JPH10204413A - Easily releasable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an easily releasable film that contains a specific modified ethylene-based copolymer, has sufficient heat sealability and adhesivity, and is easy to remove with good appearance of the unsealed area after the releasable film is removed. SOLUTION: This easily releasable film contains (A) a modified ethylene- based polymer obtained by subjecting 40-65wt.% of (i) ethylene-based polymer to graft polymerization with 60-35wt.% of vinyl monomers, and (B) a resin composition whose vinyl monomer content is 35wt.% or more in the condition that component B is composed of the same kind of ethylene-based polymer as component A and the ethylene-based polymer which is a constitutional material of component A, and that in composition A, preferably the polymer of component (i) in particle size of 0.2-3μm is homogeneously dispersed in component (ii).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of heating and bonding to a container or sheet made of a base material obtained by coating polyethylene on paper to have good heat sealability and adhesiveness. The present invention relates to an easily peelable film which can be easily peeled from a container or a sheet substrate, and has a good appearance after opening.

[0002]

2. Description of the Related Art Thermoplastic resins such as polyethylene, polypropylene, and other polyolefins, polyvinyl chloride, polystyrene, and thermoplastic polyester are known for their appearance, mechanical strength,
It is widely used in various packaging containers due to its excellent moldability, packaging workability, economy, and the like. Further, in recent years, containers in which polyethylene is coated on paper that can be easily incinerated from the viewpoint of used waste have increased. These packaging containers are mainly filled with food products such as dairy products, confectionery, natto, and soft drinks, and are heat-sealed.The packaging content is becoming more diversified as the requirements for these packaging containers diversify. It is required that not only can the device be protected, but also can be easily opened when used. Conventionally, as a heat sealing material for these packaging containers, those coated with a hot-melt adhesive or a solution-type adhesive have been used,
In these, there was a problem that the sealant adhered to the container side after opening and the appearance of the peeled surface was poor. In addition, since the film has insufficient heat resistance, it is peeled off at a high temperature, and there is a problem in the protection of contents. In order to improve such disadvantages, in recent years, various materials have been proposed which have both the property of protecting the contents and the property of easily opening the contents.
For example, a composition comprising an ethylene / vinyl acetate copolymer and a tackifier is generally used for a thermoplastic resin container. In addition, the applicant of the present invention has set forth that a composition material containing a modified resin obtained by modifying an olefin polymer with an aromatic vinyl monomer as a main component exhibits easy-opening properties with respect to the olefin polymer. (Tokho 1-4)
2967).

[0003]

However, when such a composition material is applied as a heat-sealing material for a container coated with polyethylene on paper, the heat-sealing strength is too strong, so that the lamination strength of the paper and polyethylene is lower than the lamination strength. It is strong and has the drawback that the base paper is broken at the time of peeling and the appearance of peeling is rather deteriorated. In addition, the use of an ethylene / vinyl acetate copolymer as a component was not always satisfactory in terms of processing characteristics and handling of the obtained film or laminate.

[0004]

The inventor of the present invention has conducted various studies with the aim of improving the above-mentioned drawbacks.
They have found that a film made of a modified ethylene polymer can improve the above-mentioned disadvantages, and the present invention has been achieved. That is, the easily peelable film of the present invention,
A film used as an easily peelable sealant for a container or sheet made of a substrate coated with polyethylene on paper, wherein 40-65% by weight of an ethylene polymer and 60-35% by weight of a vinyl monomer are subjected to graft reaction conditions. It is characterized by comprising a resin composition containing a modified ethylene polymer obtained by the above-mentioned method and having a vinyl monomer content of 35% by weight or more. The easily peelable film of the present invention has good heat sealability and adhesiveness to various containers or sheet base materials in which polyethylene is coated on paper, and has a property that the appearance after opening is good. .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION

[I] Modified ethylene-based polymer The easily peelable film of the present invention comprises an ethylene-based polymer 40 to
A modified ethylene polymer obtained by subjecting 65% by weight, preferably 50 to 65% by weight, and 60 to 35% by weight, preferably 50 to 35% by weight of a vinyl monomer to a graft reaction condition, A film produced from a resin composition obtained by diluting a low-molecular-weight ethylene polymer with an unmodified ethylene polymer to have a vinyl monomer content of 35 to 60% by weight, preferably 35 to 55% by weight. Here, the vinyl monomer content refers to the total amount of the amount of the vinyl monomer grafted to the ethylene polymer and the amount of the vinyl monomer homopolymer. When diluting the modified ethylene-based polymer with an unmodified ethylene-based polymer, it is preferable to dilute the same type of ethylene-based polymer as the ethylene-based polymer that is the basis of the modified ethylene-based polymer. . In particular, in the present invention, it is preferable to use modified low-density polyethylene diluted with low-density polyethylene. If the vinyl monomer content is less than the above range, the paper is heat-sealed to a substrate coated with polyethylene and then the paper breaks at the time of peeling, which is not preferable. On the other hand, when the vinyl monomer content exceeds the above range, the uniformity of the film is impaired, which is not preferable. Preferred modified ethylene polymers have a vinyl monomer content of 0.2 to 3 microns.
It has a particle size of m and a structure homogeneously dispersed in the ethylene polymer, and the particle size does not change before and after dilution. It is preferable that such a modified ethylene polymer (hereinafter simply referred to as “modified PE”) is produced by the following method.

(1) Raw materials (a) Ethylene polymer As the ethylene polymer, a homopolymer of ethylene, or ethylene and propylene, 1-butene, 1-hexene, 3-methyl-1-butene, 2-1 carbon atoms such as 4-methyl-1-pentene, 1-heptene and 1-octene
2, preferably a copolymer with about 2 to 8 olefins,
Alternatively, a copolymer of two or more of the above olefins, a copolymer of the above olefin with a non-conjugated diene, a vinyl ester, an unsaturated organic acid or a derivative thereof, a vinyl organic silane, and the like can be given. These copolymers may be of any type such as random, block or graft, and may be resinous or elastomeric. These ethylene polymers are
Mixtures of more than one species can be used.

[0007] Specific examples of the ethylene polymer include high
Medium, low density and linear low density polyethylene, ethylene
Propylene copolymer (random, block), ethylene / 1-butene copolymer, ethylene / 1-hexene copolymer, ethylene / 1-octene copolymer, ethylene / 1propylene / 1-butene random copolymer, ethylene -Non-conjugated diene copolymer, ethylene-propylene-non-conjugated diene copolymer (specific examples of non-conjugated diene include dicyclopentadiene, 1,4-hexadiene, and 5-methyl-
Examples include 1,4-hexadiene, 7-methyl-1,6-octadiene, and 1,9-decadiene. ), Ethylene-vinyl acetate copolymer, ethylene-vinyl trimethoxysilane copolymer, maleic anhydride-grafted polyethylene, ethylene-methyl acrylate copolymer, ethylene
Ethyl acrylate copolymer, ethylene / methyl methacrylate copolymer, ethylene / acrylic acid copolymer, ethylene / methacrylic acid copolymer, ethylene / acrylic acid / methyl acrylate copolymer, ethylene / methacrylic acid / methacrylic A typical example is an acid methyl copolymer. Among them, low-density polyethylene and linear low-density polyethylene are preferable in view of processability and heat resistance.

(B) Vinyl Monomer The vinyl monomer used for producing the modified PE is not particularly limited.
-Unsaturated aromatic monomers such as methyl styrene, 3-methyl styrene, 4-methyl styrene, dimethyl styrene and chloro styrene; vinyl esters such as vinyl acetate and vinyl propionate; methyl acrylate, ethyl acrylate, isopropyl acrylate; n-butyl acrylate, sec-butyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, acrylates such as octyl acrylate, methyl methacrylate, ethyl methacrylate,
Methacrylates such as n-butyl methacrylate, sec-butyl methacrylate, decyl methacrylate, 2-ethylhexyl methacrylate, glycidyl methacrylate; acrylic acid, methacrylic acid, maleic anhydride, dimethyl maleate, di (2-ethylhexyl) maleate, and the like Unsaturated organic acids; unsaturated nitriles such as acrylonitrile and methacrylonitrile; and unsaturated mono- and di-halides such as vinyl chloride and vinylidene chloride. Of these, unsaturated aromatic monomers and methacrylates are preferred, and styrene and methyl methacrylate are particularly preferred in that they can be easily modified. When the ethylene copolymer and the vinyl monomer are subjected to graft reaction conditions, a radical generator is usually used except for the reaction by radiation.

(C) Radical generator As the radical generator used for producing the modified PE, a general-purpose one can be used. However, in view of a preferable graft reaction method described later, It is preferable to use one having a decomposition temperature of 50 ° C. or higher and being oil-soluble. Here, the "decomposition temperature" is a temperature at which the decomposition rate of the radical generator becomes 50% when 0.1 mol of the radical generator is added to 1 liter of benzene and left at a certain temperature for 10 hours. . The so-called "10
Decomposition temperature to obtain a half-life of time. " When a polymer having a low decomposition temperature is used, the polymerization of the vinyl monomer may proceed abnormally, and there is a disadvantage that a homogeneous modified polymer cannot be obtained. However, conversely, those having a high decomposition temperature and those having a low decomposition temperature can be appropriately combined to perform the decomposition stepwise or continuously, and the graft reaction can be carried out efficiently.

Examples of such radical generators include 2,4-dichlorobenzoyl peroxide, t-butylperoxypivalate, o-methylbenzoyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide. Octanoyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, cyclohexanone peroxide, 2,5-dimethyl-2,5-dibenzoylperoxyhexane, t-butylperoxybenzoate, Jee
t-butyl-diperoxyphthalate, methyl ethyl ketone peroxide, dicumyl peroxide, di-t
Organic peroxides such as -butyl peroxide; and azo compounds such as azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile). The amount of the radical generator used is 0.01 to 0.01% based on the amount of the vinyl monomer used.
Within the range of about 10% by weight, the radical generator is suitably used depending on the kind of the radical generator and the reaction conditions. If the amount of the radical generator used is less than the above range, the reaction does not proceed smoothly,
If it exceeds the above range, a gel is easily formed in the modified PE, and the effect of the present invention is hardly exhibited.

(2) Production of Modified PE These raw materials are subjected to a graft polymerization reaction to modify the modified PE.
The production by the aqueous suspension grafting method described below is a particularly preferable method in that the gel content can be easily controlled. That is, the aqueous suspension containing the ethylene polymer particles, the vinyl monomer, and the radical generator is heated to a temperature at which decomposition of the initiator does not substantially occur, and After the polymer particles are impregnated, it is preferable to employ a method in which the temperature of the aqueous suspension is further raised to complete the polymerization of the vinyl monomer, and this method will be specifically described below.

(A) Impregnation Step As a typical preferred method for impregnating the vinyl monomer into the ethylene polymer particles in an aqueous medium, a preferred method is to use a radical generator (preferably) in an aqueous suspension of the ethylene polymer particles. And if necessary, other additives) dissolved vinyl monomer is added and stirred, or the ethylene-based copolymer particles are added to an aqueous dispersion of a vinyl monomer in which a radical generator is dissolved. Start by adding agitation. In the impregnation step, industrially, the temperature should be raised to a temperature at which the radical generator is not substantially decomposed, and the impregnation should be performed efficiently. In general, the temperature is from room temperature to 100 ° C., particularly 60 to 90 ° C. It is preferred to operate. In this step, the vinyl monomer is impregnated so that the amount of the free vinyl monomer is 80% by weight or less of the used amount of the vinyl monomer. Ethylene polymers are relatively compatible with vinyl monomers, so
Even if less than 5% by weight of the vinyl monomer is released, the vinyl monomer impregnates the ethylene polymer particles during the polymerization, so that the polymer particles obtained by polymerizing the vinyl monomer are modified. It does not precipitate independently of the ethylene polymer particles obtained. The impregnation time is usually about 2 to 8 hours.
The content of the ethylene polymer and the vinyl monomer in the aqueous dispersion is generally about 5 to 100 parts by weight based on 100 parts by weight of water.

Such an aqueous dispersion can be stably maintained in a dispersed state simply by sufficiently stirring, but the use of an appropriate suspension stabilizer makes it easier and more stable. Can be adjusted. Examples of the suspension stabilizer in this case include water-soluble polymers such as polyvinyl alcohol, methylcellulose, and hydroxycellulose; anionic surfactants such as alkylbenzene sulfonate; nonionic surfactants such as polyoxyethylene alkyl ether; Or a water-insoluble inorganic salt such as magnesium oxide, calcium phosphate or the like is used alone or as a mixture in an amount of about 0.01 to 10% by weight based on water. When impregnating the ethylene-based polymer particles with a vinyl monomer (and a radical generator, etc.), auxiliary materials such as a plasticizer, a lubricant, and an antioxidant can be simultaneously impregnated (these auxiliary materials are ethylene-based materials). It may already be added to the polymer, or may be added after the graft polymerization reaction).

(B) Graft polymerization step If the temperature of the aqueous suspension thus adjusted is raised to a temperature at which the used radical generator decomposes at an appropriate rate or more, the impregnated vinyl monomer Undergoes graft polymerization to produce modified PE particles. It is preferable that the aqueous suspension during the graft polymerization is appropriately stirred. The polymerization temperature should generally be appropriately selected within the range of 50 to 150 ° C., but need not be constant throughout the graft polymerization step. The polymerization is usually for about 2 to 10 hours. The polymerization pressure is usually from normal pressure to about 10 kg / cm ² . After the polymerization, if the same post-treatment as the post-treatment of the aqueous suspension polymerization of a normal vinyl monomer (for example, styrene) is carried out, the shape of the used ethylene-based polymer particles is almost maintained and the molding material is immediately The resulting modified PE particles can be used as Accordingly, the ethylene polymer used before the modification may be in a powder form, but it is more convenient to be in a particulate form in consideration of handling during the subsequent forming process. That is, the particle size is preferably such that it can be used as a molding material because the resulting modified PE can be used as it is as a molding material.
mm, preferably about 3 to 7 mm. The dimensions do not change much before and after the modification treatment.

(3) Resin composition In the modified PE polymer-containing resin composition in which the modified PE obtained by the graft polymerization alone or the unmodified ethylene polymer is blended with the modified PE, Has a vinyl monomer content of 35% by weight or more, preferably 35 to 55% by weight.
It is blended so that If the vinyl monomer content in the modified ethylene polymer-containing resin composition is less than the above range, the base paper will be broken at the time of peeling. Further, since the modified PE is sometimes used as a mixture with the unmodified PE as described above, the vinyl monomer content in the modified PE is 40
It is preferable that the content is as high as about% by weight or more.

(4) Additional Components Other additional components can be added to the above-mentioned modified ethylene polymer in an amount not to significantly impair the effects of the present invention. Additional components include, for example, other thermoplastic resins, rubber substances, inorganic fillers, pigments, plasticizers, various stabilizers (antioxidants, antistatic agents, light stabilizers, antiblocking agents, lubricants) and the like. .

[II] Method for producing easily peelable film The easily peelable film of the present invention can be produced from the above modified ethylene polymer by a film forming method such as an inflation method or a T-die method. Alternatively, by forming a laminate film by extrusion lamination molding on a base layer made of various thermoplastic resins such as aluminum foil, paper, polyester resins represented by polyethylene terephthalate, olefin resins such as polyethylene and polypropylene, and the like. Manufactured. The easily peelable film of the present invention has a thickness of usually 5 to 100 μm, preferably 10 to 50 μm.

[0018]

【Example】

Example 1 Production process of modified low-density polyethylene particles In an autoclave of 50 liter capacity, 20 kg of water, 0.6 kg of tribasic calcium phosphate as a suspending agent and 0.6 g of sodium dodecylbenzenesulfonate were mixed to form an aqueous medium. And low density polyethylene having a particle size of 3 to 4 mm (density: 0.917 g / cm ³ , MFR: 45 g / 1
(0 min) 6 kg was added and suspended by stirring. Apart from 3,
5,5-trimethylhexanoyl peroxide
6 g, and 9 g of benzoyl peroxide were dissolved in 6 kg of styrene monomer, added to the above suspension system, and nitrogen was introduced into the autoclave to adjust the inside of the system to 0.5 kg / c.
Pressurized to m ² . Further, the temperature inside the autoclave was raised to 55 ° C., and the mixture was allowed to stand for 5 hours while being stirred at this temperature, so that the low-density polyethylene particles were entirely impregnated with the styrene monomer containing the polymerization initiator. Next, the temperature of the suspension was raised to 85 ° C., and the mixture was left standing for 7 hours while stirring at this temperature to carry out polymerization. After cooling, the solid content was taken out and washed with water to obtain 12 kg of modified low-density polyethylene particles. The MFR of the resulting modified low-density polyethylene was 2.5 g / 10 minutes, and the total amount of styrene monomer and polystyrene grafted on the modified low-density polyethylene was 50% by weight.

Production and Evaluation of Releasable Film The modified low-density polyethylene particles obtained in the above-mentioned steps were treated with 35
Using a T-die molding machine having a diameter of mm, a 30 μm film was formed at a molding temperature of 230 ° C. This film and thickness 1
A 2 μm PET film was adhered via polyethylene 20 μm to form a laminated film. Using the layer of the thermoplastic resin composition of the present laminated film as an adhesive surface, paper (basis weight 2
50 g) / polyethylene (thickness: 30 μm) and adhered by heating. The heat bonding conditions were as follows: a hot plate type heat sealer, a bonding surface of 5 mm width, a bonding pressure of 2 kg / cm ² ,
The time is 0.5 seconds and the bonding temperature is 140 to 180 ° C. The peel strength was measured at a sample width of 15 mm and a tensile speed of 300 mm / min at 180 ° peel strength at 23 ° C. using an Instron tensile tester. Table 1 shows the results.

Examples 2 to 4 The modified low-density polyethylene particles obtained in Example 1 were diluted with low-density polyethylene at the ratio shown in Table 1, and evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 1 Modified low-density polyethylene particles having a polystyrene content of 65% by weight were obtained in the same manner as in Example 1 except that 4 kg of low-density polyethylene and 8 kg of styrene monomer were used. The obtained low-density polyethylene particles were subjected to film forming in the same manner as in Example 1, but a homogeneous film could not be obtained.

Comparative Examples 2-3 The modified low-density polyethylene particles obtained in Example 1 were diluted with low-density polyethylene at the ratio shown in Table 1, and evaluated in the same manner as in Example 1. Table 1 shows the results.

[0023]

[Table 1]

[0024]

[0025]

The easily peelable film of the present invention has good heat sealability and adhesiveness to containers and sheets made of a substrate coated with polyethylene on paper and has good moldability. It has the excellent properties shown and is extremely excellent in practicality.

Claims (3)

[Claims] 1. A film used as an easily peelable sealant for a container or sheet made of a substrate obtained by coating polyethylene on paper, comprising an ethylene polymer 40 to 6.
A resin composition containing a modified ethylene polymer obtained by subjecting 5% by weight and 60 to 35% by weight of a vinyl monomer to graft reaction conditions, and having a vinyl monomer content of 35% by weight or more. An easily peelable film characterized by the following. 2. A resin composition comprising a modified ethylene-based polymer and an ethylene-based polymer of the same type as the ethylene-based polymer as a constituent material of the modified ethylene-based polymer.
The easily peelable film according to claim 1. 3. A modified ethylene polymer wherein the polymer of a vinyl monomer is uniformly dispersed in the ethylene polymer with a particle size of 0.2 to 3 μm. Item 1
The easily peelable film according to 1.