Polyolefin rotational moulding foaming composition, product and preparation method

Abstract

The invention discloses a polyolefin rotational molding foaming composition, a product and a preparation method, and belongs to the technical field of foaming compositions. The problems that in the prior art, chemical foaming agents AC and the like are adopted for preparing foamed polyethylene, raw materials are prone to aging degradation, discoloration, bubble collapse, uneven foam holes and the like are solved. The polyolefin rotational molding foaming composition consists of an outer layer raw material and a core layer raw material, the raw material of the outer layer comprises linear low-density polyethylene powder; the core layer material is prepared from, by mass, 50-65 parts of high-density polyethylene, 10-20 parts of ethylene propylene rubber, 10-15 parts of plasticizer, 6.5-9 parts of water, 0.5-2 parts of sodium bicarbonate, 1-3 parts of silicon dioxide and 0-2 parts of lubricant. According to the polyolefin rotational molding foaming composition, water is used as a foaming agent, the compatibility of the raw materials is good, the aperture of a product is uniform and fine, large bubbles and serial holes basically do not exist, a good foaming effect can be achieved, and the composition is environmentally friendly, good in practicability and easy to directly recycle.

Description

Technical Field

[0001] The invention belongs to the technical field of foaming compositions, and in particular relates to a polyolefin rotomolding foaming composition, a product and a preparation method. Background Art

[0002] The application range of polyethylene roto-molding products is getting wider and wider, especially irregularly shaped hollow products are widely used in the automotive industry. The commonly used raw material is linear low-density polyethylene. The disadvantage of the raw material is low rigidity. When it is made into hollow products, it is easy to deform, affecting the use effect and appearance. To improve its shortcomings, the following methods can be used:

[0003] (1) Use high-density polyethylene with good rigidity, but the corresponding raw materials are not produced normally in China at present.

[0004] (2) Modification of linear low-density polyethylene, such as cross-linking, improves rigidity, but increases processing difficulty and increases deformation defects in the product appearance.

[0005] (3) First, the rotomolded hollow product is formed, and then the foaming and filling modification is performed. Special-shaped hollow products are usually reinforced by polyurethane foaming filling. However, the polyurethane foaming equipment is complicated.

[0006] The existing foamed polyethylene processing uses chemical foaming agents such as AC, which is a type of exothermic foaming agent, and usually has a decomposition temperature of about 200°C. The disadvantages of using it are high processing temperature, easy aging and degradation of plastic raw materials, affecting the performance, and easy escape of decomposed bubbles, causing bubble collapse, and easy discoloration and uneven pores. If DCP cross-linking modification technology is used, increasing the melt strength of polyethylene can prevent the gas in the bubbles from escaping. However, the recycling of cross-linked polyethylene is very troublesome and has a great impact on the environment.

[0007] In view of this technical problem, the prior art proposes the following solution.

[0008] Patent CN 101519504 B discloses a method for preparing polyethylene foam material using water as a foaming agent, using water as a foaming agent, and directly extruding a foamed product through a single / twin screw extruder. The foaming ratio of the prepared polyethylene foam plastic is 3-20 times, but because the water phase component (liquid phase) and the polyethylene component (solid phase) are difficult to mix evenly, the foamed product is prone to defects such as string holes and large bubbles. It is easy to break the strip during extrusion processing, and the quality of the product is difficult to control.

[0009] Patent CN 108299744 B discloses a rubber composition, and its application and production method in foamed products. The rubber composition includes: a rubber matrix and necessary components, wherein the rubber matrix includes: a content of branched polyethylene: 0 < a ≤ 100 parts; b content of EPDM and EPDM: 0 ≤ b < 100 parts, and necessary components include: 0.5 to 10 parts of a crosslinking agent, and 1.5 to 25 parts of a foaming agent. In addition to short branches such as methyl, ethyl, propyl, butyl, and amyl, the branched polyethylene also has long branches with a carbon number greater than 6. Partial or complete substitution of the EPDM in the foamed rubber composition with branched polyethylene can improve the melt strength of the rubber composition, improve the foamability of the composition, especially pre-foaming, and the obtained rubber product has a lower compression permanent deformation. However, the rubber composition must use a specific branched polyethylene, and the foaming agent used is still a chemical foaming agent, which cannot completely solve the above problems. Summary of the invention

[0010] The purpose of the present invention is to provide a polyolefin rotomolding foaming composition, a product and a preparation method. The polyolefin rotomolding foaming composition can be used to prepare various hollow products and fill the core layer of various hollow products. Water is used as a foaming agent and can achieve an application effect that is better than that of a chemical foaming agent. It is green and environmentally friendly, can effectively improve the comprehensive performance of the material, and increase the scope of use of hollow products.

[0011] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows.

[0012] The present invention provides a polyolefin rotomolding foaming composition, which is composed of an outer layer raw material and a core layer raw material;

[0013] The outer layer raw material includes linear low-density polyethylene powder;

[0014] In parts by mass, the core layer raw materials include:

[0015]

[0016] Preferably, the particle size of the linear low-density polyethylene powder is 20-40 mesh and the density is 0.931-0.934 g / cm 3 , the melt index is 5.8g / 10min.

[0017] Preferably, the particle size of the high-density polyethylene powder is 20-40 mesh and the density is 0.951-0.953 g / cm 3 , the melt index is 5.6-8.9g / 10min.

[0018] Preferably, the Mooney viscosity of the EPDM rubber is 26-61 ML (1+4) 100°C; more preferably, the Mooney viscosity of the EPDM rubber is 2.9 ML (1+4) 100°C.

[0019] Preferably, the plasticizer is one or more of dioctyl phthalate (DOP), isophthalate esters (DOIP), and phosphate esters (TOP).

[0020] Preferably, the oil absorption value of the silica is 2.6-3.6 ml / 100 g.

[0021] Preferably, the lubricant is one or both of oleamide and erucamide.

[0022] The present invention also provides a polyethylene rotomolded foam product prepared by using the polyolefin rotomolded foam composition, which consists of a core layer and an outer layer wrapping the core layer, wherein the raw material of the core layer is the core layer raw material, and the raw material of the outer layer is the outer layer raw material.

[0023] The present invention also provides a method for preparing the above polyethylene rotomolded foamed product, the steps of which are as follows:

[0024] (1) Take the raw materials according to the formula;

[0025] (2) mixing sodium bicarbonate and water, stirring until transparent, to obtain a solution;

[0026] (3) mixing the plasticizer with the solution prepared in step (2), and performing ultrasonic emulsification. When no water phase is visible, adding silicon dioxide, and stirring evenly to obtain a mixed emulsion;

[0027] (4) refining the ethylene-propylene rubber, thinning it into sheets, adding a lubricant, folding and packaging, adjusting the roller distance, and then sequentially adding the mixed emulsion prepared in step (3) and the high-density polyethylene powder, mixing them evenly to obtain a mixture;

[0028] (5) extruding and granulating the mixture to obtain foamed particles;

[0029] (6) Adding linear low-density polyethylene powder and foamed particles into a rotational molding mold, heating and molding, and obtaining a polyethylene rotational molding foam product.

[0030] Preferably, in step (2), the sodium bicarbonate and water are mixed at room temperature.

[0031] Preferably, in step (3), the stirring time is 5-10 min.

[0032] Preferably, in step (3), the ultrasonic conditions are 60w, 25°C, and 10min.

[0033] Preferably, in step (3), the roller distance is adjusted to 1.2-1.5 mm.

[0034] Preferably, in step (4), the EPDM rubber is milled using a double roll mill.

[0035] Preferably, in step (4), the mixing temperature is not higher than 100°C; more preferably, the mixing temperature is 90-95°C.

[0036] Preferably, in step (5), the extrusion temperature is not higher than 100°C.

[0037] Preferably, in step (5), the size of the granulation is: less than 1 mm in diameter and no more than 2 mm in length.

[0038] Preferably, in step (6), the temperature inside the mold is 195-230°C.

[0039] In the preparation method of the present invention, the amount of the outer layer raw material and the core layer raw material is determined according to the polyethylene rotomolded foam product and the volume of the core layer to be filled, and usually the amount of the core layer raw material added is 105wt% of the calculated amount.

[0040] In the preparation method of the present invention, during the heating and molding process, due to the different particle sizes of the outer layer raw material and the foamed particles, a polyethylene rotomolded foamed product can be directly formed. That is, the outer layer raw material gradually moves outward, and the foamed particles gradually move inward, and as the temperature rises, the outer fine particles first melt to form the outer layer, and after most of the outer layer raw material melts, the inner foamed particles melt to form a core layer.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The polyolefin rotomolding foaming composition of the invention uses water as a foaming agent, and the product has uniform and fine pores, is substantially free of large bubbles and string holes, can achieve a good foaming effect, is green and environmentally friendly, has good practicality, and is easy to directly recycle.

[0043] The polyolefin rotomolding foaming composition of the present invention selects HDPE resin and EPDM elastomer, which have good compatibility and are not easy to separate into phases. Within the processing temperature range, it can maintain a better viscosity state, thereby improving the strength of the surrounding melt when the foaming gas expands, so that the linear low-density polyethylene forms fine and uniform foaming cells, and obtains a stable cell structure.

[0044] The preparation method of the polyolefin rotomolding foaming composition of the present invention ensures uniform dispersion and distribution of each component, especially uniform distribution of water, thereby ensuring stable foaming of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0046] Figure 1 This is a schematic diagram of the structure of a polyolefin rotomolded foamed product prepared in Example 1 of the present invention;

[0047] In the figure, 1. core layer, 2. outer layer. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0049] In the following examples, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, devices, instruments, equipment, etc. used in the following examples can be obtained from commercial sources.

[0050] Examples 1-8

[0051] The polyolefin rotomolding foaming composition is composed of an outer layer raw material and a core layer raw material; the outer layer raw material is a linear low-density polyethylene powder, calculated by weight, the formula of the core layer raw material is shown in Table 1, the amount of the core layer raw material is calculated based on the to-be-filled volume of the core layer of the polyethylene rotomolding foaming product, and the actual addition amount is 105wt% of the calculated amount;

[0052] Among them, the density of high-density polyethylene is 0.952g / cm 3 , melt index is 5.6g / 10min, purchased from Qilu Petrochemical Company; density of EPDM is 0.862g / cm 3 , Mooney viscosity 2.9ML (100 (1+4)), purchased from Jilin Petrochemical Company; plasticizer is DOP, density 0.982g / cm 3 , purchased from Zibo Plasticizer Factory; tap water, density 1.0 g / cm 3 ; Oleic acid amide is a white powder with a molecular weight of 280, purchased from Shanghai Zhonghua Chemical Factory; Sodium bicarbonate is a white powder with a density of 2.20 g / cm 3 , purchased from Weifang Haizhiyuan Chemical Factory, silica is white powder with a density of 0.005g / cm 3 The oil absorption value is 3.6ml / 100g, purchased from Jiangsu Quecheng Silicon Chemical, and the density of linear low-density polyethylene powder is 0.932g / cm 3 , melt index is 5.8g / 10min, purchased from Qilu Petrochemical Company;

[0053] The preparation method of the above-mentioned polyolefin rotomolding foamed product comprises the following steps:

[0054] (1) Weigh each raw material according to the formula;

[0055] (2) mixing sodium bicarbonate and water at room temperature, stirring until transparent, to obtain a solution;

[0056] (3) ultrasonically emulsifying the plasticizer and the solution of step (2), and when no obvious water is found in the mixed system, adding silicon dioxide, stirring and mixing for another 5-10 minutes to obtain a mixed emulsion;

[0057] (4) using a double-roll mill to form a thin sheet of ethylene-propylene rubber, adjusting the roller distance to 1.2-1.5 mm, and sequentially adding the mixed emulsion and high-density polyethylene, and mixing evenly at 90-95° C. to obtain a mixture;

[0058] (5) adding the mixture to an extruder, extruding and granulating, the extrusion temperature is not higher than 100° C., and the pelletizing size is controlled to be less than 1 mm in diameter and not more than 2 mm in length, to obtain foamed particles;

[0059] (6) Adding linear low-density polyethylene powder and foamed particles into a rotational molding mold, heating at 195-230° C. to form a polyethylene rotational molding foam product having a structure such as Figure 1 As shown, it is composed of a core layer 1 and an outer layer 2 wrapping the core layer 1. The raw material of the core layer 1 is the core layer raw material, and the raw material of the outer layer 2 is the outer layer raw material.

[0060] The expansion ratio, cell size, cell uniformity and foaming density of the polyethylene rotomolded foam products prepared in Examples 1-8 were tested. The testing method is:

[0061] The foaming ratio is calculated according to the following formula:

[0062]

[0063] In the formula, - Foaming ratio; ρ1 - density of unfoamed sample; ρ2 - density of foamed sample.

[0064] Foaming density: obtained by immersion foaming according to GB / T1033-86 standard, unit: g / cubic centimeter.

[0065] Cell size: measured with a 10x magnifying glass, unit: μm.

[0066] Cell uniformity: measured with naked eyes using a 10x magnifying glass.

[0067] The test results are shown in Table 1.

[0068] Table 1 Formulations and test results of Examples 1-8

[0069]

[0070] Comparative Examples 1-6

[0071] The preparation method of the polyolefin rotomolding foamed product comprises the following steps:

[0072] (1) According to the formula in Table 2, weigh each raw material;

[0073] Among them, the density of high-density polyethylene powder is 0.952g / cm 3 , melt index is 5.6, purchased from Qilu Petrochemical Company; density of EPDM is 0.862g / cm 3 , Mooney viscosity 2.9, purchased from Jilin Petrochemical Company; plasticizer is DOP, density 0.982g / cm 3 , purchased from Zibo Plasticizer Factory; tap water, density 1.0 g / cm 3 ; Oleic acid amide is a white powder with a molecular weight of 280, purchased from Shanghai Zhonghua Chemical Factory; Sodium bicarbonate is a white powder with a density of 2.20 g / cm 3 , purchased from Weifang Haizhiyuan Chemical Factory, silica is white powder with a density of 0.005g / cm 3 , oil absorption value is 3.6ml / 100g, purchased from Jiangsu Quecheng Silicon Chemical;

[0074] (2) adding the raw materials into a mixer and mixing them uniformly to obtain a mixture;

[0075] (3) adding the mixture to an extruder, extruding and granulating, the extrusion temperature is not higher than 100° C., and the pellet size is controlled to be less than 1 mm in diameter and not more than 2 mm in length, to obtain foamed particles;

[0076] (4) Adding linear low-density polyethylene powder and foamed particles into a rotational molding mold, heating at 195-230°C to form a polyethylene rotational molding foam product, the density of the linear low-density polyethylene powder is 0.932 g / cm 3 , melt index is 5.8, purchased from Qilu Petrochemical Company.

[0077] The foaming ratio, cell size, cell uniformity and foaming density of the polyolefin rotomolded foamed products prepared in Comparative Examples 1-8 were tested in the same manner as in Examples 1-8.

[0078] The test results are shown in Table 2.

[0079] Table 2 Formulas and test results of comparative examples 1-6

[0080]

[0081] By comparing Examples 1-8 and Comparative Examples 1-6, it can be seen that the polyolefin rotomolded foamed products of Examples 1-8 have uniform pores and good structures. In Comparative Examples 1-6, the dispersion and distribution of each component are not easy to reach a uniform state, the foaming of the system is unstable, and it is very easy to form uneven pore structures and interconnected large bubbles, which deteriorates the quality of the foamed body. The key reason is that the water dispersion of the foaming system is not good.

[0082] Example 9

[0083] The roto-molded products of tractor roofs are hollow and flat, with the minimum visible gap inside being 1.0 cm and the maximum gap being 2.8 cm. When not foamed and filled, they feel soft and can be deformed by pressing. When the locomotive is running, the roto-molded products of tractor roofs are exposed to the windward side and are prone to deformation. After a certain period of use, obvious permanent deformation gradually forms, and warping deformation occurs in about a year, which can basically be judged as scrapped.

[0084] According to the formula of Example 2 and Comparative Example 2, 35 mesh linear low-density polyethylene powder and core layer raw materials are added to the rotomolding machine mold. The amount of core layer raw materials is calculated according to the required filling volume, and the actual amount is 105wt% of the calculated amount. The rotomolding process is carried out at the set temperature. During the process, it is necessary to pay attention to the vent holes of the rotomolding mold to keep them unobstructed to prevent blockage, and polyethylene rotomolded foam products are obtained. The maximum rotomolding temperature is 230°C, and the rotomolding cycle is 35min. After testing, the sample surface prepared by the composition of Example 2 is free of bubbles and smooth, the cross-sectional pores are fine and uniform (the black spots on the cross-section are the debris of the outer layer of the material when cutting), without pinholes, and no obvious string holes or collapse holes. And it feels solid and does not deform when pressed hard. In actual use, when the locomotive is running, the roof rotomolded product accepts the windward side without deformation; it has been installed and used for 3 years without deformation. The sample prepared in Comparative Example 2 has obvious string holes and collapse holes.

[0085] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the embodiments. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A polyolefin rotomolding foaming composition, characterized in that: It is composed of outer layer raw materials and core layer raw materials; The outer layer raw material includes linear low-density polyethylene powder; In parts by mass, the core layer raw materials include:

2. The polyolefin rotomolding foaming composition according to claim 1, characterized in that: The particle size of the linear low-density polyethylene powder is 20-40 mesh and the density is 0.931-0.934 g / cm 3 , the melt index is 5.8g / 10min.

3. The polyolefin rotomolding foaming composition according to claim 1, characterized in that: The particle size of the high-density polyethylene powder is 20-40 mesh and the density is 0.951-0.953 g / cm 3 , melt index is 5.6-8.9g / 10min; And / or, the Mooney viscosity of the EPDM rubber is 26-61ML(1+4)100°C; And / or, the plasticizer is one or more of dioctyl phthalate, isophthalic acid esters, and phosphate esters; And / or, the oil absorption value of the silica is 2.6-3.6 ml / 100 g; And / or, the lubricant is one or both of oleamide and erucamide.

4. A polyethylene rotomolded foamed product prepared by using the polyolefin rotomolding foaming composition according to any one of claims 1 to 3, characterized in that: It consists of a core layer and an outer layer wrapping the core layer, the raw material of the core layer is the core layer raw material, and the raw material of the outer layer is the outer layer raw material.

5. The method for preparing a polyethylene rotomolded foamed product according to claim 4, characterized in that: Here are the steps: (1) Take the raw materials according to the formula; (2) mixing sodium bicarbonate and water, stirring until transparent, to obtain a solution; (3) mixing the plasticizer with the solution prepared in step (2), and performing ultrasonic emulsification. When no water phase is visible, adding silicon dioxide, and stirring evenly to obtain a mixed emulsion; (4) refining the ethylene-propylene rubber, thinning it into sheets, adding a lubricant, folding and packaging, adjusting the roller distance, and then sequentially adding the mixed emulsion prepared in step (3) and the high-density polyethylene powder, mixing them evenly to obtain a mixture; (5) extruding and granulating the mixture to obtain foamed particles; (6) Adding linear low-density polyethylene powder and foamed particles into a rotational molding mold, heating and molding, and obtaining a polyethylene rotational molding foam product.

6. The method for preparing a polyethylene rotomolded foamed product according to claim 5, characterized in that: In step (2), the sodium bicarbonate and water are mixed at room temperature.

7. The method for preparing a polyethylene rotomolded foamed product according to claim 5, characterized in that: In step (3), the ultrasonic conditions are 60w, 25°C, 10min; And / or, adjust the roller distance to 1.2-1.5mm; And / or, the stirring time is 5-10 min.

8. The method for preparing a polyethylene rotomolded foamed product according to claim 5, characterized in that: In step (4), the ethylene-propylene rubber is milled using a double-roll mill; And / or, the mixing temperature is not higher than 100°C.

9. The method for preparing a polyethylene rotomolded foamed product according to claim 5, characterized in that: In step (5), the extrusion temperature is not higher than 100°C; And / or, the size of the granulation is: less than 1 mm in diameter and no more than 2 mm in length.

10. The method for preparing a polyethylene rotomolded foamed product according to claim 5, characterized in that: In step (6), the temperature inside the mold is 195-230°C.

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