JPH0343246A - Polyvinyl alcohol laminate and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain an agricultural cover material excellent in dimensional stability and tear strength without damaging transparency, heat insulating property, moisture permeability, durability, antistatic property and environmental safety by integrating a polyvinyl alcohol resin layer and a polyolefinic resin layer through an unsaturated carboxylic acid grafted modified polyolefinic resin layer. CONSTITUTION:A polyvinyl alcohol laminate is formed by integrating a polyvinyl alcohol resin layer and a polyolefinic resin layer through an unsaturated carboxylic acid grafted modified polyolefinic resin layer. This laminate is obtained by integrating the unsaturated carboxylic acid grafted polyolefinic resin layer with the single surface of the polyolefinic resin layer and superposing the polyvinyl alcohol resin layer thereon to integrate all of the layers under heating and pressure. The polyvinyl alcohol resin layer desirably has such a shrinkage characteristic that a dimensional shrinkage factor at the time of drying is 0-3% with respect to that at the time of wetting and the dimensional shrinkage factor at the time of wetting is 1.5-0.5% with respect to that at the time of stretching and, therefore, the layer is pref. composed of a biaxially stretched film.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a polyvinyl alcohol-based laminate that is mainly used as a covering material for greenhouses, etc. for greenhouse horticulture, and is a polyvinyl alcohol-based laminate that has excellent dimensional stability and tear strength. It's about the body.

[Conventional technology]

Transparency, heat retention, and moisture permeability are important performance requirements for agricultural covering materials used in greenhouses, etc. for greenhouse horticulture.
It is listed as an item that affects the growth condition of agricultural crops. Important factors that do not directly affect the growth condition of agricultural products include durability, non-electrostatic properties, environmental safety, etc. Polyvinyl alcohol film (thickness 50μ)
)H transmission rate is 90%, infrared transmittance is 18.6%, and moisture permeability f (40℃, 90%RH) is 1800? /l・24
The strength retention rate (exposure-year) is 60 Da, and the charging property is OCA.
It also has the characteristic that it does not generate any harmful substances when incinerated.

As described above, although polyvinyl alcohol fully satisfies the performance items required as an agricultural covering material, it has poor dimensional stability, which is the main reason why it has not been used as an agricultural covering material.

As for the degree of dimensional change, it expands by 14 to 23 da when wet, and conversely shrinks by 5 to 10% when dry.

For this reason, when it is expanded into a greenhouse for greenhouse horticulture, the pipes that make up the no.us may be damaged due to the stress caused by contraction and the weight of rainwater that collects in the slack caused by expansion. One of the means for improving this is the combination of crystallization by heat treatment and highly oriented molecules by stretching.

The heat treatment temperature ranges from the glass transition point to the pyrolysis temperature (
Temperatures of 70°C to 240°C) are used, and uniaxial stretching, simultaneous biaxial stretching, fixed-axis uniaxial stretching, and sequential biaxial stretching are used, and in particular, a combination of biaxial stretching and heat treatment is used. Yo υ
It is possible to reduce the difference in shrinkage rate between wet and dry times to 2 to 81%.0 However, when this method is used, the molecules become highly oriented, resulting in high strength and low elongation, but tearing does not occur. This has the disadvantage that the strength is significantly reduced. If the tearing strength decreases, if there is a slight scratch at the installation point or the contact point with the pipe when expanding, it will spread endlessly from that point due to wind and rain, making it unusable in a short period of time. If this occurs, it cannot be used for practical purposes.

As a means to compensate for this, a method has been proposed in which a polyvinyl alcohol film is laminated with a hydrophobic resin sheet using an adhesive to structurally increase tear strength. Films, nonwoven fabrics, paper, etc. made of polypropylene, polyamide, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, etc. are used. As the adhesive, an aqueous polyvinyl alcohol solution, a phenolic resin adhesive such as resol, an epoxy resin adhesive, a polyurethane adhesive, etc. have been proposed.

[Problem to be solved by the invention]

However, with this method, it is difficult to control the amount of adhesive applied, so the thickness of each hydrophobic resin sheet must be at least 50 μm. If the material becomes thick, the flexibility will be significantly reduced and the workability will be extremely poor. In addition, when adhering a hydrophobic resin sheet with voids such as a MEC membrane structure to take advantage of the moisture permeability of polyvinyl alcohol, the amount of application must be 3 on a dry basis to obtain sufficient adhesive strength.
f/r1 or higher is required, but the adhesive inevitably leaks from the gap and the polyvinyl alcohol surface gets dirty.
Alternatively, there may be problems such as blocking during winding.

Furthermore, the biggest drawback of this method is that since the adhesive is a liquid type, dimensional changes occur in the polyvinyl alcohol film during application and wrinkles occur during adhesion. This has the disadvantage that process passability becomes extremely poor and transparency, which is an important factor required for agricultural covering materials, is significantly reduced.

As described above, although polyvinyl alcohol film has advantageous characteristics for agricultural use as a material, it has not been used as an agricultural covering material until now.・The aim is to provide agricultural covering materials with excellent dimensional stability and tear strength without compromising heat retention, moisture permeability, durability, non-static properties, and environmental safety.

[Means to solve the problem]

The object of the present invention is achieved by a polyvinyl alcohol-based 8I layered body characterized in that a polyvinyl alcohol-based resin layer and a polyolefin-based resin layer are integrated via an unsaturated carboxylic acid graft-modified polyolefin-based resin layer. be done. In such a laminate, an unsaturated carboxylic acid graft modified polyolefin resin layer is integrated on at least one side of a polyolefin resin layer, and then an unsaturated carboxylic acid graft modified polyolefin/based resin layer is integrated onto the unsaturated carboxylic acid graft modified polyolefin resin layer of the laminate. It is obtained by overlaying a polyvinyl alcohol resin layer on top of the polyvinyl alcohol resin layer and integrating it under heating and narrow pressure.

According to the present invention, the above-mentioned polyvinyl alcohol resin layer has a shrinkage ratio of 0 to 10% in dry dimensions relative to wet dimensions.
The polyvinyl alcohol resin layer is a biaxially stretched film because it is desirable that the shrinkage rate of the wet dimension is 1.5 to 0.5% with respect to the stretched dimension. The polyvinyl alcohol film used may be formed by any known method, but is preferably a biaxially stretched film as described above. The biaxial stretching to be carried out may be any of the known methods such as simultaneous biaxial stretching, fixed-axis uniaxial stretching, and sequential biaxial stretching, but in order to stabilize the dimensions, it is necessary to ensure that the molecules are oriented in a highly balanced manner and crystallized. It is particularly desirable to adopt a sequential biaxial stretching method to achieve this. The stretching conditions are 75 to 180°C, 2 times or more in the machine direction, more preferably 3 times or more, and 1.5 times in the transverse direction.
Stretching is performed by a factor of at least 2 times, more preferably by a factor of 2 or more. Next 170
Heat treatment at ~240°C for 10-60 seconds. At this time, heat shrinkage of 0.5 to 3.0% may be applied.

The resin constituting the polyvinyl alcohol resin layer of the present invention is polyvinyl alcohol, which is a completely or incompletely saponified product of polyvinyl acetate, or polyvinyl alcohol copolymerized with other copolymer components such as ethylene, styrene, vinyl chloride, etc. Examples include alcohol-based resins and resin mixtures of polyvinyl alcohol and other polymers, but as the content of copolymerization and mixed components increases, the moisture permeability, heat retention, etc., which are the characteristics of polyvinyl alcohol, decrease. It is preferable that it is essentially polyvinyl alcohol! Yes. Regarding the thickness of the polyvinyl alcohol resin layer, if it is thin, it will not have sufficient strength.
Also, if it is thick, it becomes bulky and becomes difficult to handle, so 5-50μ is preferable, and more preferably 10-3μ.
Next, a reinforcing material made of a hydrophobic resin is adhered to the film in order to reinforce the tear strength. If a known liquid type adhesive is used at this time, the extremely serious inconvenience mentioned above will occur, but through research by the present inventors, an unsaturated carboxylic acid graft-modified polyolefin resin is used as an adhesive layer. It has been found that when used, extremely good adhesive strength can be obtained by bonding with the film under heat and pressure.

As the polyolefin resin used as the main component of the adhesive layer, polyethylene or polypropylene is preferable because a polyolefin resin with a high melting point causes thermal decomposition of the polyvinyl alcohol film.

Examples of unsaturated carboxylic acid monomers graft-modified to polyolefin resins include acrylic acid, methacrylic acid,
It is selected from among maleic acid, fumaric acid, itaconic acid, etc., but it is most preferable to use maleic anhydride. Any known method may be used to graft-modify the unsaturated carboxylic acid onto the polyolefin resin.

For example, a method may be mentioned in which a polyolefin, an unsaturated carboxylic acid, and a radical initiator such as a peroxide as a catalyst are simultaneously mixed to homogenize the melt. The amount of grafting of unsaturated carboxylic acid in the polyolefin resin layer is 0.013
If the amount is less than 1 o, sufficient adhesion will not be obtained, and the case will be 1 o! If it is more than i%, it will be partially crosslinked and the bottom formability will be poor, so %0.01 to 10
The weight is high, preferably 0.05 to 5 weight. The residue may contain other copolymer components or other polymers as necessary. The preferred thickness of the unsaturated carboxylic acid graft-modified polyolefin layer is 2 to 20μ, since if it is too thin, sufficient adhesion cannot be obtained, and if it is too thick, it will become bulky and will be difficult to handle. more preferably from 5 to 15μ.

Although such an unsaturated carboxylic acid graft-modified polyvinyl V fin-based resin has good adhesion to polyvinyl alcohol (V) film, its tear strength is weak, so it cannot be used alone as a reinforcing material. I can't afford it.

Here, by disposing a substantially unmodified polyolefin resin on one side of the unsaturated carboxylic acid graft-modified polyolefin resin, a reinforcing material with good adhesion to the polyvinyl alcohol film and high tear strength can be obtained. sell. The polyolefin resins used include ethylene, propylene, 1-butene, 1-hexene,
It also includes homopolymers such as 4-methyl-1-pentene and copolymers of these olefins. Particularly preferred is a polyolefin resin made of the same polyolefin as the unsaturated carboxylic acid graft-modified polyolefin resin to be integrated, or a polyolefin resin mainly composed of the casing or polyolefin resin. Further, other copolymer components or other polymers may be included within a range that does not significantly impair tear strength. The thickness of the polyolefin resin layer is preferably 5 to 50μ, since if it is thin, it will not provide sufficient tear reinforcement, and if it is thick, it will become bulky and have poor handling properties. It is 10-30μ.

As for possible embodiments of the unmodified polyolefin resin layer serving as the reinforcing material, it is preferable to have a completely continuous film or a film having appropriate voids. The porosity is 10 to 90 φ, preferably 20 to 75 φ in terms of the pore area relative to the total area in the planar direction. The reason for this is that 10% or less is an important factor required for agricultural applications.
, and impairs the moisture permeability, which is a characteristic of polyvinyl alcohol.If it exceeds 4.9.90%, if a scratch occurs on the polyvinyl alcohol film, the tear will spread, making it unsuitable for long-term use. It's for a reason.

Regarding the size of the void, if it is small, the transparency will decrease and the appearance will be damaged, and if it is large, the film will break and will not be able to withstand long-term use, so it is 0.01
-1ooi is preferred, more preferably 0.25-25
It is m.

The reinforcing material is a two-layer coextruded film of an unsaturated carboxylic acid graft-modified polyolefin resin and an unmodified polyolefin resin, or a two-layer coextruded film with unsaturated carboxylic acid graft modified polyolefin resin placed on both sides of an unmodified polyolefin resin. It may be a three-layer co-extruded film with holes made to satisfy the above porosity, or
It may also be a mesh-like structure in which a split yarn obtained by slitting a perforated film is woven into a plain weave. The cross-sectional shape of the casing is a two-type, two-layer lamination type (i.e., a cross-sectional shape in which the modified polyolefin layer and the unmodified polyolefin layer are laminated parallel to the tape surface) or a two-type, three-layer lamination type ( In other words, the tape yarn is spun parallel to the tape surface so that the intermediate layer is an unmodified polyolefin layer, and both sides are covered with the modified polyolefin layer. It may be a mesh-like structure in which a composite fiber or the like having a sheath coated with an unsaturated carboxylic acid graft-modified polyolefin resin is plain-woven.

By laminating the reinforcing material obtained as described above with a polyvinyl alcohol film in a dry state at a temperature higher than the melting point of the unsaturated carboxylic acid graft-modified polyolefin resin that is the adhesive surface, the reinforcing material can be laminated without wrinkles. Moreover, it became possible to obtain a polyvinyl alcohol-based laminate having dimensional stability and high tear strength.

Possible embodiments of using the laminate of the present invention as an agricultural covering material include a completely continuous film made of polyvinyl alcohol as an outer lining or inner curtain for facilities such as horticulture and funeral houses, and a method in which polyvinyl alcohol is used as an outer lining or inner lining curtain for facilities such as horticulture and funeral houses. There are methods to use it as an open one.

Alternatively, the film may be slit and woven into warp or weft yarns to form a sheet.

The laminate of the present invention may further include a resin layer, a nonwoven fabric layer, a sheet layer, etc., if necessary.

As mentioned above, the laminate of the present invention is good as an agricultural covering material, but it can also be used for purposes other than agricultural covering materials, for example, in packaging applications such as clothing and food products by taking advantage of its transparency and moisture permeability. It can also be used for - For example, by coloring the reinforcing layer, it can be used as a packaging material that takes advantage of the pattern created by the polyvinyl alcohol transparent layer and the colored reinforcing layer having voids.

The embodiments and effects of the present invention will be explained in more detail in the following examples, but these examples are merely taken as examples, and these examples are not intended to limit the present invention in any way.

Example 1 A 45% aqueous solution of polyvinyl alcohol with a degree of polymerization of 1700 and a degree of saponification of 99.9 was extruded from a die to form a film, and dried to obtain an unstretched film with a thickness of 250 μm.

This unstretched film was sequentially biaxially stretched 3.0 times in the longitudinal direction and 3.0 times in the transverse direction at 80°C to obtain a film with a thickness of 26μ.
It was heat-treated for 1 minute in 2 minutes, then immersed in warm water at 60°C for 10 minutes, and dried in a drying room at 50°C without applying tension to a moisture content of 3.8.

Next, on both sides of the 20μ thick high-density polyethylene,
Co-extrusion of two types and three layers of polyethylene polyethylene with 0.5 weight maleic anhydride of μ is coextruded, slit into 5 and 4 widths, and stretched to form a tape-like yarn with a width of 3 W % and a thickness of 30 μ. A plain weave of 9 threads/10 cTn was pressed at 150° C. and a mesh was obtained by bonding the intersections. The porosity was 53%.

The thus obtained polyvinyl alcohol film and mesh-like structure were heated to 165° C. and laminated together.

Example 2 The polyvinyl alcohol unstretched film described in Example 1 was expanded at 80°C by 3.5 times in the machine direction and further by 3 times in the cross direction.
．． Two-wheel stretching was carried out 5 times sequentially to obtain a film with a thickness of 20 μm.

This film was heated in a trench of a fixed length at 190°C for 1 minute, then immersed in warm water at 60°C for 10 minutes, and then placed in a drying room at 50°C without applying tension until the moisture content was 3.8%. It was dried in a drying cabinet.

Next, a two-layer film of high density polyethylene with a thickness of 20μ and maleic anhydride 0.5 Ft modified polyethylene with a thickness of 10μ was coextruded and stretched to form a film with a thickness of 20μ. 200 holes with a radius of 2.5 mm/rII
Opened. The porosity was 39%.

The thus obtained polyvinyl alcohol film and the perforated film were laminated at 165° C. so that the modified polyethylene layer of the perforated film served as an intermediate layer.

Comparative Example 1 The polyvinyl alcohol unstretched film described in Example 1 was heated to 80°C, and the film was stretched 3.0 times in the machine direction and 3.0 times in the transverse direction.
．． The film was sequentially biaxially stretched 0 times to obtain a film with a thickness of 26 μm.

This film is one of the fixed length! Heat treated at -2190℃ for 1 minute, further immersed in 60℃ warm water for 10 minutes,
A high-density polyethylene film having a thickness of 40 μm was extruded into a film, which was dried in a drying chamber at a temperature of °C without applying tension until the moisture content reached 3.8%, and the film was slit into 5 ml pieces. This was stretched to create a tape-like yarn with a width of 3 nods and a thickness of 30 μm, which was then plain woven into 9 yarns/10 anns, resulting in 150 yarns.
It was pressed at ℃ and the intersecting parts were glued together to form a mesh.

The porosity was 53%.

As an adhesive, a polyester/isocyanate two-component polyurethane adhesive blended in a ratio of 10075 was applied to the polyvinyl alcohol film at a dry basis of 5.
2/d coating, adhesion to the mesh structure, and then drying.

Comparative Example 2 The unstretched polyvinyl alcohol film described in Example 1 was heated to 80° C. and stretched 3.0 times in the longitudinal direction and 3.0 times in the transverse direction.
The film was sequentially biaxially stretched 0 times to obtain a film with a wall thickness of 26 μm. This film was heat-treated at 11190°C for 1 minute, then immersed in warm water at 60°C for 10 minutes, and dried in a drying room at 50°C without tension to a moisture content of 3.8%. Ta.

Next, polyethylene with a thickness of 40 μm was extruded to form a film, and the film was slit into 5 pieces. Stretch this to a width of 31o
I. Tape-like yarns with a thickness of 30 μm were plain-woven into 9 yarns/10 m and pressed at 150° C. to form a mesh with the intersections bonded. The porosity was rarely 0 at a width of 53. The polyvinyl alcohol film thus obtained and the mesh-like structure were laminated at 165° C., but they did not adhere.

Comparative Example 3 The unstretched polyvinyl alcohol film described in Example 1 was heated to 80° C. and expanded by 3.0 times in the longitudinal direction and 3.0 times in the transverse direction.
．． The film was sequentially biaxially stretched 0 times to obtain a film with a wall thickness of 26 μm.

This film is one of the best! Heat treated at 190°C for 1 minute, further immersed in 60°C hot water for 10 minutes, and heated to 50°C.
The sample was dried in a drying room at a moisture content of 38% without being exposed to heat.

Next, anhydrous maleic (1, 0, 5, φ modified polyethylene) with a thickness of 40 μm was extruded to form a film, which was slit into 5-width pieces. This was stretched to form a tape-like yarn with a width of 3 μm and a thickness of 30 μm. A plain weave of 9 strands/10 cm was pressed at 150° C. and a mesh was obtained by bonding the intersections.The porosity was 53%.

The polyvinyl alcohol film thus obtained and the mesh-like structure were laminated at 165°C.

Reference Example 1 The unstretched polyvinyl alcohol film described in Example 1 was used as the casing 1.

Reference Example 2 The unstretched polyvinyl alcohol film described in Example 1 was heated to 80°C, and the film was expanded by 3.0 times in the machine direction and further by 3 times in the width direction.
．． The film was sequentially biaxially stretched 0 times to obtain a film with a thickness of 26 μm.

This film was heat-treated at a fixed length of 11190°C for 1 minute, then immersed in warm water at 60°C for 10 minutes, and dried in a drying room at 50°C without tension until the moisture content reached 3.8%. Ta.

The light transmittance, moisture permeability, dimensional stability, and tearing strength were measured for the above 781 types of samples. The measurement method is as follows.

Transmittance: Transmittance of visible light at 600 nm was determined using a spectrophotometer.

Moisture permeability, according to the method described in JIS Z-0208,
The weight increase of the moisture absorbent in 40'C901H was determined.

Dimensional stability = After conditioning the humidity at 20°C and 65% RH for 24 hours, place it in constant temperature water at 25°C for 8 hours as a wet state, and in a dryer at 35°C and 37% RH for 13 hours as a dry state.
The shrinkage rate from the original length was measured.

Tear strong crab The single tank method described in JIS L-1096 was followed.

The results for each are shown in Table 1. From the results in Table 1, it is clear that the product of the present invention is significantly superior to the conventional product. In this way, the present invention makes it possible to provide an agricultural covering material that takes advantage of the characteristics of polyvinyl alcohol, such as transparency, heat retention, durability, non-static properties, and environmental safety, and also has excellent dimensional stability and tear strength. became.

Claims (2)

[Claims] (1) A polyvinyl alcohol laminate, characterized in that a polyvinyl alcohol resin layer and a polyolefin resin layer are integrated via an unsaturated carboxylic acid graft-modified polyolefin resin layer. (2) An unsaturated carboxylic acid graft modified polyolefin resin layer is integrated on at least one side of the polyolefin resin layer, and then a polyvinyl alcohol resin layer is formed on the unsaturated carboxylic acid graft modified polyolefin resin layer of the laminate. A method for producing a polyvinyl alcohol-based laminate, characterized by stacking and integrating under heat and pressure.