JPH0351734B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a two-component polyethylene copolymer (A) containing at least one aliphatic unsaturated carboxylic acid and its derivative as an essential component and a polypropylene (B). The present invention relates to a crosslinked polypropylene foam having excellent heat resistance and vacuum formability made of a blend polymer containing the following. [Prior art] Foams with excellent heat resistance and good moldability have been known from Japanese Patent Application Laid-open No. 56-34732, and this publication describes polypropylene with high crystallinity and polypropylene with high melt viscosity. A foam made of a blend polymer containing medium density polyethylene as an essential component has been proposed. However, although this foam has excellent heat resistance, due to the difference in melt viscosity between the two components constituting the blend polymer, when a sheet is formed from the blend polymer, the two components are not uniformly dispersed. crosslinking becomes difficult, and crosslinking unevenness is likely to occur.
And in the production of long sheet-like foam, the diameter is 1.
There was a problem that large bubbles of ~3 mmφ were generated, and the bubbles were not broken during vacuum forming and surface roughness was caused. [Problems to be Solved by the Invention] An object of the present invention is to provide a crosslinked polypropylene resin foam that does not cause surface roughness during vacuum forming and has excellent heat resistance and vacuum formability. [Means for Solving the Problems] The object of the present invention is to provide an ethylene/alkyl acrylate copolymer, which has a copolymerization ratio of 10 to 25% by weight of monomers excluding ethylene, and a melting point (Tm).
It consists of a blend polymer containing polyethylene copolymer (A) and polypropylene (B) with a temperature of 86 to 102°C as essential components, and the blend ratio (B/A) is within the range of 2 to 19 by weight. , can be achieved by a crosslinked polypropylene resin foam with a gel fraction of 15-45%. In addition, at least one copolymer selected from the group consisting of ethylene/acrylic acid copolymer, ethylene/methyl methacrylate copolymer, and ethylene/methyl methacrylate/maleic anhydride ternary copolymer. A polyethylene copolymer (A) with a copolymerization ratio of monomers excluding ethylene of 2 to 10% by weight and a melting point (Tm) of 86 to 102°C.
and polypropylene (B) as essential components, the blend ratio (B/A) is within the range of 2 to 19 by weight, and the crosslinked polypropylene type has a gel fraction of 15 to 45%. This can also be achieved by using resin foam. In the present invention, the blend polymer containing polyethylene copolymer (A) and polypropylene (B) as essential components desirably accounts for at least 90% by weight based on the total weight of the polymers constituting the foam. Examples of polyethylene copolymers (A) include ethylene/alkyl acrylate copolymers, ethylene/
Acrylic acid copolymer (EAA), ethylene/methyl methacrylate copolymer (EMMA), and ethylene/methyl methacrylate/maleic anhydride terpolymer (EMMA/MAH) are used.
Note that the polyethylene copolymer (A) may contain a small amount of a monovalent or divalent aliphatic unsaturated carboxylic acid and its derivatives as a copolymerization component within a range that does not impair the object of the present invention. The ethylene/alkyl acrylate copolymer preferably has a copolymerization ratio of 10 to 25% by weight and a melting point (Tm) of 86 to 102°C. The alkyl group in the ethylene/alkyl acrylate copolymer is not particularly limited, but from the viewpoint of sheet formability of the polymer blend, an alkyl group having 1 to 10 carbon atoms is preferred, and among them, an ethyl group is most preferred. Here, if the copolymerization ratio of the copolymer components is less than 10%, the crystallinity of the polymer will increase and the melting point (Tm) will increase, which is advantageous in terms of heat resistance, but another blend ingredient polypropylene
It is not preferable because the effect of improving vacuum formability when blending (B) is not sufficient, and 25
If it exceeds % by weight, the amorphousness of the polymer increases, the heat resistance decreases, and surface roughness of the foam tends to occur during molding, which is not preferable. The method for producing this ethylene/alkyl acrylate copolymer is not particularly limited, but it is usually a polymerization method that involves a high rate of change in the polymer, such as supplying ethylene and alkyl acrylate from one end and feeding the other end. A continuous production method can be adopted by changing the monomer charge concentration, polymerization catalyst concentration, etc. in a tubular reactor from which the product is taken out from the end. Furthermore, in the case of ethylene/acrylic acid copolymer (EAA), ethylene/methyl methacrylate copolymer (EMMA), and ethylene/methyl methacrylate/maleic anhydride terpolymer (EMMA/MAH), The copolymerization ratio of the polymerization components is within the range of 2 to 10% by weight, and the melting point (Tm) is 86 to 102°C. That is, in these copolymers, only when the copolymerization ratio of the copolymer components satisfies the above-mentioned range, can the sheet formability of the blend polymer, the vacuum formability of the foam itself, which is the object of the present invention, be achieved. This has an excellent effect on preventing surface roughness during molding. In addition, if the melting point (Tm) of these polyethylene copolymers (A) does not satisfy the above range, for example, if Tm is less than 86°C, roll adhesion is likely to occur during sheet molding, and the resulting foam This is undesirable because it tends to cause surface roughness when vacuum forming the body, and if it exceeds 102°C, elongation decreases and vacuum formability deteriorates, which is not preferable. Here, Tm is a value detected by a differential scanning calorimeter (DSC). In addition, the polypropylene (B) constituting the blend polymer of the present invention is generally a homopolymer of crystalline propylene with good stereoregularity polymerized using a Ziegler type catalyst or a crystal containing at least 70% by weight of a propylene component. propylene copolymers, such as propylene and α-olefin.
Examples include primary and tertiary copolymers. Among these polypropylenes (B), those having an ethylene content of 0.5 to 15% by weight and a melt flow rate (MFR) of 1 to 20, preferably a random or block copolymer having an ethylene component of 1 to 10% by weight. Good combination. In particular, from the point of view of suppressing the decomposition of the blowing agent during the sheeting process, it is important to use crystalline propylene with good randomness, with a random coefficient of 0.7 or less and an isotactic degree (referred to as boiling n-heptane extraction residue) of 40% or more. Ethylene copolymer is good. Here, the random coefficient is the value shown by the absorbance ratio (A720/A731) of absorption at 720 cm ^-1 and 731 cm ^-1 due to the ethylene component in the IR spectrum of the copolymer measured at room temperature, The smaller this value is, the more randomly the copolymer component ethylene is distributed in the polymer chain. The blend ratio (B/A) of these essential components (A) and (B) is 2 to 19, preferably 3 by weight.
It is within the range of ~9. If the value of (B/A) is less than 2, it will tend to stick when forming sheets, etc., making it difficult to set casting conditions.
The resulting foam also has insufficient heat resistance. Also,
If it exceeds 19, it is not preferable because the resulting foam will have insufficient vacuum formability. Furthermore, the blend polymer of the present invention contains polyethylene (C) as a third component.
It is preferable to blend 80 parts by weight or less, preferably 50 parts by weight or less per 100 parts by weight, and representative examples of this polyethylene (C) include so-called low-density polyethylene and linear polyethylene. Low-density polyethylene is a polymer obtained by radical polymerization under high pressure and is used as a raw material for cross-linked foams, and has a melting point (Tm) of less than 115°C and a density of 0.935 g/cm ³ or less. Polyethylene is good, and linear polyethylene has a melting point of 115 to 135°C, preferably 115 to 127°C,
Density is 0.915-0.945g/cm ³ , determined according to the measurement method specified in ASTM-D-1238.
Linear low-density and medium-density polyethylene having an MFR in the range of 0.1 to 50 g/10 minutes are preferred. More specifically, at least one copolymer component such as α-olefin having 4 to 20 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. It is a polyethylene copolymer copolymerized with seeds or a small amount of propylene by medium/low pressure polymerization. In addition to these polyethylenes, there is also polyethylene with a high crystalline density of 0.940 obtained by the above-mentioned medium/low pressure polymerization method.
~0.970 g/cm ³ of polyethylene with a Tm of 125-135°C can be used. The foam of the present invention is made of a blend polymer containing the two components (A) and (B) as essential components.
It is necessary to have a gel fraction in the range of ~45%, preferably 20-40%, and a drawing area ratio (K) of 0.6 or more. In other words, if the gel fraction is lower than 15%, the heat resistance will be low and surface roughness will easily occur during molding, while if it exceeds 45%, the elongation of the foam will decrease and the moldability will deteriorate. becomes worse, and it becomes impossible to obtain a product that satisfies the drawing ratio specified in the present invention. Hereinafter, one embodiment of the method for producing a crosslinked polypropylene resin foam according to the present invention will be described. A polyethylene copolymer (A) having the above copolymerization composition, polypropylene (B), and optionally a third component polyethylene (C) are blended at the above blend ratio (B/A), A known thermally decomposable blowing agent such as azodicarbonamide, dinitrosopentamethylenetetramine, etc. and, if necessary, a crosslinking agent that generates radicals upon heating are mixed, and the mixture is heated to a temperature at which the blowing agent and crosslinking agent do not decompose. Hold and shape, for example, shape into a sheet.
This formed sheet material is subjected to any known method such as ionizing radiation crosslinking method or chemical crosslinking method to obtain a gel fraction of 15 to 45%, preferably 20 to 40%.
Crosslink so that More specifically, in the case of the ionizing radiation crosslinking method, α, β, γ, X-rays, electron beams, neutron beams, etc. are used as high-energy rays, and a high-energy electron beam irradiation machine is usually used. Crosslinking is achieved by irradiating the sheet with an electron beam at a dose of ~50 Mrad. In this case, 0.1 to 10 parts by weight of various known crosslinking aids, such as divinylbenzene, diallyl phthalate,
Electron beam crosslinking may be performed by adding trimethylolpropane triacrylate or the like. Instead of this radiation irradiation, it is also possible to add an ultraviolet sensitizer such as benzophenone and crosslink by irradiating ultraviolet rays. In addition, in the case of a chemical crosslinking method, a crosslinking method using an organic peroxide such as dicumyl peroxide or ditertiary butyl peroxide, or a grafting method by kneading a vinyl silane such as vinyltrimethoxysilane with these crosslinking agents. After that, a silane crosslinking method in which crosslinking is performed by a siloxane condensation reaction, etc. can be appropriately applied. The thus obtained crosslinked molded article is heated in a hot air atmosphere or on a salt bath to rapidly decompose the foaming agent contained within the molded article, thereby converting it into a foam. In addition, to the extent that the object of the present invention is not impaired, ethylene-polypropylene random copolymer, polybutylene and Other α-olefin homopolymers or copolymers, chlorinated polyethylene, and other various polymers can be added and mixed in small amounts up to 10% by weight, if necessary. For desired purposes, lubricants, antioxidants, ultraviolet absorbers, colorants, antistatic agents, flame retardants, and various other inorganic substances that impart other properties may be added to the extent that they are not included. Further, the crosslinked polypropylene resin foam of the present invention is coated with an adhesive on at least one surface thereof by corona discharge treatment, coating, etc.
It can be laminated to improve its workability, and it can also be laminated with plastic films, sheets, other foam sheets, metal foils, and extruded laminated to create composite structures. technology can be applied. [Effects of the Invention] The crosslinked polypropylene resin foam of the present invention thus obtained has excellent vacuum formability, ranging from low expansion ratios to high expansion ratios. For example, by integrally molding polyvinyl chloride sheets, fabric sheets, etc. in a laminated state, it can be made into a variety of automobile interior parts and other products. Of course, its cushioning properties, heat resistance,
Utilizing its heat insulating properties, we can produce various packing materials, adhesive tape bases, pine base materials, heat insulating materials, cushion materials, etc.
Furthermore, it can be used and developed for many other applications such as clothing, building materials, and medical applications. Below, the effects of the present invention will be explained in more detail based on Examples. In the present invention, the melting point (Tm), drawing ratio (K), gel fraction, and surface roughness are values measured by the following method. (1) Melting point (Tm) Using a PerkinElmer Model DSC-2 differential scanning calorimeter (DSC), the endothermic peak temperature of melting after melting and recrystallization was determined as the melting point (Tm). (2) Forming drawing ratio (K) When a vacuum forming machine is used to heat a vertical cup-shaped mold with a diameter D and a depth H under the optimum heating conditions, and the foam is straight-molded, the cup is formed without tearing. The H/D at the limit of elongation into a shape was defined as the forming drawing ratio (K). Note that the D of the cup is 50 mm. (3) Gel fraction Shredded foam approx. Collect 2g and weigh it accurately (set as W ₁ ). After immersing the accurately weighed foam in tetralin at 135° C. for 3 hours, the insoluble portion is taken out, washed with methanol, air-dried, vacuum-dried, and weighed accurately (referred to as W ₂ ). The gel fraction is calculated from the values of W ₁ and W ₂ according to the following formula. Gel fraction (%) = 100 x (W ₂ /W ₁ ) (4) Apparent density (d) Cut the foam into a 10 cm x 10 cm square, measure the weight and thickness, and divide this weight by the volume. It is expressed in weight per unit volume (g/cm ³ ). (5) Surface roughness A phenomenon in which the air bubbles on the surface layer of a foam burst due to heating during vacuum forming, causing the surface of the foam to become rough. Judgments were made based on the following criteria: when oil-based magic ink was applied to a foam and wiped off with a cloth, the ink remained in spots. ○: No spots to very few spots observed (passed). ×: Many obvious spots are observed. (6) Heat resistance In accordance with the measurement method specified in JIS-K-6767, the thermal shrinkage rates in the vertical, horizontal, and thickness directions due to heat treatment are shown. Specifically, a measurement sample (foam) is marked with square marks of 10 cm both vertically and horizontally, the thickness is measured, and then heat treated in a hot air oven at 110°C for 22 hours.
After cooling to room temperature, the vertical, horizontal and thickness dimensions were measured, and the following judgment was made based on the magnitude of dimensional change (thermal shrinkage rate) due to this heat treatment. Heat shrinkage rate of ±3.0% or less: 〇 [Accepted] Heat shrinkage rate of 3.0 to 5.0%: △ Heat shrinkage rate of over ±5.0%: × In addition, the measurement of dimensional changes due to the above heat treatment is as follows:
The test was performed 5 to 10 times and evaluated. Examples 1 to 7, Comparative Examples 1 to 6 As the polyethylene copolymer (A), ethyl acrylate (EA), acrylic acid (AA), methyl methacrylate/maleic anhydride (MMA/ Ethylene/ethyl acrylate copolymer (EEA), ethylene/acrylic acid copolymer (EAA), or ethylene/methyl methacrylate/maleic anhydride ternary copolymer containing 5 to 30% by weight of MAH) Combined (EMMA・
MAH) as polypropylene (B),
Ethylene with Tm of 147℃ and MFR of 7g/10 min.
A propylene/ethylene random copolymer containing % by weight was used. Furthermore, Examples 5 and 7, Comparative Examples 3 and 6
So, as polyethylene (C), the density is 0.921g/
cm ³ and MFR of 4.8 g/10 min.
0.925g/cm ³ , melting point (Tm) 124℃, MFR 8
g/10 min linear low density polyethylene was used. These blend components (A), (B), and (C) were blended at the blend ratios shown in Table 1. To 100 parts by weight of these blended polymers, 12 parts by weight of azodicarbonamide as a blowing agent and 3 parts by weight of divinylbenzene as a crosslinking aid were added. However, only in the case of Comparative Example 3,
The amount of dibylbenzene added was 6 parts by weight. These blended polymers were mixed using a Henschel mixer and then melt extruded to obtain a molded sheet. These molded sheets were irradiated with a dose of 5 Mrad using an electron beam irradiation device (IR-2 manufactured by Nissin High Voltage Co., Ltd.). The obtained crosslinked sheet was placed on a salt bath.
Foaming was carried out by heating to 225-230°C. An evaluation test was conducted on the obtained foam sheet. The results are shown in Table 1. From the table, the foams of Examples 1 to 7 that satisfied the requirements of the present invention were foams that had no surface roughness and had excellent heat resistance. On the other hand, comparative examples 1 and 2

【table】

[Table] In the table, EA stands for ethyl acrylate, AA stands for acrylic acid, MMA stands for methyl methacrylic acid, and MAH stands for maleic anhydride. Foams whose ethylene copolymerization amount did not satisfy the requirements of the present invention had poor drawing ratio (K) (Comparative Example 1) and lacked surface roughness and heat resistance (Comparative Example 2). and 5). In addition, the blend ratio (B/
When A) was outside the specified range of the present invention (Comparative Examples 3 and 4), the vacuum formability was low, and the resulting foams had insufficient surface roughness and heat resistance. Furthermore, in the case of Comparative Example 6, in which the gel fraction was outside the range of the present invention, vacuum formability was lacking.

Claims (1)

[Scope of Claims] 1. An ethylene/alkyl acrylate copolymer in which the copolymerization ratio of monomers other than ethylene is
Consists of a blend polymer containing polyethylene copolymer (A) with a melting point (Tm) of 86 to 102°C and polypropylene (B) as essential components, with a blend ratio (B/A) of 10 to 25% by weight. A crosslinked polypropylene resin foam having a ratio of 2 to 19 and a gel fraction of 15 to 45%. 2. In claim 1, based on 100 parts by weight of a blend polymer consisting of a polyethylene copolymer (A) and a polypropylene (B),
A crosslinked polypropylene resin foam that is a blended polymer made by blending 80 parts by weight or less of polyethylene (C). 3 Ethylene/acrylic acid copolymer, ethylene/
At least one copolymer selected from the group consisting of methyl methacrylate copolymer and ethylene/methyl methacrylate/maleic anhydride ternary copolymer, wherein the copolymerization ratio of monomers other than ethylene is 2-10% by weight, melting point (Tm)
Consisting of a blend polymer containing polyethylene copolymer (A) and polypropylene (B) as essential components at 86 to 102 °C, the blend ratio (B/A) is within the range of 2 to 19 by weight, Cross-linked polypropylene resin foam with a gel fraction of 15-45%. 4 In claim 3, based on 100 parts by weight of a blend polymer consisting of a polyethylene copolymer (A) and a polypropylene (B),
A cross-linked polypropylene resin foam that is a blended polymer made by blending polyethylene (C) at 80% by weight or less.