JPS5949910B2 - coated plastic film - Google Patents

Description

[Detailed description of the invention] The present invention relates to coated plastics films.

More specifically, the present invention provides mechanical aptitude, anti-blocking,
This invention relates to an easily heat-sealable coated plastic film with excellent water resistance, abrasion resistance, etc. According to the invention, (a) α having l or more carboxyl groups;
one or more β-unsaturated carboxylic acids, and (b)
Acrylic acid alkyl ester (the alkyl group is
2 carbon atoms) and/or one or more methacrylic acid alkyl esters (the alkyl group of which has 1 to 12 carbon atoms)
and (c) one or more types selected from hydroxyalkyl esters of α, β unsaturated acids, α, β unsaturated carboxylic acid esters having epoxy groups, and vinyl-substituted aromatic hydrocarbons. Component (a) in the copolymer is 0.1 to 10% by weight, component (c) is 0.1 to 80% by weight, and has an average molecular weight of is about 5,000 to about 150,000 and has a second-order transition point of about 20 to about 100° C., applying an aqueous dispersion containing substantially particles of a copolymer to a plastic film;
A dried coated plastic film is provided.

Although plastic films such as polyester film and polyurethane film have excellent transparency and physical and chemical strength, they lack heat-sealing properties, so this drawback of plastic films has been widely used in the United States. To improve this, coatings with easily heat-sealable polymers have been used.

The most common means for imparting heat-sealability to plastic films is coating them with solutions of thermoplastic polymers dissolved in various organic solvents.

However, these methods are undesirable because of the use of a large amount of organic solvent, which poses safety problems during the manufacturing process, and food hygiene problems caused by residual solvent in the coating film.

In order to solve these drawbacks, it has been proposed to use a polymer aqueous dispersion or solution as the coating liquid. However, if the plastic film is simply subjected to normal physical or chemical surface treatment such as corona discharge treatment or oxidizing agent treatment, sufficient adhesion to the base plastic film cannot be obtained by directly coating the plastic film with the aqueous polymer dispersion. It is generally difficult to obtain.

As a means of increasing the adhesion between the base film and the coating film obtained from an aqueous dispersion or solution of the polymer,
It is common to apply a hair undercoating to the base film in advance. However, such a method requires at least two coatings on the surface of the base film, which is economically disadvantageous. Therefore, methods have also been proposed in which an aqueous polymer dispersion or solution is directly coated onto a plastic film to obtain sufficient adhesion.

For example, a method of mixing methylolated melamine or methyletherified methylolmelamine with an aqueous dispersion of an alkyl acrylate copolymer (Japanese Patent Publication No. 46-42240)
A method of improving the adhesion to the base film has been proposed.

However, although the coating film obtained in this way has improved adhesion to the base film, its thermoplasticity is impaired, and the heat-sealing properties, which are the basic properties of the coating film, are impaired or completely lost. It has the following drawbacks. Therefore, the above attempt was made to improve the adhesion of an aqueous vinylidene chloride copolymer dispersion, which has excellent protective properties such as oxygen barrier properties and chemical resistance, to a plastic film when content is applied to the plastic film. As an improvement method, it is only used as an undercoat layer.

As an example, α,
Attempts have also been made to copolymerize β-monounsaturated carboxylic acids, such as acrylic acid, and neutralize the free acid with a base such as ammonium hydroxide to create a hydrophilic copolymer with improved adhesion to the base film. reported (e.g. U.S. Pat. No. 3753)
No. 769).

However, the resulting coating film generally has drawbacks such as low mechanical strength or easy adhesion. Therefore, the above-mentioned method lacks the basic and essential requirements for a blocking-resistant and abrasion-resistant coated film. Furthermore, since this coating composition is a water-soluble copolymer, it also has the disadvantage that the concentration of the copolymer cannot be increased. As a result of detailed research on a large number of coating compositions from various angles, the present inventors discovered an acrylic ester-based coating composition that is provided in the form of an aqueous dispersion and has excellent adhesion and useful heat-sealing properties. He discovered a copolymer composition and completed the present invention.

A compositional feature of the coating compositions of the present invention is that they are aqueous dispersions in which the particular copolymers are present substantially as particles dispersed in the aqueous medium.

The characteristics of the coating composition of the present invention are that it can be applied directly to a plastic film substrate such as polyester or polyolefin without the need for an undercoat;
In addition, the coating film should have excellent adhesion to the substrate and should have satisfactory heat sealing properties, blocking resistance, abrasion resistance, water resistance, etc. of the coating film. Other features and properties will become clearer in the description below.

1 or 2 used to form the copolymers of the present invention.
Examples of α,β-unsaturated carboxylic acids having more than one carboxyl group include acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, crotonic acid, sumaric acid, and maleic anhydride.

Further, when an α,β monounsaturated carboxylic acid having two or more carboxyl groups is used, a half ester thereof may be used. These carboxylic acids are thought to be mainly involved in adhesion to plastic substrates, and the amount used is about 0.1 to about 10% by weight (weight% in the copolymer).
It is. When the amount exceeds 10% by weight, the resulting copolymer becomes highly sensitive to water and bases, and generally becomes soluble in bases.

Coatings using it tend to have reduced blocking and abrasion resistance. On the other hand, if it is less than 0.1% by weight, sufficient adhesion to plastic substrates cannot generally be expected.
Note that two or more types of these carboxylic acids may be used in combination. The other copolymerization components, acrylic acid alkyl ester and methacrylic acid alkyl ester, are, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, amyl acrylate, n-acrylate. Hexyl, 2-ethylhexyl acrylate, lawaryl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, amyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, methacrylic acid Number of carbon atoms in acrylic acid and methacrylic acid such as lawalyl
- means 12 alkyl esters. These acrylic acid alkyl esters or methacrylic acid alkyl esters are the main constituents of film formation, and there are copolymers in the following combinations.

(l) One or more acrylic acid alkyl esters, (2) One or two or more methacrylic acid alkyl esters, (3) One or two acrylic acid alkyl esters.
and one or more types of methacrylic acid alkyl esters.

It is desirable to adjust the proportion of these acrylic acid alkyl esters and/or methacrylic acid alkyl esters so that a desired secondary transition point can be obtained by adding a copolymerizable vinyl monomer as necessary.

Next, component (c), hydroxyalkyl esters of α,β-unsaturated carboxylic acids (such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl
There are meth)acrylates, etc., which have an epoxy group, α,
Examples of β-unsaturated carboxylic acid ester include glycidyl, (
There are meta)acrylates, etc.

In addition, examples of vinyl-substituted aromatic hydrocarbons include styrene, α
-Methylstyrene, etc., and one or more of these may be used. Among these, vinyl-substituted aromatic hydrocarbons effectively contribute to the hardness of the coating, and include hydroxyalkyl esters of α,β-unsaturated carboxylic acids, and α,β-unsaturated carboxylic acid esters with epoxy groups. It is thought that this may also be involved in improving the adhesion of the coating. However, improvement in adhesion is not observed when these monomers are used alone, but this can be achieved by using them in combination with an α,β unsaturated carboxylic acid having one or more carboxyl groups. Plastic films are chemically stable, and when coating them, they are generally subjected to surface activation treatment such as the above-mentioned corona discharge treatment.

However, the wetting of the aqueous dispersion onto the plastic film is not sufficient with normal surface treatments, and as a means of further improving the wetting, the aqueous dispersion is treated with an increased amount of surfactant, the addition of alcohols, and the use of excess alkali. Means such as addition to form an aqueous solution are being used. However, these methods also have many other disadvantages. That is, increasing the amount of surfactant reduces the adhesion, heat sealability, and water resistance of the coating film.

Addition of alcohol requires new investment in safety equipment, alcohol recovery and processing equipment, etc. to prevent fires and explosions, and is economically disadvantageous. The method of making an aqueous solution is
Due to the limitations of the solution clay, it is difficult to apply high molecular weight polymers, high concentration solutions, etc., and there are problems with drying of the coating film, blocking resistance, etc. The present inventors have studied these points and completed the present invention.
It is particularly preferred to combine and copolymerize hydroxyalkyl esters of α,β unsaturated carboxylic acids such as hydroxyethyl methacrylate and 2-hydroxypropyl acrylate. The preferred amount used in the copolymer is 0.
It is preferably 1 to 30% by weight, more preferably 5 to 20% by weight. As a result, V) it is possible to improve the wettability of the plastic film and reduce the amount of surfactant, and to create an easily heat-sealable coated plastic film that has even better mechanical suitability, locking resistance, water resistance, etc. as described above. is provided. In this invention, in addition to the components A, b, and c, one or more copolymerizable pinyl monomers may be added, if necessary.

Copolymerizable vinyl monomers include, but are not limited to, the following. 1) α, β monounsaturated aliphatic nitriles such as acrylonitrile and methacrylonitrile, 1i) Organic acid vinyl esters such as vinyl acetate and vinyl propionate, 111) Vinyl chlorides such as vinyl chloride and vinylidene chloride Class IV) α,β monounsaturated carboxylic acid amides such as acrylamide, methacrylamide, N-methoxyacrylamide.

When these copolymerizable vinyl monomers are used, the total amount with component (c) in the copolymer is 0.1 to 80%.
Preferably, it is used in % by weight.

One type or two or more types of these copolymerizable vinyl monomers may be used as necessary, and these are considered to be mainly involved in the hardness of the coating with the coating composition. The polymerization reaction of these copolymers is carried out in an aqueous medium, and the method is known per se (for example, Japanese Patent Publication No. 49
-36942).

The target copolymer has an average molecular weight of about 5,000 to 15
0000 and a second-order transition point of about 20 to about 100°C.
It has been found that when the average molecular weight of the copolymer exceeds 150,000, the adhesion to the plastic substrate decreases and viscous fluidity necessary for obtaining good heat sealing is lost.

It has also been found that a copolymer with an average molecular weight of 5,000 or less lacks properties as a coating film9 and cannot provide sufficient heat-sealing strength. The preferred range of average molecular weight is:
It is about 10,000 to about 80,000. In addition, the average molecular weight here is a weight average molecular weight. Secondary transition point (T
g, glass transition temperature) is about 20 to about 100°C, preferably 30 to 70°C. When the copolymer is heated to 20° C. or lower, the coating film becomes sticky and causes blocking.

On the other hand, if the temperature is 100° C. or higher, the resulting coating will be hard and have reduced flexibility, impairing heat sealability, one of the effects to be achieved by the present invention. These polymers are substantially contained in aqueous dispersions as particles.

The term "substantially particles" refers to particles that can be confirmed under an electron microscope, and the particle size of the copolymer is approximately 0.01 to 0.
．． 5 microns is preferred, most preferably 0.01-0
．． It is 3 microns. and at least 90 particles (
It is sufficient that F6 has such a particle size. Here, the aqueous medium only needs to substantially contain water, and an aqueous organic solvent such as alcohol may be mixed therein.

However, the higher the water content, the better. The concentration of the copolymer of the present invention in this aqueous dispersion is not particularly limited, but is preferably 10 to 60% by weight, more preferably 15 to 45% by weight. These aqueous dispersions may contain lubricants, antiblocking agents, antistatic agents, plasticizers, antioxidants, stabilizers, and the like, if necessary. Next, the plastic film which is the base material for the coating composition of the present invention will be explained. Plastic films to which the present invention is applied include, for example, polyethylene films,
These are polyolefin films such as polypropylene films and polyptene films, and polyester films. These may be biaxially stretched, -axially stretched or unstretched. However, the coating composition of the present invention is particularly effective for biaxially stretched materials. Further, the surface of the base film preferably has a contact angle with respect to water of 85 groups or less. Polyester films can be used as they are, but polyolefin films are preferably used after their surfaces are activated by corona discharge treatment, oxidizing agent treatment, or the like.

The plastic film that is the base material of the present invention is not particularly limited to those mentioned above, and the thickness of the film may be so-called sheet-like. All or one of the carboxyl groups of
From the viewpoint of stability of the aqueous dispersion, it is preferable that part of the aqueous dispersion be neutralized with a volatile base.

Examples of volatile bases used in this case include ammonia and lower amines. However, when an aqueous dispersion stabilizer is used in conjunction, neutralization is not necessary.
The coating composition of the present invention is also useful as an anchor coating agent for plastic films.

A plastic film can be anchor coated with the coating composition of the present invention and then top coated with an aqueous dispersion of vinyldene chloride copolymer. Furthermore, one side of the double-sided coating film of the vinylidene chloride copolymer coated film can be replaced with the coating layer of the present invention.

The aqueous dispersion used in the present invention may be copolymerized with a conductive vinyl monomer containing a sulfonate or a quaternary ammonium salt in order to impart antistatic properties to the coated plastic film. It is also possible to incorporate a polyelectrolyte.

Next, the present invention will be explained with reference to examples, and the test method used therein is as follows.

b) Cellophane tape test Pressure-sensitive adhesive cellophane tape with a size of 24m7n x 200n is firmly attached to the resin-coated surface by pressing it from end to end, and then sharply applying the adhesive tape at a 90° angle. The film was peeled off and the state of peeling of the film was observed and graded as follows.

No peeling of resin at all ・・・・・・・・・・・・・・・
... Peeling area of excellent resin 10% or less ...
・・・・・・ Good quality 10-20% ・・・・・・
Passable Upper 20% or more ・・・・・・Unspoken)
Heat-sealing strength The coated surfaces of the film and the coated surfaces were heat-sealed using a bar-type heat sealer at a heater temperature of 120, a compression pressure of 0.5kg/cm2, and a compression time of 0.5 seconds, using Tensilon from a sample of 1511 x 100 mm. The peel strength of the heat seal was measured at a tensile speed of 100 m7K/Min.

c) Blocking test Several sheets of 5011×50n film were sandwiched between two glass plates and left at 40° C. under a load of 0.5 kg/CrfL2 for 48 hours, and then left to cool in a room.

The degree of blocking of the film was ranked as follows. The film separates into individual sheets without applying any force.
If you apply a little force, it will separate into sheets... If you apply a good force, it will separate into sheets, but the coated resin will partially peel off.
・・・・・・・・・ Since the film has become a rigid film, it is impossible to separate it into sheets without destroying the film ・・・・・・・・・・・・・・・・・・
・No In addition, the monomers used are indicated by the following abbreviations.

MMA: Methyl methacrylate EA: Ethyl acrylate MAA: Methacrylic acid s)r: Styrene BA: Butyl acrylate HEMA: 2-hydroxyethyl methacrylate AA: Acrylic acid HPMA: 2-hydroxypropyl memethacrylate GMA: Glycidyl methacrylate implementation Examples 1 to 3, Comparative Example 1 530 cc of water containing 17.1 g of sodium lawalyl sulfate as an emulsifier and 1.4 g of potassium persulfate as a polymerization catalyst was placed in a polymerization container equipped with a stirrer, a cooler, and a thermometer.

The reaction vessel was then heated to about 80° C. with stirring. Then, a mixed solution of 285 g of the monomers (total) shown in Table 1 and mercabutan as a molecular weight regulator was added dropwise little by little over 3 hours. After the monomer mixture was added dropwise, the reaction vessel was kept at 80° C. for an additional 30 minutes. This aqueous dispersion was neutralized with aqueous ammonia, kept at 60° C. for 1 hour, and then cooled. This aqueous dispersion was diluted with water to a concentration of 20%,
A solid content coating amount of 1.0f was applied to the discharge treated side of a biaxially oriented polypropylene film with a thickness of 20μ and one side subjected to corona discharge treatment.
It was coated to a thickness of 1/M2 and dried at a temperature of 0°C for 1 minute to obtain a coated film. Table 1 below shows the effects on the adhesion to the base film and the heat seal strength of the coated films obtained by changing the amount of the molecular weight regulator in Examples 1 to 3 and Comparative Example 1.

Examples 4 to 7, Comparative Example 2 Similarly to Examples 1 to 3, a liquid containing the monomers shown in Table 2 and 1.0 part of mercaptan (based on 100 parts of the total amount of monomers) as a molecular weight regulator was mixed. The aqueous dispersion obtained by adding with stirring, polymerizing, and neutralizing with the theoretical amount of ammonia necessary to neutralize the acid groups of the copolymer was diluted to a solid content of 20%, and Aqueous dispersion of Wapawax (solid content 20%)
) 4 parts (per 100 parts of polymer resin) and 0.3 parts of fine powder silica (trade name: Thyroid) (per 100 parts of polymer resin)
was added to obtain a coating dispersion.

This dispersion was applied to the corona discharge treated surface of a 20 micron thick biaxially oriented polypropylene film which had been subjected to corona discharge treatment on one side so that the solid content coating amount was 1f1/M2, and the coating was dried at a temperature of 110°C for 1 minute. I got the film. Second
The test results are shown in the table.

Table 2 particularly reveals the influence of the secondary transition temperature of the polymer. Examples 8 to 17, Comparative Examples 3 to 4 Coated films were obtained in the same manner as in Examples 4 to 7, and Table 3 shows the monomers used and the test results.

Table 3 particularly reveals the influence of the amount of α,β monounsaturated carboxylic acid monomer. Examples 18-26, Comparative Example 6 Coated films were obtained in the same manner as in Examples 4-7, and Table 4 shows the monomers used and the test results.

Table 4 particularly reveals the influence of the amount of α,β unsaturated carboxylic acid monomer and the influence of the monomer composition. Example 27 The coating composition solution of Example 14 was applied to a biaxially stretched polyethylene terephthalate film with a thickness of 12 microns so that the solid content coating amount was 1.09/M2, and dried at a temperature of 110°C for 1 minute to form a coated film. I made it.

The coating film has excellent adhesion to the base film,
The heat seal strength was 1209/15ms. Example 28 On the coated film obtained in Example 2, a resin concentration of 50
% vinylidene chloride methyl acrylate copolymer, 0.2 parts of finely powdered silica (trade name: Thyroid) (per 100 parts of copolymer resin) and an aqueous carnauba wax dispersion (solid content: 20%) 3 parts (based on 100 parts of the copolymer resin) was added so that the solid content coating amount was 39/M2, and dried at a temperature of 110° C. for 60 seconds to obtain a coated film.

The adhesion between the base biaxially oriented polypropylene film and the vinylidene chloride methyl acrylate copolymer coating was excellent77)V), and the heat seal strength was 1509/15m.
It was 11. Example 29 On the coated film obtained in Example 9, a vinylidene chloride methyl acrylate copolymer coated film was obtained in the same manner as in Example 28.

The adhesion between the base biaxially stretched polypropylene film and the vinylidene chloride methyl acrylate copolymer coating film was excellent, and the heat seal strength was 1359/15 mm. Example 30 A film was obtained in which both sides of a biaxially oriented polypropylene film were coated in the same manner as in Example 9.

One side of this double-sided coated film was coated with vinylidene chloride acrylic ester copolymer as in Example 28, one side (side A) was coated with acrylic ester copolymer, and the other side (
For side B), a film coated with vinylidene chloride acrylic acid ester copolymer was obtained. A side/A side, A side/B side, B
The heat seal strength of side/B side is 145g/1, respectively.
5m1! , 115f! /1511,. 1209/151
It was 1. Examples 31 to 36, Comparative Examples 7 to 8 530 cc of water containing 17.1 f1 of sodium lauryl sulfate as an emulsifier and 1.49 g of potassium persulfate as a polymerization catalyst was placed in a polymerization vessel equipped with a stirrer, a cooler, and a thermometer.

The reaction vessel was then warmed to about 8'C with stirring.
Next, a mixed solution of monomers (total) 2859 shown in Table 5 and mercabutane as a molecular weight regulator was added dropwise little by little over 3 hours. After the monomer mixture was added dropwise, the reaction vessel was kept at 80° C. for an additional 30 minutes. This aqueous dispersion liquid was neutralized with aqueous ammonia, kept at 60°C for 1 hour, and then cooled. This aqueous dispersion was diluted with water to a concentration of 20f6, and a biaxially oriented polypropylene film (thickness 20μ) was pre-corona discharge treated and the contact angle with water was 6.
After applying it on the 0th side using a Meyer bar, apply 11
It was dried for 1 minute in a 0°C vacuum. The coverage after drying was 0.5 to 0.69/M2 in all cases. Next, the following top coat agent mainly consisting of vinylidene chloride-acrylic acid ester copolymer emulsion (vinylidene chloride 85%) was applied to the undercoat-coated surface using a Meyer bar.

Claims (1)

[Scope of Claims] 1 (a) one or more α,β unsaturated carboxylic acids having one or more carboxyl groups, and (
b) Acrylic acid alkyl ester (the alkyl group is 1)
one or more of the following (having ~12 carbon atoms),
and/or one or more methacrylic acid alkyl esters (the alkyl group thereof having 1 to 12 carbon atoms), and (c) hydroxyalkyl esters of α,β unsaturated carboxylic acids, epoxy groups α with ,
A copolymer formed by adding one or more selected from β-unsaturated carboxylic acid esters and vinyl-substituted aromatic hydrocarbons, wherein the component (a) in the copolymer is from 0.1 to 1
0% by weight, component (c) is 0.1 to 80% by weight, and the average molecular weight is about 5000 to about 150000,
A coated plastics film obtained by coating a plastics film with an aqueous dispersion containing substantially in the form of particles a copolymer having a secondary transition point of about 20 to about 100°C, and drying the coated plastics film. 2. The coated plastic film according to claim 1, which contains 0.1 to 30% by weight of one or more selected from hydroxyalkyl esters of α,β-unsaturated carboxylic acids as component (c). . 3. The coated plastic film according to claim 1, which is a copolymer in which all or a part of the carboxyl groups of the copolymer are neutralized with a volatile base.