JPH03124782A - Method for modifying surface of polyolefin - Google Patents

Abstract

PURPOSE: To improve the adhesion to a paint, a coating, an ink, an adhesive, etc., by mixing a specific copolymer with a polyolefin matrix and them molding the mixture.

CONSTITUTION: To (a) a polyolefin backbone (e.g. PP), one or a plurality of chains derived from (b) (i) not less than 60 wt.% lower alkyl methacrylate (e.g. methyl methacrylate) and (ii) 5-40 wt.% copolymrizable unsaturated compound (e.g. methacrylic acid) and having a wt. average mol.wt. of about 20,000 are graft-copolymerized to obtain a graft copolymer (B). With a polylolefin matrix (A) selected from PP, PE and a copolymer of ethylene and propylene, 2-10 wt.% component (B) is mixed and then the mixture is molded into a film, a sheet or a molded product. On this film, sheet or molded product a second substance of a paint, a coating, an ink, an adhesive or an adhesive-coated film or a sheet of paper is provided.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for improving adhesion to polyolefin surfaces and to the composites made.

[Conventional technology and issues to be solved]

Polyolefins can be processed into many useful products.

Many of these articles require some form of labeling, such as by printing, inking, spray coating, labeling, and the like. Other articles need to be laminated or adhered to other plastics, such as in multilayer bottles, coextruded sheets, and the like. Polyolefins, particularly polypropylene, polyethylene and their copolymers, are known as "non-polar"polymers;
It is difficult to attach adhesives, inks, etc.

Polyolefins can be surface modified by treating them with gases such as oxygen, ozone or fluorine, but this requires special equipment and is not always applicable to high speed processing of articles with complex shapes. A second approach is to use polymeric adhesives with polar groups incorporated into a polyolefin matrix. Such adhesives often impair the physical properties or processability of the resulting formulation.

It is therefore desirable to find polymeric adhesives that improve the adhesion of inks, coatings and adhesives to polyolefin surfaces while maintaining or increasing the physical properties of the formulation or processability during the manufacture of the final article. .

[Means to solve the problem]

The inventors have discovered that a class of graft copolymers consisting of a polyolefin backbone and the grafting of one or more chains consisting of at least 80% methacrylate ester are useful for altering the melt rheology of polyolefins and that It has been found that processability is essentially unaffected, but thermoforming and other operations at low shear rates are significantly improved compared to unmodified polyolefins. A major manifestation of this effect is an improvement in the sag resistance of the modified polyolefin. The discovery is described in Japanese Patent Application No. 1-80238. The inventor has further determined that the graft strands are about 5 to about 40.
It has been found that the surface properties with respect to printability and adhesion are improved when containing % by weight of copolymerizable unsaturated acids.

In the present invention, the backbone of the graft copolymer can be a polyolefin similar to or different from the matrix polymer to be modified. In order to achieve improved surface properties, it is desirable that the graft copolymer be well dispersed in the matrix polyolefin. Adhesive sites are then uniformly spaced over the surface of the modified matrix polymer. Therefore, it is preferred that the backbone polymer is similar to the matrix polymer.

Matrix polymers to be modified include polyethylene, polypropylene, polybutylene, poly(4-methylpentene-1), copolymers of the above-mentioned olefins, and the above-mentioned olefins, especially ethylene and small amounts of 1-alkenes, such as hexene-1 or dodecene-1. 1. Can be vinyl ester, vinyl chloride, acrylic ester, methacrylic ester, copolymer with acrylic acid and methacrylic acid.

The backbone polyolefin can be any of the possible matrix polymers listed below. Preferred are polypropylene, polyethylene, or a copolymer of propylene and ethylene. Diene monomers with non-conjugated double bonds, such as hexadiene-1,4 or ethylidenenorbornadiene, may also be present in small amounts.

The grafted chain contains from about 60 to about 95% by weight methacrylic ester, which ester is an alkyl, substituted alkyl, aryl, substituted aryl, alkaryl, substituted alkaryl, aralkyl, or substituted aralkyl. It is. Suitable examples include the esters listed below. Methyl, ethyl, butyl, dodecyl, 2-ethoxyethyl, phenyl, chlorphenyl, benzyl, p-
toluyl, and p-methylbenzyl. Additionally, the grafted chains may include acrylate esters or vinyl aromatics, such as ethyl acrylate or styrene.

The grafted chain contains from about 5% to about 40% by weight of a copolymerizable unsaturated acid, such as an unsaturated carboxylic acid, a phosphorus-containing acid, or a sulfur-containing acid. Examples of such non-carboxylic acids include p-vinylbenzenesulfonic acid, 3-sulfopropyl methacrylate, 2-hydroxyethyl acrylate monosulfate, 2-hydroxyethyl acrylate monophosphate, or p-vinylbenzenephosphonic acid. It will be done.

Preference is given to unsaturated carboxylic acids such as p-vinylbenzoic acid, monovinyladipic acid, acryloxypropionic acid, α-methylene-δ-methyladipic acid, itaconic acid, maleic acid, fumaric acid, acrylic acid and methacrylic acid. . In particular, methacrylic acid is preferred because it is easily copolymerized. The weight ratio of the graft chain to the backbone polymer is approximately 1
=9 to about 4:1. For ease of synthesis, approximately 3=2~
A ratio of about 2:3 is preferred.

Particularly preferably, the backbone is polypropylene, the methacrylate ester is methyl methacrylate, the copolymerizable acid is methacrylic acid, and the weight average molecular weight of the graft polymer is 20,000 or more. This high molecular weight contributes to the melt rheology imparted to the polyolefin matrix by the graft copolymer.

The amount of graft copolymer useful for improving adhesion to the matrix polymer depends on the amount of copolymerizable acid in the graft, the graft to backbone ratio, and the weight percent of the graft added to the matrix. It will change. A preferred range is about 0.5-2% acid based on the total formulation. If the trunk/graft polymerization ratio is 1:1, the amount of acid in the graft is 20%, and the amount of graft copolymer formulated is about 10%, then the parent acid in the formulation is about Probably 1%.

The graft copolymer can be prepared by the method described in Japanese Patent Application No. 1-80238. There, the polyolefin is dissolved in a solvent above its melting temperature and polymerization is carried out by gradually adding a monomer mixture in the presence of low radical flux. A convenient means of separating graft copolymers is devolatilization.
fizing) passing the graft copolymer solution or dispersion through an extruder to remove solvent, unreacted methacrylate monomer, and unsaturated acid. Another reason why low boiling acids such as methacrylic acid are preferred is their removal, such as in volatile removal methods.

Alternatively, the graft copolymer is made in solution and separated by precipitation with a non-solvent or cooling of the reactants.

If desired, the ungrafted methacrylate ester/unsaturated acid copolymer can be removed by suitable extraction techniques such as extraction with polar solvents such as tetrahydrofuran or acetone, or extraction with an aqueous base. For the purpose of improving adhesion, it is generally not necessary to extract the non-grafted polymer.

The graft copolymer mixture comprising an ungrafted backbone polymer and a graft copolymer, optionally with an ungrafted methacrylate/acid polymer, can be used directly for the production of the desired product. It is generally preferred to use this mixture for further incorporation into polyolefin matrix polymers. Such compounding may be accomplished using any of several mixing means, such as mill rolls, Banbury Mixer-1 extrusion, melt mixing, and the like. The blend can be processed directly into the desired article or it can be pelletized and reprocessed in suitable equipment.

Testing of surface modifications related to improved adhesion can be carried out by several test methods known in printing, gravure or adhesion technology. One method is to write on the modified and unmodified surfaces with a suitable pen containing the test ink at the same pressure and optically or visually measure the improvement in ink coverage and the resistance of the ink to scratches. That's true. Another test is to apply an aqueous or non-aqueous liquid (methylene iodide is often used) to a surface and measure the contact angle. The easier the surface gets wet, the smaller the angle will be.

The uses of such surface-modified polyolefins are obvious. - In the form of a layered bottle, it can be labeled with ink or with an adhesive-containing paper label. Other forms of modified matrix plastics, such as extruded sheets, may be labeled in a similar manner or by silk-screening a suitable label or by applying decals. In multilayer constructions, such as coextrusions or laminates, improved adhesion of the second layer is found through the use of adhesives. Improved adhesion is seen in the lamination of barrier layers on bottles, such as ethylene-vinyl alcohol laminated with ethylene-vinyl acetate adhesives.

Other uses of blends of graft copolymers and polyolefins or of graft copolymers alone include fiber spinning, fiber dyeing (
(for acceptance of dye or pigment molecules with positively charged groups)
, hot melt adhesives and extrusion coatings (for the production of polymers/fabrics, carpets, foils and other multilayer structures). The graft copolymer itself can be used as an interlayer between incompatible polymers.

The following examples illustrate the invention.

Examples 1-4 This example illustrates the preparation of a graft copolymer in which a copolymer of methyl methacrylate and methacrylic acid is grafted onto a polypropylene backbone, where the grafted chains are 38% of the total graft copolymer. .6% and the grafted chains were supplied with a composition of methyl methacrylate (MMA)/
Methacrylic acid (MAA)/ethyl acrylate) (EA
) = 76/20/4. 294.6 parts of t were added to a glass kettle reactor equipped with mechanical stirring, nitrogen inlet, reflux condenser, monomer feed pump, and temperature measurement and control means.
- Butylbenzene and 50 parts of polypropylene homopolymer (melt flow rate = 4) were charged.

The system was evacuated and purged with nitrogen four times, then heated to 140° C. with stirring until the polypropylene was dissolved. 0.1
38 parts t-butyl perbenzoate, 60.8 parts methyl methacrylate, 16.0 parts methacrylic acid and 3
, 2 parts of ethyl acrylate was added via the monomer feed pump over a period of 1 hour.

After the monomer feed was complete, an additional 26 parts of t-butylbenzene was added to the reactor and the reaction continued at 140°C for an additional hour. The reaction mixture was cooled to room temperature and all the polymer precipitated. The solvent was removed by filtration and the polymer was dried under vacuum to remove solvent and monomer. 81.4
Seven parts of the graft copolymer (mixed with ungrafted polymer) were isolated. Unless otherwise specified, graft copolymers were used without further purification. This polymer is referred to as Example 1.

The polymer was extracted with xylene/ethanol to remove the soluble polymer corresponding to the grafted chains.

In a similar manner, graft copolymers with essentially the same backbone//graft chain ratio were made. However, MMA/MAA/EA-
90,25/ 5/4.75 (Example 2), MMA/
MAA/EA=85.5/10/4.5 (Example 3
) and MMA/MAA/EA=57/40/3 (Example 4). In all cases the molecular weight of the grafted chains is greater than 20,000. Molecular weight was determined using gel permeation chromatography using poly(methyl methacrylate) standards and the extract from Example 2 had a weight average molecular weight ff of 194,000.

Examples 5-8 These examples demonstrate that the graft copolymers improve the sag resistance of polypropylene while improving surface gloss and surface energy. The formulation was made from polypropylene (same as Examples 1-4) and the graft copolymer of Example 1. Example 5 contains unmodified polypropylene, Example 6 contains 2.5% of the graft copolymer of Example 1 (acid content of the formulation ff1 = 0.19% by weight), and Example 7 contains the graft copolymer of Example 1. Contains 5% graft copolymer (formed metal ff of oriented material)
1=0.39% by weight), Example 8 contained 7.5% of the graft copolymer of Example 1 (acid content of the formulation ff1=0.
58%).

The formulations were made by mixing on a two roll mill at 195°C. They were then compression molded in a carver press in a 241 part m x 241 mm x 3.18 mm mold at 210°C under a pressure of about 6800 kg.

As a measure of sag resistance at elevated temperatures, the sag slope was measured as follows.

The sheet was secured in a frame with a 7.6 cm square opening. Metal objects were attached to the front and back of the frame to measure sag. The frame and sheet were placed in a hot forced air oven (typically 190°C). The amount of sag in the center of the sheet was then recorded as a function of time. "Slope" refers to the slope when plotted as the natural logarithm of droop (cm ) versus time, resulting in a straight line. A large slope indicates that the material is sagging quickly, and a small slope indicates that the material is sagging slowly.

The formulations of Examples 6-8 exhibited better sag resistance than the unmodified control Example 5. However, it is not as effective at reducing sag as graft copolymers made without MAA at higher temperatures.

The gloss of the molded product was visually evaluated. The control (Example 5) had a matte surface. The sample from Example 6 was slightly shiny and the samples from Examples 7 and 8 were shiny.

The energy required to mark the surface was measured. A higher number means greater polarity and more ink retention is expected. The test is ASTM D-2578-84r
This is a modification of the "Standard Test Method for Wet Tension of Polyethylene and Polypropylene Films". A series of liquids of various surface tensions are just wetted on the surface (the continuous film is
Apply to the surface until the mixture is found (determined by holding for seconds or more). The liquid used is Sherm.
an Treaters (North America)
) Inc. (Ontario, Canada) as Sherman Inks, a series of defined surface tension inks. ASTM testing states that 35 dynes/cm or higher is not a completely acceptable measure of ink, coating or adhesive adhesion. A value of 35 dynes/cm has been found to be generally predictive of adhesion to polyethylene. A correlation has not yet been established for polypropylene.

In Example 5, it was 34 dynes/am, in Example 6, 38 dynes/cm, in Example 7, 86 dynes/am, and in Example 8, 38 dynes/cm. All modified samples containing acid-containing graft copolymers showed higher surface energy values. However, surprisingly, increasing the acid content does not increase the value.

Examples 9-10 The polymer of Example 4 was blended in an amount of 10% with pellets of polypropylene matrix polymer.

Both were pre-dried. The formulations were extruded in a 25.4 mm Killon single screw extruder equipped with a 50.8 mm wide extrusion die and extruder and die assembly set temperatures of 210° C. to 1.2 to 1.3 mm thickness. extruded strips. This formulation is designated as Example 9.

The acid content was approximately 1.54% by weight. A matrix polypropylene homopolymer (melt flow rate = 4) was also extruded as Example 10 (control).

A 25.4 mm Killion extruder was used with an L-32 screw and a screw speed of 3 Orpm. A 50.8 mm die was used to make the extrudates. The extrudate was cut into pieces and air dried. The set temperature through the extruder and die assembly was 410°F.

Surface energy measurements were made on the extruded strips. Example 9 measured 36 dynes/cm vs. Example 1.0 (control) 32 dynes/cm
there were. On the surface of Example 9, ESCA measurements of the sample detected 1.7% oxygen, and for Example 10 it was 1.1%. Control values are unexpectedly high.

For unknown reasons, when the extruded sheets were granulated, dried, and compression molded into specimens as in Examples 5-8, the contact angle due to surface energy or surface warming was different from the control. There wasn't.

Examples 11-14 In this example, graft copolymers blended with ungrafted polypropylene were measured directly. Polypropylene homopolymer (
Melt flow rate-4) Hegel rafted. The polymer was dried and then compression molded at 210°C into 5 mil thick pieces. Table 1 summarizes the results. Example 14 showed strong adhesion to the metal caul plate after compression molding.

A decrease in contact angle indicates improved surface wetting. The test is,
ASTM D 724-45r Standard Test Method for Surface Warming of Paper (Contact Angle Method)". The wetting substances were water and methylene iodide (CH2I2).

Rame heart (Rame”~) to measure the contact angle.
Hart) goniometer was used.

Table 1 Contact angle (degrees) Example Acid in graft Surface energy Water Iodide (%) (dyne/am) Methylene 1
1...(control) 36 9
L, 6 54.512 L, 9
48 90.5 53J13 3.
9 >50 89.3 49.31
4 7.8 >50 Example 15 This example shows that acid groups can be introduced into a graft copolymer of methacrylate ester onto ethylene-propylene rubber and that the resulting graft has a high molecular weight. Grafts to DuPont ethylene-propylene-diene elastomer (Nordel 2722) were made at 150° C. by the solution polymerization method detailed in U.S. Pat.

Methyl methacrylate 90% 7/Ethyl acrylate 5
%/5% methacrylic acid mixture was polymerized. The radical flux was 0.0015 equivalent rad/fl/min.

When the polymer was separated by evaporation and analyzed, 56
% elastomer and 44% acrylic terpolymer. According to extraction with acetone, the mixture should contain 9% grafted acrylic terpolymer.

The ungrafted acrylic terpolymer is 127.
It was found to have a weight average molecular weight of 0.000. A blend of 20 parts of ungrafted polymer and 80 parts of methyl methacrylate commercial molding powder was found to have a notched Izo impact strength approximately twice that of the unmodified molded article.

Claims (1)

Claims: 1. A method of improving adhesion to a polyolefin surface comprising: (a) (i) a polyolefin backbone; and (ii) at least 60% by weight of a lower alkyl methacrylate and about 5-40% by weight of a copolymer. (b) blending from about 2 to about 10 weight percent of a graft copolymer comprising one or more grafted chains of a polymer derived from a polymerizable unsaturated acid with a polyolefin matrix; (b) applying the resulting mixture to a film; (c) Processing the film, sheet or molded product into a sheet or molded product;
Applying a second material consisting of a coating, an ink, an adhesive, or a film or paper coated with an adhesive, such that the adhesion between the processed mixture and the second material is the graft copolymer. A method where the adhesion between the polyolefin and the second substance is made greater than none. 2. The polyolefin matrix is polypropylene, polyethylene, or a copolymer of propylene and ethylene, the polyolefin backbone is polypropylene, and the lower alkyl methacrylate is methyl methacrylate;
2. The method of claim 1, wherein the copolymerizable unsaturated acid is methacrylic acid and the grafted chain or chains have a weight average molecular weight of at least about 20,000. 3. (a) a polyolefin matrix; (b) a (i) polyolefin backbone; and (ii) a polymer derived from at least 60% by weight lower alkyl methacrylate and about 5-40% by weight copolymerizable unsaturated acid. A composite in the form of a film, sheet or molded article comprising from about 2 to about 10% by weight of a graft copolymer comprising one or more grafted chains of. 4. The sheet, film or molded article further comprises a continuous layer of film or paper coated with paint, coating, ink, adhesive or adhesive on at least a portion of the surface of the sheet, film or molded article. Compounds described. 5. The polyolefin matrix is polypropylene, polyethylene, or a copolymer of propylene and ethylene, the polyolefin backbone is polypropylene, and the lower alkyl methacrylate is methyl methacrylate;
5. A composite according to claim 3 or 4, wherein the copolymerizable unsaturated acid is methacrylic acid and the grafted chain or chains have a weight average molecular weight of at least about 20,000. 6. The composite of claim 4, wherein the adhesion between the continuous layer and the surface is greater than the adhesion between the polyolefin matrix and the continuous layer without the graft copolymer. 7. A method of making a polyolefin composition capable of exhibiting improved adhesion to inks, coatings and adhesives, comprising: (a) (i) a polyolefin backbone; and (ii) at least 60% by weight of a lower alkyl methacrylate and from about 5 to (b) mixing from about 2 to about 10 weight percent of a graft copolymer comprising one or more grafted chains of a polymer derived from a copolymerizable unsaturated acid with a polyolefin matrix; A method comprising processing the mixture into a film, sheet or molded article. 8. The polyolefin matrix is polypropylene, the polyolefin backbone is polypropylene, the lower alkyl methacrylate is methyl methacrylate,
8. The method of claim 7, wherein the copolymerizable unsaturated acid is methacrylic acid and the processing of the mixture is by melt extrusion. 9. (a) Polyethylene, polypropylene, polybutylene, poly(4-methylpentene), a copolymer of the above olefins, and the above olefin and a small amount of 1-alkene, vinyl ester, vinyl chloride, acrylic ester, methacrylic ester, acrylic a non-polar polyolefin backbone selected from the group consisting of one or more copolymers with acid and methacrylic acid; (b) covalently grafted onto the backbone, the weight ratio with the backbone being from about 1:9 to at least one methacrylate chain in a ratio of about 4:1 and at least about 6
0% to about 80% by weight of the formula CH_2=C(CH_3)
COOR (R is alkyl, aryl, substituted alkyl, substituted aryl or substituted alkaryl) methacrylic ester monomer and from about 20 to about 40% by weight of a copolymerizable unsaturated acid; ~200,0
A graft copolymer containing methacrylate chains with a molecular weight of 0.00. 10. The graft copolymer of claim 9, wherein the backbone polymer is polypropylene, R is methyl, and the weight ratio is from about 3:2 to about 2:3.