JPS5839709B2 - Packaging methods for easily deformable items - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is easily stretchable, has high elasticity, and adheres well to packaged contents.

This relates to a method of packaging items that easily deform under small stress, such as food products such as meat and vegetables, textile products, and miscellaneous paper products, using an elastic film with excellent transparency. The present invention relates to a packaging method using a novel elastic film to replace plastic polyvinyl chloride, ethylene vinyl acetate copolymer (EV), low density polyethylene (LDPE) film, etc.

Conventionally, films for light packaging are diverse in terms of their packaging functions, and furthermore, they are diverse in terms of the raw material polymers used to form the film.

In particular, from the viewpoint of raw material polymers, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, ethylene/vinyl acetate copolymer, nylon, and polyester are mainly used.

As can be seen from these facts, at present, plastics are mostly used as the main raw material polymers for light packaging films, and natural rubber and various synthetic rubbers are hardly used.

However, this does not mean that the elastic film is unnecessary as a light packaging film.

For example, sticky wrap film (Sticky wrap film)
Plasticized polyvinyl chloride is usually used as the main raw material polymer for P film, but since this film stretches when placed in a container and has high elasticity, it can be used to package items that are easily deformed by small stress. It has been devised so that it does not deform the package and adheres well to the packaged item.

These properties are typical properties of rubber elastic bodies, and therefore, in the case of the above-mentioned adhesive wrap film, it can be seen that by plasticizing polyvinyl chloride, it has properties similar to those of rubber elastic bodies.

The reason why conventional natural rubber and various synthetic rubbers are not used as elastic materials is that these elastic materials are not made of plastic, although such elastic films are one of the most important films for light packaging. This is because it has the following fatal flaws when compared to:

a) Vulcanization is necessary in order to exhibit effective properties as an elastic body.

b) Since a vulcanizing agent is used, a film with excellent transparency cannot be obtained.

C) Plastic molding machines with excellent productivity cannot be used because the fluidity properties are extremely poor.

d) It is difficult to obtain a thin film with uniform thickness due to large molding shrinkage.

In view of this situation, the present inventors developed plasticized polyvinyl chloride and ethylene, which have elasticity most similar to vulcanized products of natural rubber and various synthetic rubbers, and which have been conventionally used as elastic films for light packaging.・Vinyl acetate copolymer (EVA)
As a result of various studies on packaging methods for easily deformable items using a new lightweight elastic film different from low-density polyethylene (LDPE), we found that a specific block copolymer consisting of styrene and butadiene or isoprene could be used as a lightweight packaging material. It was found that by using it as a base polymer for an elastic film for packaging, it is possible to package articles that are easily deformed by small stress in close contact with almost no deformation using a film that stretches easily and has high elasticity, leading to the present invention. .

That is, the present invention provides a method for packaging articles that are easily deformed by small stress, and is provided by the general formula [where B is substantially a polybutadiene casing or a polyisoprene block, B is substantially a polystyrene block, and n is is an integer from 2 to 51, and X is n +
It is a multifunctional compound to which one polymer chain is attached.

] Molecular weight 1oooo to 500000.
The packaging method described above is characterized in that it is packaged with an elastic film using a block copolymer containing 30 to 41% by weight of styrene or a mixture thereof as a base polymer.

In general, the characteristics required of elastic films for light packaging include the ability to easily stretch and not deform the packaged items due to their high elasticity, as well as the protection of the package contents, packaging workability, and the film's ability to protect the package contents. Three aspects of aesthetics are important.

Regarding the protection of the package contents, appropriate moisture resistance, gas permeability, durability, non-toxicity, and odorlessness are required.

Regarding these points, the block copolymer used in the present invention has practical advantages when compared with plasticized polyvinyl chloride, ethylene/vinyl acetate copolymers, low-density polyethylene, etc. that have been conventionally used to obtain elastic films. There is no sound.

Secondly, regarding packaging workability, properties are required that allow packaging work, bag making work, printing work, etc. to be carried out easily and efficiently, such as tensile strength, tear strength, blocking resistance,
It is necessary to have excellent thermal adhesion and printability.

In these respects, the block copolymer used in the present invention is not inferior to the other conventionally known plastics frequently used in elastic films, but rather is superior in thermal adhesion and printability.

Thirdly, regarding the aesthetic appearance of the film, it is required that the packaged product looks beautiful and has properties that arouse the desire to purchase, such as excellent transparency, gloss, printability, colorability, etc.

In this regard, the block copolymer used in the present invention has no brown color compared to the other conventionally known plastics frequently used in elastic films, and has particular features in transparency and printability.

As mentioned above, the block copolymer used in the present invention is
It has characteristics that make it suitable as a light packaging film.

Typical polymers conventionally used to obtain elastic films are plasticized polyvinyl chloride, ethylene/vinyl acetate copolymer, and low-density polyethylene. When the block copolymer used is softened, the plasticized polyvinyl chloride has transparency and strength properties that are equivalent to the block copolymer used in the present invention, but it has poor elasticity, elongation, low temperature properties, and toxicity ( It is inferior to the above-mentioned block copolymers in terms of especially the toxicity of the stabilizer.

However, ethylene/vinyl acetate copolymers are inferior to the above-mentioned block copolymers in terms of elasticity, elongation, low-temperature properties, and odor (ethylene/vinyl acetate copolymers have a pronounced vinyl acetate odor).

Furthermore, low-density polyethylene is not only inferior to the above-mentioned block copolymers in terms of transparency, elasticity, elongation, low-temperature properties, etc., but also low-density polyethylene has a large necking phenomenon and is extremely inferior as an elastic film.

As mentioned above, the elastic film using the block copolymer as the base polymer used in the packaging method of the present invention is fully satisfactory compared to conventionally used elastic films, and has particularly excellent low-temperature properties. Therefore, it is extremely effective in light packaging fields such as frozen foods.

Since the elastic film used in the present invention is a diastereomer, it cannot be processed to fix internal strain at room temperature, such as biaxial stretching, and is essentially used as an unstretched film.

As shown in formula (1) and formula (2), the block copolymer used in the present invention has elastic properties such as polybutadiene and polyisoprene in which one or both of the terminals of the copolymer are substantially composed of polybutadiene and polyisoprene. A copolymer is a block copolymer, a copolymer whose ends are essentially inelastic blocks such as polystyrene as shown in formula (3), and a copolymer whose ends are essentially composed of polystyrene blocks as shown in formula (4). , three types of copolymers commonly referred to as radial block polymers.

The molecular weight of the block copolymer used in the present invention is 1oo
The reason why the molecular weight is limited to between 10,000 and 500,000 is that if the molecular weight is less than 10,000, the strength of the film will be weak and there will be a practical problem, whereas if it is more than 500,000, the fluidity will be poor and it will be difficult to form the film.

The reason for limiting the styrene content to 30 to 40% by weight is that if it is less than 30% by weight, the strength of the film will be insufficient, and if it exceeds 41% by weight, the elasticity will be insufficient. This is because it is inappropriate.

In producing the elastic film used in the packaging method of the present invention, other additives may be added to modify the flexibility, adhesion, and other properties of the film.

Examples include fatty acid esters such as dioctyl adipate and dioctyl sepacate, phthalate esters such as dioctyl phthalate and dibutyl phthalate, and process oils such as naphthenic oil and paraffin oil.

Furthermore, when packaging contents with a high moisture content, water droplets may form on the inner surface of the film and may impede packaging.

In order to prevent this, a so-called drip-proofing agent may be mixed or applied.

As the drip-proofing agent, commonly used fatty acid esters of polyglycerin, fatty acid esters of sorbitan, fatty acid esters of hentaerythritol, etc. can be used.

Stabilizers, tackifiers, and the like can be blended within a range that does not impair the characteristics and transparency of the elastic film used in the invention.

The elastic film used in the packaging method of the present invention can be formed using conventional film forming methods such as inflation method, calender method,
It can be easily molded using an extrusion method with a T-type die.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Under a nitrogen gas atmosphere, n-butyllithium was activated in a 15% by weight n-hexane solution containing 40 parts by weight of a monomer mixture of 1,3 butadiene and styrene in a weight ratio of 50:50. 1.2 per 100g of total monomer as lithium
5 mm IJ mol was added and polymerized at 60°C for 4 hours.

After most of the monomers have been polymerized, the active solution is further added with 1,3 butadiene and styrene in a weight ratio of 65:35.
A 15% by weight n-hexane solution containing 60 parts by weight of the monomer mixture was added and polymerized at 70°C for 5 hours.

After 99% or more of the additional monomer mixture was copolymerized, 0.5 parts by weight of 2,6-ditertiarybutyl-p-cresol was added as a stabilizer to the copolymer solution, and then n-hexane was added. was evaporated to obtain a substantially B-8-B-8 type block copolymer having a styrene content of about 41% by weight.

Pelletize the above polymer, add 1.5 parts of dioctyl adipate per 100 parts by weight (belene), melt extrude using an extruder and T-type die, cast on a cooling roll circulating cooling water, and quench to obtain a thickness. A 40μ elastic film was obtained.

The properties of the obtained film are shown in Table 1.

This film was used to wrap a loaf of bread and adhere to the bottom using thermal adhesive at 10 s°C to create a packaged sample.

Good flexibility and elasticity, and excellent packaging work - J? 117,
Do not deform the contents.

A packaging with excellent transparency and gloss was created.

As a result of conducting a storage test on this packaging sample,
The softness of the bread was maintained, the package appearance was good, and the purpose of the package was fully achieved.

Example 2 In a nitrogen gas atmosphere, 4 mmol of n-butyllithium as active lithium was added per 100 g of total monomers to a 15% by weight cyclohexane i solution containing 30 parts by weight of styrene, and polymerization was carried out at 60°C for 4 hours. .

After most of the monomers had been polymerized, a 15% by weight cyclohexane solution containing 70 parts by weight of 1,3-butadiene was further added to the active solution, and the mixture was polymerized at 70°C for 5 hours.

When more than 99% of the additional monomers have been polymerized, 1 mmol of silicon tetrachloride is added per 00 g of total monomers to complete the polymerization, and 0.5 mmol of silicon tetrachloride is added as a stabilizer to the copolymer solution. After adding parts by weight of 2,6-ditertiarybutyl-p-cresol, the cyclohexane was volatilized to obtain a styrene content of about 40% by weight.

The above copolymer was pelletized, and 10 parts of aliphatic hydrocarbon resin (trade name: ECR-5) was added per 100 parts by weight of the pellets.
,, Esso Standard: Manufactured).

0.5 parts of zinc stearate and 0.5 parts of sorbitan ester of stearic acid (trade name: Nonion 5P60R)
No. 1 (manufactured by NOF Corporation) was added thereto, and an adhesive wrap film with a thickness of about 20 μm was produced using an extruder and a T-type die.

The physical properties of the obtained film are shown in Table 2.

This film was used to wrap raw meat in small expanded polystyrene trays and crimped the edges together at the bottom of the tray to create a wrapper/pull.

The flexibility, elasticity, and adhesion were good, the packaging workability was excellent, and the packaging had a sense of tension.

A storage test was conducted on this packaged sample, and the results showed that the bright red color of the raw meat was maintained and the package appearance was good, and the purpose of the package was fully achieved.

Example 3 0.5 part of sorbitan ester of stearic acid (trade name, Nonion 5P60R, manufactured by NOF Co., Ltd.) was added to 100 parts of the substantially B-8-B-S type block copolymer used in Example 1. ) was added to produce a film with a thickness of about 50μ.

Similarly compared, a film with a thickness of about 50μ made by adding 0.5 part of Nonion 5P60R' to 100 parts of low density polyethylene, ethylene/vinyl acetate copolymer (vinyl acetate content 14% by weight), 100 parts of Nonion 5P60R' to 100 parts of Nonion 5P60R' 0.
30 parts of dioctyl phthalate (COP) to 100 parts of polyvinyl chloride and a film with a thickness of about 50 μm containing 5 parts of
Films each having a thickness of approximately 50 μm were prepared to which 0.5 part of Nonionic 5P60R was added.

Vegetables were wrapped using these films, the edges were thermally bonded, and the films were stored in a refrigerator at about 5° C., and transparency, thermal adhesion, packaging workability, and storage stability were measured.

The results obtained are shown in Table 3.

As can be seen from the results in Table 3, the novel elastic film composition of the present invention is extremely useful as a light packaging film.

Claims (1)

[Claims] 1. For packaging methods for articles that are easily deformed by small stress, the general formula [where B is substantially a polybutadiene or polyisoprene block, A is substantially a polystyrene block, and n is an integer from 2 to 5, and X is n+1
It is a multifunctional compound in which several polymer chains are bonded. ] Molecular weight 10,000 to 500,000
, a block copolymer having a styrene content of 30 to 41% by weight, or a mixture thereof as a base polymer.