Foam sheet having enhanced heat resistance

Abstract

The present invention relates to a foamed sheet with improved heat resistance, wherein the average cell size is 50 to 250 μm, the degree of crystallization before heat treatment is 20% or more, and the crystallization temperature (TCC) upon cooling is 200°C or more.

Description

Technology Field

[0001] The present invention relates to a foamed sheet with improved heat resistance using a crystallization promoter. Background Technology

[0002] Previously, when manufacturing foamed sheets, a nucleating agent in the form of a master batch containing inorganic materials such as talc or calcium carbonate was used with polyethylene (PE) or polypropylene (PP) as the base resin; however, due to the use of PE or PP base resins, the degree of crystallization and heat resistance were insufficient. The problem to be solved

[0003] Therefore, the objective of the present invention is to provide a foamed sheet with increased crystallinity and improved heat resistance. means of solving the problem

[0004] To achieve the above-mentioned objective, the present invention comprises: an average cell size of 50 to 250 μm, a degree of crystallization of 20% or more prior to heat treatment, and a crystallization temperature (T) upon cooling. CC Provides a foamed sheet with a temperature of 200℃ or higher.

[0005] In the present invention, the degree of crystallization after heat treatment may be 30% or more.

[0006] In the present invention, the rate of change in thickness before and after the heat resistance test of the foam sheet under conditions of 80°C and 3 hours may be 30% or less.

[0007] In the present invention, the height of the foam sheet falling from the flat surface due to bending occurring during the heat resistance test of the foam sheet at 200°C and 30 seconds may be 0.5 mm or less.

[0008] In the present invention, the density of the foam sheet may be 500 kg / m³ or less.

[0009] In the present invention, the foamed sheet may be formed from a polyester resin composition comprising a polyester resin, a thickener, a crystallization promoter, and a foaming agent.

[0010] In the present invention, the polyester resin may be a polyethylene terephthalate resin.

[0011] In the present invention, the intrinsic viscosity of the polyester resin may be 0.65 dL / g or higher.

[0012] In the present invention, the molecular ratio of a polyester resin with a molecular weight of 10,000 or more may be 60% by weight or more based on the total weight of the polyester resin.

[0013] In the present invention, the content of the thickener may be 1% by weight or more based on the total weight of the composition.

[0014] In the present invention, the crystallization promoter may be used in the form of a masterbatch comprising a polyethylene terephthalate base resin and an inorganic material.

[0015] In the present invention, the content of the crystallization promoter may be 1% by weight or more based on the total weight of the composition.

[0016] In the present invention, the inorganic material may be talc or calcium carbonate.

[0017] In the present invention, the particle size of the inorganic material may be 8 μm or less. Effects of the invention

[0018] The foam sheet according to the present invention can increase the degree of crystallization compared to the existing one by using a crystallization promoter, improve warping after heat treatment, and improve heat resistance. Specific details for implementing the invention

[0019] The present invention will be described in detail below.

[0020] The present invention relates to a foamed sheet with improved heat resistance using a crystallization promoter.

[0021] The foamed sheet according to the present invention has an average cell size of 50 to 250 μm, a degree of crystallization of 20% or more before heat treatment, and a crystallization temperature (T) upon cooling. CC It may be a foamed sheet with a temperature of 200°C or higher.

[0022] The cell size of the foam sheet may be, for example, 50 to 250 μm, 60 to 240 μm, 70 to 230 μm, 80 to 220 μm, 90 to 210 μm, or 100 to 200 μm, taking into account physical properties such as moldability, lightness, heat resistance, and rigidity. If the cell size of the foam sheet is too large, the moldability may be poor. The cell size may refer to the average cell size, and specifically, it may refer to the average value of the lengths of the major and minor axes calculated after measuring the lengths of the major and minor axes of the cell using a scanning electron microscope (SEM), etc.

[0023] The degree of crystallization of the foam sheet prior to heat treatment may be, for example, 20% or more, 21% or more, 22% or more, 23% or more, 24% or more, or 25% or more, taking into consideration physical properties such as heat resistance; it may also be 35% or less, 34% or less, 33% or less, 32% or less, 31% or less, or 30% or less; for example, it may be 20 to 35%, 21 to 34%, 22 to 33%, 23 to 32%, 24 to 31%, or 25 to 30%. If the degree of crystallization is too low, physical properties such as heat resistance may be reduced.

[0024] Crystallization temperature (T) upon cooling of the foam sheet CC Considering physical properties such as heat resistance, ) may be, for example, 200°C or higher, 201°C or higher, 202°C or higher, 203°C or higher, 204°C or higher, 205°C or higher, or 206°C or higher; also may be 216°C or lower, 215°C or lower, 214°C or lower, 213°C or lower, 212°C or lower, 211°C or lower, or 210°C or lower; for example, 200 to 216°C, 201 to 215°C, 202 to 214°C, 203 to 213°C, 204 to 212°C, 205 to 211°C, or 206 to 210°C. T of the foamed sheet CC If the value is too low, physical properties such as heat resistance may deteriorate.

[0025] The degree of crystallization of the foam sheet after heat treatment may be, for example, 30% or more, 31% or more, 32% or more, or 33% or more, taking into consideration physical properties such as heat resistance; it may also be 40% or less, 39% or less, 38% or less, or 37% or less; for example, it may be 30 to 40%, 31 to 39%, 32 to 38%, or 33 to 37%. If the degree of crystallization is too low, physical properties such as heat resistance may be reduced.

[0026] The rate of change in thickness before and after a heat resistance test of a foamed sheet under conditions of 80°C and 3 hours may be 30% or less, 25% or less, 20% or less, or 15% or less; it may also be 0% or more, 1% or more, 2% or more, 3% or more, or 4% or more; for example, it may be 1 to 30%, 2 to 25%, 3 to 20%, or 4 to 15%. Thus, the foamed sheet according to the present invention can exhibit improved heat resistance by having a low rate of change in sheet thickness (%) before and after the heat resistance evaluation.

[0027] The height of the foam sheet detached from the flat surface due to bending occurring during a heat resistance test of the foam sheet at 200°C and 30 seconds may be 0.5 mm or less, 0.3 mm or less, 0.1 mm or less, or 0 mm, for example, 0 to 0.5 mm, 0 to 0.3 mm, or 0 to 0.1 mm. When performing a heat resistance evaluation, the foam sheet may bend; in this case, a part of the foam sheet does not touch (contact with) the flat surface (such as the ground) and remains floating away from the flat surface. The more bending occurs, the greater the height of the sheet floating away from the flat surface. In this case, the height may refer to the highest height furthest from the flat surface. Since the foam sheet according to the present invention has improved heat resistance, no bending may occur at all or almost none, that is, the height may be 0 mm or 0.1 mm or less.

[0028] The density of the foam sheet may be, for example, 500 kg / m³ or less, 450 kg / m³ or less, 400 kg / m³ or less, 350 kg / m³ or less, 300 kg / m³ or less, 250 kg / m³ or less, or 200 kg / m³ or less, taking into account physical properties such as lightness and rigidity; it may also be 50 kg / m³ or more, 100 kg / m³ or more, or 150 kg / m³ or more; for example, it may be 100 to 500 kg / m³, or 150 to 450 kg / m³. Thus, the foam sheet according to the present invention may be a low-density foam sheet that takes into account physical properties such as lightness.

[0029] Considering physical properties such as lightness and rigidity, the thickness of the foam sheet may be, for example, 1 mm or more, 1.5 mm or more, 2 mm or more, 2.5 mm or more, or 3 mm or more; it may also be 10 mm or less, 9 mm or less, 8 mm or less, 7 mm or less, 6 mm or less, or 5 mm or less; for example, it may be 1 to 10 mm, 1 to 5 mm, or 1 to 3 mm.

[0030] The foam sheet contains closed cells, and the formed (manufactured) cells are almost entirely closed cells, and the proportion of closed cells among the total cells may be, for example, 90% or more, 95% or more, 98% or more, 99% or more, or 100%.

[0031] The foam sheet has a first surface (e.g., an upper surface) and a second surface (e.g., a lower surface), and optionally, a composite material with a multilayer structure can be formed by additionally laminating another layer, such as a back surface layer, a coating layer, a resin layer, a fiber layer, and / or an adhesive layer, on the first surface and / or the second surface as needed.

[0032] The raw material of the foam sheet may be a polyester resin composition, and the polyester resin composition may include a polyester resin, a thickener, a crystallization promoter, and a foaming agent.

[0033] The polyester resin may be a polyethylene terephthalate (PET) resin as a main component, preferably. By using PET resin, it can be environmentally friendly and easy to reuse. To improve physical properties, the PET resin used in the foamed sheet may be a PET resin having a specific range for intrinsic viscosity, molecular weight, molecular weight distribution, and / or melting point.

[0034] The intrinsic viscosity (IV) of the PET resin may be, for example, 0.65 dL / g or more, 0.7 dL / g or more, 0.72 dL / g or more, 0.74 dL / g or more, or 0.76 dL / g or more; it may also be 1.0 dL / g or less, 0.95 dL / g or less, 0.9 dL / g or less, 0.85 dL / g or less, or 0.82 dL / g or less, for example, 0.65 to 1 dL / g, 0.7 to 0.95 dL / g, 0.72 to 0.9 dL / g, 0.74 to 0.85 dL / g, or 0.76 to 0.82 dL / g. If the intrinsic viscosity (IV) of the PET resin is too low, the cell size of the foam sheet increases, and moldability may be poor.

[0035] The weight-average molecular weight (Mw) of the PET resin may be 20,000 to 200,000, 50,000 to 150,000, or 60,000 to 100,000. The weight-average molecular weight can be measured by gel permeation chromatography (GPC, analytical instrument HLC-8320), and polymethyl methacrylate (PMMA) may be used as a standard sample. The unit of molecular weight may be g / mol or Da.

[0036] In particular, the PET resin may be a PET resin in which the proportion of molecules with a molecular weight of 10,000 or more, indicated by the fine molecular weight distribution, accounts for 60% or more of the total weight of the PET resin. That is, the proportion of molecules with a molecular weight of 10,000 or more in the PET resin may be 60% or more of the total weight of the PET resin, and the proportion of molecules with a molecular weight of less than 10,000 may be less than 40% of the total weight. The proportion of molecules with a molecular weight of 10,000 or more may be 60% or more, 65% or more, or 70% or more of the total weight; and may also be 100% or less, 95% or less, 90% or less, 85% or less, 80% or less, or 75% or less of the total weight; for example, it may be 60 to 100%, 65 to 90%, or 70 to 80% of the total weight. If the proportion of molecules with a molecular weight of 10,000 or more is too low, the cell size of the foamed sheet increases, and the moldability may be poor.

[0037] The differential molecular weight distribution is one of the methods of expressing the molecular weight distribution of polymeric substances, and the differential molecular weight distribution curve is a curve that expresses the amount of a substance with molecular weight M in g as a function of M.

[0038] The melting point of the PET resin may be 250°C or higher, 253°C or higher, or 256°C or higher; it may also be 300°C or lower, 290°C or lower, 280°C or lower, 270°C or lower, or 260°C or lower, for example, 250 to 300°C, 253 to 280°C, or 256 to 270°C.

[0039] Preferably, the PET resin may be a PET resin that satisfies at least two of the above-described properties, namely, an intrinsic viscosity (IV) of 0.65 dL / g or more, preferably 0.76 to 0.82 dL / g, and also has a molecular weight distribution of 10,000 or more, which is the proportion of molecules with a molecular weight of 60% or more of the total weight of the PET resin.

[0040] Particularly preferably, the PET resin may be a PET resin that simultaneously satisfies all of the above-described properties, namely having an intrinsic viscosity (IV) of 0.65 dL / g or more, a weight average molecular weight of 20,000 or more, and a molecular weight distribution of 10,000 or more, which accounts for 60% or more of the total weight of the PET resin, and a melting point of 250°C or more.

[0041] When using a PET resin having these physical properties, a cold-formed part can pass through an 80°C heat resistance cycle. The heat resistance cycle can be evaluated by maintaining the molded part in the same state as an actual car, performing 3 cycles with the following conditions as 1 cycle, observing the appearance, and determining whether there is a change in shape. The heat resistance cycle may consist of a step of standing at 80±2°C for 3 hours, 23±2°C for 1 hour, -30±2°C for 3 hours, 23±2°C for 1 hour, 50±2°C for 15 hours at 95~100% relative humidity (RH), and 23±2°C for 1 hour.

[0042] Thickeners are added to control the melt viscosity, melt strength, etc., of the foamed composition, and examples include pyromellitic acid dianhydride (PMDA) and epoxy.

[0043] The content of the thickener may be, for example, 1 to 5 weight%, 1 to 4 weight%, or 2 to 3.5 weight% based on the total weight of the composition. If the content of the thickener is too low, foaming may not occur, and the density of the foamed sheet may increase. Even if the content of the thickener is too high, particularly 5 weight% or more, there may be no further change in melt viscosity, etc.

[0044] A crystallization promoter is added to control the degree of crystallization, cell size, cell density, etc., and may be used in the form of a masterbatch containing a polyethylene terephthalate-based (PET-based) resin and an inorganic material. The masterbatch of the crystallization promoter has PET as the base resin and contains an inorganic material within the PET-based resin; for example, it may be in a form where the surface of the inorganic material is coated with the PET-based resin, or in a form where the inorganic material is dispersed within the PET-based resin. In the present invention, by using a crystallization promoter with PET as the base resin, the degree of crystallization can be increased compared to conventional methods, thereby improving heat resistance.

[0045] As inorganic materials, for example, inorganic compounds such as talc, calcium carbonate, mica, silica, diatomaceous earth, alumina, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, sodium bicarbonate, and glass beads can be used.

[0046] The content of the crystallization promoter (based on the masterbatch) may be, for example, 1 to 10 weight%, 1.5 to 4 weight%, or 2 to 3.5 weight% based on the total weight of the composition. If the content of the crystallization promoter is too low, the degree of crystallization and heat resistance may be reduced, the cell density may be lowered, and the surface roughness may be poor. If the content of the crystallization promoter is too high, wrinkles may occur on the surface of the sheet. For example, the degree of crystallization of the foamed sheet can be secured at 25% or more by using about 2% of the crystallization promoter.

[0047] The particle size of the inorganic material may be, for example, 1 to 8 μm, 2 to 6 μm, or 3 to 4 μm. If the particle size of the inorganic material is too large, the cell size may increase, and the degree of crystallinity and heat resistance may decrease.

[0048] For example, by applying PET-based talc particles (size 3 to 4 μm) as a crystallization promoter in an amount of 1.5 to 4 wt%, a PET foam sheet with a crystallization degree of 25% or more before heat treatment can be obtained, and a product with a crystallization degree of 30% or more after heat treatment can be obtained.

[0049] A blowing agent is added to foam the composition and control the density of the foamed sheet, and may be used as: gases such as N2, CO2, and Freon; physical blowing agents such as pentane, butane, propane, neopentane, hexane, isohexane, heptane, isoheptane, and methyl chloride; and chemical blowing agents such as azodicarbonamide compounds, P,P'-oxybis(benzenesulfonylhydrazide) compounds, and N,N'-dinitrosopentamethylenetetraamine compounds.

[0050] The content of the foaming agent may be, for example, 0.1 to 5 parts by weight, 0.5 to 4 parts by weight, or 1 to 3 parts by weight based on 100 parts by weight of resin.

[0051] In addition, the raw materials of the foam sheet may additionally include surfactants, UV blockers, hydrophilizing agents, flame retardants, heat stabilizers, waterproofing agents, cell size expanders, infrared dampeners, plasticizers, fire-retardant chemicals, pigments, elastomers, extrusion aids, antioxidants, fillers, anti-aircraft agents, UV absorbers, etc., for the purpose of imparting hydrophilicity, waterproofing, flame-retardant, and UV-blocking functions.

[0052] Foamed sheets can be formed through extrusion foaming. Extrusion foaming simplifies process steps and enables mass production by continuously extruding and foaming the molten resin. Furthermore, it prevents cracking between beads and granular fracture during bead foaming, thereby enabling the realization of superior compressive strength.

[0053] The foamed sheet according to the present invention can be applied to applications that do not require dip molding and require heat resistance, such as automobiles (interior materials, etc.), building materials, and electronic product back sheets (back plates for TVs, etc.).

[0054] The present invention will be explained in more detail below with reference to examples.

[0055] [Examples and Comparative Examples]

[0056] A PET foam sheet was prepared using a PET resin having the viscosity and molecular weight distributions shown in Tables 1 and 2, a thickener and a foaming agent with the contents shown in Tables 1 and 2, and a crystallization promoter with the contents and particle size shown in Tables 1 and 2.

[0057] In the example, PET-based talc particles were used as a crystallization promoter, and in Comparative Example 1, PE-based talc particles were used as a nucleating agent.

[0058] Next, the manufactured foamed sheet was heat-treated and processed under conditions of 200°C and 30 seconds.

[0059] The physical properties of PET foam sheets before and after heat treatment post-processing are shown in Tables 1 and 2. In the tables, Ash represents the inorganic content of crystallization promoters or nucleating agents within the foam sheets.

[0060] The method for measuring physical properties is as follows.

[0061] (1) Intrinsic viscosity (IV)

[0062] The intrinsic viscosity was measured at 35°C using an Uwerod viscometer by dissolving the sample in a mixed solution of phenol and tetrachloroethane (mixing ratio = 1:1 volume ratio) at a concentration of 0.5 wt%.

[0063] (2) Molecular weight

[0064] The molecular weight was measured at 254 nm using gel permeation chromatography (GPC, analytical instrument HLC-8320) after dissolving the sample in a mixed solution of chloroform and phenol (mixing ratio = 1:1 volume ratio). PMMA was used as the standard sample.

[0065] (3) Density

[0066] Density was measured using Alfa Mirage’s EW-300SG under KS M ISO 845 conditions.

[0067] (4) Cell size

[0068] The cell size was determined by measuring the lengths of the major and minor axes of the cell using a scanning electron microscope (SEM) and taking the average value.

[0069] (5) Crystallinity

[0070] The enthalpy of melting at the melting temperature and the enthalpy of crystallization at the cooling crystallization temperature were measured using Differential Scanning Calorimetry (DSC), and the degree of crystallization was calculated according to the following formula.

[0071] Degree of crystallization = ΔHm - ΔHc / ΔHm

[0072] ΔHm represents the enthalpy of melting, ΔHc represents the enthalpy of crystallization, and ΔHm represents the standard enthalpy of melting (140 J / g).

[0073] (6) T HC and T CC

[0074] Crystallization temperature upon heating (T HC ) was measured using a differential scanning calorimeter (DSC) under conditions of max. 280℃ (10℃ / min).

[0075] Crystallization temperature upon cooling (T CC ) was measured using a differential scanning calorimeter (DSC) under conditions of min. 20℃ (50℃ / min).

[0076] (7) Bending

[0077] Flexure was evaluated by measuring the maximum height of the foam sheet floating above the plane without touching the plane after heat-treating the foam sheet at 200°C for 30 seconds.

[0078] (8) Heat resistance

[0079] Heat resistance was evaluated by heat-treating the foamed sheet at 80°C for 3 hours and measuring the rate of change in thickness of the foamed sheet before and after heat treatment.

[0080] (9) Moldability

[0081] Moldability was evaluated by visually inspecting the molded product for the presence of bursting and contours after forming the foamed sheet under molding conditions of heat treatment at a surface temperature of 190°C → press (cold forming) at 20°C.

[0082] division Example 1 Example 2 Example 3 PET resin Intrinsic viscosity (IV) ㎗ / g 0.8 0.8 0.8 Molecular weight of 10,000 or more % 72 72 72 Thickener PMDA wt% 2.5 2.7 2.9 Crystallization promoter Content wt% 2 2 2 particle size ㎛ 3~4 3~4 3~4 blowing agent Hydrocarbons (pentane, butane, propane) wt% 0~5 0~3 0~3 PET foam sheet (before heat treatment processing) density kg / ㎥ 150 300 450 thickness ㎜ 3.0 1.5 2.2 Average cell size ㎛ 100~200 100~200 100~200 Crystallinity % 25 25 26 Ash % 1 1 1 T HC ℃ 126 125 126 T CC ℃ 207 207 206 Post-heat treatment processing (200℃, 30 seconds) T HC ℃ 130 131 130 T CC ℃ 207 207 206 Crystallinity % 34 33 34 Bending (200℃, 30 seconds) ㎜ 0.1 0 0 Heat resistance (80℃, 3 hours) % 10.0 11.3 7.3 Plasticity - Good Good Good

[0083] division Comparative Example 1 Comparative Example 2 PET resin Intrinsic viscosity (IV) ㎗ / g 0.8 0.6 Molecular weight of 10,000 or more % 72 50 Thickener PMDA wt% 2.5 2.5 Crystallization promoter Content wt% 2 (nucleus agent) 2 particle size ㎛ 10 3~4 blowing agent Hydrocarbons (pentane, butane, propane) wt% 0~5 0~5 PET foam sheet (before heat treatment processing) density kg / ㎥ 150 150 thickness ㎜ 3.0 3.0 Average cell size ㎛ 300~600 800~1000 Crystallinity % 13 25 Ash % 0.8 1 T HC ℃ 127 125 T CC ℃ 199 206 Post-heat treatment processing (200℃, 30 seconds) T HC ℃ 130 130 T CC ℃ 199 206 Crystallinity % 24 31 Bending (200℃, 30 seconds) ㎜ 2.0 1 Heat resistance (80℃, 3 hours) % 126.7 33.3 Plasticity - Good error

[0084] According to Tables 1 and 2, in the case of the examples, by manufacturing a PET foam sheet using a PET resin having an appropriate viscosity and molecular weight distribution, an appropriate amount of thickener and foaming agent, and an appropriate amount and particle size of crystallization promoter; appropriate density, appropriate thickness, appropriate cell size, appropriate degree of crystallization, and appropriate T HC and T CC , a foamed sheet with improved bending, enhanced heat resistance, and good moldability could be obtained.

[0085] However, in the case of Comparative Example 1, PE-based talc particles as a nucleating agent were used instead of PET-based talc particles as a crystallization promoter, and because the particle size of the nucleating agent was large, the cell size increased and the degree of crystallization was significantly lower, and T CC The resistance was low, there was a lot of bending, and heat resistance was significantly reduced.

[0086] In addition, in the case of Comparative Example 2, because a PET resin with low viscosity and a low ratio of molecular weight of 10,000 or more was used, the cell size increased significantly, warping occurred, heat resistance decreased, and moldability was poor.

Claims

Claim 1 Formed from a polyester resin composition comprising a polyester resin, a thickener, a crystallization accelerator, and a foaming agent, wherein the polyester resin is a polyethylene terephthalate resin, the molecular ratio of the polyester resin with a molecular weight of 10,000 or more is 60 to 90 weight% based on the total weight of the polyester resin, and the molecular ratio of the polyester resin with a molecular weight of less than 10,000 is 10 to 40 weight% based on the total weight of the polyester resin, the content of the thickener is 1 weight% or more based on the total weight of the composition, the crystallization accelerator is used in the form of a masterbatch comprising a polyethylene terephthalate base resin and an inorganic material, the content of the crystallization accelerator is 1 weight% or more based on the total weight of the composition, the content of the foaming agent is 0.1 to 5 weight% based on the total weight of the composition, the average cell size is 50 to 250 μm, the degree of crystallization before heat treatment is 20% or more, and the crystallization temperature (T CC A foamed sheet with a temperature of 200℃ or higher. Claim 2 In claim 1, a foamed sheet having a degree of crystallization of 30% or more after heat treatment. Claim 3 A foamed sheet according to claim 1, wherein the rate of change in thickness before and after a heat resistance test under conditions of 80°C and 3 hours is 30% or less. Claim 4 A foam sheet according to claim 1, wherein the height of the foam sheet falling from the flat surface due to bending occurring during a heat resistance test of the foam sheet under conditions of 200°C and 30 seconds is 0.5 mm or less. Claim 5 In paragraph 1, a foam sheet having a density of 500 kg / ㎥ or less. Claim 6 delete Claim 7 delete Claim 8 A foamed sheet according to claim 1, wherein the intrinsic viscosity of the polyester resin is 0.65 dL / g or higher. Claim 9 delete Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 In paragraph 1, the inorganic material is a foamed sheet in which talc or calcium carbonate. Claim 14 A foamed sheet according to claim 1, wherein the particle size of the inorganic material is 8 μm or less.

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