JPS5947992B2 - Polypropylene film with excellent printability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biaxially oriented polypropylene film with excellent printability.

Polypropylene films, which are mainly made of polypropylene, polypropylene copolymers, or mixtures thereof, have excellent mechanical properties such as strength and dimensional stability, are chemically stable, and have excellent transparency. , widely used as packaging film.

However, polypropylene films have poor printability on the surface of the film because the chemical structure of the polypropylene constituting the film is non-polar, and there are various disadvantages associated with this.

For example, the adhesion between polypropylene film and nitrocellulose, which is the binder for cellophane ink, is extremely poor, and polypropylene film cannot be printed with cellophane ink. Printing is done using ink, but this ink is not only more expensive than cellophane ink, but also
Printing speed is slow due to poor solvent removal, and solvent odor remains on the printed surface and inside of the film.
It has drawbacks such as not being able to be used as a packaging film for foods such as seaweed and confectionery. Therefore, in order to improve the adhesion between the polypropylene film and a substance having a polar group, (1) the surface of the polypropylene film is subjected to physical or chemical treatment to polarize the surface of the film.

(2) A polymer layer having a polar group is laminated on the surface of a polypropylene film by an extrusion lamination method.

However, the former method does not provide enough effect to print with cellophane ink, and the latter method does not provide enough effect to print with cellophane ink. No effect can be obtained, and no satisfactory effect can be expected.

By having the structure described in the claims, the present invention has sufficient printability not only with polypropylene ink but also with cellophane ink.
Moreover, the present invention provides a polypropylene film which has no problem of blocking property on its surface and has original transparency without sacrificing the transparency of the polypropylene film.

Next, the structure of the polypropylene film of the present invention will be explained.

The polypropylene film of the present invention comprises a base film consisting of a polypropylene film mainly composed of polypropylene, a polypropylene copolymer, or a mixture thereof, oriented in the vertical and horizontal biaxial directions, and one side or both sides of the base film. It consists of a uniform resin coating layer of a saponified vinyl acetate-unsaturated carboxylic acid copolymer containing polyalkyleneimine, which is firmly and integrally adhered and laminated to the substrate.

The polypropylene film used as the base film in the present invention is a biaxially stretched film obtained by forming a polypropylene composition mainly composed of polypropylene, a polypropylene copolymer, or a mixture thereof, and
The polypropylene composition used as the film-forming material includes not only polypropylene homopolymers, but also α-olefins such as ethylene, butene, and 4-methylbenzene, aromatic olefins such as styrene, and putadiene. Polypropylene copolymers of propylene and monomers copolymerizable with propylene such as representative dienes, or polypropylene or polypropylene copolymers, and known blends of these, such as polyethylene and various ethylene copolymers. The main components are blends of poly-α-olefins, polystyrene, synthetic rubber, terpene resins, polyamides, polyesters, polyethers, and polypropylene or polypropylene copolymers.

The type and amount of the copolymerization component of the polypropylene copolymer or the blend component of the blend may be selected as long as the film obtained by forming this composition does not lose its characteristics as a polypropylene film. In addition, in the polypropylene composition that is the film forming material, if necessary, antistatic agents, antioxidants, ultraviolet absorbers, pigments, dyes, etc., which are known as additives for ordinary thermoplastic synthetic resin films, may be added. Of course, a lubricant, inorganic fine powder, etc. may be added. Furthermore, the polypropylene film serving as the base film in the present invention includes not only a single-layer polypropylene film produced from the composition described above, but also a multi-layer film obtained by laminating such a polypropylene film with a general-purpose resin such as polyethylene or polyester. However, when using such a multilayer film as a base film,
Of course, the resin coating layer made of the saponified vinyl acetate-unsaturated carboxylic acid copolymer containing polyalkyleneimine is provided on the polypropylene surface of the multilayer film.

The polypropylene film oriented in the vertical and horizontal directions, which is used as the base film in the present invention, is obtained by subjecting the formed film to a normal biaxial stretching process. Strong and integral adhesion and lamination between the film and the resin coating layer made of a saponified vinyl acetate-unsaturated carboxylic acid copolymer containing polyalkyleneimine can be achieved by attaching the polypropylene film, which is the base film, to the desired one or both sides of the polypropylene film. Corona discharge treatment is applied to both sides of the back surface, and then an aqueous solution of a saponified vinyl acetate-unsaturated carboxylic acid copolymer containing polyalkylene imine is applied to the treated surface, and this coated layer is dried. easily obtained by

The corona discharge treatment applied to the base film for the purpose of forming a strong and integral resin coating layer made of a saponified vinyl acetate-unsaturated carboxylic acid copolymer on the surface of the base film includes, for example, the spark gap method, the vacuum tube method, and the solid method. Methods used for normal corona discharge treatment, such as the state method, can be used as is, but in order to obtain a uniform resin coating layer, the treated surface of the polypropylene film must be 40 dy.
It is preferable to perform the corona discharge treatment so that the wetting tension is approximately T1e/Cm or more.

The resin coating layer according to the present invention is composed of a specific combination of saponified vinyl acetate monounsaturated carboxylic acid copolymer containing polyalkyleneimine, and the resin coating layer contains When polyalkyleneimine is not added, that is, a resin coating layer formed only from a saponified vinyl acetate monounsaturated carboxylic acid copolymer is not sufficiently suitable for the printing ink that is the object of the present invention. A resin coating layer formed only of alkylene imine has a severe blocking property, and is accompanied by a disadvantage in this respect.

Furthermore, when the saponified vinyl acetate monounsaturated carboxylic acid copolymer in the resin coating layer of the present invention is replaced with another similar product, the desired effects of the present invention are sufficiently exhibited. It cannot be done.

Incidentally, not only a resin coating layer formed of a saponified vinyl acetate polymer, but also a resin coating layer formed of a saponified vinyl acetate polymer to which polyalkylene imine is added can be used to print the print obtained by the present invention. No significant effect on aptitude can be obtained. Therefore, it is necessary and essential that the resin coating layer in the present invention is composed of a specific combination of saponified vinyl acetate monounsaturated carboxylic acid copolymer containing polyalkylene imine. It is a requirement. The proportions of each component in the composition consisting of polyalkyleneimine and saponified vinyl acetate monounsaturated carboxylic acid copolymer constituting this resin coating layer are as follows:
It is preferable to select from the range of 0.1 to 10% by weight of polyalkyleneimine and 99.9 to 90% by weight of saponified vinyl acetate monounsaturated carboxylic acid copolymer. This is because when the ratio of polyalkylene imine increases, not only does the adhesion of the formed resin coating layer to cellophane ink decrease, but also the resin coating layer exhibits a blocking phenomenon. This is because when the ratio of the saponified monounsaturated carboxylic acid copolymer increases, the adhesion of the formed resin coating layer to the cellophane ink decreases, making it impossible to fully achieve the effects aimed at by the present invention. As explained above, the resin coating layer in the present invention is as follows:
It is composed of a saponified vinyl acetate monounsaturated carboxylic acid copolymer and a polyalkylene imine added thereto, but the resin coating layer may contain antistatic material as necessary. There is no problem even if additives such as anti-oxidants, antioxidants, ultraviolet absorbers, pigments, dyes, lubricants, and inorganic fine powders are mixed.

The saponified vinyl acetate monounsaturated carboxylic acid copolymer, which is the main component in the resin coating layer of the present invention, can be easily obtained by copolymerizing vinyl acetate and ethylenically unsaturated carboxylic acid and saponifying the copolymer. Specific examples of ethylenically unsaturated carboxylic acids in this case include monobasic acids such as acrylic acid, methacrylic acid, and crotonic acid, maleic acid, maleic anhydride, fumaric acid, and itaconic acid. dibasic acids, and half-esterified products thereof,
There are fully esterified products, and all of them can be used alone or as a mixture.

The optimum copolymerization ratio of vinyl acetate and unsaturated carboxylic acid varies depending on the type of carboxylic acid.
Vinyl acetate 99.1-70 mol%, unsaturated carboxylic acid 0
．． Within the range of 1 to 30 mol%, especially vinyl acetate 99.5 to 30%
Preferably, the content of the unsaturated carboxylic acid is 90 mol % and the unsaturated carboxylic acid is selected within the range of 0.5 to 10 mol %. In addition, the degree of saponification of this saponified vinyl acetate monounsaturated carboxylic acid copolymer is as follows:
In general, those saponified to 50 mol% or more, especially 80 mol% or more are preferred. Further, the polyalkylene imine which is another component in the resin coating layer in the present invention includes, for example, polyethylene imine, polypropylene imine,
Water-soluble materials such as polybutylene imine, copolymers thereof, or mixtures thereof can be used, and polyethylene imine is particularly preferred because it has a remarkable effect of improving printability. Since the thermal decomposition temperature of this product is rather low, care must be taken because the resin coating layer may be colored yellow if the temperature in the drying step during the formation of the resin coating is set too high.

The polypropylene film of the present invention has the above-mentioned structure, and has a polypropylene film that is firmly adhered to the base film on one side, or on both the front and back sides of the biaxially oriented polypropylene film, which is the base film. The laminated resin coating surface has excellent printability not only for printing ink for polypropylene film but also for general cellophane ink, and the blocking phenomenon is completely suppressed. In this way, a polypropylene film is obtained which has the same transparency as the base film despite the presence of the resin coating layer.

Hereinafter, the structure of the polypropylene film of the present invention will be explained based on production examples, and the results of the printability test of the obtained polypropylene film will also be shown.

Example 1 [η] 2.2 measured in tetralin at 35°C
, boiling n-heptane extraction residue (1.1.) 9796 polypropylene is melt-extracted, cooled and crystallized on a 300C tilt roll to form a sheet, heated with a 135°C roll, and then Utilizing the difference in circumferential speed, the film was stretched 5 times in the longitudinal direction, and then further stretched 8 times in the transverse direction at a tenter temperature of 160° C. to obtain a biaxially stretched polypropylene film as a base film.

This film was surface treated with a spark gap type corona discharge treatment machine (Tomoe Kogyo FfS) to give a surface wetting tension of 38 dyne/Cm, and then treated with carboxylic acid-modified polyvinyl alcohol (T33O: Nippon Gosei Kagaku Kogyo Co., Ltd.). ), carboxylic acid copolymerization ratio 5 mol%, saponification degree 9
polyethyleneimine (15 mol%) in a 10% aqueous solution of
T: A coating agent containing 1% of Sogo Yakuko Co., Ltd. was coated with a #7 metal ring bar and then dried at room temperature for 24 hours to form a uniform resin coating on one side of the biaxially stretched polypropylene film serving as the base film. A polypropylene film A in which the layers were firmly adhered and laminated was obtained.

The adhesive strength between the resin coating layer and the base film in the obtained polypropylene film A was evaluated based on the adhesiveness test (zero peel test) described later, and the results are shown in Table 1.

Further, the resin coating surface of the obtained polypropylene film A was printed with cellophane ink (CCST: Toyo Ink Co., Ltd.) using a #6 metaling bar, and this was left at room temperature for 1 hour to dry. Thereafter, the adhesion of the ink to the resin coating surface was evaluated by the same adhesion test (zero peel test) as described above, and the results are shown in Table 1.

For reference, in place of the coating agent shown in the previous example, a coating agent to which no polyethyleneimine was added, that is, a 10% aqueous solution of carboxylic acid-modified polyvinyl alcohol, was used. 1 Cf of polyethyleneimine was added to polypropylene film B obtained according to the method of
Polypropylene film C obtained according to the method of the example except that 10Cfi aqueous solution of polyvinyl alcohol was used, and polypropylene obtained according to the method of the example The adhesive strength between each resin coating layer and the base film in Film D and the adhesion of ink to the resin coating layer surface are shown in Table 1.

In addition, the adhesive strength and adhesion tests shown in Table 1 are as follows:
The adhesion test (zero peel test) was conducted using the following method.

Adhesion test (zero peel test) Apply an adhesive tape made of acetate tape (manufactured by Sumitomo 3M Co., Ltd., trade name Tanding Tape) to the surface to be tested of the polypropylene film without entrapping air, and then peel it with your finger. After pressing, peel it off at 180 degrees and observe the degree of peeling of the desired resin layer or ink.
Evaluation was made according to the following criteria.

Evaluation criteria

Claims (1)

[Claims] 1. Polypropylene oriented in vertical and horizontal biaxial directions,
A uniform resin coating layer of a saponified vinyl acetate-unsaturated carboxylic acid copolymer to which a polyalkylene imine is added is laminated on at least one side of a polypropylene film mainly composed of a polypropylene copolymer or a mixture thereof. A polypropylene film with excellent printability. 2. Excellent printability according to claim 1, wherein the polyalkylene imine in the uniform resin coating layer of the saponified vinyl acetate-unsaturated carboxylic acid copolymer to which polyalkylene imine is added is polyethyleneimine. polypropylene film. 3 The saponified vinyl acetate-unsaturated carboxylic acid copolymer in the uniform resin coating layer of the saponified vinyl acetate-unsaturated carboxylic acid copolymer to which polyalkyleneimine has been added is 70 to 99.9 mol of vinyl acetate. %, and 0.1 to 30 mol % of an unsaturated carboxylic acid, and wherein at least 50 mol % of the vinyl acetate component is saponified.