JP7809918B2 - Thermoplastic resin pellets, easily peelable adhesives, laminates, and container lid materials - Google Patents

Description

The present invention relates to thermoplastic resin pellets that are easily peelable from components such as containers that have polyethylene as their adhesive surface, an easily peelable adhesive, a laminate, and a lid material made from the same.

In recent years, there has been a noticeable trend toward placing greater importance on environmental adaptability and hygiene when it comes to food containers, and containers made from polyvinyl chloride, which emits harmful gases when burned, and polystyrene, which is suspected of having adverse health effects from leaching, are being replaced by containers made from polyethylene and polypropylene.

In particular, the use of paper containers laminated with polyethylene has increased significantly, such as cup-shaped yogurt containers, instant ramen containers, and confectionery containers, made by extrusion-laminating polyethylene onto paper.

The above-mentioned containers require lids that can be handled safely during transport without breaking, and that are easily peelable so that even women and children can open them.

For this reason, the above-mentioned easily peelable lid material has a layer (sealing layer) on the outermost layer that comes into contact with the polyethylene surface of the container and heat seals it, and an easily peelable adhesive with a specific composition is used for the sealing layer.

Examples of easily peelable adhesives include: 1) a composition in which a resin that is generally poorly adhesive to polyethylene (e.g., polypropylene) is mixed with a resin that can bond to polyethylene (e.g., polyethylene, ethylene-vinyl acetate copolymer, etc.); 2) a so-called hot melt composition in which a tackifier and low-molecular-weight wax are mixed with an ethylene-vinyl acetate copolymer; 3) a high-molecular-weight hot melt composition that makes the above hot melt type extrudable; 4) a composition in which low-density polyethylene is blended with high-molecular-weight polybutene (see, for example, Patent Document 1); 5) an easily peelable adhesive for polyethylene consisting of a polyethylene-based resin, a crystalline polybutene resin, and a low-molecular-weight wax (see, for example, Patent Document 2); and 6) an easily peelable adhesive for polyethylene consisting of a polyethylene-based resin, a crystalline polypropylene-based resin, and a low-molecular-weight polyethylene wax (see, for example, Patent Document 3).

Japanese Patent Application Publication No. 1-315443 Japanese Patent Application Laid-Open No. 2003-129018 Japanese Patent Application Laid-Open No. 2007-112955

However, when polyethylene resin is dry-blended with polypropylene or polybutene resin pellets, cracks can occur in the molten film during molding, or thickness accuracy can be poor, resulting in areas with low adhesive strength, resulting in poor peelability. On the other hand, when pellets obtained by pre-melting polyethylene resin with polypropylene or polybutene resin pellets are used, molding processability is improved, but the peeled surface tends to become stringy when opened, resulting in a poor peel appearance. As a result, it has been difficult to achieve high opening strength while maintaining excellent molding processability and a good opened appearance.

As a result of extensive research to solve the above problems, the inventors discovered that thermoplastic resin pellets with a specific phase structure have excellent moldability, and when the sealing layer is made thin, they exhibit high tear strength, resulting in good sealing properties and an excellent appearance on the peel surface, leading to the present invention.

That is, the present invention relates to the following [1] to [11].
[1] A thermoplastic resin pellet comprising a thermoplastic resin (E) and a thermoplastic resin (F) incompatible with the thermoplastic resin (E), wherein the thermoplastic resin pellet has a cut surface, when the pellet is cut parallel to the flow direction in which the pellet is extruded from a die, in which the thermoplastic resin (E) forms a matrix phase, the thermoplastic resin (F) is dispersed in the matrix phase to form domain phases, the domain phases have an average major axis in the range of 5 μm or more and 20 μm or less, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) is in the range of 3 or more and 15 or less.
[2] The thermoplastic resin pellet according to [1], characterized in that the thermoplastic resin (E) is a polyethylene-based resin, and the thermoplastic resin (F) is at least one selected from the group consisting of crystalline polybutene resin, crystalline polypropylene, crystalline ethylene-propylene copolymer, and crystalline ethylene-propylene-butene-1 copolymer.
[3] Thermoplastic resin pellets according to [1] or [2], characterized in that they contain 60 to 90 parts by weight of thermoplastic resin (E) and 10 to 40 parts by weight of thermoplastic resin (F) (the total of (E) and (F) is 100 parts by weight).
[4] An easily peelable adhesive comprising the thermoplastic resin pellets according to any one of [1] to [3].
[5] The method for producing thermoplastic resin pellets according to any one of [1] to [3], characterized in that the thermoplastic resin (E) and the thermoplastic resin (F) are mixed, melt-kneaded, and then produced using a granulation facility selected from the group consisting of an underwater cut facility, a strand cut facility, and a hot cut facility.
[6] A laminate comprising a sealing layer (A) / an intermediate layer (B) / a substrate (C) laminated in this order, and the sealing layer (A) is made of the easily peelable adhesive described in [4].
[7] The laminate according to [6], wherein the intermediate layer (B) is made of a polyethylene-based resin (D) having a melt mass-flow rate of 0.3 g/10 min or more and less than 200 g/10 min, the ratio of the thickness of the seal layer (A) to the sum of the thicknesses of the seal layer (A) and the intermediate layer (B) is 5% or more and less than 50%, and the thickness of the seal layer (A) is 1 μm or more and less than 20 μm.
[8] The laminate according to [6] or [7], wherein the polyethylene resin (D) constituting the intermediate layer (B) satisfies the following requirement (a):
(a) The swell ratio (SR) calculated by dividing the diameter (D) of a strand extruded at a temperature of 235°C and an extrusion rate of 3 g/min using a melt indexer used in JIS K 7210 by the orifice diameter (D0) of the melt indexer is 1.7 or more and 3.0 or less.
[9] The laminate according to any one of [6] to [8], wherein the polyethylene resin (D) constituting the intermediate layer (B) is a low-density polyethylene.
[10] The laminate according to any one of [6] to [9], wherein the polyethylene resin (D) constituting the intermediate layer (B) is an ethylene-α-olefin copolymer.
[11] A container lid material comprising the laminate according to any one of [6] to [10].

The thermoplastic resin pellets of the present invention have excellent moldability and maintain excellent processability, especially when the sealing layer is made thin. They also have excellent sealing properties for adherends with polyethylene adhesive surfaces, and the appearance of the peeled surface is also excellent. Therefore, they are useful as easy-peel adhesives and as packaging materials for containers with polyethylene adhesive surfaces, and are particularly ideal as lid materials for containers with polyethylene adhesive surfaces.

The present invention is described in detail below.

One embodiment of the thermoplastic resin pellets of the present invention are thermoplastic resin pellets containing a thermoplastic resin (E) and a thermoplastic resin (F) that is incompatible with the thermoplastic resin (E). When the pellets are cut parallel to the flow direction extruded from a die, the thermoplastic resin (E) forms a matrix phase, and the thermoplastic resin (F) is dispersed in the matrix phase to form a domain phase. The domain phases have an average major axis in the range of 5 μm to 20 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) is in the range of 3 to 15.

There are no particular restrictions on the thermoplastic resin (E), and examples include polyethylene resins, polypropylene resins, ethylene-α-olefin copolymers, acid-modified versions of these olefin resins, ethylene-vinyl acetate copolymers, ethylene-α,β-unsaturated carboxylic acids, or esters thereof. Among these, polyethylene resins are preferred when the adherend side is polyethylene, and polypropylene resins, ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-α,β-unsaturated carboxylic acids, or esters thereof when the adherend side is polypropylene. In particular, when the adherend side is polyethylene, low-density polyethylene is preferred among polyethylene resins in terms of extrusion lamination processability.

The melt mass flow rate of thermoplastic resin (E), measured in accordance with JIS K6922-1, is not particularly limited, but is preferably 10 to 200 g/10 min.

There are no particular restrictions on the thermoplastic resin (F) that is incompatible with the thermoplastic resin (E), and examples include crystalline polybutene resin, crystalline polypropylene, crystalline ethylene-propylene copolymer, crystalline ethylene-propylene-butene-1 copolymer, and saponified ethylene-vinyl acetate copolymer. Among these, when the thermoplastic resin (E) is a polyethylene-based resin, crystalline polybutene resin, crystalline polypropylene, crystalline ethylene-propylene copolymer, and crystalline ethylene-propylene-butene-1 copolymer are preferred.

Furthermore, from the standpoint of moldability, it is preferable that the thermoplastic resin (F) that is incompatible with the thermoplastic resin (E) has a melting point of 150°C or less.

The melt mass flow rate of the thermoplastic resin (E) and the incompatible thermoplastic resin (F), measured in accordance with JIS K7210, is not particularly limited, but is preferably 1 to 30 g/10 min, and particularly preferably 0.5 to 10 g/10 min.

There are no particular restrictions on the blending ratio of thermoplastic resin (E) and incompatible thermoplastic resin (F), but a ratio of 60 to 90 parts by weight of thermoplastic resin (E) to 10 to 40 parts by weight of incompatible thermoplastic resin (F) (the total of (E) and (F) is 100 parts by weight) is preferred, as this will result in good easy-open properties and good moldability.

A low-molecular-weight polyethylene wax (G) may be blended into the mixture of thermoplastic resin (E) and thermoplastic resin (F) that is incompatible with thermoplastic resin (E). The low-molecular-weight polyethylene wax (G) preferably has a number-average molecular weight of 1,000 to 10,000 as measured by GPC.

There are no particular restrictions on the blending ratio of low-molecular-weight polyethylene wax (G), but blending 3 to 20 parts by weight of low-molecular-weight polyethylene wax (G) per 100 parts by weight of the total of thermoplastic resin (E) and incompatible thermoplastic resin (F) is preferred, as this improves moldability and peel appearance.

In one embodiment of the thermoplastic resin pellet of the present invention, when the pellet is cut, the thermoplastic resin (E) forms a matrix phase, and the thermoplastic resin (F) is dispersed in the matrix phase to form a domain phase. The domain phase has an average major axis in the range of 5 μm to 20 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) is in the range of 3 to 15.

These thermoplastic resin pellets have a so-called sea-island structure, in which the thermoplastic resin (E) forms the sea portion (matrix) and the thermoplastic resin (F) forms the island portion (domain), and flat-shaped domains made of the thermoplastic resin (F) are dispersed.

In the present invention, the domain average major axis is the average major axis of the elliptical domains that appear on the cross section when a thermoplastic resin pellet is cut near the center. The domain average major axis is in the range of 5 μm to 20 μm, and is preferably 6 μm to 15 μm, more preferably 6 μm to 12 μm, since this improves the opening strength and peel appearance.

In the present invention, the ratio of the domain major axis to the domain minor axis is determined by cutting a thermoplastic resin pellet near its center, and measuring the major axis of the elliptical domain that appears on the cross section, and the length in the width direction perpendicular to the major axis of the elliptical domain, from the minor axis. The ratio of the domain major axis to the domain minor axis (major axis/minor axis) is in the range of 3 to 15 μm, and since this improves the peel appearance, it is more preferably 3 to 12, and even more preferably 3 to 10.

The thermoplastic resin pellets, which are one embodiment of the present invention, may be produced by any method, but are preferably produced by melt-kneading a mixture of thermoplastic resin (E) and thermoplastic resin (F) that is incompatible with thermoplastic resin (E) using granulation equipment such as underwater cutting equipment, strand cutting equipment, or hot cutting equipment.

The above thermoplastic resin pellets are used as an easily peelable adhesive and as a sealing layer for laminates.

One embodiment of the laminate of the present invention comprises a sealing layer (A), an intermediate layer (B), and a substrate (C) laminated in this order, with the sealing layer (A) comprising the above-described easily peelable adhesive.

The intermediate layer (B) is preferably made of a polyethylene resin (D) having an MFR of 0.3 g/10 min or more and less than 200 g/10 min, as measured in accordance with JIS K6922-1.

If the MFR of the polyethylene resin (D) is less than 0.3 g/10 min, the extrusion load during extrusion lamination will be large, resulting in poor processability and low tear strength when the laminate is heat-sealed and peeled off, which is undesirable. Furthermore, if the MFR is 200 g/10 min or more, the melt tension during melting will be insufficient, making stable molding and processing difficult, which is also undesirable.

There are no particular restrictions on the polyethylene resin (D) other than the MFR, and examples include linear polyethylenes such as high-density polyethylene and ethylene-α-olefin copolymers, low-density polyethylene, ethylene-vinyl acetate copolymers, and ethylene-unsaturated carboxylic acid copolymers. Low-density polyethylene or ethylene-α-olefin copolymers are particularly preferred. Among ethylene-α-olefin copolymers, copolymers of ethylene and an α-olefin having 3 to 8 carbon atoms are more preferred, and copolymers of ethylene and 1-butene are most preferred. Two or more of these resins may be mixed and used. Two or more of the same resins with different physical properties such as MFR may also be mixed and used.

Furthermore, the polyethylene resin (D) preferably has a swell ratio (SR) of 1.7 or more and 3.0 or less, and more preferably 1.7 or more and 2.5 or less. Using a resin with an SR within this range for the intermediate layer (B) improves moldability during extrusion lamination and also reduces appearance defects such as stringiness at the peeled surface when the laminate is heat-sealed and peeled off, which is preferable.

The SR can be measured using a melt indexer as specified in JIS K 7210, by dividing the diameter (D) of the strand extruded at a temperature of 235°C and an extrusion rate of 3 g/min by the orifice diameter (D0) of the melt indexer.

Additives typically compounded in polyolefin resins, such as antioxidants, lubricants, antistatic agents, antifogging agents, and antiblocking agents, can be added to the sealing layer (A) and intermediate layer (B) that make up the laminate of the present invention in the required amounts as long as they do not impair the performance of the laminate of the present invention.

In the laminate of the present invention, the ratio of the thickness of the sealing layer (A) to the sum of the thicknesses of the sealing layer (A) and the intermediate layer (B) is 5% or more and less than 50%, and preferably 5% or more and 40% or less.

When the ratio of the thickness of the sealing layer (A) to the sum of the thicknesses of the sealing layer (A) and the intermediate layer (B) is 5% or more, the extrusion rates of the sealing layer (A) and the intermediate layer (B) are well balanced when they are co-extrusion laminated, enabling stable molding processing. It is not preferable for the thickness of the sealing layer (A) to be less than 50%, because the distance over which the sealing layer (A) breaks when the laminate is heat-sealed and peeled is not too long, making it less likely to cause poor appearance upon peeling, such as stringiness.

There are no particular restrictions on the thickness of the sealing layer (A), but to prevent peeling and other peeling defects in appearance, it is preferably 1 μm or more and less than 20 μm, and more preferably 1 μm or more and 15 μm or less.

There are no particular restrictions on the substrate (C) that constitutes the laminate, which is one embodiment of the present invention, and materials that are generally used as substrates for lid materials can be used. Examples of substrate (C) include stretched or unstretched films such as polyester film, polyamide film, and polypropylene film, as well as aluminum foil.

The outside of the substrate (C) can be further laminated with one or more layers of polyolefin film, polyester film, polyamide film, saponified ethylene-vinyl acetate copolymer film, paper, etc.

There are no particular limitations on the method for laminating the sealing layer (A) and intermediate layer (B) to the substrate (C). Examples include a method in which the sealing layer (A) and intermediate layer (B) are each formed into a single-layer film by cast molding or inflation molding, and then sequentially laminated by dry lamination; a method in which the single-layer film sealing layer (A) and substrate (C) are sandwich-laminated with the resin of the intermediate layer (B); a method in which the substrate (C) and intermediate layer (B) are extrusion-laminated, and then the sealing layer (A) is tandem-laminated; and a method in which the sealing layer (A) and intermediate layer (B) are co-extrusion-laminated to the substrate (C). Among these, the method of co-extrusion laminating the sealing layer (A) and intermediate layer (B) to the substrate (C) is preferred because it provides good adhesion between the layers and is economically advantageous.

When laminating by extrusion lamination, an anchor coating agent may be applied in advance to a substrate such as a plastic film (e.g., polyester film or polyamide film), paper, or aluminum foil. It is also preferable to perform ozone treatment during processing to laminate with various plastic films, aluminum foil, etc.

The laminate of the present invention can be used, for example, as a lid, more preferably as a lid for polyethylene containers. The object to which the laminate is adhered needs only to have at least a polyethylene surface, and may be a container or sheet that uses a barrier packaging material such as vinylidene chloride, ethylene-vinyl alcohol copolymer, or aluminum in its construction.

Examples of objects to which the laminate can be bonded include laminated containers obtained by cartoning a structure in which low-density polyethylene is laminated onto paperboard, and more specifically, paper cups for yogurt or instant ramen, etc.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. Unless otherwise specified, the reagents used were commercially available products. The measurement methods used in the examples are described below.

~Melt Mass Flow Rate (MFR)~
The MFR of each material used was measured in accordance with JIS K6922-1.

~Swell ratio (SR)~
The SR of each material used was measured using a melt indexer specified in JIS K 7210, by dividing the diameter (D) of the strand extruded at a temperature of 235°C and an extrusion rate of 3 g/min by the orifice diameter (D0) of the melt indexer.

Example 1
In the thermoplastic resin constituting the seal layer (A), the thermoplastic resin (E) was a low-density polyethylene having an MFR of 58 g/10 min (manufactured by Tosoh Corporation, trade name Petrothene 248), and the thermoplastic resin (F) was a crystalline polypropylene having an MFR of 7 g/10 min (manufactured by Japan Polypropylene Corporation, trade name Novatec PP FW4BAT, melting point 138 ° C.), and the blending ratio of the two was 65/35 by weight. The mixture of thermoplastic resin (E) and thermoplastic resin (F) was melt-kneaded using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd., TEX25α-III), a screw configuration with a weak kneading specification with one kneading section, a processing temperature of 180 ° C., and an extrusion rate of 20 kg/h. After melt-kneading, underwater cutting (UWC) equipment was used to obtain thermoplastic resin pellets, which are the thermoplastic resins of the mixture. When the obtained thermoplastic resin pellet was cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 6 μm, and the ratio of the major axis to the minor axis (major axis/minor axis) was 4.

A film prepared by dry laminating a 12 μm-thick polyester film (PET) and 7 μm-thick aluminum foil was used as the substrate (C). An isocyanate-based anchor coating agent (a 3/1 mixture of Takelac A-3210 and Takenate A-3072, both manufactured by Mitsui Chemicals, Inc.) was applied to the aluminum foil side of the substrate (C). The intermediate layer (B) and sealing layer (A) were then co-extrusion laminated using a 90 mm/65 mm co-extrusion laminator at a processing speed of 120 m/min in the order substrate (C)/intermediate layer (B)/sealing layer (A), yielding a laminate.

The intermediate layer (B) was made of a polyethylene resin (D) containing a low-density polyethylene (Petrothene 209, manufactured by Tosoh Corporation) having a density of 924 kg/ ^m3 and an MFR of 45 g/10 min and a low-density polyethylene (Petrothene 360, manufactured by Tosoh Corporation) having a density of 919 kg/m3 and an MFR of 1.6 g/10 min (MFR: 17 g/10 min, SR: 1.81). The temperature inside the extruder cylinder was 340°C, and the layer thickness was 25 μm.

The resulting thermoplastic resin pellets were used to process the sealing layer (A) under the following conditions: extruder cylinder temperature: 280°C, die temperature: 335°C, layer thickness: 15 μm.

The moldability of the obtained easily peelable resin pellets was assessed by visual inspection for film cracks. The results were rated as ◯ (no film cracks or holes) or × (film cracks or holes). The thickness of the laminate was also measured to confirm the thickness precision of the sealing layer. The results were rated as ◯ (deviation of 2 μm or less), △ (greater than 2 and less than 5 μm), or × (5 μm or more). The width of the molten film of the laminate was also measured to confirm the neck-in width. The results were rated as ◯ (50 mm or less), △ (greater than 50 and less than 80 mm), or × (80 mm or more). In all cases, the evaluation results of ◯ and △ were considered good.

This laminate was used as a lid for the opening of a paper cup container (flange outer diameter 100 mm) with a 30 μm thick low-density polyethylene laminated to the inner surface, and was heat-sealed using an overlap heat-sealing machine (manufactured by Sunny Pack Co., Ltd.) so that the adhesive surfaces of the structure were in contact. The heat-sealing conditions were a temperature of 170°C, a pressure of 4.0 MPa/cup, and a time of 0.8 seconds.

After cooling to room temperature, the laminate of the present invention was peeled off from the paper cup container at a 90-degree angle using a tensile tester (Tensilon RTE-1210, manufactured by Orientec Co., Ltd.) and the strength of the force required for peeling was measured. The pulling speed was 300 mm/min. The force required for peeling peaked immediately after opening began, and the strength at this peak was taken as the opening strength.

In addition, the peeled surface of the paper cup container after peeling the laminate was inspected visually to determine the degree of stringiness (peeling appearance). The results were evaluated on a three-point scale: ○ (almost no stringiness, good appearance), △ (a small amount of stringiness), and × (a large amount of stringiness, poor appearance). Observation results of ○ and △ were judged to be good.

Table 1 shows the results of measurements of film cracking, thickness accuracy, and necking to assess molding processability, and of opening strength and peel appearance to assess adhesive properties.

Example 2
Thermoplastic resin pellets and laminates were prepared in the same manner as in Example 1, except that the processing temperature was 200°C instead of 180°C in the same thermoplastic resin pellet preparation method as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains that appeared on the cut surface was 10 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 3. The results are shown in Table 1.

Example 3
In the same thermoplastic resin pellet production method as in Example 1, a screw configuration with medium mixing specifications with two kneading sections was used instead of a screw configuration with weak mixing specifications with one kneading section, and a processing temperature of 200 ° C instead of 180 ° C. Thermoplastic resin pellets and laminates were produced in the same manner as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 6 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 9. The results are shown in Table 1.

Example 4
Thermoplastic resin pellets and laminates were prepared in the same manner as in Example 1, except that the processing temperature was 200°C instead of 180°C and strand cutting equipment was used instead of underwater cutting equipment, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were carried out. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 10 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 10. The results are shown in Table 1.

Example 5
Thermoplastic resin pellets and laminates were prepared in the same manner as in Example 4, except that the blending ratio of thermoplastic resin (E) and thermoplastic resin (F) was 80/20 by weight instead of 65/35 by weight, and the molding processability, opening strength, and opening appearance were evaluated. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 10 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 10. The results are shown in Table 1.

Example 6
Thermoplastic resin pellets and a laminate were prepared in the same manner as in Example 2, except that the thickness of the intermediate layer (B) was 32 μm instead of 25 μm and the thickness of the seal layer (A) was 8 μm instead of 15 μm, and evaluation of moldability, measurement of opening strength, and evaluation of opening appearance were carried out. The results are shown in Table 1.

Comparative Example 1
In the same thermoplastic resin pellet production method as in Example 1, except that a screw configuration with medium mixing specifications having two kneading sections was used instead of a screw configuration with weak mixing specifications having one kneading section, thermoplastic resin pellets and laminates were produced in the same manner as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 4 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 2. The results are shown in Table 2.

The resulting laminate had a lot of stringiness on the peeled surface, and the appearance after opening was poor.

Comparative Example 2
In the same thermoplastic resin pellet production method as in Example 1, except that a screw configuration with medium mixing specifications having two kneading sections was used instead of a screw configuration with weak mixing specifications having one kneading section, and a strand cutter was used instead of an underwater cutter, thermoplastic resin pellets and laminates were produced in the same manner as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 4 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 4. The results are shown in Table 2.

The resulting laminate had a lot of stringiness on the peeled surface, and the appearance after opening was poor.

Comparative Example 3
In the same thermoplastic resin pellet production method as in Example 1, except that a screw configuration with strong kneading specifications having three kneading sections was used instead of a screw configuration with weak kneading specifications having one kneading section, thermoplastic resin pellets and laminates were produced in the same manner as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 2 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 18. The results are shown in Table 2.

The resulting laminate had low tear strength, significant stringiness on the peel surface, and a poor appearance after opening.

Comparative Example 4
Thermoplastic resin pellets and laminates were prepared in the same manner as in Example 4, except that a screw configuration with strong mixing specifications and three kneading sections was used instead of a screw configuration with weak mixing specifications and two kneading sections, and evaluations of molding processability, opening strength, and opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains appearing on the cut surface was 15 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 18. The results are shown in Table 2.

The resulting laminate had a lot of stringiness on the peeled surface, and the appearance after opening was poor.

Comparative Example 5
In the same thermoplastic resin pellet production method as in Example 4, a single-screw extruder (PDA40, manufactured by Placo Co., Ltd.) was used instead of a twin-screw extruder, and a screw configuration with a strong kneading specification with one kneading section was used. Thermoplastic resin pellets and a laminate were produced in the same manner as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction of extrusion from the die, the average major axis of the elliptical domains appearing on the cut surface was 25 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 10. The results are shown in Table 2.

The resulting laminate had low tear strength, significant stringiness on the peel surface, and a poor appearance after opening.

Comparative Example 6
Thermoplastic resin pellets and laminates were prepared in the same manner as in Example 1, except that the processing temperature was 250°C instead of 180°C in the same thermoplastic resin pellet preparation method as in Example 1, and evaluation of molding processability, measurement of opening strength, and evaluation of opening appearance were performed. When the obtained easily peelable adhesive pellets were cut near the center parallel to the flow direction, the average major axis of the elliptical domains that appeared on the cut surface was 30 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) was 12. The results are shown in Table 2.

The resulting easily peelable adhesive pellets suffered from film cracking during molding, resulting in poor molding processability, making it impossible to obtain a laminate for adhesive evaluation.

Claims (11)

A thermoplastic resin pellet comprising a thermoplastic resin (E) and a thermoplastic resin (F) incompatible with the thermoplastic resin (E), wherein the thermoplastic resin (E) is a polyethylene-based resin, and the thermoplastic resin (F) is at least one selected from the group consisting of crystalline polybutene resin, crystalline polypropylene, crystalline ethylene-propylene copolymer, and crystalline ethylene-propylene-butene-1 copolymer; the thermoplastic resin pellet comprises 60 to 90 parts by weight of the thermoplastic resin (E) and 10 to 40 parts by weight of the thermoplastic resin (F) (the total of (E) and (F) is 100 parts by weight) ; the thermoplastic resin pellet is characterized in that, when the pellet is cut parallel to the flow direction in which it is extruded from a die, the thermoplastic resin (E) forms a matrix phase, and the thermoplastic resin (F) is dispersed in the matrix phase to form domain phases, the domain phases have an average major axis in the range of 5 μm to 20 μm, and the ratio of the domain major axis to the domain minor axis (major axis/minor axis) is in the range of 3 to 15 . 2. The thermoplastic resin pellet according to claim 1, wherein the thermoplastic resin (E) is a low-density polyethylene. 3. The thermoplastic resin pellet according to claim 1, wherein the thermoplastic resin (F) is a crystalline polypropylene. An easily peelable adhesive comprising the thermoplastic resin pellets described in any one of claims 1 to 3. A method for producing thermoplastic resin pellets according to any one of claims 1 to 3, characterized in that the thermoplastic resin (E) and the thermoplastic resin (F) are mixed, melt-kneaded, and then produced using pelletizing equipment selected from the group consisting of underwater cutting equipment, strand cutting equipment, and hot cutting equipment. A laminate comprising a sealing layer (A), an intermediate layer (B), and a substrate (C) laminated in this order, wherein the sealing layer (A) is made of the easily peelable adhesive described in claim 4. The laminate described in claim 6, characterized in that the intermediate layer (B) is made of a polyethylene-based resin (D) having a melt mass-flow rate of 0.3 g/10 min or more and less than 200 g/10 min, the ratio of the thickness of the sealing layer (A) to the sum of the thicknesses of the sealing layer (A) and the intermediate layer (B) is 5% or more and less than 50%, and the thickness of the sealing layer (A) is 1 μm or more and less than 20 μm. 8. The laminate according to claim 6, wherein the polyethylene resin (D) constituting the intermediate layer (B) satisfies the following requirement (a):
(a) The swell ratio (SR) calculated by dividing the diameter (D) of a strand extruded at a temperature of 235°C and an extrusion rate of 3 g/min using a melt indexer used in JIS K 7210 by the orifice diameter (D0) of the melt indexer is 1.7 or more and 3.0 or less. A laminate according to any one of claims 6 to 8, characterized in that the polyethylene resin (D) constituting the intermediate layer (B) is low-density polyethylene. A laminate according to any one of claims 6 to 9, characterized in that the polyethylene resin (D) constituting the intermediate layer (B) is an ethylene-α-olefin copolymer. A container lid comprising the laminate described in any one of claims 6 to 10.