JP2009067010A - Method for manufacturing polyvinylalcohol-based film, and film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyvinylalcohol-based film that can efficiently form a mat surface on the surface of the polyvinylalcohol-based film with simple equipment and very efficiently and easily switch between a polyvinylalcohol-based film having the mat surface and a polyvinylalcohol-based film with a mirror finished surface without the mat surface, and the polyvinylalcohol-based film obtained by the method. <P>SOLUTION: The method for manufacturing the polyvinylalcohol-based film is characterized by spreading an aqueous solution containing 10-70 wt.% polyvinylalcohol-based resin, on a rotating heated roll for mirror finish to dry on the roll for mirror finish, and then pressing a heated nip roll with a surface roughness SRa=1-100 μm to form the mat surface on the surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a polyvinyl alcohol film having a mat surface, and more specifically, the mat surface can be efficiently formed on the surface of the polyvinyl alcohol film with simple equipment. A method for producing a polyvinyl alcohol film which is very efficient and easy to switch between a polyvinyl alcohol film having a matte surface and a mirrored polyvinyl alcohol film having no matte surface when producing the polyvinyl alcohol film About.

  A polyvinyl alcohol film (hereinafter referred to as “PVA film”) is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, and then forming the film by a solution casting method (casting method). Generally, it is manufactured by.

  However, water-soluble PVA films, that is, PVA films made of polyvinyl alcohol resin having a high degree of saponification have high hydrophilicity, so they easily absorb moisture and are not easily separated from each other. It is easy to cause so-called blocking. Accordingly, it is known that the blocking phenomenon caused by the moisture absorption can be prevented by forming a mat surface on at least one surface of the PVA film in order to prevent the blocking.

  As a conventional method for forming a matte surface on a film, a technique for forming a matte surface on a film surface by plasma treatment of the film surface in a vacuum vessel (for example, Patent Document 1) or a lubricant is used as a resin composition for the film. A technology for forming a matte surface by adding a technology, a technology for forming a matte surface by adding a transparent inorganic filler to the resin composition of the film and uniformly giving fine irregularities to the surface of the film, and two A technique using a combination of techniques is known. (For example, Patent Documents 2 and 3)

JP 63-6030 A JP-A-62-138540 JP-A-53-39344

  In Patent Document 1, since it is necessary to perform processing in a vacuum vessel, the equipment is expensive, and from the viewpoint of stably performing plasma processing on the film surface, it is complicated in terms of work such as setting vacuum conditions, and the production efficiency. Etc. were also not preferable.

In addition, in the technique of forming a matte surface by adding a filler or a lubricant to the resin composition of the film, the filler or the lubricant to be added affects the processability when forming the film, and the film After forming, for example, when used as a water-soluble film, problems such as physical properties such as fillers or lubricants dispersed in the solution and soiling the printed surface of the curved surface printing may occur, so under extremely limited conditions It could only be used with.
For example, in the case of film processing a material composed of a polyvinyl alcohol-based resin composition, it is very difficult to use a hydrophobic lubricant in the hydrophilic polyvinyl alcohol-based resin composition. Can be mentioned.

  In addition, in the technique of forming a matte surface by adding a transparent inorganic filler to the film resin composition and uniformly imparting fine irregularities to the surface of the film, the film is uniformly dispersed in the resin composition of the film. Since it is necessary, it is complicated in work, and quality problems such as variations in the mat surface formed on the film surface may occur.

  In Patent Documents 2 and 3, the PVA film, like the above, is complicated in work and has problems from the viewpoint of stable production and the like, and further improvement has been demanded.

  On the other hand, in the case of PVA film only, a method of spreading and drying a PVA solution on an embossed metal roll to form a matte surface is employed, but the embossing is transferred uniformly and reliably from the metal roll to the film. In order to achieve this, it was necessary to keep the viscosity of the PVA-based solution, which is the resin composition of the film, low. As means for keeping the viscosity of such a PVA-based solution low, it has been adopted to reduce the concentration of the polyvinyl alcohol-based resin from various viewpoints such as cost and workability. However, since the moisture content in the PVA-based solution becomes high, the drying process takes time, resulting in a decrease in production speed and a very low production efficiency. It was.

  In general, printing or the like is necessary when manufacturing a PVA film for packaging, so the surface of the PVA film must be glossy finished. Therefore, a mirror-finished metal roll is used in the manufacturing process. There is a need.

  In addition, at the manufacturing site, it is often necessary to switch from a PVA film with a matte finish to a PVA film with a glossy finish. For this reason, the embossed metal roll is replaced with a mirror finished metal roll. There was a need.

For this reason, the production process of the PVA film is complicated, the labor burden is large, and the production efficiency is not good, so that early improvement has been desired.

Therefore, the present invention solves the above-mentioned problems, and an aqueous solution composed of 10 to 70% by weight of a polyvinyl alcohol-based resin is applied to a rotating heated mirror-finished roll (hereinafter referred to as “mirror roll”). After spreading and drying on a mirror surface roll, a mat surface is formed on the surface by pressing a heated nip roll having a surface roughness (SRa) = 1 to 100 μm. A method is provided.

According to the present invention, a mat surface can be easily imparted to a PVA film, a mat surface can be formed on one surface of the PVA film, and a mirror surface can be efficiently formed on the other surface.
Since the blocking of the film can be prevented by the matte surface, it is particularly useful for a PVA-based film in which blocking easily occurs.

  In the present invention, it is preferable that the heated nip roll rotates synchronously with the heated mirror roll.

  Thereby, the damage to the PVA-type film which may be caused by the difference in rotational speed between the mirror surface roll and the nip roll can be prevented.

  In the present invention, the surface of the PVA-based film having one mat surface has a surface roughness SRa = 0.5 μm or more and the other surface having no mat surface (hereinafter referred to as “mirror surface side”). It is possible to provide a method for producing a PVA-based film having a surface roughness (SRa) of less than 0.5 μm.

  As a result, the surface having the matte surface has a surface roughness (SRa) of 0.5 μm or more, and the mirror surface has a surface roughness (SRa) of less than 0.5 μm. A PVA-based film having both properties and anti-blocking properties can be obtained.

  Furthermore, in the present invention, the saponification degree of the polyvinyl alcohol resin is preferably 80% or more.

  As a result, even a so-called highly saponified polyvinyl alcohol resin having a saponification degree of 80% or more is dried by a mirror roll, so that the resin does not adhere to the mirror roll, and a stable film Molding is possible. Moreover, in the PVA film, when a polyvinyl alcohol resin having a saponification degree of 80 to 90% suitable as a material for the water-soluble film is used, mat processing and printing for preventing blocking of the PVA film surface are performed. Therefore, it is essential to secure a smooth surface.

  According to the present invention, when a polyvinyl alcohol-based resin having a saponification degree of 80 to 90% is used as a material for a PVA-based film, in addition to the above stable film forming, ensuring smoothness and matting can be easily performed. The effect of being able to carry out efficiently etc. can be show | played especially notably.

  The PVA-based film obtained by the present invention has excellent transparency and high anti-blocking properties, and is composed of a polyvinyl alcohol-based resin, so it is widely used from general packaging materials to food packaging materials. There are uses.

  According to the present invention, a uniform matte surface can be stably imparted to a PVA film, and the film forming speed can be increased as compared with a conventional method of spreading a PVA aqueous solution on an embossed metal roll. Production efficiency can be improved.

  In addition, according to the present invention, in the manufacturing process, it is easy and quick to switch between a PVA film having a mat surface and a PVA film having only a so-called mirror surface on which no mat surface is formed, The work efficiency at the time of switching the production can be dramatically improved.

  In addition, according to the present invention, by causing the nip roll to rotate synchronously with the mirror roll, it is possible to prevent damage to the surface of the PVA-based film that may be caused by a rotational deviation between the nip roll and the mirror roll.

  In addition, according to the present invention, since a PVA-based film having a mat surface roughness (SRa) = 0.5 μm or more can be obtained, the other surface roughness (SRa) is less than 0.5 μm, so-called mirror surface. Even if it exists, the PVA-type film which can prevent blocking reliably can be obtained.

  Furthermore, according to the present invention, even a polyvinyl alcohol resin having a saponification degree of 80% or more can be used, and a polyvinyl alcohol resin having a high saponification degree, which was difficult to be molded by a conventional production method, is obtained. It can be easily formed into a film, and in addition, a matte surface can be imparted.

  In addition, according to the present invention, a film obtained from such a highly saponified polyvinyl alcohol resin has high transparency and no toxicity, so that a PVA film suitable for food packaging can be obtained.

Furthermore, since the PVA film obtained by the present invention has a matte surface, blocking does not occur and the surface roughness SRa of the matte surface is stable.

Hereinafter, the present invention will be described in detail.
Polyvinyl alcohol and / or a derivative thereof is used as a raw material for the PVA film applied to the present invention as long as the effects of the present invention are not impaired. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, and alkyl esters thereof, acrylamide and the like. It is done. In the present invention, the polyvinyl alcohol resin refers to a polyvinyl alcohol resin and / or a derivative thereof described above.

  The degree of polymerization of the polyvinyl alcohol resin is generally 1000 to 10,000, preferably 1500 to 10,000. The degree of saponification may be changed according to the use, but it is preferable to use a water-soluble film having a saponification degree of 70% to 95%, preferably 75% to 90% or less. As the packaging film, it is preferable to use a polyvinyl alcohol resin having a saponification degree of 90% or more, more preferably 95% or more.

  In the present invention, an aqueous solution made of a polyvinyl alcohol-based resin (hereinafter referred to as “an aqueous solution such as PVA”) is used.

  In the present invention, first, the polyvinyl alcohol resin powder is usually washed to remove sodium acetate contained in the resin. At the time of the washing, washing with methanol or water is performed. However, since washing with methanol requires solvent recovery, a washing method with water is preferable.

  Next, the water-containing polyvinyl alcohol resin after washing, that is, the wet cake is dissolved to prepare an aqueous solution of the polyvinyl alcohol resin. From the viewpoint of adjusting the concentration of the polyvinyl alcohol resin, it is preferable to dehydrate the wet cake. . The dehydration method is not particularly limited, but a method using centrifugal force is preferable.

  In the present invention, when the wet cake is dissolved, a stirring device such as a Hobart mixer, a Henschel mixer, a kneader mixer, or a twin screw extruder can be used. It is preferred to use an apparatus. It is preferable from the viewpoint that uniform stirring can be performed when stirring is started when steam is blown into the dissolution tank of the stirring device and the resin temperature reaches 40 to 80 ?. If the resin temperature is less than the lower limit value, the load on the motor increases. If the resin temperature exceeds the upper limit value, the polyvinyl alcohol resin is hardened and uniform dissolution becomes difficult.

  Further, an aqueous solution such as PVA is preferable because when the inside of the can is pressurized when the resin temperature reaches 90 to 100? Then, when the resin temperature reaches 130 to 150 ?, the blowing of water vapor is terminated, and stirring is continued for 0.5 to 3 hours while adjusting to a desired concentration.

  The concentration of the polyvinyl alcohol resin in the aqueous solution such as PVA obtained by these methods is preferably 10 to 70% by weight. This is because when the concentration of the polyvinyl alcohol resin is less than 10% by weight, the drying load increases and the production efficiency decreases, and when it exceeds 70% by weight, the viscosity becomes too high and uniform dissolution becomes difficult.

  Further, an aqueous solution such as PVA may be prepared by adding an additive such as a plasticizer in an aqueous solution of a polyvinyl alcohol resin. Examples of the plasticizer include polyols and condensates thereof, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. Although the usage-amount of a plasticizer is not restrict | limited in particular, It is preferable to set it as 20 weight% or less in a PVA-type film.

  Furthermore, in the present invention, from the viewpoint of uniformly dissolving the polyvinyl alcohol resin in water in the mixing / stirring step of the polyvinyl alcohol resin and continuously and efficiently supplying it to the heated mirror roll, a twin screw extruder Is preferably used. That is, an aqueous solution such as PVA is discharged from the twin-screw extruder, and supplied and spread on a heated mirror roll.

  In the present invention, the mirror roll used for spreading an aqueous solution such as PVA refers to a drum-type roll and an endless belt. In this invention, when discharging aqueous solution, such as PVA, to a mirror surface roll with a twin-screw extruder, a drum type roll is preferably used as the mirror surface roll.

  In this invention, when using the said coating device, the thickness of a PVA-type film can be adjusted with the said coating device. Moreover, when discharging a PVA-type aqueous solution to a mirror surface roll with a twin-screw extruder, it is also possible to obtain a PVA-type film having a desired thickness by adjusting the gap between the twin-screw extruder and the mirror surface roll. The PVA film is preferably adjusted to a thickness of about 10 to 150 μm from the viewpoint of water solubility, printability, and processability.

  Further, the surface temperature of the mirror roll is maintained at 80 to 100 ?, preferably 90 to 98? From the viewpoint of film formation stability and production efficiency.

  In the present invention, the PVA aqueous solution is spread on a heated mirror roll, dried and formed into a film, and then pressed with a nip roll. A matt roll is applied to the film surface by pressing the nip roll. From the viewpoint of the uniformity of the mat surface and stable application, when the moisture content of the film (JISK7251) is dried to 30 to 50% by weight, It is preferable to press. Here, pressing means that the nip roll is brought into contact with the film surface to such an extent that a matt roll is formed by providing the nip roll with substantially uniform fine irregularities on the film surface.

  Further, the nip roll applied in the present invention has a surface roughness (SRa) of 1 to 100 μm from the viewpoint of the uniformity of the matte surface applied to the film surface and the anti-blocking property of the PVA film provided with the matte surface. It is preferable that

  The surface roughness (SRa) in the present invention refers to that measured under the following conditions using a stylus type three-dimensional surface roughness meter as an index of flatness.

Temperature: 23? ± 2?
Humidity: 50% ± 10%
Thickness of the PVA film of the present invention: 0.8 μm (Before measurement of surface roughness (SRa), temperature: 23
It is cured for 24 hours under the conditions of ± 2? And humidity: 50% ± 10%. )
Measuring instrument: Kosaka Laboratory 3D surface roughness measuring instrument SE-30K
Low frequency cut: 0.25mm
High cut: R + W,
X pitch: 1μm
Y pitch: 2 μm
Feeding speed in the X-axis direction: 0.2mm / sec
Z measurement magnification: 1000
Leveling: least squares method

  Further, the surface temperature of the nip roll is heated and maintained at 80 to 100 ?, preferably 90 to 98? From the viewpoint of film formation stability and production efficiency.

  In the present invention, after the mat surface is formed on the PVA film by the nip roll, the PVA film is further dried using a known drying apparatus such as a drying roll, a floating dryer, a drying oven, etc. You may adjust to rate.

  Any of the drying apparatuses may be used for drying, but it is preferable to use a plurality of drying rolls having a diameter of 200 mm to 2000 mm whose surface is hard chrome plated or mirror-finished. That is, the PVA film can be efficiently dried by alternately passing the front and back surfaces of the formed PVA film through a plurality of drying rolls.

  The surface temperature of the drying roll is not particularly limited, but is preferably 60 to 100 ?. If the surface temperature is less than 60 ?, a sufficient drying effect may not be expected. On the other hand, if it exceeds 100 ?, the PVA film may be excessively dried. In the case of such excessive drying, the PVA-based film obtained according to the present invention can be subjected to a desired stretching process in the stretching process. However, when the stretching process is performed, problems such as insufficient stretching can occur. Sometimes, it is not preferable.

  On the other hand, the moisture content may be adjusted to a desired level by absorbing water by spraying water on the PVA film.

  Moreover, after forming a mat | matte surface in a PVA-type film as mentioned above, functionality, such as an improvement of tearing strength, can also be provided to the said film by extending | stretching as needed.

  Furthermore, in the present invention, when the mat surface is formed on the film on the mirror roll by nip roll, the film has a high water content of 50 to 30% by weight, so that the friction between the mirror roll and nip roll is large. May cause scratches due to the friction on the film surface. Therefore, the surface of the PVA film can be prevented from being scratched by minimizing the friction, that is, by rotating the mirror roll and the nip roll synchronously to make the friction substantially zero. it can.

  In the present invention, the surface having one mat surface of the PVA-based film has a surface roughness (SRa) of 0.5 μm or more, and the surface having no other mat surface has a surface roughness (SRa) = By setting the thickness to less than 0.5 μm, it is possible to obtain a PVA film having excellent surface smoothness, i.e., printability, and anti-blocking properties.

  In the present invention, from the viewpoint of the anti-blocking effect of the PVA-based film, the surface roughness (SRa) of the surface on the mat surface side is 0.5 μm or more, more preferably 0.5 μm to 5.0 μm, still more preferably 0.8. 5 μm to 3.0 μm. The surface roughness (Sra) of the mat surface of the PVA-based film can be adjusted by controlling the nip roll surface roughness (SRa) or by controlling the nip roll pressing force.

  On the other hand, in the present invention, the surface roughness (SRa) of the surface on the mat surface side is 0.50 μm or more, more preferably 0.6 μm to 2.0 μm, from the viewpoint of preventing blocking of the PVA film. The surface roughness (SRa) on the mirror surface side of the PVA film can be adjusted by the surface roughness (SRa) of the mirror surface roll.

  In addition, according to the present invention, a PVA-based film having a mirror-side surface roughness (SRa) of less than 0.5 μm can be obtained. That is, by making each surface of the PVA-based film have the above surface roughness (SRa), a PVA-based film having smoothness, that is, excellent printability and anti-blocking properties is obtained. Can do.

(Example)
EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.
<Polyvinyl alcohol>
JP-10 J Poval Co., Ltd. Saponification degree 88.0% Polymerization degree 1000
HCW Kuraray Co., Ltd. Saponification degree 99.9% Polymerization degree 1700
Example 1
Using JP-10 with a twin-screw extruder (Toshiba Machine made in two different directions D = 38 mm L / D = 38), the concentration of polyvinyl alcohol (hereinafter referred to as “PVA”) is 50%. An aqueous solution of PVA was prepared, and an aqueous solution of 93? PVA was spread on a mirror surface roll maintained at a surface temperature of 95 ?, so that the moisture content of the spread film was approximately 15% (JIS K7251). It was made to dry. Furthermore, the surface roughness (SRa) rotated in synchronization with the mirror surface roll = 50 μm, and the mat surface is formed on only one side by pressing the film on the mirror surface roll with a nip roll whose surface temperature is kept at 100 °. A film was obtained. The surface roughness (SRa) of the mat surface of the PVA film was 1 μm.
The obtained PVA-based film of the present invention is composed of PVA, so that it has excellent water solubility, and since one surface is subjected to a matte treatment with a surface roughness (SRa) = 1 μm, it also has excellent antiblocking properties.

  According to the present invention, the mat surface can be efficiently formed on the surface of the polyvinyl alcohol film with simple equipment, and in addition, the polyvinyl alcohol film and the mat surface having the mat surface when the polyvinyl alcohol film is manufactured. Since it is very efficient and easy to switch with a mirror-finished polyvinyl alcohol film that does not have a surface, it is very useful industrially.

Claims (5)

  An aqueous solution consisting of 10 to 70% by weight of a polyvinyl alcohol resin is spread on a rotating heated mirror-finished roll, dried on the mirror-finished roll, and then heated with a surface roughness SRa = 1 to 100 μm. A method for producing a polyvinyl alcohol film, comprising forming a matte surface on a surface by pressing a nip roll.   2. The method for producing a polyvinyl alcohol film according to claim 1, wherein the heated nip roll rotates synchronously with the heated mirror-finished roll.   The surface of one side having a mat surface of the polyvinyl alcohol film has a surface roughness SRa = 05 μm or more and the surface having no other mat surface has a surface roughness SRa = less than 0.5 μm. The manufacturing method of the polyvinyl alcohol-type film of Claim 1 or 2 characterized by the above-mentioned.   The method for producing a polyvinyl alcohol film according to any one of claims 1 to 3, wherein the saponification degree of the polyvinyl alcohol resin is 80% or more.   The polyvinyl-alcohol-type film obtained by the manufacturing method in any one of Claims 1-4.