JPH0559204A - Preparation of stretched polyethylene molding having void - Google Patents

Abstract

(57) [Summary] [Structure] A polymer obtained by using a cyclopentadiene-based monomer as a main component, a hydrogenated resin obtained by hydrogenating the polymer, or a standard polystyrene equivalent of the polymer and the hydrogenated resin. 10 to 100 parts by weight of cyclopentadiene resin having a weight average molecular weight (Mw) of 700 or more and a softening point (ring and ball method) of 170 ° C. or more and a density of 0.9
100 parts by weight of high density polyethylene of 40 or more is blended,
A composition heat-treated at the softening point or higher is molded into an unstretched original fabric by a melt extrusion method, and then at least one side of the original fabric is irradiated with an electron beam, and subsequently stretched at least 3 times in at least one direction. The apparent density is reduced to 0.
A method for producing a polyethylene-based void-containing stretched molded article, wherein the stretched molded article is 92 or less. [Effect] It is possible to obtain a polyethylene-based stretched molded product that retains the strength and rigidity peculiar to high-density polyethylene, is lightweight, and has an opaque pearly luster. The productivity and the uniformity of molded products are improved as compared with the conventional technology.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyethylene-based void-containing stretched molded product. More specifically, the present invention relates to a method for producing a void-containing stretched molded product having a pearly luster, which is prepared by blending high-density polyethylene and a specific cyclopentadiene resin.

[0002]

2. Description of the Related Art Cavity-containing moldings are lightweight and have properties such as opacity, light-shielding properties, decorative properties, pearly luster, and paper-like properties. For decoration materials, calligraphic printing paper, etc., and packing materials as tapes, ribbons or filaments,
Widely used for weaving threads.

Conventionally, as a method for producing a void-containing stretched molded product, (1) a method of adding a foaming agent at the time of molding to form a large number of foams, (2) JP-B-63-24532, There is known a method of forming a void by stretching a composition containing a large amount of an inorganic filler as described in JP-A-63-117043. However, these methods have the following drawbacks. That is,
Regarding (1), foaming is likely to become coarse and gloss decreases, and it is difficult to obtain a uniform and fine foam with a thin film such as a film or a thin fibrous material. The stretching has a drawback that it tends to be broken by stretching and it is difficult to manufacture a thin film. Regarding (2), the addition of a large amount of an inorganic filler has the advantage that many cavities occur during stretching, but on the other hand, the fluidity of the resin during extrusion decreases,
Screen pack clogging, moisture absorption or coarse foaming due to inorganic filler, occurrence of unevenness due to poor dispersion, difficulty in resin replacement, resulting in significant reduction in productivity such as stretching breakage during thin film stretching, Further, the obtained product also has drawbacks that it has a low glossiness, only a dull product can be obtained, and the impact resistance and strength are also low.

[0004]

The object of the present invention is to eliminate the above-mentioned drawbacks of the conventional method, to improve the productivity, and to form uniform and fine voids which are difficult to obtain in a system containing a large amount of inorganic filler. It is an object of the present invention to provide a method for producing a stretched and contained product.

[0005]

As a result of intensive studies to solve the above-mentioned problems, the inventors have surprisingly found that a specific high-softening point resin or a specific hydride thereof is added to a specific polyethylene in a specific amount. A method for obtaining a novel void-containing stretched molded product by stretching the blended composition under specific conditions was found, and it was previously proposed in Japanese Patent Application No. 2-228213. However, this method still has problems in terms of productivity, such as uniform stretchability of the thin film and easy breakage of the film when stretched at a high draw ratio. As a result of further intensive studies, the present inventor has carried out a cavity-containing stretch molding in which the properties of the molded article are extremely improved while the characteristics of the molded article are maintained by crosslinking a part of the composition before stretching. The present invention has been reached by finding a method for manufacturing a product.

That is, the constitution of the present invention is as follows.
It consists of 3). 1) A polymer obtained by polymerizing a cyclopentadiene-based monomer as a main component, a hydrogenated resin obtained by hydrogenating the polymer, or a standard polystyrene-equivalent weight average molecular weight of the polymer and the hydrogenated resin ( Mw) is 700 or more and the softening point (ring and ball method) is 170 ° C. or more, and 10 to 100 parts by weight of a cyclopentadiene resin and 100 parts by weight of high-density polyethylene having a density of 0.940 or more are blended to obtain the softening point or more. By molding the composition heat-treated in step (1), by molding an unstretched raw material by a melt extrusion method, irradiating at least one surface of the raw material with an electron beam, and subsequently stretching it in at least one direction by 3 times or more, A method for producing a polyethylene-based void-containing stretched molded article, which has an apparent density of 0.92 or less.

2) A component in which the cyclopentadiene resin has a weight composition ratio (B) / (A) of the cyclopentadiene monomer (A) and the vinyl aromatic hydrocarbon (B) of 0 to 0.3. A polymer obtained by polymerizing the polymer, a hydrogenated resin obtained by hydrogenating the polymer, or the polymer and the hydrogenated resin, and having a weight average molecular weight (M
w) is the formula Mw ≧ 700 + 2200X (where X is the composition ratio [(B) / (A) + (B)]. Production method.

3) A polyethylene-based cavity according to item 2), wherein the hydrogenated resin obtained by hydrogenating a polymer obtained by using a cyclopentadiene monomer as a main component has an ultraviolet absorbance of 1.0 or less and an iodine value of 30 or less. Method for producing stretch-formed product.

The high-density polyethylene used in the production method of the present invention is prepared by using a so-called Ziegler catalyst, a transition metal oxide catalyst, a metal coordination catalyst or an organometallic catalyst.
Ethylene alone or small amount of propylene, butene-1, pentene-1, 4-methyl-pentene-1, octene-1
Among the polymers, copolymers, and mixtures of these polymers obtained by polymerizing α-olefins and ethylene with ethylene under medium pressure or low pressure, those having a density of 0.940 or more. It is known that this high-density polyethylene is characterized by showing a high degree of crystallinity by X-ray diffraction,
Of these, the melt flow rate (hereinafter referred to as MFR) whose density is in the range of 0.945 to 0.965 and measured under test condition 4 of JIS K7210-1976 (190 ° C., 2.16 kgf). Is preferably in the range of 0.1 to 30.

As a raw material for the polymer obtained by using the cyclopentadiene-based monomer as the main component in the production method of the present invention, cyclopentadiene-based monomers such as cyclopentadiene, dicyclopentadiene and their multimers, or those Or a fraction containing 70% by weight or more of a cyclopentadiene-based monomer obtained from a by-product fraction when ethylene is produced by thermally decomposing petroleum naphtha or the like (hereinafter, referred to as CPD fraction). Minutes) can be used.

Most of the CPD fraction, other than the cyclopentadiene-based monomer as the main component, is a saturated hydrocarbon that is inactive in polymerization, but in addition to this, it is used as a polymerization component together with a cyclopentadiene-based monomer. The polymerizable component may include an aliphatic olefin, an aliphatic diolefin, a cyclic olefin, etc., but the concentration is preferably low, and is preferably 1/10 or less of the cyclopentadiene monomer in terms of weight. As a component copolymerizable with the cyclopentadiene monomer, vinyl aromatic hydrocarbons such as styrene, vinyltoluene, α, β-methylstyrene, indene and alkyl-substituted indene, and petroleum naphtha can be treated in the same manner as the CPD fraction. A so-called C fraction containing the above vinyl aromatic hydrocarbon as a main component, which is a by-product when it is decomposed to produce ethylene.
_{Although 9} fractions can be mentioned, the amount of these copolymerization components is less than 30%, preferably 10% or less of the total polymerization components.

The preparation of the polymer obtained by using the cyclopentadiene type monomer used in the production method of the present invention as a main component is
The cyclopentadiene-based monomer or the cyclopentadiene-based monomer containing a small amount of a copolymerizable component is reacted with nitrogen in the presence or absence of a solvent such as benzene, xylene, toluene, n-hexane or kerosene. Polymerization is performed in an atmosphere of an inert gas such as. The polymerization conditions are preferably a polymerization temperature of 220 to 320 ° C., a polymerization time of about 0.2 to 10 hours, and a pressure at which the polymerization system can be maintained in a liquid phase. Such polymerization may be carried out in one step or may be repeated in two or more steps, and a radical initiator or the like may be added to this reaction system in order to adjust the polymerization average molecular weight. Such a series of polymerization reactions can be carried out by any of batch method, semi-batch method, and continuous method.
In order to obtain a polymer or a copolymer having a high weight average molecular weight and a high softening point by this polymerization reaction, it is preferably 230
Polymerize at a high temperature of ℃ or higher for a long time of 3 hours or longer, or after the first stage of polymerization, distill off unreacted components and solvent, and then hold at a high temperature of 230 ℃ or higher for several hours under reduced pressure. However, multi-stage polymerization of two or more stages such as carrying out the second stage polymerization is preferred.

The polymer obtained by using the cyclopentadiene-based monomer as the main component has a higher ability to form cavities, which is the object of the present invention, as the amount of the cyclopentadiene-based monomer component increases, and the content of the component is 70% by weight or more. What is contained is desirable, and what contains 90 weight% or more is especially desirable.

The hydrogenated resin used in the production method of the present invention is
It can be obtained by hydrogenating a polymer obtained by using the cyclopentadiene-based monomer as a main component by a conventionally known method. As the method of this hydrogenation, in the molten state of the polymer, for example, nickel, palladium,
Using a hydrogenation catalyst such as a metal such as cobalt or a metal oxide, preferably a temperature of 150 to 300 ° C., 10 to 1
Hydrogenate under hydrogen pressure of 50 kg / cm ² .

The cyclopentadiene resin of the present invention has a weight average molecular weight (Mw) of 700 or more and a softening point (ring and ball method) of 170 ° C. or more among the polymers and hydrogenated resins obtained by the above-mentioned method. Limited to ones. The Mw and softening point can be changed depending on the degree of polymerization and the copolymerization composition, but in the present invention, if the Mw does not reach 700, the cavity forming ability, which is the object of the present invention, will be insufficient, and the Mw will exceed 700. Similarly, those having a softening point of 170 ° C. or lower similarly lack in cavity forming ability, and those having a softening point of 150 ° C. or less hardly form voids and tend to be transparent rather than polyethylene alone. The cyclopentadiene-based resin of the present invention includes a cyclopentadiene-based monomer (A) and a vinyl aromatic hydrocarbon monomer (B) in a weight composition ratio (B) /
A polymer obtained by polymerizing a component in which (A) is 0 to 0.3, a hydrogenated resin obtained by hydrogenating the polymer, or the polymer and the hydrogenated resin, which are converted into standard polystyrene. It is preferable that Mw corresponds to the value of the formula Mw ≧ 700 + 2200X (where X is represented by the composition ratio [(B) / (A) + (B)]). That is, in the case of a cyclopentadiene-based homopolymer or its hydrogenated resin, the softening point exceeds 170 ° C even with Mw700, and it can be used, but the copolymerization of cyclopentadiene-based monomer and vinyl aromatic hydrocarbon monomer In the case of a combination or a hydrogenated resin thereof, it is preferable to increase Mw at a constant ratio in proportion to the vinyl aromatic hydrocarbon monomer. Among them, a hydrogenated resin hydrogenated to have an ultraviolet absorbance of 1.0 or less and an iodine value of 30 or less has excellent compatibility with polyethylene, can be stably processed, and has a high whiteness and a cavity forming effect, and is lightweight. Opacification is remarkable, which is particularly preferable. Conventionally, it is known that polyethylene is made transparent by adding hydrogenated petroleum resin to polyethylene, but the hydrogenated resin used in the present invention has a large Mw and a high softening point, and therefore its effect is completely different. In this way, it is possible to obtain a molded product having unique properties which are completely different from those of the prior art, in which a number of cavities (voids) are generated in the molded product by stretching, and the weight is reduced and whitening and opacity are achieved. The weight average molecular weight Mw in the production method of the present invention is expressed as a standard polystyrene conversion value measured by ordinary gel permeation (GPC). That is, in the present invention, GPC (Model HLC-802 manufactured by Tosoh Corporation) was used under the following measurement conditions. Column; GH8P + G400H8 + G300H8 + G2
000H8X2 solvent; tetrahydrofuran (THF), column constant temperature bath temperature: 40 ° C, THF flow rate: 1.2 ml / min, sample concentration: 0.005 g
/ 1ccTHF detector: Differential refractometer

The composition used in the production method of the present invention contains 5 to 100 parts by weight of the cyclopentadiene resin with respect to 100 parts by weight of high-density polyethylene, and is heat-treated at a temperature above the softening point of the cyclopentadiene resin. It is a thing.
In order to obtain a method for producing a void-containing stretched molded product which has excellent productivity and a stable molded product in a wide molding range, the compounding amount is preferably 7 to 80 parts by weight, more preferably 10 to 50 parts by weight. It is particularly preferable to add. If the blending amount is less than 10 parts by weight, the void forming effect is insufficient, and if it exceeds 100 parts by weight, extrusion unevenness and stretch rupture become severe during molding, which makes molding substantially difficult, which is not preferable. In the above composition, various additives known to be added to polyethylene as necessary, for example, processing stabilizers, antioxidants, lubricants, slip agents, antistatic agents, various polymers, inorganic fillers, etc. You may mix.

This composition is produced by mixing a predetermined amount of high-density polyethylene and a cyclopentadiene resin in a solid state with an ordinary blender or mixer and then heating at a temperature above the softening point (ring and ball method). To process. Specifically, using an extruder, a Banbury mixer, or the like, melt kneading is performed at a temperature not lower than the softening point of the resin and not lower than the melting temperature of polyethylene. From a practical point of view, it is particularly preferable to melt and knead, cool and cut to obtain a pelletized composition.
Further, a method in which a large amount of the resin is blended with polyethylene to prepare a masterbatch composition, and then the resin is blended with polyethylene to be used as a mixed composition is also useful. The composition thus obtained is subjected to melt extrusion using an extruder and a die (or a nozzle) to form an unstretched raw fabric, and then at least one surface of the unstretched raw fabric is irradiated with an electron beam. As a result, a part of the original fabric is crosslinked. This electron beam irradiation method may be a known method described in Japanese Examined Patent Publication No. 2-47334, but in the case of the present invention, it is not particularly necessary to perform it in an inert gas atmosphere, and irradiation is performed in the presence of air. Good to go. The degree of crosslinking by electron beam irradiation is preferably such that the gel fraction of the polyethylene component of the unstretched raw fabric is 5% or more.

Next, the electron-beam-irradiated unstretched raw material is heated and stretched in a uniaxial or biaxial direction at a predetermined magnification by a usual roll method, tenter method or tubular method to obtain a void-containing stretched molded article. To get This stretching may be performed in one step or in multiple steps. In the case of biaxial stretching, either simultaneous or sequential stretching may be performed. The stretching temperature is not higher than the melting point of the polyethylene, preferably in the range from the softening point of the resin to the melting point, specifically 70 to 135 ° C., preferably 100 to 1
It is 30 ° C. If the stretching temperature is less than 70 ° C., the softening of the resin is insufficient and uniform and stable stretching cannot be performed. On the other hand, if the stretching temperature exceeds the melting point of polyethylene, uniform stretching occurs but stretch orientation does not occur, resulting in insufficient cavity formation. A molded article aimed at by the present invention cannot be obtained. Further, it is desirable that the stretching ratio is 3 times or more, preferably 4 times or more in one direction or in the longitudinal and transverse directions. If the stretching ratio is less than 3 times, uniform stretching is difficult, and the thickness and formation of cavities are highly uneven, which is not preferable.

The stretch-molded product obtained by the production method of the present invention may be heat-treated at a temperature not higher than the melting point of the polyethylene while being stretched or relaxed as necessary after stretching, as in the case of ordinary stretch-molded products. Known surface treatments such as corona treatment and plasma treatment can also be performed in an atmosphere of air, oxygen, nitrogen or the like. The stretch-molded product obtained by the production method of the present invention has numerous voids (voids) formed inside the molded product, and the apparent density thereof is 0.92 or less, preferably 0.89 or less, and particularly preferably 0. 0.85 or less, which is significantly lighter than conventional high-density polyethylene stretched molded products, and the molded products are opaque with a total light transmittance of 30% or less, excellent surface gloss, and a unique pearl. It has a luster.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The characteristic values referred to in the present invention were evaluated by the following methods. Softening point (ring and ball method): Based on JIS K2207.
However, if the softening point is 140 ° C. or higher, measure with a silicon bath. (Unit; ° C.) Density: Based on 4.2 of JIS K6760-181 polyethylene test method. (Unit: g / cm ³ ) Apparent density: The weight per 1 m ^{2 of the} molded product was measured and 1
Converted per cm ² and the value ordered by thickness cm (unit: g / c
m ³⁾ UV absorption: a polymer 0.1g was dissolved in spectroscopic methylcyclohexane 100 ml, measure ultraviolet absorption spectrum, shown in the maximum absorbance wavelength in the range of 265～276Nm. Iodine value: According to JIS K0070-1966. The g number of iodine added to the unsaturated components in 100 g of the sample is shown. Melt flow rate (MFR): JIS K7210
-Test condition 4 (190 ° C, 2.16 kgf) of 1976. (Unit: g / 10 min) Total light transmittance: According to JIS K6714. (unit;
%) Gel fraction: Expressed as the extraction residue after extraction treatment in boiling xylene for 6 hours. (unit;%)

Cyclopentadiene resins used in Examples and Comparative Examples were obtained as follows. Polymer obtained from cyclopentadiene-based monomer as a main component: Distillation of 75% by weight of dicyclopentadiene obtained by steam cracking of petroleum naphtha and saturated hydrocarbon in xylene under known nitrogen atmosphere. The unreacted raw materials and the solvent were removed by heat polymerization, and the second-stage polymerization was continued under reduced pressure and kept at a temperature of 200 ° C or higher for a certain period of time, then cooled and solidified to obtain a petroleum resin (Table 1 ^{* 1} ) Hydrogenated resin obtained by hydrogenating a polymer obtained by using cyclopentadiene monomer as a main component: Obtained by hydrogenating the above-mentioned petroleum resin by a known method described in the text (Table 1 ^{* 2} )

Examples 1 to 5 100 parts by weight of high density polyethylene powder having a density of 0.956 and MFR 1.5, 0.1 part by weight of tris (2,4-di-t-butylphenyl) phosphite as an antioxidant,
0.2 parts by weight of calcium stearate and a predetermined amount of cyclopentadiene resin (Table 1 ^* ) were mixed, mixed for 3 minutes with a Henschel mixer, and then mixed with a single screw extruder.
The mixture was melt mixed at 00 ° C., cooled and cut to obtain a composition.
Each of the obtained compositions was melt-extruded at 230 ° C. using a T-die extrusion sheet molding machine and rapidly cooled by a 70 ° C. cooling roll to form a sheet having a thickness of 0.5 mm. This sheet was irradiated with an electron beam of 20 megarats in the air on both sides using an electron beam irradiation device to obtain a raw sheet. Next, this raw sheet is made into a 115-
The film was stretched 3.5 times in both longitudinal and transverse directions at a temperature of 120 ° C. and heat-treated at the same temperature for 3 seconds while being relaxed by 3% to obtain a biaxially stretched film. Table 1 shows the gel fraction of the raw sheet and the characteristic values of the obtained film.

Comparative Example 1 The procedure of Example 1 was repeated except that the cyclopentadiene resin was not used. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that a cyclopentadiene resin having a softening point of less than 170 ° C. was used. The results are shown in Table 1.

Comparative Example 3 The procedure of Example 5 was repeated except that an alicyclic resin was used instead of the cyclopentadiene resin. The results are shown in Table 1.

[0026]

[Table 1] As is clear from Table 1, the film consisting only of high-density polyethylene has a high density and a high total light transmittance, and is transparent, but the film of the present invention has a very low density and a total light transmittance, and contains a high degree of voids. It can be seen that it is a lightweight and opaque film.

Example 6 The same amount of the antioxidant and calcium stearate used in Example 1 and 30 parts by weight of the hydrogenated resin used in Example 1 were added to a high density polyethylene powder having a density of 0.960 and MFR 0.8. The mixture was blended, melt-mixed at a temperature of 200 ° C. using an extruder, cooled, and cut to obtain a pelletized composition. The obtained composition was melt-extruded at 220 ° C. using a T-die extrusion sheet apparatus in the same manner as in Example 1 and rapidly cooled with a cooling roll at 80 ° C. to form a sheet having a thickness of 0.3 mm, and the same electron beam was used. Both sides of the sheet were irradiated with an electron beam of 20 megarats using an irradiation device to obtain a raw sheet having a gel fraction of 10%. Next, this raw sheet was stretched 6.5 times in the longitudinal direction on a roll at 110 ° C. using a roll stretching machine, heat-treated and cooled to obtain a wound uniaxially stretched film. This film is highly opaque with a thickness of 55μ, an apparent density of 0.81, and a total light transmittance of 26%, and is opaque. As a result of observing the cross section with a microscope, it contains countless fine cavities. Was recognized.

Comparative Example 4 A sheet having a thickness of 0.5 mm was prepared in the same manner as in Example 1 by using the composition used in Example 1, and the sheet was cut into a square having a width of 9 cm to obtain a raw sheet. With a pantograph type biaxial stretching machine, the temperature with the most uniform stretching property is selected in the range of 115 to 125 ° C., and longitudinal and transverse stretching is performed 3.5 times in two directions at the same time. Heat treatment was performed for a second to obtain a biaxially stretched film having an average thickness of about 45μ. 20 sheets of this raw sheet were stretched and 13 sheets were stretched and broken, and the obtained stretched film had a thickness unevenness (variation range from the average value) of 10 cm square in the central portion of 7 sheets, which was 56% on average. It was In addition, the same raw sheet as in Example 1 was stretched 20 sheets, the number of which was two or less was broken by stretching, and the thickness unevenness was 18 sheets which was good at 14% on average.

[0029]

EFFECTS OF THE INVENTION The manufacturing method of the present invention can solve the problems of productivity and uniformity of void-containing stretched molded products which have been a problem in the prior art. Moreover, it retains the strength and rigidity peculiar to high-density polyethylene, and has added excellent features such as weight reduction, opacity and pearlescent luster, and is used as a packaging material for films, sheets, tapes, yarns, fibers and hollow containers. It is an industrially extremely superior material that can be used in a wide range of applications such as decorative materials, packing materials, synthetic paper, and non-woven fabrics.

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Claims (3)

[Claims] 1. A polymer obtained by using a cyclopentadiene-based monomer as a main component, a hydrogenated resin obtained by hydrogenating the polymer, or a standard polystyrene-equivalent weight average molecular weight of the polymer and the hydrogenated resin ( Mw) is 700 or more and the softening point (ring and ball method) is 170 ° C. or more, and 10 to 100 parts by weight of a cyclopentadiene resin and 100 parts by weight of high-density polyethylene having a density of 0.940 or more are blended to obtain the softening point or more. By molding the composition heat-treated in step (1), by molding an unstretched raw material by a melt extrusion method, irradiating at least one surface of the raw material with an electron beam, and subsequently stretching it in at least one direction by 3 times or more, A method for producing a polyethylene-based void-containing stretched molded article, which has an apparent density of 0.92 or less. 2. A component in which the cyclopentadiene resin has a weight composition ratio (B) / (A) of cyclopentadiene monomer (A) and vinyl aromatic hydrocarbon (B) of 0 to 0.3. A polymer obtained by polymerizing the polymer, a hydrogenated resin obtained by hydrogenating the polymer, or the polymer and the hydrogenated resin, and having a weight average molecular weight (M
The polyethylene-based void-containing stretched molded product according to claim 1, wherein w) has a value of the formula Mw ≧ 700 + 2200X (where X is a composition ratio [(B) / (A) + (B)]. Production method. 3. A polyethylene-based void-containing stretch according to claim 2, wherein the hydrogenated resin obtained by hydrogenating a polymer obtained by using a cyclopentadiene monomer as a main component has an ultraviolet absorbance of 1.0 or less and an iodine value of 30 or less. Method for manufacturing molded article.