JP7679588B2 - Container inner surface coating method - Google Patents

Description

The present invention relates to a method for applying a liquid repellent to the inner surface of a plastic container.

In plastic containers that contain viscous contents such as mayonnaise or ketchup, it is necessary to improve the slipperiness of the container's inner surface in order to ensure smooth discharge of the contents. For example, a lubricant is added to the base resin that comes into contact with the contents (see Patent Document 1, etc.).

In the invention described in Patent Document 1, a lubricant made by mixing a surfactant with an HLB value of less than 1 and an unsaturated fatty acid amide is added to the base resin that comes into contact with the contents of the plastic bottle, resulting in a plastic bottle with excellent sliding properties for the contents.

JP 2013-10541 A

However, when adding a lubricant to the base resin of a plastic container, it may be necessary to reconsider the molding conditions, and as a simpler method, coating (applying) a liquid repellent to the inner surface of the plastic container is being considered.

However, when coating with a liquid repellent agent, the formation of a thin, uniform liquid repellent layer is a challenge. Because the inside of a plastic container is a small space, it is known to be very difficult to apply by spray coating, for example. When applying by spraying from the mouth of a plastic container inwards, it is difficult to apply a thin, uniform coating over the entire surface of the container, and there may be some areas that are too thickly coated or dripping due to excessive application.

The present invention was made in consideration of the above-mentioned conventional circumstances, and aims to provide a method for coating the inner surface of a container that can apply a liquid repellent agent thinly and uniformly to the inner surface of a plastic container without causing thick coating or dripping.

In order to achieve the above-mentioned object, the method for coating the inner surface of a container of the present invention is characterized in that, when applying a liquid-repellent agent to the inner wall surface of a plastic container to form a liquid-repellent layer having an uneven surface, the plastic container is laid horizontally, a long, shaft-shaped nozzle is inserted into the container, and the liquid-repellent agent is sprayed from the tip of the nozzle while rotating the plastic container, and the inclination angle of the plastic container is changed when coating the bottom surface and shoulder portion of the plastic container.

By inserting a long, thin shaft-shaped nozzle into the container and applying the liquid-repellent agent, the liquid-repellent agent reaches every corner of the plastic container, achieving application to the entire surface of the container. In addition, by rotating the plastic container while applying the agent, a thin, uniform application is achieved, and thick coating and dripping are also eliminated.

The present invention provides a method for coating the inner surface of a container that can apply a liquid repellent agent thinly and uniformly to the inner surface of a plastic container without causing thick coating or dripping.

FIG. 1 is a schematic front view showing an example of a plastic container. FIG. 2 is a schematic cross-sectional view of a main part showing the layer structure of a plastic container. FIG. 1 is a diagram showing a state in which a shaft-shaped nozzle is inserted into a plastic container to perform application. FIG. 13 is a diagram showing the ejection direction of the liquid repellent agent. FIG. 2 is a schematic side view showing the configuration of a coating device. 1 is a photograph showing the surface state of a liquid-repellent layer when the rotation speed of a plastic container is set to 600 rpm. 1 is a photograph showing the surface state of a liquid-repellent layer when the rotation speed of a plastic container is set to 800 rpm. 1 is a photograph showing the surface state of a liquid-repellent layer when the rotation speed of a plastic container is set to 1000 rpm.

Below, an embodiment of a method for coating the inner surface of a container to which the present invention is applied will be described with reference to the drawings.

Figure 1 is a diagram showing an example of a plastic container 1 to which the application method of the present invention is applied. As shown in Figure 1, the plastic container 1 is a container that holds contents. Examples of contents include viscous substances such as mayonnaise and ketchup. The plastic container 1 is configured to squeeze the body 14 or the like to dispense the contents from a spout 12 having a screw thread 11 formed thereon, and the spout 12 is usually sealed with a cap 13 attached. The plastic container 1 is a blow-molded body formed, for example, by blow molding.

The plastic container 1 may have a single-layer structure or a multi-layer structure, but a multi-layer structure is preferable. Figure 2 shows an example of the layer structure of the plastic container 1, which comprises, in order from the inside surface side of the container 1, an innermost layer 2, an intermediate layer 3, an adhesive resin layer 4, a barrier layer 5, an adhesive resin layer 6, and an outermost layer 7. The layer structure of the plastic container 1 is not limited to this, and may, for example, omit at least one of these layers, or may further comprise another layer.

The outermost layer 7 is composed of a resin composition containing a thermoplastic resin such as polyolefin, and this resin composition preferably contains a lubricant. This can prevent problems caused by poor slipperiness on the surface of the plastic container 1.

The barrier layer 5 is made of a resin with high gas barrier properties. Examples of such resins include ethylene vinyl alcohol copolymer (EVOH: saponified ethylene vinyl acetate copolymer, etc.) and aromatic polyamide. By providing the barrier layer 5, it is possible to effectively suppress oxidative deterioration of the contents due to oxygen permeation.

The intermediate layer 3 is composed of a resin composition containing a thermoplastic resin such as polyolefin. The intermediate layer 3 can be omitted. The intermediate layer 3 may be a repro layer made by recycling flash generated during the blow molding of the container 1.

The adhesive resin layers 4 and 6 are composed of an adhesive resin. Examples of adhesive resins include acid-modified polyolefin resins (e.g., maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene). The adhesive resin layers 4 and 6 improve the adhesion between the barrier layer 5 and the outermost layer 7 or the intermediate layer 3. Instead of providing the adhesive resin layers 4 and 6, an adhesive resin may be blended into the barrier layer 5.

The innermost layer 2 is the layer that comes into contact with the contents and is composed of a resin composition that contains a base resin. The base resin is preferably a thermoplastic resin such as polyolefin. Examples of polyolefin include polyethylene and polypropylene. In addition, filling particles may be added to the base resin, and the inner surface of the innermost layer 2 (i.e., the inner surface of the plastic container 1) may be provided with an uneven shape due to the presence of the filling particles.

When providing an uneven shape to the innermost layer 2, it is preferable to set the ten-point average roughness Rz to about 7 to 500 μm, more preferably 10 to 300 μm, and most preferably 10 to 100 μm. By setting it within this range, it is possible to particularly improve the sliding properties.

The filler particles used to provide the innermost layer 2 with an uneven shape are particles capable of imparting an uneven shape, and may be filler particles containing at least one of an organic component and an inorganic component.

Suitable inorganic components include, for example, 1) metals such as aluminum, copper, iron, titanium, silver, and calcium, or alloys or intermetallic compounds containing these metals; 2) oxides such as silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, and iron oxide; 3) inorganic or organic acid salts such as calcium phosphate and calcium stearate; 4) glass; and 5) ceramics such as aluminum nitride, boron nitride, silicon carbide, and silicon nitride.

As the organic component, for example, organic polymer components (or resin components) such as acrylic resins, urethane resins, melamine resins, amino resins, epoxy resins, polyethylene resins, polystyrene resins, polypropylene resins, polyester resins, cellulose resins, vinyl chloride resins, polyvinyl alcohol, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-ethyl acrylate copolymers, polyacrylonitrile, polyamide, etc. can be suitably used.

In the plastic container 1 having the above configuration, the sliding properties are improved by applying a liquid repellent agent to the inner surface and forming a liquid repellent layer 20 on the surface of the innermost layer 2. The method of applying the liquid repellent agent to the inner surface of the plastic container 1 is described below.

In this embodiment, the liquid repellent agent is applied to the inner surface of the plastic container 1 by inserting a long, thin shaft-shaped nozzle 30 into the plastic container 1, as shown in FIG. 3. The size of the plastic container 1 is arbitrary, but for example, the capacity is about 100 mL to 300 mL, and the diameter is about 10 mm to 50 mm.

The nozzle 30 is composed of a shaft portion 31, which is an elongated tubular member, and a nozzle head 32 provided at the tip of the shaft portion 31. The shaft portion 31 is a hollow tubular member, and the liquid repellent agent is supplied to the nozzle head 32 at the tip through the hollow portion. The liquid repellent agent supplied to the nozzle head 32 is sprayed in a predetermined direction from a spray hole provided in the nozzle head 32.

As the liquid repellent to be applied to the inner surface of the plastic container 1, any agent that has oil and water repellency can be used, but it is preferable to use a liquid repellent agent that can form a liquid repellent layer with an uneven surface that exerts a lotus effect, such as a dispersion liquid in which a fluorine-based compound is dispersed in a solvent such as ethanol.

The liquid repellent used in this embodiment contains at least one type of hydrophobic particles and hydrophobic/oleophobic particles.

The hydrophobic particles usually have an average primary particle diameter of 3 to 100 nm, preferably 5 to 50 nm, and more preferably 7 to 30 nm. By setting the average primary particle diameter within the above range, the hydrophobic particles are in a moderately aggregated state, and gas such as air can be retained in the voids in the aggregates, resulting in excellent sliding properties. In other words, this aggregated state is maintained even after adhesion to the uneven surface, so excellent sliding properties can be exhibited.

The hydrophobic particles are not particularly limited as long as they have hydrophobic properties, and may be those that have been made hydrophobic by surface treatment. For example, hydrophilic oxide fine particles may be surface-treated with a silane coupling agent or the like to make the surface hydrophobic. The type of oxide is also not limited as long as it has hydrophobic properties. For example, at least one of silica (silicon dioxide), alumina, titania, etc. may be used. Among these, hydrophobic silica fine particles are preferably used as the hydrophobic oxide particles. In particular, hydrophobic silica fine particles having trimethylsilyl groups on the surface are preferred in that they provide better non-adhesive properties.

As the oleophobic particles, for example, composite particles in which the surface of oxide fine particles is coated with a fluororesin or the like can be used. As the oxide fine particles, for example, at least one type of oxide fine particles such as silicon oxide, titanium oxide, aluminum oxide, zinc oxide, etc. particles (powders) can be used. In particular, silicon oxide particles are preferable. These oxide fine particles can also be commercially available products.

The liquid repellent is generally used in the form of a dispersion in which at least one of the hydrophobic particles and the oleophobic particles is dispersed in a solvent.

Examples of solvents that can be used include organic solvents such as aromatic hydrocarbons such as toluene and xylene, alicyclic hydrocarbon solvents such as methylcyclohexane and cyclohexane, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as methyl ethyl ketone and acetone, and alcohol solvents such as isopropyl alcohol and denatured ethanol. These can be used alone or in combination of two or more kinds.

The plastic container 1 may be heated before applying the liquid repellent agent. For example, the heating conditions include placing the container in a thermostatic bath at 120°C for about 1 minute, removing it and immediately applying the agent. Alternatively, the inside may be heated with a heat gun for about 10 seconds and then immediately applied. By heating the plastic container 1 beforehand, the solvent is more easily evaporated during application, and the drying time is shortened, resulting in the formation of a liquid repellent layer with excellent surface irregularities.

When applying the liquid repellent using the nozzle 30, first, the nozzle 30 is inserted into the plastic container 1 from its opening. At this time, the nozzle 30 is inserted into the plastic container 1 so that the central axis of the nozzle 30 and the central axis of the plastic container 1 are roughly aligned. In this example, the plastic container 1 is laid horizontally, but this is not limited to this and the plastic container 1 may be tilted at any angle.

Next, while rotating the plastic container 1, the liquid repellent agent is sprayed from the nozzle head 32 of the nozzle 30, and the liquid repellent agent is applied to the inner surface of the plastic container 1. When applying the liquid repellent agent, it is possible to rotate either the plastic container 1 or the nozzle 30, but by rotating the plastic container 1, centrifugal force is applied to the liquid repellent agent adhering to the inner surface, which is advantageous in applying the liquid repellent agent thinly and uniformly.

When applying, the nozzle 30 is moved axially (in the direction of the central axis of the shaft portion 31) while applying. For example, the nozzle 30 is inserted so that the tip of the nozzle 30 is positioned near the bottom of the plastic container 1, and then the application is performed while moving the nozzle 30 in the direction of pulling it out. The nozzle 30 may move in the direction just once, or may move back and forth within the plastic container 1. The movement speed of the nozzle 30 is basically constant, but it can be changed according to the shape of the plastic container 1, for example by slowing down the movement speed of the nozzle 30 in areas where the shape of the plastic container 1 is large to increase the amount of repellent applied.

The direction in which the liquid repellent agent is sprayed from the nozzle head 32 is arbitrary, but if the spray direction is axial, for example, it may not be possible to form a sufficient coating on the corners near the bottom of the plastic container 1 or the shoulders near the mouth. To avoid such inconvenience, it is preferable to set the spray direction θ of the liquid repellent agent from the nozzle head 32 to an oblique direction, as shown in FIG. 4. By setting the spray direction θ of the liquid repellent agent from the nozzle head 32 to 20° to 60°, for example 30° or 45°, it is possible to apply the liquid repellent agent evenly to the entire inner surface of the plastic container 1.

Figure 5 shows an example of an apparatus for carrying out the above-mentioned coating method. The coating apparatus shown in Figure 5 is composed of a container holding mechanism 41 for holding and rotating the plastic container 1, and a nozzle driving mechanism 51 for inserting and moving the nozzle 30 into the plastic container 1.

The container holding mechanism 41 has holder parts 42, 43 that grip the plastic container 1, and these holder parts 42, 43 clamp and hold the plastic container 1. The holder parts 42, 43 can also be rotated by a rotation mechanism, and by rotating these, the held plastic container 1 is rotated. The rotation speed can be adjusted as appropriate. Furthermore, the container holding mechanism 41 has a tilting mechanism that can change the tilt angle of the plastic container 1 held by the holder parts 42, 43, and by changing the tilt angle of the held plastic container 1, it is possible to apply the agent to the bottom surface, shoulders, etc. of the plastic container 1 with pinpoint accuracy.

The nozzle drive mechanism 51 includes a support base 52, a linear motion mechanism 53, and a nozzle support block 54. The nozzle support block 54 to which the nozzle 30 is attached is moved in the direction of the arrow by the linear motion mechanism 53. In addition, a liquid repellent agent is supplied to the nozzle 30 via the nozzle support block 54.

When applying the repellent agent, the plastic container 1 is attached to the holder parts 42, 43 of the container holding mechanism 41, and the nozzle drive mechanism 51 is operated to move the nozzle support block 54 toward the container holding mechanism 41 and insert the nozzle 30 into the plastic container 1. Next, the holder parts 42, 43 (plastic container 1) of the container holding mechanism 41 are rotated and the nozzle 30 is moved, so that the repellent agent is sprayed from the nozzle 30 to apply the repellent agent to the inner surface of the plastic container 1.

After the coating is complete, the liquid-repellent layer formed on the inner surface of the plastic container 1 must be dried, but it is preferable to continue rotating the plastic container 1 even during drying. If the rotation of the plastic container 1 is stopped while the liquid-repellent layer is still wet, the liquid may drip and cause unevenness.

When applying the liquid repellent agent, it is important to adjust the rotation speed of the plastic container 1 appropriately. Specifically, it is preferable to set the rotation speed of the plastic container 1 to 400 rpm to 1000 rpm. If the rotation speed of the plastic container 1 is less than 400 rpm, there is a risk of liquid dripping. If liquid dripping occurs during application of the liquid repellent agent, the liquid repellent layer in that area may peel off from the inner surface of the plastic container 1, and sufficient sliding performance may not be obtained. Conversely, if the rotation speed of the plastic container 1 exceeds 1000 rpm, the surface of the liquid repellent layer formed may become too flat, and sufficient sliding performance may not be obtained.

In addition, it has been found that in the application of the aforementioned liquid repellent agent, the surface state of the coating film (liquid repellent layer) formed can be controlled by the application conditions, such as the rotation speed of the plastic container 1 during application. For example, by changing the application conditions, the surface of the liquid repellent layer 20 formed changes, such as the surface state of the liquid repellent layer 20 being flat or having fine irregularities. In addition, the longer the drying and solvent evaporation process is taken, the flatter the surface of the liquid repellent layer 20 formed will be, and shortening the time will result in irregularities.

When fine irregularities are formed on the surface of the liquid-repellent layer 20, the physical effect of the lotus effect is added to the chemical effect of the liquid-repellent agent, improving the sliding properties. In other words, high sliding properties can be achieved even if the inner surface of the plastic container 1 is not provided with irregularities in advance. On the other hand, when irregularities are formed on the surface of the liquid-repellent layer 20, the liquid-repellent layer 20 tends to peel off easily.

In view of these circumstances, it is preferable for the surface of the liquid-repellent layer 20 to have appropriate irregularities, and in order to achieve this, it is preferable to set the rotation speed of the plastic container 1 during application to 600 rpm to 800 rpm. By setting the rotation speed within this range, the surface condition of the liquid-repellent layer 20 formed can be made appropriate, and a liquid-repellent layer 20 with excellent sliding properties and resistance to peeling can be formed.

As described above, according to the container inner surface coating method of this embodiment, it is possible to apply a liquid repellent agent thinly and uniformly to the inner surface of the plastic container 1, and it is possible to realize a container inner surface coating method that does not cause thick coating or dripping, etc.

Although an embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention.

1. Preparation of plastic containers A plastic container having the shape shown in Figure 1 was prepared by direct blow molding of the parison. The volume of the prepared container was 150 mL and the diameter was 40 mm. Polyethylene (melting point 112°C) was used as the base resin for the innermost layer of the parison.

2. Coating of liquid repellent agent Using the device shown in Figure 5, a liquid repellent agent was applied to the inner surface of a plastic container. The liquid repellent agent was a dispersion liquid in which a fluorine-based compound was dispersed in ethanol. The direction of the liquid repellent agent ejected from the nozzle was 45°. Under these conditions, the rotation speed of the plastic container was changed in the range of 300 rpm to 1100 rpm to form a liquid repellent layer, and samples 1 to 6 were created.

3. Evaluation The slip-down performance was evaluated for the prepared samples 1 to 6. The evaluation method was as follows.
Contents: Extra virgin olive oil Test method: Using a syringe, a small amount of olive oil was dripped onto a small sample piece (a small piece cut from a plastic container) placed on a slope (incline angle 3°), and the amount of liquid that started to slide down was measured from the weight difference of the syringe. Three measurements were taken per sample, and the average value was calculated. The higher the sliding performance, the more easily the sample slides down with a small amount (low load), so the sliding performance was evaluated in three stages based on the measured amount of liquid.
The results are shown in Table 1.

From Table 1, we can see that good sliding performance can be achieved by optimizing the rotation speed of the plastic container.

The surface state of the liquid-repellent layer formed is shown in Figures 6 and 7. Figure 6 is a photograph showing the surface state of the liquid-repellent layer when the plastic container is rotated at 600 rpm, Figure 7 is a photograph showing the surface state of the liquid-repellent layer when the plastic container is rotated at 800 rpm, and Figure 8 is a photograph showing the surface state of the liquid-repellent layer when the plastic container is rotated at 1000 rpm. There is a tendency for the surface to become flatter the faster the plastic container is rotated.

Sample 1 showed considerable peeling of the liquid-repellent layer, and its performance was insufficient. Sample 2 also showed some peeling of the liquid-repellent layer, and its performance could not be said to be sufficient. When the rotation speed of the plastic container during application was set to 600-800 rpm, the liquid-repellent layer had a good surface condition and exhibited good sliding performance. When the rotation speed exceeded 800 rpm, the surface of the liquid-repellent layer became too flat, and a decrease in sliding performance was observed.

1 Plastic container 20 Liquid repellent layer 30 Nozzle 31 Shaft portion 32 Nozzle head

Claims (8)

When applying a liquid repellent agent to the inner wall surface of a plastic container to form a liquid repellent layer having an uneven surface,
Place the plastic container horizontally,
A long, thin shaft-shaped nozzle is inserted into the container, and the liquid repellent agent is sprayed from the tip of the nozzle while the plastic container is rotated.
A method for coating the inside surface of a container, characterized in that the inclination angle of the plastic container is changed when coating the bottom surface or shoulder portion of the plastic container . The method for coating the inner surface of a container according to claim 1, characterized in that the liquid repellent agent contains at least one type selected from hydrophobic particles and hydrophobic/oleophobic particles. The container inner surface coating method according to claim 1 or 2, characterized in that the rotation speed of the plastic container is 400 rpm to 1000 rpm. The container inner surface coating method according to claim 1 or 2, characterized in that the rotation speed of the plastic container is 600 rpm to 800 rpm. The method for coating the inner surface of a container according to any one of claims 1 to 4, characterized in that the nozzle is moved in the axial direction. 6. The method for coating the inner surface of a container according to claim 1, wherein the direction in which the liquid repellent agent is ejected is set to 30° to 45° with respect to the axial direction of the nozzle. The method for coating the inner surface of a container according to any one of claims 1 to 6, characterized in that the plastic container is preheated. The method for coating the inner surface of a container according to any one of claims 1 to 7, characterized in that the plastic container is rotated even when drying after the liquid repellent agent is applied.

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