JPS5855170B2 - Composition for coating plastics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition for coating plastics and a coated plastics film.

More specifically, the present invention relates to a plastics coating composition comprising an aqueous dispersion containing a specific copolymer, and a coated plastics film coated with the composition with excellent heat sealability.

According to the present invention, (a) one or more α, β-, β-carboxylic acids having one or more carboxyl groups, and (b) an acrylic acid alkyl ester (
The alkyl group has 1 to 12 carbon atoms)
species, and/or one or more methacrylic acid alkyl esters, the alkyl group of which has from 1 to 12 carbon atoms, and, optionally,
(C) A copolymer formed by adding one or more types of copolymerizable vinyl monomers, wherein the component (a) in the copolymer is about 0.1 to about 10% by weight, and an average molecular weight of about 5,000 to about 150,00
0.0C and a second-order transition temperature of about 20 to about 100C. A coated plastic film coated with the coating composition is provided.

Although plastic films such as polyester films and polyolefin films have excellent transparency and physical or chemical strength, they do not have heat-sealing properties. , coated with an easily heat-sealable polymer.

The most common method for imparting heat-sealability to plastic films is coating them with a solution of a thermoplastic polymer dissolved in various organic solvents.

Although this method has the advantage of relatively easily achieving adhesion to plastic films, the solvent used to dissolve these copolymers is usually extremely volatile and highly flammable.
Therefore, there is a risk of ignition and explosion, and the vapor may be toxic, which poses safety problems.

Furthermore, it is difficult to completely remove the solvent from the coating film during the coating process, and trace amounts of solvent tend to remain in the coating film.

This residual solvent is unfavorable in terms of food hygiene.

Therefore, in order to reduce this residual solvent, it is necessary to reduce the coating speed or to use a large amount of drying equipment, which is extremely uneconomical.

In addition, as the polymer concentration increases, the polymer solution viscosity increases, so that practical coatings have the disadvantage that the polymer concentration must be lowered.

Such disadvantages in the properties of plastic film products (residual solvents) and in production can be avoided by forming the coating composition into an aqueous polymer dispersion or solution.

However, if the plastic film is only 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 achieved by directly coating the plastic film with an aqueous polymer dispersion. It is generally difficult to obtain.

Usually, as a means of increasing the adhesion between the base film and a coating film obtained from an aqueous polymer dispersion or solution, the base film is usually undercoated in advance.

However, such a method requires coating the surface of the base film at least twice, which is economically disadvantageous.

Therefore, a method has 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 adhesion to a 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 a coating film, are impaired or completely lost. It has the following drawbacks.

Therefore, the above attempt was made to develop a method for improving adhesion when coating plastic films with an aqueous dispersion of a vinylidene chloride copolymer, which is easy to heat seal and has excellent protective properties such as oxygen barrier properties and chemical resistance. It is only used as an undercoat layer.

As an example, α,
There have also been reports of attempts to copolymerize β-unsaturated carboxylic acids, such as acrylic acid, neutralize the free acid with a base such as ammonium hydroxide, and create a water-soluble copolymer with improved adhesion to the base film. (e.g. U.S. Pat. No. 3,75
No. 3,769).

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, abrasion-resistant coating 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 have discovered an acrylic ester-based coating composition that is provided in the form of an aqueous dispersion and has excellent adhesion and useful heat sealability. He discovered a polymer 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 film-like substrate of plastics such as polyester or polyolefin without the need for an undercoat;
It also has excellent adhesion to the base material, and the heat sealability of the coating film.
Blocking resistance, abrasion resistance, water resistance, etc. should be satisfactory.

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 1 carboxyl group include acrylic acid, methacrylic acid, maleic acid, iconic acid, citraconic acid, crotonic acid, fumaric acid,
Examples include maleic anhydride.

Further, when an α,β-unsaturated carboxylic acid having two or more carboxyl groups is used, its half-carboxylic acid may be used.

These carboxylic acids are thought to be mainly involved in adhesion to plastic substrates, and the amount used is:
from about 0.1 to about 10% by weight (in the copolymer).

When the amount is 10% by weight or more, the resulting copolymer becomes extremely sensitive to water and bases, and generally becomes soluble in bases.

Coatings using it tend to have poor 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 of these carboxylic acids may be used in combination.

Examples of the other copolymerization components, acrylic acid alkyl ester and methacrylic acid alkyl ester, include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, amyl acrylate, and n-acrylate. -hexyl, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, amyl methacrylate, n-hexyl methacrylate,
Acrylic acid and methacrylic acid having 1 to 1 carbon atoms, such as 2-ethylhexyl methacrylate and lauryl methacrylate
It means two 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.

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

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, copolymerizable vinyl monomers include, but are not limited to, the following.

1) Vinyl-substituted aromatic hydrocarbons such as styrene and α-methylstyrene; 11) α such as acrylonitrile and methacrylonitrile;
β-unsaturated aliphatic nitriles, ) organic acid vinyl esters such as vinyl acetate and vinyl propionate, V) vinyl halides such as vinyl chloride and vinylidene chloride, ■) acrylamide, methacrylamide, N-methoxy α, β-unsaturated carboxylic acid amide such as acrylamide, vi) α such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc.
, β-unsaturated carboxylic acid Q-hydroxyalkyl esters, vID α,β-unsaturated carboxylic acid esters having an epoxy group such as glycidyl (meth)acrylate.

Among these copolymerizable vinyl monomers, more preferable results can be obtained by using one or more of the monomers i) Vi) Vii) as component (c).

The content of these copolymerizable vinyl monomers is preferably 0 to 80% by weight in the copolymer.

In addition, when using a hydroxyalkyl ester of α,β-unsaturated carboxylic acid, one or more of them can be used at 0.1
It is preferable to use up to 30% by weight, with 5 to 20% by weight giving more preferable results.

One type or two or more types of these copolymerizable vinyl monomers may be used as necessary, and these are thought to be mainly involved in the hardness of the coating with the coating composition, but Vi)Vil) The seven substances listed above will also be involved in improving adhesion.

However, the adhesion cannot be improved by using monomers (1) and vID alone, but it can be achieved by combining it with an α,β-unsaturated carboxylic acid having one or more carboxyl groups.

The polymerization reaction of these copolymers is carried out in an aqueous medium, and the method is a method known per se (for example, Japanese Patent Publication No. 49-1999).
36942).

The desired copolymer has an average molecular weight of about 5,000 to about 150,000 and a second-order transition point of about 20 to about 1000C.
It is.

It has been found that when the average molecular weight of the copolymer exceeds 150,000, the adhesion to the plastic substrate decreases, and the viscous flow required to obtain good heat sealing disappears.

It has also been found that a copolymer with an average molecular weight of 5,000 or less loses its properties as a coating film and cannot obtain sufficient heat seal strength.

The preferred range of average molecular weight is about 10.000 to about s
o, ooo.

□ Note that the average molecular weight here is the weight average molecular weight.

The secondary transition point (Tg, glass transition temperature) is about 20 to about 10
The temperature is 0°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 obtained film will be hard and have reduced flexibility, and heat sealability, which is one of the effects to be obtained by the present invention, will be impaired.

These polymers are substantially contained in aqueous dispersions as particles.

The term "substantially particles" refers to particles that can be confirmed under electron microscopy, and the particle size of the copolymer is approximately 0.01.
~0.5 micron is preferred, most preferably 0.01
~0.3 micron.

It is sufficient that at least 90% of the particles have such a particle diameter.

Here, the aqueous medium may 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, it is 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 that is the base material for the coating composition of the present invention will be explained.

Examples of plastic films to which the present invention applies are:
These are polyolefin films and polyester films such as polyethylene film, polypropylene film, and polybutene film.

These may be two-wheel stretched, uniaxially stretched or non-stretched.

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 water of 85° or less.

Although polyester films can be used as they are, it is preferable to activate the surface of polyolefin films by corona discharge treatment, oxidizing agent treatment, etc. before use.

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. From the viewpoint of stability of the aqueous dispersion, it is preferable that all or part of the combined carboxyl groups be neutralized with a volatile base.

Examples of volatile bases used in this case include ammonia and lower amines.

However, when using stabilizers for aqueous dispersions,
No need to neutralize.

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 vinylidene chloride copolymer dispersion.

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.

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

b) Cellophane tape test Pressure-sensitive adhesive cellophane tape measuring 24 mm x 200 mvt is repeatedly pressed from end to end on the resin-coated surface to firmly stick it, and then the adhesive tape is suddenly peeled off at an angle of 900° to break it. The state of film peeling was observed and graded as follows.

No peeling of resin at all ・・・・・・・・・・・・・・・
・・・ Peeling area of excellent resin 10% or less ・・・・・・
Good (upper) 10-20% ・・・・・・ Rotated upper 20% or more (not allowed) Heat seal strength: Align the coated side of the film with the coated side and use a bar-type heat sealer to heat the heater to a temperature of 120℃. °C, crimping pressure 0.51
9. Heat seal with a pressure bonding time of 0.5 seconds 1
The peeling strength of the heat seal was measured from a 5 mm x 100 mm sample using Tensilon at a tensile rate of 1007 rLr/L/in the current conditions.0 Blocking test Several sheets of 50 mm x 50 mm film were separated from two pieces of glass. It was placed between plates and left at 40°C under a load of 0.5'Pcyrt for 48 hours, and then allowed to cool to room temperature.

The degree of blocking of the film was ranked as follows.

The film separates into one sheet without applying any force...
・・・・・・ If you apply a little force, it will separate into sheets ・・・
When the food is added, it separates into sheets, but the applied resin partially peels off.
・・・ It is a hard block and cannot be separated into sheets without destroying the film ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・Not possible In addition, the monomers used are indicated by the following abbreviations.

MMA: Methyl methacrylate EA Ethyl diacrylate MAA: St methacrylate: Styrene BA Butyl diacrylate HEMA: 2-hydroxyethyl methacrylate AA HPMA diacrylate: 2-hydroxypropyl methacrylate GMA
Niblicidyl Methacrylate Examples 1 to 6, Comparative Examples 1 to 2 In a polymerization vessel equipped with a stirrer, a cooler, and a thermometer, sodium lauryl sulfate 17.1.9 as an emulsifier and potassium persulfate 1.9 as a polymerization catalyst were added. 530 cc of water containing 4 g was added.

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 mercaptan 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 heated for another 30 minutes.
0℃? I kept it.

This aqueous dispersion liquid was neutralized with aqueous ammonia and heated to 60°C.
The mixture was kept for 1 hour and then cooled.

This aqueous dispersion was diluted with water to a concentration of 20%,
A solid content coating amount of 1.0 g is 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.
/m' and dried at a temperature of 110° C. for 1 minute to obtain a coated film.

In the following Table 1, in Examples 1 to 6 and Comparative Examples 1 to 2,
It shows the effects on the adhesion to the base film and the heat seal strength of coated films obtained by changing the monomer composition and the amount of the molecular weight modifier.

Examples 7-10. Comparative Example 3 As in Examples 1 to 6, a mixture of 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 added while stirring, The aqueous dispersion obtained by polymerization and neutralization with the theoretical amount of ammonia necessary to neutralize the acid groups of the copolymer was diluted to a solid content of 20%, and an aqueous dispersion of carnauba wax was prepared. Liquid (solid content 20%
) (100 parts of polymer resin) and 0.3 parts of finely powdered silica (trade name: Thyroid) (based on 100 parts of polymer resin) were added to obtain a coating dispersion.

This dispersion was applied to the corona discharge treated surface of a biaxially oriented polypropylene film having a thickness of 20 microns and one side of which had been subjected to corona discharge treatment, so that the solid content coating amount was 1 g/i, and the coating was dried at a temperature of 110°C for 1 minute. Got the film.

Table 2 shows the test results.

Table 2 particularly reveals the influence of the secondary transition temperature of the polymer.

Examples 11-20. Comparative Examples 4-5 Coated films were obtained in the same manner as in Examples 7-10, and Table 3 shows the length of the monomer used and the test results.

Table 3 reveals in particular the influence of the amount of α,β-unsaturated carboxylic acid monomer.

Example 21 The coating composition of Example 17 was applied to a biaxially stretched polyethylene terephthalate film with a thickness of 12 microns so that the solid content coating amount was 1-0 g/m, and the coating was dried at a temperature of 110°C for 1 minute. made a film.

The adhesion of the coating film to the base film was excellent, and the heat seal strength was 120 g/15 cm.

Example 22 On the coated film obtained in Example 5, 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 dispersion of Karnara/i, f7 Tux (solid content 20 %) 3 parts (copolymer resin 100
parts) was added so that the solid content coating amount was 3.9 parts m, and dried at a temperature of 110°C for 60 seconds to obtain a coated film.

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 150.9 parts 15 mm.

Example 23 On the coated film obtained in Example 12, a vinylidene chloride methyl acrylate copolymer coated film was obtained in the same manner as in Example 22.

The adhesion between the base biaxially oriented polypropylene film and the vinylidene chloride methyl acrylate copolymer coating film is excellent, with a heat seal strength of 135 g/15 mm.
Met.

Example 24 A film was obtained in which both sides of a biaxially stretched polypropylene film were coated in the same manner as in Example 12.

One side of this double-sided coated film was coated with salt: hibinylidene acrylic ester copolymer as in Example 22, one side (A side) was coated with acrylic ester copolymer, and one side (B side) was coated with vinylidene chloride. An acrylic ester copolymer coated film was obtained.

Heat seal strength 't of A side/A side, A side/B side, B side/B side, 145 ji/15 mm, respectively.

115 g/i 5mm, 120. ? /151m.

Examples 25-28 Coated films were obtained in the same manner as Examples 7-10 using the monomers shown in Table 4.

Table 4 also shows the test results of the coated film.

Claims (1)

[Scope of Claims] 1 (a) one or more α, β-, and β-carboxylic acids having one or more carboxyl groups;
and (b) one or two acrylic acid alkyl esters, the alkyl group of which has 1 to 12 carbon atoms.
and/or one or more methacrylic acid alkyl esters (the alkyl group of which has 1 to 12 carbon atoms) and, if necessary, one or more of (C) a copolymerizable vinyl monomer. A copolymer comprising a species or two or more species, wherein the proportion of (a) in the copolymer is about 0.1 to about 10% by weight, and the average molecular weight is about 5,000 to about 150,00
1. A composition for coating plastics comprising an aqueous dispersion containing substantially in the form of particles 10 to 60% by weight of a copolymer having a secondary transition temperature of 0 and a secondary transition temperature of about 20 to about 100'C. 2 (c) The copolymerizable vinyl monomer for ff is α
. The composition according to claim 1, which is a hydroxyalkyl ester of β-TRI carboxylic acid, an ester of α,β-unsaturated carboxylic acid having an epoxy group, and a vinyl-substituted aromatic hydrocarbon. . 3. The coating composition according to claim 1 or 2, wherein the copolymer has a secondary transition point of 30 to 70'C. 4. The coating composition according to claim 1 or 2, wherein the copolymer has a particle size of 0.01 to 0.5 microns. 5. The coating composition according to claim 1 or 2, which is a copolymer in which all or a part of the carboxyl groups of the copolymer are neutralized with a volatile base.