JPS6131438A - Method for coating synthetic resin container - Google Patents

Abstract

PURPOSE:To coat a synthetic resin container with a film exhibiting a uniform good surface conditions with a high peel strength in a small amount of a resin, by coating the surface of container with a polyvinylidene chloride resin solution dividedly twice or more. CONSTITUTION:A synthetic resin container is coated with a plyvinylidene chloride solution. In the process, a resin solution with 2-40wt% solid content is first prepared, and used to form the first layer having <=4mum thickness when dried. The polyvinylidene chloride resin solution is then applied to the resultant first layer in a required number of times, dried and hardened to form the second layer. The resin used for forming the first layer is copolymer of vinylidene chloride with another copolymerizable monomer, and the lower content of the vinylidene chloride monomer than the resin for forming the second layer is used. The solution is used under shear force in forming the first layer, and a drawn polyethylene terephthalate container is used as the container.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method of coating a synthetic resin container with a polyvinylidene chloride resin, and more particularly, the present invention relates to a method of coating a container made of a synthetic resin with a polyvinylidene chloride resin. The purpose of the present invention is to provide a synthetic resin container having a polyvinylidene chloride resin coating layer with excellent peel resistance and surface properties.

(Prior Art) Containers made of synthetic resin do not break like glass containers, and are becoming widely used in various fields. In particular, polyethylene terephthalate stretched containers have various advantages in terms of transparency, lightness, strength, etc., and have been gaining popularity in recent years.
It was widely used as a packaging container for soy sauce, juice, salad dressing, alcoholic beverages, etc., and also began to be used as a container for carbonated drinks. However, although the gas barrier properties of polyethylene terephthalate resins are better than those of olefin resins, they are inferior to polyvinylidene chloride resins, which have the best gas barrier properties among synthetic resins.

For this reason, in the case of a container with a small internal volume, the contents to be packaged are greatly affected by oxygen gas etc. that permeate through the container wall, and the dissipative contents are dissipated into the atmosphere through the container wall. There is a large degree of

Therefore, improving the gas barrier properties of stretched containers made of polyethylene terephthalate is essential for maintaining the quality of the contents and for small-capacity containers.Therefore, the container walls are coated with polyvinylidene chloride resin, which has good gas barrier properties. It is considered to do.

However, even when attempts are made to coat polyvinylidene chloride resin on the wall surface of a polyethylene terephthalate stretched container using conventional coating methods such as spray coating and dipping coating, the wetting of polyvinylidene chloride resin to polyethylene terephthalate resin is poor. In addition, due to the poor fluidity, the condition of the coated surface after curing is poor, and surface irregularities and bubbles are likely to occur in the coating, making it impossible to obtain a product of good quality. In order to improve the adhesion with polyethylene terephthalate resin, it is sufficient to improve the wettability of the coating liquid to the surface to be coated.Methods to improve wetting include surface treatment of the surface to be coated, such as corona discharge treatment, flame treatment, and chemicals. Techniques such as chemical cleaning treatment and formation of an anchor coat are generally known.

(Problems to be Solved by the Invention) However, these treatment methods have drawbacks such as complicated steps and difficulty in treating the resulting wastewater. An even bigger drawback is that even if a polyvinylidene chloride resin coated surface with good surface properties is obtained, the formed film has no peeling resistance and is easily peeled off with cellophane tape, etc., and during actual transportation. There is a drawback that the coating may peel off when containers are rubbed together or due to impact with other hard objects.

(Means for Solving the Problems) As a result of intensive research into a method for uniformly coating the wall surface of a synthetic resin container with polyvinylidene chloride resin, the present inventor has discovered that polyvinylidene chloride resin coating liquid can be coated with ordinary primer. After forming a thin undercoat layer (first layer), a topcoat layer (second layer) is formed using the same polyvinylidene chloride resin coating solution.
layer), it is possible to form a film on the surface of a synthetic resin container with a relatively small amount of resin applied, a uniform and good surface condition, and a good peel resistance strength, and this knowledge This is the first step in completing the present invention.

That is, the present invention provides a method for coating a synthetic resin container with polyvinylidene chloride resin, in which the polyvinylidene chloride resin coating liquid is applied in two or more times, and the solid content is reduced in the first coating step. , 2 to 40% by weight of the resin coating solution described above is used to form a first layer having a dry thickness of 4 grm or less.

Next, a polyvinylidene chloride resin coating liquid is further applied to the first layer a required number of times, and then dried and cured to form a second layer.A synthetic resin container is coated with polyvinylidene chloride resin. This is the way to do it.

To explain the method of the present invention in detail, the method of the present invention is effective not only for coating polyethylene terephthalate but also other plastic containers, but it is more efficient when applied to stretched containers made of polyethylene terephthalate. , Also, since there is a strong social demand, the following
The method of the present invention will be explained in detail using a polyethylene terephthalate stretched container as a representative example.

The polyethylene terephthalate stretched container (hereinafter simply referred to as container), which is a typical object of the method of the present invention, is manufactured from conventionally known polyethylene terephthalate, and any known container can be used. If it is not contaminated with oil or the like during or after molding, it can be used without requiring special surface treatment such as cleaning or corona treatment, and a film with sufficient performance can be formed.

The polyvinylidene chloride used for the coating in the method of the invention is known as a resin coating per se, is readily available on the market, and can be used freely in the method of the invention.

These coating fluids are generally in the form of aqueous latexes or emulsions, for example homopolymers of vinylidene chloride, copolymerized with other copolymerizable monomers such as acrylic monomers or methacrylic monomers. It may be a combination, and is generally obtained with a solid content of 45 to 50% by weight, but in the formation of the first layer in the present invention, the formation of a film and the leveling property of the formed film are Considering this, the lower the solid content is, the better. However, if the solid content is too low, liquid stability becomes a problem. For example, if the solid content is less than 2% by weight, it becomes difficult to form a first layer with a smooth surface. Also, if the solids content becomes too high, drying will be too rapid, coating methods will be limited, and alcohol stabilization will be lost. Therefore, in the method of the present invention, the solids content is about 2 to about 4
It is preferred to use a polyvinylidene chloride resin coating in the range of 0% by weight.

Generally, as the solid content of the polyvinylidene chloride resin coating liquid decreases, the leveling properties of the formed film improve, but the film becomes more likely to break on the container surface during application. This is presumed to be due to the interaction of wetting and flow with the container surface, but the details are unknown. Preventing this membrane breakage 11-
Adding a surfactant is effective for this purpose, but commercially available products already contain a considerable amount of surfactant, and excessive addition of surfactants may deteriorate the peel resistance of the cured film. This will happen.

As a result of various studies to solve these problems, the present inventor found that when alcohol is added to a coating liquid with a low solid content,
We have discovered that this problem of membrane breakage can be solved. However, if the amount of alcohol added is too large, the resin liquid emulsion will aggregate and lose liquid stability. Therefore, the amount of alcohol added is preferably 30% by weight or less of the coating liquid, more preferably 1% to 12.0% by weight, and most preferably 5% to 15% by weight. .

The polyvinylidene chloride aqueous emulsion of the above coating liquid is
When polyvinylidene chloride is a copolymer of vinylidene chloride and an acdal or methacrylic monomer, a copolymer containing a large amount of acrylic or methacrylic monomers has a high bond with the surface of the container, which is the base material. Although the adhesion is good, there is a drawback that the higher the proportion of the comonomer, the more the oxygen barrier properties of the formed film deteriorate. Therefore, the present inventor used a copolymer with improved adhesion by increasing the amount of acrylic or methacrylic monomer to form the first layer, and vinylidene chloride to form the second layer. We have found that it is desirable to use a homopolymer or a copolymer with a high vinylidene chloride monomer content. For example, if the polyvinylidene chloride used to form the first layer and the second layer are both copolymers with other copolymerizable monomers, the other copolymer in the resin for forming the first layer may The monomer is preferably about twice as large as the comonomer in the second layer forming resin. Of course, the method of the present invention is not limited to such preferred embodiments, and the first layer and the second layer may be made of the same high barrier type acrylic system,
Even in the case of an aqueous emulsion of a copolymer containing a small amount of methacrylic thread-conducting comonomer, the adhesive force direction -L can be clearly seen by the method of the present invention.

Although ordinary dipping and spraying methods are effective for coating the first layer, the present inventor has developed a method that forms an even and thin coating film and further dramatically improves the effects of the present invention. I found out. The method involves impregnating a carrier such as sponge or felt with the aqueous emulsion and applying the emulsion by pressing it against a rotating container. In other words, applying shear force while applying the emulsion. This is the way to do it.

In such a preferred method, the pressure with which the emulsion-impregnated carrier is pressed against the container surface is 2 g/
If it is crn' or higher, the stronger the better.

If the pressure is too high, the container body will deform and coating will become impossible, so it is desirable to increase the pressure as much as possible while still being able to coat the container. In addition, the rotation speed is managed by circumferential speed, and 3+*
/min to 320 m/min, preferably 30 m/min to 1 min.
80m/min, more preferably 40-7 minutes to 100m
/minute range. The first layer of the container coated with the coating liquid is formed by curing the polyvinylidene chloride at a temperature below the deformation temperature of the container.

As described above, the first layer, which is the main feature of the method of the present invention, is formed, but the subsequent second layer may be formed after or before the first layer is cured. The method may be any conventionally known method. The second layer is formed by using a common vinylidene chloride resin coating solution and coating it once or multiple times to form a film with a thickness of preferably about α~/rμm when dry, and then Drying and curing completes the process of the invention.

(Operation/Effect) According to the present invention as described above, the first layer acts as a primer on the surface of the capacitor which is the base material, and the adhesive force of the coating layer consisting of the first layer and the second layer to the container surface is increased. Since the improvement is markedly improved, there is no need for the complicated pretreatment of the container surface as in the conventional technology.Also, even though the first layer, which is a thin film, has a low gas barrier property, the second layer can be made of polyvinylidene chloride resin, which has a high gas barrier property. can be used, making it possible to provide various containers with excellent overall gas barrier properties.

Although the present invention has been described above using a stretched container made of polyethylene terephthalate as a representative example, it goes without saying that the present invention can similarly produce excellent effects on containers made of other resins.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Example 1 Polyvinylidene chloride aqueous emulsion L-520 (solid content 48%, vinylidene chloride monomer unit 90% by weight) manufactured by Asahi Kasei Kogyo Co., Ltd. was used as a coating liquid for the undercoat layer, and the emulsion was mixed with a solid content of 10%. The solution was diluted with distilled water and ethyl alcohol so that the ethyl alcohol content was 10% by weight. Felt was impregnated with this undercoat liquid, and applied to a polyethylene terephthalate stretching container at a pressure of 20 g/cml and a circumferential speed of the container of 50 m/min, and then heated with a far infrared heater for 1 minute to form a 2 gm transparent film. After that, the L-520 thick liquid was spray coated and cured for 6 minutes to obtain a polyethylene terephthalate stretched container coated with a polyvinylidene chloride resin and having good peel resistance.

Example 2 An aqueous emulsion of a polyvinylidene chloride copolymer containing 1.8 times as much acrylic comonomer as L-520 polyvinylidene chloride was prepared so that the solid content was 10% by weight and the alcohol content was 10% by weight. An undercoat solution was prepared. Using this, the coating liquid was applied and formed into a film on the same polyethylene terephthalate stretching container as in Example 1 under the same undercoating conditions as in Example 1, and then the L-520 coating liquid was spray coated and cured for 6 minutes. As a result, a polyethylene terephthalate stretched container having good peel resistance was obtained.

Example 3 A container similar to that in Example 1 or 2 was subbed in the undercoating liquid prepared in Example 2 by dipping, and immediately dipped in L-520 coating liquid without curing, and then cured for 6 minutes. A polyethylene terephthalate stretched container with good peelability was obtained.

Example 4 After curing the undercoat layer as in Example 2, topcoating was applied by dipping as in Example 3 to obtain a polyethylene terephthalate stretched container with good peel resistance.

Example 5 A container primed as in Example 3 was coated with L-520 coating solution by spray coating, cured for 6 minutes,
A polyethylene terephthalate stretched container with good peelability was obtained.

The following comparative example was made using a polyethylene terephthalate stretching container similar to the example.

Comparative Example 1 After spray coating with L-520 coating liquid, it was cured for 6 minutes.

Comparative Example 2 After spray coating L-520 coating liquid, it was cured for 10 minutes.

Comparative Example 3 After dip coating L-520 coating liquid, it was cured for 10 minutes.

When the peeling resistance of the coating layer of the containers obtained in the above Examples and Comparative Examples was examined, the results shown in Table 1 below were obtained.

Yes %1-j (- Total coating amount 11.11# Peelability Appearance (dry thickness) Example t 13 ■ 02
13 ■ 0 3 13 ■ 04 13
■ 0 5 13 ■ O Comparative example 1 13 ■ Δ2
13 ■ Δ3 13
■ O Notes ■ Does not withstand peeling off cellophane tape.

■Resistant to peeling off sellotape.

■Even if the lea is scratched, it can withstand tape peeling.

■■Although it is above, it cannot withstand peeling of 5mm 3×3 gobans.

■Resistant against peeling.

Claims (4)

[Claims] (1) In the method of coating a synthetic resin container with polyvinylidene chloride resin, the polyvinylidene chloride resin coating liquid is applied in two or more times, and in the first coating step, the solid content is Using 40% by weight of the above resin coating liquid, form a first layer having a dry thickness of 4 μm or less, then further coating the first layer with a polyvinylidene chloride resin coating liquid a required number of times, A method of coating a synthetic resin container with a polyvinylidene chloride resin, the method comprising: then drying and curing to form a second layer. (2) The polyvinylidene chloride resin for forming the first layer is a copolymer of vinylidene chloride and another copolymerizable monomer, and contains more vinylidene chloride monomer units than the polyvinylidene chloride resin for forming the second layer. Process according to claim 1, characterized in that the amount is low. (3) The method according to claim (1), wherein the first layer is formed while applying a shearing force to the polyvinylidene chloride resin coating liquid. (4) The method according to claim (1), wherein the synthetic resin container is a stretched polyethylene terephthalate container.