JP5036988B2 - Resin composition for liner material used for injection molding of metal PP cap and metal PP cap with liner - Google Patents

Description

  The present invention relates to a resin composition for a liner material used for injection molding of a metal PP cap, particularly a resin composition for a liner material used for injection molding of a heat-resistant metal PP (pill fur proof) cap, and a metal PP with a liner using the same. More specifically, it is related to the cap. More specifically, after the contents are hot-filled and sealed, it can withstand retort sterilization at 130 ° C. for 30 minutes, and leakage caused by dropping during storage and handling is also eliminated. The present invention relates to a liner for a heat-resistant metal PP cap having good openability and a metal PP cap with the liner. PP is an abbreviation for “piper proof”, and once it is opened and opened, it is clear that it has been opened even if it is re-opened. It refers to the structure that reveals that the seal has been opened.

  A PP cap provided with an olefin resin liner on the inner surface of an aluminum alloy plate cap (hereinafter abbreviated as “aluminum cap”) is widely used as a container lid with excellent hygienic properties and sealing performance. However, when heat treatment such as heat sterilization after bottling is performed, leakage due to thermal deformation or thermal shrinkage is a problem.

  In order to solve this problem, Patent Document 1 discloses (i) a hydrogenated styrene / butadiene block copolymer, (ii) a liquid paraffin, and (iii) a propylene-based resin blend as a container lid liner. It is proposed to use.

  The blend of (i) hydrogenated styrene / butadiene block copolymer, (ii) liquid paraffin, and (iii) propylene-based resin is hot-filled at 95 ° C., and then heated with 90 ° C. hot water. Although it can withstand heat sterilization in the case of showering for a minute, it has been found that leakage still occurs quite frequently when retort sterilization at 130 ° C. for 30 minutes is required. The reason for this is not yet clear enough, but even if the hydrogenated styrene / butadiene block copolymer used is relatively excellent in heat resistance, it does not exhibit compression set or permanent elongation in the high temperature range of 130 ° C. described above. Since it is large, it is considered that a non-negligible thermal deformation or a thermal shrinkage occurs between the container mouth and the container lid, and a minute gap is generated in the sealed part.

  Further, in Patent Document 2, the polymer composition described in Patent Document 1 has a large range of the liquid paraffin compounding amount of 20 to 80% by weight, and when the liquid paraffin compounding amount is large, the resin composition molding process Although it has good properties, it may cause wax float (the oily substance that appears as liquid paraffin separates from the liner material and floats in the form of droplets or forms an oil film on the surface of the content liquid). If the amount is too small, there will be a problem in the formability, so a countermeasure is proposed.

In the invention described in Patent Document 2, a hydrogenated styrene / isoprene copolymer is used instead of the hydrogenated styrene / butadiene block copolymer described in Patent Document 1, and instead of the propylene-based resin described in Patent Document 1, Flow rate [230 ° C., 21.18 N (2.16 kgf) load] is 0.1 to 100 g / 10 min crystalline polypropylene resin or melt flow rate [190 ° C., 21.18 N (2.16 kgf) load] is 0 The solution is achieved by using together a polyethylene resin having a density of 1 to 50 g / 10 min and a density of 0.940 g / cm ³ or more.
Certainly, this method eliminates the problem of the wax float of Patent Document 1 and can sufficiently withstand a sterilization treatment for 3 minutes in a hot water shower at 90 ° C., but a liner using this resin composition is 125 ° C. And cannot be used for applications requiring sterilization conditions of 30 minutes. Further, there is an invention described in Patent Document 3 as an invention substantially the same as the invention described in Patent Document 2, but also in this invention, a liner that can withstand sterilization conditions at 130 ° C. for 30 minutes has not been obtained.

  In order to solve these problems, the present applicant previously disclosed in Patent Document 4 that the hydrogenated styrene / conjugated diene block copolymer in the invention of Patent Document 2 In order to give good extrudability to a resin composition containing a hydrogenated styrene / conjugated diene block copolymer that does not exhibit the fluidity and to selectively use those having the unique property of In addition to polypropylene resin, it has been found that the above problems can be solved at once by combining silicone oil and fine powder talc having an average particle size within a specific range. It was intended for production and was not intended for production of a liner by injection molding.

Japanese Patent Laid-Open No. 2-57569 JP-A-11-106565 JP-A-11-130910 JP 2005-133068 A

  The object of the present invention is particularly excellent in injection moldability, does not generate a wax float phenomenon, and has excellent heat resistance and impact resistance that the contents can withstand retort sterilization at 130 ° C. for 30 minutes. Leakage due to heat shrinkage is effectively eliminated, and metal that has sufficient flexibility and rubber elasticity to eliminate leakage due to dropping during storage and handling, and also has good openability when opening. It is an object to provide a resin composition for a liner material used for injection molding of a PP cap and a metal PP cap with a liner obtained by injection molding using the resin composition.

The first of the present invention is
(A) 30 to 40 hydrogenated styrene / isoprene elastomer having a melt flow rate (MFR) of 0 g / 10 min at 230 ° C. and a load of 21.18 N (2.16 kgf) (that is, it does not flow under these conditions) weight%
(B) 10-20% by weight of polypropylene resin
(C) 40-60% by weight of liquid paraffin
(D) A metal PP cap containing 3 to 15 parts by weight of a lubricant comprising (i) silicone oil and (ii) amide wax with respect to 100 parts by weight of the total amount of (a), (b) and (c). a liner material for a resin composition used in the injection molding, when the stress value after compressive stress relaxation index at 50% compression [30 minutes at the 125 ° C. B, the initial stress value was a, ( B ÷ a) is a value indicating with × 100] of Ri der 70 or more, the load at the 125 rupture time when the 50% elongation retention in ° C. is not less than 10 minutes, and the melt flow rate (230 ° C. Is a resin composition for a liner material used for injection molding of a metal PP cap, characterized in that it is 1 to 20 g / 10 min .
The second invention relates to a metal PP capped liner, wherein the La Inert consists liner material resin composition of claim 1, wherein.

The hydrogenated styrene / isoprene elastomer (a) used in the present invention is a hydrogenated product of a styrene / isoprene copolymer, preferably a styrene / isoprene block copolymer, and is hydrogenated in an inert solvent. It can be obtained by a known method such as hydrogenation in the presence of a catalyst. The hydrogenation rate is preferably 95% or more.
This hydrogenated styrene / isoprene elastomer has a melt flow rate [230 ° C., 21.18 N (2.16 kgf) load: JIS K7210-1995, test condition No. 14] cannot be measured, and there is no fluidity. That is, the melt flow rate of the hydrogenated styrene / isoprene elastomer is 0 g / 10 min . By using this non-flowable hydrogenated styrene / isoprene block copolymer, when it is made into a final resin composition, it is flexible at room temperature and compressive stress does not decrease much at 130 ° C. As a result, 130 Leakage (liquid leakage) due to thermal deformation or heat shrinkage is effectively prevented under heat sterilization conditions at 30 ° C. for 30 minutes, and leakage due to dropping during storage and handling is also effectively prevented. The hydrogenated styrene / isoprene elastomer having no fluidity is rich in elasticity when made into a final resin composition, but cannot be heated, melt-extruded or injection-molded due to lack of fluidity.
Therefore, in the present invention, in addition to the (i) hydrogenated styrene / isoprene elastomer, it is indispensable to blend the components (b) to (d).

  The amount of the hydrogenated styrene / isoprene elastomer needs to be 30 to 40% by weight. If it is less than 30% by weight, the heat resistance of the resin composition is deteriorated and the resin composition cannot withstand retort sterilization. On the other hand, if it exceeds 40% by weight, the MFR of the resin composition becomes small, and short shots, burrs and the like occur in injection molding.

  The viscosity of the hydrogenated styrene / isoprene elastomer in a 5 wt% toluene solution is preferably 300 to 1000 mPa · s at 30 ° C. When the pressure falls below 300 mPa · s, when retort sterilization is performed at 125 ° C. for 30 minutes, the amount of hydrogenated styrene / isoprene elastomer in the resin composition for liner material must be 40% by weight or more. In addition to the risk of being lost, the injection moldability also deteriorates. On the other hand, if it exceeds 1000 mPa · s, cracks may occur in the sealed portion during retort sterilization, and the sealing performance may deteriorate.

Examples of the polypropylene-based resin (b) include propylene homopolymers and copolymers mainly composed of propylene (published on January 5, 1994 by Sangyo Kenkyukai,
Practical plastic encyclopedia, see pages 28-33).
Usually, as the polypropylene-based resin, a homopolymer of propylene, a copolymer of propylene (main component) and ethylene and / or an α-olefin having 4 to 12 carbon atoms can be used.
As a preferable polypropylene resin, one having the following physical properties can be used.
MFR [230 ° C., 21.18 N (2.16 kgf) g / 10 min ]
(Test conditions of JIS K7210 Table 1, No. 14)
: 1 to 60 g / 10 min , preferably 5 to 40 g / 10 min
Specific gravity: 0.89 to 0.92, preferably 0.90 to 0.91
Hardness (Rockwell R type)
: 80-120, preferably 85-115
Heat distortion temperature [0.45 MPa (megapascal), ASTM D648]
: 100-150 ° C, preferably 105-145 ° C
The MFR is particularly preferably in the range of 5 to 40 g / 10 min , since the moldability of the resin composition is good and the impact resistance as a cap and the drop sealing property are excellent. The heat distortion temperature is most preferably in the range of 105 ° C. to 145 ° C. from the viewpoint of heat-resistant sealing performance and impact resistance of the cap.

  The usage-amount of the said polypropylene resin needs to be 10 to 20 weight%. If it is less than 10% by weight, the MFR of the resin composition becomes too small, the flow characteristics of the resin composition are deteriorated, the injection moldability is deteriorated, and the cause of poor sealing is exceeded. The heat resistance will deteriorate and it will not be able to withstand retort sterilization.

The liquid paraffin (c) is a hydrocarbon oil obtained by purifying a relatively light lubricating oil fraction, for example, a spindle oil fraction, by washing with an acid (for example, sulfuric acid).
This liquid paraffin needs to occupy 40 to 60% by weight in the resin composition. If it is less than 40% by weight, the MFR of the resin composition becomes too small, the injection molding characteristics deteriorate, and short shots, burrs, etc. occur. On the other hand, if it exceeds 60% by weight, the heat resistance of the resin composition is deteriorated, and there is a possibility that it cannot withstand retort sterilization.

  As the silicone oil which is one component of the lubricant (d), one having a kinematic viscosity of 100 to 10000 cst (20 ° C.), particularly 100 to 1000 cst (20 ° C.) is preferable, and a specific silicone oil has the kinematic viscosity. Dimethyl silicone oil and methylphenyl silicone oil are preferred. If the kinematic viscosity is less than 100 cst (20 ° C.), there is a problem in food hygiene, and if it exceeds 10,000 cst (20 ° C.), mixing and dispersibility into the composition become insufficient.

  The amide wax, which is another component of the lubricant of (d), is a fatty acid monoamide and / or bisamide. Examples of fatty acid monoamides include oleic acid amide, erucic acid amide, stearic acid amide, palmitic acid amide, and lauric acid amide. Fatty acid bisamides include methylene bis stearic acid amide, ethylene bis oleic acid amide, ethylene bis lauric acid amide, and the like. Is mentioned. In the present invention, these are used singly or in combination. By using this, the effect of reducing the opening torque is brought about.

  The use ratio of (i) and (ii) of the lubricant is preferably 1: 1 to 3: 1.

The usage-amount of a lubricant needs to be 3-15 weight part with respect to 100 weight part of total amounts of said (I), (B), and (C). When the amount is less than 3 parts by weight, the frictional force between the resin composition and the can body is large, and the unsealing property is too poor, and the suitability is lacking.
On the other hand, if the amount is 15 parts by weight or more, the lubricant bleeds on the surface of the resin composition and the flavor characteristics are deteriorated.

  The resin composition for liner material needs to have a compressive stress relaxation index of 70 or more in stress relaxation at 50% compression at 125 ° C. Below 70, when a bottle sealed with a metal PP cap equipped with this resin composition is sterilized by retort, the compressive force for maintaining the sealing property is insufficient, which results in poor sealing.

The rupture time when the resin composition for a liner material is stretched and held at 125 ° C. by 50% needs to be 10 minutes or more. When the breaking time is less than 10 minutes, when the bottle is sealed with a metal PP cap equipped with a resin composition for a liner material and sterilized by retort, the liner material may be subjected to tensile stress and the liner material may be broken. .

  In order to lengthen the breaking time when the elongation is maintained at 50%, (i) the hydrogenated styrene / isoprene elastomer is dispersed sufficiently uniformly in (b) polypropylene resin and (c) liquid paraffin. (In this case, liquid paraffin is absorbed by the elastomer as a softening agent, and it is presumed that the polypropylene resin is a dispersion medium and the liquid paraffin-containing elastomer is a dispersoid). The size of the dispersed particles is 10 μm. It is preferable to be as follows.

The melt flow rate (MFR) of the resin composition for a liner material (when the load is 21.18 N at 230 ° C.) needs to be 1 to 20 g / 10 min . When the MFR is less than 1 g / 10 min , the injection moldability is deteriorated such that short shots, burrs and the like are generated. On the other hand, when the MFR exceeds 20 g / 10 min , the fluidity of the resin composition is deteriorated. that Bali is likely to occur at the time of injection molding of the things is good.

  In the resin composition for a liner material of the present invention, it is possible to use additives conventionally blended in the resin composition for a liner material, such as various stabilizers such as antioxidants, dyes and pigments, as necessary. it can.

  When the resin composition for a liner material used for injection molding of the metal PP cap of the present invention is used, (1) it can sufficiently withstand retort sterilization, (2) it has an appropriate openability, and (3) good flavor. Characteristic (flavor characteristic means that the lubricant bleeds and gives the odor of the lubricant. In other words, if the content is contained, the odor of the lubricant deteriorates due to the odor of the lubricant. If it is bleed, the flavor is bad, and if it is not bleed, the flavor is good. (4) It has excellent injection moldability, and (5) High. Having a sealing property, it is possible to meet all the requirements for a liner material for a resin composition used for injection molding of metal PP cap that.

  Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited thereto.

Examples 1-7 and Comparative Examples 1-9
Styrene / isoprene elastomer A:
230 ° C., 21.18N MFR is 0 g / 10 min .
A 5 wt% toluene solution having a viscosity of 700 mPa · s at 30 ° C. Styrene / isoprene elastomer B:
230 ° C., 21.18N MFR is 0 g / 10 min .
A 5 wt% toluene solution having a viscosity of 250 mPa · s at 30 ° C. Styrene / isoprene elastomer C:
230 ° C., 21.18N MFR is 0 g / 10 min .
Viscosity of 5 wt% toluene solution at 1100 mPa · s at 30 ° C. Polypropylene resin: 230 ° C., 21.18N MFR of 20 g / 10 min Liquid paraffin: Viscosity at 25 ° C. of 68 mPa · s Lubricant: Silicone Oil A: 350 cst / 20 ° C. Amide wax: Erucamide

A mixture containing the raw materials shown in Table 1 was stirred and mixed with a Henschel mixer and melted through a twin-screw extruder adjusted to 200 ° C. to obtain a pelletized resin composition for a liner material. This was injection molded into an aluminum cap in 42 mm to obtain a metal PP cap with a liner.

(1) MFR is a value measured under conditions of 230 ° C. and 21.18 N using a melt index tester manufactured by Yasuda Seiki Seisakusho.
(2) Dispersibility of the resin composition for liner material The resin composition for liner material is compression-molded at 230 ° C to a thickness of 1 mm and rapidly cooled. At this time, it was examined whether or not the molded sheet had cracks, and when the center portion of the sheet had cracks, it was determined that the dispersibility was poor.
(3) Flavor characteristics The resin composition for a liner material is compression-molded at 230 ° C. to a thickness of 1 mm and rapidly cooled. The sheet is stored at room temperature for 1 week and evaluated for bleed on the sheet surface. When there was no bleed, it was evaluated as “good”, and when there was bleed, the flavor characteristics were evaluated as “poor”.
(4) Retort sterilization suitability An aluminum cap equipped with a resin composition for a liner material is wound around a steel bottle can filled with hot water at 90 ° C., and this is subjected to a retort treatment at 125 ° C. for 30 minutes at room temperature. After cooling, the degree of vacuum in the can is measured. If the degree of vacuum is in the normal range (45 kPa to 55 kPa), it is judged as acceptable ◯, otherwise it is regarded as unacceptable.
(5) Opening ability The opening torque of a retort-sterilized test can was measured. The instrument for opening torque was Sympo Sangyo Co., Ltd. TNK100B-5. The opening torque was evaluated by measuring the opening torque with a torque meter after filling. The evaluation of the opening torque is a value obtained by multiplying a numerical value of 1/4 to 1/2 of the cap diameter (D = 47 in this test) by 0.098 (unit: N · m) is 1.2 N · m to 2 The case of 3 N · m was marked as ◯, and the others were marked as x. If the opening torque is less than (1/4) × 0.098N · m of the cap diameter, that is, D × 0.024N · m (1.2N · m in this test), leakage will occur due to the cap loosening due to impact. If the opening torque is larger than ½ × 0.098 N · m of the cap diameter, that is, D × 0.049 N · m (2.3 N · m in this test), it is difficult to open.
(6) Sealing property A test can sterilized by retort was dropped from a height of 20 cm and 30 cm onto an iron plate with an inclination angle of 15 degrees with the cap surface down, and the reduced state of each vacuum degree was examined.
Those having a degree of vacuum of 44 kPa or more were evaluated as good sealing performance, and those having a vacuum level of less than 44 kPa were evaluated as poor sealing performance.
(7) Elongation and Breaking Characteristics of Resin Composition for Liner Material Time until a resin composition for liner material is compression-molded at 230 ° C. to a thickness of 1 mm, punched into a dumbbell shape and elongated by 50% at 125 ° C. Was measured.
(8) Compressive stress relaxation index of resin composition for liner material The resin composition for liner material is compression molded at 210 ° C. to a thickness of 2 mm, punched into 16 mmφ, and this test specimen is used as a specimen by stacking two sheets. To determine the initial compressive stress value A. Next, the specimen was compressed 50% with a compression jig using a tensile tester [Toyo Seiki Seisakusho STR5 VE5D] set at 125 ° C., and a stress value B after holding for 30 minutes was determined. ÷ A) The compressive stress relaxation index was calculated by × 100.
(9) Injection moldability When the resin composition for a liner material was injection-molded, the success rate of 99.99% or more was evaluated as ◯, and the lower one was evaluated as ×. The injection molding was performed according to the description in Japanese Patent Application Laid-Open No. 2003-236879 relating to the applicant's application. The injection molding conditions are as follows.
a Preheating step The predetermined temperature of the shell was previously heated to 80 to 90 ° C.
b Liner molding step The inner wall of the resin passage is heated to a predetermined temperature (for example, if the synthetic resin forming the liner is polyethylene, the temperature is around 200 ° C., and if the polypropylene is a polypropylene, the temperature is around 210 ° C.). The synthetic resin material passing through the resin passage can be maintained in a molten state.
When a synthetic resin material in a molten state is supplied to the resin passage during the liner molding process, a synthetic resin material having a predetermined injection pressure (for example, a pressure of about 20 to 28 Mpa) It is injected into the space. The temperature of the injected synthetic resin material is reduced to about 80 to 100 ° C., and is maintained on a predetermined liner even after release.
In this implementation, a cooling process (for example, blowing cooling air) as described in the above publication is not employed, but can be appropriately employed.

<Evaluation>
Comparative Examples 1, 2, 3, 4, 5, 6, and 7 indicate that the MFR of the resin composition for a liner material is inferior in the injection characteristics when the MFR is outside the range of 1 to 20 g / 10 min . The comparative example 3 has shown the fall of the retort disinfection suitability and the fall sealability by the dispersibility defect of the resin composition for liner materials. In Comparative Example 8, since the lubricant is less than 3 parts by weight, the unsealing property is poor. Comparative Example 9 shows poor flavor characteristics because the lubricant is 15 parts by weight or more. Moreover, since the stress relaxation index | exponent is less than 70, the comparative examples 1, 4, 5, and 7 have shown the fall of retort disinfection suitability and fall sealing performance.

Claims (2)

(A) 30 to 40 hydrogenated styrene / isoprene elastomer having a melt flow rate (MFR) of 0 g / 10 min at 230 ° C. and a load of 21.18 N (2.16 kgf) (that is, it does not flow under these conditions) weight%
(B) 10-20% by weight of polypropylene resin
(C) 40-60% by weight of liquid paraffin
(D) A metal PP cap containing 3 to 15 parts by weight of a lubricant comprising (i) silicone oil and (ii) amide wax with respect to 100 parts by weight of the total amount of (a), (b) and (c). a liner material for a resin composition used in the injection molding, when the stress value after compressive stress relaxation index at 50% compression [30 minutes at the 125 ° C. B, the initial stress value was a, ( B ÷ a) is a value indicating with × 100] of Ri der 70 or more, the load at the 125 rupture time when the 50% elongation retention in ° C. is not less than 10 minutes, and the melt flow rate (230 ° C. Is a resin composition for a liner material used for injection molding of a metal PP cap, wherein the composition is 1-20 g / 10 min . A metal PP cap with a liner, wherein the liner comprises the resin composition for a liner material according to claim 1 .