JP7413625B2 - Molded object and its processing method - Google Patents

Description

The present invention relates to a molded article made of a resin composition containing a thermoplastic resin and an additive having bleed properties, and a method for treating the molded article.

Molded bodies made of resin compositions containing thermoplastic resins are used for various purposes including packaging bodies such as containers and bags. Additives are added to the resin composition as appropriate depending on the intended use of the molded article. Among additives, additives having bleed properties are known to exhibit desired functions by oozing (bleeding) onto the surface of a molded article after molding. Antifogging agents, antistatic agents, and the like are known as additives having bleeding properties.

For example, in synthetic resin film bags containing foods such as fruits and vegetables, additives with bleeding properties are added to the resin composition to prevent moisture from condensing during refrigeration and impairing the transparency inside the bag. An antifogging agent is added as an antifog agent. By increasing the amount of such additives added, the effect (antifogging effect) of the additive can be enhanced.

On the other hand, as the amount of additives added increases, blocking occurs between the films due to stickiness, resulting in problems such as reduced workability and ease of handling. In order to solve such problems, Patent Document 1 proposes adding a specific antifogging agent to a polyethylene resin film.

Japanese Patent Application Publication No. 4-279643

However, the amount of additives having bleed properties that bleed onto the surface of the molded product is greatly influenced by the manufacturing environment of the molded product and the storage environment of the molded product until it is actually used. Specifically, when a molded body is manufactured and stored in the summer, the amount of additive bleeding increases, and when a molded body is manufactured and stored in the winter, the amount of additive bleed is decreased. Therefore, the current situation is that changing the additive alone is not sufficient to achieve a balance between achieving good additive effects throughout the year and suppressing stickiness due to additive bleeding.

Therefore, in the present invention, we provide a molded article that can suppress stickiness, and also provide a molded article that can suppress stickiness while expressing good effects of additives regardless of the manufacturing environment and storage environment of the molded article. The purpose is to provide a processing method.

In order to solve the above problems, a molded article as an embodiment of the present invention is made of a resin composition containing a thermoplastic resin and an additive having bleeding property, and the additive content in the resin composition is can be configured such that the effect of the additive after the molded body is heated for a predetermined period of time is better than the effect of the additive on the molded body immediately after molding. Here, the effect of an additive is a comprehensive effect that includes not only the original effect of the additive (for example, anti-fog performance when the additive is an anti-fog agent) but also the stickiness of the molded product due to additive bleeding. means an evaluation.

The thermoplastic resin may be composed mainly of polyolefin.

The additive may be an antifogging agent, and the effect of the additive may be antifogging performance.

Even if the shape of the molded object is a film or sheet, a product composed of a film or sheet, or a roll formed by winding a band or cylindrical body made of a film or sheet into a roll. good.

As a method for treating the molded body, the molded body can be heated for a predetermined period of time.

The heating treatment temperature may be 30°C to 80°C.

According to the above aspect, the effect of adjusting the additive content in the resin composition after the molded body is heated for a predetermined period of time is better than the effect of the additive in the molded body immediately after molding. Since the amount is made small, stickiness on the surface of the molded article can be suppressed. Moreover, by subjecting the obtained molded body to a heating treatment for a predetermined period of time, stickiness can be suppressed while exerting the favorable effects of the additive, regardless of the manufacturing environment and storage environment of the molded body.

Evaluation pattern diagram used for antifogging evaluation of the molded article of this embodiment

Embodiments of the present invention will be described below. The molded article of the present invention is made of a resin composition containing a thermoplastic resin and an additive having bleeding properties. Thermoplastic resin is a resin that can be molded by heating and melting, such as extrusion molding, inflation molding, injection molding, and blow molding. Examples of the thermoplastic resin include, but are not limited to, polyolefin, polyvinyl chloride, ethylene-vinyl acetate copolymer, and polyvinylidene chloride.

Thermoplastic resins can be used alone or in a blend of two or more. When the molded body is a packaging body for foods such as fruits and vegetables, polyolefin can be suitably used as the thermoplastic resin. In this case, the resin composition may contain polyolefin as a main component, and may also contain a thermoplastic resin other than the main component. When the main component is polyolefin, the content of polyolefin in the resin composition may be 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more.

When the molded body is used at low temperatures, it is preferable to use polyethylene because it has excellent strength at low temperatures. Examples of polyethylene (PE) include linear low density polyethylene (LLDPE), low density polyethylene (LDPE), high density polyethylene (HDPE), and medium density polyethylene (MDPE). Among them, it is preferable to use LLDPE because it has excellent transparency and rigidity.

The additive has a bleed property with respect to the thermoplastic resin, and specifically includes, but is not limited to, an antifogging agent and an antistatic agent. The content of the additive in the resin composition is such that the effect of the additive after heating the molded body for a predetermined period of time is better than the effect of the additive on the molded body immediately after molding. .

The resin composition may contain other additives that do not impair the purpose of the present invention, such as stabilizers such as antioxidants, colorants such as dyes and pigments, slip agents, and anti-blocking agents. agent (AB agent), etc. can be blended. The resin composition of the present invention can be molded into a single layer as it is, or it can have a laminated structure in which one or more other resin compositions are laminated on the side opposite to the side where the additive bleeds and exerts its effect. It is also possible to do this.

There are no particular restrictions on the shape of the molded product, but from the viewpoint of the large influence of the amount of bleeding caused by heating treatment, it is preferably in the form of a film or sheet. The thickness of this film or sheet is preferably 1 μm or more, more preferably 5 μm or more. Further, it is preferably 1.0 mm or less, more preferably 0.5 mm or less, and even more preferably 0.1 mm or less. The shape of the molded object is not limited to a film or sheet shape, and may be a product (packaging bag, packaging container, etc.) made of a film or sheet, or a belt-shaped body or tube made of a film or sheet. A roll-shaped body formed by winding the shaped body into a roll-shape may also be used.

When producing the above-mentioned molded article, a resin composition may be prepared by mixing a thermoplastic resin and an additive, and the molded article may be molded by extrusion molding, inflation molding, injection molding, blow molding, or the like. When molding the molded product into a film or sheet, inflation molding or extrusion molding can be suitably used.

The obtained molded body is heated for a predetermined period of time. The treatment temperature of the heating treatment (aging treatment) may be adjusted as appropriate depending on the type of additive, but it is preferably 30°C or higher, more preferably 40°C or higher. Further, the temperature is preferably 80°C or lower, more preferably 60°C or lower, and even more preferably 50°C or lower. Although the treatment time for the heating treatment varies depending on the thickness of the molded article, it is preferably 12 hours or more. Further, the time period is preferably 168 hours or less, more preferably 144 hours or less, and even more preferably 72 hours or less.

Hereinafter, the present invention will be explained in detail by showing examples. Note that the present invention is not limited to these Examples. In this example, a packaging bag for storing fruits and vegetables was manufactured. Specifically, a resin composition was prepared by using polyethylene as a thermoplastic resin and adding an antifogging agent as an additive having bleeding properties. The resin composition was formed into a film-like cylindrical body by inflation molding, and this was wound into a roll shape to produce a roll-shaped body.

The roll-shaped body, which is a molded body, was heated and then subjected to bag-making processing to produce a packaging bag. The packaging bags were evaluated for their antifogging properties, and were stored in a stacked state in an exterior bag, and the handling properties when taking out a single packaging bag from the exterior bag were evaluated. For comparison, the roll-shaped molded body was made into a bag without being subjected to heating treatment to produce a non-heated packaging bag, and its antifogging properties and handleability were evaluated. The details are described below.

[Preparation of resin composition]
A resin composition was prepared using the following components as shown in Table 1. As the AB agent, a masterbatch containing LLDPE as a base resin was used, and as the additive (antifogging agent) having bleeding properties, a masterbatch containing LDPE as a base resin was used. The amount of AB agent and the amount of antifogging agent in the table indicate the amount of active ingredient. In addition, the amount of LLDPE in the resin composition indicates the total amount of the small amount of base resin contained in the masterbatch of the AB agent, and the amount of LDPE indicates the amount including the small amount of base resin contained in the masterbatch of the antifogging agent. .
・Thermoplastic resin: LLDPE (density: 0.921 g/cm ³ , MFR: 2.2 g/10 min)
・Thermoplastic resin: LDPE (density: 0.929g/cm ³ , MFR: 1.3g/10 min)
・AB agent: Synthetic zeolite ・Anti-fog agent: Contains polyglycerin fatty acid ester and polyoxyethylene alkyl ether

[Preparation of molded body]
The prepared resin composition was molded into a continuous cylindrical shape with a thickness of 30 μm by inflation molding. The cylindrical body was rolled into a roll shape. Note that the inflation molding was carried out in the winter, when antifogging properties tend to be less likely to develop. The inflation molding conditions are as follows.
・Molding temperature: 180℃
・Molding environment: 10℃ 49%RH

[Heating treatment of molded object]
A heating treatment was performed by allowing the roll-shaped body, which was a molded body, to stand still for 48 hours in a room maintained at 40°C. After the heating treatment, the rolled body is pulled out and heat-sealed at predetermined intervals in a direction orthogonal to the length of the cylindrical body with a constant width, and the cylindrical body is sealed at a position close to the heat-sealed part. A packaging bag was manufactured by cutting the body.

[Evaluation of molded object]
(1) Anti-fog performance Place a transparent cup filled with 70ml of water on the paper with the evaluation pattern printed on it, and place the sample (packaging bag) over the cup with the side on which you want to check the anti-fog performance facing down. and sealed with a rubber band. Thereafter, the cup was left for 2 hours in a refrigerator maintained at 5°C. The appearance of the evaluation pattern placed under the cup was observed through the film placed over the taken-out cup, and evaluation was performed by scoring based on the following criteria. If the evaluation result is 4 or more, it is determined that the product is at a practical level. The evaluation results are shown in Table 1. The evaluation was based on the average value of three samples.

FIG. 1 is an evaluation pattern diagram for evaluating antifogging properties. As shown in the figure, the evaluation pattern includes a solid red ring pattern 1 and a solid black ring pattern 2 arranged concentrically and alternately at intervals. The outer diameter D of the red solid ring pattern 1 having the largest diameter is 4 cm. The evaluation criteria using the above evaluation pattern are as follows.
5: The circle clearly looks like a perfect circle (no water droplets attached at all).
4: Only a portion of the circle appears distorted (one large water drop).
3: The circle appears partially distorted (there are about 2 to 10 water droplets).
2: I can see the difference between the red circle and the black circle, but the whole thing is blurry.
1: You can't tell the difference between the red circle and the black circle because of the large water droplets.
0: The difference between a red circle and a black circle cannot be discerned due to fine water droplets.

(2) Handling of the packaging bag The handling of the packaging bag was evaluated. Specifically, a stack of 100 specimens was placed in an outer bag. Then, the condition was evaluated when one hand was placed in the outer bag and one specimen was picked from the top of the bundle, and whether the bag opened by twisting the specimen once between the thumb and forefinger was evaluated. During the evaluation, accelerated evaluation was performed assuming long-term storage by storing the sample in an environment of 50° C. and 40% RH for 8 weeks with a 50 kg weight placed on the outer bag containing the sample.

The evaluation was done by scoring based on the following criteria. The greater the stickiness caused by the antifogging agent, the lower the evaluation. As a packaging bag, if the promotion evaluation is 6 points or more, it is judged to be at a practical level. The evaluation results are shown in Table 1. In addition, for the numerical value of evaluation, the results of picking the specimen three times were each scored, and the average value thereof was used.
10: Only one piece can be taken out, and the entire bag opens when taken out.
9: Only one sheet can be taken out. Twist the bag once with one hand (thumb and forefinger) to open the mouth.
8: The bags stick together and you have to take out two pieces, but when you take them out, the entire bag opens.
7: The bags will stick together and you will have to take two pieces. Twist one bag once with one hand to open the mouth.
6: The bags stick together and three or more pieces can be removed, but each bag opens completely when taken out.
5: Bags stick together and 3 or more pieces can be removed. Twist one bag once with one hand to open the mouth.
4: Only one sheet can be taken out. Even if I twist the bag once with one hand, it won't open.
3: The bags will stick together and you will have to take two pieces. Even if you twist one bag once with one hand, it won't open.
2: Bags stick together and 3 or more pieces can be removed. Even if you twist one bag once with one hand, it won't open.
1: I can't pick up the bag in one go with one hand.

(3) HAZE value The transparency of the packaging bag after heating treatment and the packaging bag without heating treatment was evaluated by the HAZE value measured in accordance with JIS K7136. Generally, if the HAZE value is 10.0% or less, it is determined that the content is at a sufficiently visible level.

[Evaluation results]
From Table 1, No. 1 has a small amount of antifogging agent at 1920 ppm. 1 and no. No. 2 had a low evaluation of antifogging properties regardless of whether heating treatment was performed or not. In addition, No. 2 has a large amount of antifogging agent at 3600 ppm and 4200 ppm. 7 and no. 8 is No. 1 and no. Although the evaluation of antifogging properties was higher than that of Sample No. 2, the amount of bleeding of the antifogging agent increased, resulting in a decrease in handleability.

On the other hand, No. 2 has an antifogging agent amount of 2040 ppm. 3 and no. 4. No. 4 with an antifogging agent amount of 2280 ppm. 5 and no. It can be seen that No. 6 has low anti-fogging properties when unheated (see No. 3 and No. 5), but exhibits good anti-fogging properties after being heated (No. 4 and No. 5). (see 6). In addition, it was found that good handling properties were maintained even after heating treatment since the amount of antifogging agent bleed was small.

Note that, as the inflation molding conditions this time, the heating temperature of the resin composition was set at 180°C, but even if this was set to a higher temperature of 200°C, similar results were obtained in terms of antifogging properties and ease of handling. This shows that it is difficult to adjust the amount of antifogging agent bleed even if the molding conditions are changed, and that a heating treatment is necessary. In addition, No. 1~No. The packaging bag made using the film No. 8 has a HAZE value of 10% or less in both the unheated state and the heated state, indicating that it has good transparency. confirmed.

From the above, regarding the additive content in the resin composition constituting the molded object, the effect of the additive after heating the molded object for a predetermined period of time is better than the effect of the additive in the molded object immediately after molding. By adjusting the amount to such an amount, it is possible to suppress stickiness of the molded product. Thereafter, by heating the molded body for a predetermined period of time, the effect of the additive can be expressed satisfactorily regardless of the manufacturing environment and storage environment of the molded body.

Incidentally, the amount of the additive in the molded article can be determined by appropriately using a conventionally known method. To explain an example of quantitative analysis, when the molded object is in the form of a film or sheet, it is pulverized using a cutter or the like, and then extracted with an appropriate solvent. The solvent in the extract is evaporated to collect solid matter, and the type of additive is identified from the retention time of the detected peak through gas chromatography analysis. If the additive can be identified, it is possible to quantify the additive in the molded article using a separately prepared calibration curve based on the area of the detected peak.

By quantitatively analyzing the amount of additives in the molded body, we found that the effect of the additive content after the molded body was heated for a predetermined period of time was greater than the effect of the additive in the molded body immediately after molding. It becomes possible to determine whether the amount is better.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the invention. In this embodiment, linear low-density polyethylene is used as the thermoplastic resin, but the thermoplastic resin is not limited to this, and other thermoplastic resins may be used. Further, in this embodiment, an example in which an antifogging agent is used as an additive has been described, but the present invention is not limited to this, and other additives having bleeding properties (for example, an antistatic agent, etc.) may be used.

Note that the constituent features disclosed in the embodiment and the above-mentioned modification can be combined with each other, and new technical features can be formed by combining them.

1 Circular pattern (solid red color)
2 Circular pattern (black solid color)

Claims (6)

A molded article made of a resin composition containing a thermoplastic resin and an antifogging agent , wherein the thermoplastic resin is a polyolefin containing 50% by mass or more of polyethylene, and the antifogging agent is a polyglycerol fatty acid. A molded article containing an ester and a polyoxyethylene alkyl ether, wherein the content of the antifogging agent in the resin composition is 2040 ppm to 2280 ppm . The molded article according to claim 1 , wherein the polyethylene is at least one selected from linear low-density polyethylene, low-density polyethylene, high-density polyethylene, and medium-density polyethylene . A claim in which the shape of the molded object is a film or sheet, a product composed of a film or sheet, or a roll formed by winding a band or cylindrical body made of a film or sheet into a roll. 2. The molded article according to 1 or 2 . A method for treating a molded body using the molded body according to any one of claims 1 to 3 , comprising heating the molded body at 30° C. to 80° C. for 12 hours to 168 hours. Method. A method for preparing a resin composition containing a thermoplastic resin and an antifogging agent, wherein the thermoplastic resin is a polyolefin containing 50% by mass or more of polyethylene, and the antifogging agent is a polyglycerin fatty acid ester. and polyoxyethylene alkyl ether, and when the resin composition is molded, it does not exhibit antifogging performance immediately after molding, and the molded body is heated at 30° C. to 80° C. for 12 hours to 168 hours. A method for preparing a resin composition, which comprises blending the antifogging agent in an amount that exhibits good antifogging performance after drying. 6. The method for preparing a resin composition according to claim 5, wherein the polyethylene is at least one selected from linear low-density polyethylene, low-density polyethylene, high-density polyethylene, and medium-density polyethylene.

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