JPS6030697B2 - Polyvinyl alcohol film and its laminate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyvinyl alcohol film and a laminate thereof.

More specifically, the present invention relates to polyvinyl alcohol films and laminates thereof that reflect heat rays and ultraviolet rays and can therefore be effectively used as food packaging films, agricultural films, and the like. Conventionally, polyethylene films kneaded with aluminum powder have been known for the purpose of reflecting heat-resistant springs (wavelengths of 5 to 15 nm) and ultraviolet rays, but polyethylene films inherently have oxygen gas barrier properties and water vapor permeability. Therefore, these properties do not change at all even if aluminum powder is mixed.

These oxygen gas barrier properties and water vapor permeability are important properties for food packaging films and agricultural films, and we can add the property of reflecting heat rays and ultraviolet rays to them without essentially impairing these properties. If this can be done, the utility value of such a film as a food packaging or agricultural film will be further increased.

Polyvinyl alcohol film inherently has oxygen gas barrier properties and water vapor permeability, but it is generally formed from an aqueous solution of polyvinyl alcohol.
If ordinary aluminum powder is mixed into the aqueous molding solution, gas, especially hydrogen gas, will be generated, making film molding impossible, and even if it is possible, the film strength will be significantly reduced, and the aluminum powder will also black. Filling with aluminum powder is done using polyethylene foam.
It cannot be done as easily as in the case of Lum.

However, if aluminum powder with a grain size of about 100 or less and whose surface is coated with a gas generation inhibitor so that it is stable even in an aqueous medium is added as an aqueous aluminum paste to an aqueous polyvinyl alcohol solution, and a film is formed from this mixed aqueous solution. It has been found that molding is easy and the strength and color tone of the molded film are not impaired.

The aluminum particles mixed into the polyvinyl alcohol film have a particle size of about 100 French or less, preferably about 50 French
Its surface is coated with a gas generation inhibitor.

Gas generation inhibitors include saturated or unsaturated fatty acids,
Specifically, stearic acid, palmitic acid, lauric acid,
Oleic acid is shown as a typical example, and examples of other fatty acids are described in Hakama Seki No. 52-149282. When mixed with a polyvinyl alcohol aqueous solution for film forming, it is preferable to use the aluminum powder in the form of an aqueous paste. and other additives as necessary to prepare an aqueous paste. In this way, particles with a diameter of about 100, the surface of which is coated with a gas generation inhibitor,
The aluminum powder below A is about 0.5 to 10% by weight, preferably about 1 to 5% by weight as a powder after film forming.
It is used in the form of an aqueous paste in such an amount that it is contained in the film in proportions of .

If the content is less than this, the effect of mixing aluminum powder will not be seen, and if it is more, the strength of the formed film will be reduced. The polyvinyl alcohol to be formed into a film preferably has a degree of polymerization of about 1000 or more, a degree of saponification of about 95 mol % or more, and a hot water dissolution temperature of about 5 pi or more.

Additionally, the addition of glycol, which is commonly used as a softener, increases the ease of handling as a polyvinyl alcohol film, but when this is used as an agricultural film, the water-soluble softener dissolves in water. Since there is a risk that the additive may fall on the cultivated plants and damage the plants, it is desirable to keep the amount added to a minimum and to select the type.
During film forming, in order to more completely suppress gas generation, it is desirable to control the unevenness of the aqueous polypynyl alcohol solution to around 7.0 psi or to keep the temperature as low as possible, for example, below 8.0 psi. Thereafter, the polyvinyl alcohol concentration is about 5-60%, preferably about 10-40%.
% film-forming stock solution is cast onto a rotary drying drum (roll) or belt through a slit or coated with a roll coater, and is dried to form a film. The polyvinyl alcohol film according to the present invention can be laterally layered and integrated with the other side of a nonwoven fabric sheet whose at least one side has been heat-treated. This is generally carried out by pressing the preferably rough fiber surface of a nonwoven fabric sheet onto the film-like material of polyvinyl alcohol, which contains a large amount of water and is in a heated and softened state immediately after film formation. be exposed.

Depending on the degree of compression, the polyvinyl alcohol layer is inserted into the nonwoven fabric sheet, preferably with one side of each of the nonwoven fabric sheet and the polyvinyl alcohol layer forming both sides of the laminate, and then a drum (roll) or By drying the moisture on the belt, the nonwoven fabric sheet and the polypinyl alcohol film-like material are laminated and integrated.

Alternatively, a laminate may be obtained by casting a polyvinyl alcohol film-forming stock solution onto a nonwoven fabric sheet in the form of a film and press-bonding the film. Alternatively, the nonwoven fabric sheet and the polyvinyl alcohol film produced in advance or immediately after extrusion are bonded together, and the polyvinyl alcohol film is bonded by applying water to the surface of the polyvinyl alcohol film and heating it, or by spraying heated steam. It is also possible to employ a method in which both layers are laminated and integrated by bringing them into a water-containing and heat-softening state and then press-bonding them. Furthermore, it is also possible to use a lamination method in which a nonwoven fabric sheet and a preformed polyvinyl alcohol film are bonded together using an adhesive, such as a solution of a polyurethane adhesive, to integrate the two.

In this case, it is difficult to obtain a sufficiently high adhesive strength compared to the above-mentioned casting method, but heat retention and moisture permeability can be controlled by the adhesive layer. As shown in the drawing, a cross-sectional view of one embodiment of the laminate according to the present invention, a polyvinyl alcohol film containing aluminum powder 4 is laminated and integrated on the fiber face 3 side opposite to the heat-treated surface 2 of the nonwoven fabric sheet 1. Layer 5 is crimped with a little more pressure than natural contact without pressure, and penetrates into the fiber layer to about half the thickness of the nonwoven fabric sheet, so that the nonwoven fabric sheet and the aluminum powder-containing polyvinyl alcohol film are bonded together. are strongly bonded together, and the fiber layer that does not participate in the bonding functions as an air enclosing layer to improve heat retention.

If the pressure applied during crimping is further increased, the depth of penetration of the polypynyl alcohol layer can be made equal to the entire thickness of the nonwoven fabric sheet. The nonwoven sheet to be laminated with the polyvinyl alcohol layer preferably consists of a spunbond nonwoven sheet consisting of a continuous laminate of a polyolefin such as polypropylene, polyethylene, polyamide or polyester; It is a bulky sheet in which many layers are stacked or intertwined three-dimensionally, and because it contains a large amount of air, it has excellent heat retention properties. Therefore, bulkier materials are preferable, and from this point of view, it is preferable to use a structure in which continuous laminates including long fibers are assembled, such as a continuous fiber sheet-like deposit made by spunbond method, rather than short fibers. One side of this sheet-like deposit is preferably subjected to heat treatment, such as heat-enbossing using a heated metal roll, particularly spot bonding, in order to increase mechanical strength and suppress fluffing.

In this case, the other surface may be a rough surface of the nonwoven fabric sheet, or may be heat-treated. For example, if a nonwoven fabric sheet with a relatively coarse fiber density is used, which is made up of thick filaments of about 3 deniers or more, it is better to increase the density through heat treatment and reduce the voids to create a polyvinyl alcohol layer with fewer pinholes. can be formed, and a laminate without water leakage etc. can be obtained. On the other hand, when a nonwoven fabric sheet with relatively high fiber density composed of thin filaments of approximately 3 deniers or less is used, adhesion with the polyvinyl alcohol layer is better if the rough surface is left without heat treatment. It is. When the laminate constructed in this manner is heat-treated at about 100 to 180°C, preferably about 110 to 130 pm, the crystallinity of the polyvinyl alcohol surface increases, resulting in an improvement in hot water dissolution temperature and mechanical strength. do.

Furthermore, mechanical strength can also be improved by adding a humidity conditioning process. Furthermore, by using a film that is embossed from the polyvinyl alcohol layer side or that has been embossed on one side in advance, not only flexibility is imparted, but also mutual adhesion (blocking property) is improved. The polyvinyl alcohol layer that constitutes a part of the laminate has very low permeability to gases other than water vapor, so when combined with the presence of the fiber layer of the nonwoven fabric sheet, it further improves heat retention, while moisture is transferred to the outside by internal diffusion. This has the effect of preventing internal overhumidity and water droplets from falling. Moreover, the presence of aluminum powder in the polyvinyl alcohol layer further improves heat retention due to its thermal ant spring and UV transmission prevention effects, and the lighting can be made more effective in the cultivation of dew-chrysanthemums, kame-teru strawberries, etc. This makes it possible to save electricity and adjust moisture permeability. Thus, when this laminate is used as an agricultural film or a food packaging film, the nonwoven sheet has a date of about 20 to 6 females/female, preferably about 30 to 5 females/female,
Particularly favorable properties are obtained when the aluminum powder-containing polyvinyl alcohol layer has a thickness of about 10 to 75 mm, preferably about 30 to 50 mm.

Next, the present invention will be explained with reference to examples.

Example 1 Polypynyl alcohol adjusted to pH 7 (degree of polymerization 13)
Aqueous paste of aluminum powder (Asahi Kasei product AW600; average particle size: 1
0 μm, 44 sieve residue 0.1%, aluminum concentration 6
5%) was added so that the weight ratio of aluminum powder to polyvinyl alcohol solid content was 1.65% or 2.50%.

This mixed aqueous solution is 50qo, and the surface temperature is 9y.
When the film was cast onto a heated rotating drum of 30 mm, a film with a thickness of 30 mm could be formed without any gas generation observed. The tensile test results of this film in each of the longitudinal and lateral directions are shown in Table 1 below. The measurements were carried out at a temperature of 2 psi, a relative humidity of 65%, and a tensile rate of 300 ribs/min. Table 1 Example 2 Polypropylene was blended with an ultraviolet absorber, and continuous fibers with a weave of 3 denier were melted and threaded using a spunbond method to obtain a nonwoven fabric with a fabric weight of 4/m.

This nonwoven fabric was passed between a Empos roll heated to 160° C. and a nylon roll, and spot bonding was applied to one side of the nonwoven fabric to suppress the occurrence of fuzz. On the other hand, the mixed aqueous solution prepared in Example 1 (aluminum powder content: 2
．． 5% by weight) was formed into a film through a slit and cast onto a heated roll, and the fiber layer opposite to the heat-treated side of the nonwoven fabric sheet was placed on top of the film, and the roll was lightly pressurized and dried with hot air. . The strength test results of the laminate thus manufactured are shown in Table 2 below.

Table 2 Next, the infrared transmittance was measured, and a value of 1.5% was obtained for light with a wavelength of 12.5 french, while that of the laminate containing no aluminum powder was 2.5%.

Furthermore, in order to investigate the insulation effect, one of the guidelines, the thermal conductivity (Kca / time / °C), was set at 20 °C on the inside and 5 °C on the outside.
When measured under the same conditions at ℃, a value of 4.5 was obtained, which is better than 6.7 for a nonwoven fabric (with a weight of 40 g) and 5.1 for a commercially available polyvinyl chloride sheet (thickness 50 A). ing. When this laminate was embossed with a cloth grain (don gloss) pattern from the polyvinyl alcohol film layer side, flexibility was further imparted and the blocking method was also improved.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of one embodiment of a laminate according to the present invention.

Claims (1)

[Scope of Claims] 1. A polyvinyl alcohol film whose surface is coated with a gas generation inhibitor that is a saturated or unsaturated fatty acid and which contains about 0.5 to 10% by weight of aluminum powder having particles of about 100 μm or less. . 2. On the other side of the nonwoven fabric sheet, at least one side of which has been heat-treated, about 0.5% of aluminum powder is coated on the surface with a gas generation inhibitor, which is a saturated or unsaturated fatty acid, and has a particle size of about 100μ or less. ~10% by weight
A laminate made by integrating polyvinyl alcohol layers. 3. The laminate according to claim 2, which is embossed from the polyvinyl alcohol layer side.