JPH0134152B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to laminated plastic sheets, and more particularly to laminated plastic sheets for producing plastic containers with improved oxygen barrier properties. The present invention particularly provides a layer mainly composed of ethylene-vinyl alcohol copolymer and a coating layer composed of vinylidene chloride-acrylic (methacrylic) copolymer (hereinafter also referred to as polyvinylidene chloride resin) in an adjacent position. This is based on the new finding that when provided, an oxygen permeability coefficient lower than that of any of the layers can be obtained. Furthermore, the oxygen permeability coefficient is cc・
It is expressed in units of cm/cm ² · sec · cmHg, and is a coefficient unrelated to the dimension of thickness. Plastic containers allow oxygen to permeate through the container walls to varying degrees, and if this permeation cannot be ignored, it may be necessary to use containers for long-term storage of food or containers for cosmetics that require fragrance retention. It becomes inappropriate for the field. For this reason, the development of plastic containers whose walls are made of resin with excellent oxygen barrier properties is being actively conducted. Currently, the resin with the best oxygen barrier properties among melt-extrudable thermoplastic resins is saponified ethylene-vinyl acetate copolymer (ethylene-vinyl acetate copolymer).
(vinyl alcohol copolymer), but this saponified copolymer has poor moisture resistance, i.e., water vapor barrier properties, and furthermore, its oxygen permeability coefficient tends to increase significantly with increasing humidity, thus making it difficult to use in practical plastics. When used in containers, this drawback is overcome by layering moisture-resistant resins such as polyolefins in a sandwich pattern to form a multilayer laminate. Another disadvantage of plastic containers whose walls are made of ethylene-vinyl alcohol copolymer is that they are highly transparent to ultraviolet rays. Although the purpose of preventing food from going rancid may be somewhat satisfied, the ultraviolet light transmitted through the container wall may alter the quality of pigments, fats and oils, animal proteins, various beverage extracts, etc., resulting in changes in the flavor and appearance of the food contents. , there is a problem of impairing hygienic properties. Conventionally, as a means of blocking ultraviolet rays in plastic containers, it has been known to incorporate an ultraviolet absorber into the resin constituting the plastic container, but such a method has problems with the hygienic properties of the container, and Its ultraviolet blocking effect is still not fully satisfactory. When the present inventors provide a resin layer mainly composed of an ethylene-vinyl alcohol copolymer and a coating layer of a vinylidene chloride-acrylic (methacrylic) copolymer described in detail below in an adjacent position, this lamination It has been found that the plastic sheet exhibits an oxygen permeability coefficient lower than that of any of the layers, and that the plastic sheet with this laminated structure is also significantly superior in its UV blocking properties. That is, an object of the present invention is to provide a laminated plastic sheet that has excellent barrier properties against gases such as oxygen. Another object of the present invention is that, in addition to the above-mentioned low oxygen permeability coefficient, it also has ultraviolet blocking properties, and therefore, when molded into a container, the contents can be stored stably for a long period of time without deterioration. It is possible to provide a plastic container made of laminated plastic sheets. Still another object of the present invention is to provide a multilayer plastic sheet in which the moisture resistance of the ethylene-vinyl alcohol copolymer layer and the tendency for oxygen permeation to increase with increase in humidity are simultaneously improved. According to the present invention, a plastic substrate having at least one surface made of a resin mainly composed of an ethylene-vinyl alcohol copolymer is provided with a 99° 70% by weight of vinylidene chloride, 1% to 30% by weight of at least one of acrylic or methacrylic monomers, and 0 to 100 parts by weight of other monomers based on 100 parts by weight of the total amount of the monomers. It is substantially composed of at least one type of ethylenically unsaturated monomer, and has an oxygen permeability coefficient of 9×10 ^-14 cc cm/cm ² at 20°C and 100% RH.
sec・cmHg or less and water vapor permeability coefficient (JISZ-
Provided is a laminated plastic sheet characterized in that it is provided with a coating layer mainly composed of a copolymer having a copolymer having a copolymer having a copolymer having ^a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a ^copolymer having a copolymer having a copolymer having a copolymer having a copolymer having a 0208) of 3×10 −3 g·cm/m 2·day or less. In Figures 1-A to 1-D showing examples of the layer structure of the laminated plastic sheet of the present invention, at least one surface 1 is ethylene-
A plastic substrate 2 made of a resin mainly composed of a vinyl alcohol copolymer, and a coating layer 3 mainly made of a vinylidene chloride-acrylic (or methacrylic) copolymer provided in a position adjacent to the resin surface 1. It consists of As shown in Figure 1-A, the plastic substrate 2 consists of a single layer of resin mainly composed of ethylene-vinyl alcohol copolymer, and as shown in Figure 1-B, vinylidene chloride is coated on both surfaces 1 and 1'. - A coating 3, 3' of an acrylic (methacrylic) copolymer may be provided. Furthermore, the plastic substrate 2 may be made of a laminate of a resin mainly composed of ethylene-vinyl alcohol copolymer and other resins. For example, as shown in Figure 1-C, the substrate 2 is ethylene-
It can be composed of a resin layer 4 mainly composed of a vinyl alcohol copolymer (hereinafter simply referred to as ethylene-vinyl alcohol copolymer) and a moisture-resistant thermoplastic resin layer 5 of other resins, particularly polyolefin resin. . In any of these cases, the ethylene-vinyl alcohol copolymer layer 4 is adjoined to it, that is, as both surface layers in FIG. 1-B, and as the innermost layer or the innermost layer in FIG. 1-C. As the outermost layer, a coating layer 3, 3' of vinylidene chloride-acrylic (methacrylic) copolymer is provided.
Furthermore, in FIG. 1-D, this container substrate 2 is
It consists of both inner and outer layers 4, 4' of ethylene-vinyl alcohol copolymer and an intermediate layer 5 of thermoplastic resin. A combined covering layer 3, 3' is provided. An important feature of the present invention is that, as already mentioned above, when the ethylene-vinyl alcohol copolymer layer and the vinylidene chloride-acrylic (methacrylic) copolymer coating layer are provided in an adjacent positional relationship, this laminated sheet can
This is based on the completely unexpected finding that, when compared at the same thickness, the oxygen permeability is lower than that of either layer. Figure 2 shows that when the thickness of the ethylene-vinyl alcohol copolymer is t _EV and the thickness of the vinylidene chloride-acrylic (methacrylic) copolymer layer is t _CA , the total thickness t _CA + t _EV is constant at 15μ. As,
The ratio of _tCA / ( _tCA + _tEV ) and 37℃, relative humidity 0% to
The relationship with oxygen permeability at 15%RH is shown. Referring to FIG. 2, the coated plastic container made from the laminated plastic sheet of the present invention has an oxygen permeability that is significantly lower than curve B, which is the harmonic average value of both resin layers, as shown by dashed curve A. and, quite surprisingly, over a fairly wide range of ratios of t _CA /(t _CA + t _EV ), rather than that of the ethylene-vinyl alcohol copolymer, which has a lower oxygen permeability coefficient. It can be seen that the oxygen permeability is low. Similarly, Figure 3 shows the case where t _CA + t _EV is 15μ.
The ratio of t _CA / (t _CA + t _EV ) and the relative humidity at 27°C and 100% RH
and the relationship with oxygen permeability at 93% RH. As already mentioned above, the ethylene-vinyl alcohol copolymer exhibits a relatively high oxygen permeability under high humidity conditions, and even in this case, the coated plastic container formed from the laminated plastic sheet of the present invention has a As shown in curve A′,
It shows an oxygen permeability significantly lower than the harmonic average value B′ of both resin layers, and within a certain range of the ratio of t _CA /(t _CA + t _EV ), vinylidene chloride-acrylic (which has a smaller oxygen permeability coefficient) It can be seen that the methacrylate copolymer exhibits a lower oxygen permeability at the same thickness than the methacrylate copolymer. The results in Figures 2 and 3 show that the total thickness is 15μ.
Therefore, it is safe to assume that the oxygen permeability shown in these drawings represents the oxygen permeability coefficient itself, excluding the thickness factor. For example, according to page 287 of "Polymer and Moisture" published by Koshobo on September 1, 1971, the oxygen permeability of a laminate is generally calculated as the harmonic average value of the oxygen permeability of each layer (the 7.16) on page 7.16), the significant decrease in oxygen permeability in the laminated plastic sheet of the present invention is not caused by the mere lamination effect of both resin layers;
It will be understood that this is based on the physical or chemical interaction between both resin layers. According to the present invention, it is possible to significantly reduce the oxygen permeability of the laminated sheet as described above, and in particular, by coating the surface of the ethylene-vinyl alcohol copolymer with a thin vinylidene chloride-acrylic (methacrylic) copolymer. By providing this, it becomes possible to reduce the humidity dependence of oxygen permeability. In the present invention, both resin layers satisfy the following inequality: 0.95≧t _CA / (t _CA + t _EV ) ≧0.005, especially 0.75≧ t _CA / (t _CA + t _EV ) ≧0.008, t _CA ≧0.5μ, especially t _CA ≧1.0 It is desirable to set it so that μ is satisfied. In addition, the thickness ( _tEV ) of the ethylene-vinyl alcohol copolymer layer varies depending on its ethylene content and degree of saponification, but in general, _tEV ≧3.0μ, especially _tEV ≧5.0μ. It is desirable to provide a system that satisfies the following. According to the present invention, excellent ultraviolet blocking properties can also be obtained by providing a coating layer of vinylidene chloride-acrylic (methacrylic) copolymer on the ethylene-vinyl alcohol copolymer layer. The fact that the laminated sheet of the present invention has excellent UV blocking properties will be readily apparent by referring to FIG. That is, curve A in FIG.
When a sheet made only of vinyl alcohol copolymer is molded into a container, the relationship between wavelength and transmittance is shown for the container wall. According to this curve A, the wavelength of the plastic sheet is 210 to 210.
It can be seen that it exhibits a fairly high transmittance for ultraviolet light of 400 mμ, similar to visible light. On the other hand, curve B shows the thickness of the vinylidene chloride-acrylic (methacrylic) copolymer layer relative to the ethylene-vinyl alcohol copolymer layer of the plastic substrate.
This is the wavelength-transmittance curve for the 30μ coating, and from this curve B, it is found that the ethylene-vinyl alcohol copolymer layer of the plastic substrate has a slight
It can be seen that UV blocking properties can be obtained by simply providing a 30μ coating. In the laminated plastic sheet of the present invention,
A further unexpected advantage is that this UV protection is permanently obtained. That is, curves C and D in FIG. 4 represent the coated plastic container of curve B.
60℃, 25 hours and 60℃ with Weatherometer, respectively.
This is a wavelength-transmittance curve after 50 hours of ultraviolet exposure. According to these curves C and D, in the laminated plastic sheet of the present invention, the more it is irradiated with ultraviolet rays, the more its transmittance to ultraviolet rays is suppressed to a lower level, and the more it shifts to the absorption wavelength side. It is clear that there are. Thus, the laminated plastic sheet according to the present invention is
The more UV rays are irradiated, the more UV rays are prevented from passing through, and even when exposed to UV rays for a long time, the overall amount of UV rays transmitted can be suppressed to a significantly low level. It becomes. The reason for this is that vinylidene chloride-acrylic (methacrylic)
This seems to be because conjugated diene bonds are formed in the copolymer layer, and these conjugated diene bonds act to absorb more ultraviolet rays. The copolymer used as the coating layer in the present invention is 99%
Contains as essential components at least one of vinylidene chloride in an amount of 70 to 70% by weight, particularly 96 to 80% by weight, and 1 to 30% by weight, particularly 4 to 20% by weight of an acrylic or methacrylic monomer; It optionally contains up to 100 parts by weight of other ethylenically unsaturated monomers per 100 parts by weight of the total amount of monomers. As the above-mentioned acrylic or methacrylic monomer, acrylic acid, methacrylic acid or derivatives thereof are used, and preferred examples include the following formula: In the formula, R ₁ represents a hydrogen atom, a halogen atom, or a methyl group, and X represents a nitrile group (-C≡N) or a (In the formula, Y is an amino group, a hydroxyl group, an alkyloxy group, a cycloalkyloxy group, an aminoalkyloxy group, a hydroxyalkyloxy group, an alkoxyalkyloxy group, a haloalkyloxy group, a glycidyloxy group, an aryloxy group, an aralkyloxy group) is a group represented by ), especially acrylic acid, acrylonitrile,
Acrylamide, methyl acrylate, ethyl acrylate, methyl α-chloroacrylate, propyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, cyclohexyl acrylate, glycidyl acrylate, acrylic acid-2
- Hydroxyethyl, acrylic acid monoglyceride, phenyl acrylate, methacrylic acid, methacrylonitrile, methacrylamide, methyl methacrylate, amyl methacrylate, glycidyl methacrylate, methacrylic acid monoglyceride, 2-hydroxypropyl methacrylate, beta methacrylate
-methoxyethyl, β-aminoethyl methacrylate, and γ-N,N-diethylaminopropyl methacrylate. These acrylic or methacrylic monomers can be used alone or in combination of two or more. Acrylic or methacrylic monomers particularly suitable for the purpose of the present invention include (i) nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, (ii) methyl acrylate, ethyl acrylate, Methyl methacrylate, methacrylic acid-2-
Ester monomers such as hydroxyethyl, glycidyl acrylate, glycidyl methacrylate, acrylic acid monoglyceride, methacrylic acid monoglyceride, methoxyethyl acrylate, methoxyethyl methyl methacrylate, and (iii) a combination monomer of the above (i) and (ii). . Ethylenically unsaturated monomers other than vinylidene chloride and acrylic or methacrylic monomers include:
Vinyl aromatic monomers such as styrene and vinyltoluene; Vinyl esters such as vinyl acetate and vinyl propionate; Diolefins such as butadiene and isoprene; Methyl vinyl ether, glycidyl acrylic ether, vinyl chloride, ethylene trichloride,
Ethylene tetrachloride, vinyl fluoride, vinylidene fluoride, ethylene trifluoride, ethylene tetrafluoride, maleic anhydride, fumaric acid, vinyl succinimide,
Examples include vinylpyrrolidone, and these monomers may be used alone or in combination of two or more. Examples of suitable copolymers include, but are not limited to: Vinylidene chloride/acrylonitrile copolymer, vinylidene chloride/acrylonitrile/methacrylonitrile copolymer, vinylidene chloride/methacrylonitrile copolymer, vinylidene chloride/acrylonitrile/glycidyl acrylate copolymer, vinylidene chloride/acrylonitrile/glycidyl methacrylate Copolymer, vinylidene chloride/acrylonitrile/monoglyceride acrylate copolymer, vinylidene chloride/ethyl acrylate/glycidyl acrylate copolymer, vinylidene chloride/methyl methacrylate/styrene copolymer, vinylidene chloride/acrylonitrile/styrene copolymer combination, vinylidene chloride/acrylonitrile/ethylene trichloride copolymer, vinylidene chloride/acrylonitrile/vinyl chloride copolymer, vinylidene chloride/acrylonitrile/methacrylic acid monoglyceride/ethylene trichloride copolymer, vinylidene chloride/methoxyethyl methyl methacrylate/ Methyl methacrylate/ethylene trichloride copolymer. In the copolymer used in the present invention, it is important to have 70% by weight or more of vinylidene chloride units in terms of UV blocking properties and gas barrier properties; In order to be able to coat plastic containers without causing damage, it is important to contain at least 1% by weight of acrylic monomer or methacrylic monomer. Additionally, to improve adhesion to various plastic substrates, the formula In the formula, each of R ₂ and R ₃ is a hydroxyl group, and these two hydroxyl groups may be dehydrated to form an oxirane ring in an amount of 0.5 to 15% by weight based on the total monomers. It is desirable to use it in Furthermore, for the purpose of further improving the coating performance on plastic substrates, up to 100 parts by weight of other ethylenically unsaturated monomers may be added per 100 parts by weight of the total amount of vinylidene chloride and acrylic or methacrylic monomers. is allowed to contain. The copolymer used in the present invention is generally prepared by emulsifying or suspending the constituent monomers in an aqueous medium by the action of an emulsifier and a dispersant, and then carrying out emulsion polymerization or suspension polymerization in the presence of a radical initiator. can be easily obtained by As the radical initiator, peroxides, azo compounds, or redox catalysts, which are known per se, are used. The copolymer used in the present invention generally has a molecular weight sufficient to form a film. The polymer used in the present invention is generally difficult to mold by hot melting, and is used in the form of a solution in an organic solvent or in the form of an aqueous emulsion or latex to coat a plastic substrate by the method described below. The ethylene-vinyl alcohol copolymer that forms the plastic matrix has a low ethylene content.
A saponified ethylene-vinyl acetate copolymer having a saponification degree of 90% or more, especially 95% or more is preferably used in an amount of 20 to 80% by mole, particularly 25 to 60% by mole. Instead of using this ethylene-vinyl alcohol copolymer alone, within a range that does not impair gas barrier properties, that is, within a range that does not exceed 50% by weight of the total,
Other resins such as olefin resins, polyamides, etc. can be blended and used. The moisture-resistant thermoplastic resin used in combination with the ethylene-vinyl alcohol copolymer has a water vapor permeability coefficient of 5×10 ^-1 g・cm/m ²・day (JIS
Z-0208) The following thermoplastic resins, especially low-, medium-, or high-density polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-
Olefin polymers such as butene copolymers, ionomers, ethylene-vinyl acetate copolymers, and ethylene-acrylic acid ester copolymers; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate/isophthalate; nylon 6, nylon 6,
6. Polyamides such as nylon 6, 10; polystyrene, styrene-butadiene block copolymer, styrene-acrylonitrile copolymer, styrene-
Butadiene-acrylonitrile copolymer (ABS
Styrenic copolymers such as polyvinyl chloride and vinyl chloride-vinyl acetate copolymers; Acrylic copolymers such as polymethyl methacrylate and methyl methacrylate-ethyl acrylate copolymers Coalescence; polycarbonate, etc. These thermoplastic resins may be used alone or in the form of a blend of two or more. As the moisture-resistant thermoplastic resin, it is desirable to use polyolefins such as polyethylene and polypropylene from the viewpoints of economy and moldability. If there is no adhesiveness between the moisture-resistant resin layer and the ethylene-vinyl alcohol copolymer layer, a known adhesive layer may be interposed between the two layers. Examples of such an adhesive layer include olefinic resins graft-modified with ethylenically unsaturated carboxylic acids such as acrylic acid, maleic acid, and maleic anhydride or their anhydrides. In addition, instead of interposing an adhesive between the two, for example, as disclosed in Japanese Patent Publication No. 11263/1983, at least one of the moisture-resistant resin layer or the ethylene-vinyl alcohol copolymer layer contains a thermoplastic material. A carbonyl group polymer may be included to improve the adhesion between the two. In the present invention, a latex or an organic solvent solution of the above-mentioned copolymer is applied to a multilayer film or sheet formed by laminating the above-mentioned plastic substrate by coextrusion molding, dry lamination, sandwich lamination, etc. Apply,
It is then dried to form a coating layer to form a laminated plastic sheet. As the aqueous latex of the copolymer, one having a solid content concentration of 20 to 65% and a viscosity of 3 to 500 centipoise is preferably used, while as an organic solvent solution, tetrahydrofuran, ethyl acetate, methyl ethyl ketone, cyclohexane are used. , dimethyl formamide, dimethyl sulfoxide,
Solid content concentration in organic solvent such as dioxane is 5 to 60
% solution is used. The above-mentioned latexes or solutions can be applied to plastic substrates by dip coating, flow coating, spray coating, brush coating, roller coating, electrostatic coating, slush coating, centrifugal coating, or flow coating. Coating methods known per se can be used, such as spread coating methods, electrophoretic coating methods, and combinations thereof.
The coating method may be carried out in one step or in a multi-stage coating method of two or more steps.Furthermore, in order to improve the wetting properties of the plastic container substrate, flame treatment or anchoring agent may be applied before coating, if necessary. Pretreatment such as corona discharge treatment, surfactant coating treatment, chemical etching treatment, etc. may be performed, and conductive treatment or the like may be performed to impart conductivity. Drying of the applied copolymer layer varies depending on the thickness of the coating film, but it is generally dried at a temperature of 40 to 150°C.
Drying for about 2 seconds to 60 minutes is sufficient. In addition, in the present invention, the gas and fragrance blocking effect is sufficiently exhibited by the above-mentioned drying alone; however,
If necessary, aging (heat treatment) at a temperature of 30° C. to 120° C. for 30 seconds to 7 days after drying will further enhance the effect. In the present invention, satisfactory results can be obtained if the vinylidene chloride copolymer is provided at a thickness of generally 0.5 to 50 μm, particularly 1 to 40 μm. The wall thickness of the plastic substrate varies depending on the type of container to be molded, but is generally between 0.05 and 2.5 mm.
In particular, the thickness is preferably in the range of 0.1 to 1.5 mm, and in the case of multiple layers, the ratio of the moisture-resistant resin layer and the ethylene-vinyl alcohol copolymer layer is 1:10 to 200:1,
In particular, it is desirable to have a thickness ratio of 1:2 to 150:1. The present invention is particularly useful for blocking ultraviolet light in plastic containers that require transparency. The laminated plastic sheet of the present invention can be made into a container such as a cup or a bottle by applying a forming method known per se, such as drawing or stretch forming such as vacuum forming, pressure forming, plug assist forming, etc. can. In this case, by performing pressure molding, plug assist molding, etc. at a temperature at which the constituent resin layer can be stretched, it is possible to impart monoaxial or biaxial molecular orientation to the container wall. When the laminated plastic sheet of the present invention is molded into the form of a container, it is desirable to form the copolymer layer on both surfaces of the wall surface. On the other hand, for the purpose of blocking the release of gas and aroma from the contents or odor components from the plastic layer, the layer structure should have a copolymer layer only on the inner surface. You can also do it. The copolymer layer used in the present invention exhibits the excellent advantage of being resistant to these processes and of not losing its adhesion to the substrate. In the present invention, when forming the copolymer layer,
If desired, compounding agents known per se can be included in the copolymer. For example, reinforcing agents, fillers, plasticizers, heat stabilizers,
One or more of antioxidants, ultraviolet absorbers, thickeners, thinners, antiblocking agents, lubricants, leveling agents, colorants, etc. are added to the copolymer according to known formulations. Can be mixed. Of course, additives such as pigments, antioxidants, antistatic agents, ultraviolet absorbers, and lubricants may be added to at least one of the melt-moldable moisture-resistant thermoplastic resin and the ethylene-vinyl alcohol copolymer, as desired. One or more of these may be added in a total amount of 0.001 to 5.0 parts per 100 parts by weight of the resin. For example, in order to reinforce the container when this laminated plastic sheet is molded into a container, fiber reinforcing materials such as glass fiber, aromatic polyamide fiber, carbon fiber, valve, cotton linter, etc., or carbon black,
One or more types of powder reinforcing materials such as white carbon, or flaky reinforcing materials such as glass flakes and aluminum flakes are added to the thermoplastic resin.
It can be blended in a total amount of 2 to 150 parts by weight per 100 parts by weight, and for the purpose of increasing the amount, heavy to soft calcium carbonate, mica, talc, kaolin, gypsum,
Clay, barium sulfate, alumina powder, silica powder,
5 as a total amount of one or more types of magnesium carbonate etc. per 100 parts by weight of the thermoplastic resin.
There is no problem even if it is blended in an amount of 150 parts by weight according to a recipe known per se. The laminated plastic sheet of the present invention takes advantage of the above-mentioned advantages and can preserve various foods, seasonings, drinks, medicines, cosmetics, agricultural chemicals, etc. for a long period of time. Useful as a raw material for lightweight plastic containers. The invention is illustrated by the following example. Here, in each example described later, the laminated plastic sheet of the present invention is molded into the shape of a container,
The following characteristic values were measured. Oxygen permeability (Qo ₂ -D and Qo ₂ -W) and wavelength under each humidity condition described in each example
The ultraviolet transmittance (UVT) at 280 mμ was measured according to the method below, and the results were calculated. (i) Oxygen permeability (Qo ₂ -D) under low humidity (0%RH/15%RH): The inside of the empty container to be measured is replaced with nitrogen gas in a vacuum, and the mouth of the container is sealed with a rubber stopper. After sealing and covering the contact interface between the mouth and the rubber stopper with epoxy adhesive, the container was stored for a certain period of time in a constant temperature and humidity chamber at a temperature of 27°C and a humidity of 15% RH. The concentration of oxygen that permeated into the interior was determined using a gas chromatograph.
According to the following formula, 0% RH inside the container and 15% outside the container.
Calculate the oxygen gas permeability at RH (hereinafter referred to as low humidity) and temperature of 27℃, and further utilize the fact that thickness and oxygen permeability are inversely proportional to coat polyvinylidene chloride resin. The oxygen gas permeability was converted so that the sum of the thickness (t _CA ) and the thickness of the ethylene vinyl alcohol copolymer (t _EV ) was 15 μ. Therefore, Qo ₂ -D means the value of oxygen gas permeability at t _CA +t _EV =15 (μ). The results are the average values of N=3 measurement results. Qo ₂ = m x ct/100/t x Op x A [cc/m ²・day・atm] where m: Amount of nitrogen gas filled into the container [ml], t: Storage in a hot tank Period [day], ct: Oxygen concentration in the container after t days [Vol%], A: Effective surface area of the container [m ² ], Op: Oxygen gas partial pressure (=0.209) [atm]. (ii) Oxygen permeability (Qo ₂ −W) under high humidity conditions (100% RH/93% RH): Fill the empty container to be measured with 200 c.c. of distilled water in advance, and then vacuum the inside of the container. After replacing the inside with nitrogen gas, sealing the mouth of the container with a rubber stopper, and covering the interface between the mouth and the rubber stopper with epoxy adhesive, the temperature of the container was set at 27°C. And the humidity is reduced to 93% by the saturated aqueous solution of potassium nitrate.
After storing for a certain period of time in a constant temperature and humidity chamber controlled at %RH, the concentration of oxygen that permeated into the container was determined using a gas chromatograph, and calculated using the formula described in the section on oxygen permeability under low humidity in (i). Therefore, we calculated the oxygen gas permeability under conditions of 100% RH inside the container and 93% RH outside the container (hereinafter referred to as high humidity) and a temperature of 27°C, and further calculated the oxygen gas permeability when the thickness and oxygen permeability were reversed. Using the proportional relationship, the coating thickness of polyvinylidene chloride resin (t _CA ) and ethylene
The oxygen gas permeability was converted so that the sum with the thickness of the vinyl alcohol copolymer ( _tEV ) was 15μ.
Therefore, Qo ₂ -W means the value of oxygen gas permeability at t _CA +t _EV =15 (μ). The results are the average values of N=3 measurements. (iii) Ultraviolet transmittance (UVT): The body or bottom of the obtained container was cut into a predetermined size, and a recording spectrophotometer manufactured by Hitachi, Ltd. was used. As in the case of Figure 4, the wavelength is 201 to
Measurement was carried out over 700 mμ, and the wavelength was 280 mμ.
(arrow in Figure 4)
It was expressed as Example 1 A saponified ethylene-vinyl acetate copolymer (ethylene-vinyl alcohol copolymer) with an ethylene content of 59 mol% and a degree of saponification of 96% was made into a saponified product with a diameter of 40 mol%.
The ethylene-vinyl alcohol to a thickness of 1.1 mm was produced by a known melt extrusion method using an extruder equipped with a metering screw with an effective length of 800 mm and a single-layer flat die (lip width: 300 mm). A sheet of copolymer monolayer was obtained. Next, 89% by weight of vinylidene chloride, 4% by weight of acrylonitrile, and 5% by weight of methyl methacrylate were applied to the inner and outer surfaces of the single-layer sheet obtained.
A polyvinylidene chloride resin latex (dispersion medium: water, solid content: 52% by weight) having a composition ratio of 2% by weight and methyl acrylate is applied to the outer surface of the sheet by a known flow coating method. After drying in an air circulation oven at 80°C for 2 minutes, it was applied to the inner surface of the sheet by a known slush coating method, and then dried in the oven for 80°C.
Further drying was performed at ℃ for 3 minutes. Then, a laminated sheet having a layer structure as shown in FIG. 1-B (the base material was the above-mentioned ethylene/vinyl alcohol copolymer, and the inner and outer surfaces were the above-mentioned polyvinylidene chloride resin) was obtained. The average film thickness (coat thickness) of the polyvinylidene chloride resin applied to the outer surface of the obtained laminated sheet was 10.7μ, and the coat thickness on the inner surface of the sheet was 7.4μ (total thickness: 18.1μ). ). Next, the laminated plastic sheet was formed into a cylindrical cup having a diameter (inner diameter) of 4 cm, a height of 11 cm, and an average wall thickness of 0.4 mm by a known plug-assisted vacuum-pressure forming method. The coated laminated cup obtained in this way,
And for comparison, the oxygen permeability (Qo ₂ - D and Qo ₂ - W) and the wavelength is
Various measurements of ultraviolet transmittance (UVT) at 280 mμ were performed. The results are shown in Table 1. Furthermore, after filling the above two types of cups (single cup and coated cup) with 135 c.c. of tap water and sealing the mouth with laminated film containing aluminum foil,
It was left in a constant temperature bath adjusted to ℃ and 10% RH for 21 days. After 21 days, reduce the amount of tap water in each cup.
It was weighed using a top plate capable of weighing up to 500 mg, and the moisture loss (=1 - moisture content after standing/moisture content immediately after filling) was determined. The water loss was 0.84 for the ethylene-vinyl alcohol copolymer cup, whereas it was 0.84 for the ethylene-vinyl alcohol copolymer cup coated with polyvinylidene chloride resin of the above thickness on the inner and outer surfaces. It was impossible to measure weight loss within the range that the balance could detect.

[Table] Furthermore, the above two types of laminated cups were filled with 18 cans of commercially available grape concentrate, and after sealing the mouth with a laminated film containing aluminum foil, the temperature was adjusted to 30℃ and 80% RH. in a constant temperature bath (hereinafter referred to as dark place), and adjusted to 30℃ and 80%RH.
The two types of filled cups were placed in a constant temperature bath (hereinafter referred to as a light place) equipped with a 1000 Lux light source and stored for 3 months. After that, the grape concentrate filled in each cup was taken out, and the absorbance of each grape concentrate at a wavelength of 520 mμ was measured using a spectrophotometer, and the rate of change in absorbance (=absorbance after storage/
The absorbance immediately after filling was calculated. The results are shown in Table 2. All values are average values of n=3.

[Table] Example 2 Upper layer extruder with a built-in metering type screw with a diameter of 65 mm and an effective length of 1430 mm, a diameter of 40 mm
A lower layer extruder equipped with a metering screw with a diameter of 32 mm and an effective length of 704 mm, an extruder for the adhesive layer with a built-in metering screw with a diameter of 32 mm and an effective length of 704 mm, and three layers with a lip width of 520 mm. A laminate sheet with a three-layer structure consisting of the following layers was obtained by a known co-extrusion method using a flat die (total thickness of the sheet: 0.8 mm, composition ratio: upper layer: adhesive layer: lower layer = 1:0.1) :1) Upper layer: Isotactic polypropylene with melt index of 1.4 g/10 mm and density of 0.91 g/cc Adhesive layer: Maleic anhydride modified polypropylene (manufactured by Mitsubishi Yuka Co., Ltd., P-40B) Lower layer: Contains ethylene The amount is 25 mol% and the degree of saponification is
99.6% ethylene-vinyl alcohol copolymer Next, the lower layer of the obtained laminated sheet (ethylene-vinyl alcohol copolymer)
Polyvinylidene chloride resin latex (dispersion medium: water, solid content concentration: 30% by weight) having a composition ratio of 90% by weight vinylidene chloride and 10% by weight acrylonitrile on the surface of the vinyl alcohol copolymer layer)
was applied by a known dip coating method and dried at 60° C. for 30 minutes using a circulating air oven. Furthermore, aging (heat treatment) was performed for 2 days at 40°C in an air constant temperature bath. And 1st-C
A coated laminated sheet was obtained having a layer structure as shown in the figure (one surface was the above-mentioned isotactic polypropylene, and the opposite surface was the above-mentioned polyvinylidene chloride resin). The average film thickness (coat thickness) of the polyvinylidene chloride resin coated on the surface of the lower layer of the obtained sheet was 4.4 μm. The coated laminated sheet was then molded into a rectangular laminated cup (inner volume:
540ml) was obtained. In this case, the cup was molded so that the upper layer (isotactic polypropylene layer) was the outer layer of the cup, and the polyvinylidene chloride resin layer was arranged on the inner surface of the cup. The oxygen permeability (Qo ₂ - D and Qo ₂ -W) and ultraviolet transmittance (UVT) at a wavelength of 280 mμ were measured. The results are shown in the third section.

[Table] Furthermore, regarding the two types of laminated cups mentioned above,
After filling the full amount of commercially available white miso and sealing the mouth with a laminated film containing aluminum foil, it was heated to 30℃ and 80%
The two above were placed in a constant temperature bath adjusted to RH (hereinafter referred to as dark place) and a constant temperature bath adjusted to 30°C, 80% RH and equipped with a 1000 Lux light source (hereinafter referred to as bright place).
Each type of filled cup was left standing and stored for 4 months. After that, we took out the white miso filled in each cup and measured the brightness of each white miso using a color difference meter.
The rate of change in brightness (=brightness after storage/brightness immediately after filling) was calculated. The results are shown in Table 4. All values are average values of n=3.

【table】 [Brief explanation of drawings]

Figure 1-A, Figure 1-B, Figure 1-C, and Figure 1
-D is an enlarged sectional view showing several examples of the layer structure of the plastic sheet of the present invention, and FIG. t _CA + t _EV )
Thickness of vinylidene chloride resin layer (t _CA )
Curve A is a diagram showing the relationship between the ratio and oxygen permeability (measured temperature 27℃, relative humidity: 0% RH inside the container, 15% RH outside the container, t _CA + t _EV is converted to 15μ). is the measured value, curve B is the harmonic mean theoretical value, and Figure 3 is:
t _CA / (t _CA + t _EV ) and oxygen permeability under high humidity conditions (measurement temperature 27°C, relative humidity: 100% RH inside the container, 93% RH outside the container, t _CA + t _EV is converted to 15μ) ), where curve A' is the actual measured value, curve
B' is the harmonic mean theoretical value. Figure 4 is a diagram showing the relationship between wavelength and transmittance in plastic containers. Curve A is the transmittance of the container wall made of polyolefin/ethylene vinyl alcohol copolymer, and curve B Curves C and D show the transmittance of container wall A with a coating of vinylidene chloride/acrylic (methacrylic) copolymer, and curves C and D, respectively, with container wall B exposed to ultraviolet light. Reference numbers 1 and 1' are the ethylene-vinyl alcohol copolymer resin surface, 2 is the plastic container substrate, 3 and 3' are the vinylidene chloride-acrylic (methacrylic) copolymer coating layer, and 4 is the ethylene-vinyl alcohol copolymer resin surface. 5 indicates a moisture-resistant thermoplastic resin.

Claims (1)

[Scope of Claims] 1. A plastic substrate on which at least one surface is made of a resin mainly composed of an ethylene-vinyl alcohol copolymer, in a positional relationship adjacent to the resin surface mainly composed of the ethylene-vinyl alcohol copolymer. 99-70% by weight vinylidene chloride, 1-30
% by weight of at least one acrylic or methacrylic monomer and at least one other ethylenically unsaturated monomer in an amount of 0 to 100 parts by weight based on 100 parts by weight of the total amount of the monomers. The oxygen permeability coefficient at 20℃ and 100%RH is 9×10 ^-14 cc・cm/cm ²・sec・cmHg or less and the water vapor permeability coefficient (JISZ-0208) is 3×10 ^-3
g・cm/ ^cm2 . 1. A laminated plastic sheet characterized by being provided with a coating mainly composed of a copolymer having a surface resistance of less than 100 days. 2. The plastic sheet according to claim 1, wherein the plastic substrate is made of a single layer of resin mainly composed of ethylene-vinyl alcohol copolymer, and the coating layer is provided on both sides of the substrate. 3. The plastic sheet according to claim 1, wherein the plastic substrate is a laminate of a moisture-resistant thermoplastic resin that can be melt-molded and a resin mainly composed of an ethylene-vinyl alcohol copolymer. 4 The ethylene-vinyl alcohol copolymer has an ethylene content of 20 to 80 mol% and a saponification degree of
The plastic sheet according to claim 1, which is 90% or more of ethylene-vinyl alcohol copolymer.