо-lite, manufactured by AnMo Electronics Corporation).
When there was a dent with a diameter of 40 μm or more on the film surface, “Yes” was evaluated, and when the size of the dent was less than 40 μm, “No” was evaluated.

(Film appearance: die line)
The film surface was visually observed, and a die line was evaluated as “present” when a straight line was visible in the film conveyance direction, and a die line was evaluated as “not present” when a streak was not visible.

(Attaching to casting roller)
The releasability of the casting roller was visually observed. The case where sticking occurred on the casting roller during 2 hours from the start of film formation and the conveyance became impossible was evaluated as “Yes”, and the case where there was no such sticking was evaluated as “No”.

(Moisture content after drying)
Ten films 30 × 30 mm □ after drying on a casting roller were taken, and the moisture content was measured using a heat drying moisture meter (MX-50, manufactured by A & D). Measurement conditions are a heating temperature of 105 ° C. and a heating time of 60 seconds.

According to the present invention, since the moisture content of the sheet-like composition at the mold outlet is low, the drying process can be simplified and the productivity can be improved. Moreover, since the amount of water vapor entrained in the gap between the sheet-like composition immediately after the mold is discharged and the casting roller is reduced, a water-soluble film having no appearance defect can be obtained.

Claims (6)

A step (A) of extruding a raw material composition containing a water-soluble resin and water from a mold to form a sheet-like composition, and a step (B) of conveying the sheet-like composition with a casting roller,
In step (A), the moisture content of the sheet-like composition at the mold outlet is 20 to 55% by weight,
When the die exit is x and the contact point between the sheet-like composition and the casting roller is y, the linear distance between x and y is 10 mm or more,
In the step (B), the casting roller surface temperature is higher than the dew point temperature of the atmosphere around the casting roller. 2. The water-soluble film according to claim 1, wherein an angle of a minor angle (∠xyz) formed by x, y, and z is 100 ° or more and less than 180 °, where z is the axial center of the casting roller. Manufacturing method. The method for producing a water-soluble film according to claim 1 or 2, wherein, in the step (B), the touch roller is pressed from the outside at the contact point between the sheet-like composition and the casting roller. The method for producing a water-soluble film according to claim 1 or 2, wherein in the step (B), air is blown from the outside at the contact point between the sheet-like composition and the casting roller. The method for producing a water-soluble film according to claim 1 or 2, wherein in step (B), air is sucked from the inside at a contact point between the sheet-like composition and the casting roller. 6. The method for producing a water-soluble film according to claim 1, wherein the water-soluble resin contains a polyvinyl alcohol resin.

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