JPS6050229B2 - Easy-peel adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive composition that imparts easy peelability to the sealed portion of a packaging container having a heat-sealed portion made of a thermoplastic such as polyethylene.

BACKGROUND ART In recent years, bags or boxes sealed by thermocompression bonding of thermoplastic films such as polyethylene or paperboard laminated thereon have been widely used as packaging containers.

In particular, the latter box made of paperboard laminated with a thermoplastic plastic film has begun to be widely used as a sealed container for liquids such as milk and juice. The sealing portion of such a container is required to have two seemingly contradictory properties.

One of them is seal strength and the other is peelability. That is, a container filled with contents may be exposed to some degree of impact during handling during transportation or storage, and the seal portion must be able to withstand such impact and maintain hermeticity. On the other hand, the sealing portion of the opening must have appropriate releasability, and direct heat sealing of a polyethylene film or the like poses a problem in this respect.

In other words, when polyethylene is directly heat-sealed, the heat fusion properties are extremely strong, so women, children, etc. who are weak in strength have the disadvantage that they cannot easily obtain an opening to take out the contents due to peeling. . Further, if the container is peeled off forcefully due to the opening, peeling may not occur at a predetermined adhesive surface, and other parts may be destroyed, making it difficult to continue using the container. Particularly when sealing film-laminated paperboard, the paperboard may be torn irregularly and the shape of the opening may be deformed, making it difficult for the contents to flow out, especially if the contents are liquid. cause complaints. Also, in this case, a fluffy paperboard part appears at the opening, and the liquid content permeates through, making it susceptible to deterioration due to contact with air, so if you want to store the liquid content without using it all at once,
There are also problems that make it extremely unsanitary. In order to improve the disadvantages caused by the adhesive strength of the sealing part of the opening being too high, we have added an easily peelable adhesive such as polyethylene to the heat-sealed part to reduce the heat-sealing strength appropriately. It is known to apply an anti-adhesive agent.

Examples of such anti-adhesive agents include those made by mixing dimethylpolyshicataxane and hydrogen polysiloxane with an organometallic chelate catalyst, and those made by using cyclized rubber as a vehicle and containing dimethylpolysiloxane and wax. It has been known. However, in the former method, since an organic metal catalyst is added for the purpose of increasing adhesive strength, the composition has poor stability, gels, and cannot be stored for a long period of time, making it extremely uneconomical. On the other hand, in the case of the latter, the adhesive force of the cyclized rubber used as the vehicle to polyethylene is strong, so even if wax, dimethylpolysiloxane, etc. are included as a mold release agent, the adhesive strength may not be reduced enough depending on the sealing conditions. It has the disadvantage that it is difficult to balance the composition, such as not exhibiting easy peelability.

The purpose of the present invention is to provide a new easy-to-peel adhesive that eliminates the drawbacks of the conventional easy-to-peel adhesives mentioned above. The present invention was completed based on the discovery that the resulting composition has excellent printability and coating suitability, and that appropriate releasability can be imparted by applying this to a thermoplastic film such as polyethylene. be. That is, the easily peelable adhesive of the present invention is characterized by being formed by dissolving a cellulose derivative and a phospholipid in an organic solvent. The present invention will be explained in more detail below.

In the present invention, cellulose derivatives used include, for example, cellulose ethers such as methylcellulose, ethylcellulose, and carboxymethylcellulose, and cellulose esters such as cellulose acetate, nitrocellulose, cellulose acetate butyrate, and cellulose propionate.

These cellulos. The properties of these derivatives vary depending on their molecular weight and degree of substitution, but in general, the three hydroxyl groups of the glucose anhydride unit can be reduced to 0.5% by esterification or etherification.
1 to 2.8 are substituted. Industrially, the degree of substitution is 1.6.
-2.6 is used. Especially the degree of substitution is 1.6
! Those with a range of ~1.9 are water-soluble and have a degree of substitution of 2.0
Since those having 2.8 to 2.8 are soluble in organic solvents, it is preferable to dissolve them in organic solvents depending on the purpose in the range of 2.0 to 2.6 to form a film having water resistance, chemical resistance, etc. is possible,
Dissolves in an organic solvent at a concentration of 1-2% by volume and has a viscosity of 0.
．． 2-10p0iSq1 preferably 0.5-5p0is
e (25°C) range is preferably used. Among these cellulose derivatives, ethylcellulose is particularly preferably used. Phospholipids are derivatives of glycerophosphoric acid, with α-glycerophosphoric acid and β-glycerophosphoric acid as the core, and include phosphatidic acid with fatty acids added, phosphatidylglycerin, cardiolipin, and lecithin (phosphatidylcholine) and phosphatidyl that have nitrogen-containing atoms. ethanolamine, phosphatidylserine, etc.
These include plasmalogens such as acetal phospholipid, which contains acetaldehyde instead of fatty acids, and inosite phospholipid, which contains inosite.

Among these, those having nitrogen-containing atomic groups are preferred, and lecithin represented by the general formula is particularly preferred. Here, -CORl and -COR2 are fatty acid radicals.
Residues such as palmitic acid, stearic acid, oleic acid, and linoleic acid are shown in the table. These phospholipids are contained in large amounts in animal bodies, and lecithin in particular is manufactured industrially from soybeans and is economical. These phospholipids do not need to be pure products, and a mixture containing lecithin as a main component and also containing other phospholipids is preferably used. The reason why the composition of the present invention containing these cellulose derivatives and phospholipids acts effectively as an easily peelable adhesive is not necessarily clear, but the -0H group in the cellulose derivative and the hydrophilic and lipophilic groups in the phospholipid It is thought that these effects work together to form a coating film with appropriate releasability to polyethylene, etc., and also act as a release agent during high-temperature fusion of polyethylene, etc., reducing the adhesiveness of the sealed portion.

Coating films made solely of cellulose derivatives also have the effect of reducing adhesive strength, but such coating films have the drawbacks of being brittle and having low abrasion resistance, and also have insufficient printability when dissolved in organic solvents. be.

By adding phospholipids to such cellulose derivatives, the above-mentioned drawbacks can be eliminated and the exfoliation effect can also be increased. However, an excessive amount of phospholipid is not preferable because the adhesiveness of the coating film becomes large, causing blocking, and even inhibits printability before coating. For the above reasons, the acid combination ratio of the cellulose derivative and phospholipid is 1 (1) part (by weight, same hereinafter) of the former to 0.5 to 10 parts, preferably 0.5 to 50 parts of the latter. A range is used.

Incidentally, FIG. 1 shows the influence of the blending ratio of both components in the coating film on the seal strength. In other words, Fig. 1 shows that polyethylene laminated paper is heat-sealed directly with or without a coating film made of various ethyl cellulose/lecithin mixtures at 220°C and 5k91cr111... and then subjected to shovel type tensioning. Seal strength measured with a testing machine, where a is a direct seal of polyethylene, b is a coating film of ethyl cellulose alone, and c
mg is the case when a mixed coating film of ethyl cellulose/lecithin is provided, and the composition ratio is 12/1, 12/2, 1
2/3, 12/4, and 12/5 (the ethyl cellulose concentration in the coating solution is all 12%).

In addition, in the case of b-g, the easily peelable coating film was provided on only one of the pair of polyethylenes to be bonded, with a thickness of 4 μm.As shown in FIG. Thermal adhesive strength of 0.8kg/1577177!
It can be seen that the strength can be reduced to a moderate strength of about 114 or less in the order of 0.05 to 0.2k9/15, and that it can be controlled as desired, and that the addition of lecithin is also useful for lowering the seal strength. The easily peelable adhesive composition of the present invention can be obtained by dissolving the cellulose derivative and lecithin in an organic solvent such as an aromatic, ester, ketone, or alcohol alone or in combination.

The organic solvent is used when the amount of cellulose derivative in the composition is 1 to 2.
It is used in an amount of 0% (weight %, same hereinafter), preferably 3 to 15%. Dissolution can be easily achieved using any stirring means such as a propeller mixer. Additives such as natural or synthetic resins, plasticizers, auxiliaries, inorganic fillers, pigments, etc., which are generally used as adhesive vehicles, can be added to the composition of the present invention thus obtained. Examples of such additives include natural resins such as dammar resins, pine resins, silica resins, petroleum resins, ester-modified pine resins, cyclized rubbers, vazine-modified phenolic resins, rosin-modified maleic resins, alkyd resins, ketone resins, and chlorinated resins. Rubber, chlorinated polyethylene, chlorinated polypropylene, vinyl oxide/vinyl acetate copolymer, ethylene/vinyl acetate copolymer, polyvinylidene chloride, polyamide resin,
Synthetic resins such as urethane resins and epoxy resins, plasticizers such as esters such as phthalic acid, citric acid, sebacic acid, adipic acid, etc. are generally known as mold release agents.
Dimethylpolysiloxane, wax, liquid paraffin,
Low molecular weight polyethylene, oleic acid amide, etc. Animal and vegetable oils such as linseed oil, tung oil, castor oil, soybean oil, safflower oil, sulfur oil, lard, etc. Inorganic fillers such as finely powdered silica, calcium carbonate, magnesium oxide, sedimentation Examples include barium sulfate, alumina white, and zinc white.

In order to maintain the performance of the compositions of the invention, the total amount of these auxiliary additives preferably does not exceed 1 (4) parts, especially not more than 50 parts, based on 10 (2) parts of cellulose derivative. The composition of the present invention thus obtained can be printed in a desired pattern on a desired portion of the seal portion by conventional means such as gravure printing, flexographic printing, or a roller coater method.

This will be explained in more detail below with reference to Examples.

Example Ethyl cellulose N-7 (manufactured by Hercules CO.)
1? Lecithin (manufactured by Ajinomoto Co., Inc.) 2 parts dimethylpolysiloxane (manufactured by Toray Industries, Inc.) 1 part low molecular weight polyethylene (
Allied Chemical CO. made)
1 part toluene
(1) Ethyl acetate
? Part 1 (4)
The above components were put into a container equipped with a propeller mixer, and stirred for 3 minutes to mix and dissolve to obtain an adhesive with a viscosity of 1 poise.

A pattern of this adhesive was printed on the outflow opening in the heat-sealed part of polyethylene laminated paperboard (Potlatch (USA) base paper) for remilk cartons using a gravure printing method.
When dried at 0° C., a good easily peelable layer with a thickness of about 4 μm could be formed without blocking, guide roll rubbing, or staining.

Next, the above-mentioned paperboard was formed into a cardboard shape, and after crimping between the 5k91CT111 and 5k91 CT111 ribs using a heating frame at 220°C, the peel strength was measured by pulling the sealed part with a chopper type tensile tester. .15k9/15T
Wt results were obtained.

Furthermore, it was confirmed that there was no deformation such as damage to the paperboard or fuzzing of the paperboard on the peeled surface, and there was no problem with the spillage of the contents.

[Brief explanation of drawings]

The drawing is a graph showing the difference in seal strength when the composition of the present invention is applied and not applied to the sealing surface of polyethylene laminated paperboard.

Claims (1)

[Scope of Claims] 1. An easily peelable adhesive composition containing a cellulose derivative and a phospholipid dissolved in an organic solvent. 2. The composition of item 1 above, further comprising one or more of dimethylpolysiloxane, low molecular weight polyethylene, an inorganic filler, and a pigment.