JP6318655B2 - Foam and production method thereof - Google Patents

Description

  The present invention relates to a polyethylene resin composition comprising a specific high-density polyethylene and a specific high-pressure low-density polyethylene, a foam excellent in compression durability and secondary processability, and a method for producing the same.

  Polyethylene resin foams are used in a wide range of applications, mainly for cushioning materials, cushioning materials, shock absorbing materials and the like. In recent years, plastics have been required to be recyclable from the viewpoint of reducing environmental impact, and there is a trend to reduce costs and reduce waste by making a smaller amount of raw material highly foamed. Accordingly, there is a growing need for a non-crosslinked foam that is easy to recycle and capable of being highly foamed, rather than a crosslinked foam that is difficult to recycle in a polyethylene resin foam. Polyethylene having a high melt tension is necessary as a polyethylene that can meet such needs, and a low-density polyethylene having a long chain branch produced by a high-pressure method (hereinafter, high-pressure method low-density polyethylene) is preferably used. Yes. Non-crosslinked foam made of high-pressure low-density polyethylene is flexible and excellent in compression durability, and is used for cushioning applications that are repeatedly compressed, while the foam is heated again for secondary processing. There was a problem that the molding temperature range was very narrow due to the sudden change in viscosity. In order to solve such a problem, a technique (for example, refer to Patent Documents 1 and 2) in which high-pressure low-density polyethylene is mixed with linear low-density polyethylene or high-density polyethylene is disclosed.

JP 60-222222 A JP 2006-274038 A

  However, the techniques disclosed in Patent Documents 1 and 2 use a linear polyethylene that has a low melt tension and does not exhibit foamability, and therefore, flexibility during repeated compression is impaired, and frequent compression is required. It was difficult to apply to the use of shock absorbing material. An object of the present invention is to overcome the above-described problems and to provide a non-crosslinked polyethylene foam having a high expansion ratio, excellent compression durability and secondary processability.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have carried out a foam molding of a polyethylene-based resin composition comprising a specific high-density polyethylene and a specific high-pressure method low-density polyethylene. The present inventors have found that a non-crosslinked polyethylene foam excellent in next processability can be obtained, and have completed the present invention.

That is, the vinylidene group amount (Vd) is 1.2 pieces / 10 ⁴ C or more and 2.1 pieces / 10 ⁴ C or less with respect to 100 parts by weight of high-density polyethylene, and melt flow rate (MFR) (measurement conditions: 190 ° C., 2.16 kg load) is a polyethylene-based resin composition containing 5 to 233 parts by weight of a high-pressure low-density polyethylene of 0.1 g / 10 min or more and 6.0 g / 10 min or less. The present invention relates to a foam using an ethylene-based resin composition having a melt tension (measurement conditions: temperature 190 ° C., take-off speed 0.5 m / min) of density polyethylene of 50 mN or more and 200 mN or less, and a method for producing the foam.

  The high-density polyethylene used in the polyethylene-based resin composition used in the present invention is not particularly limited, and as the high-density polyethylene, a polymerization catalyst such as a Ziegler-based catalyst or a metallocene-based catalyst is used. Those produced by processes such as slurry polymerization and high-pressure ion polymerization can be used.

The density of high-density polyethylene used in the present invention (HDPE) (B) is preferably from 940~970kg / ^{m 3,} more preferably from 940~960kg / ^{m 3,} most preferably 940~950kg / ^{m 3} is there. If the density is within this range, the resulting foam is excellent in secondary moldability, which is preferable.

  The MFR of the high density polyethylene used in the present invention is preferably 1 to 50 g / 10 minutes, more preferably 1 to 40 g / 10 minutes, and most preferably 1 to 30 g / 10 minutes. An MFR within this range is preferable because the expansion ratio is increased when the composition of the present invention is subjected to foam molding.

  The MFR of the high elastic low density polyethylene used in the present invention is 0.1 g / 10 min or more and 6.0 g / 10 min or less, preferably 0.5 g / 10 min or more and 5.0 g / 10 min or less, more preferably 1 0.0 g / 10 min to 5.0 g / min. If it is less than 0.1 g / 10 minutes, the expansion ratio is lowered, and if it exceeds 6.0 g / 10 minutes, bubbles are likely to break during foaming, which is not preferable.

  The melt tension (measurement conditions: temperature 190 ° C., take-off speed 0.5 m / min) of the high-elasticity low-density polyethylene used in the present invention is preferably 50 mN to 200 mN, preferably 60 mN to 180 mN, more preferably 70 mN to 160 mN. is there. When the melt tension is within this range, the sheet extrusion moldability, the expansion ratio, and the properties of the foam are excellent.

  The molecular weight distribution of the highly elastic low density polyethylene used in the present invention is not particularly limited, but from the viewpoint of extrusion processability, the dispersity Mw / Mn is preferably 7 or more and 12 or less, and more preferably 8 or more and 11 or less. If the degree of dispersion is within this range, the sheet extrusion moldability, the high foaming ratio and the properties of the foam are excellent.

  In the production of the high-pressure low-density polyethylene used in the present invention, in the presence of a radical polymerization initiator, in the presence or absence of a solvent, a chain transfer agent is added mainly for the purpose of adjusting the molecular weight as necessary, Although it can be produced by a continuous vessel type or tubular type high pressure polyethylene production apparatus equipped with a high pressure compressor, a vessel type polymerization apparatus that can easily control the temperature distribution inside the reactor is preferably used. In the low density polyethylene of the present invention, the average reaction temperature in the reactor is made as high as possible to increase the amount of vinylidene groups, and at the same time, the MFR is lowered as much as possible. It is easy to optimize the reaction pressure and the temperature of ethylene supplied into the reactor so that the desired vinylidene group amount and MFR are obtained after a temperature gradient is generated in the reactor. And it can manufacture efficiently.

  The polymerization pressure is from 100 MPa to 400 MPa, preferably from 150 MPa to 190 MPa. Within this pressure range, a low density polyethylene having a high vinylidene group amount and a low MFR can be obtained, which is preferable.

  The reaction temperature is 100 ° C. or higher and 330 ° C. or lower, preferably 200 ° C. or higher and 280 ° C. or lower. The difference between the maximum temperature and the minimum temperature inside the reactor is 10 ° C. or more and 200 ° C. or less, preferably 13 ° C. or more and 100 ° C. or less. If the temperature of the reactor is 100 ° C. or higher and the temperature difference between the upper part and the lower part of the reactor is within the above range, it is preferable because a low density polyethylene having a high vinylidene group amount and a low MFR can be obtained.

  The supply amount and temperature of ethylene supplied to the reactor depend on the reaction pressure and reaction temperature, and are appropriately changed to obtain the desired vinylidene group amount and MFR. The ethylene supply amount is also changed appropriately depending on the production rate. obtain. The ethylene supply rate is 10 kg / h or more and 30 kg / h or less, and the ethylene temperature is 10 ° C. or more and 100 ° C. or less. If the ethylene supply rate is 10 kg / h or more and the ethylene temperature is 10 ° C. or more, low density polyethylene is preferable because it can be produced at a production rate excellent in economic efficiency.

  Examples of radical polymerization initiators include oxygen, hydrogen peroxide, diethyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, dicumyl peroxide, t-butyl peroxybenzoate, and di-t-butyl peroxyacetate. T-butyl peroxypivalate can be used, and an initiator having an optimal decomposition temperature can be selected according to the reaction temperature. The amount of the initiator used in the present invention is appropriately adjusted according to the kind of the initiator, the temperature inside the reactor, the ethylene flow rate introduced into the high-pressure reactor, and the temperature of ethylene, and is strictly limited to a specific range. Although not obtained, it is generally 1-25 kg / h.

  Chain transfer agents can be used mainly for the purpose of suppressing the increase in molecular weight, and can also be used for the purpose of increasing the amount of double bonds. Examples of chain transfer agents include aliphatic hydrocarbons such as ethane, propane, butane, pentane and hexane, olefin compounds such as propylene, 1-butene, isobutene and 1-hexene, aldehyde compounds such as formaldehyde, acetaldehyde and propionaldehyde, Examples thereof include aromatic hydrocarbons such as benzene and toluene.

  The high-pressure low-density polyethylene used in the present invention has a large change in melt viscosity and melt tension when pelletized by melt extrusion compared to conventional high-pressure low-density polyethylene. The temperature of the granulator is 120 to 200 ° C, preferably 120 to 180 ° C, more preferably 120 to 150 ° C. When the temperature during granulation exceeds 200 ° C., the increase in melt tension and melt viscosity becomes significant in the granulation process, and the torque of the extruder increases when performing extrusion lamination using the obtained pellets. It is not preferable. If the temperature during granulation is 120 ° C. or less, the torque of the extruder used for granulation is high and the productivity is low, which is not preferable. Further, the granulation rate can be appropriately changed depending on the ability of the granulator to be used.

  There is no restriction | limiting in particular in the granulation method of the high pressure method low density polyethylene used by this invention, The well-known method generally used can be used. Examples of granulation methods include strand cutting and underwater cutting. The screw in the extruder of the granulator used in the present invention is preferably a single screw extruder provided with a single flight type screw without a kneading zone in which a strong shearing force is not applied to the molten resin and the resin is difficult to generate shear heat. .

  The composition comprising high-density polyethylene (A) and high-pressure method low-density polyethylene (B) constituting the polyethylene-based resin composition used in the present invention has a high-pressure method low density with respect to 100 parts by weight of high-density polyethylene (A). It is 5-100 weight part of polyethylene (B), Preferably it is 5-70 weight part, More preferably, it is 5-50 weight part. When the high-pressure method low-density polyethylene (B) is less than 5 weights, the expansion ratio is lowered, and the compression durability is also lowered. On the other hand, when the amount exceeds 100 parts by weight, secondary processing becomes difficult, which is not preferable.

  When blending the high-density polyethylene (A) constituting the polyethylene-based resin composition used in the present invention and the high-pressure method low-density polyethylene (B), known methods such as extrusion kneading and roll kneading can be used.

  In the polyethylene resin composition used in the present invention, as long as the properties of the composition are not impaired, a stabilizer, a lubricant, a flame retardant, a dispersant, a filler, a foaming agent, a foam nucleating agent, a crosslinking agent, Ultraviolet ray inhibitors, antioxidants, and colorants can be added. Moreover, it can also be used by mixing with other thermoplastic resins. Examples of the thermoplastic resin include linear low density polyethylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene / vinyl alcohol copolymer, polystyrene, and maleic anhydride grafted products of these resins. it can.

  The foam made of the polyethylene-based resin composition of the present invention has excellent compression durability because the expansion ratio is 3 times or more. However, when the expansion ratio is less than 3 times, the foam is inferior in compression durability. Can only be obtained.

  As a method for producing a foam comprising the polyethylene resin composition of the present invention, any method may be used as long as a foam is obtained. For example, the polyethylene-based resin composition of the present invention, a bubble adjusting agent such as talc, an anti-shrinkage agent and the like are added as necessary, and supplied to an extruder, heated and melted, kneaded, and further supplied with a foaming agent. After the foamable molten resin mixture is prepared, the extrusion resin temperature, the extrusion die internal pressure, the discharge amount, etc. are adjusted, and the foam is extruded from the die at the tip of the extruder to the low pressure region and foamed. Further, by selecting a die attached to the tip of the extruder according to the shape of the foam, a foam such as a round bar, a sheet, or a plate can be produced. For example, when a strand die, an annular die, and a slit die are used, a round bar shape, a sheet shape, and a plate-like foam can be produced, respectively.

  The resin temperature at the time of extrusion is preferably within Tm ± 10 ° C., more preferably within Tm ± 5 ° C., relative to the melting point Tm of the polyethylene resin composition. Here, melting | fusing point of a polyethylene-type resin composition is made into the peak vertex temperature calculated | required from the test piece which performed fixed heat processing by the heat flux DSC curve based on JISK7121 (1987).

  Examples of foaming agents in extrusion foaming include inorganic gas foaming agents such as carbon dioxide, nitrogen, argon and air; volatilization of propane, butane, pentane, hexane, cyclobutane, cyclohexane, trichlorofluoromethane, dichlorodifluoromethane, and the like. Azodicarbonamide, barium azodicarboxylate, N, N-dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydrazide), which is liquid or solid at room temperature and generates a gas upon heating, Chemical blowing agents such as diphenylsulfone-3,3′-disulfonylhydrazide, p-toluenesulfonyl semicarbazide, trihydrazinotriazine, biurea, zinc carbonate and the like can be mentioned. 100 parts by weight of polyethylene resin composition Is preferably to 1 to 20 parts by weight, particularly preferably in the range of 5 to 15 parts by weight.

  The use of the foam comprising the polyethylene resin composition of the present invention is not particularly limited, and can be suitably used as a heat insulating molded body such as a buffer container, a building material, and a heating device.

  According to the present invention, it is possible to obtain a polyethylene resin composition capable of molding a foam having a high expansion ratio and excellent compression durability and secondary workability.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Below, the measuring method used by the Example and the comparative example is shown.
(1) Amount of vinylidene group The resin was pressed under nitrogen at 150 ° C. for 2 minutes to prepare a 200 μm-thick film, and a characteristic absorption peak of vinylidene group was 888 cm ⁻ using a Spectrum One infrared spectrophotometer manufactured by PerkinElmer. ¹ was used for quantitative analysis, and the number of vinylidene groups per 10,000 carbon atoms (numbers / 10 ⁴ C) was determined.
(2) Density The density was measured in accordance with JIS K6922-1 (1997).
(3) Melt tension (MS)
Using a capillary viscometer (Toyo Seiki Seisakusho, product name: Capillograph) with a barrel diameter of 9.55 mm, a flat die with a length of 8 mm, a diameter of 2.095φ, and an inflow angle of 90 ° C is used in a constant temperature room at a set temperature of 23 ° C. Then, 18 g of resin was filled at a temperature of 190 ° C., and the tension required for pulling at a piston lowering speed of 10 mm / min and a take-up speed of 0.5 m was defined as a melt tension.
(4) Melt flow rate (MFR)
The measurement was performed according to JIS K6922-1.
(5) Physical properties and moldability evaluation of extruded foam sheet [Foaming ratio]
A foam having a width of 5 cm, a length of 5 cm, and a thickness of 1.5 cm was cut out from the extruded foam sheet obtained by molding the polyethylene resin composition of the present invention, and the weight W (g) was measured. JIS K 6767 The apparent density was calculated according to the following formula.

Apparent density (g / cm ³ ) = W / (5 × 5 × 1.5)
The expansion ratio was determined from the apparent density by the expansion ratio = 1 / apparent density.

[Foam sheet properties]
The appearance of the extruded foam sheet obtained by molding the polyethylene resin composition of the present invention and the state of bubbles in the cross section were visually evaluated. ○: The surface was smooth and uniform, x: The surface was smooth The bubble state was non-uniform regardless of the nature, and was evaluated in two stages.

[Foamed sheet compression durability]
From the extruded foam sheet obtained by molding the polyethylene resin composition of the present invention, a foam having a width of 5 cm × a length of 5 cm × a thickness of 1.5 cm was cut out, and a tensile tester (manufactured by A & D Corporation, In the compression cycle mode (trade name Tensilon), the operation of unloading after compression to 80% of the thickness of the test piece was repeated 10 times, and the displacement at which the load was 0 (N) in the return direction was defined as the residual displacement. Using the residual displacement and the original thickness, the residual strain was calculated according to the following equation, and the residual strain was evaluated in two stages: ○ if less than 20%, and × if 20% or more.

Residual strain (%) = 100 × residual displacement (mm) / 15 (mm)
[Secondary workability (thermoformability)]
The extruded foam sheet obtained by molding the polyethylene resin composition of the present invention was molded at a molding heater temperature of 140 ° C. using a vacuum molding machine equipped with a mold having a major axis of 100 mm and a depth of 50 mm. The secondary workability was evaluated in two stages: ○: 100%, x: 0 to 90%, based on the ratio of acceptable products (no breakage of the molded body and no cracks) in 10 shots.

[Secondary workability (bending workability)]
A test piece having a width of 10 mm and a length of 100 mm was cut out from an extruded foamed sheet obtained by molding the polyethylene resin composition of the present invention, bent by hand, and the presence or absence of cracks or cracks in the ten test pieces. It checked visually and evaluated in two steps, (circle): 100% and x: 0-90% from the ratio of the pass product (a crack and there is no crack) in 10 shots.

Synthesis example 1
21.1 kg / h of ethylene compressed by a reciprocating high-pressure compressor was injected into a Bessel type reactor at a temperature of 45 ° C., 7.1 g / h of t-butyl peroxide was added as a polymerization initiator, the pressure was 180 MPa, the reactor Polymerized continuously at an upper temperature of 257 ° C. and a reactor lower temperature of 276 ° C., density 919 kg / m ³ , vinylidene group content 1.2 / 10 ⁴ C, melt flow rate (MFR) 1.7 g / 10 min A high-pressure low-density polyethylene C1 having a melt tension (MS) of 149 mN was obtained.

Synthesis example 2
20.5 kg / h of ethylene compressed by a reciprocating high-pressure compressor was pressed into a Bessel type reactor at a temperature of 42 ° C., 11.5 g / h of t-butyl peroxide was added as a polymerization initiator, pressure was 180 MPa, reactor Polymerized continuously at an upper temperature of 257 ° C. and a reactor lower temperature of 276 ° C., a density of 919 kg / m ³ , vinylidene group content of 1.3 / 10 ⁴ C, MFR of 2.0 g / 10 min, MS 136 mN Density polyethylene C2 was obtained.

Synthesis example 3
22.5 kg / h of ethylene compressed by a reciprocating high pressure compressor was injected into a Bessel type reactor at a temperature of 40 ° C., 12.9 g / h of t-butyl peroxide was added as a polymerization initiator, a pressure of 180 MPa, a reactor temperature 257 ° C. at the top, the reactor was continuously polymerized at a temperature 277 ° C. lower, density 919 kg / ^{m 3,} the amount of vinylidene group 1.4 pieces ^/ 10 4 C, ^{MFR2.2g /} 10 min, low density polyethylene MS131mN C3 was obtained Synthesis Example 4
21.8 kg / h of ethylene compressed by a reciprocating high pressure compressor was injected into a Bessel type reactor at a temperature of 33 ° C., 13.5 g / h of t-butyl peroxide was added as a polymerization initiator, pressure was 188 MPa, reactor Low density polyethylene with continuous polymerization at an upper temperature of 256 ° C. and a reactor lower temperature of 277 ° C., density 918 kg / m ³ , vinylidene group content 1.4 / 10 ⁴ C, MFR 2.5 g / 10 min, MS 122 mN C4 was obtained.

Example 1
(1) Production of polyethylene-based resin composition The high pressure produced in Synthesis Example 1 with respect to 100 parts by weight of high-density polyethylene (Nipolon Hard 4000, density: 965 kg / m ³ , MFR: 5 g / 10 min, manufactured by Tosoh Corporation) After adding 20 parts by weight of low density polyethylene (C1) and dry blending, barrel temperature is C1: 180 ° C, C2: 200 ° C, C3: 220 ° C, die head: The mixture was melt-mixed at 220 ° C. and pelletized by strand cutting.
(2) Production of foam comprising polyethylene resin composition 100 parts by weight of the above polyethylene resin composition and 0.1 parts by weight of talc (trade name: MS, manufactured by Nippon Talc, average particle size: 8 μm) as a foam nucleating agent After dry blending with the polyethylene-based resin composition for foam molding contained, foaming of a single screw extruder (screw diameter 50 mmφ, L / D = 36, manufactured by Kyodo Shin) having a volatile liquid injection hole in the middle of the barrel Using a molding extrusion equipment, the dry blend was supplied at 15 kg / hour, and after melt kneading, a compressed liquid butane was press-fitted and dispersed from the injection hole at 120 g / hour, and a slit die (set at 130 ° C.) A sheet-like foamed molded product was extruded from a width of 500 mm.

  The obtained polyethylene extruded foam sheet has high surface smoothness and uniform fine cells, the expansion ratio is 30 times, and the compression durability, heat workability, and folding workability are all good. there were.

Examples 2-3
Nipolon Hard 5700 (made by Tosoh Corporation, density: 954 kg / m3, MFR: 1 g / 10 minutes) and Nipolon Hard 2300 (made by Tosoh Corporation, density: 952 kg / m3, MFR: 7 g / 10 minutes) as high-density polyethylene A polyethylene foam sheet was obtained in the same manner as in Example 1 except that was used. Regardless of which high-density polyethylene is used, the extruded foam sheet has uniform fine cells with high surface smoothness, a foaming ratio of 30 times or more, compression durability, heat workability, and bending processing. The property was also good.

Examples 4-6
A polyethylene foam sheet was obtained in the same manner as in Example 1 except that C2, C3, and C4 produced in Synthesis Examples 3 to 5 were used as the high-pressure low-density polyethylene. Regardless of which high-density polyethylene is used, the extruded foam sheet has uniform fine cells with high surface smoothness, and has a foaming ratio of 28 to 35 times, compression durability, thermal workability, and bending. Workability was also good.

Comparative Example 1
After extruding a polyethylene sheet in the same manner as in Example 1 except that Petrocene 203 (manufactured by Tosoh Corporation, density: 918 kg / m ³ , MFR: 8 g / 10 min) was used as the high-pressure method low-density polyethylene, Although foamed, the sheet did not foam.

Comparative Example 2
After extruding a polyethylene sheet in the same manner as in Example 2 except that Petrocene 213 (manufactured by Tosoh Corporation, density: 918 kg / m ³ , MFR: 8 g / 10 min) was used as the high-pressure method low-density polyethylene, Although foamed, the sheet did not foam.

Comparative Example 3
Extruded polyethylene sheet in the same manner as in Example 3 except that Petrocene 212 (manufactured by Tosoh Corporation, density: 919 kg / m ³ , MFR: 12.5 g / 10 min) was used as the high-density low-density polyethylene. Thereafter, foaming was performed, but the sheet did not foam.

Comparative Example 4
After extruding a polyethylene sheet in the same manner as in Example 1 except that Petrocene 360 (manufactured by Tosoh Corporation, density: 924 kg / m ³ , MFR: 3 g / 10 min) was used as the high-pressure method low-density polyethylene, Although foamed, the sheet did not foam.

Comparative Examples 5-6
Extrude a polyethylene sheet in the same manner as in Comparative Example 1 except that C1 produced in Synthesis Example 2 was used as the high pressure method low density polyethylene and the addition amount of the high pressure method low density polyethylene was changed to 2 parts by weight and 120 parts by weight. Although foaming was performed after molding, the sheet did not foam.

Claims (3)

The vinylidene group amount (Vd) is 1.2 pieces / 10 ⁴ C or more and 2.1 pieces / 10 ⁴ C or less, and melt flow rate (MFR) (measurement condition: 190 ° C.) with respect to 100 parts by weight of high-density polyethylene. , 2.16 kg load), a foam having a foaming ratio of 3 times or more, comprising a polyethylene resin composition containing 5 to 100 parts by weight of high-pressure low-density polyethylene having a load of 0.1 g / 10 min to 6.0 g / 10 min. 2. The foam according to claim 1, wherein the high-pressure low-density polyethylene has a melt tension (measurement conditions: temperature 190 ° C., take-off speed 0.5 m / min) of 50 mN or more and 200 mN or less. The vinylidene group amount (Vd) is 1.2 pieces / 10 ⁴ C or more and 2.1 pieces / 10 ⁴ C or less, and melt flow rate (MFR) (measurement condition: 190 ° C.) with respect to 100 parts by weight of high-density polyethylene. , 2.16kg load) is 0.1 g / 10 min or more and 6.0 g / 10 min or less, and a polyethylene resin composition containing 5 to 100 parts by weight of high-pressure low-density polyethylene is supplied to an extruder, and melted and melt-kneaded. 3. The method for producing a foam according to claim 1 or 2, wherein after the foaming agent is supplied, the foaming agent is extruded and foamed in a low pressure region.